Old Slope Soarers never die.......

[PaulJ]

Back in the late 70s I was into slope pylon racing and designed a model which I called the "Lapwing". It had a fibreglass fuselage with a 7% V-tail. It was only two channel, Aileron and Elevator, and the Elevator was mechanically coupled to flaps to help it round tight pylon turns. It had a fairly thin wing with a sharp leading edge and almost flat-bottom section. It needed 2:1 aileron differential which was achieved by the geometry of the servo output and the rake of the Aileron horns. I made several variants of the model and really don't remember what happened to most of them but somehow, one old fuselage/tail survived two house moves and never got thrown out, though it was in a fairly tatty state. Well, in the long January evenings I decided to "refurbish" it and build a new wing for it........ And I have to say, I am quite pleased with the result.

Instead of the original one servo and belcranks for the Ailerons, the wing now carries a servo in each wing for the Ailerons and a Flap servo in the middle. There is only the Elevator servo in the fuselage. I am using the recently converted Sanwa Black Custom Transmitter with one of Mike_K's amazing GTB encoders, using the Aileron Differential mixer for the Ailerons and one of the programmable mixers to couple the Elevators with the Flaps. It all works like a charm...... And now all I need is a decent hill and a good breeze!

Paul

[_AL_]

Very nice. That would have been a hot one in the 70s.

[PaulJ]

That would have been a hot one in the 70s.

It was!

[Mike_K]

Hi Paul

It looks fast just sitting on the grass! It's probably even faster in the air. Did you make the fuselage moulds yourself? Glass fuselages take a lot of work making the moulds before you even make the first one, I'm impressed.

I'm pleased you've worked out how to use the free mixers on the transmitter for Flapperons or whatever the technical name is for mixing elevator into the ailerons. Did you do this in the 1970s or is it a new innovation for you?

Hopefully we'll see it at Ivinghoe...

[Martin]

I think the term is "coupled flap and elevator."
Control line stunters used to (and still) have it - usually a simple mechanical linkage where both surfaces are driven, in opposite directions, from the same bellcrank.
I used to race F3F slope soarers, and it definitely gave a noticeable increase in speed. The idea is that when the glider is pulling a lot of g, in tight turns, then you get less drag from the wing if it has an increased camber, but when the wing is lightly loaded in straight flight, there is less drag with a lower camber wing. The most practical way to have a variable camber wing is by use of flaps. Drooping leading edges were tried, but having a hinge nearer the front of the wing creates more parasitic drag.

The F3F guys called the mix, 'snap flap'. I think F3B has the same - you'd have one mode for launch, another for thermalling, a crow brake mode for landing, and the snap flap mode for general hooning about and making tight turns.

[Shaun]

Nice job Paul.

Snap Flap was a pre programmed mix in the Multiplex 3030 transmitter.

[PaulJ]

Yes, I made the fuselages myself but it was my first go at fibreglass and it wasn't a very good mold. The finished article needed quite a lot of work to make it look OK. There was a Mk2 (Lapwing-S) for which there was a much better mold.... I still have that mold, so maybe I'll build one of those next year?

The Flaps were originally mechanically coupled and only had maybe 1cm movement with full elevator. Just enough to give a bit more lift in the centre of the wing with minimal extra drag, and effectively give some "washout" at the tips to prevent it from tip-stalling as you screw it round the turns. In this refurbished version with the flaps on a separate channel, I should be able to experiment with the Flaps a bit more.

Paul