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  #1  
Old 02-10-2022, 01:38 PM
Mitchell Gant Mitchell Gant is offline
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Default Asymmetrical thrust and stability

Hi I’m new to the forum but have been flying for about 30 years-cert 2 with Tripoli. For a little while now I’ve thought about trying a scale/semi scale Hound dog Missile with thrust being from the lower “engine” tube. Anyone had experience in such matters?
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Old 02-10-2022, 01:51 PM
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tbzep tbzep is offline
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Quote:
Originally Posted by Mitchell Gant
Hi I’m new to the forum but have been flying for about 30 years-cert 2 with Tripoli. For a little while now I’ve thought about trying a scale/semi scale Hound dog Missile with thrust being from the lower “engine” tube. Anyone had experience in such matters?

It would have to be angled so that the thrust lines up to go through the CP. If your ramjet tube is large enough to set a motor tube inside at the proper angle, it might be possible to get a stable flight. The actual missile's engine pod is angled just the opposite of that. As small as our models are, the thrust line will need to be pretty accurate.

I imagine you are familiar with the Fliskits Deuce model. You might talk to some guys that have flown these models and their upscales to see how stable their models have been if one motor failed to ignite.

I've seen upscales of the model from mid power into fairly large HPR models. What size are you planning on building? I'd definitely build a boilerplate model to experiment with before spending a lot of time finishing one!
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Old 02-10-2022, 02:47 PM
Mitchell Gant Mitchell Gant is offline
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My thought was about 1/4 scale-6” engine tube with 5.5” missile. 54 mm k550.I wonder if I could angle the motor tube inside the “engine pod” enough while keeping the slung look. Should be enough room I would think.
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Old 02-10-2022, 03:53 PM
shockwaveriderz shockwaveriderz is offline
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The diagram here shows a good side view:

https://weaponsandwarfare.com/2021/...-hound-dog/amp/

Appears to me that you could dimension the model around the real engine dimensions,such that the engine tube is straight, within the lower tube.
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Old 02-10-2022, 06:44 PM
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Quote:
Originally Posted by Mitchell Gant
My thought was about 1/4 scale-6” engine tube with 5.5” missile. 54 mm k550.I wonder if I could angle the motor tube inside the “engine pod” enough while keeping the slung look. Should be enough room I would think.

For heaven's sake, boilerplate test fly that at a much smaller size (like D12 or E power) to work out the physics first.
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Old 02-10-2022, 06:51 PM
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Ez2cDave Ez2cDave is offline
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Quote:
Originally Posted by georgegassaway
For heaven's sake, boilerplate test fly that at a much smaller size (like D12 or E power) to work out the physics first.


Amen, George !

It is much better to get chased by a BP "D" or "E" motor, than a "K" motor.

Take George's advice !

Dave F.
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Old 02-11-2022, 01:26 AM
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georgegassaway georgegassaway is offline
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Sometimes, when I've considered converting, or adapting something to fly, whether scale, or plastic model, I've ended up with this line from the movie "War Games".



Or Kenny Rogers' line:

"You gotta know when to hold 'em, know when to fold 'em".

If challenged to build a model of that, I'd have to fold 'em.

Not saying it can't be done, but.... that's quite a challenge to try to get to work, without onboard guidance to handle what seem to me are inevitable major problems.

Also, BTW, that side profile suggests it might have yaw/roll coupling problems ( Mental exercise to grasp yaw-roll coupling: take an over-stable 4 finned rocket, break one fin off on the yaw axis. Fly it. If it is over-stable enough, it will fly (not go unstable), but it'll roll like crazy as any yaw angle will act on the one fin like an aileron to make it roll, due to the opposing fin missing).

BTW - I did "fold 'em" and/or choose not to play, when it came to doing a scale shuttle model with engines in the two SRB's, to provide most of the thrust for the model. After some boilerplate testing of enignes in SRB's that had poor to bad results, I went with one big single (offset) engine in the ET, much as the Estes model of NASA's shuttle did.

I HAVE seen videos of shuttles people did that had engines in the SRB's, many failed. But a couple worked. Well, worked once. I never saw any follow-ups on those to indicate the reliability rate. My boilerplate testing criteria for clustering SRB's was that to even consider doing it for a real model with hundreds of hours of work in it, the boilerplate testing needed to work well at least 10 times in a row. I never got to 1 times in a row.
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Last edited by georgegassaway : 02-11-2022 at 11:32 AM.
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Old 02-11-2022, 07:45 AM
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tbzep tbzep is offline
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Quote:
Originally Posted by Mitchell Gant
My thought was about 1/4 scale-6” engine tube with 5.5” missile. 54 mm k550.I wonder if I could angle the motor tube inside the “engine pod” enough while keeping the slung look. Should be enough room I would think.

Definitely start small and work your way up. That's pretty dang big chunk of motor and wood bits to go squirrly if your math isn't spot on.

Like George said, if you can't get it to work on a small scale, move on to another project or look at yours from a completely different point of view.
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  #9  
Old 02-15-2022, 02:42 PM
Mitchell Gant Mitchell Gant is offline
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I will definitely start small. I did this when I built a flying shop-vac for the Science Channel Odd Rockets Challenge at LDRS 30. (Built a flying plastic teapot 1st, then scaled up. Flew on a K550. Took 3rd place.)
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  #10  
Old 02-15-2022, 02:46 PM
Mitchell Gant Mitchell Gant is offline
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As far as yaw-roll coupling I plan to add a lexan fin to the bottom.
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