Use of ailerons for braking.

[David Hall 9]

Hi, I have a new 2m esoarer with composite wing, the HK Sigma. This wing has a large aileron precut into the panel, it's around 60% of the span and 30% chord.

As the model is not pre equipped with flaps (and I'm not keen to cut into the wing)... can the aileron surface be used to add a flap / spoiler function into it to give some form of braking? Any recommendations for a starting point?

Dave

[The Wright Stuff]

I'm not familiar with the model, but yes, certainly in principle that would work, and is very easy to try - without making any irreversible changes to the model.

You will probably need to mix in some elevator, and experiment, but start small. No more than 2 mm up/down from centre. Be aware that ailerons are intended to work most effectively from the neutral position and so will become less effective as you get further from that state. If you go too far, you could get some very nasty stalls.

If you have a spare variable channel on your Tx, you could set it up so that you can adjust the angle whilst in flight (and preferably up high)!!!

You are likely to get far better results from spoilerons than flapperons with a model like this, since the latter can be very tricky to set up without tip stalling, especially this far out along the wing.

With outboard spoilerons, you are effectively attempting to kill the lift. The effect as brakes in themselves will be minimal, hence my advice that a small deflection ought to be effective. The braking effect comes from lifting the nose.

Good Luck

Edited By The Wright Stuff on 13/06/2017 12:49:19

[Dickw]

With a heavy 2 servo 2m wing soarer I use ailerons up at about 45 degrees to act as spoilers for landing. Having both ailerons up reduces the chance of tip stall and allows a much slower, nose up, high drag approach. You will need to use some elevator compensation but if this can be added with a mixer then you can foget about that after a few experiments.

Experiment high up ( 2 mistakes high!) to start with so you can judge the elevator compensation required and to find out if you still have effective alieron control. If you can reduce, or reverse, aileron differential while the ailerons are up that will help with lateral control.

Dick

[TIM Shaw]

Not seen the model either, but just had a look at the specs and it seems to be a 2m electric Thermal Soarer, using Drela foils?

If that is so its landing speed is likely to be pretty low already, so I doubt you need brakes as such.

The problem with using outboard ailerons as flaps is that you induce wash-in when you deploy them, and since you are likely to be flying slowly anyway (you would want flaps to help you use light lift, so you are likely to be "scratching",) then you could very well induce a tip stall.

So I would say I have never had any success using outboard ailerons as flaps.

If you use them as spoilerons however - ie you pop them up, you kill the lift without increasing speed allowing you to lose height more quickly, and you induce wash-out, which improves any tip stalling tendencies it may have.

However, unlike TWS I would say that in order for spoilerons to be really effective you need to pop them quite a long way up, and you would probably need a little elevator compensation mixed in.

A small amount of reflex (maybe 1 to 2 mm) might give you a faster glide too, if for instance you were trying to fly out of sink, but be aware that any discontinuity in your trailing edge will cause drag and reduce overall efficiency.

Small caveat here - my experience is with RG14 warm liners and HN foiled slopers, which are both intended to fly fast, and I haven't played with them on Drela foils.

[Piers Bowlan]

I agree, Reflexed ailerons should work well to reduce lift and increase the rate of decent, if that is what is required. I would not attempt to use them as flaperons as this is a recipe for stalls and spins. As TWS has suggested, you will probably need some elevator mix to compensate for the trim change when you reflex the ailerons. I suggest 30 degrees of reflex is probably safe and still give you roll control but it is a case it of suck it and see - best tried at altitude!

[Former Member]

[This posting has been removed]

[David Hall 9]

Thanks All... The intent is to help landing accuracy on time (F5J/Esoaring comps). I am new to these comps. Some kind of braking seems to be desirable. The model will be set up with some camber change, at the time of servo installation, I will leave scope for more upward movement and play with it....at altitude.

[The Wright Stuff]

Posted by TIM Shaw on 13/06/2017 12:59:40:

However, unlike TWS I would say that in order for spoilerons to be really effective you need to pop them quite a long way up, and you would probably need a little elevator compensation mixed in.

A small amount of reflex (maybe 1 to 2 mm) might give you a faster glide too, if for instance you were trying to fly out of sink, but be aware that any discontinuity in your trailing edge will cause drag and reduce overall efficiency.

I can see what you are saying and why you are saying it. It might well be that 30 or 45 degrees of up works well in the end. But I would not start there - 60% of the span and 30% of the chord is a large area. A faster glide can be controlled by putting the nose up a little with elevator - which is likely to be the intuitive response anyway. Total loss of effective aileron control is less pleasant - although I do note that the model has a healthy dose of dihedral, and Tom is absolutely right about the rudder...

[MattyB]

Here is the model - it looks very much like a 2m version of a bagged DLG from the early 2000s (a bit like the famous Taboo GT):

On that basis you probably want to try both spoilerons (flaperons reflexed up 45-70 degrees with reverse aileron differential) and extreme DLG style brakerons (flaps down 70-80 degrees with additional differential) and decide which you prefer. You probably want these on the throttle stick so you can modulate it quickly to control glide slope (the throttle can either be on a side slider or on the throttle stick in a different flight mode).

When I first saw DLG brakes I could not believe they worked - everything I thought I knew told me they should turn the model into a tip stalling nightmare - but the combination of planform, aerofoil and extreme light weight seems to allow the "rules" to be bent. Hit the brakes and a good DLG just stops in mid air and descends under full control; it's eerie to watch first time! Personally I think the brakerons will work best, but try both at height and see.

PS - Remember when you use at extreme flap deflection angles (up or down) the rudder becomes your prime direction control; keep that left thumb mobile or add in a tad of CAR mix as the brakes come in.

Edited By MattyB on 13/06/2017 14:39:41

[TIM Shaw]

Posted by The Wright Stuff on 13/06/2017 14:05:32:

Posted by TIM Shaw on 13/06/2017 12:59:40:

I can see what you are saying and why you are saying it. It might well be that 30 or 45 degrees of up works well in the end. But I would not start there - 60% of the span and 30% of the chord is a large area. A faster glide can be controlled by putting the nose up a little with elevator - which is likely to be the intuitive response anyway. Total loss of effective aileron control is less pleasant - although I do note that the model has a healthy dose of dihedral, and Tom is absolutely right about the rudder...

Absolutely agree with all that, and with Matty too.

As regards rudder though - I'd use it all the time with that dihedral, not just for landing....

[Steve Houghton 1]

My experience using spoilerons on a glider is that they can be quiet effective at helping to lose height and bring the model down. However, depending upon the model, spoilerons can also have the effect of speeding up the model, even with quite a large defection, and then the model can come in quite quickly.

I have a 2m esoarer with outboard ailerons. Without using spoilerons the model will just float on forever, not seeming to lose much height. But reflex the ailerons about 70% and it loses height nicely, but it doesn't half pick up some speed.

I found that with the 70% reflex, there was still enough roll control left to make any adjustments if needed.

On the other hand, I have a PSS glider that doesn't pick up any extra speed but the spoilerons are very effective at bringing that much heavier model down on the slope.

Steve

A470soaring

[MattyB]

This video shows how effective DLG brakes really are - watch for the change to a substantially nose down attitude, but without any pickup in speed...

 

Edited By MattyB on 13/06/2017 17:35:15

[David Hall 9]

Thanks for your suggestions and ideas. It has taken this long to try it. Other models and an OpenTx installation then config got in the way.

I have set up as spoilerons. They deflect upwards to around 35 degrees and have some elevator mix to compensate the pitch change. They are very effective at killing speed without losing any control. As the wing has a large dihedral, the rudder remains as an effective control as the aileron authority lessens. No need to consider separate flaps as a means of braking.

Dave