Exploding Rocket Motors. E9 motor malfunction (video)

[ThirstyBarbarian]

One thing I've heard recommended for using black powder motors in cold conditions is to just keep the motors warm until right before use. Don't let them sit in a range box in cold weather. You could carry them in a pocket in your jacket until time to launch, then load up the motor and launch ASAP before it cools down.

 

[YodaMcFly]

Agreed. So, is that a design flaw? It seems that if two of them did not have that problem, then they could have made the third one not have that problem? I realize that requires some re-engineering, and maybe it is not worth the money to them.

I remember the Packard-Bell computers from the 90s. They were selling so many PCs that if you got a bad one, they would just give you a new one. The slow-down they would have incurred by additional QA measures wasn't worth the loss of profit to them.

Of course, pretty soon Acer, Dell, HP and Compaq took over the market; so maybe it didn't work out for them after all.

Anyway, as long as no one else is producing 24mm E motors, Estes has no competition and controls the market.

I remember well those days of the PC wars.

But, to the more important point ... I believe there are E loadings available for the Aerotech 24/40 case.

Now I'm curious.

 

[aerostadt]

The numbers off of the failed rocket motor are A 06 28 11 1. I think they are anyways. I say that because the 28 is printed upside down which means the 06 could be a 90 if it's also printed up side down.

Mbecks, thanks for the update on the motor code. I will add it to my list. It is similar to one of the numbers that I already have on the list. The E9's and E12's that I have failed did not have as long as a delay time as yours (E9-8). It makes me wonder for example if E9-4's and E9-8's are made on the same day.

There are several popular explanations for why these motors fail. One is that the cold propellant experiences an unfavorable temperature gradient as the hot flame temperature advances and cracks due to the thermal stresses. Another explanation is that the solid propellant may separate from the cardboard casing causing extra burning surface. Another explanation is that temperature cycling can promote the two paths just mentioned, readying extra burning surface available for when the motor is ignited. I have had E9's and E12's go bad even in warm weather, but I think that cold weather is more likely to cause a CATO. I think that the motors probably have a failure rate. Maybe one motor out of a pack of 3 might be good and the rest are bad. I wrote a science project on this effect back in 1965. A summary of that project is attached.

View attachment ambient temp effect on model rocket perfomance.pdf

 

[Bat-mite]

I remember well those days of the PC wars.

But, to the more important point ... I believe there are E loadings available for the Aerotech 24/40 case.

Now I'm curious.

Sorry, I meant to write, "no one else is producing 24mm black powder E motors...".

 

[YodaMcFly]

Sorry, I meant to write, "no one else is producing 24mm black powder E motors...".

Gotcha... Yeah, if you want 24mm BP, they're the only game in town.

But, if I understand the physics of it (and not to get too far into a discussion that would go in the restricted section), isn't the problem related to the simple physics of trying to cast a solid slug of BP that big?

And, tangentially, to the point of "should they be decertified" ... In Brinley's Manual, he repeatedly mentions that you should expect your projects to blow up and do other strange things. I'd hate to think we're moving back in that direction with motors that are supposed to be safe.

 

[Cabernut]

Come to think of it, I remember once seeing a pack of E9s where there was a bit of manufacturing damage on the end, as if the "ram rod" had been slightly off center and dinged the casing when packing the engine.

Given that the E9s/E12s reputation for failure is purely anecdotal without the actual numbers, I still can't help but speculate on the cause.

I wonder if there are some engineering gremlins that pop up when packing the extra 1" for the 95mm casings?

Or perhaps the BP "grain" length to width ratio is more vulnerable to catos when it gets a bit long?

 

[ThirstyBarbarian]

As far as I know, the larger 29mm E16 and F15 motors aren't having many catos. I would have expected an equal or greater number of problems as the E9 and E12 motors have, but anecdotally, I haven't noticed that.

 

[markkoelsch]

Gotcha... Yeah, if you want 24mm BP, they're the only game in town.

But, if I understand the physics of it (and not to get too far into a discussion that would go in the restricted section), isn't the problem related to the simple physics of trying to cast a solid slug of BP that big?

And, tangentially, to the point of "should they be decertified" ... In Brinley's Manual, he repeatedly mentions that you should expect your projects to blow up and do other strange things. I'd hate to think we're moving back in that direction with motors that are supposed to be safe.

Brinley was not a hobbyist. People should not expect their commercially purchased rockets to explode. This gets to a couple of reasons for motor certification- that the hobbyist can expect to safely operate a motor, that they perform as advertised, and if there is something wrong with it that can loose certification.

 

[rstaff3]

As far as I know, the larger 29mm E16 and F15 motors aren't having many catos. I would have expected an equal or greater number of problems as the E9 and E12 motors have, but anecdotally, I haven't noticed that.

I have flown a bunch of the 29mm BP motors with 100% success. But then, I flew TONS of E9's early on and never had a problem. My E9 problems started after the E12's came out. Just some non-scientific observations....thinking out loud so to speak.

 

[tab28682]

Agreed. So, is that a design flaw? It seems that if two of them did not have that problem, then they could have made the third one not have that problem? I realize that requires some re-engineering, and maybe it is not worth the money to them.

I remember the Packard-Bell computers from the 90s. They were selling so many PCs that if you got a bad one, they would just give you a new one. The slow-down they would have incurred by additional QA measures wasn't worth the loss of profit to them.

Of course, pretty soon Acer, Dell, HP and Compaq took over the market; so maybe it didn't work out for them after all.

Anyway, as long as no one else is producing 24mm E motors, Estes has no competition and controls the market.

Probably not a design flaw. I think more E9 motors work as designed than fail. Seems more like an intermittent manufacturing error, combined with the occasional heat cycling issue.

 

[tab28682]

As far as I know, the larger 29mm E16 and F15 motors aren't having many catos. I would have expected an equal or greater number of problems as the E9 and E12 motors have, but anecdotally, I haven't noticed that.

Just a guess, but the manufacturing tooling for the 29mm BP motors is likely to be significantly newer and less worn than the tooling for the 24mm BP motors.

 

[Bat-mite]

It may be anecdotal, but some rocketry clubs call a heads-up anytime someone launches with an Estes 24mm E.

 

[ThirstyBarbarian]

It may be anecdotal, but some rocketry clubs call a heads-up anytime someone launches with an Estes 24mm E.

Mine does!

 

[boatgeek]

Last time I saw one launch, I was about to tell the kids next to me that those motors have a high rate of failure. I didn't so I didn't jinx the flight. The flight turned out to be jinxed anyway. Loud pop about 20 feet up and confetti falling down. I'm torn because I have a project (Falcon Heavy with drop-off boosters) that would be perfect with a central E12 and side C11 motors, but I don't want to put the effort in and then have it go bang instead of whoosh. I even have the motors in my garage, slowly heat cycling every time we take the car in or out...

 

[RocketDestroyer]

I had an E9-4 CATO this October. It was a warm day and I had purchased the motors the day before the launch. The motor exploded about 20 in the air severely damaging my Mega Mosquito. It blew both ends out of the motor and shot the motor casing up into the top of the rocket removing the glued in motor block in the process. The date code on mine was A 01 12 16. Anybody want the other two motors from the pack? (Just kidding)

Terry

Mbecks, can you tell us the lot number for your E9 CATO?

The bad motor list that I have is as follows:

C11
A 11 08 10

E9
09-04-12
06-28-11
06-14-01 A
A 01 12 16
A 09 15 14
A 1-12-16

E12
A 08-18-11
A 11 15 11

 

[Cabernut]

Since we don't have access to M.E.S.S. data, is there some sort of poll or tracking of some sort that would work to gain some sort of insight into motor failure rates based on our own individual purchase, load/prep and launches?

For example, I have personally had only one cato - C11-0 lot# A 06 28 11 - out of a total 5 C11s launched this year. I have also launched 3 out of 3 E9-4s successfully, lot A 06 22 12.

 

[Daddyisabar]

Recently at the club a member was flying an E9-4 and I asked his motor's date code, it was 1-12-16. So I boldly announced to the crowd before the launch that he was very brave man to fly that motor. Everyone chuckled. 5-4-3-2-1 START! KABOOM! I flew a fresh pack of 1-12-16's this Summer in my Smaug rocket, a three motor cluster. Two of the three CATOed and blew Smaug's head clean off, the third was able to lift Smaug off the rod and crash him near the pad. The Decimation of Smaug. Even the high power boys who mix their own motors are scared of the 1-12-16 E9's. I have seen that date code blow on at least four club launches. It takes a real man to consistently launch them E9's with a bad batch coming out about an average of once year. But the big bangs always give the old dudes a chance to reminisce about the good old days of the F-100. Heck, I just had my first A10-3T CATO in my little HO JO not long after the dude blew up that E9. The smell of fear pervaded as the clouds of white smoke drifted away and we picked up little bits here and there.

Lets be safe and go launch some AT G76 Mohave Green reloads! Just hope we don't get some from the bad batch of those motors. The Pad Fuhrer won't let VMAX fly. I guess the only thing to do is to get a thick piece of leather and bite down hard like they did in the old Western movies. Pour some rot gut whiskey over the wound and it will clear right up. Don't be afraid of dem ENGINES! Where is the DUKE when you need him? The Cavalry will soon be coming over the hill.

 

[dhbarr]

Lets be safe and go launch some AT G76 Mohave Green reloads! Just hope we don't get some from the bad batch of those motors.

The g76g is my go-to. Can you elaborate?

 

[Daddyisabar]

The g76g is my go-to. Can you elaborate?

I too like the G76 Mohave Green reloads and have had no problem with them in the past. But recently some very experienced guys have had multiple problems, so I doubt it was building errors. I had heard of four or so failures but blew it off since I am a HUGE AT and ESTES HOMER. Then I saw one go for real. BANG! Really cool as it quickly blew the fin can off the rail. They found the deformed case, forward and aft closures and the top men said it was probably a hidden air bubble in the grain or a really bad mix. All I know was that it was cool, but not as cool as those single use H-135 CATOS were awhile back, they had lots of fire! With more motors available today and with many old ones still in the pipeline, the chances of seeing awesome CATOs seems to be increasing. I know some guys that still have some early batch F44's and questionable E9's in their box. Time for some rocketry Russian Roulette if you have expendable rockets and a whole lotta guts!

 

[dhbarr]

Hrmm, seems like I need to weigh all my g76 grains. In retrospect I should probably weigh all my motors & log them.

 

[Daddyisabar]

With all the pressures the remaining motor manufactures are under I would give them a break. Just put in the supplied igniter, say a nice prayer and push the dern button.

 

[rstaff3]

Have fun, be happy. If your flight isn't cool, it's really cool

 

[Daddyisabar]

Repairing a rocket after a massive CATO can be fun too. All the King's horses and all the King's men can actually put Humpty Dumpty back together again!

 

[ThirstyBarbarian]

As a public service, someone should mount an effort to gather up all the "bad batch" motors out there, take them out to the desert, make a huge pile, and light it up!

 

[YodaMcFly]

Brinley was not a hobbyist. People should not expect their commercially purchased rockets to explode. This gets to a couple of reasons for motor certification- that the hobbyist can expect to safely operate a motor, that they perform as advertised, and if there is something wrong with it that can loose certification.

But that's precisely my point; at the time Brinley wrote that, "hobby rocketry" as we know it now was barely off the ground, especially considering that it was pre-Information Superhighway. What he wrote was with the intention of keeping people from blowing themselves up doing what was largely an "unsafe hobby".

I realize that, if people don't file their MESS reports, we don't have data, and that the plural of "anecdote" is not "data", but it *seems* like something strange is going on.

 

[YodaMcFly]

As a public service, someone should mount an effort to gather up all the "bad batch" motors out there, take them out to the desert, make a huge pile, and light it up!

You could sell tickets. Or pay-per-view.

 

[Steve Shannon]

As a public service, someone should mount an effort to gather up all the "bad batch" motors out there, take them out to the desert, make a huge pile, and light it up!

Yeah!

 

[rstaff3]

I will take all bad batch motors and dispose of them...if they are free.

 

[Andy Greene]

Repairing a rocket after a massive CATO can be fun too. All the King's horses and all the King's men can actually put Humpty Dumpty back together again!

Sadly , I have 2 - they actually fly great a few inches shorter

 

[mbecks]

That CATO woke me and my wife's safety distance back up. We have had so many good launches that we weren't the full 30" away. We were probably only 10 or 15 feet away. Won't be doing that any more.