Ailerons as Flaps - Up or Down?

[EvilC57]

I have a Seagull Models Sea Eagle F3A type model, which as well as being well over the weight optimistically specified by Seagull (I think its made of plywood & concrete!), is very slippery and regardless of my efforts to scrub off speed on the approach, always comes in to land somewhat ballistically. Although I have achieved some decent 'greaser' landings with it, it's always been a bit of a handful, and so is usually reserved for windier days when there's some head wind to slow it down.

 

The model has no flaps as such, however by adding a flaperon mix into my DX8 Tx, and by getting the ailerons to go UP progressively on positions 1 & 2 of the Flap switch, I can successfully increase the landing approach sink rate, so the model is not across the patch and gone before I can get it back on the ground.

 

Ailerons UP slightly for landing was confirmed to me by one of our very experienced fliers, and seems to work OK without any nasty pitch changes. However, looking on YouTube recently, everyone explaining how to drive various transmitter flap menus, has their ailerons going DOWN (like conventional flaps) for landing.

 

I know about ailerons going UP while flaps go down on (say) a glider for crow braking, but who is right for direction when using ailerons alone as flaperons?

 

[Nigel R]

Depends on the model.

 

Going up, they will dump some lift. Gives a steeper, if perhaps slightly faster, approach. Viable solution. If you're happy I'd stick with this.

 

Going down may risk tip stall. Model dependent I think. In theory you should get drag and some lift. You could try this as well. Maybe make your flap switch do up for pos 1, neutral at pos 2, and down for pos 3. Then try them at height.

 

Or get a bit more serious, modify the model, you could saw the ailerons in half and add a pairs of servos - the outboard bits of ailerons do most of the hard work.

 

Other leftfield answers? Add a fuselage mounted flap (a few full size lightplanes do this, ex: http://flykr2s.com/bellyboard.html ), add some spoilers to the wing upper surface, add some thin, flat (i.e. ply) split flaps to the wing underside (forward of the existing ailerons).

Edited May 21, 2021 by Nigel R

[Simon Chaddock]

A slippery airframe with a high(ish) wing loading is bound to have a fast flat approach which takes practise to master. 

As Nigel says how you use flaperons depends on what you want to achieve. Up ailerons will reduce the lift for any given speed which means it will fly a bit faster. Down will increase the lift so it will be able to fly a bit slower but it does add the possibility of a significant and unrecoverable wing drop if you stall. To prevent this you may need to fly that bit faster to keep a bigger margin above the stall speed tending to defeat the objective.

You have to decide if a slightly steeper but faster approach is better than a slightly slower one with a potential catastrophic side effect.

 

By far the best solution is to add flaps inboard of the ailerons particularly if they go down to nearly 90 degrees just as they did in a Spitfire. They will create a significant amount of extra lift at no extra angle of attack as well as generating additional drag giving a slower steeper approach. Just as important it leaves the outer wing below the stall angle of attack so the ailerons will continue to function albeit with slightly reduced effectiveness.

Such flaps will not turn a 'hot ship' into a slow trainer but it can make a noticeable improvement.     

 

[Chris Walby]

Only my non technical opinion, what the others have said +

 

Flaps or ailerons going down will add lift, but you don't get something for nothing! IMHO the stall then becomes more abrupt be it one wing tip stall or both wings. it then becomes more pronounced to have good throttle control as in some cases a lot of the lift is generated off the propwash. Dump the throttle and it will fall out of the sky.

 

Flaps down to about 45 degrees just keep adding lift and drag, anything beyond 45 degrees just adds drag. if you have full length ailerons I don't suggest anything as extreme as that anyway.

 

set a mix up with aileron and flap on a TX knob, get up high and try various degrees of flap t see what the stall looks like, if you are happy try a landing, if not back to normal and use the arrester wire! 

[SIMON CRAGG]

Just a thought, what size prop is fitted?

 

If its really pitchy, it will always try and fly fast even with the revs knocked back.

 

Maybe worth trying less pitch / increased diameter?.

[EvilC57]

OK thanks chaps. Yes the model has a very high wing loading of around 35oz/sq.ft. So on balance, it seems safer to me to (as Simon suggests) to come in faster with ailerons up, but with a higher rate of decent, than to put the ailerons down and risk an unrecoverable stall. In which case, I think I’ll stick with Plan ‘A’ (ailerons up slightly for landing).

 

It has an OS 55AX, with an APC 12x7 prop. And weighs around 6.5lbs, when Seagull suggest that the finished model with engine should be around 5lbs.

[Piers Bowlan]

As others have said, full span flaperons are not recommended because of the increased likelihood of a tip stall and departure into uncontrolled flight turning onto final unless the speed is kept up (which defeats the object). Inboard flaps are best if you want a lower stall speed and increased rate of decent. Personally I wouldn't use more than 45 degrees of flap even with separate flaps and ailerons..

Edited May 21, 2021 by Piers Bowlan

[Denis Watkins]

You must be heck of a good flyer Evil, to control that particular model to land at all in one piece, with flaps UP.

Just my take on it, as a flyer

25° flaps Down, for some drag and some lift, for controlled arrival without tip stall.

Edited May 21, 2021 by Denis Watkins

[Martin Harris - Moderator]

This model has full span ailerons Denis so I would agree with those advocating raising them.
 

This changes the chord line and in order to provide sufficient lift, presents the airframe in a more draggy attitude with an altered aerofoil, steepening the glide path i.e. the lift/drag ratio decreases. 
 

Using them in the conventional flap direction would mean that the downgoing aileron will add more induced drag - with a tapered wing especially, a tip stall is more likely at any time while turning or making an adjustment in roll. 

[EvilC57]

Ha! I don’t know about that Denis, although I have had the odd round of applause when I’ve got it back down safely ?.

 

I may try reversing the aileron direction to go DOWN on landing sometime, to see what difference it makes; although as I said earlier, I don’t want to risk it stalling on the way in.

Edited May 21, 2021 by EvilC57

[Chris Walby]

35oz/sq.ft......dream on ?  My Vulcan is pushing beyond 45 oz/sq ft....that doesn't have flaps and lands without a flair...or not much!

 

 

Still think its worth a go with a little aileron (at height) to see if you can squeeze a little bit out without a impacting the stall characteristics.

 

I need to try this with another model that has a vicious tip stall and lands like a rocket so not much choice for me (I'll keep you posted)

[MattyB]

I am definitely in the reflex camp too - this would be my recommendation based on trimming out warmliners which have a similar setup (high wing loading, highish a/r, flaperons only)...

1. Setup your flapperons on an analogue control (dial or slider). If you don't have one of those set it on a 3 pos switch with 0, 30 and 45 degrees reflex respectively (utilise slowing if your TX has it to slow the transitions between states)
2. Take the model up nice and high - at least 2-3 mistakes (say 300-400ft)
3. Bring the engine back to tickover, let speed stabilise then add the reflex at around 30 degrees
4. Bring the model slowly and gently back towards the stall with elevator, seeing what it does. You will be steadily losing height at this point.
5. Increase the throttle to maintain height and see how stably you can fly in a high AoA (some models do this better than others, and it is also partially dependent on other factors such as CG position). Remember the model is hugely inefficient in this setup, with lots of drag being produced from the wing and fuselage at high AoA, hence  the additional throttle
6. If the stall is benign and it doesn't drop a wing but it's still not flying slow enough you can probably increase the reflex to 40-45 degrees. If so, repeat steps 2-5
7. If the model stalls abruptly or spins, reduce the reflex 10 degrees and repeat steps 2-5
8. Keep playing with AoA, reflex and throttle setting until you have a stable, nose high setting you'd be happy to use on a landing approach. If you have it setup right forward speed should be slower than before, but rate of descent similar to without the reflex. Flying like this at a high AoA is scary at first, but remember the wing is well washed out and resistant to tip stall in this state - you'll get used to it if you go steadily in stages
9. Fly the model around getting gradually lower as you gain confidence. Remember to be gentle on the ailerons; wide, sweeping turns are the order of the day!
10. Land the model from a long straight approach using your new setup and skills. Don't forget to ease off the up elevator and let it float just before touchdown, otherwise you might land tail first.

[John Stainforth]

One method for landing a "hot" model (particularly on a hard runway) that I found works for me is to fly it in very flat with no flap for a "wheels" landing and then flick on spoilerons (ailerons up) the instant after touch-down.

[Frank Skilbeck]

If you are going to try ailerons down to increase lift, it would be worth dialling in some differential so you increase the aileron up movement with aileron control, this would reduce the down movement of the ailerons when trying to pick up a wing as any more down movement would add more drag on that side causing some yaw and potentially a wing drop on the side you are trying to pick up.

 

You wouldn't normally want aileron differential on an aerobatic model like this as it may make rolls a bit barrelly, so having a separate flight mode for landing would be useful.

[Piers Bowlan]

3 hours ago, Chris Walby said:

35oz/sq.ft......dream on ?  My Vulcan is pushing beyond 45 oz/sq ft....that doesn't have flaps and lands without a flair...or not much!

Still think its worth a go with a little aileron (at height) to see if you can squeeze a little bit out without a impacting the stall characteristics.

I need to try this with another model that has a vicious tip stall and lands like a rocket so not much choice for me (I'll keep you posted)

Deltas don't need flaps as they can fly at high Alpha before stalling, however once they get onto the back of the 'drag curve' they quickly slow down and sink. Beware!

Concorde doesn't have flaps either.

Nice photo Chris. ?

Edited May 21, 2021 by Piers Bowlan

[DaveB1]

This is the power of this forum. A great question posed, that many will have pondered and some really thoughtful answers from those with great experience. No one size fits all put down, but some good ideas that many of us can play with. Thx all

[perttime]

Try both. A few mistakes high.

[MattyB]

1 hour ago, Frank Skilbeck said:

If you are going to try ailerons down to increase lift, it would be worth dialling in some differential so you increase the aileron up movement with aileron control, this would reduce the down movement of the ailerons when trying to pick up a wing as any more down movement would add more drag on that side causing some yaw and potentially a wing drop on the side you are trying to pick up.

 

You wouldn't normally want aileron differential on an aerobatic model like this as it may make rolls a bit barrelly, so having a separate flight mode for landing would be useful.

Agreed, and if you you choose reflex (particularly at higher deflections - say 45 degrees or more) inverse differential (more down than up) can be a useful addition to your landing flight mode. I am not sure whether that is possible on a DX8 though, certainly the v1 that a club mate has seemed quite limited but I have heard the second generation sets are significantly more flexible.

Edited May 21, 2021 by MattyB

[Piers Bowlan]

You may well be right Matty but instinctively I would have thought that 45+ degrees of full span reflex would have turned a challenging model in calm conditions into  one that is very unforgiving? The wing here is thin and symmetrical so my gut feeling is that a few degrees of aileron droop (max 5 degrees ) might help reduce the landing speed because of the increased camber. At the end of the day it will still be a very slippery model with a high wing loading. Putting the model on a diet too, if that were possible, might help! The proof of the pudding etc... 

[EvilC57]

I found that in fact, that around 2 to 4mm of UP on the ailerons, switched as required on positions 1 & 2 on the flap switch at the start of the landing approach gives the model an appreciably steeper glide path. Nowhere near the 45 degrees people have mentioned on here, which with this model, I imagine would be far too drastic.

[Martin Harris - Moderator]

The 45 degree guidance is more relevant to crow braking I would think.  Great when a plan comes together...!

[GrumpyGnome]

@EvilC57Glad i's sorted. think I may do something similar to my Ultrastick 10cc s it just floats on and on and on..........

 

GG

[Simon Clark]

Hello

Full span ailerons do limit your options. If adding flaps is not a practical option then you could also consider removing the inner portion of the ailerons and re-fitting them to the wing in a fixed position, then using up aileron can be used more effectively as a brake. Of course this may be more difficult to do than say.

 

I would also definitely look at the engine / prop setup - it is amazing the problems caused be high idle and high pitched props. I would try going down a bit on pitch as has already been suggested, maybe a 12x6 or 13x6. Also try to get your idle as low as possible. I always use on board glows with this type of model and this allows me to get a very  reliable low idle and I have found this to be the most significant thing to make landing easier on this type of plane.

 

Good luck

Simon