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Old 02-23-2011, 12:21 AM
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blackshire blackshire is offline
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Default MGR-3A Little John question?

Hello All,

I have a question about the MGR-3A Little John un-guided artillery rocket, *not* the delta-finned XM47 test version that Estes and other model rocket companies have depicted in scale kits, but the operational version that had small, long-chord rectangular fins.

Has anyone ever built and flown scale models of the XM51 (MGR-3A) rectangular-finned version? The reason why I ask is because the full-scale rocket was spun on its launcher at 3.5 revolutions per second before firing, and I was wondering if any flying scale models of it also had to be spun at launch (or equipped with a *lot* of nose ballast if not spun) in order to fly stably. Below are links to photographs and information on the Little John:

http://www.postwarv2.com/littleJohn/photos.html
http://sill-www.army.mil/FAMAG/1960...PAGES_20_25.pdf
http://www.redstone.army.mil/histor...LITTLEJOHN.html
http://travel.webshots.com/photo/21...042020642IxzOzM

I hope this material will be useful.
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Old 02-23-2011, 11:00 AM
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I always wonderd why they called it the clockwork rocket.
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Old 02-23-2011, 11:54 AM
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Quote:
Originally Posted by blackshire
Has anyone ever built and flown scale models of the XM51 (MGR-3A) rectangular-finned version? The reason why I ask is because the full-scale rocket was spun on its launcher at 3.5 revolutions per second before firing, and I was wondering if any flying scale models of it also had to be spun at launch (or equipped with a *lot* of nose ballast if not spun) in order to fly stably. Below are links to photographs and information on the Little John:



CG in front of the CP. It is not only a good idea, it's the law...


Bill
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Old 02-23-2011, 07:05 PM
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Quote:
Originally Posted by Bill
CG in front of the CP. It is not only a good idea, it's the law...
I am well aware of the importance of the order of those letters--what I'm curious about is whether any flying model of that version of the Little John (if anyone has ever built one) had to have a balance point akin to that of a clock pendulum in order to fly straight. In other words, I'd rather *not* have to try to stuff a 12" mylar parachute into a BT-5 size Sport Scale MGR-3A Little John to support a heavy plastic nose cone filled with lead fishing sinkers and epoxy if I don't have to.
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http://www.lulu.com/product/cd/what...of-2%29/6122050
http://www.lulu.com/product/cd/what...of-2%29/6126511
All of my book proceeds go to the Northcote Heavy Horse Centre www.northcotehorses.com.
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Last edited by blackshire : 02-23-2011 at 07:12 PM. Reason: This ol' hoss done forgot somethin'.
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Old 02-23-2011, 09:37 PM
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Quote:
Originally Posted by blackshire
I am well aware of the importance of the order of those letters--what I'm curious about is whether any flying model of that version of the Little John (if anyone has ever built one) had to have a balance point akin to that of a clock pendulum in order to fly straight. In other words, I'd rather *not* have to try to stuff a 12" mylar parachute into a BT-5 size Sport Scale MGR-3A Little John to support a heavy plastic nose cone filled with lead fishing sinkers and epoxy if I don't have to.



An inherently unstable rocket cannot be made to fly straight under power unless it is spun at a high enough rate to behave gyroscopically. You would probably have to shoot it out of a long rifled barrel in order to do that. Canting the fins will not spin it fast enough, plus you would need to have the launch rod going through the axis, i.e. a cluster of motors around a central launch lug. Then you will begin to have problems with centrifigal force causing combustion to burn through the side of the motor cases.


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