I would submit that full size planes are more that 1% different when built side by side on the same assembly line. That's a danged close tolerance for what was mainly hand work. If you talk to people who restore these aircraft they will tell you there are lots of differences between the same plane, same series. It's just the way it is. I agree with Pittsdriver. Besides you can't begin to scale the Mass of a plane, just something to consider

Scale appearance is just that. Your plane must be a scale of whatever documentation you bring. If the documentation is in "error," it should not matter. You're scale building skills are in question, not the variances in documentation that happen to be in the public domain. As far as margins of error, 1% can be overly generous. On a 100" wingspan plane, a 1" error would be ridiculous. I would rather consider a standard to be aligned with the scale itself. For example, the margin for error on a 1/8 plane is 1/8", for a 1/4 plane, 1/4", etc.

Scale flying is another matter. Flak said it best: "The aircraft reduces in size, but the air molecules don't."

Scale flying of a scale-appearance airplane CANNOT BE DONE.

Here's why:

Reynold's Number (RN) for minature (scale) airplanes is dramatically different than for their full-scale counterparts. Airfoils of the same section at different scales (different RN) have different aerodynamic properties (i.e., cL, cD). Also, of course as you scale a plane up, areas increase as a square of the scale and mass as a cube of the scale (please don't quibble about differences in the mass of aluminum and balsa). Thus, the wing loading is also vastly different between scale and full-scale. Then, there is propeller performance (jet guys, please cut me slack), which for the same basic aerodynamic reasons is also vastly different (although most won't notice the difference in RPM )

Taking all this into consideration, in some cases, pilots will be able to fly their scale bird at "scale speed." If that is the case, it is also most certainly the case that the attitude of the plane is not the same as would be for the full-scale. For example, to fly a scale plane at a "scale" landing speed, your angle of attack would be higher (to achieve the necessary lift) than that of the full-scale (although some might argue that a few degrees of AOA is not very noticable). When I've heard people say, "that plane looks great flying at a scale speed," they mostly mean it looks good going relatively slow, and this is a VERY subjective judgement.

"Scale" should only apply to appearance, objectively judged against documentation. Alternatively, scale flight should be considered a separate objective/category, so airfoils, wings, and control surfaces can be modified to produce more "scale" flying characteristics.

- George

Considering that "Scale" is judged from 15 feet I would doubt that any one could tell if the deminsions were correct or not. ALL.. let me repeat ALL scale judging is SUBJECTIVE; given that the judges do not use blueprint drawings and calipers etc. of our plane. Convincing the judge that YOUR PLANE is an accurate reproductive effort of your documentation is your GOAL. How WELL you convince them to that end is how well you are rewarded. Its that simple. As for Scale Flight. it is once again an attempt to Convince the judges that YOUR PLANE is flying as if it were the "Real Thing". Thats easier to do with some types of planes than others. Scale flight isnt only limited to the actual physics of a body in motion in a fluid (air) but also the manuver types and their execution etc. SEEING IS BELIEVING...for the Judges. You Convince them they have seen the "real thing" and your Rewarded! That simple..BobH.

Maybe yes, maybe no. I say it depends on the subject, the designer and the builder.

For example:

http://www.allaboutguppys.com/supgup/gupcomp.mov

This is a video of the Super Guppy model I designed and that my brother and I built and video of the full-size prototype merged for a side-by-side comparison (so to speak) of the scale speed of the model.

Scale speed CAN BE DONE.

It just takes a model with a light enough wing loading so that it doesn't stall while flying at the scale speed.

Dan

Nice movie... and model (I just love that pregnant airplane). Anyway, I agree with you and distinguish my statement...

Scale SPEED is possible... Scale FLIGHT is not.

As I said, you can achieve the speed, but the flying will be different, technically speaking. As I also said, the differences in flying characteristics may be unnoticeable.

Your Guppy probably has a full-scale wing loading of 200 - 250 oz/in2. On a 1:10 scale plane, if you can get 20 - 25 oz/in2 in your model, that's a very good job of building to get a scale wing loading. However, there will still be a change in airfoil performance due to lower Reynold's number (i.e., coefficients of lift and drag change). And if you lower the wing loading further, below scale, to compensate for the change in airfoil lift performance, you will no longer have a scale weight, and obviously many flight characteristics change with weight.

The better way to achieve scale FLIGHT would be to change the wings on the scale plane to a low-Reynolds Number airfoil which has lift & drag coefficients that match that of the full-scale and possibly also slightly adjust the size of the wings to better match overall lift & drag. Of course, you should match the scale wing loading.

Bob, you're right, there's certainly subjectivity in all judging. But like ice skating, scale flight is nearly entirely subjective (unless you're judge happens to be a former pilot of the full-scale plane). At least with scale appearance, if there's a question regarding, say, that funny little patch on the elevator, you can point to the drawing/picture as proof of the authenticity.

George, I would agree that you can (and should) show the distinctive features of your plane with your documentation. The over all apparence and relative sizes of the parts should match your docs. I was only making the cast that small deviations on size (say less than 1/4) are difficult to detect from the 15 feet judging distance.

Another thing to think about:

Flaps -

how fast to they deploy and how far on the real plane. Do you keep the same angle and rate at which they move from retracted to extended position. And then to complicate matters do we really have to prove to the flight judges how far the flaps extend, at the Nats one year the judges wanted to see the flaps and retracts move before the flight, but no proof was offered to how far the flaps were extended and how fast they move.

Landing gear -

take the AT-6, the gear retracts with hydraulics and the port and starboard gear retract at different time and rates. Do we ever prove how fast the gear retracts, does it take 5 seconds, 10 seconds or 20 seconds? obviously the gear up in 1 second with air (un-restricted) is not right but if we slow it down how much is scale and how do you prove it. And do we even have to prove how fast the gear retracts.

My vote is make something that looks right and has good flight realism.

Scale speed as already been discussed, cubs fly slow and fighters fly fast.

Fred Cronenwett

Thanks! It was a really cool model.

For the most part, I agree.

Because the full-size weighs more and is traveling at a higher speed, it will carry a lot more inertia through the manuevers. So, even though the full-size appears to be flying slowly, it is able to carry more energy through the manuevers.

This visual effect can be duplicated, but it takes a lot of extra work on the part of the pilot and the model needs to be overpowered so that the excess engine thrust can make up for the lack of inertia in vertical manuevers like loops.

Da