Differences in airframes
 

I'm curious... what causes some planes to stall very easy and violently at low speeds compared to others? For example, why, for airplanes like a geebe or a sukohi, do you need to keep the speed up, vs an extra? Is it just the wing design? Or is there something else that contributes to it?

RE: Differences in airframes
 

HI LANCE! Too high of a wing loading combined with wing designs that aren't producing much lift at the wing tips causes planes to" fall of the table" Highly tapered wings, with symetrical airfoils don't fly too well slowly, BUT if you remove enough weight from such a plane, even these wing designs will perform OK. I have seen a full scale GEE BEE that excelled at low speed aerobatics, because they scrapped the low drag racing wing, and built the rest of the plane with up to date techniques that are lighter. You have to get way up in scale towards full size before alot of scale wing designs begin to work well in model aircraft at low speeds.

RE: Differences in airframes
 

Lance -if you can make it light enough -the airfoil can be anything -
add enough power to that and the cg can be anywhere--sounds goofy but I can proof it.
for models - the working parameters are really a LOT different than what is used on almost all man carring stuff - simply because the defined task is completely different.
for many models - a simple light slab is just fine -as long as it holds it's shape.
much of the rest of it is whimsy.

RE: Differences in airframes
 

You're right about wing loading and airfoil, but the cg isn't related to wing loading and there are definite limits to cg location beyond which the airplane is not flyable regardless of power or wing loading.

RE: Differences in airframes
 

I shouldnt touch this with a 10 foot pole...but depends on your definition of "flying".

RE: Differences in airframes
 

Yep, it really comes down to wing loading and to some extent the airfoil selection.

There's funfly semi scale GeeBees that fly slowly super great and Extras that came out way to heavy and have some building errors in the wing that make it an accident waiting to happen.

I've flown a very badly designed Cub that was a violent snap roll into a flat spin model. It wasn't even that heavy but it WAS slightly semi scale and probably had a very bad airfoil. It only flew 3 flights before it entered a spin at a height below that required to tuck and then pull up.

So it's not the basic shape but a lot of factors all put together..... and it can be a big list at times.

RE: Differences in airframes
 

Hmmm, ok. I have a ohio r/c 28% sukohi, and I've been told it snaps really bad, and you cannot fly it slow or else it will stall. So I was looking at building a new wing for it. Would building a wing like the funtana for my sukohi improve flight? So something like a naca0013 for the root rib and around a naca0020 at the tip? Compufoil would make quick work of it, and this would help to prevent the tips from stalling out. I could also increase the wing area some, as well as get rid of alot of weight, since the wing is build like a tank and weighs alot. Also, would a built up wing or a foam core wing be ideal in this situation? Thanks!

RE: Differences in airframes
 

On any of these semi scale "IMAC" types -- wing loading is everything -
you simply can't build these things light enough - Impossible
No amount of clever airfoiling will fix these being overweight. None Zippo -Nada
The problem simply put is that these planes must utilize a very broad range of speed and controlled attitude
Formula ?
lots of power - extremely low weight.
Don't believe me ?
look at the winningist full scale areobats - that IS the formula.
So -just lookat all the construction methods YOU can use - pick the lightest and build the wing with a simple 12% (aprox) sym section - stiff and strong count a lot.
forget any washout etc..
you want a wing loading -on this size -for aerobatics and 3D--under 30 oz ft --also power -2-1

RE: Differences in airframes
 

Hmmm, well from what I can tell, most people are getting theirs in around 18-20 pounds. With 1360 sq in of wing, that puts the wing loading right around 30-35 oz/sq ft. Kinda high. That's part of the reason I wanted to build a new wing. Use as much composate material that I can, improve the airfoil a little bit, and hopefully get the wingloading down on it. I also have alot of work to do on the fuse. This thing is solid wood all the way through, including a ply motor box that extends all the way back to the canopy. I plan on drilling out quite a bit of that to cut weight. The builder of the plane also enlarged the tail section, so I have a bit bigger rudder and elevator to play with.

RE: Differences in airframes
 

Lighten it up as much as you can. You won't regret a moment spent doing that later on. Drill everything and then wear out your arms with some sheets of sandpaper. Go easy on the finish for even less weight.

As for the wing it seems to be a fairly generic airfoil. If you don't mind building a second wing and want something that is stall resistant I can recomend the Eppler 474. Some buddies of mine that were flying control line combat needed an airfoil that would turn super tight at high speeds. The stock airfoil was stalling under the G loads and tossing the model into the circle on them. A change to the Eppler 474 eliminated the stalling so well that they were able to turn tighter with the same loss of airspeed without fear of stalling or they could open the turns up to match the competition but keep more of the airspeed for a solid advantage in coming out of the corners.

Also making the tips about 10% wider will help to avoid tip stalling a lot.

It looks like it would be worth the time. That's a pretty good lookin' ship.