High Lift Wings

[Simon Chaddock]

A couple of weeks back I read with interest the recently posted article Tony Nijhuis wrote in 1985 about the construction and flight of his Airbus 400M.

 

An interesting subject (just look at those 8 bladed props!) even if the full size one has not even flown yet!

 

Like modern airliners the 400M will make use of sophisticated flap aerodynamics to generate a high level of lift from a relatively small wing to give good take off and landing performance yet an efficient high speed cruise.

Tony had to significantly increase the wing area of his model to achieve a reasonable level of performance.

This set me thinking - just how much of these clever high lift systems could actually be effectively modelled?

Could you for instance build a wing of just 50% area and retain the same landing speed?

 

Yes it might be a bit complicated (e.g. leading edge droops and multiple slotted area increasing flaps) but it would certainly look impressive when deployed.

 

I believe Barry Wetherall used flap rails (i.e. area increasing) on his Westland Whirlwind.

 

Just thoughts at the moment.

[Matt]

I've been toying with the arrangement of flap hinges to make them move back and down, just by moving the hinge point, with some success. But only in the virtual world of my PC. I havn't tried it for real as yet, due to being the worlds slowest builder.

 

The only problem I could forsee would be in making the structure stong and ridgid enough to cope with flying loads.

 

I'd love to be able to figure out a 'self deploying' system for slats...I believe the Lysander had them but could be wrong. Anyone know for sure...or how they worked?

[Andy Harris]

On a 40-60 size model airframe high lift wings could make it a 'cornered ferret' to fly, with vastly different characteristics in the upwind and downwind parts of the circuit.

 

   Rolls would be tricky and inverted flight may not be possible.

 

Still I guess the full size wouldn't do inverted well either

[Simon Chaddock]

The only plane I flew in with automatic slats was the Morane-Saulnier Rallye Commodore which we used as a glider tug.

 

The full span slats were on free running rails, angled in such a way that they were flush with the wing when in and forward and down a bit when out.

Obviously someone had done their sums right as in normal flight the aerodynamic pressure kept them in but at high angles of attack the change in the airflow direction was sufficient to cause them to come out. 

 

The air show demonstration stunt was to fly slowly, alternatively banking quickly left and right (thus temporarily increasing the angle of attack on the down moving wing) to make each slat come in and out. Without those slats doing this would have been rather asking for trouble!

Not easy to model though.

 

Aerobatics? As long as you have sufficient power the reduced wing area will just mean higher speeds so manoeuvres will just take up more space but rolling should not be a problem. Neither for that matter would inverted flight. A good flap arrangement could result in a fully symmetrical wing section when retracted but a highly under cambered one when extended.

 

   

[Simon Chaddock]

Whilst waiting for bits of the Hamilcar to dry I have doodled some thoughts on a possible high lift wing.

My experience is that on small size models with low wing loadings slots (either on the leading edge or on flaps) do not function well as the airflow seems to stick to the wing surface to considerably higher angles of attack than on full size. In addition the boundary layer does not scale so model slots have to have a much bigger gap (with further drag penalties) to get a reasonable airflow through them.

So the object is to take a conventional symmetrical wing section and convert it into a significantly under cambered one by using a two part flap.

My idea is that the first flap section would be full span but the aft section would be split with the inboard part moving as a double flap and the outer moving independently as an aileron.

 

At 40" span, 6" chord and 1" spar depth I reckon I could make it out of balsa and 2mm Depron to go on the Wing Dragon to see how well it works! It would have 70% of the originals wing area.

 

With slightly more exotic spar materials I am sure a higher aspect ratio, smaller area wing would be possible.

 

Of course it may not work at all!

[Former Member]

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[Terry Whiting]

Simon.,

 

I'm sure many moons ago there was an artical in RCM&E of a glider wing similar to your concept.

[Simon Chaddock]

A bit more doodling.

If I was going to build a "high lift" wing for the Wing Dragon it would look something like this.

A simple "plank" wing with an aspect ratio of 6.5. Not exactly a sail plane but rather better than the 4.7 of the original!  

The two larger servos move the main flap and the inboard second flap (slightly complex linkage) and the smaller servos, mounted in the flap itself, move the ailerons.

All the surfaces would be stiff enough to allow them to be hinged only at their ends to prevent wing bending loading the flap, thus reducing the servo loads.

Still a doodle at the moment.

[Former Member]

[This posting has been removed]

[Simon Chaddock]

Eric

Interesting using one servo to perform both camber changing and aileron but I have concerns about altering the effective flap angle to provide roll forces when in a really high lift, slow speed configuration.

I had in mind a landing approach that would need considerable power applied.

Taken to extreme it could look like this!

 

[Simon Chaddock]

Before I attempt the extreme high lift wing above I thought it might be prudent to try an intermediate version on the Wing Dragon.

 

The task is to obtain an improved aerodynamic performance (both speed and glide angle) with the same wing span and power yet maintain the same landing speed.

 

It will have just 65% of both the wing area and frontal area of the original and feature simple half span flaps but overall be no heavier (with 4 servos) than the current 2 servo Depron wing.

 

It will retain a Clark Y section but of reduced thickness/chord ratio and be tapered 2:1 root to tip. With only a 2mm Depron skin a double tapered balsa spar should maintain sufficient stiffness.

The plan and the prototype tapered box spar.

The balsa/depron/balsa spar construction.

The rest of its construction will have to go in a build blog. 

[Erfolg]

Camber changinging, flaps and slats have been used by both free flight and RC models.

With some free flight models, the trailing edge is decambered, for the climb phase and the camber increased for the glide.

 

There have been many RC models with camber changing, mainly gliders, decambered when traveling between lift and cambered for climbing in lift. My understanding that the difference in performance is not massive. The STOL Mk1/2 etc, had fixed flaps and slats, climbed very well, but went nowhere fast. A number of scale models have fixed slats ie Fiesler Storch etc.

 

With regards to automatic slats  and full size, the Bf 108 and 109 had them. Apparently not to good on the 109 as they could cause snatching in tight slow turns,

 

My guess is that they work up to a point, but do regard judgement from the model pilot to get the systems to work effectivily whilst flying.  

[Simon Chaddock]

I agree Erflog, the glider boys are trying to improve their performance over a wide speed range. Very difficult to do.

 

I am really only looking at two regimes. A smaller wing to reduce drag at high speed yet achieve high lift at low speed for landing (at the expense of efficiency) yet retain adequate control - a bit like any modern airliner.