Flap pockets cut

[FLTpilot]

Don’t see an area for modifications and building so I’ll post here......
I have a question and am not too sure where to turn. I’m adding details to Dynams Hawker Tempest and finding a balance between real life and the duty the model will perform needs to be a balance (like weathering, I guess). I’m adding flaps and have successfully cut the foam down with a dremel and router bit to a certain depth to allow a thin plastic ‘floor’ to support the thinned foam above and then have a 1.5 to 2mm flap. So the question is the real aircraft flaps run from the wing root to the aeilrons and are split into 2 flap sections. They angle at the split which will cause binding when they deploy which can most likely be clearanced so I’m not too worried about that. Moreso wondering if a flap that long (to be inline with the real plane) is overkill or detrimental to a rc flyer?
What I lack is experience in flying different acft with different configurations so I cant make a judgement on the full length as opposed to the inner only area for the flaps. I have the pockets cut out for the inner flaps and figure if I do the outter also I’ll need to use 2 9 gram servos per side to deploy. Does this sound reasonable?
I know it might be much to hypothesize an answer but any comment would be appreciated.

[fhhuber]

Its hard to accurately predict the results of adding flaps to some models. Split flaps can be even more unpredictable.

Usually, you get some added low speed stability due to forcing the center section of the wing to stall before the tips.
Often you get nose down due to the drag, but ballooning with power or if you deploy the flaps at speed.
Sometimes all you get is added drag, especially with split flaps.

Its better to use linkage between inner and outer flap to prevent the need for more servos We even use links between the 3 flap sections per side on 50 CC Corsairs. The links are typically lighter and you have less electrical load on the RX system. (adding 2 servos to the load on the BEC is potentially pushing it and should call for load testing... adding 4 will require testing to see if the BEC can handle it)

A compromise typical for that aircraft is to straighten the hinge line and do the flaps in one section each wing.

If going ahead with the 2 sections per side, you can completely avoid binding by making the hinge line lower using Robart Hinge points (or similar style hinging) installed at a slight angle so a bit of the hinge(including the pivot point) is below the wing with flaps up. The binding didn't happen in the full scale because the hinges were at the bottom surface of the wing.

[FLTpilot]

Thank you for your thoughts!
Some things I didn’t even consider.... the load on the BEC for one. It would seem minimal as flap deploy or retract is a short term thing but I guess there is that ‘short term’.... 2-4ish seconds... while other servos would most likely be in duty at the same time.
My reason behind using 2 servos was the possible load on the link when deploying a surface into the airstream which might over stress the connect point. Just thought I’d double the servos to keep this in check. Maybe not such a good idea. Lol
I would be at a loss as to how to make the link but can find out easily enough I suppose. But your info is having me lean more toward keeping the inner flaps only and leaving the outer surface as is.
If I would go the distance for the entire split flap I was considering how to keep the binding from happening and your suggestion was in the mix but my concern was strength in the attachment point with mounting the hinges on the surface as opposed to in the cutout section and into the wing and inner surface of the flap. I had planned on four doorhinge style hinges in either mounting position. Simplest seems to be leaving the outer flaps uncut and move forward with my experiment forgoing the perception of reality like the real plane.
Something inside is pushing for those outer flaps! But I’ve already gone beyond the KISS principle ....
thanks again!

[FLTpilot]

PS - the hingeline is indeed straight in the inner section already making for a relatively easy modification

[fhhuber]

Servos have a minimum idle current demand. And there will be some load from "Bernouli effect" trying to pull the flaps down when commanded to be up. You can't quite get to a position where the flaps impose no load because of the swirling effects of the gap between upper surface TE and lower with the split flap making the surface want to flutter.

[FLTpilot]

Servos have a minimum idle current demand. And there will be some load from "Bernouli effect" trying to pull the flaps down when commanded to be up.

Ok so there is some current being utilized to maintain position with some additional from “Bernoulli effect”... wouldn’t this work to keep the flap tucked up since lift is created under the wing effectively lifting the airframe? I could understand this if the flaps were completely free top to bottom of wing as it’s own surface but in my case the flaps are under the upper wing entirely.

[FLTpilot]

You can't quite get to a position where the flaps impose no load because of the swirling effects of the gap between upper surface TE and lower with the split flap making the surface want to flutter.

ive been reading and rereading this and I’m afraid it’s beyond my understanding of aerodynamics. Sorry.

[fhhuber]

Airflow over the surface of the wing attempts to pull the top and bottom of the wing away from each other, in addition to the creation of lift.

[FLTpilot]

I thought I would share my decision and progress. I decided to put 'scale' flaps in and use one servo to actuate them. Additionally I will use a Castle BEC to handle all servos to kill that issue. The linkage as seen in the photo is being modified. The linkage works very well but I'm not comfortable with what it might do when airborne. If it might jam in some way. It remains to be seen if Bernoulli effect will adversely affect my arrangement.