Limit of birch ply

[Theory]

always looking forward to the next project, and the “max performance” EZI-65 is still high on my list

Curious what the max air speed of 3/16” 10ply Baltic Birch ply is, and if it can take a Mach flight or if I would be better served with a custom set of G10 fins.

 

[boatgeek]

always looking forward to the next project, and the “max performance” EZI-65 is still high on my list

Curious what the max air speed of 3/16” 10ply Baltic Birch ply is, and if it can take a Mach flight or if I would be better served with a custom set of G10 fins.

Depends on the fin size, of course, but I've seen 1/8" birch ply go to M1.6. Those fins were reasonably sized for a 54mm rocket.

 

[blackjack2564]

Putting a nice bevel on them will go long way in keeping them in one piece.

 

[Theory]

Rodger that

Thank you!

 

[heada]

Like said above, bevel the edges. I then coat the edges in thin CA and sand smooth. Fill any voids before coating with CA. I've had birch ply go M1.1 in near MD.

 

[Ez2cDave]

always looking forward to the next project, and the “max performance” EZI-65 is still high on my list

Curious what the max air speed of 3/16” 10ply Baltic Birch ply is, and if it can take a Mach flight or if I would be better served with a custom set of G10 fins.

Hi, Theory !

Chuck's project thread has a huge discussion on fin failure . . .

Flutter is the "killer of fins" on high-velocity flights. Fin planform ( shape ) has everything to do with Flutter. Generally, the Span of the Fin has the greatest effect on Flutter, given the same material thickness. The longer the Span, the LOWER the velocity at which it will Flutter.

Dave F.

 

[Theory]

Understood

Flutter due to shape isn’t so much a concern as the EZI “Nike” shape is proven

I am more concerned about the ply delaminating at high speed. The project will be near Mach on a K1127 or K2050

 

[Ez2cDave]

Theory,

What about using "fin cuffs" or simply a wrap of fiberglass or carbon fiber over the leading edge ?

Dave F.

 

[Theory]

Yea, I may glass em...

 

[Ez2cDave]

Yea, I may glass em...

Good "insurance policy" . . .

Dave F.

 

[rharshberger]

Understood

Flutter due to shape isn’t so much a concern as the EZI “Nike” shape is proven

I am more concerned about the ply delaminating at high speed. The project will be near Mach on a K1127 or K2050

Delaminating shouldn't be a problem....unless its caused by fin flutter.

 

[OverTheTop]

As others have commented, you should be good to well into supersonic. Fin shape will determine how far it will go in without flutter. 3/16" is fairly thick so should be nice and stiff. Are they going to be through-the-wall, or not? What planform are the fins?

 

[Ez2cDave]

As others have commented, you should be good to well into supersonic. Fin shape will determine how far it will go in without flutter. 3/16" is fairly thick so should be nice and stiff. Are they going to be through-the-wall, or not? What planform are the fins?

This is a LOC EZI-65, for reference . . .

Dave F.

 

[blackjack2564]

EZ-I was designed for long burn I-65 motor and is rated up to J's. It's a lightweight rocket for 54mm long burns, spank'n it hard is OK with some mods.

If you are going to stick kick butt K's in it you may wish to re-think....highly recommend a wrap or 2 of 6oz, glass on airframe.

Built stock I would be more worried about airframe failure than the fins with high thrust motors. Be a shame to re-kit on first flight...lol

 

[Theory]

The initial idea is to “sleeve” the airframe with epoxy saturated couplers.

The fins are TTW so no worries there. If I need to go G10, I will, just curious if “naked” ply would work

...and yes I am looking to push it with a Loki K1127 or an AT K2050.