Author Topic: Aerosol foam sandwich profile... (Read 3379 times)

Dennis Moritz · « **on:** January 31, 2010, 07:10:18 PM »

Has anyone tried using an aerosol foam sandwich for a profile fues? My thought is to build a 3/8" outline for the fues aft of the wing trailing edge, allowing sufficient balsa to support the tail section etc. Covering one side with 1/16" balsa, spraying in the foam, trimming after dry and closing up the other side with another sheet of 1/16". Resulting in a filled-in hollow profile.

Douglas Ames · « **Reply #1 on:** January 31, 2010, 07:25:18 PM »

My first thought would be that truss style braces & "air" would be stronger/lighter than foam.
Foam might work better up front under the ply doublers (core cutouts) for vibration absorbtion?

Russell Shaffer · « **Reply #2 on:** January 31, 2010, 08:09:24 PM »

Very interesting idea. Please try it and let me know. I personally thing the non-waterbased foam would be the best.

sleepy gomez · « **Reply #3 on:** January 31, 2010, 08:22:30 PM »

I build my fuselages with a sandwich. I use 1/16" cedar for the sides and 1 lb white foam for the meat. This is fairly light and BULLET proof. Another another advantage is that I can make the fuse wider than you would with a balsa plank, about 3/4" to 1". This method adds great torsional rigidity not usually found in profiles. Why cedar? Balsa is expensive and I have a table saw. I don't use balsa anymore. For spars etc. I use poplar. The Home Depot is my hobby shop. My 600 sq in Tapeworm (foam wing and stabilator) weighs 48 ounces with an OS 40.

Paul Taylor · « **Reply #4 on:** February 10, 2010, 08:41:06 PM »

Quote from: sleepy gomez on January 31, 2010, 08:22:30 PM

I build my fuselages with a sandwich. I use 1/16" cedar for the sides and 1 lb white foam for the meat. This is fairly light and BULLET proof. Another another advantage is that I can make the fuse wider than you would with a balsa plank, about 3/4" to 1". This method adds great torsional rigidity not usually found in profiles. Why cedar? Balsa is expensive and I have a table saw. I don't use balsa anymore. For spars etc. I use poplar. The Home Depot is my hobby shop. My 600 sq in Tapeworm (foam wing and stabilator) weighs 48 ounces with an OS 40.

Hey Sleepy,
Got any photos?

phil c · « **Reply #5 on:** February 11, 2010, 09:44:34 AM »

I ran an article in CLW last year detailing how to make a profile fuselage using composite construction. Balsa, a bit of ply, hardwood motor mounts, and epoxy/glass for the front end. 1/16 in. balsa and 1 lb white foam from the spar back. jl Cover the balsa with plastic film firmly ironed down and you have an easy to build profile that is very light and stiff. A thin layer of urethane glue(Gorilla glue or similar) or a very thin layer of epoxy is plenty to glue the sides to foam. You can even use spray on contact cement, but you have to mask it to keep it off the outline wood. The outline can be as thin as 1/16 in. if you are willing to round the edges of the fuse and tape the outline in place while the glue dries. Otherwise, 2-3 laminations of 1/16 in. strip are plenty. All the strength comes from the sides. And make the fuse 5/8-3/4 in. wide, as sleepy says. The extra thickness makes even the lightest profile astonishingly stiff.

The foam in place insulation foams end up to around 2-3 lb/cu.ft. and will add an excessive amount of weight to the tail end. Same thing using 1/64 ply for the sides. It is way heavier and stronger than it needs to be.

Wynn Robins · « **Reply #6 on:** February 11, 2010, 08:14:36 PM »

you will have to add a lot of weight on top of the fuse when the foam is expanding as it REALLY expands....it is not very strong however, so I would at least creat "cells" using balsa in the fuse and fill those up - but then again, why fill them up?

a built up profile fuse is lighter and stronger.......

expading foam IS good for repairing foam core wings from the inside tho.....

sleepy gomez · « **Reply #7 on:** February 11, 2010, 10:15:47 PM »

Paul, I don't have any photos except of the finished plane. Next time I build (soon) I will post sequential build photos. SLEEPY

Paul Taylor · « **Reply #8 on:** February 12, 2010, 09:16:33 PM »

Thanks Sleepy,
Or maybe I can see it at Brodaks this year?

Robert McHam · « **Reply #9 on:** February 12, 2010, 09:53:40 PM »

Quote from: Wynn Robins on February 11, 2010, 08:14:36 PM

you will have to add a lot of weight on top of the fuse when the foam is expanding as it REALLY expands....it is not very strong however, so I would at least creat "cells" using balsa in the fuse and fill those up - but then again, why fill them up?

a built up profile fuse is lighter and stronger.......

expading foam IS good for repairing foam core wings from the inside tho.....

I can't help but think that by adding a lot of weight to prevent over expansion would make a more dense center thus unduly creating excess mass where you don't want it, via compression. I think it would be much more desirable to let it expand without resistance to gain maximum lightness. Even so the overall density will be varied and still more dense then many lighter foam sheets that are readily available to sandwich like the meat tray foam.

Robert

sleepy gomez · « **Reply #10 on:** February 13, 2010, 08:33:26 PM »

Paul I would love to go to Brodak's. However SS check does not cover travel expenses. SLEEPY

Wynn Robins · « **Reply #11 on:** February 14, 2010, 06:04:54 PM »

Quote from: Robert McHam on February 12, 2010, 09:53:40 PM

I can't help but think that by adding a lot of weight to prevent over expansion would make a more dense center thus unduly creating excess mass where you don't want it, via compression. I think it would be much more desirable to let it expand without resistance to gain maximum lightness. Even so the overall density will be varied and still more dense then many lighter foam sheets that are readily available to sandwich like the meat tray foam.

Robert

if you intend to fill the fuse voids once built - you will need to add weight to the fuse sides to hold them on as this foam expands with quite some force - as I said - if you were going to fill void in a built up profile - you are better leaving them as voids - as air is lighter...... I have built many built up profile fuselages, and there is no need for foam in between layers......

John KruziK · « **Reply #12 on:** February 14, 2010, 07:29:38 PM »

Sleepy could you post the finished pics? Thanks John

PerttiMe · « **Reply #13 on:** February 15, 2010, 11:47:05 AM »

I don't think the aerosol foams are particularly light. The result will probably not be very uniform either. In some circles (scale R/C combat, at least) many use shaped blocks of insulation foam covered with paper, for fuselages: quick, cheap.

Kim Mortimore · « **Reply #14 on:** February 16, 2010, 12:39:31 PM »

Where do you buy the 1 lb white foam? Can you get it in sheets thin enough for profile cores or do you have to slice it off a block?

Thanks,
Kim Mortimore

PerttiMe · « **Reply #15 on:** February 20, 2010, 11:46:23 AM »

If you are asking me, I think we are on different continents: don't know what is available in your area.

Check your hardware / construction / home improvement stores.

Wayne Collier · « **Reply #16 on:** February 21, 2010, 11:44:18 AM »

Quote from: Wynn Robins on February 14, 2010, 06:04:54 PM

if you intend to fill the fuse voids once built - you will need to add weight to the fuse sides to hold them on as this foam expands with quite some force - as I said - if you were going to fill void in a built up profile - you are better leaving them as voids - as air is lighter...... I have built many built up profile fuselages, and there is no need for foam in between layers......

I think he was meaning to add the foam with only one fuselage side in place. The foam could then expand freely. The excess would be trimmed away before adding the other fuselage side.

phil c · « **Reply #17 on:** February 21, 2010, 02:36:55 PM »

Quote from: Kim Mortimore on February 16, 2010, 12:39:31 PM

Where do you buy the 1 lb white foam? Can you get it in sheets thin enough for profile cores or do you have to slice it off a block?

Thanks,
Kim Mortimore

Most lumber yards have it in various sizes. i think I've even seen it in sheets as thin as half an inch, which would be good for a profile. Or get a thicker sheet, block your're hot wire 5/8 off the bench, and slide the block of foam through to get a perfect sheet.

sleepy gomez · « **Reply #18 on:** February 25, 2010, 10:10:32 AM »

Answering Paul Taylor and John Kruzik: Foam/ wood sandwich fuselage. I use 1/16" sides (cedar) or 3/32" balsa would be okay. I use either epoxy (expensive but quick) or Titebond for the laminating adhesive. Sandwiching in dryer antistatic sheets on each side of the foam makes the fuselage a lite weight baseball bat! I'm attaching photos but I didn't get all the construction photos I should have. Motor mounts are epoxied to one fuselage side. A 3/16" ply doubler is added to that side back to the spar. The photos are representative of several planes I have built.
I also use another method. Two poplar stringers, say 1 1/2" wide, run from nose to tail. They are spaced to cradle the wing and fit to the motor mounts. 1 pound white foam fills the void between and is added to top and bottom of fuselage. This makes a foam surface that can be rounded and shaped as desired. Once the stringers are encapsulated in the foam and then covered with silkspan (50/50 Elmers/water + gelatin) the fuse is quite strong. All my planes are foam wing/foam stab/foam fuselage. I build planes for under $20. Again, with my usual 50/50 finish. I will have to make several posts to get all the the photos in. SLEEPY

Paul Taylor · « **Reply #19 on:** February 25, 2010, 09:14:14 PM »

Thanks Sleepy for the photos.

That is just too cool !!!

Some one else thinking outside the box.

Pinecone · « **Reply #20 on:** March 11, 2010, 05:40:44 AM »

Quote from: PerttiMe on February 15, 2010, 11:47:05 AM

I don't think the aerosol foams are particularly light. The result will probably not be very uniform either. In some circles (scale R/C combat, at least) many use shaped blocks of insulation foam covered with paper, for fuselages: quick, cheap.

I fly RC Combat, and we tend to use foam covered with bi directional fiber tape. VERY strong, as attested by some serious midairs.