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  #1  
Old 06-14-2020, 12:17 AM
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Default Do old black powder motors really perform better than new ones? - a small test

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
File Type: pdf NovaPayloader(4)-5-12-20_flights.pdf (134.2 KB, 56 views)
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Old 06-14-2020, 05:44 AM
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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.
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Old 06-14-2020, 08:29 AM
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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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Old 06-14-2020, 10:52 AM
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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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Old 06-14-2020, 04:48 PM
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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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Old 06-14-2020, 07:40 PM
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Quote:
Originally Posted by tbzep

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.


Exactly
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Old 06-14-2020, 11:34 PM
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The wind variations I tried to account for by both NOT adjusting the rod angle during the entire set of flights and, as I noted before, intermixing the various ages. If you look at the flight numbers on the first column you can reconstruct the actual order of flights. The winds that day were quite light, which was about as ideal as it gets for doing something like this.

I also cleaned the rod after every third flight, though I probably should've done it every time.

I'm not sure about the 1-2% altimeter error. I flew the same one on all flights...and these devices are quite good these days.

But I agree that this was not enough flights to prove anything definitively. What it disproves, I think, is the idea that old motors are significantly better than new ones. The idea that was advanced in that other thread was that they are just not as good as they used to be, and I don't think that is true.

I would rather say that the oldest motors had the most accurate delays. I had, anecdotally, noticed that older motors (and by this I mean those from the 1990s) tended to run short delays. These data tend to agree with that as well.

I think AltimeterThree reports burn times to the nearest 0.05s,.

For what it's worth, I was out with the same model today and flew it twice off a mini (10mm) rail using two more B6-4s from that 2019 bulk box. Both flights were toward the upper end of the range from the data I posted, that that is confounded a little by using a different, lighter altimeter countered by the added weight of the rebuild after the last flight lawn dart from the data posted above.
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Old 06-15-2020, 09:51 AM
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The 1-2% error I mentioned came from various altimeter manufacturers over the years. I'm not really up to date on all of the ones available today. Some, such as Perfectflite's larger altimeters claim 0.1% error. They don't have that information listed for the smaller MR sized Firefly, so I'd guess it's a little higher. From the few minutes I poked around, it does look like manufacturers are advertising smaller margins of error these days on their higher end products.

Jolly Logic promotes some fuzzy logic by saying the "precision" of acceleration is measured to the nth decimal. It really refers to display precision, and just means the info that is displayed goes to that many decimal places, regardless of sensor accuracy. Altitude says it is displayed to the nearest foot. Barometric and/or G sensors could be off considerably and their advertisement would still be valid. The timer is probably the most accurate measurement by a considerable margin.

Even with perfect altimeter accuracy, I see plenty of variables which will prevent consistent altitudes in motors such as ever so slight wind changes, rod friction, temperature/humidity, propellant batch variations within the same year, individual motor propellant load variations, igniter leads hanging on a little longer on some flights, etc. I'd love to see you (heck, all of us) have the time and resources to enjoy another hundred flights and tighten up the data you already recorded.
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Old 06-15-2020, 10:56 AM
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Doing it with flights is fun but I think we can all agree that total impulse is in the ball park through the years. To tease out differences a serious experimenter would be putting motors on a test stand. Even then I don’t know if a motor from 1977 fired in 1977 would produce the same curve as the 1977 motor fired today.
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Old 06-15-2020, 01:57 PM
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Quote:
Originally Posted by 5x7
Doing it with flights is fun but I think we can all agree that total impulse is in the ball park through the years. To tease out differences a serious experimenter would be putting motors on a test stand. Even then I don’t know if a motor from 1977 fired in 1977 would produce the same curve as the 1977 motor fired today.


Well, serious or not, this experimenter doesn't have a test stand (though I have thought about rigging something a few times).

Certainly agree with your last point. We need a TARDIS or some other way to time travel to even attempt to answer THAT question.

I'm satisfied that there is no clear "the old stuff is obviously better" indication from this, which is really what I set out to find out.
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