Wing loading.....again
 

Is a model with a high wing loading of over 30 oz/ft2 difficult to fly??
I plan to build a war plane of over 32 oz/ft2 but have no experience to say if this will be a difficult to fly model
Can some one tell me what in “normal” wing loading? Can the big birds with high wing load handle better than the small ones? Which is the most accepted formula when evaluating this characteristic weight in ounces divided by wing area or the cubic formula and the upper limits for these values??
Thanks

Marcos

RE: Wing loading.....again
 

Marcos,

You got it right when you say the big birds handle a higher wing loading better than smaller planes. From my experience I would say that a 32 oz wing loading is okay for .60 size and up. If a plane is smaller than that and has a 32 oz wing loading, things will get interesting with high landing speeds to be expected. On the other hand, if you have a quarter scale warbird with a 32 oz loading, that would be considered very light. It'll be interesting to see what the aero guys say on this thread.

RE: Wing loading.....again
 

A 32 oz/ft^2 loading model can be difficult to fly. Size matters. As noted, bigger is better when loadings get much above 24 oz/ft^2.
There is no upper limit on loading. Anything can be made to fly given sufficient power.
Whether it flies well, is a different matter.
Small and heavy is a twitchy difficult to fly situation...
For warbirds, larger... 60 inch span or > works well.

RE: Wing loading.....again
 

OK.....thanks for your coments. But can we put some numbers on this issue??
What is big?? Top Flite has a Giant P51 84.5" wing span with 32-35 oz/ft2. Is this is too "heavy" for a plane this big?
Is there any rule to follow? Where should be the limit between "small and big" and "light and heavy" . Sorry for being too specific...............
Thanks

Marcos

RE: Wing loading.....again
 

From what I've seen and flown, the large P-51 are *****cats!
There is a unique P-51 situation though.
It's very sensitive to elevator movement. They fly well with astonishingly little movement.
In my experience, along with this is the requirement to do wheel landings! They bounce badly when a 3-pointer is attempted, or the approach speed gets too low.
This is presuming scale-type flight is on the menu. The Mach 2 P-51s with the 2x recommended motor sizes are a different breed, and need to be treated as highly-loaded racers.. Don't try to float to a landing... the usual cautions for loaded twitchy airplanes.

RE: Wing loading.....again
 

There is no doubt that the size affects the scale effect and greatly changes how the wing loading affects a model.

I would suggest that to determine if the wing loading is good for your case you should examine a number of designs of various types from trainers and sport models to pattern and scale models for designs that are close to your intended size range. To keep it meaningful I would say you should examine everything that is within 10% of the size you are concerned with to keep the size scale effect in mind. From that you can determine the range of wing loadings for the type and size of model you are interested in. Probably scale if I'm reading between the lines correctly.

Once you have a range of wing loadings for reasonably successful models I would say that if you can stay on the lighter side of the range you model will fly well with fun type attributes. If you come out on the heavy side of the range you will have a model that will demand more attention and judgement to avoid attitudes that will result in disaster. And it probably won't be much fun to fly on a regular basis.

RE: Wing loading.....again
 

Wing area is a "square" factor of scale.

Appropriate wing loading is based on a "cubic" factor of scale.

If the scale is doubled... the area you get is (scale)^2 or 4X the original. The load carryable by the model is a factor of (scale)^3*K.

"K" is a coeficient of the airfoil and the wing design. (I made up the variable... I'm sure there is a huge long formula to replace it somewhere) K will be some value less than 1.0

You can experimentally determine K for any given wing planform and airfoil combination.

This assumes the same airspeed and angle of attack at all scales....

RE: Wing loading.....again
 

Here's a data point or two.

I built a large electric model with a group of guys for last year's DBF competition. Anyway, the basic plane was 72" span with a wing area of about 840 square inches. It had to be very strong, etc, so empty (but ready to fly) it weighed 11 pounds. That gives a wing loading of around 30oz/sq ft. Fully loaded with the two payload items it had to carry, it weighed 17 pounds, which brought the wing loading to over 40oz/sq ft. On a 30" span model, these wingloadings would have resulted in very bad manners. This plane, however, flew almost like a trainer. Even when fully loaded it was still easy to take off, fly and land. Only the landing rollout became much longer. (need brakes? ;) )

Big models can handle much larger wing loadings, as the others here have already explained. Having enough power always helps also.

-David