T Tail Elevator

[Levanter]

I have had a part built Sophisticated Lady on the shelf for some time and this week I decided to finish it off.

Not having tried film hinges before I thought I would have a go using this method for the elevator. Many many years ago I built a Caprice and that has a de-thermaliser tailplane to put it into a descending mush when the fuse burns through.

Following this theme I wondered whether the elevator alone would have enough authority on its own to put the Sophisticated Lady into a mush. The reason for asking is that with the film hinge I will have limited travel in one direction and say up to 90 degrees travel in the other. Should I therefore arrange to have as much up-elevator as possible and more limited down?

Or maybe it's not going to work anyway so it doesn't matter.

Levanter

[Peter Miller]

Personally I would say that the elevator would not have the authority to put the model into that complelety stalled attitude that a dethermaliser does.

But it is an awfully long time since I did any serious free flight flying. A Calypso Major at the RAF Champs in the late 50s

[MattyB]

I agree - without significantly increasing the horizontal tail and elevator area I doubt this will be effective. A better way to escape from big air with RE aircraft is a spin or (if it won’t spin) flying inverted (which with the wing section on that will be super inefficient, exactly what you want!).

Edited By MattyB on 08/11/2020 09:35:37

[Levanter]

Thanks Peter and MattyB

I'll just go with the advised travel on the plan.

Just one more question. How do you get inverted? Off the top of a loop or bottom of a bunt? I image it will be seriously unstable.

Levanter

[MattyB]

Off the top of a loop - bunting a model like this poses too much risk of reaching disintegration speed! It will be very unstable, but remember you are just trying to escape from a big thermal - the best way to do that is to fly inefficiently in a straight line, you shouldn’t need to turn. It’s worth practising at a low enough altitude you can see what is going on in a non-crisis situation, that way you will know what to expect if you are doing it at specked out range!

[Levanter]

Thanks MattyB

Perfect

Levanter

[Frank Skilbeck]

Could you add spoilers into the wing, that would make dumping lift much more controllable.

[Levanter]

I have a 2m Sonata converted to electric (again half finished) that has spoilers so it will be interesting to compare the two.

One day that is!

Levanter.

[Levanter]

I have a 2m Sonata converted to electric (again half finished) that has spoilers so it will be interesting to compare the two.

One day that is!

Levanter.

[Frank Skilbeck]

Once you've used spoilers then you'll probably miss them on models that don't have them.

Years ago I had a 2 channel Multiplex Alpha H, got into a huge thermal off the slope, decided the best way out was to loop down, was great for the first 3-4 loops and then the wing snapped off, that stopped it from going up............................

[MattyB]

Posted by Frank Skilbeck on 08/11/2020 13:41:03:

Could you add spoilers into the wing, that would make dumping lift much more controllable.

Retrofitting spoilers is generally a complete pain - I tried once in an old bring and buy RE job, but quickly decided it would be harder than building a new wing and flew it as it was!

[Peter Miller]

One of the old dethermalisers used was a parachute attached to the tail. That would work. You could even arrange a second operation to release the line once the model was down to a safe height.

[Matt Carlton]

Perhaps some thin ply plates let into the fuselage sides using a servo to 'pull' them open against a band, somewhat like the fuselage air brakes on many jet aircraft.

Going further with the parachute idea, if it were mounted in a streamlined fairing on top of the wing, it could be located at the CG to permit a vertical descent? Given the band on wing, it need not be a permanent fixture.

Just a thought.

[Martin Harris - Moderator]

I've used large simultaneous upward deflections mixed in with ailerons on several gliders (around 45 degrees), which have been very effective - even on a 4m Discus. Easy to program on most transmitters these days assuming you have separate aileron channels/servos. Aileron control has still been effective enough especially if they are deployed once established on an approach.

Edited By Martin Harris on 16/12/2020 00:44:57

[Slope445]

I’ve used the tipped up (like 70 degrees) aileron method on my 100 in. Ventus. An added on, contoured, thin piece of fiberglass installed on the top of a 2 meter Phoenix and a tipped up central flap method on a 100 in. Trendy. 
 

All worked well to dump altitude. 

Edited May 30, 2021 by Slope445

[Piers Bowlan]

On 15/12/2020 at 21:40, Matt Carlton said:

Perhaps some thin ply plates let into the fuselage sides using a servo to 'pull' them open against a band, somewhat like the fuselage air brakes on many jet aircraft.

Going further with the parachute idea, if it were mounted in a streamlined fairing on top of the wing, it could be located at the CG to permit a vertical descent? Given the band on wing, it need not be a permanent fixture.

Just a thought.

I like that idea, in fact I did consider doing it on my PSS A4 Skyhawk (speed brakes) but I thought it probably had enough built in drag as it was and didn’t need them! I don’t even think they need to be ‘let in to the fuselage sides’, just a couple of hinged pieces of 1mm ply operated by a single servo would not cause very much drag when closed and be highly effective when open. May not cause too much of a trim change either.

Edited May 30, 2021 by Piers Bowlan