Instructor

My Feedback: (16)

Thank you Flychatch for those kind words. I also fly turbine jets. Whith those I do most of my flying at half throttle or less. The only time I use full throttle is on take off and vertical manauvers. When I call landing, I lower the flaps first to slow the plane down and then I lower the landing gear. I set up my landing speed by slowing the plane down to where I want it for touch down and then I fly it at that speed right down to landing. During this time the turns are made with ailerons and RUDDER. Altitude is controled with power not elevator. The only time I use the elevator is to establish the flair for touchdown. Done right, it works everytime......

Larry

otrcman

Agreed. Exponential can go a long way toward smoothing out some of the twitchyness that is a dead giveaway for a scale model. Not only does a scale model with expo look more realistic to observers, but it also feels smoother and more realistic to the pilot. The slowed response to pilot input has the same effect as adding mass (inertia) to the model.

But remember Abu's quote in the first posting of this thread ? "I, for one, don't want a model that flies BETTER than the original. I don't want a RE-ENGINEERED version...." Adding exponential gearing to our R/C flight control system really is "RE-ENGINEERING", but the end result is that the model flies more realistically. Isn't that what we want ?

So here we are, considering some "RE-ENGINEERING" of the model to make it fly more realistically. My view is that, in scaling down an airplane, we have preserved the external appearance of the prototype, but we have drastically altered the physical dynamics in the scaling process. So, in order to preserve the physical dynamics, it may be necessary to make some engineering changes in a way that does not alter the static appearance of the model.

Are you with me so far ? Certain kinds of "RE-ENGINEERING" may be necessary and desirable to make our models more scale-like in their motions and how they "feel" to us.

Dick

abufletcher

I disagree. I do think we can FEEL how the model is flying (perhaps for the reasons explored in the "psychology" thread). Having it LOOK right is also pleasing, but I only fly for me and no one else at my club has any idea was "scale flying" might be. I think from there perspective, my flights are "boring." But inside my head I'm striving to match what my eyes are seeing with what my mind thinks it should be seeing.

abufletcher

I guess I wouldn't considering this "re-engineering" since the originals didn't have an RC system to start with. Some compromises must be made. To some degree the need for exponential comes from the fact that the technology of RC transmitters and transmitter sticks are "too precise." It's all electronics and computers. Imagine instead an "analog" transmitter with sticks attached to cables and pulleys with a certain amount of play and slop. Additionally, imagine that instead of pushing around a 1" long stick with the tip of your thumb, you were grabbing a 2 foot long stick with a full fist.

I'm also just philosophically opposed to "re-designing" WWI aircraft since, IMHO, they were, for the most part, build exactly like our WWI models. Sure, we can't exactly scale everything down, but we can accept the basic structural design of the original.

valleyk

Why do you think they make models for wind tunnel tests when designing full scale aircraft. Of course scale models replicate the full size flight characteristics. I guess there is no aeronautic engineers in the forum.

fred985

square patterns,,??,,,having taken all my flight training in my 450 stearman and going to lots of air shows allong with p 40s etc,,,i found that most all of us flew "navy" patters,,,,just faily long continues turns in the pattern. square turns in a p 51 at redused speeds are to much like work. we just set up our speed and desent and rounded out the patter. believe me its lots more fun in a heavy big plaNE. CHECK OUT THE WEIGHT OF A 450 STEARMAN. THEY ARENT A LIGHT LITTLE J-3 FOR SURE. sorry,,,i keep hitting the cap lock.

FireBee

My Feedback: (34)

I too try to improve my flying with expo and mostly focus on scale type maneuvers. I use some dual rates, mixes etc to make flying easier for me , as Im not in the cockpit to do certain things, and hopefully better and safer. But Practice makes perfect.

I'm with you getting bigger and now 1/4 scale looks small on the WW-I scene.

Kent Walters has been pushing scale speed for many years. His articles are worth a read.

Reynolds numbers is what allow scale wind tunnel models to replicate full scale. And some very long formulas.

I must say though, After 10 years I still "feel it" when I think back to a midair I had.
Painful adrenaline rush to save something so valued to you but with little control available. But hey I walked away from that one. My ducted fan Phantom stripped a big yellow rockwell P-51 of its starboard wind and stab. Neither of us at fault. we shook hands. I subsequently rebuilt mine as I loved that plane.

Jetdesign

My Feedback: (8)

It is all because the viscosity of air can not be scaled along with our models.

Reynolds number is a ratio of inertial forces (including size and weight) to viscous forces. You can change the size, shape, and weight of the model and the control surfaces, but you can not change the viscosity of the air (for all our intents and purposes). So a big part of the reason 'bigger flies better' is because the model is less 'out of scale' with the viscosity.

BobH

My Feedback: (2)

Well put Joe, For our purposes viscosity can also be expressed as a condition of Molecular size. In our case the full scale molecules vs. our models. While we share the same size molecules the density of those affecting our scale models is not proportional to those affecting the scale counter parts. The smaller the model the faster the needed speed to make up that difference.

So we can never really fly exactly like the 1:1 model becuse we are different! What we can do is approximate the full scale flight as best we can. There are different methods unto that end

otrcman

Well, there is at least one "aeronautic engineer" on the forum. I spent most of my career as a NASA flight test engineer at Edwards AFB. A lot of my work involved subscale models and trying to understand the implications of size and mass differences.

Wind tunnel testing of reduced size models is a science in itself, and no knowledgeable engineer will ever try to tell you that a wind tunnel model tells him everything he needs to know about a full sized airplane. In some areas the tunnel models are most useful, and in other areas they are practically useless. Even interpretation of useful data can be a black art.

Reynolds Number explains PART of the differences between full size and scaled down, but only part. Dynamic scaling, that is accounting for body motions, is a subject unto itself and depends on many parameters beyond Reynolds Number.

My point is that a dimensionally scaled model is really only good for static display. If it does fly at all, it is hardly more than a vague representation of the real thing. Until you replicate the physical motions of the airplane all you really have is an object that looks great in a still picture.

Dick

sensei

What years did you work at Dryden? I was employed there from 1980-1989 before I moved to San Antonio and opened my own aerospace components company. I only ask because maybe I know you or My dad knew you while he was still alive.

Bob

otrcman

[/quote]

What years did you work at Dryden? I was employed there from 1980-1989 before I moved to San Antonio and opened my own aerospace components company. I only ask because maybe I know you or My dad knew you while he was still alive.

Bob

[/quote]

I was at Dryden from June 1964 until June 1980. From there I moved on to work for JSC on the Orbiter. PM me with your Dad's name if you will.

Dick

sensei

What years did you work at Dryden? I was employed there from 1980-1989 before I moved to San Antonio and opened my own aerospace components company. I only ask because maybe I know you or My dad knew you while he was still alive.

Bob

[/quote]

I was at Dryden from June 1964 until June 1980. From there I moved on to work for JSC on the Orbiter. PM me with your Dad's name if you will.

Dick
[/quote]
PM sent.

Bob

abufletcher

Maybe I don't understand what you mean, but I feel like I have to disagree...particularly for WWI models. I'm convinced that exact scale (or very nearly exact scale) of many WWI aircraft will fly just fine. Mick Reeve's Sopwith kits demonstrate that. They have a scale airfoil and (essentially) 100% scale outlines and appearance. And they fly just fine. Do they fly differently than the fat-airfoil, long nose, increased tail surface BUSA kits? Sure. But which one probably flies more like the WWI original?

sensei

Scaling is scaling and it doesn't matter if it is a WWI bird or a present day aerobatic bird, what is important is with all dimensional criteria perfectly matched from full scale to our models, the closer we get to a 1:1 ration in regards to physical size, balance, wing loading, and power loading, then closer things are to realistic flying of that model, and yes there is still that pilot stuff needed to pull it off. Now the further you get away from a full scale and it's attributes... This is one of the reasons why model designers re-engineer airfoils and other attributes in the first place.

Bob

abufletcher

Again, I disagree. I think a lot of the "re-engineering" we see has nothing to do with trying to retain a scale "flight envelop." I think it's about usually about making a scale model fly more like a trainer...or an Ugly Stik. Again, I'm primarily talking about WWI models.

sensei

The great thing is we can agree to disagree. I will state this though, while I was was designing giant scale aircraft for Aerotech R/C, the thought of making my designs fly like a trainer or an ugly stick never crossed my mind... All this doesn't change the that facts about the flight performance effects of scaling though and that is what we are really talking about.

Bob

abufletcher

Does Aerotech offer any WWI models?

sensei

I don't think so, but again, scaling is scaling and there is nothing magic about WWI aircraft over any other aircraft when it comes to the effects of scaling.

Bob

TFF

One thing I have noticed is all models crash scale. All our models fly better, the ones that do fly, than scale. They have to, our control feedback loop is too slow. By the time we see what we need to correct, the full scale has already made five corrections. We have the experience of picking our CG while they are stuck with what they got, always aft. If they had a rotary they had gyroscopic precession turning the plane in a different direction than control input, few modelers have dealt with that.
Weight distribution is off. Put some WB wheels on a 1/6 Sopwith Camel; do real wheels scale that heavy, no.
I like this chart http://www.mnbigbirds.com/Scale%20Factors%20Page.htm

LesUyeda

"I disagree. I do think we can FEEL how the model is flying (perhaps for the reasons explored in the "psychology" thread)."

I do not find the my flying feels anything like the real experience my son gave me with a rented plane, and I have been doing RC flying since 56.

Les

scale dail

My Feedback: (8)

I had to jump in here. On my two 4 engine bombers, I have adjusted the controls on the B-24 at least to make it "fly like a truck" as I have read that the full size plane was very sliggish. A freind of mine flew it and thought something was wrong. Yes, you have to move the stick over quite a bit to get it to do anything. It gives me more of a feel of how the full size plane might fly. Too bad the transmiters dont't have a control yoke instead of a stick.

BobH

My Feedback: (2)

Don, I may be mistaken but I think you are missing the engineering points. No one is saying that Scale models can't fly well. Nor is anyone saying that they can't fly convincingly. However its an illusion that we create with our flying skills and our planes. Its NOT THE PHYSICS of the full scale plane that is being replicated but an approximation. We can't have 1:1 physics unless we are 1:1 scale. On that there can be no disagreement.

And Aerotech doesn't make WWI planes.

otrcman

Right on, Bob. "Its NOT THE PHYSICS of the full scale plane that is being replicated but an approximation." That was my original premise in starting this thread. And the question that I posed was: What can be done to more accurately duplicate flying characteristics ?

Several constructive suggestions have been made regarding piloting technique to make models fly more realistically. But what about gust response ? That's the "twitchiness" that we see when watching a model fly.

And not to gang up on you, Don, but have you ever considered the non-scale implications of attaching a rigid servo link to an all-movable rudder such as the DRI has ? On a real DRI there is no fixed fin, and the rudder is free to trail with the local slipstream regardless of how badly the airplane is sideslipping. The rudder contributes almost nothing to directional stability. Only the pilot's active effort keeps the airplane from sideslipping. When you attach a servo to the rudder on the model, the rudder is converted to a fixed (but controllable) fin. This change has a profound effect on how the scale model flies relative to the full scale airplane.

Another example of non-authentic scaling is rigidly attaching the elevator to a servo. On a real WWI plane the elevator is free floating and contributes very little to pitch stability. What we are doing by making the elevator rigid is effectively making the horizontal stabilizer far larger.


Dick

Instructor

My Feedback: (16)

May I ask you how the pilot is controling the Fin/Rudder? If I'm not mistaken, doesn't the DR-1 have cable
controls for the Fin/Rudder and the Elevator? If so, then the pilot uses the Fin/Rudder to sideslip the DR-1 by
moving the rudder pedals or tiller bar in the cockpit the same
way he controls the pitch with the control stick hooked to the elevator by cables.....

Larry