Correcting some previous posts

[globemaster3c17]

I just had a little chat with my aerodynamics professor about a couple of things I've debated with some folks on here. The two point is question concerned zoom climbing upwind vs. downwind, and stalling when turning downwind. I learned that I was wrong about a couple of things, yet still right is some ways. So I'm taking a bit of a pacifist view right now.
Zoom climb. The prof. said that if you use the ground as your frame of reference (pretty straight forward for an R/C pilot) it is possible to have a difference in the two climbs. He said that it would be noticable with a glider, but not measureable in a powered airplane. So while flying downwind, the plane has a higher kinetic energy, but it takes a bigger radius to go from level to a vertical flightpath. If you were flying upwind, you would have a potential to climb less, yet the transition from level to vertical also takes less distance. He didn't really get in to why theres a difference between a glider and a powered airplane on this, other than it has to do with the fact that model planes have a pretty high power to weight ratio.
The downwind turn stall. This is a situation that is related to the weight of an airplane. It's not a factor for full-size airplanes because they take so much more distance and time to turn around compared to model airplanes. Model airplanes can turn really fast and at high g-loads, and that is the underlying reason they can have a problem with this. Aerodynamically, there isn't a difference in turns related to the wind, as the airplane moves with the wind. But there is a difference when newtonian physics comes in to play. The air has to accelerate the plane for it to turn, and how fast you turn affects how well it can do that. I understood it by comparing it to driving a car on ice. If you turn too fast, the car is pointed in a new direction, yet you are still moving in your original direction. Take the same car and turn slowly, and the direction the car is pointed and the direction of travel are the same. It's kind of along those lines why some people have stalled when they turned downwind.

[Sparky Paul]

The old "downwind turn"..
The plane is flying in wind, the pilot sees it RTG. The flight path of the plane is altered by the pilot to that which he has seen when flying "no wind". This means he tightens the turn because he sees the plane is moving downwind more than expected.
That's what creates the stall, not Newton. :)
Climbing upwind or downwind.
The distance the plane is from the flier differs. Upwind, it remains close. Downwind it gets smaller faster. The actual -rate- of climb is the same, it's the preception once again RTG that is altered.

[globemaster3c17]

I don't dobt one bit about the pilot being a primary cause for stalling while turning downwind. That's what I wrote in another post. I figured it was due to guys reducing the throttle to keep the plane going the same speed, as the plane appears to speed up. As for the climb, I'm thinking it would be pretty hard to KNOW a model plane climbs higher on one climb versus another, (unless the differences are pretty substantial) as they generally don't use altimeters.
My reason for making this post is to show that in some ways, both sides of both arguments are right, up to a point. The way my prof. explained it, things made sense to me. Whether or or not I'm effectivly transferring that same information to everyone that reads this, well, that's up in the air.
I guess something that could also demostrate what I'm talking about with the turn, involves the Blue Angels. I've seen one of their planes flying really low over the runway, then suddenly pitch up (it's low enough that it looks like the tail with hit the runway). It takes a bit before the plane actually starts climbing. A similar occurance would happen with a really high rate of turn. The plane is changing heading faster than it can change its direction of travel. If you turned slowly, it's not an issue. Turn really fast, then it can be an issue.
Planes fly in the air, and so the speed that really matters to a plane is airspeed. But if you know much about flying, you know there's not much dealing with flying that is cut and dried. I wasn't thinking about everything related to the topic in my other posts. I didn't understand how the guys that had an opposite view could stand so firmly on what they said. So I consulted a person that I would call an expert with no hessitation before calling him that. He showed me that I wasn't exactly right with my view, but I wasn't completely wrong either.

[Sparky Paul]

The Blue Angels thing is inertia and aerodynamics.
The abrupt pitch up occurs before the air can adjust to the new AOA. Without adding power, the plane would continue on the orginal flight path until drag and lack of power intervenes.
A plane flies a circular level path in the air when turning if there's no reference to something on the ground.
Once the ground reference intervenes, and the flight path altered to accomodate, then the position of the plane with respect to the wind speed and direction, its flight path, and the position of the ground reference point affect what the is doing.
With a Flight Simulator that provides a history of the flight's ground track, fly a constant altitude-constant airspeed-constant bank angle for a circle or two, with no wind.
Then add the wind, and fly the same conditions, and observe the resultant ground track.
It will be a cycloid moving with the wind.
Now if you pick an object out the left window and fly a constant circle around that in the same wind, the flight path will show a continuously changing bank angle and groundspeed as you try to keep it circular.

[vintage1]

Exactly. The reason why you stall on a downwind turn is you pull it really much tighter because the plane doesn't seem to want to 'come around'

Once you have a 'feel' for drift angles etc, it doesn't happen. You start the turn much earlier than seems reasonable, and realise that once its 90 degrees to the wind its STILL moving away at a rate of knots, and then pull it slowly round the last leg to beat upwind again.

Either your professor is useless at explaining, or doesn't understand it.

Either way I'd change schools :D

[robert harik]

It is much easier to understand if you fly full scale too, and you can see whats happening from the perspective of the cockpit.
His professor probably does not fly models, and even if he does, it takes a little thinking to discover whats happening.
Most people I know that fly both models and full scale understand the concept.

[globemaster3c17]

Ok, I'm really not sure what to make of Paul and Vintage's posts. Vintage, you agree with what my prof. said in your first sentence, then say he isn't any good on your last two, or are you being sarcastic and I'm reading you wrong? I don't quite understand sentence #3. The prof. in question is the most knowledgable person I've ever met. I've had him in advanced aerodynamics, advanced aircraft systems, aviation meteorology, and for this semester multi-engine ground and aircraft powerplants. I have yet to hear of a question being asked that he couldn't answer correctly on the spot. "Attention to detail" is his favorite phrase, and a lot of the students here don't like him because he's too picky on answers, but I like him because I've learned a lot from him.
As for Paul, your first sentence is pretty much what I've been talking about. As for the rest of it, although you are making some valid points, your points are not dealing with the subject of this post. They are points that every pilot should know, but I've realized a lot of R/C pilots don't always know that, which is understandable since they don't have to have ground training before flying like full-size pilots do. I don't need a flight simulator, I have the view out of an actual window. :)
What I'm talking about with the high rate of turn would occur irreguardless of wind. I'm thinking it's just more appearant when turning downwind because the pilot intentionally slows the plane down without realizing it. While I've never experienced the situation, another guy posted on here saying that he's watched guys slow their planes down when turning downwind, yet the guy flying would say he didn't reduce the throttle at all. So if you take a guy reducing throttle when he turns downwind, coupled with turning at a really high rate of turn, I can see why some people stall while turning downwind. Not to even mention the fact that stall speed goes up with an increase in bank angle.
I don't agree with all the reasons other people have claimed is the cause of the stall on the downwind turn. But I now do see how it could happen under a particular circumstance. That is the reason for this post. It wasn't to start up a whole new debate. I just wanted the guys that I've argued with quite a bit over this to know that, in a very limited amount, I see what they were talking about, and why I've changed my view slightly. There's plenty of stuff on here I don't agree with, but that's not what I'm trying to get at.

[vintage1]

Lets juts say that leaving guts aside, the reasons poeple stall planes on downwind tirns is because they are standing on the ground, not flying the plane inside.

Birds don't make these mistakes, and neither do full size pilots unless they are looking at the ground.

I didn't understand what you said your professor said, thats all, and not sure what Newton has to do with any of it, or kinetic enegy, or inertia.

[robert harik]

The reason for down wind stalls in models as opposed to full scale aircraft is , model pilots use ground speed as their stall speed reference and full scale pilots use their airspeed indicator.

If a model normaly flies at a ground speed of 35 mph in no wind, but the wind is blowing 10 mph, its upwind ground speed will be 25 mph as you turn downwind its ground speed will be 45 (almost double).
Comparing the two speeds, the pilot thinks he has plenty of air speed going down wind and slows down the airplane to a more comfortable ground speed, but too low of an airspeed. The airplane is at or close to a stall.
At this point any turn, tight or not and your going to stall and crash.

Full scale pilots watch their airspeed indicator as their reference to stall speed and it does not matter if you turn upwind , dowind or crosswind your airspeed will always stay the same.

[Ollie]

A R/C pilot was in the air balloon. The pilot of the R/C aircraft piloted a perfect circle around the balloon at a perfect bank. The R/C aircraft of air speed was at 20 feet per second. Balloon of the wind at 20 feet per second past of a point on the land. For a person on the land for the R/C aircraft varied for land at zero to 40 back zero speeds over the circle at no change of bank. Oops.

[robert harik]

delete

[globemaster3c17]

Ollie was making a good example of frame of reference.
I realized one reason why you guys weren't quite following me here. The debate this post was a response to isn't even on this forum. You can read it here though. http://spadworld.net/viewtopic.php?t=8930
I got it mixed up with another big debate that actually was on rcgroups. Both occured on about the same days, and I'm on both forums several times each day. Oops, brain fart.

[robert harik]

Ollie, Thought about your post and that is a neat way of putting it.
Mine was a bit clumsier.

Globmaster , I am saying the same thing I said in another post anyway.
Brain fart here too!

[altur]

Could I ask a dumb question here? .When speaking about a 'downwind' turn, are you referring to a turn from flying downwind into wind, or vice versa?

[Threshold]

Why does the plane have a higher kinetic energy when flying downwind? Its flying at the same speed. Does that also mean that the rotation of the earth has some effect on kinetic energy as well?

Yes forcing the plane to turn or climb faster than the air can accomodate the change of direction causes a high speed or power on stall.

Downwind the plane seems to be flying faster and losing altitude so we pull up and boot in lots of aileron and cause the high speed stall, I always couple aileron with rudder for landing and taking off and that has saved many a plane in critical conditions.

[altur]

Threshold, An old rusty memory, but isn't kinetic energy = m x v(squared) So what v are we talking about huh? (Thinks - that can't be right, maybe someone will correct me)

Anyway, isn't that why satellites are launched with the spin of the earth - less energy to escape velocity AND ( a real Ripley) it takes longer to fly from Aust to UK than return ( or vice versa) - or so the airline schedules say !!!!!

[globemaster3c17]

altur, the downwind turn refers to turning to a downwind heading.
As far as the kinetic energy is concerned, it depends on your frame of reference. The equation for kinetic energy is 1/2 mv^2. If you make a relatively slow turn with your frame of reference moving with the wind, the airplane has the same speed and therefore the same kinetic energy reguardless of which way it is heading in relation to the wind. But if your frame of reference is the ground, then the plane has more kinetic energy flying downwind compared to flying upwind while at the same airspeed. In the end, it doesn't matter which reference you use, you get the same results.
For the satellites, say 200 mile high orbit requires a speed of 2,000 MPH to maintain orbit. Let's also say that the equator of the earth is moving at 1,000 MPH. So when you lauch from the equator, head east, as you are already moving east at 1,000 MPH. You would only have to increase another 1,000 MPH to reach 2,000 MPH. If you launched heading west, you would have to increase speed by 3,000 MPH to get an orbit speed of 2,000 MPH.
The difference in trip time on an airliner is mainly due to prevailing wind. Unless I'm getting it backwards, it takes longer to fly from the central U.S. to California than it takes to fly from California to the central U.S. This is a lot more noticable in the winter because the jetstream is farther south.

[vintage1]

Kinetic energy is relative. Because (linear) velocity is relative. Which is why if you fly at 750mph and someone fires a bullet at 751mph into the back of your head, it won't kill you.

Its why rear ending another car at 31mph when you are doing 32mph is not so serious as a head on collision.

There is no absolute (linear) velocity. Its all realative.

There is absolute rotational speed tho. There is always a rotational speed at which two balls on a piece of spring will be closest to the axis.

I aksed MY phsyics teacher about this years ago.

I asked him 'zero rotation relative to what?'

He paused a long time and looked very hard at me, and said 'relative to the average fixed mass of the rest of the universe'.

It was a few years later I realised he had been trying to find the simplest way to explain relativity to a 15 year old schoolkid, without sounding smart, and without actually telling a lie, or evading the question.

And 40 years on, nearly, I take my hat off to him for the best possible answer he could have given...

[altur]

Hi and thanks. Couple of points. Methinks there is a nought missing from that orbital velocity :p - just as I forgot that 1/2 :eek: Second, qantas reckon its not the prevailing winds - half northern, half southern hemisphere and mainly north/south track. I think they reckon its the world turning under them. :D :D Must check out what they say - I think I read it somewhere.

Me, I think it's just that one way it's all uphill and down coming back :cool:

I hope we are on the right forum to discuss these weighty topics? I enjoy a good 'discussion', but sometimes the lack of understanding is a concern - particularly when the comments are from full-size ( airplane) pilots. As modellers, the price is generally just the model. The other thing is that I find I am spending a lot of time - even if it is just re-reading the 'books' to support an argument. Is cutting into my 'building' time :( :(

PS I do subscribe to the " it doesn't matter what the direction of the wind is" school of thought. ie, the world is not flat after all. Who would have guessed :D :D :D

[altur]

Vintage good post mate - like your examples.

[vintage1]

It has been pointed out to you that whether you believe that green is the devils color, or the state of ripeness of apples that have a high acidity content, matters little as long as you realise that eating the critters gives you stomache ache, and desist.

The ability to get the right answers for all the wrong reasons has kept the human race alive a long time, and airline pilots are only human. In teh case of QANTAS pilots tho, one has one's doubts...:D

Personally I am sure the reason its quicker flying back to Asutralia is because of two main factors. They are keen to get home and have a beer, and the plane is always empty :D :D

[Sparky Paul]

If the earth's rotation created a shear in the wind due to the rotation, then perhaps that could explain any difference in flight times, presuming the climbs and descents and altitudes during flights in each direction are consistent.
But if the earth's rotation did create this shear due to the inertial effects of the atmosphere, there would be a varying wind from the same direction but of a differing strength based on altitude all over the world. This is not the case.
Ergo, someone is doing his sums wrong. :)

[altur]

Vintage Your posts are getting better and better - must be 'improving with age' huh.

Just as an aside, re the 'green apples' - did you know that the really green ( even when ripe) apple known around the world (and renowned for cooking) as the 'Granny Smith' is reputed to come from Sydney where it was named after the finder who had a mutation occur to her apple tree. Ho hum

Agree with your assessment of Qantas pilots. Thought it was only me :rolleyes:

Re 'empty' airplanes, they had better not be - I've got shares in Qantas. Which only proves that BA is much smarter than me ;) Actually, the real reason the planes fly empty is that we stopped bringing out 'convicts' when air travel became popular - too good for those 'bloody Pom's'. Bring back the Clipper ships I say. :p

[vintage1]

Oh, I only meant to say they are empty going back :D

Plenty of takers for the outbound flights...

The days of 'the way you can tell if its a plane full of Poms just landed is the whining goes on after the engines have stopped' are sadly over....

What were all those jokes about what airline names really meant.

I can remember..

BA = Bloody awful
SABENA = such a bad experience, never again.


Ah. Good old Google
QANTAS:


Queasy and Nauseous, Tired And Sick
Queenies And Nymphomaniac Transvestite Air Stewards
Queers And Nymphos Trained As Staff
Quick And Nasty Transportation, Australian Style
Quite A Neat Trick, Arriving Safely
Quite A Nice Trip, Any Survivors?
Quits Air-travel, Next Time Approaches Ship

http://wallofjokes.shacknet.nu/Transportation/Airline_NamesSlogans.html

[Sparky Paul]

But..
Quantas ain't never had no fatal crashes!

[altur]

Yes - a proud record. Keep it up guys - many of them are modellers you know. Doesn't stop us poking fun at them tho'. LoL

Vintage - keep it up. The laughs are getting louder. Even my wife Bev is reading your posts.