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Query about high-performance design

I'm in the very beginning of planning a high performance rocket, based on an H650 or I700 motor system, and am quite concerned about airframe failure. I'm wondering at what point people start reinforcing airframes, and the benefits of different materials. From what I've read, anything approaching mach needs to be reinforced with fiberglass, at a minimum. What about effective gravity? I mean, at what point does reinforcement become "mandatory"? 35 Gee? 50 Gee?

My first estimates suggest that this rocket will pull about 40G, but if I shrink the rocket a bit (a distinct possibility, chasing mach....) it could easily hit 65G+.

I can see several different solutions. Obviously, buy fiberglass airframe tubing, and work from that. Are there different types of tubing? Any dealer recommendations? Any specific problems working with the product for a 3FNC thru-the wall rocket? I've worked with G10 finstock quite a bit, and suspect the material would be similar. (fins would likely be 3/32" G10, FWIW)

Reinforcement of phenolic tubing is also in mind. I've looked at Aerosleeves, and like the look of the product. I'm particularly thiking in terms of carbon fibre, but wonder if that is overkill? Also, I read that fiberglass creates a product somewhat more flexible that CF. Does this matter?

Because I like to putter and have people willing to teach me the process, I'm leaning towards reinforcing an existing phenolic tube, so I'll ask-- any airframe tube preferred for this purpose? I've used mostly flexible phenolic from Red Arrow, so my exposure to other brands is limited.

Any "DON'T do this" comments?

I'm still scanning the web, looking at what other folks have done, but figured I'd tap the expertise in here as well.

TIA

Kevin OClassen

Reply to
Kevin OClassen
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Depends alot on your l/d & what the internals are...

Reply to
Andy Eng

That really depends on the mass distribution, dimensions and mechanical properties of the components, etc. Can you provide a simple schematic for what is mounted where, and some dimensions?

Dave

Reply to
dave.harper

A U.S. Rockets BANSHEE flies great on a H640 motor (full H).

It is a thin, lightweight paper rocket.

Reply to
Jerry Irvine

Don't believe everything you read. MR has been measured to M1.42 using plain paper body tubes and 1/16" plywood fins. If you are shooting for max speed with high thrust motors, minimum mass is most important. You have to decide if your fiberglass airframe will weigh less than an ordinary airframe of the same strength.

Unless you have very poor construction, acceleration is not a problem. It is the airloads at or approaching max q, that can cause your airframe to fail.

There are lots of mate4rals and building techniques. It comes down to an individuals choice of how much money to spend, what equipment is available or required, what skills he has or wants to develop, etc. Even if it is overkill for your rocket requirements, you can look at this project as an opportunity to learn and develop advanced building skills.

If you insist, DON'T violate the safety code.

Reply to
Alan Jones

The old Mosquito hits over 100 Gs on an A10, and is nothing more than balsa.

Reply to
Bob Kaplow

I watched Wildman's level 3 something-or-other shred at max Q a few years ago out at Lemoile. Tim thought that he had sufficiently braced the airframe internally by adding all kinds of expanding foam. The problem is that foam has no structure to it, so it didn't add stiffness.

If you are going to go Mach and above you'll want internal radial ribs from the full-length engine stuffer tube out to the inside of the airframe. This is what I have done on a bunch of medium power models that tended to suffer various shreds and collapses. The ribs provide a whole bunch more longitudinal stress bearing depth than just a reinforced airframe by itself.

Think on it and ask around to see if there is a more cost-effective or lighter solution.

Reply to
Marty Schrader

I assume that by "rib" you mean something more like "stringer" (ah, the shortcomings of language). "Circular" ribs will add very little longitudinal stiffness, although they will add radial stiffness. In terms of max Q, you'd want the rocket to have sufficient longitudinal stiffness AND a relatively high moment of inertia (i.e. hard to bend), and you're not as concerned with radial stiffness.

If you meant something more like a "stringer", then yes. You can definately increase the longitudinal stiffness and the bending moment of inertia with stringers along the inside of the rocket. Say 8 of these 40deg apart. That should get you relatively high longitudinal stiffness AND a higher benind moment.

Dave

Reply to
dave.harper

Pardon, that should be "8 of these 45deg apart".

Dave

Reply to
dave.harper

Or "9 of these at 40deg apart". :)

Reply to
Dave Grayvis

3 fins or 4 fins?
Reply to
Alan Jones

Sorry Dave, I don't understand the terms Rib or Stringer. I'm currently building a minimum diamter 38mm rocket so I'm definately interested. Do you have a picture or link you could post?

Thanks for any help,

Reply to
Strudleman

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