Cox Engines Forum
You are not logged in! Please login or register.

Logged in members see NO ADVERTISEMENTS!


Playing With Foam Cox_ba12




Playing With Foam Pixel

Log in

I forgot my password

Search
 
 

Display results as :
 


Rechercher Advanced Search

Latest topics
» Carl Goldberg Shoestring
by NEW222 Today at 9:22 pm

» Tank Cleaning and an Old Rant from my Youth
by Ken Cook Today at 8:24 pm

» Designing a Tee Dee RC carb
by dckrsn Today at 6:56 pm

» COX 049 Product Engine '76 - type confirm .
by balogh Today at 5:46 pm

» Home made fuel nipple for COX Tee Dee RC carb
by balogh Today at 3:56 pm

» Contest - Contest - Contest
by Admin Today at 2:42 pm

» COX TeeDee09 RC in flight with the Cosmic Wind
by balogh Today at 12:16 pm

» Fall S.M.A.L.L. Friday
by Kim Today at 10:33 am

» Big Brother
by NEW222 Yesterday at 3:18 pm

» Cox Engine Stories
by rsv1cox Yesterday at 7:39 am

» It's raining Cox engines
by rsv1cox Yesterday at 7:19 am

» Simple Baby Ringmaster build
by MauricioB Yesterday at 12:09 am

Cox Engine of The Month
October-2021
MauricioB's

"Babe Bee .049 r/c"



PAST WINNERS
CEF Traveling Engine

Win This Engine!
Forum Store
CEF Ear Savers
Gallery


Playing With Foam Empty

Playing With Foam

Go down

Playing With Foam Empty Playing With Foam

Post  andrew Wed Aug 25, 2021 4:59 pm

Recently, I've been experimenting and building with foam board, both with and without the paper backing.  Without the backing, it's pretty flimsy so I needed a strong, but lightweight material to add strength in certain locations.  I've settled on fiberglass window screen -- it's light, flexible and incredibly strong, plus CHEAP. After wiping down with acetone (there may be release agents on it, maybe not), I stick it on like fiberglass using Elmer's ProBond Advanced glue.  The glue choice is probably not too important, but I don't think CA would be the best bet.  It should work great for reinforcing the butt joint in a wing.  I have also laminated it between sheets -- adds a lot of stiffness.

The downside is that it is not very smooth, but at the speeds we fly, I doubt parasitic drag is a big player.

Here's a little I-beam spar test piece -- finished product is nicely trimmed.


Playing With Foam Spar_110
Playing With Foam Spar_210

That I-beam is made from Dollar Tree foam board (20"x30" board is $0.99 IIRC), 3/16" thick after the paper is removed.  The beam is 3/4" wide, 1"tall and 7.125" long; weight is 3.19 grams.  I supported each end on 3/4" blocks, then loaded it with 6.4 pounds W/O much deflection.  My weights were 25.75 ozs.  The 5th weight caused twisting deflection.  This beam had screen only on one flange and when tested, I put it on the bottom -- under tension.

I have two other constructions with the screen running vertically -- each supported over 8 pounds.  I'll see if I can get some pics this evening.
andrew
andrew
Diamond Member
Diamond Member

Posts : 1431
Join date : 2011-08-11
Age : 73
Location : Western Kentucky

http://web2.murraystate.edu/andy.batts/ps/POWERSUPPLY.HTM

Back to top Go down

Playing With Foam Empty Re: Playing With Foam

Post  sosam117 Wed Aug 25, 2021 6:09 pm

You can use the lightweight spackle from DAP to fill in the window screen on your spar.
https://www.dap.com/products-projects/product-categories/patch-repair/drywall-spackling/fast-n-final/

I have been using this spackle for almost a year on my planes to fill in the balsa grain before painting/doping.
It is white in color and if you add one or two shots of water from a bottle sprayer to thin it out it fills the grain extremely well.
Though you really don't need to thin it out as is.
Just if it seems to be drying out?
After it dries, I lightly sand it with 320 or 400 grit sand paper to knock off the high spots.
sosam117
sosam117
Platinum Member
Platinum Member

Posts : 549
Join date : 2016-03-23
Location : Suburb of Chicago, Illinois

Back to top Go down

Playing With Foam Empty Re: Playing With Foam

Post  andrew Wed Aug 25, 2021 6:39 pm

@sosam117 wrote:You can use the lightweight spackle from DAP to fill in the window screen on your spar.

That's a good idea and absolutely true.  I have been using it for some time, even as a filler for cut foam wings.  

It seems to be a mixture of glass microspheres and an air drying binder.  I once tried to thin it enough to paint on as a primer, but ended up with the microspheres floating to the top and liquid in the bottom.  That didn't work out ..........


Last edited by andrew on Wed Aug 25, 2021 8:45 pm; edited 1 time in total
andrew
andrew
Diamond Member
Diamond Member

Posts : 1431
Join date : 2011-08-11
Age : 73
Location : Western Kentucky

http://web2.murraystate.edu/andy.batts/ps/POWERSUPPLY.HTM

Back to top Go down

Playing With Foam Empty Re: Playing With Foam

Post  rdw777 Wed Aug 25, 2021 7:21 pm

That’s a lot of weight to support with that little mass…. Congratulations! …. Good engineering….. I think the fg caps are key… Still without adding much mass….I remember the Ace foam wing kits instructed to add strapping tape to the top and bottom of their foam wings…. Made them much stiffer!!… The KM series foam airfoils look interesting for quick builds…. Would be interesting to compare deflection on one of those

Robert
rdw777
rdw777
Gold Member
Gold Member

Posts : 120
Join date : 2021-03-11
Location : West Texas

Back to top Go down

Playing With Foam Empty Re: Playing With Foam

Post  andrew Wed Aug 25, 2021 11:58 pm

@rdw777 wrote:….I remember the Ace foam wing kits instructed to add strapping tape to the top and bottom of their foam wings…. Made them much stiffer!!… The KM series foam airfoils look interesting for quick builds…. Would be interesting to compare deflection on one of those.

Robert -
I still have a couple of molded foam wings with strapping tape on the bottom -- it added significant stiffness!!

Here are a couple of "foolin' around" pieces.  The verticals in each are 3/4" tall.  The double laminate is 5.375" long and weighs 3.1 grams.  The larger piece is 6.5" long and weighs 4.7 grams.  I loaded both with just over 8 pounds (3628 grams) in the center -- the pics were after the load test.  Obviously, they're not very long, but are still strong enough to be used as a spar in a foam wing. Having the screen laminated within the foam or on both sides seems to help reduce the tendency to twist under load. This approach is almost identical to sailboat construction where nidacore, hexcel, honeycomb composite, closed cell foam or balsa is sandwiched between fiberglass layers, except it's a ton cheaper and much easier to lay up.

Playing With Foam Lamina11
Playing With Foam T-spar12
andrew
andrew
Diamond Member
Diamond Member

Posts : 1431
Join date : 2011-08-11
Age : 73
Location : Western Kentucky

http://web2.murraystate.edu/andy.batts/ps/POWERSUPPLY.HTM

Back to top Go down

Playing With Foam Empty Re: Playing With Foam

Post  andrew Thu Aug 26, 2021 12:17 am

You mentioned the KM series airfoil -- I'm not familiar with those.  Did you perhaps mean the KF (Kline-Fogleman) series found in foamys?  I've built a few of those, but without using the fiberglass screen.  I wish I had applied a strip, maybe 4 strands wide on the bottom, at the spar location, to help maintain the shape -- this stuff is so tough that I can't pull a 4 strand piece apart -- not saying much at my age. Sad

The flying wing is 36"; the conventional wing is about 34".

Playing With Foam Img_2010
Playing With Foam Img_2011Playing With Foam Img_2012
Playing With Foam Img_2013
andrew
andrew
Diamond Member
Diamond Member

Posts : 1431
Join date : 2011-08-11
Age : 73
Location : Western Kentucky

http://web2.murraystate.edu/andy.batts/ps/POWERSUPPLY.HTM

Back to top Go down

Playing With Foam Empty Re: Playing With Foam

Post  rdw777 Thu Aug 26, 2021 6:09 am

Interesting work on the laminate beams and stress testing them….If you wanted you could make an example a bit longer, say 12”, Then support it at set intervals, weight it, and measure deflections…. You could then establish a curve to see how longer sections may behave….. If you like doing that sort of thing Very Happy

Yup, KF…. Not KM….My bad…I had a couple of wings with true wing type air foils and they were pitch sensitive with speed change….. Your flying wing is a single fold with a spar?….How does it fly?….I thought about another flying wing someday and maybe using KFm4….. Basically symmetrical….. Bet it would be stout with the fg mesh laminated in….

Playing With Foam 1110f410
rdw777
rdw777
Gold Member
Gold Member

Posts : 120
Join date : 2021-03-11
Location : West Texas

Back to top Go down

Playing With Foam Empty Re: Playing With Foam

Post  Sponsored content


Sponsored content


Back to top Go down

Back to top


 
Permissions in this forum:
You cannot reply to topics in this forum