Airfoil Sections

[Dai Fledermaus]

A number of flyers at our club design and build their own Foamies, and in every case they are electric delta wing types. Apart from their delta design they all have one thing in common, they only have a nodding acquaintance to what we normally recognise as an airfoil section, but they all fly very well indeed even at low speed. The wings are normally made up of a sheet of Depron with another piece glued on top, perhaps to about a third of the wing cord. Apart from a rounded leading edge nothing much else is done to shape a profile to the wing section.

Teeny Trainer is supposed to be a model to learn to fly on which hardly as anything in the way of an airfoil. The designer John Rutter claims that the optional built up wing only just improves the glide a bit. Honker and the Honker Bipe have a bit more in the way of an airfoil section, but only just. Most of the smaller scale Warbirds I see about our club field have quite thin wing sections, which on the face of it might not generate much lift, but they clearly do. So my question is how much of an airfoil section does a model aircraft need to have in order for it to fly acceptably or is this subject opening to big a can of worms?

[Former Member]

[This posting has been removed]

[Denis Watkins]

We all read books Dai, but my favourite book is one dated 1948 on the subject of Aerodynamics,

And even then, they had tremendous success with model flying

Using "flat plate wings"

Just look at the indoor guys maintaining flight with flat surfaces.

[Dai Fledermaus]

Thanks Dave, your description of these delta wings is spot on. I didn't know what they were called.

[Former Member]

[This posting has been removed]

[Nigel R]

IIRC at very low speeds and very small chords (i.e. indoor airframes), air behaves a bit differently and conventional sections just don't buy you very much; at typical model sizes and speeds, the big factors are LE roundness/size for stall characteristics and camber for some extra lift over a flat or symmetric.

I guess if you're building pylon racers then section probably matters to get minimum drag at high speed, and if you're building gliders you probably want to extract as much lift from your wing as you can. Other contest categories might mandate a particular choice (like, sharpish L.E. for crisp stall on F3A aerobats).

As for the rest of us, we usually have bags of power to overcome any aerodynamic inefficiencies that any given airfoil might produce. All a bit pub fact, but that's my understanding.

Personally... Either NACA2412 on sport types, or NACA 0012 on an aerobat. Then adjust thickness and highpoint / spar position to fit in retracts or aileron servos or whatever.

[Outrunner]

Back in the nineties Nigel Hawes produced a series of models that had a flat plate wing and around 48in span. IIRC they were all free plans and flew very well.

Phil.

[Piers Bowlan]

I think one significant factor with these flat plate wings is not only the performance that you are trying to achieve but also the wing loading. Depron and foam models are obviously very light but when used with a delta configuration the wing loading is very low indeed. Light models with low wing loadings fly better. Some of Nigel Hawes designs, Fizza, Whizza and his popular Tucano had sheet wings but were built of light balsa with no ply doublers or landing gear to add weight. Another excellent model with a flat plate wing is Ron Laden's Pushycat. If you look at the plan the structure is kept to the absolute minimum to save weight. It flies superbly.

I believe some wind tunnel testing was carried out recently with the KF series of aerofoils and they weren't found to be particularly efficient but what size the aerofoils were I have no idea. They clearly work at model sizes, - must be something to do with 'flees fly but elephants don't.' Another word for that could be 'Reynolds Number'.

[PatMc]

"Reynolds Number" is 2 words.

[Nigel R]

"one significant factor with these flat plate wings is not only the performance that you are trying to achieve but also the wing loading."

Bingo!

They're also a pretty good answer for something you want to go fast, without the refinements of an actual pylon race model:

Ultimate Warrior

[Piers Bowlan]

Posted by PatMc on 14/08/2017 21:16:49:

"Reynolds Number" is 2 words.

Touché PatMc 

Edited By Piers Bowlan on 15/08/2017 10:02:18

[kc]

There is some info on Kline Fogleman sections here