stall speed

[thermal]

In general, if my understanding is correct, a lighter wing loading will result in a plane that can fly slower before stalling...all other things being equal. How does this apply with respect to biplanes? The extra wing and bracing obviously adds weight and drag. Does the increase in wing area usually overcome the weight and drag to result in a plane that can be flown slower?

My objective is to build a light weight plane (10 to 12 ounce AUW) that can be flown relatively slowly and is as compact as possible. Is a biplane a better subject to meet these criteria as opossed to a monoplane?

Thanks for any insight,
Bob

[Sparky Paul]

Biplanes tend to be more manuverable than a monoplane of equivalent size.
For a very light airplane, any difference in stall speed would probably difficult to discern regardless of the wing configuration.
And if it's overpowered sufficiently, stalling will be a choosable option, not something that might be accidental.

[vintage1]

In general, if my understanding is correct, a lighter wing loading will result in a plane that can fly slower before stalling...all other things being equal. How does this apply with respect to biplanes? The extra wing and bracing obviously adds weight and drag. Does the increase in wing area usually overcome the weight and drag to result in a plane that can be flown slower?


Yes, I find MOST weight comes from the fusealage. You can cram a lot more wing area on a fuselage if you use two wings. nless you go 'slowstik' type of model ...



My objective is to build a light weight plane (10 to 12 ounce AUW) that can be flown relatively slowly and is as compact as possible. Is a biplane a better subject to meet these criteria as opossed to a monoplane?

Thanks for any insight,
Bob

Yes. Sounds like about 30" of stick and tissue biplane and a 300 power unit is where you want to head.

Sparky has it right on manouverability. Biplanes can be very responsive - low moment of inertia etc. The downside is they get tossed around by wind..

[banktoturn]

In general, if my understanding is correct, a lighter wing loading will result in a plane that can fly slower before stalling...all other things being equal. How does this apply with respect to biplanes? The extra wing and bracing obviously adds weight and drag. Does the increase in wing area usually overcome the weight and drag to result in a plane that can be flown slower?

My objective is to build a light weight plane (10 to 12 ounce AUW) that can be flown relatively slowly and is as compact as possible. Is a biplane a better subject to meet these criteria as opossed to a monoplane?

Thanks for any insight,
Bob

Bob,

I don't know whether a biplane is the best overall choice, but it shouldn't suffer in terms of stall speed. The extra drag of a biplane's bracing does not affect stall speed, it just requires more power to fly. In principle, the wings of a biplane should be lighter, for a given strength, than the wing of a corresponding monoplane. This is, in fact, why biplane designs were originally used. To take advantage of this potential benefit, you need to recognize that a wing's ability to withstand the bending forces that it encounters in flight is a primary limitation. This is what limits the span of sailplanes, for example. The wings of a biplane are of roughly half the span of a corresponding monoplane wing, so they don't need to be built as sturdily, particularly at the root. If you build your biplane wings exacly the same way you would have built your monoplane wing, then you have missed the opportunity to save any weight. You should be able to save more weight in the construction of the biplane wings than you add in bracing between the wings.

Good luck,

banktoturn

[biber]

Its not only the shorter wing that leads to a stiff, light weight and easy to build wing. For that you could simply increase the chord wich by same area reduces span. The main advantage is achived by the combination of vertikal distance between the two wings together with the vertikal cantilevers and the diagonal wires between them also working as cantilevers . This means the effective stuctural thickness of the pair of wings (in terms of bending stresses) is theyre distance to each other. thanks to this composition a biplane is easy to build, lightweight, and very stiff if done correctly. The bending stress is divided into simple pushing, pulling or possibly both for each component of the structure, wehter it is a spar, wire or cantilever. No component of the wings airframe has to withstand bending stresses anymore wich would cause a heavy construction. Look at the pitts s1 for example. There is no way to combine such a heavy engine with a lighter an stronger airframe! And each lb counts if you want to torque. I think all the other aspects on this topic mentioned in the upper postings are also correct (especially the thing with the higher rollrate) but this is/was often the main reason for an engineer to choose building a biplane an not a mono.

[BMatthews]

My objective is to build a light weight plane (10 to 12 ounce AUW) that can be flown relatively slowly and is as compact as possible. Is a biplane a better subject to meet these criteria as opossed to a monoplane?

Thanks for any insight,
Bob

Yes a biplane is the best design for this purpose unless you're willing to live with the odd look of the very low aspect ratio wings on a modern fun fly 3D style model.

All else being equal the same wing area in a monoplane will offer better low speed performance but if overall size is an issue then a biplane is the ideal planform.

As mentioned in biber's comprehensive answer the gap plays a part in how efficient the wings will be in a biplane. For best efficiency the interwing gap should be 1/5 chords. But good performance can be had at 1 to 1 1/4 chords gap. Do not go less then 1 chord or the wings will not work as well as they would otherwise. At around 1 chord you start to get significant interferance in the airflow of one wing to the other.

[thermal]

Thanks for all of the insightful replies. I think I'll have a go at constructing a biplane of the type I described and see how it turns out. I'll keep you posted.

Thanks,
Bob

[PfalzPflyer]

Have you considered a triplane? Then again, considering your avatar... perhaps a triplane is taboo! ;)

Dean in Omaha

[flieslikeabeagle]

The Wattage Sopwith Camel flies very slowly...heavily cambered wings, lots of wing area, light wing loading. The wingspan is roughly 36", chord 6" (same for both wings). The AUW of my Camel is about 15 oz, with a GWS 350C-CS and 2S, 1500 mAh Kokam lipo.

This model has, erm, not the best design, and requires significant mods to make it fly well. With lots of help, I finally got mine flying pretty well. It is very draggy, and flies more like a blimp than like a 'plane, but it does well in small baseball parks too small for anything else I own.

-Flieslikeabeagle