Building Wings, Ratio?

[Marv829]

Is there a standard for the ratio between a wings root chord dimension and how long the wing span should be? Or is it just engineered for the specific air foil and how much span and chord will be required for the designers goals? I was just curious if there was a general rule of thumb for the chord to wing span ratio.

Thanks,

-Marv

[Andy W]

There is no standard or rule. It depends on the style of model, intended flight envelope.
..a

.. on reflection, I guess you could say - chord:span < 1:1 :)

[phat23]

Basic aspect ratio rule-of-thumb (or at least a starting point) is 5-7:1 for a standard trainer type wing and 10-16:1 for a glider.

But as Andy said, it depends on the model, etc.

[Rotozuk]

You guys need to go into more detail on how the aspect ratio affects the dynamics of the planes performance. For example why is a higher aspect ratio popular for a glider or for that matter a prop?

My current design only has a 3:1 ratio. I'm looking for a stall resistant design that uses a very thick airfoil that will lift a rather heavy load at slow speeds and hopefully land at slow speeds also. I have no plans for speed in this ship. Compact easy to build wing are what I am after.

-Wayne

[Salto]

Some broad generalisations that may help:

High Aspect Ratio (AR) wings (long thin wings) have lower induced drag than low AR ones. On gliders this translates to a flatter glide slope. On powered planes it translates to less power needed to maintain level flight and therefore more power available for speed or climbing.

High AR wings are more difficult to build strong and stiff.

Very low (<2:1) AR wings, like deltas, or pizza box flyers, have a nice soft stall or even no discernable stall at all. But they have very high drag at high angles of attack. Medium low (4 or 5:1) AR wings retain a soft stall and are good for slow speed 3D type models where you have a lot of spare thrust available to overcome the high drag.

If you are low on thrust, nothing will beat a nicely made, high AR wing.

For a given wing area, high AR wings are bigger, so are more difficult to store and transport.

High AR wings are more vulnerable to crash and landing damage.


Anyone care to add some more?

Graham.

[Ollie]

You begin by desiding what type of flight characteristics you want the plane to have. Then you try to quantify and prioritize those characteristics. This data then becomes a standard against which you can judge the virtue of the many design decisions to resolve conflicting objectives that are involved. You can start with the characteriatics of the model that the equipment came from. Calculate its performance and deside how you want to modify it for "improvement." The process goes something like this: analyze, modify, reanalyze, judge results and consider new modifications. With sufficient iterations, the process should converge on your objectives.

Nature evolves its designs by a slow process of random variations and natural selection. You can evolve your designs so very much faster by insiteful variations.

Equations analyze. Design decisions synthesize.

[raptor22]

I'd like to add that low AR wings give faster top end speed.

--Alex

[vintage1]

Is that true though? Gliders are VERY fast and VERY slippery - or they can be.

I think the use of low AR wings for high speed is more a question of structural strength at high G.

[Ollie]

F-15 wing of angle sweep AR high to low . Flap + chord + of AR too.

>200 MPH Designs ARs ~0.5 to ~10 for R/C's Delta to DS glider's.

raptor22:
Think: Engr.: Equations analyze (math): DESIGNS decisions synthesize!!!

[Highflight]

The answers are obviously across the board because the "general" question as originally posed has no exact answer.

In the RC community, we have everything between flying lawnmowers and stop signs, to 150mph deltas. Then we go from the extemes of airfoils found on many gliders to the fat, short, stubby wings on some 3D models.

This all means that there can be no answer to the question until the SPECIFIC question is asked as to how one wants the aircraft to perform, and at what (relative) speed.

Any of the basic books on Radio Control Aircraft Design will point you in the right direction.

Highflight

[Ollie]

The formulas you are looking for will analyze a design but they won't synthesize a design for you much less optimize a design. Seeking an optimum design is an art rather than a science because it involves subjective trade off judgements between conflicting objectives.

It has been truely quipped that," An aircraft is a set of compromizes flying in formation." It has also been said, of aircraft design, with only slight exaguration, that,"Everything affects everything else."

In other words, there isn't a deterministic solution to your objective. IMO, that's why you can't find a computer program that does everything you want.

[Rotozuk]

If I was going to build a fast MODEL plane it would have a high aspect ratio wing with a thin airfoil.

If I was going to build a slow wing that i wanted to keep in the air for a long time, and stay in the air longer then my buddies, it would be a high aspect ratio wing with a thicker airfoil.

If I wanted to do crazy aerobatics it would have a pretty low aspect ratio and a rather thick air foil.

If I wanted to haul up a bunch of weight and have a gentle stall and easy packaging and light weight structure it will probably have a low aspect ratio high lift air foil.

These can all be argues, but this is my typical starting point. But the aspect ratio is just a building block.

I really love a high aspect ratio wing, and in our world of aviation they are pretty easy to build for the strengths we need. The larger a plane gets, and the higher the loads on the wing get the harder it is to build that same structure.

I say experiment for yourself.. Make up different planes and see what you think!

-Wayne

[rtideas]

I found an UAV, the P.L.A.N.C. (http://www.theissaviation.com/planc.html) It has a very low AR 21"wingspan / 36.5" length = .57 AR.

Doesn't that seem quite odd?

I question the usefulness. But they seem to have a gov't contract so it must be of some value.

[Sparky Paul]

rt, that's a collection of the "compromises" Ollie mentions.. If there were one configuration that could do everything, we'd see it. As it is, the mission determines the shape.

[Rotozuk]

Interesting plane. Looks like it uses elevator and rudder on the tips.. Lots of interior space. The speeds are rather high though, but so is the payload. Small and compact with hardly anything to break off.

Interesting design.

[rtideas]

I'm aware of the compromises, and many times, by bad luck (or lack of homework ;) ), but other than deltas, I have not seems any good examples (I learn by example, occasionally) of such a low AR. Even PBFs are usually =>1 AR.

It just seems well out of the norm--and totally intriguing. Just trying to learn more and understand its best usage would be.

[Ollie]

The DS gliders are for 249 MPH no dives!