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  #1  
Old 01-20-2011, 02:14 PM
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foamy foamy is offline
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Default Think this will work?

These are the parts I've picked out—some of you know about these sizes far better than me.

I think it can be staged—am I mistaken? Will the booster tumble?

Will the rocket fly correctly with the fins up the body that far?

Best way to get a 'chute in there?

Unrelated: What does CATO mean?

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Old 01-20-2011, 02:39 PM
stefanj stefanj is offline
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I would not count on that booster tumbling. The swept fins and balsa transition up front suggest that it will want to make a ballistic trajectory.

Upper stage stability might be a problem. The upper stage fins are VERY far forward. The balsa tail cone will add a fair amount of weight in the rear.

I'd put the parachute in the BT-70 section.

OTOH . . . really nice illustration job!

CATO = "Catastrophic failure," as in a motor failing in a spectacular fashion.
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Old 01-20-2011, 03:18 PM
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My take: the booster might tumble, but it depends on where the CG winds up. Making a "boiler plate" and hand tossing will tell you if you have "arrived".

What is more problematic is the upper stage. My guess is that it is an unstable design, with those fins as far forward as they are on the airframe. Unless you have a hollow balsa boattail, and I mean like at most 20 grams or so, and add some serious nose weight, you will have a 2nd stage "sky writer". I am not saying it is impossible, but I am saying you need to compensate heavily. An alternative is to add a set of clear fins near the end of the boattail to move the CP further aft.

If you haven't read the Handbook of Model Rocketry, 7th Edition by G. Harry Stine, there are some very good explanations on the relationship between the CG and CP for stable flight.

Interesting design, BTW.

Greg
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Old 01-20-2011, 03:18 PM
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foamy foamy is offline
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Quote:
Originally Posted by stefanj
I would not count on that booster tumbling. The swept fins and balsa transition up front suggest that it will want to make a ballistic trajectory.


Kinda what I was thinking.

Quote:
Upper stage stability might be a problem. The upper stage fins are VERY far forward. The balsa tail cone will add a fair amount of weight in the rear.


Didn;t consider that. Doh!

Quote:
Originally Posted by stefanj
I'd put the parachute in the BT-70 section.


My problem is that I don't think it 'd fit, but I don't know.

Quote:
OTOH . . . really nice illustration job!

CATO = "Catastrophic failure," as in a motor failing in a spectacular fashion.


Thanks, I just redid a tech drawing (as close as I could get to scale) using off the shelf parts and thanks for the explanation. I thought it meant the motor going, but wasn't sure.

I appreciate the reply.
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Old 01-20-2011, 03:25 PM
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Quote:
Originally Posted by GregGleason
My take: the booster might tumble, but it depends on where the CG winds up. Making a "boiler plate" and hand tossing will tell you if you have "arrived".

What is more problematic is the upper stage. My guess is that it is an unstable design, with those fins as far forward as they are on the airframe. Unless you have a hollow balsa boattail, and I mean like at most 20 grams or so, and add some serious nose weight, you will have a 2nd stage "sky writer". I am not saying it is impossible, but I am saying you need to compensate heavily. An alternative is to add a set of clear fins near the end of the boattail to move the CP further aft.

If you haven't read the Handbook of Model Rocketry, 7th Edition by G. Harry Stine, there are some very good explanations on the relationship between the CG and CP for stable flight.

Interesting design, BTW.

Greg


Thanks Greg. I'll try and locate that book.

The design isn't mine—it's a Tiamat (C). It's the first missile (program) tested at Wallops FF in '46. Actually, I'm not sure what number this particular "C" model was as there was the Tiamat (A) that had only three fins and a very "Buck Rogers" type of booster. They switched to a different, single nozzle, four-finned booster and added another fin to the Tiamat (Tiamat [B]). The "C" model got the swept wings and it's the only line drawing of the Tiamat program that I can find. I'm going to check one last resource. I really dig the old-school look of these things.

The first one. Tiamat (A) Cordite propelled. They went with a more efficient fuel and booster for the rest of 'em. As far as I know, the A model got dropped from an airplane once and shot off the beach once. It started life as an Army Air Force air-to-air missile, but that didn't last long.


Last edited by foamy : 01-20-2011 at 03:44 PM.
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Old 01-20-2011, 03:47 PM
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Ha! When I first saw it I thought it looked like a rocket from the 1940s!

Interesting history, that one. Thanks.



Greg
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Old 01-20-2011, 04:51 PM
stefanj stefanj is offline
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Interesting photo.

The booster's fins look more "delta" than swept. If you do that, you'll get a booster that is more likely to tumble. You can also put on fake angled motor tubes.

It is hard to tell from the angle shown, but the sustainer fins could be farther back than your design shows. In any case, you can move them back. Just leave a token gap between the rear end of the root edge and the rear end of the tube.
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Old 01-20-2011, 09:46 PM
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There's a little bit more information about it here.

Hughes JB-3 Tiamat. That is one wild looking rocket.

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Old 01-21-2011, 12:08 AM
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  #10  
Old 01-21-2011, 07:25 AM
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Quote:
Originally Posted by stefanj
Interesting photo.

The booster's fins look more "delta" than swept. If you do that, you'll get a booster that is more likely to tumble. You can also put on fake angled motor tubes.

It is hard to tell from the angle shown, but the sustainer fins could be farther back than your design shows. In any case, you can move them back. Just leave a token gap between the rear end of the root edge and the rear end of the tube.


Would that technique pass for Sport Scale?

Here's the drawing I was going on:

And photos of both B and C being launched.


A front view of A.
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