testing some old BP and composite motors

Alan Whitmore

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TMT has recently simplified and "streamlined" the Data Acquisition and Recording package to make our testing sessions simpler and less prone to mistakes. I needed to test out the equipment and there are no commercial motors in the queue, so I looked around for something to run some tests with. I have a box of old BP motors, and a few new ones of the same size, so I tested the new equipment in my driveway, with some Estes B6 and C6 motors.
The "old" motors are from 2002, and have been stored "inside", according the the kind man who gave them to me, loose in a box, with no plastic wrap. That's all I know. The "new" motors were purchased from Apogee Components in June, and have 2016 date codes. I ran 2 old C6's, 3 new C6's, 2 old B6's and 2 new B6's. All of the total I and average I figures are well within the required parameters, as are the delay times, both old and new. Every delay time is short, often very close to the criterion for rejection. Not a single delay time, old or new, was less than a second too short.

The interesting observation was with a pair of motors I had never heard of. Even my year-long search of the archives had not turned up the Apogee C10-7, and there were 2 in the box in their original polythene wrap. This is a weird little motor, 18mm composite propellant, somewhat short, only 51mm long, black plastic case and a plastic nozzle, Packaged with an ancient 'copperhead', which I discarded. There was no date stamp on the motor or in the instructions, so I have no idea about the actual age. There must have been some form of copper in the propellant, because there was a brief spark of blue in the flame, and the total impulse and average thrust figures were precisely within requirements. Nominal 7 second delay, and the observed delay times were 16.57 and 16.64 seconds. Say wha!?!? I almost gave up and stopped recording. None of you have any Apogee C10's or or likely to acquire any, so we can close the discussion of these little anomalies.

I can only make one generalization about these observations. Both old and new, the total impulse, average thrust, and delay element timing for this small group of motors was essentially all the same. the big difference is in the vigor of the ejection charges. All of the new motors left the tube on top of the load cell with a smart 'pop', travelling off into the trees around the launch site. All of the older motors fired the ejections charges like a micro-sneeze, the motors left the firing tube at a crawl, sometimes only barely leaving the tube. My general admonition is that elderly BP motors may give you total impulse, average thrust, and delay charge timing very similar to the newer versions of the same motors, but the power of the ejection charges are not what you will expect.

Alan Whitmore
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smstachwick

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That’s interesting. Do you think this is an effect of aging charges or just a “that’s how they were built then” kind of thing?
 

Johnly

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I put a 20 year old I300T-M on a test stand a while back and it performed perfectly within NFPA Specs.
Since then, I've been a nearly 100% Blue Thunder guy when purchasing motors that might be around for a while.
 

Alan Whitmore

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That’s interesting. Do you think this is an effect of aging charges or just a “that’s how they were built then” kind of thing?
I think it must be the result of degradation over time of the ejection charge or the way it is sealed. It is hard to imagine that any manufacturer would let a motor leave the factory without sufficient e-charge to separate even a small rocket into halves.
Alan
 

BEC

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In flying older Estes motors I’ve observed similar things as you saw with the B6s and C6s. Of course, to me, 2002 isn’t that old. I’ve flown some that date back to the early 1970s without issues.

Estes delays tend to run short generally (the newly-released C5-3s being the exception). And anecdotally (and not generally measured) they seem to shorten a little when they are really old.

The Apogee (made by Aerotech?) motors sound interesting….and seem to support the idea that old Aerotech delays are often “bonus” delays. Assuming they are near in age to the NAR cert data (so 1991) that’s a doubling of the delay in ~30 years. Yike!
 

UhClem

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The C10's were a very nice motor and I used a few in egglofters. The only downside was they were shorter than your average 18mm motor. This resulted in the gradual eating away of the motor mount aided perhaps by the obstruction of a thrust ring set for a normal 18mm motor. Which I didn't notice until it failed at NARAM 41.

Earning me a Best Midwest Qualified Flight award.

I just looked at the old motor collection and counted seven C10's of various delays.
 
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