Aerotech RMS motor issue

[jettinjas]

I saw the sticky about reporting motor malfunctions, however, since this was my first time using an Aerotech motor, I thought I would post here so as to determine whether it was my fault that caused the issue.

I launched an Aerotech ARCAS rocket using a RMS 24/40 case and F24-4W reload kit. The problem I had was the ejection charge did not work. The rocket never separated and consequently the parachute never deployed. When I removed the motor from the rocket, I noticed that the red ejection charge cap was still installed on the top. When I removed the top of the casing, it appeared as though the delay charge had been spent/burned (forgive my lack of proper terminology) but I could not tell what had happened to the ejection charge.

Has anyone had experience with this sort of problem that might be able to help a rookie understand what I might have done wrong?

Thanks

Jason

[BrianURocket]

After installing the ejection charge, did you put the motor vertical and tap it a few times to make sure the BP was against the delay grain?

[mikec]

Has anyone had experience with this sort of problem that might be able to help a rookie understand what I might have done wrong?

Was the BP still in there? Too much grease plugging the hole in the top of the forward closure is a pretty common mistake.

[jettinjas]

Brian,

I did that, however I didn't necessarily keep it vertical from that point forward. I brought it to the field from my house laying on its side. Should I not install the ejection charge until I get to the field so as to keep the ejection charge upright? Or can I have tap it a few times again when I get to the field (which I didn't do)

Thanks,

Jason

[jettinjas]

Mike,
There was definitely something in there, but I couldn't tell if it was BP, or just ash.

Also, I used the grease sparingly. Could not using enough grease cause an issue?

Thanks,

Jason

[MarkII]

I don't think that the quantity of black powder in an ejection charge would leave much, if any, visible ash if it was burnt. All that would remain would be a very scant amount of soot at most. But the fact that the cap was still in place is proof that the ejection charge didn't ignite, because there is no way that you would have even found the cap if it had. I have pre-assembled 24/40 reloads, including installing the ejection charge, without taking any particular care to keep the motor upright; in fact, I know that I didn't do so. It didn't matter, the ejection charge still ignited as it should. I just made sure that I tapped the motor a couple of times to "settle" the BP in the well before I loaded the motor into the rocket. It isn't a difficult or delicate operation by any means.

Was the delay element burned up? If the delay doesn't burn, it can't ignite the ejection charge. The delay element should ignite at the same time as the rest of the motor. If it doesn't it is usually because some grease got onto the face that was against the propellant (aft end of the element). Conversely, it may burn but not ignite the ejection charge if there was grease on the forward face of the element. In both scenarios, the presence of grease inhibits burning.

The only other scenario in which the ejection charge doesn't ignite is if the hole in the bottom of the charge well is blocked, so that none of the black powder can come in contact with the burning delay grain.

[cavecentral]

Grease plgging the hole or coating the end of the delay are the causes that I have been cautioned against. I have very few failures with AT. All of those were a delay being a bit too long.

The most common issue I heard recently on this forum was blow by causing the ejection to fired during the burn (0 delay or even negative). I noticed the delay fits in the insultator looser, or the insulator fits in the bulthead loose pretty often. All of mine that I noticed this, I added a wrap or masking tape to friction fit it tighter and hopefully prevent blow by ejection.

[jimzcatz]

He said the delay was spent/burnt.

[karlbaum]

I would pay close attention to the ejection well hole. If it has grease in it, that could cause the ejection not to fire. I had an ejection malfunciton that was caused by the hole being too carbonized from previous flights. Now I make sure I clean that little hole to the original diameter.

[troj]

It's improbably that the BP would burn, but the red cap be retained at the top of the motor.

A more likely case is that the forward end of the delay was contaminated, or something was blocking the hole, preventing the BP from being ignited by the delay.

-Kevin

[hardinlw]

There is another possibility. The -4 delay is going to have a long spacer. If you install the delay assembly upside down (I've had TARC teams do that) then most of the BP can migrate down into the forward closure. I would think that the pressure would still have pushed the red cap off even if it didn't develop enough pressure in the airframe to pop the nose cone off.

[GaryT]

You never said if you actually put IN the BP? With AT loads the user has to put in the BP, With CTI it comes pre loaded, It may sound like a pretty ridicules question to ask but with it being your 1st reload and all you may have missed it.

[troj]

Something else I just thought of....

Is there a paper plug in the red cap with the black powder? If so, did you remove the paper cap before putting the cap on the motor?

-Kevin

[jettinjas]

Wow, thanks to everyone who has offered help!!

Gary, I pulled the top cap off of the smaller red cap containing the BP, and it appeared as though there was BP in it, which I then installed on the top of the forward closure.

Kevin, if there was a paper cap, I didn't see it, but will surely check the other 2 ejection caps I have.

Larry, I installed the delay charge so that it was at the top, and the delay spacer was at the bottom next to the propellant. I thought that was the correct orientation, but maybe not. Also, I will certainly check to see if the hole is open and unobstructed.

One final question: if you are supposed to grease the o-ring between the delay charge and the top of the forward closure, won't the delay charge get some amount of grease on it from the o-ring?

Thanks again to everyone who has replyed...I am excited to try launching again (once I rebuild the rocket)!!

Jason

[jettinjas]

Well, I think I may have stumbled onto what caused my problem. I followed along with a YouTube video from Apogee Rockets when assembling the motor. Only now did I read the comments below that the video is incorrect.

I put the aft o-ring in next to the propellant as he did in the video, and then the nozzle. After checking the Aerotech instructions, the correct sequence is the nozzle and then the o-ring. I assume that may have been my problem

Thanks again to everyone for the help!!

Jason

[New Ocean]

Not sure how that mistake prevented the BP from burning... if you had BP in there and the delay clearly burnt, I am shocked the cap didnt fall off. My biggest guess is no BP to begin with.

Glad that the motor didnt CATO with the O-ring in the wrong place. Confused why apogee keeps a video up if it is wrong!

Hey at least the motor case is okay.

[Rex R]

it would appear that Tim was reading from the instructions for a 38mm motor(in which the aft o-ring does go in before the nozzle).
rex

[jettinjas]

Rex,

Do you think that putting the o-ring in first may have caused my problem, or something else?

Jason

[stantonjtroy]

I had the exact same thing happen with the same case/load. Killed my first Interceptor E. I have to agree with the assesment of the powder not seating all the way down in the well. On mine I assembeled and loaded the motor in the rocket but was unable to launch for a couple hours. In that time it was turned in every direction one can imagine (my then 9year old engaging the enemy at warp speed). I failed to point it up and tap it to ensure proper seating of the powder and it met it's demise in the manner you've described to the letter. Since then I always give the lower end of the rocket a couple taps/knocks to be sure the powder is seated and have not had a repeat of the problem. I won't say for sure that was the problem but the results do seem to support it. FWIW

[plano-doug]

I failed to point it up and tap it to ensure proper seating of the powder... Since then I always give the lower end of the rocket a couple taps/knocks to be sure the powder is seated and have not had a repeat of the problem.

I always pack the powder with wadding on top, then tape over that. This holds the powder in position regardless of how the rocket gets turned.

Keep in mind that, if the powder is unpacked, at motor burnout, it will be weightless and if not constrained, can still begin floating up from the delay grain. I'd say that's a stretch, but nonetheless, the idea is to keep it packed so it can't move around.

Doug

.

[Rex R]

I don't imagin it helped matters much. I can picture a scenario where the aft o-ring seal fails at motor burn out, then when the ejection charge goes off a portion of the hot gas going around the nozzle as well as through it. I'd suggest checking that case and aft closure carefully for damage from 'blow-by'.
rex

[jettinjas]

Doug,

For future launches, I'm definitely going to "retap" the motor immediately prior to launching to ensure the BP is seated properly.

[jettinjas]

Rex,

I'll check that as soon as I get home from work

[RimfireJim]

I always pack the powder with wadding on top, then tape over that. This holds the powder in position regardless of how the rocket gets turned.

Keep in mind that, if the powder is unpacked, at motor burnout, it will be weightless and if not constrained, can still begin floating up from the delay grain. I'd say that's a stretch, but nonetheless, the idea is to keep it packed so it can't move around.

Doug

.

That's the way I was taught (though w/o the tape) by one of our very own forum members, PunkRocketScience, and it made a lot of sense to me. A little dab o' dog barf 'll do ya.

[stantonjtroy]

I always pack the powder with wadding on top, then tape over that. This holds the powder in position regardless of how the rocket gets turned.

Keep in mind that, if the powder is unpacked, at motor burnout, it will be weightless and if not constrained, can still begin floating up from the delay grain. I'd say that's a stretch, but nonetheless, the idea is to keep it packed so it can't move around.

Doug

.

I actually started doing that on all my AT 29mm and larger. The 24mm is a little tighter. That and I'm gonna switch it over to a 24mm ProX anyway.

[blackbrandt]

I am starting to freak out now about using single use motors...

[new2hpr]

I am starting to freak out now about using single use motors...

Why would this discussion freak you out about single use? If anything, it should give you focus to correctly assemble, fly, and enjoy reloadables. Sometimes things go wrong, even if you do everything right. I've had a 3-motor cluster (E9s) blow all three nozzles on the pad and sit there slowly burning. I've had my L1 rocket fly perfectly several times before paint, then get 3 zippers on one flight once the beautiful automotive paint was added. Yet I keep going. I wish I knew who originally said it regarding the violent loss of a cherished rocket, "If that sort of thing bothers you, go get a train set."
-Ken

[cavecentral]

I lost or damaged 5-6 rockets this year on maiden flights. Damaaged my Vindicator dual deploy, tree my LOC Wolverine and 38/720 case, damaged my smallest dual deploy, damaged my foirst hand made G10 tubes and nose cone rocket, and my slinky rocket. Just get good at repairing, and don't focus on every little chip in the paint.

[Zeus-cat]

Why would this discussion freak you out about single use? If anything, it should give you focus to correctly assemble, fly, and enjoy reloadables. Sometimes things go wrong, even if you do everything right. I've had a 3-motor cluster (E9s) blow all three nozzles on the pad and sit there slowly burning. I've had my L1 rocket fly perfectly several times before paint, then get 3 zippers on one flight once the beautiful automotive paint was added. Yet I keep going. I wish I knew who originally said it regarding the violent loss of a cherished rocket, "If that sort of thing bothers you, go get a train set."
-Ken

I got into trains last year. Trust me, rockets are far more reliable and less frustrating.

[Nerull]

I am starting to freak out now about using single use motors...

If you're worried about assembly, go ProX. A trained monkey could put them together correctly. Aerotech isn't difficult if you take your time and read the directions, but CTI is considerably simpler to fly. Easier cleanup too. And, at least in the ones I've flown since getting my 29mm case, they ignite so well that the rocket will be in the air before the LCO can finish the word 'Launch'. I don't see myself using my AT hardware again, unless I get stuck somewhere without a CTI vendor.