Profile Fuselage

[Bruce Guertin]

Here's a question that I've been wondering about for a while:

Is it better to laminate two pieces of 1/4" balsa or just stick with the traditional 1/2" balsa? I understand there may be a weight penalty for the adhesive used in the lamination process.

[Tim Wescott]

What is "better"?

I poo-poo'd the idea of laminating until I was stuck without any 1/2" sheet and made some.  The result was better.  The theory that I believe is that because the grain doesn't quite match from side to side the assembly is stiffer in torsion.

You don't need much glue to make a good lamination, so self control will be rewarded in a light weight fuselage.  I use yellow aliphatic glue and make sure there's a couple of weeks of drying time before I paint (that's usually not a problem with me).  Epoxy or Gorilla foaming glue would give you a guaranteed cure, but especially with the epoxy you want to be sparing with the glue.

Best, if you don't crash and if your local contests accept wider fuselages is a 3/4" thick assembly with a core made from 1/2"x1/4" sticks 1/2" tall, and about 8-lb 3/32" side panels.  You need to be careful about the weight of your glue even there.

[Perry Rose]

Build it like the Mo'Best. Half inch or three eighths nose to in back of the wing then sticks to the tail covered nose to tail with 1/64 ply and 1/16 nose doublers with a 3/8 balsa tripler.

[Mike Alimov]

Yep, I'm with Tim on this.  If you insist, then two 1/4" sheets glued together are stronger (but heavier) than a single sheet of 1/2".  However, neither is optimal, and will result in a "twisty" tail. 

Here's a picture of my 13-yr old building the fuselage of this year's Nats airplane.  1/2" thick "frame" with 1/64" plywood on both sides.  The stiffest profile fuselage I've ever seen, and bare-wood weight was identical to the same size built-up fuze (SV-11 ARC).  However, because the plywood grain is much denser than balsa, finished weight was minimal.  Balsa requires a lot of finishing product (dope, filler, etc) to cover the pores.  Next time will eliminate a lot of solid wood in the nose (electric!) and go to 3/4" thickness.

The 1/64" plywood is not cheap; hobby shops want about $25-28 for a 12"x48" sheet.  It is cheaper if you buy 1/2 sheets (24"x48") from Aircraft Spruce, and especially if you go together and split the shipping costs with buddies in the area.

[Jim Hoffman]

 I concur with Tim W that two pieces of 1/4 inch balsa laminated is noticeably stiffer than 1/2 inch.

Strongly recommend you laminate with a thin coat of slow cure epoxy.  Any glue that dries by evaporation is liable to cause a warp.  Apply a thin coat and scrape off excess with a credit card.  Set on flat surface and load up with weights

I also put carbon matt in the center during the lamination process, it will require a tiny bit more epoxy.  Zero added strength or stiffness because it is in the neutral axis, but a fine visual indicator as you sand.

The weight added with the epoxy is barely measurable and well worth it

[Tim Wescott]

... 1/2" thick "frame" with 1/64" plywood on both sides.  ...

I was gifted with a plane built that way.  It was an absolute joy to fly, but when I crashed it (through utter stupidity, BTW) it proved practically unrepairable.

So if you go there -- don't crash!

[Ken Culbertson]

We had a thread on this about a year back.  Strongest and lightest I have found is to make the frame aft of the wing center line out of 1/4" carbon fiber target arrow shafts sheeted with 1/8 balsa. Like the one Mike pictured earlier. I have two built this way and the tails don't wiggle at all.

Ken

[Steve Helmick]

Yep, I'm with Tim on this.  If you insist, then two 1/4" sheets glued together are stronger (but heavier) than a single sheet of 1/2".  However, neither is optimal, and will result in a "twisty" tail. 

Here's a picture of my 13-yr old building the fuselage of this year's Nats airplane.  1/2" thick "frame" with 1/64" plywood on both sides.  The stiffest profile fuselage I've ever seen, and bare-wood weight was identical to the same size built-up fuze (SV-11 ARC).  However, because the plywood grain is much denser than balsa, finished weight was minimal.  Balsa requires a lot of finishing product (dope, filler, etc) to cover the pores.  Next time will eliminate a lot of solid wood in the nose (electric!) and go to 3/4" thickness.

The 1/64" plywood is not cheap; hobby shops want about $25-28 for a 12"x48" sheet.  It is cheaper if you buy 1/2 sheets (24"x48") from Aircraft Spruce, and especially if you go together and split the shipping costs with buddies in the area.

So, it looks to me like the wing is a 2-piece bolt-on system? This would also make it easier to use CF tubes in the fuselage for stiffness...to make Ken happy! Tail is removeable also? Seems like a real good idea to me!!! Any more detail pictures would be much appreciated.    Steve

[Mike Alimov]

So, it looks to me like the wing is a 2-piece bolt-on system? This would also make it easier to use CF tubes in the fuselage for stiffness...to make Ken happy! Tail is removeable also? Seems like a real good idea to me!!! Any more detail pictures would be much appreciated.    Steve

As much as I want to keep Ken happy, this plane has zero carbon content. 
And yes, the wings that came with the ARC were kept separate, and attach in a take-apart fashion using simple 3/32” aluminum tabs and #4 sheet metal screws driven into the hardwood hard points ( the wing joiners supplied in the arf, cut in half and relieved for the thickness of the aluminum). Tail is not removable, didn’t have time for that.
Since I’m getting all kinds of requests and questions about this, I will make a separate thread about it, hopefully some time this weekend.

[ericrule]

I agree with Jim Hoffman. Laminate using the epoxy method he describes and certainly add the carbon fiber between the laminations. Light, Stiff and simply will not twist.