Aerodynamics and the crash of the B-52

[GaryMC1]

This is going to be a continuation of the B-52 crash discussion in the Crash forum. Or, at least the aerodynamic aspect of it.

Please bear with me while I recap. In late August, Gordon Nichols' beautiful scale B-52 crashed on a windy day at the British Nationals.

The weather was overcast, gusty, and winds 25-30 knots or more, straight down the runway.

The aircraft took off, climbed, and began a right turn downwind. Upon entering the downwind, the right wing rose up, then dropped, and continued to drop, the airplane entered into a steep right dive, passed vertical, continued in it's roll, and crashed. (Others will argue it was a left wing drop, but from reviewing the video and the account of two eye witnesses, the airplane rolled right)

It is my belief, backed by two full sized instructors and several other full sized pilots, that the airplane lost airflow over the wing, and stalled. The loss of airflow over the wing was due to a loss of airspeed due to a downwind turn.

Most people tell me I'm crazy, and you can read my dissertations in the Crash Forum, along with simulated data from Microsoft Flight Simulator.

I believe that the very strong wind coupled with a probable reduction in power due to a perceived 'high speed', and indeed it would be a high ground speed, caused flow over the wings to be diminished to the point that the aircraft could no longer fly.

In this thread, I would like to ask simple questions of those who would doubt me, and get their responses. If they can convince me, all the good for them. If I can convince them...well, that's my goal.



The first question is this.

How is lift created?

Let's discuss that one question, and when we come to a consensus, I'll ask the next question.

Gary

[Ben Diss]

Correction: After the completion of the downwind turn, the airplane flew level for two seconds. Thereafter it began to roll and crashed. The video shows this two seconds of level flight very clearly. During the downwind turn when the airplane was banked (assuming that no loss or gain of altitude occurred) the wing loading was higher and thus the stall speed would have been higher. When the airplane leveled out at the completion of the successful downwind turn (again assuming no loss or gain of altitude) the stall speed would have returned to normal. It is AFTER this occurred that the airplane began the fatal bank and dive.

http://www.teambanana.co.uk/b52crash2.wmv

-Ben

[Sparky Paul]

From the description, this is a typical stall due to excessive pulling of elevator in a banked condition, due to the perceived high speed downwind which generally leads to tightening the turn beyond what the airplanes' real airspeed can support.
It's not the first to do this, nor the last that will, nor even unique crashing in this situation.
It's due solely to the perception of position/airspeed relative to the pilot on the ground.
Discussing lift isn't needed.

[Ben Diss]

The crash occurred after the turn was completed, not during the turn. The roll began from straight and level flight.

Agreed that a discussion of lift isn't needed.

-Ben

[ETrain]

Darn, I was hoping the first question was going to be: Is airspeed independent of wind? :D

Best of luck to you Gary with your job hunt, by the way.

[Sparky Paul]

Looking at the video, it's almost certain a radio failure.
Interestingly enough, this 8 EDF B-52 did the same thing last Sunday. Traced to receiver battery failure.

[GaryMC1]

In the other thread, it was reported by someone close to the team that there were NO mechanical or radio failures, and we have to assume that was the case.

So, going on that, my initial question still stands.

How is lift created.

Eric, the answer to this question will eventually lead to your question. :)

Gary

[gkamysz]

Few will agree on how lift is created. Many threads will attest to that.

What is the second question?

Greg

[ETrain]

Gary,

Chapter 3 of the classic Wolfgang Langewiesche's "Stick and Rudder - An Explanation of the Art of Flying" is entirely dedicated to lift and buoyancy. If it took Wolfgang 10 pages to cover the topic, it's going to be difficult to sum it up nicely in a short forum post. I would say, however, that if the downwind was 10 kts or 300 kts, it would make no difference to the lift of the airplane.

Eric

Edited to add:
In fact, the first statement of chapter 3 is: "Lift is one of the most confusing things in flying to talk about. On no other subject is there so much difference between what the engineer claims and what the pilot knows." :D

[Sparky Paul]

In the other thread, it was reported by someone close to the team that there were NO mechanical or radio failures, and we have to assume that was the case.

So, going on that, my initial question still stands.

How is lift created.

Eric, the answer to this question will eventually lead to your question. :)

Gary
"we have to assume that was the case."
No we don't.
A plane in unaccelerated level flight is not going to depart as this one did unless something commands it to.
Loss of signal does that.
The second likely cause would be due to flying a grey airplane against a grey background, and the pilot becoming disoriented. As it's in "right pattern" flight, if the pilot perceives erroneously a right turn, and "corrects" with left command, the plane spirals down to the left as we see.
A sudden loss of lift.. no way. A sudden redistribution of lift, no way.
It's mechanical.. radio failure, or human.. disorientation. Not Bernoulli taking the day off.

[mwraight]

How is lift created?

Let's discuss that one question, and when we come to a consensus, I'll ask the next question.

Unfortunately you're never going to get a consensus of how lift is created. Everyone and their brother has an opinion. No one thinks they're wrong, everyone knows that they're right. The question kind of reminds me of the post in "off topics" where someone asked for a person to describe what it means to be a conservative and what it means to be liberal WITHOUT being inflammatory. No one came even close to the objective and they shut it down!

There are a number of accepted theories - but they aren't accepted by everyone. You have scientists who buy into one theory, engineers another, pilots another - so forth and so on, ad infinitum, ad nauseum.

[raptor22]

Wanna go through that discussion, just read this thread:

http://www.rcgroups.com/forums/showthread.php?t=267388

--Alex

[slipstick]

How lift is created is really very simple. It's created by airflow over one or more surfaces. The rest is just detail ;).

If you can manage to find a consensus on the detail from that recent thread I'd be interested to know.

However I don't believe it has anything to do with the B52 crash. That looks a lot more like pilot error caused by disorientation as Paul (and most of the people who were actually present) have suggested. Conditions were not good. I was at Barkston the day before (winds only about 20mph) and saw that B52 flying perfectly steadily but it was not at all easy to accurately spot its attitude against that cloudy grey sky.

Steve

[vintage1]

I plump for gusting and pilot error frankly.

I have done almost the same thing with slow light models in breezy conditions.

You are flying along straight and level and the wind comes along in a smooth gust, and teh nect thing you know, the model is falling out of the sky through lack of airspeed and/or a downdraught. I have pulled as much elevator as I dared and full throttle and seen the model lose 3 foot of height as it raced off downwind...with the gust.

Of course as soon as the gust passes, the model is suddenlty full of execess airspeed and shoots up like a rocket.

Or inded the other way about when flying into a guts: Intially the model rockets up, and groundspeed slows to a crawl, then as the gust passes the model falls out of the sky, but usually it has enough height that way.

I rarely fl now in such adrerse conditions: The challenge is at best curious, and not much fun, and the chances of model damage landing through wind shear and turbulence are too great.

OK for a fast foamie, but not so much on a slower scale job.

[Andy W]

As large and heavy as that model was, it was very much tossed around by wind gusts on climbout. As a side note, I feel he had not reached a safe altitude or airspeed before initiating his turn. Also, in the turn, he has a severe bank angle and a significant nose-up attitude. He survives the turn, however, and the model is then flying much faster, in the shakey close-up video clip, you can see how little it is now being tossed around. The fact that he did come out of that turn safely proves this model has tolerance of low airspeed and/or high wingloading (which was probably doubled during that turn!) This provides more evidence that even gusts of 20-30mph would not cause that model to slowly depart from level flight condition.

Neither would a stall, for that matter. Just because the model is heavy, it's can't deny the laws of physics. Full-scale aircraft are quite a bit heavier than this model, yet they too depart from level flight in a very severe fashion if stalled. We practice stall-spins in full-scale gliders from gentle turns close to stall speed, induced with rudder (typical landing approach). I describe the feeling as if the wing tips are held with two strings, and you cut one of the strings - the wing that stalls falls off immediately, and the nose is pointing at the ground in about a second.

This model slowly entered a gentle roll which - without the usual elevator compensation - put it into a nose-down attitude from which more altitude would now be needed to recover. This was not induced by external conditions or aerodynamics, it was either component failure or pilot error.
..a

[GaryMC1]

AAAaaaaaagggggggghhhhhhhhhhhhhh!!!!

:D

Okay. Can we all agree that air flowing over a curved surface, in this case, an airfoil, creates an area of lower pressure as the air molecules speed up, allowing an area of higher pressure below the airfoil to produce 'lift?'

Also, can we agree that this 'lift' is produced by the air flowing over the wing, and it doesn't matter if the airplane is moving forward through the air mass, or the airplane is stationary and the airmass is moving past the airfoil?

Gary

[Ben Diss]

No. Lift is not that simple. You have completely disregarded the Newtonian forces involved as well as the vertical component of thrust.

-Ben

[Andy W]

It is my belief, backed by two full sized instructors and several other full sized pilots, that the airplane lost airflow over the wing, and stalled. The loss of airflow over the wing was due to a loss of airspeed due to a downwind turn.



Your belief is incorrect. All evidence I have seen suggests that airflow was not lost over the wing. If it did, it would not have slowly banked over as shown in the videos available.

In direct answer to your question, however - yes, lift is generated when air flows over a wing at an appropriate speed and angle of attack.
..a

[Andy W]

Can we all agree that air flowing over a curved surface, in this case, an airfoil, creates an area of lower pressure as the air molecules speed up, allowing an area of higher pressure below the airfoil to produce 'lift?'

Actually, I'd have to disagree with this one, my answer above as based on the second part of your question.
..a

[slipstick]

Okay. Can we all agree that air flowing over a curved surface, in this case, an airfoil, creates an area of lower pressure as the air molecules speed up, allowing an area of higher pressure below the airfoil to produce 'lift?'

No. This is not a complete and accurate explanation of the way lift is produced. If it were flat plates wouldn't produce lift, and they do.


Also, can we agree that this 'lift' is produced by the air flowing over the wing, and it doesn't matter if the airplane is moving forward through the air mass, or the airplane is stationary and the airmass is moving past the airfoil?

I can agree with this provided it's changed to "The majority of lift is produced by the air flowing......".

Now what ?

Steve

[GaryMC1]

Okay, I give up. I have my beliefs, all of you have yours.

I should have just kept quiet about this. I disagree with all of you, but that's what's so great about this forum, is we can disagree and still be friends and civil to one another. And, I'm going to let it go.

Thank you all for your input. Andy, please close this thread.

Gary

[Sparky Paul]

...
Thank you all for your input. Andy, please close this thread.

Gary
.
???
Why?
Apparently you have some idea connected with lift which explains this crash.
What is that idea?

[leccyflyer]

Gary

Threads are not closed because one person has decided that they don't want to contribute to it anymore.

Brian

[Ben Diss]

Brain- Is that your opinion, or do I sense a little post-moderator leakage?

:)

-Ben

[olmod]

Ive watched that clip a few times now ,and just before the fatal left bank it looked like he tried to right bank,i wonder if there was an alleron linkage breakaway,wich ended up in puting it into a left bank, what does the pilot think surely he would have the best opinion. :rolleyes:

[leccyflyer]

Ben

It's my opinion and it's also the policy of the site that you'd be able to find stated in several threads if you'd care to search- site suggestions would be a good place to start.

Brian

[Ben Diss]

Brian- You write with the tone of a moderator...yet you aren't. Thanks for the advice, but none was asked for.

-Ben

[leccyflyer]

Ben

Gary requested that the thread be closed because he had finished with it- that isn't the way things are done here. They were not done that way before I was asked to be a moderator, they were not done that way whilst I was a moderator and unless I'm mistaken then they won't be done that way in the future.

If you want to make another one of your big issues out of it then take it to another thread.

Brian

[Ben Diss]

Brian- This isn't your thread and this isn't your forum. If you want to play moderator and tell me what to do then I suggest you were wrong to resign. As it stands now you have no more say here then anyone else. Gary asked a MODERATOR (not you) to close the thread. Let the moderator represent the interests of this site.

-Ben

[ETrain]

Geez... I think it's cool for members to let other members know what the general policies of the Ezone are. It happens all the time, and it's helpful. Now a moderator will probably have to step in... :rolleyes:

Gary,

I'm sorry you've decided to pull out. I still strongly believe that a steady wind, whether 10 kts or 100 kts, will not alter the airspeed regardless of flying upwind or downwind (this was the main point of contention in the other thread). I was curious how your thoughts on lift could shed some light on how you arrived at your opinion. I still don't understand how commercial airliners in the jetstream and gliders at high altitude already close to stall could keep flying if everytime they turned downwind they had a huge hit on airspeed (in the other thread, your example was 15kts reduced airspeed for 40kts of downwind).

Eric

[robert harik]

E train you are correct. If you are in the airplane and can watch the airspeed indicator, it can be blowing and gusting like hell outside and no matter which way you turn, your airspeed will stay the same.
The only thing that changes is your ground speed.
This "downwind stall" stuff is only seen (described) in models, never in full scale aircraft, because it is the perception of the modeler who is flying with ground speed as his stall speed reference.

[gkamysz]

Gary what is the point you are trying to make? Yes it was headed downwind when it departed but it was certainly flying. Could it be that the pilot throttled back, well I don't know, ask him. It seems suprising to me that for such an expensive model there was no telemetry to help fly the model. Telemetry would have been a fraction of the total cost and would have been very useful. Oh well.

I'm just glad the crash didn't cause any serious personal or property damage. Or we might all be feeling the effects.

Regarding downwind turns. There are all kinds of disagreements about this topic. Airspeed change with regard to wind direction is somewhat related to the momentum of the model.

For an extreme instance. A model is flying at 60MPH airspeed into a 60MPH headwind. It's very gusty and the wind drops to 0MPH instantly. What is the model's airspeed at this instant? Well we know that the model is generating thurst and it will accelerate relative to the ground but this takes time. During that time the model will probably stall. The same thing happens in the downwind turn. This time the model has some time to build that momentum during the turn to downwind. Depending on many variables the model may or may not have enough actual airspeed to fly upon completion of the turn.

Similar conditions occur during landing into a stiff headwind. The model is fine until it gets close to the ground. All of a sudden it stall and drops. Depending on conditions of the surroundings boundary layer air near the ground has a much lower velocity than air just a few feet above it. For full scale this isn't an issue. For models it can be quite pronounced.

All of these effects get smaller as airplanes get larger just due to relative scale of things. Gusty winds of 40MPH are nothing for an airliner which takes off at 150+MPH.

My opinion.

Greg

[Sparky Paul]

Greg
The video doesn't present any obvious problems with the plane's speed. It appears to be stable, and nothing obvious disturbs its attitude, until the left turn commences.
If that is perceived by the pilot as a right turn due to silhouetting, then the command to recover reinforces the left turn. Been there, done that.
I've had receiver battery in-flight failures also, which have resulted in spirals into the ground, and once a nose-down pitch into the ground. No response to throttle back or any flight control input.
A receiver switch failure, OTOH, with the plane in level flight resulted in a fly-away, with a gentle landing distance away.

[Roj]

AAAaaaaaagggggggghhhhhhhhhhhhhh!!!!

:D

Okay. Can we all agree that air flowing over a curved surface, in this case, an airfoil, creates an area of lower pressure as the air molecules speed up, allowing an area of higher pressure below the airfoil to produce 'lift?'

Also, can we agree that this 'lift' is produced by the air flowing over the wing, and it doesn't matter if the airplane is moving forward through the air mass, or the airplane is stationary and the airmass is moving past the airfoil?

Gary

By stopping here Gary, readers will only assume that you were going to go down the path of reasoning that if a static plane held aloft by a moving airmass were to turn 180 degrees it would lose it's lift.
Knowing that you are a full size pilot, I know you would have a better understanding of aerodynamics than this.
So please put up the rest of your theory. Put it up for crtiticism. There are people on this forum with lesser understanding of aerodynamics than you, and there are people with greater. Some criticism will be unfounded, some will be valid.

[altur]

Hey guys. This is supposed to be a thread devoted to 'Modelling SCIENCE'. Can we please keep it to that? Gary has tried to get the discussion going along those lines. The 'crash' forum went the other way, with aerodynamic issues becoming confused, and I suggested a couple of times we discus the 'science 'aspects here. All we seem to have achieved is to change forums.

[Roj]

If dispelling the "downwind turn" myth cannot be discussed in the "modelling science" forum, which forum should it be discussed in altur?
The only other suitable forum I can see is "Humour."

[altur]

for Gary, I think your problems with accepting the conventional wisdom of the entire aviation world, despite your claims of support from instructors/pilots, is that you are getting too bound up in your conception of how lift is developed etc. Does it matter? Remember that whatever the explanations that are offered, they are just that - explanations that are an attempt to describe what is happening.

You ask the question whether it matters whether the air flows over the wing or the wing flows through the air - in practice NO, the net result is the same. What does matter I suggest is that in the attempts at explaining HOW it happens it does matter. And a lot of the confusion that arises, such as 'the air flows back up the top of the wing' type of explanation just lead to confusion.

It is a lot easier to understand if you just accept the basics, and proceed from there. As that well known saying goes - "lift happens", - and it can be mathematically dealt with.

It is also a lot easier to comprehend if you use mathematics to explain the effects.

I would ask you to answer a two questions here and would appreciate your answering both

1. Do you have, or can any of those who support your ideas assist, any authoritive text supporting your theories. If so, could you list them.

2. Will you accept mathematical arguments or quotes derived from accepted texts such as the flying training manuals of the US Navy, the Royal Air Force, the Royal Australian Air Force, the UK AOPA, and from several other (accepted world wide ) flying training texts.

That's enough for now. Alan

[mwraight]

E train you are correct. If you are in the airplane and can watch the airspeed indicator, it can be blowing and gusting like hell outside and no matter which way you turn, your airspeed will stay the same.
The only thing that changes is your ground speed.
This "downwind stall" stuff is only seen (described) in models, never in full scale aircraft, because it is the perception of the modeler who is flying with ground speed as his stall speed reference.

This statement is not entirely true. If you're flying along with a 20kt headwind, and it shifts quickly to a 20kt tailwind, you will definitely see a change in your airspeed indicator. I have been flying numerous times when it was gusty, turbulent and nasty and the airspeed indicator needle will get a definite workout. Generally though the aircraft will do a pretty good job of accelerating back to it's original airspeed quickly - power + pitch does equal performance. But airpseed is affected by the wind momentarily - hence why it is recommended that when making an approach in gusty conditions you carry extra airspeed.

Lets say your plane has a 50kt stalling speed. You're on approach into a 10kt headwind. Your airpseed indicator shows you doing 60kts. Suddenly the wind changes to a 10kt tailwind. Congratulations, you now have a big insurance claim.

If the wind comes from behind the plane fast enough you will no longer be flying. I'm beginning to look at the downwind stall in a new light and am slowly believing. It exists in the model aviation world, due mainly to slow airspeeds and also pilot error. It could happen to a full scale, but it's going to be a big gust that does it, not just turning downwind. It's probably the same in the model world, but we're dealing with planes that have low airspeeds - and a gust of just a few MPH's is enough to end the game. If we had an airspeed indicator on the model that we could see, it would happen less. Using the airplane's ground speed is a terrible frame of reference because it is absolutely useless in regards to what's happening aerodynamically to the model.

[mwraight]

Ooops...my bad.

[nuevo]

I agree with Sparky Paul's assessment. It was a very slow roll, induced by pilot disorientation. The profile of the plane goes completely black (in the video at least) just before that roll commences, and the pilot had just completed a slight rolling maneuver to level the plane. (not the my opinion is going to change any minds...)

[altur]

Roj, What I was trying to get across is Posts that relate to what was happening to the ill-fated B 52, such as radio failure, whether it was turning left/right, whether the pilot misread the attitude etc. are not, in themselves, related to the 'science' aspects of the how's and why's of aircraft flight.They are better presented in the 'Crash' forum
By all means, and this is what I have been advocating for some time, let us discuss the myths and other misconceptions, but do it in a fashion that offers explanations that can be scientifically established.

Often, we see Posters qualify their words with 'my opinion' or such. What we are discussing is not a matter of 'opinion'. It is established FACT, or an opposed view of such. Such views , to be accepted, must be capable of being mathematically supported. This is not to say one needs to be a 'rocket scientist' to understand the mathematics - every PPL student needs to know and be able to understand this knowledge, and it is in every flying training text that I have come across.

[KillerWatt]

No "rocket science" of air flow dynamics is needed to explain the '52's roll and crash........Obviously a shot from the "grassy knoll" brought the '52 down ......... kw

[altur]

Best explanation so far KW - but post it in the 'crash' forum ( just to please me huh?)

What used to be called 'the golden bullet'

[Sparky Paul]

Shouldn't the science aspect of what could have created this crash, other than mechanical/human error be discussed here?
I think so.
And once it's reasonably agreed that aerodynamics isn't at fault, the remaining "usual suspects" can be discussed as distasteful as this might be.
Hopefully without personal conflicts taking up space.
"just the facts, man"...
The postulated 180° shift in wind isn't noticeable in the video. It certainly would be had it existed.
Any experienced sloper has experienced what can happen with a 90° shear when going across the slope. The attitude change in roll is instantaneous, when one wing experiences a wind direction completely different than the other wing.
Presumably such a change from headwind to tailwind would have -some- visible effect on the plane's attitude in pitch at least.
Doesn't happen.
It flies along level and rolls left, without any large pitch or roll change at all. The pitch position at the terminus of the video is quite consistent with a normal descending flight path, with no corrections to the attitude occuring at the airplane.
Consistent with radio failure.
Disorientation with control more likely would show a tightening roll, and a pitch up change, neither of which are seen.
The images aren't clear enough to pick out the aileron positions.. possibly these can be determined with a better copy of the video.. but if these don't change to anything that could be expected as a result of a restoring command, then again, radio failure is #1 on the culprit list.
The right aileron -should- be up, and the left down, if there is control of the plane.

[GaryMC1]

This statement is not entirely true. If you're flying along with a 20kt headwind, and it shifts quickly to a 20kt tailwind, you will definitely see a change in your airspeed indicator. I have been flying numerous times when it was gusty, turbulent and nasty and the airspeed indicator needle will get a definite workout. Generally though the aircraft will do a pretty good job of accelerating back to it's original airspeed quickly - power + pitch does equal performance. But airpseed is affected by the wind momentarily - hence why it is recommended that when making an approach in gusty conditions you carry extra airspeed.

Lets say your plane has a 50kt stalling speed. You're on approach into a 10kt headwind. Your airpseed indicator shows you doing 60kts. Suddenly the wind changes to a 10kt tailwind. Congratulations, you now have a big insurance claim.

If the wind comes from behind the plane fast enough you will no longer be flying. I'm beginning to look at the downwind stall in a new light and am slowly believing. It exists in the model aviation world, due mainly to slow airspeeds and also pilot error. It could happen to a full scale, but it's going to be a big gust that does it, not just turning downwind. It's probably the same in the model world, but we're dealing with planes that have low airspeeds - and a gust of just a few MPH's is enough to end the game. If we had an airspeed indicator on the model that we could see, it would happen less. Using the airplane's ground speed is a terrible frame of reference because it is absolutely useless in regards to what's happening aerodynamically to the model.


Thank you!

In a real airplane, usually, the airspeed is high enough, and the power setting is high enough that when we turn the airplane, upwind, crosswind, downwind, we don't see the effect.

As demonstrated in the Crash forum, in my second set of Flight Simulator examples, we did see a 15 knot or so decrease in Indicated Airspeed, BUT, we were at a slow speed. As our Indicated airspeed was higher, we didn't see that much of a difference, and when we got over 110 KIAS, we didn't see a change at all.

My belief was that because of the requirements of keeping the airplane 'in the box' for the show, Mr. Nichols probably had the throttle back, expecting, rightly so, that the wind was going to increase the groundspeed. I believe that he was closer to his stall speed then he expected, and when he turned downwind, the airmass or airflow didn't come back up over the wing, but he took enough of a hit in airspeed that it caused the airplane to fall below stalling speed.

By the way, I've gone back and done some serious looking at the video that was shot, and used a video editing program to slow down and enhance the footage (there wasn't too much to work with), and I believe that the airplane actually rolled slightly to the left on roll out, then leveled out, and then rolled back to the right. By looking at the frames, you can see the white paint over the cockpit and forward part of the fuse, back to about the wings, which matches the beginning of the video. This white area could only be seen if the airplane had rolled to the right.

With a high enough tailwind, although some of it would carry the plane along and increase groundspeed, the overall effect would be a decrease in airspeed, to the point where the wing would stall. I believe that in this case, the wind, which looking at the windsock straight out, was probably close to 30 knots. Now, I don't know the stalling speed of this airplane...really, how many of us know the stalling speed of our airplanes?...but if he was close to it because the power was reduced, then it is possible that the relative airflow over the wing was reduced to the point of a stall.

As I tried to explain earlier, in the Crash forum, on the ground, unless we have telemetry from the airplane, we can not tell the airspeed of the airplane. We can only see the groundspeed.

If you held out a piece of paper out of car, and were headed into a 20 mph hour wind (car not moving) the paper would blow backwards. If you accelerated the car to 20 mph, there would be 40 mph of wind flowing over the paper. However, if you turned the car 180º, the paper would still 'fly' in the same direction as it did before (car being still) but if you accelerated to 20 mph, with the wind at your back, then there would be no relative movement of the paper. Do you all agree with that?

Now, I agree that momentum will carry the airplane through the air mass, and that the airmass will exert a force on the airplane, pushing it. But, it will also rob the airplane of 'relative airflow' over the wing. The faster the airplane moves, the less impact this has, as demonstrated in the Crash Forum. But, if you are close enough to the stall speed, it will be enough to rob the airplane of the critical lift it needs to continue to fly. That's why you get a couple of seconds of 'stable flight' coming out of the turn, the momentum dies off, and without an increase in power, the airplane will stall.

Most pilots, R/C or full scale, don't fly airplanes close to the stalling speed in turns with a significant tailwind (or what would become a tailwind). Hence they don't see the disasterous results that we saw with this accident.

If Mr. Nichols had telemetry onboard the B-52, he might have seen the decreasing airspeed, and even knew that he was approaching stall speed, but given the amount of time he had, he probably wasn't watching the telemetry, but flying the airplane instead, and wouldn't have had enough time to react. Even if someone else was watching the airspeed, he would have to correlate the information, figure out what it meant, and passed the word to increase power. Could that all have happened in 2-3 seconds? We may never know, but it is unlikely.

Someone else posted that they had seen the airplane fly the day before in winds of 20 knots or so. Who knows how close it came the day before to having the same incident happen? It's possible that the airplane was actually on the verge of a stall then, but still had enough power and relative airspeed to continue without a problem.

We are dealing with a very small window of airspeeds here, but in this case, I believe that it was enough to bring the airplane down.

I get frustrated because this is so clear to me. I can see it, how it works, the beauty of it, and I can't find the words, or whatever it takes to show other people. Plus, it's hard to do it in a forum like this where I can't actually talk to someone, other than typing it. So, I get angry, mainly at myself, for not making it clear enough.

I am probably sorry I ever started this thread, but it's here now, so let's try.

For the person who suggested reading material, bring it on. And no, I can't show you anything. But, maybe your material will help me show you.

Gary

[mwraight]

No, it couldn't have possibly been a shooter from the grassy knoll. There was, in fact, a black helicopter seen hovering in the area moments before and for a few seconds after the crash. After the accident numerous black vehicles pulled up and men in black suits and sunglasses began milling about. No one can corroborate this account as they were threatened with 'pain of death' for talking about it. The video you have all seen is not actual, but was fabricated on a Hollywood soundstage - incidentally the same one used to film portions of the Lunar Landing.

[GaryMC1]

Sparky,
It is my understanding that the aircraft was scale enough that it did not have ailerons. The real B-52 doesn't, it uses spoilers. Or, so I've been told. In looking at what pictures I could find of it, there are several with spoilers up, for a turn, but I can find no documentation that mentions spoilers over ailerons.

Gary

[ETrain]

So, if your theory is true, why can you absolutely NOT assess a constant wind speed/direction in an airplane without ground references? If a constant wind actually had an effect on airspeed (as you said in the previous thread), why can't you gauge airspeed one direction and then 180 degrees from that direction, and determine the wind direction based on the change in airspeed? It absolutely does not happen.

I also balk at your contention that:

"In a real airplane, usually, the airspeed is high enough, and the power setting is high enough that when we turn the airplane, upwind, crosswind, downwind, we don't see the effect."

I can assure you that I fly in the pattern (as do many people) at an airspeed close enough to stall that if there is a 15 kt airspeed difference going from upwind to downwind, there would be entire chapters and flight instruction sessions based solely on this effect. My thottle is certainly not "high" in the pattern, nor is my airspeed, but at times the west texas winds are very, very high. If your theory was true, it would be deadly practically daily. I fly relatively slow flying planes (Cessna 172, Cherokee 160/180) in Lubbock, TX, where the wind is often 20-30 kts, and I can assure you that in that pattern I have definitely been within 15-20 kts of stalling, yet going from upwind to downwind NEVER affects my airspeed indicator (other than gusts, which is a different story). There is NO 5 kt or 10 kt or 15 kt drop in airspeed in a 25 kt constant wind no matter what direction I turn. It simply absolutely does not happen. And many, many people fly close enough to stall speeds that a 5, 10 or 15 kt drop in airspeed based on wind direction would certainly be deadly (gliders for sure), and it would be very well documented. You certainly could never do ground reference maneuvers as each time you made the downwind part of an S-turn, you’d be practically stalling with the wind as it is.

Again, I am not speaking of gusts (+30 kts to - 30kts in an instant), and that is a completely different story.

I contend:
A CONSTANT wind has absolutely no bearing on airspeed at all, whether upwind, downwind, or crosswind.

I feel certain that you do not agree with the previous sentence, but if I'm wrong and you're speaking only of gusts, then please let me know and I apologize for the confusion.

Eric

[GaryMC1]

No Eric,
I'm not speaking of gusts.

But, I will ask you to do something. The next time you take your 172 up, on a windy day, climb to 2,500, and repeat the demonstration I did with Flight Simulator. Fly upwind, and reduce your speed to 65 knots. Slowly turn the aircraft 180º, without touching the power, and maintaining your altitude.

You should find that you need to have the nose higher to maintain the altitude, and that your airspeed will slow. Depending on the amount of wind will depend on how far you slow down. Trim the airplane so that you're basically hands off slow flight, and then gently, 10º bank angles, and maintain altitude, turn around. Tell me if the airplane airspeed changes, without touching the throttle. Tell me if the stall horn bleats.

Thank you.

Gary

[Roj]

If you held out a piece of paper out of car, and were headed into a 20 mph hour wind (car not moving) the paper would blow backwards. If you accelerated the car to 20 mph, there would be 40 mph of wind flowing over the paper. However, if you turned the car 180º, the paper would still 'fly' in the same direction as it did before (car being still) but if you accelerated to 20 mph, with the wind at your back, then there would be no relative movement of the paper. Do you all agree with that?


Gary

Gary, this reasoning is flawed.
A plane or bird has kinetic energy relative to the air around it, the ground is irrelevant. If wind is 20mph, and the ground speed of the plane was 20mph into the wind, it would have a ground speed of 60mph and maintain a wind speed of 40mph (NOT ZERO) when turned around 180 degrees in level flight.
This is such a fundamental point that I can't believe anyone could misunderstand it.

Similarly, when flying "crosswind" across a slope, the air doesn't fly across the wings, as Sparky suggested, as far as the plane is concerned it is always moving forwards. This is basic relativity, not witchcraft.

[ETrain]

Gary,

I'll be happy to because I love to fly... :D

But I can assure you no such thing happens as I have often, often done 15, 30, and 45 degree turns round and round at a CONSTANT throttle and a CONTSTANT airspeed and a CONSTANT altitude for practice. If wind affected me, I would always have to adjust the throttle to keep a constant airspeed. The fact is, I can pick any throttle setting that allows me to stay in the air, and turn until my heart is delighted, and I will see no airspeed change no matter which way I'm facing. It all goes back to the fact that you cannot tell a constant wind based on airspeed without a reference to the ground (or gps, etc). Again, how could there not be huge BOLD, flashing warnings in flight instruction if a direction change from upwind to downwind could possibly cause a loss of airspeed (regardless of the amount)??? There would be a huge warning to preemptively increase your throttle when making the downwind turn because you are so close to stall, but there is not, because it does not happen.

Eric

[leccyflyer]

The B-52 that crashed was originally fitted with spoliers for roll control. Reportedly these were ineffective and thus ailerons were added.

[mwraight]

ETrain - I'll agree with you that a constant wind from a constant direction will not affect your airspeed appreciably. A sudden gust or abrupt change in direction will...but not for terribly long.

Your turn to downwind will not cause you any problems in this regard in the steady wind. If you turned downwind and were hit from behind by a huge high speed gust, you might have a different story. You might stall, you might have the warning horn go off, it might come and go so fast you never notice it but for a split second. Generally it's not going to knock you out of the sky. You'll accelerate with the airmass and continue flying at your previous airspeed. 20 ft off the ground is another story. That's why you carry your approach speed plus 1/2 the gust factor -- just in case that wind decides to try and catch you from behind. Say you carry a normal approach speed of 1.3 Vso - and you add 1/2 the gust factor - you've got a nice little cushion. If you stall at 50kts, 1.3 times the gust factor gives you an approach speed of 65kts, say it's gusting 25kts (you said you have strong winds there). Your approach speed would now be about 77 - 78 kts. Thats 27 to 28 kts above stalling speed...a very good cushion - and you would have to have a tailwind gust at or above that speed to give you a wakeup call. Something like that isn't a common occurence. We have a lot of built in padding on the full scale.

Now imagine your average model airplane - it has a very low stalling speed. I would estimate my Eagle II stalls at about 5 to 7 knots. Maybe a top speed of 35 - 45 knots. A big suprise gust from behind will be enough to end the game. Hopefully I'm three mistakes high and have time to recover -- maybe it happens so quickly I never notice it happens. But it can and does happen - especially at such critically slow airspeeds that most of our model fly at. But its the low speeds that make me willing to at least begin seeing credibility in what they call the "dreaded downwind stall". It doesn't happen just for the reason of turning downwind...I believe there are other factors involved...and there's probably a better name for the phenomenon. Pilot error and no airspeed information are still at the top of the list of culprits.

You don't need any more proof that a plane can be taken down by wind from behind than a Microburst. Yes the downflow it dangerous, but the tailwind outflow is more than enough to down even a large airliner.

But when you're flying around in nice stead state winds, for all intents and purposes you are a part of the airflow and moving with it...and the ground means nothing. Our models should be so fortunate!

[ETrain]

It doesn't happen just for the reason of turning downwind...I believe there are other factors involved...and there's probably a better name for the phenomenon. Pilot error and no airspeed information are still at the top of the list of culprits.

I agree 100%. The frame of reference is critical - inside the full scale I'm constantly checking my airspeed indicator, when I'm flying my models I'm making my best guess (hopefully erring on the side of a high airspeed) based on groundspeed and what I think the wind to be doing then.

I believe gusts to be an entirely different beast, and my ASI agrees as it jumps around! :D However, when it's basically a steady wind, I maintain that it is no problem to make a turn at a constant airspeed, attitude, thottle setting, and altitude. If a constant wind changed my airspeed, this would not be the case. It would also be possible to determine wind direction without ground reference, which is not the case.

Eric

[robert harik]

Lets say your plane has a 50kt stalling speed. You're on approach into a 10kt headwind. Your airpseed indicator shows you doing 60kts. Suddenly the wind changes to a 10kt tailwind. Congratulations, you now have a big insurance claim.

If the wind comes from behind the plane fast enough you will no longer be flying. I'm beginning to look at the downwind stall in a new light and am slowly believing. .

An airplane does not fly in a vacumm with the wind blowing against it.

A airplane flys with the airmass, the only thing tail or head wind is relevent to is ground speed.

If you are flying at 60kts airspeed and the airmass you are in accelerates 10kts in your direction of travel ,then you will still have a airspeed of 60kts, but now a ground speed of 70kts.

[KillerWatt]

Eye witnesses report at least 2 seperate upward rising streaks of light rose from the ground to the clouds where the '52 was and then a large, brite explosion was seen......also, a submarine and two unidentified speed boats were witnessed leaving the crash scene aat a high rate of speed......Radar tapes verify the unidentified targets leaving the scene................kw

[leccyflyer]

Probably well over a hundred modellers, or various levels of experience, have commented on this crash on various fora around the world. One constant theme has been the complete lack of concensus on which direction the model actually turns and spiralled in, whilst in more or less level flight, with a nominal amount of wing rocking prior to that event. There are many people absolutely convinced that the model was in a right spiral, there are many people absolutely convinced that the model was in a left spiral and there are people who have changed their minds, some more than once.

The event was the British Nationals Championships - three days of competition flying of hundreds of models, every single one of which was smaller than the B-52 and therefore even more liable to be subject to such deadly variations in the wind direction and speed. Has there been a mass of reports of models falling from the sky as a result of loss of lift on turning downwind? If there has then I haven't seen it. The importance of that point is that this particular crash is not a good data point to use as an illustration of any theory of loss of lift due to wind direction. There are other likely explanations for what happened.

The video shows that model was being buffetted from when it left the ground. The conditions were undoubtedly blustery and difficult to fly in. There is no denying that and in truth in those conditions and in fact the BMFA handbook guidelines for public flying displays advises


No flying will take place if the surface wind speed exceeds 25 knots, or if the visibility is less than 500 metres.

Presumably there would have been a calibrated windsock on the airfield - it's an RAF station temporarily "borrowed" by the BMFA for the weekend - and whether or not the windspeed was greater than 25 knots would presumably have been monitored.

That said what I'm seeing and what I would have imagined anyone experienced in flying models would also recognise as a distinct possibility is what looks like a simple case of being unsure of the exact attitude of the model and making an incorrect control input, that worsened a wing drop rather than make it better.

I appreciate that the video is a poor representation of reality but you can't get away from the fact that this was a grey aeroplane against a very grey sky and that it's inherently a horrible shape for visual orientation clues. In sillouette it is virtually impossible to state which way round the model is in many of those video frames. The signifiant lack of any concensus as to which way the model went in is as clear an indication as you could have that orienting the model was difficult- that's with the benefit of freeze frame, slo-mo video and sitting in the comfort of your own chair. The crash was over in a couple of seconds. Once that model was pointing at the ground there was no recovery possible, it had departed from controlled flight and would have needed hundreds of feet to get back under control.

In order to discount that disorientation was a major factor requires denying that the pilot is human. The impression is that because the pilot is experienced and has worked up to this giant model that his eyes cannot have been momentarily deceived and that he simply "wrong sticked it". There is absolutely no basis for that whatsoever. The ground is full of holes made by experienced pilots and inexperienced pilots alike.

The downwind turn has been kicked around on modelling fora for years, and in modelling magazines for many many years before that. If anyone can point me to an NTSB or AAIB accident report, or equivalent, that shows me that loss of lift due to flying downwind has been a contributory cause in an accident then I'll be very interested. I appreciate that windshear and microbursts descrbe similar phenomena. In contrast I'd bet that the number of model aeroplanes that are said to crash due to the downwind turn is in the thousands- it's likely the second most commonly cited cause of crashing, next to "interference". Many examples of both causes are more honestly attributed to pilot error and much of that comes down to the different frame of reference- we fly our models with reference to groundspeed, rather than airspeed - and the typical lack of any indication of airspeed available to the model flyer. So if you don't keep your speed up and overdo it on cutting the throttle back to stop your model from rushing away downwind, then you are likely to to stall and crash, not due to any change in the flight regime of the model imparted due to the wind, but due to you being deceived and trying to fly the model with reference to groundspeed.

Brian

[altur]

Gary From your post 49, you are demonstrating that you have absolutely no understanding of some of the basics of flying an aircraft, or how an aircraft flies. This is not meant to be personal, but it is a very serious situation for a 'licenced pilot' to openly expound such fundamental mistakes.

You claim that you are supported in your arguments by other pilots and two flying instructors. I cannot believe that any flying instructor would be licenced if he held such erroneous ideas.

Please answer the questions I have posed to you in post 37

Pending your reply, let me, as a retired Chief Flying Instructor with some 15 years experince in ab-initio training, try and explain in simple terms why I make the above statements.

1. In s&L flight, Lift = Weight and Thrust = Drag

2. In a turn, Lift has to be greater than Weight, in order that portion of the lift is directed towards the centre of the turning circle to provide the acceleration which makes the aircraft turn. If the aircraft is not to descend, the Lift has to be increased by increasing the Coefficient of Lift so that the vertical component of the Lift is still equal to the weight. To achieve this, a pilot MUST apply UP elevatorThis is why the nose attitude must be higher in a turn. As a consequence of increasing the C of L, the Coefficient of Drag is also increased and the aircraft slows down - unless the power (thrust) is increased to compensate. At low angles of bank, the small decrease in airspeed is normally accepted and power settings are normally left unaltered. However, at higher angles, such as in a 'steep turn, this decrease is not acceptable as the aircraft may approach the stall. It is a matter of simple geometry that the lift has to be increased to twice the value that is required in s&l in a 60 degree angle of bank turn. In this attitude, power has to be increased considerably, as the stalling speed has increased by approx 1.4 times.

If you do not understand all of this, you should not hold any sort of pilot licence.

The above is NOT my opinion - it is standard practice, and is taught to every licenced pilot world-wide.

[altur]

Hey guys - copy this

"PILOT ERROR" IN UAV CRASH
Well, this was bound to happen sooner or later. Pilot error has been blamed in the crash of an Air Force Predator unmanned aerial vehicle (UAV) in Nevada last June 14. An Air Force investigation concluded that an instructor pilot allowed a student pilot to continue a badly botched approach past the point of no return; the Predator was damaged to the tune of $4.2 million. More...

[Andy W]

A plane or bird has kinetic energy relative to the air around it, the ground is irrelevant. If wind is 20mph, and the ground speed of the plane was 20mph into the wind, it would have a ground speed of 40mph (NOT ZERO) when turned around 180 degrees in level flight.


I think Roj's explanation highlights the flaw in Gary's thinking..
..a

[Ben Diss]

But, I will ask you to do something. The next time you take your 172 up, on a windy day, climb to 2,500, and repeat the demonstration I did with Flight Simulator. Fly upwind, and reduce your speed to 65 knots. Slowly turn the aircraft 180º, without touching the power, and maintaining your altitude.


Gary-

Every single licensed pilot has done this already. We are taught to fly the airplane at minimum controllable airspeed. In this flight condition where the stall warning horn is blaring we are taught to climb, descend and turn. Often the turn will be a complete 360 degrees. I have performed this maneuver in different aircraft in calm wind and strong wind. I have never seen the airspeed change during the turn.

-Ben

[Andy W]

We do it in sailplanes too.. similar results. .. until we deliberatley kick in full rudder - then it gets fun! :D

If conditions are gusty we do add half of estimated gust speed to our usual 10 knots above stall approach speed for pattern and final. However, as I pointed out in my description of this model's flight above, it was certainly controllable at much lower airspeed than it was flying at when it started it's bank. Not only was this model not brought down by any external factors, but if it had been, it would have looked very much different.
..a

[Roj]

A plane or bird has kinetic energy relative to the air around it, the ground is irrelevant. If wind is 20mph, and the ground speed of the plane was 20mph into the wind, it would have a ground speed of 40mph (NOT ZERO) when turned around 180 degrees in level flight.


Actually I did my math wrong, The corrected statement is this of-course:

"If wind is 20mph, and the ground speed of the plane was 20mph into the wind, it would have a ground speed of 60mph and maintain a wind speed of 40mph (NOT ZERO) when turned around 180 degrees in level flight."

Which is what I'm sure everyone assumed I meant as it is such an elementary principle.

[GaryMC1]

Gary, this reasoning is flawed.
A plane or bird has kinetic energy relative to the air around it, the ground is irrelevant. If wind is 20mph, and the ground speed of the plane was 20mph into the wind, it would have a ground speed of 60mph and maintain a wind speed of 40mph (NOT ZERO) when turned around 180 degrees in level flight.
This is such a fundamental point that I can't believe anyone could misunderstand it.

Similarly, when flying "crosswind" across a slope, the air doesn't fly across the wings, as Sparky suggested, as far as the plane is concerned it is always moving forwards. This is basic relativity, not witchcraft.


Roj,
I'm not talking ground speed. I'm talking airspeed. The confusion between ground speed and airspeed is one of the biggest issues in this. I don't *care* about groundspeed, other than what a pilot on the ground would perceive. In a strong breeze (not a gust, although a gust is possible in this instance), it's the flow of the airmass that matters.

You said "If wind is 20mph, and the ground speed of the plane was 20mph into the wind, it would have a ground speed of 60mph and maintain a wind speed of 40mph (NOT ZERO) when turned around 180 degrees in level flight."

That sentence contradicts itself. If you have a groundspeed of 20 mph, and the wind, I'm assuming you mean on the nose of the airplane, of 20 mph, you will will have an airspeed of 40 mph. This provides that the airplane is relatively close to the ground, and all other factors are equal. You still will have a ground speed of 20 mph. Assuming that you now turn the airplane around, to have a tail wind, the groundspeed would increase. The airspeed, depending on the aircrafts stall speed, will decrease. Now, before I started the Flight Sim experiments, I would have said that the airspeed would decrease to zero, but I've learned that was wrong, at least partially. You would see a decrease in airspeed, possibly even an appreciable decrease. The airmass will carry the aircraft along, but at a constant power setting and altitude, you should lose some indicated airspeed.

As to the crosswind, you're right, it doesn't. At least not to the extent of a tailwind. Sometimes the airplane will crab into the wind, but most times you are flying fast enough already that it doesn't make a difference.

My whole point in this is that at speeds near the stall speed, and ONLY then a tailwind, gust or not, can slow the relative airflow over the wings to the point of a stall.

Obviously, if your are some percentage over the stall speed, you won't notice the difference. Most pilots, whether R/C or full scale, don't usually fly near enough to the stall speed to see this. Furthermore, most R/C pilots have no way to tell the airspeed of their aircraft anyway, and almost all will automatically adjust power to compensate if they see the airplane getting near a stall. But, again, with such relatively slow stall speeds of R/C airplanes, most pilots don't fly that slow.

Gary

[Ben Diss]

My whole point in this is that at speeds near the stall speed, and ONLY then a tailwind, gust or not, can slow the relative airflow over the wings to the point of a stall.


Let me see if I understand your point. I'm flying in an airplane that stalls at 61 kts. My airspeed is 63 kts. The stall horn is blaring. I'm carrying power to maintain level flight. I'm flying directly into a 20 kt wind. If I turn 180 degrees, the airplane will stall? Is that right?

-Ben

[ETrain]

Roj,
Obviously, if your are some percentage over the stall speed, you won't notice the difference. Gary

Sure you would, because in all of the full-size examples you've been giving, you'd notice the airspeed indicator changing without you moving the throttle! Again, this would make constant attitude, throttle, altitude, and airspeed turns impossible, and since peole do these all the time (including a version for the private pilot's license test), I think someone would have noticed. They would be downright impossible in the wind around here.

It was already discussed why your flight sim images were very misleading. For those who weren't in the previous thread, here's a link to Gary's screenshots (scroll down a little bit):
http://www.rcgroups.com/forums/showthread.php?t=270028&page=11&pp=15

As pointed out before, the nose of the airplane is in an entirely different pitch when he is comparing the airspeeds of downwind vs. upwind.

Eric

[pimmer]

Gary, you are proposing something absurd here. This is not even debatable. This is basic flight physics. You are simply wrong. If you ever do start flying real airplanes as PIC, then you will have to come to a better understanding than this, or you will be endangering your passengers. The same rationale that tells you to increase throttle after a turn to downwind, will tell you to reduce throttle after a turn from downwind to upwind. THAT will KILL you one day. I refer you to my analogy from the other post on this subject:


You are in a hot air balloon, with your airplane. There is an overcast layer. You have called DUATS and they say that there is a 50mph constant wind on top of the overcast layer. This concerns you a little, but the wind is blowing in the direction you want to go, so what the heck, go for it!

You get in your balloon and climb up, through the clouds, and you feel the balloon accelerate with the increasing wind speed. After a while, you are 5000 feet above the overcast layer and completely enveloped in the winds. At this point you will feel ZERO wind, since you are traveling along with it. It will seem like a dead calm day to you. The overcast layer below is completely featureless. You are too far away to make out any detail. Oops, you forgot to bring a compass! Oh well, you will just have to stay aloft for a time equal to the distance you wanted to go divided by 50mph, and then descend.

Now start your airplane and drop it over the side. Your job is to fly a race track pattern from downwind to upwind in front of you. But, wait a minute! How will you know where upwind is? How do you know anything about the wind speed? Can you even point with your finger what direction you are traveling? You are moving along with the wind. You feel no wind. You drop your airplane over the side anyway and fly it. There is no wind. It will be like flying in a dead calm day.

This is precisely the situation our models find themselves in at any appreciable altitude above our heads. They do NOT feel any difference between an upwind turn or downwind turn. Wind does not exist for them. They are like the balloon. Or the airplane you were flying from the balloon. If we pretend that there IS a difference, then we are not fully in control of the aircraft, we are approaching the margins of that control. There will come a time when we cross that margin, because we are perceiveing events from an independent inertial frame of reference, and a loss of control will occur. I want to make sure that RC students that are reading this understand this point. I have had to teach it to many. All I have to do is watch somebody fly in wind, and I can immediately tell if they understand this. They throttle back in the downwind leg turn, and throttle up in the upwind leg turn. They do it without thinking. It is dangerous. It will eventually bite them in the backside.

[pimmer]

Gary, please explain your thoughts on what I just said, and stop using the MS Flight simulator situation. It has been debunked.

[Andy W]

Gary, you are proposing something absurd here. This is not even debatable. This is basic flight physics. You are simply wrong

:D

Don't sugar coat it.. we're all friends here. Come on, tell him how you really feel!

..a

[Roj]

Roj,
Assuming that you now turn the airplane around, to have a tail wind, the groundspeed would increase. The airspeed, depending on the aircrafts stall speed, will decrease.


Gary, in a constant wind in stable level flight AIRSPEED DOESN"T CHANGE. It doesn't matter which way you turn. Upwind. Downwind. Crosswind. I'm no pilot but even I understand this fundamental.

If your plane can fly at ground speed 20mph into a 20mph headwind, it has an airspeed of 40mph. Turn around 180 degrees, and it's ground speed will become 60mph. Airspeed is STILL 40mph. There is no contradiction here. This is not my opinion, its the physics of the world we live in.

Read pimmer's hot air balloon example.

[Andy W]

To be fair, I found this in one of my flight manuals (direct quote): "The additional speed also provides a safer margin above stall airspeed. This is very desirale on gusty days because variations in the headwind component will have a considerable effect on indicated airspeed"

The momentum of an aircraft in turbulent conditions will prevent it from instantly responding to sudden changes in wind speed (gusts). In full-scale soaring, we add a small safety margin to our landing speed to allow for this. THIS DOES NOT APPLY IN THIS SITUATION, however, as this model was flying far in excess of it's stall speed at the time of the "incident" (as clearly explained above)..
..a

[GaryMC1]

It's a conspiracy, that's what it is! :D

Folks, I deeply appreciate everything you say. I thank you for trying to show me that I'm wrong.

I guess what I need to do is, after I get working again (being unemployed is such a pain in the behind), is to go to the airport on a windy day, and rent an airplane and instructor, and go try this for myself. That's the only way that I can convince myself that you are right.

Although I believe that I am correct, for the time being, I will bow to you. If and when I can get the money necessary to do empirical research, and will prove to myself that I am correct, or prove that I'm wrong, I will post the results.

Until such a time, you are right, and I'm wrong. By the way, I don't mind being wrong, as if you aren't learning something every day, then that day is a waste. But, unless I can prove to myself that I am wrong, I will still have my doubts.

Gary

[banktoturn]

Gary, in a constant wind in stable level flight AIRSPEED DOESN"T CHANGE. It doesn't matter which way you turn. Upwind. Downwind. Crosswind. I'm no pilot but even I understand this fundamental.

If your plane can fly at ground speed 20mph into a 20mph headwind, it has an airspeed of 40mph. Turn around 180 degrees, and it's ground speed will become 60mph. Airspeed is STILL 40mph. There is no contradiction here. This is not my opinion, its the physics of the world we live in.

Read pimmer's hot air balloon example.

I'm not a pilot, so help me out here. I understand that the plane will end up at the same airspeed, regardless of the direction of the wind. It does seem to me that it would take some time for that to happen though. As you point out above, if you start at 20 mph ground speed into a 20 mph headwind, you have a 40 mph airspeed. When you make your 180 degree turn, you will end up with a groundspeed of 60 mph, with the same airspeed, but doesn't it take some time for that acceleration to happen? It seems to me that there would be a short period of time when your airspeed is indeed affected by a turn relative to the wind. Am I missing something here? Please explain the "instantaneous acceleration" paradox that I am experiencing.

Thanks,

banktoturn

[Andy W]

It happens gradually as you transition during the turn. Just as you don't suddenly end up facing the other way, you don't suddenly have positive airspeed in the other direction.
Again - I fly full-scale sailplanes - we don't have engines - we can't accelerate in level flight. I can make a 180 degree or even a 360 degree or higher turn with minimal loss of altitude, and certainly no loss in airspeed (you lose altitude alowly in level flight in no lift conditions anyway).. we do it a lot looking for thermals!
..a

[pimmer]

I'm not a pilot, so help me out here. I understand that the plane will end up at the same airspeed, regardless of the direction of the wind. It does seem to me that it would take some time for that to happen though. As you point out above, if you start at 20 mph ground speed into a 20 mph headwind, you have a 40 mph airspeed. When you make your 180 degree turn, you will end up with a groundspeed of 60 mph, with the same airspeed, but doesn't it take some time for that acceleration to happen? It seems to me that there would be a short period of time when your airspeed is indeed affected by a turn relative to the wind. Am I missing something here? Please explain the "instantaneous acceleration" paradox that I am experiencing.

Thanks,

banktoturn



A, refreshing, perfectly legitimate question. In the example above, the airspeed went from 40mph in one direction, to 40mph in the other direction. This is the same thing as a ground speed of 20mph in one direction, to a groundspeed of 60mph in the other direction. Both changed values by 80mph, with one frame of reference sliding by the other at 20mph. There is no "instantaneous" change. The change occurs continously during the turn.

In both frames of reference, the model had to go through a change in momentum of 80mph. It does not matter if you start from +20 and go to -60 or start from +40 and go to -40. The net change in momentum is exactly the same. If you move one endpoint, the other moves by that same amount.

If the wind was 100mph, the groundspeed change would be -60 to -140, the airspeed change would be +40 to -40. The airspeed change will ALWAYS be +40 to -40. No matter what the wind speed is. Since the model always points into the airstream, it always sees a positive airspeed over the same point on it's surface. Hence, the -40 I mentioned is really +40 to the model.

[Roj]

I'm not a pilot, so help me out here. I understand that the plane will end up at the same airspeed, regardless of the direction of the wind. It does seem to me that it would take some time for that to happen though. As you point out above, if you start at 20 mph ground speed into a 20 mph headwind, you have a 40 mph airspeed. When you make your 180 degree turn, you will end up with a groundspeed of 60 mph, with the same airspeed, but doesn't it take some time for that acceleration to happen? It seems to me that there would be a short period of time when your airspeed is indeed affected by a turn relative to the wind. Am I missing something here? Please explain the "instantaneous acceleration" paradox that I am experiencing.

Thanks,

banktoturn

There really isn't any acceleration. The windspeed is unchanged.
It takes the same energy to maintain a groundspeed of 20mph into a 20mph headwind, as it does to maintain a 60 mph groundspeed with a tailwind of 20mph.

When you fly a 180 degree turn in dead calm, your plane doesn't turn around and all of a sudden find itself flying backwards. It maintains its forward airspeed and kinetic energy through the turn.

[mwraight]

Quoting Robert Harik:
An airplane does not fly in a vacumm with the wind blowing against it.

A airplane flys with the airmass, the only thing tail or head wind is relevent to is ground speed.

If you are flying at 60kts airspeed and the airmass you are in accelerates 10kts in your direction of travel ,then you will still have a airspeed of 60kts, but now a ground speed of 70kts.

It is true that you are flying with the airmass - just like a boat on a river. BUT you are assuming that your airplane accelerates with that airmass instantly, which it doesn't. If you get a 10kt wind from behind it will take you a few seconds to get an increase in groundspeed. If that wind comes from behind violently it's a different story. If you were flying west at 60kts with 10kt tailwind and that wind suddenly gusted to 30kts - you're not going to be able to accelerate with the wind fast enough to avoid a stall. No problem - you can point the nose down and accelerate. Eventually the plane will accelerate to the speed of the airmass...but it's not instantaneous, just like your car can't accelerate from 0 - 60 in 0 seconds...it takes awhile!

If your above statement was totally true then we wouldn't need to carry 1/2 the gust factor in our approach speed for safety.

Assuming gentle, friendly winds you're right...but in nasty, gusty, blustery, mean winds you can have problems.

I was flying a C-182 with 5 skydivers in it here in Arizona. We very commonly had gusty wind conditions and very strong thermals. Lots of windshear. The plane was always flying at 80kts in the climb. If I had a dime for everytime the airspeed indicator fell into stall range, the stall warning horn went off, or I had to nose down to avoid a stall --> I would be a very rich man. Now had the air always been calm and friendly, never trying to suprise me from behind, then it would've never happened.

Gusts can come up on you faster than the plane can accelerate with the gust.

[dag214]

I have looked at the video like everyone else. Being a full scale pilot I really dont think the tail wind had anything to do with the crash, however I do believe that a sudden gust or turbulances could have brought down this plane. Keep in mind that with a 30 mph tail wind the plane would seem to be really moving fast and it would be easy for the pilot to pull back on the throttles believeing he is going fast. Also this B-52 had spoilers on it they control the wing be decreaseing lift. If one wing is starting to loose lift (from getting to slow) and you crank in the oppiste controls you are know loosing lift on both wings. Just a few thoughts. I have flown many full scale planes were in a 30 knot wind my airspeed goes up and down by as much as 40 knots while getting close to the ground. Not fun.Also keep in mind that when an aircraft is in the air its movement is relative to the air moving around it. It's like if you are driving a boat in a fast moving river, if you turn down stream the water doesnt come up over the back of the boat, the boat just start to drift down stream with the flow of water. This is the same as in the air. At least when I was in engineering class thats what the told us. and if the plane made it thru the tight turn it made with out stalling if the down wind movement could have had anything to do with it the plane never would have made it to wings level. Just a few thoughts. You can also load this aircraft (the B-52) into a sim called X-plane (an FAA aproved sim) and fly the plane close to stall and head into a 50 knot tail wind and nothing happens. The plane just keeps on flying.

[dag214]

I have looked at the video like everyone else. Being a full scale pilot I really dont think the tail wind had anything to do with the crash, however I do believe that a sudden gust or turbulances could have brought down this plane. Keep in mind that with a 30 mph tail wind the plane would seem to be really moving fast and it would be easy for the pilot to pull back on the throttles believeing he is going fast. Also this B-52 had spoilers on it they control the wing be decreaseing lift. If one wing is starting to loose lift (from getting to slow) and you crank in the oppiste controls you are know loosing lift on both wings. Just a few thoughts. I have flown many full scale planes were in a 30 knot wind my airspeed goes up and down by as much as 40 knots while getting close to the ground. Not fun.Also keep in mind that when an aircraft is in the air its movement is relative to the air moving around it. It's like if you are driving a boat in a fast moving river, if you turn down stream the water doesnt come up over the back of the boat, the boat just start to drift down stream with the flow of water. This is the same as in the air. At least when I was in engineering class thats what the told us. and if the plane made it thru the tight turn it made with out stalling if the down wind movement could have had anything to do with it the plane never would have made it to wings level. Just a few thoughts. You can also load this aircraft (the B-52) into a sim called X-plane (an FAA aproved sim) and fly the plane close to stall and head into a 50 knot tail wind and nothing happens. The plane just keeps on flying.

[Sparky Paul]

Unless the long-sought for "air pocket" has finally been discovered, there's no aerodynamic reason for this crash.
As for the direction of the turn/descent, if the plane went to the right, as right is commonly defined, two things would have happened. It would have gotten -bigger- in the video, not smaller as it turned, and it would have crashed near the camera, not on the other side of the trees.

[altur]

Mwraight - of course you are correct in all you say.- been there,done that. But as far as the 'effects of turning downwind' discussion, inertia and gust effects are not in question. Gary's argument has been rather that there is a change in airspeed when turning downwind even in a uniform airmass.

However, I think that this question of inertia/energy change is where many modellers have their problems in grasping the concept. To see an aircraft 'suddenly' increase its GROUNDSPEED for no obvious reason seems like getting the proverbial 'free lunch'. As has been pointed out, what is often not realised is that the turn is not instantaneous. it takes time - a minute at 3 degrees/sec. By the time the aircraft is halfway around the turn, it already has acquired half the additional G/S ( lets use the KISS principle) that it will ultimately have downwind.

Think about a helicopter for a minute. If it was flying into wind and the pilot rotated the fuselage 180, it would not be 'instantaneously' flying downwind, even though it was pointing in that direction. This would be the situation where the inertia effects would become apparent, and it would take time and control changes for the helicopter to reach a steady airspeed/groundspeed downwind. I suspect that this is why helicopters change direction in the usual way ( so, sue me if I'm wrong :D)

[mwraight]

Altur - I agree wholeheartedly...if you turn downwind in a uniform airmass you're not going to get a change in indicated airspeed. As you turn slowly from upwind to downwind your airspeed will not change - your groundspeed will slowly increase as you accelerate with the new wind direction (it's like having ball bearings on your shoes and skating on a moving belt - it will take awhile to accelerate with that wind pushing you instead of pushing against you).

To be fair, and to prove I have an open mind, I tried the MS Flight Sim experiment. I selected a Boeing 737. I put the wind speed steady at 100kts from 360 degrees. I used the autopilot to ensure that everything remained as steady as possible. With a 260kt airspeed I flew 360 degrees - then had the plane execute a gentle 180 degree turn downwind. There was no change in airspeed, no change with the power settings. The airplane slowly accelerated to a higher groundspeed. I expected these results. I also tried it in a C-182. When I turned downwind I got a small decrease in IAS. This was due to the nose of the aircraft going up to maintain altitude in the turn - not due to turning downwind. It will happen no matter what direction you turn.

My theory on the B-52 is that it was hit by a gust - this could be a gust from any direction - front, back, up, down, etc. Any windshear is capable of stalling the airplane - which is why they have turbulent penetration airspeeds and manuevering speeds. If you're flying a C-172, for example, below design maneuvering speed the airplane will ALWAYS stall out before you can cause structural damage. Pull full back on the yoke - stall. Get hit by a huge burst of wind shear - stall. Excluding mechanical failure (which we'll never know until they form the Model Airplane NTSB "Go Team" :) )
If it was gusty that day I would vote that a gust of wind stalled the plane out and it was unrecoverable.

If you want to recreate this in a flight sim...take a small Cessna and do some slow flight with the turbulence set to heavy!! :)

[peterangus]

Regarding post #76. Acceleration paradox.

A turning aircraft does experience acceleration, but it is lateral, towards the centre of the turn. This accounts for the obvious change of momentum. It occurs just the same when circling in still air as when circling in moving air.

Lateral acceleration produces zero change in forward speed.

[Andy W]

My theory on the B-52 is that it was hit by a gust - this could be a gust from any direction - front, back, up, down, etc.
..
If it was gusty that day I would vote that a gust of wind stalled the plane out and it was unrecoverable.

If you want to recreate this in a flight sim...take a small Cessna and do some slow flight with the turbulence set to heavy!! :)

Please study the video of this model on takeoff. During the takeoff, it is most certainly being affected by the wind.

Then study the model as it rolls away towards the ground. It is most certainly not being affected by wind.

Go ahead and see what happens when you recreate this situation in a flight sim - you will not see a gradual departure from level flight - if you stall, you will fall out of the sky!

..a

[Roj]

Regarding post #76. Acceleration paradox.

A turning aircraft does experience acceleration, but it is lateral, towards the centre of the turn. This accounts for the obvious change of momentum. It occurs just the same when circling in still air as when circling in moving air.

Lateral acceleration produces zero change in forward speed.

This is correct, a change in direction does constitute acceleration, but we were referring to acceleration in its simple sense of "change in forward speed".

[dag214]

Andy W
If you look at the data of swept wings and stall They dont just fall out of the sky. I have stalled alot of swept wing planes and no of them fell out of the sky they all started a turn toward the high wing and start a large spiral that some times intered into a spin. If you go into the flight sim X-plane(a FAA approved sim). You can load a real B-52 into the sim and stall it and it will start a slow roll as the wing start to stall. If you go on the web and look at the real video of fighters being stalled they all drop a wing then enter into a spiral. If you cross control the flight controls you may beable to inter into a flat spin. Also in x-plane if you fly the real B-52 at near stall and hit it with a 30 knot gust of wind from the tail the plane does just what we all seen on the tape. Find some one at the field with a delta and ask them to stall and just watch what happens.

[Andy W]

That's very interesting, but I didn't ask anyone to consider the theory of swept wings and their stall charectaristics. I asked that they study the video.

When this model was affected by gusts at low airspeed it was, to put it bluntly, all over the sky! Even at a significant angle of attack, at low airspeed, in those conditions, the model flew out of it just fine. This shows that it would have to be in a fairly uncontrollable state to stall and lose control.

When it started to roll before the crash, it was not being affected by wind at all. It was flying straight and level, with no wind effects visible at all.

..a

[altur]

Dag - Your post reminds me of flying C 47's in Korea. Sometimes, as we cruised along at around 7000ft, we would get a USAF Sabre come alongside and formate. It was not unknown for the pilot of the C 47 to ease back on the throttles ( we were rotten to the core) whilst cheerily waving to the fighter jock and distracting him until the inevitable happened. As we laughed our miserable heads off, he would literally 'fall out of the sky' - only to reappear some minutes later shaking his fist etc.

[altur]

Further to the above, and with regard to the explanations being offered as possible causes for the B 52 crash, I can vividly remember as pilot of a C 47 taking off with some 28 parachutists aboard and as we entered the cross-wind turn being hit with a gust - probably entered a 'willy willy' ( strong thermal). The aircraft continued to roll to the left and the ailerons went 'limp' ( for want of a better term). The roll continued until the wings were almost vertical before the controls became positive again, and all this at only about 500ft. Need I say what was 'trumps' that day.

[RANSWrench]

I vote for windy conditions. Throttled back too far on down wind to keep within percieved airspeed envelope and stalled. I do it all the time with my CD-PCW in 20+ winds. My stall is some where around 15-20 that puts me at 35+ groundspeed on my downwind just to keep flying. I can easily fall below this and fall out of the sky if i'm not paying attention. Many factors can play into which wing stalls first. Also when its gusty you need to factor in the changing wind speeds and add this to equation. This looks like a very likely accident to me. The biggest disadvantage that an R/C pilot has is having to estimate airspeed. In the "real world" the airspeed indicator is the primary instrument. When you no longer have airspeed it takes a lot of altitude to get it back as demonstrated in the film.

[mwraight]

Andy - I'm not sure how you determined that the plane was not being affected by the wind before it started the roll and crash. Firstly, the aircraft is high enough that much of the minor movements would be indiscernable. Secondly, the film is so jumpy that no one would be able to determine with any accuracy whether the plane was flying stable or being buffeted by the wind.

This is not a real B-52, therefore it is not going to handle like one. Delta wings on models are not the world's most stable things. Delta wings aren't the most stable things on any size aircraft - but certainly being on a model it exacerbates the problem of stability.

Regardless of the apparent groundspeed of the aircraft, the airspeed could've been low enough that a gust of wind or buffet of turbulence could've put an end to the flight. Remember that an aircraft can stall at any attitude - if the critical angle of attack has been exceeded. A gust of wind or buffet is enough to change the angle of attack to well past critical. I watched the crash sequence a number of times. Ruling out a plausible mechanical failure - it looks like the classic stall & spin crash. But from the quality of the video, the distance of the aircraft, the unsteadiness of the camera and the speed at which every thing transpired - it would be nearly impossible for anyone to determine with 100% accuracy what happened. I'm sure the NTSB would be much better equipped for this situation!

Are there any more videos of this crash than the one posted on the first page of this thread? I'd be happy to look at them and get another perspective.

[leccyflyer]

There are two videos of the aircraft in general circulation.

The longer one at the Team Banana website, which has mostly been referred to here shows the complete flight, but is somewhat lacking in clarity.

The first video posted, which I think is available here -

http://mysite.wanadoo-members.co.uk/duggy/b52.wmv

has a clearer picture, but intense camera movement and failure to track the model makes this of less use in seeing what happened.

The model was flying more or less straight and level, going downwind with a couple of wing "rocks" for at least a couple of seconds before the fateful rollover and crash. That suggests to me that the unavoidable result of freak aerodynamics of the type being discussed in this thread aren't the culprit.

I think that the explanation offered early on in the other thread- that the pilot may have looked down momentarily to change something on the transmitter- like trims, switches or timer - and on looking back up to the model got a miscue from one of these wing rocks and simply "wrong sticked" it, with the inevitable consequences for a model with previously demonstrated lack of control authority.

There has been more than one person who claim to have spoken to the pilot himself regarding this. One thread on a UK discussion forum was taken down almost immediately, but the one on the UK radio controlled newsgroup remains, allegedly identifying disorientation as possibly relevant to the immediate post-crash "What the Heck Happened?" procedure

http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&frame=right&th=5466f189d4241a26&seekm=chug36%24ap%241%40titan.btinternet.com#link6

I suppose that we might find out in due course what the actual cause of the crash was.

Brian

[vintage1]

Further to the above, and with regard to the explanations being offered as possible causes for the B 52 crash, I can vividly remember as pilot of a C 47 taking off with some 28 parachutists aboard and as we entered the cross-wind turn being hit with a gust - probably entered a 'willy willy' ( strong thermal). The aircraft continued to roll to the left and the ailerons went 'limp' ( for want of a better term). The roll continued until the wings were almost vertical before the controls became positive again, and all this at only about 500ft. Need I say what was 'trumps' that day.

I've had precisely this effect with a rudder only low wing model with inadequate dhedral.

A cross wind appraoch, and some kind of turbulence cocked the wing up at 45 degrees.

Reverse rudder was not enough to pull out of the ensuing sideslip into the ground. Which took many seconds to complete.

I think its very important to distinguish between steady wind conditions, and turbulence.

Just because a model in grond effect and where turbulence is lower (near the ground) seems able to cope does NOT mean that making a steady flight over e.g. a bank of trees in the same wind conditions will be similar.

You can get massive turbulence where wind hits trees. I regularly fly over such and know to expect it.

I can't really say that the model in this case was or was not, subject to some kind of wind shear, but my experience says it would certainly be possible to knock it into a 45 degree bank - even at that scale.

And potentially the model, at that bank and speed might not have had the control authority to recover.

Especially if it got a gust in the tail to lower airspeed to reduce aileron effectivity... been there, done that too...


I've been on a full sized airliner landing in the teeth of wind gusting between 50 and 80mph, coming into land at Heathrow. We were all OVER the place. Up and down +- 100ft over the glide path at the least. The engines were surging from idle to damn near full power, G from weightless to 2g within seconds, wings rocking all over the place. We landed with a LOT more power than I have ever landed in an airliner, and in less rollout space on one of the short runways (NE approach into SW gale)

The turbulenec was less over the runway and nearer the ground. Up at 500 ft or so it was MASSIVE.


Why all this? Simply to make the point that wind shear and turbulence, whether you choose to call it - air pockets, bumps, line squalls or whatever - certainly exists, and the ONLY counter is to fly WAY in excess of stall speed and WAY high. Because you simly cannot predict which way the plane will get flung, or how much altitude it needs to pull out.

Flying an RC model under these conditions is MUCH harder. You can't feel the plane dropping when you get a tailwind gust. You have to guess from what is happening. Guess wrong and its crunch time, I've had my little parkflyers ripping downwind at what looked like huge speed, with noses up and full power on and losing height steadily (not stalling: Got past that one) and then, as the gust passes, suddenly they are climbing like homesick angels with a huge excess of airspeed.

Conversely, turn em into wind and put the nose down to make airspeed and groundspeed, the wind drops, and so do they! Like stones.

Flying in a steady wind is one thing. Turbulence is QUITE another.

[clipclop]

Ive read most of the posts and looked at the video several times , my evaluation is .
1/ the wind was gusty with about a 30-40deg cross wind factor comeing from the left rear of the vidoe opperator -look at how the tent/tarp is being blown .
2/ on the downwind leg just prior to the spin/crash the aircraft seems to have lost airspeed and is descending.the model then appears to be hit by a gust from the right rear causeing a left stall spin into the ground .
factors that may have caused this are :-
1/ the wind at 30-50ft+ may well be well above ground speed causeing the pilot to missread the true airspeed and throttle back to far.
2/ when struck with the gust/windshere the aircraft is stalled and pushed into a left spiral - if you watch the background trees you can clearly follow the left spin .
looking at the cloud formations the day was not favourable to fly or fly slow .
Stewart

[Sparky Paul]

I have done Vintages "low dihedral" sideslip any number of times with my Eindecker. The obvious wing-low nose high attitude of such a manuver is NOT seen in the B-52 flight,
There is nothing obvious relateable to any disturbance, atmospheric or aerodynamic in terms of attitude changing, except there is nothing that would indicate any control inputs to prevent the left turn once it starts.

[Threshold]

I think the pilot get disorientated, increasing the angle of bank and when he saw how much height he was losing he pulled up causing the spiral dive. The first rule in that situation is to level the wings. Then pull up. If you pull up while the wings are banked you enter a spiral dive making the bank worse. It also increased speed in the last few seconds again telling me he was pulling up. I don't think gusts had anything to do with it except perhaps to induce the initial bank.

It makes me laugh to see some of the guys in this thread so adamant about downwind stalls etc, what you think you see is not always what is happening. No wonder we all thought the earth was flat for so long ;)

I keep hearing "my plane will only hold a knife edge when its flying upwind" at my field and nothing will persuade them otherwise. Also "there was no wind to hold my plane up, my plane only glides well in a good wind" this on a flat field with no slope in sight.

What I have seen is wind gradient stalling a model. Long grass, 20mph wind, dead stick, 30ft up ground speed zero, model descends and the nose is held level, ground speed still zero, by the time its 5ft off the ground the wind speed is about 5mph due to friction from the grass and the pilot is still hauling up keeping ground speed zero so now the air speed is 5mph and SPLAT.

So many cartwheels happen at out field with people taking off crosswind, and they let the upwind wing get high as they rotate so again wind gradient grabs that high wing, they put in full opporsite aileron which stalls the low wing and over they go. I keep telling them to couple aileron with rudder on a switch for take off and landing which would help in that situation but they are too macho to do that. Rather carry on crashing planes than admit they need computer coupling :rolleyes:

[Roj]

2/ when struck with the gust/windshere the aircraft is stalled and pushed into a left spiral - if you watch the background trees you can clearly follow the left spin .
Stewart

The plane can be seen to spin either right or left as we are viewing a 2 dimensions only and there are no obvious clues to which is the top and which is the bottom of the plane. We are seeing only a silhouette. The background trees don't favour one direction over the other.
Apparently eye witnesses reported that the spin was to the right. As they were watching it in 3 dimensions, they are probably correct.

[Grejen]

I think that the explanation offered early on in the other thread- that the pilot may have looked down momentarily to change something on the transmitter- like trims, switches or timer - and on looking back up to the model got a miscue from one of these wing rocks and simply "wrong sticked" it, with the inevitable consequences for a model with previously demonstrated lack of control authority.

This would be my take on it as well. I remember when I first saw the vid, I instantly recalled the first time I lost orientation really badly. The path of the my plane was almost identical to that of the buff. I let it get into the south (bright) part of the sky on an overcast winter (low sun) day. My pupils contracted, the plane turned into a black shadow and I left sticked to correct a situation my brain knew was impossible.

btw - there was little to no wind at the time of my crash. I'm betting that if 'turbulance' was involved at all in the B52 crash it was only to trigger an incorrect reaction as stated.

I've come to recognize that peculiar twisted feeling in my head when my eyes don't agree with my brain. What I do is freeze! Wait, then react in very small amounts until everything agrees again. And yes, even with thousands of minutes of stick time I still loose orientation and react the wrong way tho it hasn't lead to a crash recently. - knock knock.

[Grejen]

he he :D - someone start a poll. When the actual pilot chimes in we declare winners.

[dag214]

Here is a sim I ran putting the specs. I found the web of the B-52. I entered it into X-plane (a FAA approved sim). I found that the stall speed as close as I could figure with the weight and wing loading was around 37 knots clean(flaps up) If you have the plane flying in the down wind at 55-65 knots it doesnt take much wind shear (20-30 knot gust) to make it stall. And every time the plane stalled it intered a slow roll. Here is the data out put from my video of my sim. I have no way to post the video. If some one knows how I can do this let me know. I also found out if the rudder would have ran full right you almost get the same kind of death roll.