Wings & speeds - slightly off topic

[Jeffx 0]

Hi, we are doing a project looking at wing shapes and their vortex.

Thinking of gluing threads along wings to see where they tangle and how much depending on the shape.

 

Was wondering if you'd heard anyone tried this before as dont really want to be spending hundreds of pounds on models and find the scale is too small to show sensible results.

What is the typical airspeed of, say, a 600mm and a 1m wingspan beginners electric rc plane?

If not too fast its maybe something we could do with just the wings and bodywork towed along offroad

 

Thanks if you reply

[Bravedan 106]

The size of a RC model has no single relationship to its speed. Drag (and that relates into aerodynamic shape), Power, etc.

 

http://physics.info/drag/

 

I have a less than one metre plane that can achieve over 100mph, a two metre plane which isn't capable of more than 50 mph, and another 2 metre plane that regularly achieves more than 90mph and would do more if it was re-propped for speed (note, no more power available, same wing, same drag, and so it hasn't that much to do with wing shape or section!!

 

The fastest RC plane in the world is currently a Glider undertaking Dynamic Soaring (you'll have to read that up) is around 4 metres span and has achieved 505mph.

 

A typical trainer type plane of pretty much any size will be flight capable in the 10 to 45 mph zone. It will have a lifting section wing designed more for stability and a degree of self righting than maximum speed.

 

I'm sure than the tuft test is hardly innovation, have you not looked?? I don't have time to look around but seconds gave me................... http://en.wikipedia.org/wiki/Tuft_%28aeronautics%29

[Jeffx 0]

Thanks, we know its not an innovation, except the information out there involves using wind tunnels or full size aircraft.

We wondering if anyone had tried on model aircraft more within our budget.

Some small models do have wing tip extensions but we're expecting those are more for style than effect.

 

I guess its down to the local hobby shop for some foamboard and dowel to start experimenting what size wing and speed combination we need to be looking at if its not been done before at this level. It maybe the best way to go anyway as messing with wing tips on full rc foam/balsa models could get tragic quite quickly, with some expensive bits getting trashed.

[Bravedan 106]

Wing tip extensions/fences are fitted to RC planes for a number of reasons usually quite a long way far from day to day full sized practice:-:-

 

1. To promote lift and/or stability when in "knife edge", that is stunt flying with the wing vertical and so generating little or no wing/tailplane lift.

A RC plane usually flies with the nose high to give some upward thrust from the propulsion, putting the fuselage (which might also be deliberately shaped to help by having a large side area forward) and any wing fences at an incidence angle for lift.

This will be very inefficient since these are at a drag inducing angle, but an RC plane often has far more power to weight available for such moves than full size.

 

2. To act purely as a stabiliser/rudder replacement, such as on swept "chevron" shaped flying wings, particularly those with no pod or fuselage, and also where a rear facing prop is centrally mounted and so a central fin would cause other issues.

 

Hope this helps................

 

BTW, look at Kline-Fogelman flat plate airfoils if you have not been there before

[Bravedan 106]

the information out there involves using wind tunnels or full size aircraft.

 

Which I expect is because the rc plane has to transition through quite different conditions to normal forward flight during take off and landing, likely negating the effect of tuft flight "readings".

[alan 0]

Jeffx, there must be tons on line but here are two good books if you like reading:

Model Aircraft Aerodynamics by Martin Simons

The Simple Science of Flight by Henk Tenneke (my favourite)

 

The early innovators of flight used to test wing sections by whirling them around on a bicycle wheel with the spindle vertical. It would be quite easy to knock something up to whirl a wing (with cotton tufts added) around. You could even add one of those tiny cameras on the other end of the whirling arm to record the effects on the tufts of the changes you make. Post the results here!

 

Here's my experience of flat foil sections: years ago I thought "if flat wings work for little planes, maybe they work for big ones too". I built a plane with about 56" span, 10" to 12" chord and 3/4" thick and completely flat except for a 1/2 round leading edge. After the first few flights I added a cambered top surface and it was greatly improved.

[Jeffx 0]

 

Spinning wheel, now theres an excellent idea, only transition being speed up and slow down.

Even better should be able to manage that indoors in the warmth and light.

Hole in a table , dowel rod, top support, wings attached facing opposite ways, thats going to be fairly quick to knock up.

 

On an american forum about foamboard self build they suggested using the digital settings on a transmitter to check the before and after level flight trim for overall change, and then doing one side only for checking additional lift.

Though that requires first learning to fly an rc exactly level of course, which I doubt is as easy as drilling a hole in a table.

 

Have some foamboard and and details off a website how to put together a sinple sandwich style wing that should be cheap, quick and easy to try different shapes.

 

So hopefully not too long before we have something to share on this.

 

cheers,

 

[Jeffx 0]

 

!!!

Fast, worthwhile, and relatively easy as it turns out.

& all done indoors!

The tricky bit was building the jig to rotate the wing.

 

The jig used a 1" dowel as an axle, one end inserted into a wooden block and mounted vertically through a box on an old dressing table stool, The wing middle was to be screwed to the block.

 

The rectangular wing was then constructed from foamboard. 33" span with 6" depth as base of the wing, then a middle layer 4.5" glued on, then a top layer of 3" to finish off. As the wing was rotating around the middle like helicopter blades the upper layers were in two halves making leading edges in opposite directions. Also a slot was left at the wingtip in the middle layer to make it easy to add extra sections on.

To test it we taped on alternate red and black thread about 1/2 inch apart and each about 6" long, just the outer part of the wings.

 

Handcranked there was no thread tangle. So I added a headless nail in the bottom of the axle and attached a drill. Gave it a good run but still no thread tangle.

Until I used my skin as a brake to run the drill at about 2 revs per second when we got reliable repeatable good tangle in the expected direction and from edge to 3, 4 inches towards the middle.

4 different style wingtip extensions were then made and tried out. At the same 2 rps the wingtip fence & upright tip had repeatable result of no tangle except the outer two threads which had slight crossover.

A hoerner wingtip, and blended style upright wingtip were not quite so good but repeatably better than none. This may have been size or positions rather than basic design.

 

Start to finish this took 4 hours, with all the model work, photos, and wingtip design done by my son.

Overall an excellent quick involving project for introducing youngsters to aerodynamics it turns out.

 

Of course what happens with different shaped wings, different speeds, landings, and the rest may well be completely different, but I think we may well go on and work towards giving it a go on a trainer rc plane now we know its quite probable it can be shown 'live' at this scale.

 

Have a bunch of photos if anyone wants see more detail.

Credits to flitetest.com for the wing design, camfc for the great suggestions that made it possible.

 

Thanks.