G-202 split flap configuration
 

In a previous thread by Hans Meij, it was suggested that flaps would be beneficial for his Giles wing. I've just about finished my Midwest G-202 but haven't flown it yet (need to break in the engine and paint the cowl and wheel pants). Based on that thread's commentary as well as numerous posts about how bad this plane is about tip-stalling, I'm seriously considering incorporating split flaps to help prevent tip-stalling during landing and deadsticks.

I've reviewed the article cited by Ollie as well as my copy of the Andy Lennon model airplane design book and I am looking for a bit more detail and/or suggestions. The Lennon book goes into exhaustive detail on slotted flaps, but I'm obviously too far gone for that implementation. Without too much effort, I can put a split flap, a little over 8" wide, one rib bay from the fuselage. I can make it as long (chord-wise) as I want, but the Lennon book suggests 20% of the chord, which would be 3" in this part of the wing.

Some questions I have at the moment is:

- Should the flap be rectangular or match the wing tapered planform (I'm thinking rectangular to provide a symmetrical area to the airstream, but I'll defer to the experts)?
- Is there an ideal position along the chord if it can't be on the trailing edge (it can't). Should I put it as far back as possible or put it near the thickest part of the wing?
- Is a 3" flap big enough since it's not very wide or should I make it longer chordwise (wider spanwise is really not possible without seriously tearing up the wing)?
- For an 11lb model, will Monokote hinges be sufficient for a flap? Putting pinned or CA hinges with some type of surface hinge will be tricky, but I can probably figure something out if necessary.

Thanks in advance for any help you can provide!

A pic of the space available
 

I finally got the guts to cut a hole in my still-fresh covering job to see what opportunities I have. For reference, I've attached a pic...the servo tube is somewhat in the way and will limit my flap location as far as servo mounting opportunties go, but I think it's still do-able...

G-202 split flap configuration
 

Depending on the type of flying you will be doing, you could spit the aileron at the 30% mark and have the inboard for flaps. Put 4 servos in the wing (2 inboard panel) ( 2 aileron) then if you want to use the entire surface as aileron, you can do it or if you decide to use the inboard as flaps, you can do that as well. It will act a lot like the H9 Stick. You should be able to crow and a lot of other maneuvers with the Giles

G-202 split flap configuration
 

Geistware, if I were not finished with the wing, this would be my choice as well (and I'll probably do this on future planes just for grins anyway). I would have lengthened and split the aileron and installed more hinge points.

However, at this point I think I need to try something else as I don't believe there are enough hinges to safely split the aileron into two parts.

LATER:

I spent some more time looking at it and I would basically have to cut off the ailerons and make new ones. The current ailerons were built per plans and only have about 30 degrees max deflection, arguably not quite enough for flaps. I'm going for the gusto and installing 4" wide split flaps just ahead of the ailerons (this is really the best configuration I can do with the servo wire tube in place).

G-202 split flap configuration
 

Another posibility is to install the flap flush with the inboard section of the wing and allow it to hinge down to give inboard lift. I don't know what the effect will be while flying, but you should get a lot of drag and inboard lift when deployed.

G-202 split flap configuration
 

If I'm understanding your description, that's actually what I'm calling split flaps even though they aren't at the trailing edge of the wing. I'm wrestling with how to hinge it, but once I get that figured out it should be smooth sailing...

G-202 split flap configuration
 

OK, I understand. If you put that at the leading edge, you are going to have a spoiler effect and loose all laminar flow on the bottom surface. You will have to slot the front of the flap to make sure that you maintain some laminar flow!

I know you already know this. One question that I do have, how are you going to maintain strength at the hinge line of the flap. If you are flying at any reasonable speed, you are going to have problems with the servo or flap. You will be moving a lot of air!

G-202 split flap configuration
 

The hinge line will be around the 60% point of the chord...the picture will illustrate what I'm getting at although the structure is far from finished. The uncovered balsa sheet will be the flap surface and will pivot at the top edge some predetermined angle.

That was my concern with Monokote hinging...I'm working on a way to either put pinned hinges or CA hinges. CA is probably the easiest, although I haven't use a CA hinge in years (don't generally like 'em). I'm not sure I follow on slotting the flap...split flaps create lift and a ton of drag and aren't supposed to be slotted.

I'm planning on using fairly strong mini servos (thinking Hitec HS-225BB...67in-oz of torque) and I am using a 6V power source. I'm going to set up the linkage so the arm and link are colinear when the flaps are down...if the servo has the grunt to get the flap in position, then it can hold it with very little effort.

G-202 split flap configuration
 

OK, I understand now. I would worry about the lack of laminar flow. You my not like the results.

G-202 split flap configuration
 

Hmmm...I'm not sure how any split flap could have laminar flow. Even "real" split flaps like the Spitfire had couldn't have possibly been laminar. Do you have back copies of Model Aviation? There's an article from July 2001 that describes essentially what I'm trying to do to my G-202...

Darn. Maybe I'm off the weeds again. Maybe I should just recover the thing and go fly it. I'm used to landing hot anyway... <g>

G-202 split flap configuration
 

Don't mind me. It looks more like a spoiler than a flap. You want to increase lift and drag, not reduce lift. This is just my opinion. Do it any way and see what happens!

G-202 split flap configuration
 

Just to be clear, it's on the bottom of the wing, so the effect the split flap has on the wing is to create an upward reaction force from the airstream being deflected downward by the flap. It's only about 1/4 the wing panel and near the fuse, so it shouldn't adversely affect aileron response (I hope).

I guess if I were to go ahead an do it, the worst that could happen is it doesn't work and I've added a few ounces to the wing. I could even yank the servos and glue the flaps up permanently to remove most of the added weight. See how I'm rationalizing this? :D

G-202 split flap configuration
 

Let me know how it works.

G-202 split flap configuration
 

if you are worried about take off and landings and need flaps....since you already operate 2 servo ailerons you might as well program them to be used as flaps also.

since you cut out aileron to make some flaps now you will need a lot of aileron travel to create same effect as before. ( need more servo travel and you would be needing to use high rates to get required effect)

bobi

G-202 split flap configuration
 

Snsmith,

The low aspect ratio spoiler you are talking about on the bottom of the wing isn't what I had in mind.

If I were you I would shorten the present aileron up to the the inboard hinge and lengthen the root trailing edge piece to take up the space. I would thin the trailing edge on the bottom by 1/32 of an inch from the wing root to the inboard end of the aileron and install a 1/32 ply split flap about 3 inches wide and as long as possible between the fuselage and the inboard end of the shortened aileron with the trailing edge of the split flap corresponding to the trailing edge of the wing. I would use 3M Book Tape for a hinge. If you don't want to mess with the wing root sheeting, so be it. Just overlap the 1/32 ply and live with the 1/32 bump in the airfoil contour at the flap hinge line! Only you will notice it on the bottom of the wing and performance won't be affected perceptably with the flap closed.

The reasons for this are that a long narrow flap is more effective and much easier to drive than a short wide one. Having the inboard end of the flap almost graze the fuselage side cuts most of the vortex that would otherwise be generated. This greatly increases the lift available from the flap and decreases the angle of attack needed at the wing tip for a given airspeed. The resultant decrease in tip angle of attack gives more tip stall margin which is what this modification was about from the beginning.

G-202 split flap configuration
 

Thanks for the input Ollie...it sounds like you are recommending that I build in true split flaps versus the spoilers suggested in the cited article. I can do this but it's more work than I was planning/hoping to do (and make it look halfway decent).

If I were to not shorten the aileron, but make a flap just on the wing root, it would be 8.5" long (for a 32" wing panel, 72" wingspan). While probably not optimal, would it provide some low speed lift so I don't have to gut my wing, particularly if I make it graze the fuse sides as suggested?

This would obviously be far easier and less intrusive on the completed wing if it would be "enough" (clearly a subjective term). I'm not a novice flyer and usually land hot, but would like some margin based on the feedback I've received on this bird.

Thanks again!

Split Flaps
 

The 8.5 inch long split flaps sound like a reasonable compromise if you use them mainly for tip stall margin without trying to reduce the landing speed much.

G-202 split flap configuration
 

Thanks for the quick feedback Ollie...margin is exactly what I'm looking for. I'm not trying to turn it into a trainer, just try to get margin on tip stalling on landings, particularly when deadstick.

Thanks again!