Expanding foam FPV wings

[Userofmuchtape&glue]

Hey all.

A idea I have been thinking about lately, is the use of expanding foam to fill up the cavities in ft wing designs. All my builds get saggy, particularly along the leading edge.

You could even make a mold like this and churn wings out that way.

what do you all think?

And on a side note, how do symmetrical airfoil wings fly? as in flying wings? that way I don't have to make two molds for each half of the wing.

Abe

 

[Userofmuchtape&glue]

I just tried it. filled up the cavities in a section of wing. will report back when it dries.

 

[Namactual]

Interesting idea. I am looking forward to the test results.

My only concern would be the expanding foam deforming the foamboard wing, or out right ripping it apart.

Symmetrical airfoils fly great, they just need a little AoA to create lift like a flat plate. In 100% forward flight they just do not create any lift. You can fix this by mounting the wing to the fuse with a little built in AoA, or just ignore it and add a little up trim to the elevators.

 

[Userofmuchtape&glue]

Thanks Namactual, yeah I am worried about it popping apart too. I will use less foam next time, but had a bit of trouble squirting it in there.

Yep okay, and reflex would help the symmetrical wing to create lift to. Will draw up some plans for the mold and build it when I finish my workshop.

Abe

 

[Fluburtur]

I did some research on that last night and apparently this stuff is rather heavy, also it needs contact with air to dry so the inside will take really long to get solid. In my case I would want to use it in a mold with no skin to make foam planes but im not sure it is strong enough either, this calls for some testing.

Also for flying wings I found airfoils such as the PW51 are nice but they are not symmetrical, im not sure how symmetrical airfoils fly but I know my flying wings with a bit of washout needs almost no up trim to fly.

 

[Hai-Lee]

When using expanding foam to fill a wing cavity or a fuselage cavity it is good to cut a number of holes in the wing, (normally on the underside), for access when filling and to allow the foam to have a pressure relief when the expansion is occurring. The holes also hasten the setting process and allow the foam to expand to the maximum extent possible and thereby become the lightest it can. Fill slowly and allow the foam to expand behind you as you move the nozzle from fill point to fill point.

CF spars can be embedded and held in place using a pair of false FB wing ribs with holes for the spar to rest in.

When the foam has set you can trim off the excess with a sharp knife and a little sandpaper so that it cannot be seen and does not upset the aerodynamics.

Done properly it does add weight but it is manageable, done poorly the wing will distort badly and there could even be a problem with extreme weight gain and one wing becoming much heavier than the other!

Have fun!

 

[thenated0g]

Shane (flashgangster) and i played around with this back in like early 2015 with our versa wings. It can definitely add strength for not much weight.

 

[thenated0g]

When using expanding foam to fill a wing cavity or a fuselage cavity it is good to cut a number of holes in the wing, (normally on the underside), for access when filling and to allow the foam to have a pressure relief when the expansion is occurring. The holes also hasten the setting process and allow the foam to expand to the maximum extent possible and thereby become the lightest it can. Fill slowly and allow the foam to expand behind you as you move the nozzle from fill point to fill point.

CF spars can be embedded and held in place using a pair of false FB wing ribs with holes for the spar to rest in.

When the foam has set you can trim off the excess with a sharp knife and a little sandpaper so that it cannot be seen and does not upset the aerodynamics.

Done properly it does add weight but it is manageable, done poorly the wing will distort badly and there could even be a problem with extreme weight gain and one wing becoming much heavier than the other!

Have fun!

Yeah depending on if you have the fast or slow expanding foam, you can actually rip your wing open.

 

[thenated0g]

as far as using the expanding foam to make your own wings, i would recommend just going to home depot and getting solid wall insulation. Cheaper and less mess.

 

[Userofmuchtape&glue]

Yeah not really liking it so far, it added a heck of a lot of weight for not much strength. It dried spongy, but.it could be the.brand . So will have to try some other brands and see how it goes.

Might still be good for LEs though.

 

[Hai-Lee]

Abe,
The sagging of the wing LE is puzzling to me. Do you mean a softening and alteration of shape over time due to moisture, hangar rash, and impacts?

I use a couple of different tricks for greater LE rigidity and even some level of impact resistance.
One method is to use a CF tube in the LE which normally requires the removal of some foam along the LE prior to gluing and folding.
A second method, (my personal favourite), is to embed a strip of 1mm Balsa along the LE and then the glue is applied and the wing folded.
There are a few other materials I have not tried but thin Ply strips or the PVC strips appearing in model shops lately do appeal to me.

For further reinforcement or fixing against warping I use more strips of the 1mm Balsa. Greatest benefits have been in reinforcing FB wing spars and stopping wing TEs and control surfaces from warping over time. Of course The FB wing should be sealed with Minwax and then the finishing colour scheme applied.

When doing a 1 metre wing span model, (for high strength), a single 75mm wide sheet of 1mm Balsa is more than is needed to do the entire aircraft, (fuselage included).

Just what works for me!

Have fun!

 

[Bricks]

You want to strengthen an airplane with out much added weight it is a little tricky at first but works very well.

Everything you need to know about newspaper and glue.

https://www.rcgroups.com/forums/showthread.php?1552848-Newspaper-glue-covering-improvement

 

[Userofmuchtape&glue]

Bricks thanks, found the newspaper method a few months ago. I love it!

Hailee since I am using xps foam without paper moisture is not a issue, but yeah they weaken with age and use.

Sorry I am on a phone so will reply in depth later this week.