Aerotech 24/40 reload success w/ a question

[Astronot]

I just recently replaced my 24/40 case because I severely damaged my first one because I didn't know what I was doing.

You can refer to this thread if you wish. Aerotech 24/40 Test stand CATO

Thanks to you guys and/or gals I was able to figure out what I did wrong and learn from my mistake.

I just recently performed a second test stand firing of my replacement case and I consider it a success (No motor case damage and motor performed as expected), but I do have a question about what I found when I disassemble the motor case for cleaning.

The motor was much harder to assemble this time. I had to back off of the forward closure just to get the aft closure started. Once the aft closure was started I tightened the forward closure all the way and then proceeded to install the after closure with the tool I bought when I purchased my hardware originally.

OK, here are the pictures of what I found. By the way, I tried to take a picture of the motor in the thrust phase but when it ignited it startled me enough to throw my camera aim off. :sad:

The reload was an E18-7W. Very long delay. I didn't think it would ever fire the ejection charge.

I have a question about the aft O-ring, It looks like it suffered significant burn through and the case liner seems to have a dimple or crease in it. I don't know if you can see it in the photograph but the crease goes down most of the length of the case liner. I can only assume that this dimple occurred when I was tightening done the aft closure.

Thanks for the feedback and help,

David

 

[nute]

Everything looks about normal to me. It's a good sign that it was tricky tightening the aft closure- on all 7 of my 24/40 flights it's taken a couple tries to get the closure to thread, and no CATOs yet...

I have a feeling, and I am no expert on this, that if there was a significant burn through of any of the O rings, there would be an immediate CATO, and severe damage to the case and/or closures. As for the dimple/crease I'm not sure I have ever had anything like it, but I wouldn't worry. It could have occurred during tightening, during firing, or during removal of the liner post-firing.

Seems like you had a successful static test! Is this your first successful reload firing? Congratulations!

Nate

 

[blackbrandt]

Just saying, my first 24-40 motor blew the aft closure on the pad, and I had significant trouble tightening it.

 

[Astronot]

Seems like you had a successful static test! Is this your first successful reload firing? Congratulations!

Nate

Yes. This was my second firing and my first success. Thanks for the feedback.

David

 

[Astronot]

Just saying, my first 24-40 motor blew the aft closure on the pad, and I had significant trouble tightening it.

Did you ever determine what caused it to blow the aft closure?

David

 

[Astronot]

I just wanted to add a few more pics of what I'm seeing on the aft o-ring and case liner. Can you see the crease or dimple in the liner?

Just let me know if this looks normal.

David

 

[nute]

Just saying, my first 24-40 motor blew the aft closure on the pad, and I had significant trouble tightening it.

Very interesting, I've never seen a 24mm blow up in person actually. Was it seated fully?

I just wanted to add a few more pics of what I'm seeing on the aft o-ring and case liner. Can you see the crease or dimple in the liner?

Just let me know if this looks normal.

David

Now that I see the O-ring, it definitely looks different than all of mine in both 24 and 29mm sizes. Mine have always come out looking similar to how they went in, aside from soot and maybe some minor indents or marks. I would expect something of that magnitude- it looks like the whole O-ring was destroyed- (is it still of a rubber- like consistancy, or is it fully charred through?) to cause a full out failure.
The wrinkle/crease/dimple doesn't look too out of the ordinary though. I find all this very intriguing.

Nate

 

[chadrog]

Did you ever determine what caused it to blow the aft closure?

David

The threads, being very fine, are easy to cross thread - just saying.

 

[blackbrandt]

I didn't get the closure tightened enough.

Did you ever determine what caused it to blow the aft closure?

David

 

[blackbrandt]

Very interesting, I've never seen a 24mm blow up in person actually. Was it seated fully?


Nate

https://plus.google.com/photos/1146...5919737517461390978&oid=114663914452024336351

Flip through these next few photos. That is when I blew the aft closure on an E28.

 

[nute]

https://plus.google.com/photos/1146...5919737517461390978&oid=114663914452024336351

Flip through these next few photos. That is when I blew the aft closure on an E28.

Nice photos of an unfortunate event.

how was the damage to the hardware/ rocket?

 

[Astronot]

Now that I see the O-ring, it definitely looks different than all of mine in both 24 and 29mm sizes. Mine have always come out looking similar to how they went in, aside from soot and maybe some minor indents or marks. I would expect something of that magnitude- it looks like the whole O-ring was destroyed- (is it still of a rubber- like consistancy, or is it fully charred through?) to cause a full out failure.
The wrinkle/crease/dimple doesn't look too out of the ordinary though. I find all this very intriguing.

Nate

The O-ring still has some elasticity to it, but it's definitely charred!

David

 

[Rex R]

one item I noticed from the pictures is that, the nozzle cap was fully seated...you should rethink that. as you may have noticed it didn't come off when the motor came up to pressure...this can cause erratic flights when the rocket tries to take the launch leads for a ride. you only need the to hold the motor starter in place against the weight of the clips no more. in general about an 1/8" of the nozzle in the cap should be all you need. those aft O-rings can be a 'joy' to seat, a non pointed round tooth pick can help in seating. also check the outside of the nozzle for casting flash as that can hinder the seating process too.
Rex

 

[blackbrandt]

Yeah, My dad was taking photos on burst mode.

The only damage was to my pride, and the aft closure. Ken Allen of Performance Hobbies replaced it for free (the aft closure, not my pride). The streamer inside caught the motor casing and kept it from shooting into another dimension.



I still have the aft closure, I made it into a necklace. It is bent into an oval. (You might be a rocket geek if...)

Nice photos of an unfortunate event.

how was the damage to the hardware/ rocket?

 

[Astronot]

one item I noticed from the pictures is that, the nozzle cap was fully seated...you should rethink that. as you may have noticed it didn't come off when the motor came up to pressure...this can cause erratic flights when the rocket tries to take the launch leads for a ride. you only need the to hold the motor starter in place against the weight of the clips no more. in general about an 1/8" of the nozzle in the cap should be all you need. those aft O-rings can be a 'joy' to seat, a non pointed round tooth pick can help in seating. also check the outside of the nozzle for casting flash as that can hinder the seating process too.
Rex

Nice catch. Thanks for the tips.

David

 

[nute]

Yeah, My dad was taking photos on burst mode.

The only damage was to my pride, and the aft closure. Ken Allen of Performance Hobbies replaced it for free (the aft closure, not my pride). The streamer inside caught the motor casing and kept it from shooting into another dimension.



I still have the aft closure, I made it into a necklace. It is bent into an oval. (You might be a rocket geek if...)

That is a very cool sounding necklace!!! LOL:cyclops:

 

[bill_s]

There's a possibility you didn't have enough lube on the O-ring (or more likely, not spread) and it was kinked or something. I usually push it down in the slot with an object first also.

With the leave the forward closure loose trick, it's a good idea to go and tighten the forward closure as soon as the rear is threaded (I've forgotten for a few seconds). Otherwise, with the rear tightened more, you have more resistance and will want to tighten it more, mis-estimate, which may make it hard to remove later.

 

[blackbrandt]

That is a very cool sounding necklace!!! LOL:cyclops:

Yeah, raises lots of questions.

 

[Astronot]

OK. I figured it out, but not without your help. I went and assembled another reload and this time I looked for that slot you mentioned. I was thinking a slot in the case, but the slot you are talking about is the slot around the edge of the nozzle. That's when it hit me. Like a bone head, I installed the aft O-ring between the fuel grain and the nozzle, not between the nozzle and the aft closure. That's why the O-ring was so charred. I'm lucky I didn't have another CATO.

Thanks for all your time and help,

David

 

[nute]

Well there's your problem!
You got real Lucky- I've heard of a few instances where that mistake resulted in the rapid disassembly of the motor. ..
Did you by any chance watch the video by Apogee components on reload assembly where he makes the same mistake?

Glad you figured it out! Beginners luck I guess...

Nate

 

[JPVegh]

A forum member put together some nice drawings and animations for assembly of the AT hobby motors.

https://www.rocketryforum.com/showthread.php?39177-AeroTech-Hobbyline-RMS-Assembly-Diagrams-Videos

 

[Astronot]

A forum member put together some nice drawings and animations for assembly of the AT hobby motors.

https://www.rocketryforum.com/showthread.php?39177-AeroTech-Hobbyline-RMS-Assembly-Diagrams-Videos

That's a great resource. Thanks for pointing it out. I downloaded all the PDFs.

 

[n3tjm]

One tip I have with regards to loading the RMS 24/40. Don't tighten the forward closure all the way until after getting the aft closure on. This makes getting the closure installed so much easier. Just don't forget to tighten the forward closure all the way before inserting the ejection charge and installing the motor into the rocket

 

[SacEsq]

Forgive me if I missed this somewhere in this thread but are you using silicone grease on the o-rings? I have been told that failure to do so may cause the ring to catch and bind when tightening the closures thus causing a failure.

 

[Astronot]

Forgive me if I missed this somewhere in this thread but are you using silicone grease on the o-rings? I have been told that failure to do so may cause the ring to catch and bind when tightening the closures thus causing a failure.

It wasn't mentioned earlier, but yes. I am using the grease provided with the hardware.

David

 

[Astronot]

I consider the third test a complete success! No anomalies during function or during dis-assembly. All the O-rings looked good. You can see the nozzle O-ring is in it's proper place. The O-ring at the top of the delay element had some ash on it, but once I cleaned it off, it look fine. The igniter wire fell away as it is suppose to, the end cap also blew away on ignition and got out of the way. The delay was nice and long (E18-7W) and the ejection charge blew when it was suppose to. Thanks you for all your help. You guys helped my dial this in. I feel more confident moving on the the 29mm RMS now. I'm not gonna test fire any of those reloads. I don't have as many of them and they are more expensive. I feel like I have cut my teeth now.

I have included some pictures of round three dis-assembly.

David

 

[Rex R]

ayup looks nominal, might I suggest a dynamic test or three...say an E18-4 in that goliath you have .
the problem with apogee's motor assembly video is that he was using/following the instructions for a 38mm reload instead of the instructions for the 29mm motor. I would recommend getting in the habit of double checking that the instructions you're using are in fact the right ones for the motor/reload you're working on. sure it may add a few seconds to your assembly time...but if it removes repair time... baby wipes work well for removing grease from your pinkies too .
Rex

 

[dpower]

OK. I figured it out, but not without your help. I went and assembled another reload and this time I looked for that slot you mentioned. I was thinking a slot in the case, but the slot you are talking about is the slot around the edge of the nozzle. That's when it hit me. Like a bone head, I installed the aft O-ring between the fuel grain and the nozzle, not between the nozzle and the aft closure. That's why the O-ring was so charred. I'm lucky I didn't have another CATO.

Thanks for all your time and help,

David

That happened to me once too, and it didn't CATO, so I didn't figure it out until disassembly. The thing about AT reloads is that each case size assembles a bit different, so if I haven't assembled a particular casing recently, I go back through the directions. It's kind of a bummer that the AT HPR cases are moving to the EZ style, I'd rather know where each and every piece goes, and have it be my fault if it fails.