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Old Sep 08, 2012, 09:32 AM
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Originally Posted by Wookster View Post
So what would you experience in a full scale aircraft if for instance you were flying over a nascar oval track. If you had to keep your aircraft directly over the track and run that pattern, would the downwind leg present any unique challanges?
As has been posted by cfircav8r, doing that (in normal winds, not 60 mph) is a routine part of pilot training in full-size planes. It is usually done at fairly low altitude (1,000 ft) so the trainee is able to see what is happening to the plane relative to the ground track. That is what I was referring to earlier when I talked about ground-reference maneuvers. And yes, it presents challenges, which is why it is part of the training. If done correctly, on the downwind leg would the pilot would observe that the ground speed increased while the airspeed would remain the same, and that the turn to the crosswind leg would have to be made sooner and with a steeper bank to prevent being pushed out of the pattern. The ground track would be the same as in a landing pattern and would remain an oval, not a tear-drop as someone said in an earlier post.

There is no difference between flying full size planes and RC models except for the perception problem.
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Old Sep 08, 2012, 10:39 AM
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[QUOTE=kaptondave;22675050]
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Originally Posted by Wookster View Post
So what would you experience in a full scale aircraft if for instance you were flying over a nascar oval track. If you had to keep your aircraft directly over the track and run that pattern, would the downwind leg present any unique challanges?/QUOTE]As has been posted by cfircav8r, doing that (in normal winds, not 60 mph) is a routine part of pilot training in full-size planes. It is usually done at fairly low altitude (1,000 ft) so the trainee is able to see what is happening to the plane relative to the ground track. That is what I was referring to earlier when I talked about ground-reference maneuvers. And yes, it presents challenges, which is why it is part of the training. If done correctly, on the downwind leg would the pilot would observe that the ground speed increased while the airspeed would remain the same, and that the turn to the crosswind leg would have to be made sooner and with a steeper bank to prevent being pushed out of the pattern. The ground track would be the same as in a landing pattern and would remain an oval, not a tear-drop as someone said in an earlier post.

There is no difference between flying full size planes and RC models except for the perception problem.
there is, rate of turn relative to bank angle for one. Also as you get smaller you have to start changing the airframe. Ever notice how the control surfaces become a larger part of the wing, tail, and elevator as the plane gets smaller.

you say part of normal training (not 60mph winds) well, how many of us fly our 1/10th scale planes in less than 6mph winds? doesn't happen around here. Again thats another difference between full scale and RC. .

Power to weight ratio is also another difference. Many rc pilots can hit stall and never have to drop the nose. just power up. My twist 40 doesn't really stall it transitions from flying on the wing to on the prop. Not sure a cessna could pull that off.

The physics are all the same in full scale and rc, it's just that the numbers in the equation are very different.
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Old Sep 08, 2012, 12:49 PM
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Originally Posted by kaptondave View Post

... there is, rate of turn relative to bank angle for one. Also as you get smaller you have to start changing the airframe. Ever notice how the control surfaces become a larger part of the wing, tail, and elevator as the plane gets smaller.
I am not convinced that what you say is true but none of it negates the original premise that downwind turns are no different than any other turn, and that the idea they cause stalls if false. This morning I had a 7 -10 mph wind at my flying site. I took my Radian up to a couple hundred feet, put the nose into the wind, cut the power and slowed down to zero groundspeed. It hovered nicely, bobbing just a little in the wind current. I then executed the dreaded downwind turn, and guess what. It turned smoothly and flew downwind at a brisk speed with no sign of a stall or loss of altitude.
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Old Sep 08, 2012, 07:33 PM
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[QUOTE=kaptondave;22676325]
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I am not convinced that what you say is true but none of it negates the original premise that downwind turns are no different than any other turn, and that the idea they cause stalls if false. This morning I had a 7 -10 mph wind at my flying site. I took my Radian up to a couple hundred feet, put the nose into the wind, cut the power and slowed down to zero groundspeed. It hovered nicely, bobbing just a little in the wind current. I then executed the dreaded downwind turn, and guess what. It turned smoothly and flew downwind at a brisk speed with no sign of a stall or loss of altitude.
Isn't that the upwind turn? Do we identify it as the turn from downwind, or to downwind? I was under the impression it was the from downwind.

The differences in scale are numerous. Some more obvious than others. Show me a micro size scale bird that doesn't have a rediculous size prop compared to the real thing. The turn rate is the same basic principle that allows for movie directors to make scale models of a scene and slow it down to half speed to look like the real thing.
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Old Sep 08, 2012, 08:51 PM
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Originally Posted by kaptondave View Post

Isn't that the upwind turn? Do we identify it as the turn from downwind, or to downwind? I was under the impression it was the from downwind.
A right turn is a turn to the right. A downwind turn is a turn downwind.

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The differences in scale are numerous. Some more obvious than others.
With respect to the downwind turn issue scale is immaterial. It is simply a matter of aerodynamics.
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Old Sep 09, 2012, 01:26 AM
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[QUOTE=kaptondave;22679698]
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Originally Posted by Wookster View Post
A right turn is a turn to the right. A downwind turn is a turn downwind.

With respect to the downwind turn issue scale is immaterial. It is simply a matter of aerodynamics.
Aerodynamics, mass, drag, power, speed, and not to mention the one variable that cannot be scaled down. Time.

In WWI the germans realized the deficiencies of scale in air tunnel testing. Prior to their research all scaled down models suggested that thin airfoils were the best airfoils. Once the germans realized this flaw they created a fat wing biplane that would have failed miserably in those wind tunnels. it was the Dr. VII I believe. the thick wing gave forgiving flight characteristics and extremely slow stall speeds. In fact the common practice of its pilots was to slow down to the point their enemies could not stay behind them. the fat wing also allowed for internal structure that eliminate a large portion of the rigging wires that were slowing most aircraft of the time down. If you were to take that same aircraft, scale it down and try and get max performance and the lowest possible airspeed you would end up with a thin undercambered airfoil. I sure dont see many undercambered wings on any modern aircraft To say scale is immaterial is akin to saying gravity is immaterial.
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Old Sep 09, 2012, 10:24 AM
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[To say scale is immaterial is akin to saying gravity is immaterial.
Please read this carefully and try to understand. You have not done well at that to this point.

I did not say that scale was immaterial in global context. This is a thread about whether or not airplanes have a tendency to stall when making downwind turns. What I said was that scale is immaterial in that regard.

The thread is not about airfoil design, control surface size ratio or any of the other things that you have brought up in your arguments. If you wish to discuss those things please do it elsewhere. There is a topic called Modeling Science that might be a good choice.
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Old Sep 09, 2012, 10:34 AM
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..is it true to say that if an aircraft does not have enough air speed then it will get into difficulties (stall) on a downwind turn..?
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Old Sep 09, 2012, 11:17 AM
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Originally Posted by kaptondave View Post
Please read this carefully and try to understand. You have not done well at that to this point.

I did not say that scale was immaterial in global context. This is a thread about whether or not airplanes have a tendency to stall when making downwind turns. What I said was that scale is immaterial in that regard.

The thread is not about airfoil design, control surface size ratio or any of the other things that you have brought up in your arguments. If you wish to discuss those things please do it elsewhere. There is a topic called Modeling Science that might be a good choice.
Buddy, do you have anthing better to do than come onto a web forum and insult people? I don't particularly care if I convince you that scale has an effect on the downwind turn. Thats your problem.. if you think turning a full scale plane in a 25mph wind is the same as a parkflyer, well thats your failing. you can 't seem to comprehend the fact that while it may take 30 seconds for a full scale plane to turn 180 degrees small parkflyer can do it in as little as half a second. Of course scale has no effect, right? Maybe if you took the time to stop thinking you were so much smarter than everyone here we could actually have a conversation. At this point I don't think it's worth it. No sense in feeding trolls. I'm done with you.
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Old Sep 09, 2012, 12:08 PM
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..is it true to say that if an aircraft does not have enough air speed then it will get into difficulties (stall) on a downwind turn..?
Not exactly. If the plane has enough airspeed to maintain straight and level flight it should be able to execute a downwind turn without stalling. The problem is that if the margin is small and the turn is not made carefully a stall is likely, because when the wing is banked for the turn some lift is lost.
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Old Sep 09, 2012, 01:07 PM
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if you think turning a full scale plane in a 25mph wind is the same as a parkflyer, well thats your failing.
One again you miss the point and misstate what I have said. Where did I say that I could turn a full scale plane at the same speed as a park flyer? I am a full-scale pilot and know better than that.

It is common knowledge that with a scale model of any vehicle speed needs to be scaled, but again that has nothing to do with the downwind turn. As I posted above, if the model is flying with an airspeed sufficient to maintain level flight (with sufficient margin), no matter what the scale factor is, it can the turned without stalling. Scale factor is irrelevant in that regard.

Please keep this discussion on topic.
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Old Sep 09, 2012, 01:48 PM
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Originally Posted by kaptondave View Post
Please keep this discussion on topic.
I do not consider the matter of scale to be off topic. It might seem that way to someone who believes scale has nothing to do with a downwind turn, but he brought it into the discussion in good faith and related it to the turn, and it is certainly possible that scale might be a factor for RC pilots.

It is true what you say, that there should be no problem if the airspeed is maintained with a margin. Wookster's point is that it is too easy to make an immediate turn with a small model, and that relates to the subject of this forum.
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Old Sep 09, 2012, 02:25 PM
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The point is there is no tendancy to balloon when turning into the wind or to loose lift when turning away from the wind, in F/S or models. It is a perception issue. In full scale when I introduce steep turns to students they will climb when making left turns and dive when making right turns. When I ask them why that happened the majority will blame the wind, when in reality it is because they are sitting left of center and the sight picture of the horizon should look different for each turn but they try to make it the same. On a left turn it should fill more of the windshield and the right it should fill less, but initially they try to even it out. Once they accept that their turns stay nice and level. We trust our eyes too much and that is the main problem.
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Old Sep 09, 2012, 04:08 PM
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I do not consider the matter of scale to be off topic. It might seem that way to someone who believes scale has nothing to do with a downwind turn, but he brought it into the discussion in good faith and related it to the turn, and it is certainly possible that scale might be a factor for RC pilots.
OK, clearly I do not believe that the scale of a model has anything to do with the downwind turn stall debate but if you believe it is a factor maybe you can tell me how.

Let's try a hypothetical. Say you are flying two scale models of the same plane, say a Cessna 172, directly upwind into a wind that is 50% 0f stall speed. One is 1/10 scale and the other is 1/25 scale. Both are flying best L/D speed. Execute a standard rate (30 degree bank) down-wind turn on both. What scale-related difference will there be with respect to any tendency to stall in or immediately after the turn?

If you prefer some other scenario feel free to choose one.
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Old Sep 09, 2012, 04:10 PM
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Originally Posted by kaptondave View Post
Not exactly. If the plane has enough airspeed to maintain straight and level flight it should be able to execute a downwind turn without stalling. The problem is that if the margin is small and the turn is not made carefully a stall is likely, because when the wing is banked for the turn some lift is lost.
i'll take that as a yes then..
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