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  #31  
Old 10-25-2012, 01:06 PM
Jerry Irvine's Avatar
Jerry Irvine Jerry Irvine is offline
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During moments of non Safety Code compliant rocket activity decades ago I have seen them used to target humans on the other team. All they do on a direct hit is leave a welt. Model rockets are even pretty safe when intentionally misused.

Jerry
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  #32  
Old 10-25-2012, 02:24 PM
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Back in the early 80's I knew of several TOY shoulder-fired simulated-bazookas with a "flour payload" using model rockets with D12 motors. Some had stick-stabilization (lousy on a horizontal plane), some had fold-out fins, and some had stubby fins. The folding-fin ones flew fairly straight. NONE of the launches were anywhere near vertical nor did they resemble anything close to the safety code other than most were electrically launched.
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  #33  
Old 10-26-2012, 11:49 AM
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Thanks to all for your input.

After thinking things over in greater detail I've come to the conclusion that my sand bag idea is a bad one. Any object not secured into a fixed position within the airframe would surely slide rearward under acceleration and forward on deceleration. Not good.

I did experiment by placing exactly 2 ounces (57 grams) of loose clay powder within the nose cone and noting the shift in overall center of mass when the clay was all the way forward versus all the way aft. The nose cone is approximately 14" in length, tip to base, and the shift in CM was about 1/4" in favor of the forward weight. (I did place a spent AT G80 motor containing sand fill to represent liftoff weight in the motor mount.)

It looks like this bird will need about 3 ounces of something in or on the nosecone to acheive one caliber CM/CP, and it won't be in a bag.

Maybe I should stick to my political posts?
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  #34  
Old 10-26-2012, 12:02 PM
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Quote:
Originally Posted by ghrocketman
I'm willing to test-fire the rocket horizontally toward a cinder-block wall to test the penetration of sand vs. lead/epoxy. That's test-subject A-PLENTY !



Do you have any particular wall in mind? And, if we're going to waste a perfectly good nosecone, why not try one of your famous fecal tricks?
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  #35  
Old 10-26-2012, 01:19 PM
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I will let you pick the wall. Build one specific for the test ?
Not sure how a 'fecal trick' plays into this though.
Dog Turd filled nose cone perhaps ?
YOU FILL it, and I will launch it toward the wall.

Seriously though, lead shot mixed with epoxy pours well into nose cones and is about the best material for adding noseweight.
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  #36  
Old 10-26-2012, 01:43 PM
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Quote:
Originally Posted by ghrocketman
I will let you pick the wall. Build one specific for the test ?
Not sure how a 'fecal trick' plays into this though.
Dog Turd filled nose cone perhaps ?
YOU FILL it, and I will launch it toward the wall.


Seriously though, lead shot mixed with epoxy pours well into nose cones and is about the best material for adding noseweight.


Duly noted and this is the probable route I'll pursue. I'm not nearly as concerned about an ejection failure scenario as I am about improper CM/CP relationship.
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  #37  
Old 10-26-2012, 02:20 PM
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Agree.
An ejection failure is an unlikely, but possible event.
An improper CP/CG relationship GUARANTEES an unstable and often disasterous flight.
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  #38  
Old 10-29-2012, 01:26 PM
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Quote:
Originally Posted by ghrocketman
Agree.
An ejection failure is an unlikely, but possible event.
An improper CP/CG relationship GUARANTEES an unstable and often disasterous flight.


Sometimes, it's not the lead in the nose but the rocks in my head that cause the problems!

Yesterday was a beautiful day here in North Tejas. Deep blue skies, light winds and temperatures in the upper fifties. So we loaded up my latest bird and headed up to a friends 15 acre flat pasture for a test flight of the unpainted airframe. I re-checked the CM/CP relationship and discovered that even without adding nose ballast I was good to go.

Empty weight was 816 grams sans motor. Installed G80-7T Estes/AT motor. Perfect flight, straight as an arrow. Ejection event....no chute! Then the sickening thud.

For some unknown reason I had placed the chute under the recovery harness and although the nose and harness ejected the chute hung up just inside the end of the body tube.

I shall rebuild. And next time, NO DRINKIN!
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  #39  
Old 10-30-2012, 11:30 AM
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Ouch !
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