Would a motor lose thrust with age?

I did a flight test of a rocket of "pretty much" my own design today. I say "pretty much" because it was made from parts of an old Estes kit that the original body tube had gotten crushed on. The motor mount and Nose cone are stock but I modified the fins somewhat and used an 18 inch long body tube I got from Semroc to come up with my own generic 4FNC design. I plugged the thing in Open Rocket to test for stability and also did an swing test on it. Today was the first test flight with an A8-3 which I figured would be underpowered but I have to be careful because I'm using a pretty small launch area. Anyway the rocket flew straight and true but did not gain enough altitude to even let the chute get ejected and open before it hit the ground. I'm guessing it maybe got 150 feet of altitude, if that. The thing is that the motor was really old.....I mean like year and years. I was probably risking a CATO even trying it but I had it on hand so I threw caution to the wind and gave it a shot. The motor performed properly but I'm trying to decide if the lack of altitude was because of my first thought which is that the bird was woefully underpowered or if the age of the motor might have caused it to lose some thrust. Trying to gauge what I should be using in this bird and not sure if what I saw today was a representative sample of "A power". Thoughts?

What was the full liftoff weight of the fully loaded rocket (with motor) and did you compare that the the manufacturer's maximum recommended liftoff weight?

Was it an older Estes motor, in which case they do not cato with age, only with abuse - BUT if it was from the years of the Poopy Clay they could suffer from nozzle failure/erosion and lose a lot of thrust. Poopy Clay motors were produced and sold around the time of Star Wars Episode 1 and have a powdery white clay that crumbles if you look at it the worng way (or use the motor).

Never thought to weigh it. It's an Estes motor and it was really old. Could actually be twenty or more years old now that I think of it. I had a bunch of rocket stuff stored over the years. This particular one was just lose in my storage box but I have some other ones that are still in "flight packs" which are packaged with recovery wadding, igniters, and plastic igniter plugs. Got some older C6-3's too but don't want to "jump the fence" on power.

UPDATE....Just figured out the date code on the motor....circa 1994 so would that have had the "Poopy Clay"? BTW these motors were stored in a well insulated but unheated building for awhile so there might have been some temp cycling. Georgia doesn't have huge weather extremes though. I can go buy new motors and will but I just hate not to use these. Got six more A8-3's and four C6-3's.

Do you still have the fired motor? Just look at the nozzle and compare it to another A8-3. If chunks of it are missing or the diameter of the hole is bigger then the nozzle eroded...

I've never heard of BP motors getting weaker with age, but maybe in a long term humid environment? Dunno. The risk I always hear about is outright failure (CATOs), not reduced performance.

Nozzle looks to be eroded. Hadn't thought about it till I looked but it does. I will keep experimenting. The other A8-3's I have are newer.

Last June in 2013, my buddy launched his big Red Max on an old AT motor...guessing 20 years old.....and the propellant was fine. The delay, on the other hand, had degraded and took twice the amount of time to get to ejection. Almost wrecked that maiden flight from within 5' from the ground when it finally deployed the chute. Maybe you should consider testing the other motors on some tree fodder rockets?

I fly 35 to 40 year old motors often, with perfect results. Most recenty 3 40 year old well travelled A8-3s, they were Estes so they are even still certified.

You would know if the nozzle blew out. It sounds like you probably just underpowered your rocket. Weigh it. An A8-3 has a max lift off of 3.0oz.


Jerome

JeromeK99 said:

You would know if the nozzle blew out. It sounds like you probably just underpowered your rocket. Weigh it. An A8-3 has a max lift off of 3.0oz.


Jerome

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Agreed. I have motors from early 80's and have performed flawlessly.
Stored in unheated sub zero conditions to high humidity 90+ seasonal changes. Loose, not packaged.
I still have a few of the old old "Igniters" with the sticky discs. The discs are basically worthless now, not that they were ever much good.
I remember before them, Estes advised us to use masking tape. The role in my field box is junk now, guess it's time to throw it away.

Year codes A and B had most of the Poopy Clay, but my memory is now getting fuzzy about when the Poopy Clay went away and the current "Strong Like Ox Clay" arrived. Year code A was 1996. The Poopy Clay motors arrived just at the same time as a bunch of very heavy rockets that had lots of plastic and really were near the maximum liftoff weight of the recommended motors - assuming the motors worked properly. The Poopy Clay would erode as the motor fired, and the larger and irregular nozzle produced much less thrust and also vectored thrust.

Look at the motors. if the clay powdery white or not? if you have Poopy Clay, contact Estes and they may send you replacement motors. They do not want you to crash rockets.

You do not weigh the motor.


You weigh the entire loaded rocket to see what it's liftoff weight would be - and this includes wadding and motor. Motors cannot lift more than their recommended maximum liftoff weight. The exact same motor with a longer delay will have a lower liftoff weight because the long delay time will allow a heavier rocket to coast until it hits the ground. If you launch anything that weighs more than the motor recommends, then it might fall out of the sky if the thrust level is too low or it will not go very high or fast and it will coast into the ground before the ejection charge goes off.

RocketMike said:

UPDATE....Just figured out the date code on the motor....circa 1994 so would that have had the "Poopy Clay"? BTW these motors were stored in a well insulated but unheated building for awhile so there might have been some temp cycling. Georgia doesn't have huge weather extremes though. I can go buy new motors and will but I just hate not to use these. Got six more A8-3's and four C6-3's.

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No, but they do tend to lose their hair and get a little flabby around the middle..oh, wait. Never mind.

I ran some simulations and got interesting results. I guess I should have though to do that in the first place but better late than never. I have nothing to weigh the rocket with but according to the sim the rocket weight is 3.72 ounces with an A8-3 and the projected altitude is just a shade under 60 feet! That would explain the lack of performance I experienced! Jumping up to a B6-4 would produce a rocket weight of 3.78 ounces and the altitude would climb to 201 feet. Now we are getting somewhere. A C6-3 produces a rocket weight of 3.96 ounces and the max altitude would be 560 feet. So yes, obviously an A8-3 is out of the question for this particular rocket.

I would bet you just put enough weight and drag modifying it to put it out of the recommended range for A8-3. Even a new A8-3 doesn't really lift a stock Big Bertha very far these days (certainly not the 80 feet expected from RocSim or OpenRocket).

I think I'm going to pick up some B6-4's this weekend. As I said, I have some C6-3's which is probably what I should be flying it on but I'm really iffy because of the small size of my launch area. The search is ongoing for a suitable launch area that is bigger than what I have now but for right now, lower altitude launches are better than no launches. Roy, one of these days I'm going to get to one of the SOAR launches but the timing isn't good for me right now. I would have thought about the Lily launch but I have to work part of the day Saturday.

Mass isn't everything. Drag is a factor as well. I have the Estes Black Hawk, basically their rebranded version of the Centuri Buck Rogers Starfighter, for which the recommended first flight motor was an A8-3. I followed the instructions, tried it with an A8-3, and it behaved just like the OP's rocket, ejecting its parachute just in time to avoid crashing. It's since flown very nicely on B6-4s.

Since then I've found it hard to trust Estes' table of maximum liftoff masses. Partly because in those days the A8-3 was supposed to be able to lift 4oz; these days it can only lift 3oz. Partly because the B6-4, C6-3 and C6-5 all have the same maximum liftoff mass, 4oz. And partly because the E9-6 allegedly has a higher maximum liftoff mass (12oz) than the D12-5 (10oz). Yeah, right. :lol:

I also fly very old Estes and other BP motors often some over 40 years old. To date the only difference I've ever noticed on motors from as far back as when they went from paper caps to clay is that the older clay get really hard and sometimes didn't burst at ejection. remedy is to scratch a X across the clay cap before installing the motor. Since discovering this little trick I've not had a recurrence of the problem regardless of the age of the motors.

Age doesn't cause CATO's, Abuse; mainly bad Storage practices (Heat cycling) does. If you motor are kept indoors or in a controlled environment they should perform per spec almost indefinitely.

A rocket thats built to fly on A8-3 is definitely going to be sensitive to being "built heavy". OpenRocket seems to be a fair piece of software, my only rockets built based on sims with it are a beefed up double tubed Blue Bird Zero (to fly on 24mm composite Es and Fs ) and a Semi-Scale SA-3 Goa scratch build https://www.rocketryforum.com/showthread.php?70827-SA-3-Goa-Semi-Scale-2-Stage-with-Cluster-Booster the I was really worried about the stability but OpenRocket nailed it and it flew wonderfully. I have found that its necessary to weigh the rocket after construction and the override the weights in OpenRocket then re-run the Sim portion.

On the subject of weighing rockets, what type of scale would one use? I have small digital gram scale I use for weighing rotor blades on my RC heli but I think a rocket is too big for it. In fact I know it is. So what's the scale of choice? Hopefully something inexpensive.

I use our kitchen scale, it weighs in either lbs/ozs or grams, the grams is what I use since it gives me a smaller interval of mesurement(it doesnt do 10ths or 100ths of ozs) , then I just do a mass override in OpenRocket. Some people use the ones from Harbor Freight like this one which is good for up to 11 lbs https://www.harborfreight.com/digital-scale-95364.html HF has others ones as well, my kitchen scale only goes up to about 3 lbs. If you need to increase the size of the weighing plate just put a dinner plate on top of the scale and Zero the scale, I have also built a small cradle I can set on the scale to weigh rockets horizontally.

I am old too. On my older motors I have discovered that if I place one of my little blue pills in the forward end, that the motor and rocket goes up quick with a straight powerful thrust. The only problem is occasionally having to wait four hours for it to come back down agin.

RocketMike said:

On the subject of weighing rockets, what type of scale would one use? I have small digital gram scale I use for weighing rotor blades on my RC heli but I think a rocket is too big for it. In fact I know it is. So what's the scale of choice? Hopefully something inexpensive.

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Harbor Freight has a couple very inexpensive digital gram scales that are Well worth the very bucks they cost. I personally like the 500g pocket scale which generally runs between 9 and 13dollars depending if you can catch them on sale.

The Only side note to these .1g scales is you have to have 500grams of weights to calibrate it before use. I have 6 of these little scales all over the house, range boxes and van I've noticed no difference in mass on even my lightest competition models using these scales one in the shop, another on the field. An excellent product for my money.
I think I have more tied up in certified weights then in scales LOL! Weighs can be had at McMaster-Carr or other industrial supplies.

I fired some A8-3s and C6-5s over the past few months that were 20+ years old, part of my old stash from when I was a teenager. All of them worked just as well as the newer ones I fired alongside them. I don't think they were ever stored in an attic, although I know they were kept in several non-climate controlled garages over the years.

I'd have to look in my range box but I think there are still a couple of C6-7s in there waiting for another multi-stage or really light rocket to go up in.

Just a little further update..... Today I went by Hobby Lobby and picked up some B6-4's and I plan on trying a launch with one of those tomorrow. As stated above, Open Rocket predicts 201 feet. Still not a whole lot of altitude but I have be real careful because of the size of my launch area. I'll just have to see how it goes.

B6-4 was definitely the ticket. Plenty enough altitude for a good chute deploy and everything......including the tree the rocket got hung in on the way down. Ahh well, as I said, my launch area is small and maybe this rocket was a bit too much for it. I'm hoping maybe I get lucky and the wind blows it down but it's too high to go after.

Launched a Baby Bertha on an old Centuri B6-6 which CATO'd, blowing the motor mount free.