speed20

My Feedback: (31)

Can anyone give any pointers on how to build in washout in foam wing cores that are precut. I'm familiar with washout in a built up wood wing, but haven't done it with a foam core. Any tips will be appreciated.

All Day Dan

My Feedback: (5)

You can live without washout. If you’re concerned about stalling or tip stalling, just land faster and you’ll avoid it. I never use it. Dan.

Boomerang1

If you have inset ailerons you can cheat a little & just adjust both ailerons up a little.

ARUP

Put an appropriate wedge under the cores-in-shucks while the sheeting glue cures.

speedracerntrixie

My Feedback: (29)

I personally never build airplanes with washout, then again I don't build airplanes that would need it either. Unless it's going to be a heavy scale project with a narrow tip cord I see no reason to put washout in.

ARUP

That's nice but the poster wants to know of ways to incorporate washout into foam wings. Correct?

speedracerntrixie

My Feedback: (29)

Why not enlighten him so he has the knowledge to decide if he really needs it or not? I read your suggestion and wasn't quite sure how it was going to work. The wedge would give washout only at the tip. Usually when it's done on a foam wing the entire wing has a slight twist. Aerodynamically shouldn't make a difference but I was unable to figure out how you were going to accomidate the rise in the shucks when the assembly was weighted down. Perhaps more detail is in order?

BMatthews

Well, since speed20 didn't say what sort of wing it is perhaps it is one which SHOULD have some washout.

Speed, you'll need to hold the twist in while the sheeting goes on and cures. Once the sheeting is bonded the wing is not going to budge. I second the shimming idea but with a slight twist. So that the foam beds can't sag I would suggest that you use a wing size panel of something like 1/2 inch plywood and screw one edge down and one end down. Then shim along the free edge and end to produce a nice smoothly graduated washout. For the other wing remove the screws from the one end and shift time to the other end and re-shim along the edge and opposite end to duplicate the washout twist but the other way around for the other wing.

And no, you can't just flip the beds around to swap the leading and trailing edges. You need to move the shims or you'll simply make a very large and odd looking propeller....

speedracerntrixie

My Feedback: (29)

Yes you are correct, we don't know what the airplane is and it could very well be one that would benefit from washout. Once we find that out then the OP can move forward. BMatt, your suggestion works a bit better as the entire bottom of the shucks will be supported. There are some options here again depending on the model type and size, it may even be easier to have new panels cut with the appropriate amount of washout if in fact it is deemed needed.

aspeed

It can be carved/sanded into the ailerons if they haven't been covered or painted yet. That is the easiest.

sensei

As already mentioned you can trace the left and right bottom wing shucks onto a 2" thick piece of styrofoam, and cut out on a band saw or hot wire, next use two strait edges setting the first on the root rib end at 0 degrees and setting the second on the tip rib end at 2 or 3 degrees washout or whatever you desire, now using your hot wire scarf the foam blocks off. Now you can set the bottom shucks on top of your washout blocks, glue your skins and vacuum bag with the top shucks in place and you will have perfectly set washout in your wings.

Bob

ARUP

The poster determines the 'appropriate' wedge. No info in post if washout needed throughout span or just at tip. Once the sheeting is glued in place whatever method is chosen will 'lock' that wing forever. Personally, I'd make a wedge the same size as the wing planform and I'd do this by cutting washout into the upper or lower shuck if thick enough. If the shuck isn't then a supporting wedge will have to be made. I can cut elliptical foam cores by using the appropriate templates and 'wedges' but I find foam wings boring to build. However, I know my way around foam wings and still fab one every now and again! The poster didn't ask about that, though! Sorry if I offended you, Speed.

ps2727

Speed,
If you are going to cut your own cores it is simple to raise the trailing edge of the tip core to produce the desired washout in the core. It's the best way in my view because you
can still use the cores in the sheeting process to keep the washout where you want it.
If the cores are already cut and can be "twisted" it is possible to build in washout. If it is a thick, stiff core you may not be able to twist it.
I would make two identical ply rectangles large enough to draw the root and tip airfoils onto, say 2 inches high. Mark a centerline on each and draw the root airfoil on one and the tip on
the other, but on the tip put the leading edge on the centerline and raise the trailing edge to match the desired washout. Drill holes in the ply and mount to the core with drywall screws so the airfoil drawing matches the core. We now have a core with a ply rectangle attached to each end. If we now place the assembly on a flat surface with the root ply
flat the tip ply will want to rest with the leading edge above the table. If you force the tip ply onto the table (weights, glue it down, etc.) it will twist the wing with the correct washout.
If the wing is sheeted while holding it in position it will lock the twist in. If the ply parts have parallel edges the wing could be sheeted on one side, the wing flipped, and
weighted down again to sheet the other side. The same ply parts are used on the other core (you'll have to draw the airfoils on both sides of the ply parts) and the washout
will be identical on both cores, which is the important bit.
I'm sure there are other ways to do it.
Paul

speed20

My Feedback: (31)

Thanks for the suggestion Paul , I understand what washout is and what it does, and how along with flaps, can really tame a heavy warbird . I just never dealt with building washout into a precut core. Thanks again

BMatthews

Normally this is by far the best way to do it. That way the washout is smoothly graduated through the whole span and the sheeting will sit smoothly on the cores.

Easy yes. But it changes the airfoil from what it should be to something quite different. The resulting new airfoil might well have a lower stall angle due to removal of some of the camber.

Bob, if I'm reading this right you're suggesting making NEW bottom shucks? Or are you suggesting washout beds cut from foam that the cores and core shucks sit on for sheeting to twist in the washout?

I'm sort of thinking that angled plates with known angles would be pretty slick. They could be used on more than one occasion when needed.

speedracerntrixie

My Feedback: (29)

We still don't know what airplane we are making all this fuss over.

HighPlains

My Feedback: (1)

Even if the wings were sheeted you can add washout. You can do this with a diagonal cut through the bottom sheeting, then epoxy the seam and hold the twist into the wing as the glue sets. Not necessary in this case, but it is a technique in cases where the wing has a warp built in or you need to add washout.

sensei

Yes I am suggesting washout beds, if you already have a set of hot wired wing cores and shucks then just cut washout beds for the core to sit on for sheeting in the washout, if you are going to vacuum bag the skins on as many of us do, then the beds would make an excellent complete under support vacuumed down against a flat stable surface without a chance of creating a bow in any direction.

Bob