1/16th Poplar Plywood

[Motorman]

Why don't they make 1/16th lite ply? I'm making a profile fuselage with a Brodak 40 for power. There's only a sliver of balsa above the maple "H" so I need X amount of stiffness from plywood to connect the engine mount to the wing root.

I have 1/64", 1/32", 1/16" birch ply and 1/8" poplar ply. I want to sheet both sides but, I'm trying to keep the nose light. Do you think I could get away with 1/32" on both sides?

Thanks,
MM

[Brett Buck]

Why don't they make 1/16th lite ply?

   I think you would likely do better in terms of strength/weight ratio with 1/16 hard balsa or 1/64 aircraft plywood. Lite ply is very weak and relatively heavy.

     Brett

[Motorman]

Here's what I've got. Not much wood above the maple.

[Peter Grabenstein]

I quit using plywood doublers for years now.
Epoxy glass fiber sheet (Radio Shack ?) (0,8mm - 1.0mm) is my choice.
It's strong , fuel proof and not much difference in weight .
Last but not least... the good thing
less vibrations at the nose section.
Think about, ....foam.
Please scroll to post #73 and
see pics of my yellow Comp. C.G. Shoestring.

http://www.rc-network.de/forum/showthread.php/375913-Rainbow-35/page5

p.s.
the blue one in post #74 only has one ,outside.

HAPPY BUILDING
Peter

[Steve Helmick]

MotoMan needs to study the Dick Mathis designed Excalibur(s) and Coyote. He used 1/2" balsa on both sides of solid 1/2" balsa fuselage. The nose of mine withstood a vertical crash (courtesy of my flying buddy who couldn't decide which way to turn it...combat fliers tend to do that). However, if using 1/64" ply on the fuselage sides, I'd probably run that full length...or at least to the wing high-point.

I am wondering why the emphasis on building the nose "light". Better to put 1 oz of tail weight than 5 oz of nose weight. I've seen enough tailheavy planes to convince me that building the nose light is a problem waiting to happen. Somewhat like keeping the landing gear to minimal length to save weight. Just don't!
  Steve   

[Randy Cuberly]

MotoMan needs to study the Dick Mathis designed Excalibur(s) and Coyote. He used 1/2" balsa on both sides of solid 1/2" balsa fuselage. The nose of mine withstood a vertical crash (courtesy of my flying buddy who couldn't decide which way to turn it...combat fliers tend to do that). However, if using 1/64" ply on the fuselage sides, I'd probably run that full length...or at least to the wing high-point.

I am wondering why the emphasis on building the nose "light". Better to put 1 oz of tail weight than 5 oz of nose weight. I've seen enough tailheavy planes to convince me that building the nose light is a problem waiting to happen. Somewhat like keeping the landing gear to minimal length to save weight. Just don't!
  Steve   

I agree with Steve.  The nose/motor mount is the wrong place to sacrifice strength, stiffness, and vibration resistance for light weight!

Nice looking construction don't compromise it!

Randy Cuberly

[goozgog]

   I don't mean to be critical of Motorman's design.
It looks very well executed.
I do want to show a different design objective
that has been extremely successful.

   The picture shows the nose of my Enigma
profile and the ST.60 installation.
    You can see the Lite Ply box that looks like
a cheek cowl on the inboard side. This box
and the maple engine bearers , that extend
back to the wing, do an excellent job of
damping engine vibrations.
This has resulted in excellent engine characteristics
from the stock ST.60.
   The box edges extend across the engine bearers
and are glassed to the center section of the wing.
   
Cheers!

[Steve Helmick]

The inboard cheek looks good, Mr. Goozgog. In addition, one might consider a Lite-ply box to enclose the fuel tank, open in the front but tied into the wing on the back end. This would allow shimming the tank up/down just like a full fuselage...but would require removing the engine to do so.  Steve 

[phil c]

1/16th hard balsa is plenty strong, unless you plan to crash regularly.  Either cover it with solidly ironed down Monocote, or if you are going for an extra pretty finish apply a layer of very light fiberglass or carbon fiber matt as a first layer.

The real key to stiffening up the rear of a profile fuselage is to make it thicker- up to 5/8 for the core(3/4 in finished) and don't taper it except behind the stab leading edge.

Pete Grabenstein's suggestion- thin epoxy/glass for doublers is excellent.  Goozog's ply box idea is great too.

It's alway great to hear ideas from somebody that's actually tried them out successfully.

[Dan Berry]

Could the weight difference between 1/19 birch and 1/16 poplar be more than maybe ten grams?
I'm having a hard time imagining that's too much weight.

[goozgog]

The inboard cheek looks good, Mr. Goozgog. In addition, one might consider a Lite-ply box to enclose the fuel tank, open in the front but tied into the wing on the back end. This would allow shimming the tank up/down just like a full fuselage...but would require removing the engine to do so.  Steve 

Hello Steve,
   I named this design "Enigma" because it's  structured
like a full bodied plane but meets the dimensions rules
for profiles.
  I think another box around the tank would be pushing
the rules too far.
 I don't know if a second box would be an improvement.

   The aluminum tank mount in the picture was a failure.
I quickly replaced it with the usual ply mount.

BTW, call me Keith.
"Goozgog" is my boat's name.
There are too many "Keith's" here anyway.   

Cheers!

[Chuck_Smith]

I've always admired the Goldberg Shoestring/Buster cheek cowl concept. It worked pretty good, was light and simple. IIRC it was made of 1/4" balsa.

[Steve Helmick]

Hello Steve,
   I named this design "Enigma" because it's  structured
like a full bodied plane but meets the dimensions rules
for profiles.
  I think another box around the tank would be pushing
the rules too far.
 I don't know if a second box would be an improvement.

   The aluminum tank mount in the picture was a failure.
I quickly replaced it with the usual ply mount.

BTW, call me Keith.

"Goozgog" is my boat's name.
There are too many "Keith's" here anyway.   

Cheers!

Ok, Mr. Keith...the tank enclosure I suggested would be legal per the NW Profile Stunt rules, but as the Profile event is unofficial, i.e., not AMA or PAMPA supervised, it may not be legal everywhere, for sure.

My boat's name is "You POS". Yes, it's a Nitro bass boat, how did you know?  Steve

[Motorman]

I went with 1/32" birch ply on both sides of the nose. Nothing new really. The LG and tank mount points have 1/2" maple dowel between. Epoxy was probably overkill but the nose is pretty solid now. 1/32" hard balsa from the ply back to the flap area (still have to cover the outboard side). The slot for the flaps will be filled after wing installation. Top and bottom longeron has CF laminate. Plan on leaving the truss exposed and covering with transparent film.

MM