Flaps

[Capt Kremen]

Apart from a few gliders, most of my models do not employ flaps. In general 'sports' flying I have not noticed appreciable difference, save trim change, to warrant the extra servo, associated linkages and requirement of another channel on the receiver.

However, I have a couple of scale models in preparation, full-size versions of which employ flaps. To get some practice in before these fly, I've just finished a 'sport' model to get familiar with toggling 'Flaps 1', and 'Flaps 2' on the Tx. Notionally 15 degree (take-off) and 30 degree down (short finals, to land).

How do regular flap aficionado set-up their angle of dangle? i.e. From what datum do you measure the flap deployment angle? chord datum? airfoil trailing edge? Do you convert degrees required into mm deflection to measure as per other control surfaces? I made up a card template with the angles on which looks about right but wonder is there a better/correct way. What regular 'flappers' use? Thanks.

[Jon H]

I have flaps on all of my warbirds and i essentially look for as much flap as i can get. With a warbird i am mostly looking for high drag as i want a reasonably steep approach and all that drag keeps the speed under control.

If i fly a model, and it feels like i have too much flap angle then i can always take it out later. I also try and use a variable slider when i can so that i can feed in more/less flap as i need it.

In general, no flaps on takeoff. You dont want the added drag and given our models have high power/weight you might as well go flapless.

Be aware of the added drag when landing, pull the nose up a few degrees and some models will stop dead almost right away. Be aware too that you might need an elevator flap mix. Again, it varied depending on model but in general lowering flaps causes a nose down pitch, especially if you have retracting gear as well. However, if your model is very light (like a funcub) and essentially has no need for flaps other than for fun, the model will pitch up with flap deployment. The same is also try if you fly too fast, obviously.

Which models are you building?

[Martin Harris - Moderator]

I must say that balancing the drag from flaps with throttle gives very satisfying approach control - the instant and so controllable response to varying the throttle on the approach path is almost hypnotic at times.

Edited By Martin Harris on 16/05/2020 17:57:07

[Andy J]

Have added to flaps on two models in the past and currently in the process of adding them to a 84" Sparrowhawk. Angle of dangle is not important and have gone for max deflection on the two models I have flown (Hurricane and mid size seagull Sparrowhawk) based on the control geometry installed. IMO Flaps on fast models is all about adding drag rather then scale looking simply to try and get the landing speed down to something practical that allows a short landing run.

[Capt Kremen]

Thanks for your valued input chaps.

I am not dismissing flaps, on my gliders they are essential, just never been bowled over with the effort/benefit effect on a sports model.

In prep are the VQ 'Piper TriPacer PA-22' and a Seagull 'Chipmunk'. Both I imagine could live quite happily performing flapless landings. Still, they are scale, the fullsize use 'em and why have that extra toggle/lever/slider on the trannie if you don't bother with it

[Jon H]

I have a 72 inch piper Tomahawk and i have about 45 degrees of flap. It really helps with the landing and due to its massively long takeoff run its the only model i have where i use a small amount of flap, mayb 20%, for takeoff.

[Frank Skilbeck]

Posted by Jon - Laser Engines on 16/05/2020 17:35:48:

Be aware of the added drag when landing, pull the nose up a few degrees and some models will stop dead almost right away. Be aware too that you might need an elevator flap mix. Again, it varied depending on model but in general lowering flaps causes a nose down pitch, especially if you have retracting gear as well. However, if your model is very light (like a funcub) and essentially has no need for flaps other than for fun, the model will pitch up with flap deployment. The same is also try if you fly too fast, obviously.

Which models are you building?

On a couple of high wing models with flaps, a Glenns Maule (now no more) and a Seagull Maxi Lift (Laser 150) the flaps cause the nose to pitch up, same with my friends Wilga. On my Maxi Lift I have around 60 Deg Flap for landing, this allows very steep approaches and short roll out. Without flap it just floats on forever. Another friends Zero also required a touch of down elevator mixed in with the flaps.