In the “Any sign of the C5-x yet?” thread, the discussion at one point turned to the assertion that old motors actually perform better than new ones. I jumped in with both feet suggesting that I could at least take a small stab at figuring this out by doing some test flying in a model in which I have literally hundreds of altimeter-equipped flights (over four examples of the model) - the Nova Payloader.

Thanks to donations to my club and some binge buying when I first got back into rockets I had access to some old but apparently well stored motors. So on May 11th I took a Nova Payloader and an AlitmeterThree and 10 B6-4s up to Sixty Acres to do some flying. Three of them were dated 5 H 6 (June 5th, 1977), three of them dated 7 X 10 (October 7, 1993) and four of them dated H180119. I also took along a couple of B8-5s from 1995 and some Q-Jet B4-4s.

I proceeded to put a total of 14 flights on the model pretty much as fast as I could prep it, fly it, download the data from the A3, make some notes, and repeat. Ten of them were on the B6-4s listed above. I mixed up the ages of the motors in the flight sequence to try to minimize the effects of the weather. Before the last B6-4 flight I flew one of the B8-5s just for amusement sake, then flew three Q-Jet B4-4s to compare (and see how consistent they were).

The one impression I was most left with was that the recent motors (all from the same bulk box) are more inconsistent than the older ones. Both the highest and lowest altitudes of the 10 B6-4 flights were on the 2019 motors.

So....here’s the data from those flights plus four more a few days later.

All of these are on the same model the last one (flight 50) had such a wimpy ejection charge the ‘chute didn’t come out (and the A3 didn’t detect an ejection). It streamlined in the last 100 feet...so needed some extensive rebuilding afterward .

Attached Files

NovaPayloader(4)-5-12-20_flights.pdf (134.2 KB, 60 views)

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Bernard Cawley
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Thanks for doing that. The NAR B6-4 motor certification page is from tests in 1995. I asked them for recent data and they said recent data is within specs of 1995 so they don't have it in a shareable format. It looks like that extends back to 1977 too.

Bernard,

Your data matches up with the results we got from my nephew's science fair project over two years from 2016-2017. We launched an Estes Aerobee clone some 60 times on B6-4s with an Altimeter2. All of the engines were purchased at about the same time and were presumably from recent lots. Although we were researching the effect of various nose shapes on peak altitude, we ultimately decided that thrust variation and delay time variation from motor-to-motor was of greater effect than what shape the pointy end had. I'll see if he has that data stashed away somewhere as my copy resides forever lost in a hard drive that spins and whirles but is otherwise inaccessable.

At the time, I remember being disappointed at the inconsistency; sort of still am. I don't know enough about black powder chemistry to know if I'm being unreasonable. My take would be that the motor variation would preclude model rocketry from being the basis of any true science experimentation, unless, of course, you made hundreds of launches.


As to Bernard's data, I suspect we'd need a bunch more launches of both old and new motors to draw any definitive conclusions.

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Interesting data Bernard, thanks for posting that. Just an observation but I noticed all the flights with the oldest 5 H 6 date code have the shortest burn times and the longest delays in the table. Shorter than the NAR B6-4 motor certification page from 1995.

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Steve Naquin
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With ammunition, accuracy is affected by automated mass production. Sharp shooters hand load their ammo so that the powder charge can be controlled with much more consistency. Bullet seating, etc. are also factors, but the powder charge is a biggie. I'm sure the various Mabel decedents are good, but because they are automated, fast, and rely on mechanical, pneumatic, and or hydraulic processes to charge and press propellant, there are going to be inconsistencies. I have a feeling that the charges thrown into mass produced ammo are held to a higher degree of accuracy than MR motors, so I could easily see a considerable difference in performance from motor to motor. I suppose you could check the mass of each motor to try to find consistency, but you don't know if the few grams difference comes from propellant, delay, ejection charge, clay, or even paper casing material. We have often seen incredible differences in ejection charges, which are sometimes easily gauged with the naked eye and ear.

This doesn't count the slight breeze variations that will affect rod friction and weathercocking. Even tiny variations would cause several feet of altitude change. There is also the 1-2% altimeter error. A foot or two by itself it isn't much, but tacked onto other variables, it adds up. Even with extremely consistent motors, I'd be shocked to see every flight fall inside a 10' window.

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Exactly