24/60 F35W -- Waaaay early ejection

[4regt4]

Hello, one and all...

I recently had an F35W that blew the ejection roughly a second after burnout. OpenRocket projected 1790ft, it managed 982ft. Broke the shock cord.

The nitty and the gritty: After disassembly, I noticed that the delay insulator tube was *inside* of the propellant liner tube, and the forward seal washer was folded in half and lodged in the liner tube just below where the delay tube ended up. In other words, the delay goodies got pushed into the main liner tube. See attached photo of the remains. More curious, the delay insulator tube was near pristine. Just a small bit of charring/soot on one spot on the outside, and the inside (where the delay grain previously resided) just had a very light coat of dark gray soot. It honestly looks like it could be used again. The forward insulator washer had the center mostly burned away leaving it as a ring roughly the size of the o-ring that was directly above it. In the photo, the end of the propellant liner that has the most charring was the forward end.

All of the 24/60 motors in my stash (F35W, F51NT, F63R, F62FJ) have a slip of paper in the package saying it's likely necessary to peel a layer of paper off of the motor liner tube to get it to fit. I did that, but it still did not even come close to fitting. So I carefully sanded the exterior of the tube - rotating, not back and forth longitudinally. Eventually I got it to fit. FWIW, this motor casing has been previously used successfully with F63R and F62FJ.

The delay insulator tube was a "reasonable" fit in the forward closure. Didn't rattle around, but easily would fall out if tipped upside down. When I get a delay insulator that is very loose, I'll do a wrap of masking tape just to help keep it centered in the closure so it will (hopefully) maintain more even contact with the delay o-ring. That was not the case here.

Edit: The supplied 8 second delay was not drilled.

It seems like the "fire" in the combustion chamber somehow made its way past the delay grain to the BP. How it did this, I'm not sure, as the delay insulator shows little evidence of any burning.

Ideas?

Hans.

 

[kjhambrick]

Hans --

Probably a dumb Q, but ...

Did you install a 1/16-inch tall delay spacer aft of the delay grain in the delay insulator ?

-- kjh

see #11 in the RMS 24/60 F35W-8 Motor Assembly Drawing

 

[FlyAwaySam]

It could be that the delay insulator was loose. Back when I was doing ARC launches we made the mistake of peeling it on the F62FJs which caused a similar effect although the ejection happened almost right at burn out.

 

[4regt4]

Hans --

Probably a dumb Q, but ...

Did you install a 1/16-inch tall delay spacer aft of the delay grain in the delay insulator ?

-- kjh

see #11 in the RMS 24/60 F35W-8 Motor Assembly Drawing

Yeah, the delay spacer was there. It's a shorty with the 8 second delay grain.

Hans.

 

[4regt4]

It could be that the delay insulator was loose. Back when I was doing ARC launches we made the mistake of peeling it on the F62FJs which caused a similar effect although the ejection happened almost right at burn out.

The delay insulator was perhaps a touch loose. As I mentioned, I give them a wrap of masking tape if they appear to be too loose. Perhaps I should have taped this one. Can I have do-overs?

Hans.

 

[SolarYellow]

Only Space-X gets do-overs.

 

[4regt4]

Only Space-X gets do-overs.

I should get one. I stuck a recent landing. (same event, but different day, as this F35 ejection issue..)

Hans.

 

[terryg]

If the delay insulator is loose at all, I add some making tape and trim it to be flush with the top and bottom of the insulator (it does not take much). If the main liner is still too tight after peeling a layer then I carefully peel a second one.

 

[4regt4]

The delay insulator was perhaps a touch loose. As I mentioned, I give them a wrap of masking tape if they appear to be too loose. Perhaps I should have taped this one. Can I have do-overs?

If the delay insulator is loose at all, I add some making tape and trim it to be flush with the top and bottom of the insulator (it does not take much). If the main liner is still too tight after peeling a layer then I carefully peel a second one.

Yeah, like I said above, I add tape to the delay insulator when they are loose. This one wasn't very loose, and it may have been too snug if I had wrapped it. I should have tried, nonetheless.

Hans.

 

[terryg]

You do not need to use much, a 3/8" strip will often be enough.

 

[4regt4]

You do not need to use much, a 3/8" strip will often be enough.

Hmmm...

I've assumed that it would be desirable to do a complete circumferential wrap to keep things symmetrical, keep the delay centered. Looks like I should rethink that.

Hans.

 

[rcktnut]

I use cellophane (Scotch) tape. I had to use it many times on my 29- 40/120 loads, never had a problem. Easier to work with.

 

[4regt4]

I use cellophane (Scotch) tape. I had to use it many times on my 29- 40/120 loads, never had a problem. Easier to work with.

I was wondering about that. I was concerned that it would melt and fuse to the closure. Good to know it's usable.

Hans.

 

[rcktnut]

It never melted, the delay insulators always slid right out, just used some last week on a G-64.

 

[4regt4]

It never melted, the delay insulators always slid right out, just used some last week on a G-64.

Actually, this is great news. Thanks.

Hans.

 

[rcktnut]

Here is another thread on the issue: I even tape my high power delay insulators if they are loose. The O-ring seals differently but I don't take any chances. Again never a problem with the HPR loads either.
https://www.rocketryforum.com/threads/at-29-40-120-early-deployment-issue.136925/

 

[4regt4]

Here is another thread on the issue: I even tape my high power delay insulators if they are loose. The O-ring seals differently but I don't take any chances. Again never a problem with the HPR loads either.
https://www.rocketryforum.com/threads/at-29-40-120-early-deployment-issue.136925/

Never had an issue with the high power cases, but crashing stuff isn't good. So a belt-and-suspenders approach isn't bad.

Hans.

 

[WizardOfBoz]

Does anyone ever use Kapton(R) tape? Temperature rating to 260°C.

 

[4regt4]

Does anyone ever use Kapton(R) tape? Temperature rating to 260°C.

I've heard of it, but need to check into it. If it's thick, it may not work for this application. I should get some anyway. Worst case, it'll go well on my shelf of seldom used glue and tape.

Hans.

 

[WizardOfBoz]

I bought a roll that was pretty thick to do thermal/electrical insulation in a laptop that I upgraded the CPU in. You can get different thicknesses. Some info:

A representative Kapton® film thickness is 1 mil (0.03mm), silicon adhesive is 1.6 mil (0.04mm) thick which give a total thickness of 2.6 mil (0.07mm).
Kapton® is a available in thicknesses from 0.3 mil (7.5 µm) to 5 mil (125 µm). It is a good insulator and can function even when exposed to heat.

For comparison, 3M 2090 (Blue) is 5.4 mil thick.

 

[WizardOfBoz]

I have a whole bunch of seldom used tapes, paints, glues, lubricants and... tools. I've got lots of tools. I used the Kapton tape once, but this conversation sparked a thought. I understand that dual deploy electronics terminals often get pretty corroded. I was thinking that putting Kapton over the terminals might avoid some of that.

 

[4regt4]

I'm continuing to wonder if the propellant liner/insulator is a contributing factor, if not the whole cause of the issue. Here me out:

The liner is what compresses all 3 o-rings, right? I mean, if the liner were too short, the closures would simply seat on the motor casing and not compress the o-rings. And the insulator washer sits on top of the liner. If the liner were too short, then the insulator washer would not put pressure on the delay and its liner, and they would not compress the delay o-ring. None of this sounds good. We need an intact liner of the correct length.

Take a look at the attached photo. (I aligned the lens to photograph the forward end, which kind of makes it appear that the aft ends are not lined up. But they are (or very close), and the plastic containing the new one doesn't help that perception.) The burnt liner is ~1/8" shorter than a new one. i.e. 1/8" burned off. As there is a little bit of pristine material on the aft end (although it's obviously uneven), it appears that most of the burning/shortening occurred on the forward end. This could give slack to the washer, and the delay elements, releasing any compression of the delay o-ring.

If my theory is correct, it could explain the timing of the ejection event. It didn't occur right at burn out, but a second or two later. But well before the 8 second delay. The liner could have gradually burned until it could no longer support the insulator washer. My theory is that removing as much material as was needed to insert the liner into the casing could have made it vulnerable to excessive burning and failure. Also, the washer was much more burned than I normally see. About half (or more) of the motors I disassemble have a washer that is more or less intact. The others show some erosion on the I.D. This washer had perhaps only 1/8" or so of its circumference intact. (see original photo)

If this is correct, I'm expecting a Nobel prize for my analysis.

Hans.

 

[Ronz Rocketz]

The theory is sound. Something like this happened at ARLISS the other week. I think it was a L motor. The ejection occurred about 1000ft up. The theory is that the motor burned in the core and around the liner. About half of the propellent wasn't burned. Fortunately, this occurred while Karl Baughman was watching, so he took the motor with him to Aerotech for the analysis. The rocket was destroyed, but the motor and liner are warranty.

 

[4regt4]

The theory is sound. Something like this happened at ARLISS the other week. I think it was a L motor. The ejection occurred about 1000ft up. The theory is that the motor burned in the core and around the liner. About half of the propellent wasn't burned. Fortunately, this occurred while Karl Baughman was watching, so he took the motor with him to Aerotech for the analysis. The rocket was destroyed, but the motor and liner are warranty.

Hopefully you're on that Nobel prize committee...

Hans.

 

[3stoogesrocketry]

Hans.

View attachment 669733

Quick analysis. The delay insulator tube has charring on the inside. Heavier at the bottom if my eyes are correct. Did you recover the delay grain casting tube or the delay spacer if there was one?

After the launch button was pushed , how long did it sit on the pad smoking coming up to pressure before it took off?

I also recently learned from Gary the liners will shrink lengthwise durring / after the burn.

And there was no damage to the forward closure correct ?

 

[4regt4]

Quick analysis. The delay insulator tube has charring on the inside. Heavier at the bottom if my eyes are correct. Did you recover the delay grain casting tube or the delay spacer if there was one?

After the launch button was pushed , how long did it sit on the pad smoking coming up to pressure before it took off?

I also recently learned from Gary the liners will shrink lengthwise durring / after the burn.

And there was no damage to the forward closure correct ?

Actually, the delay insulator is near pristine. There is only a light coat of dark gray soot on the inside. I could probably wipe most of it off. There is some minor charring on a small section of the outside. It's hard to photograph the inside of a tube very well, so it looks darker than it really is. As I originally mentioned, it looks good enough that it could be used again. Didn't see any trace of the delay casting tube or spacer, but they could easily be in the charred mess inside the main liner tube. If so, they aren't recognizable.

I do remember the delay spacer (it was tiny - like 1/16" long) fitting very loosely.

Launch was fairly quick, especially by White Lightning standards. Not like Blue Thunder, though. I did a very light dip in ProCast - the nozzle is fairly small and won't accept a heavy hand at dipping. I double checked both mine and my wife's notes. She normally make notations of chuffs or other launch abnormalities.

The motor casing (including closures) came through unscathed. Initially I expected some surface damage to the inside of the motor case, but it cleaned up perfectly.

Hope that helps....

Thanks for the comments,

Hans.

Edit: I don't know if you looked at the OP or not, but I'll re-mention that the delay insulator was found *inside * of the motor liner, with a folded insulator washer under it.

 

[3stoogesrocketry]

Actually, the delay insulator is near pristine. There is only a light coat of dark gray soot on the inside. I could probably wipe most of it off. There is some minor charring on a small section of the outside. It's hard to photograph the inside of a tube very well, so it looks darker than it really is. As I originally mentioned, it looks good enough that it could be used again. Didn't see any trace of the delay casting tube or spacer, but they could easily be in the charred mess inside the main liner tube. If so, they aren't recognizable.

I do remember the delay spacer (it was tiny - like 1/16" long) fitting very loosely.

Launch was fairly quick, especially by White Lightning standards. Not like Blue Thunder, though. I did a very light dip in ProCast - the nozzle is fairly small and won't accept a heavy hand at dipping. I double checked both mine and my wife's notes. She normally make notations of chuffs or other launch abnormalities.

The motor casing (including closures) came through unscathed. Initially I expected some surface damage to the inside of the motor case, but it cleaned up perfectly.

Hope that helps....

Thanks for the comments,

Hans.

Edit: I don't know if you looked at the OP or not, but I'll re-mention that the delay insulator was found *inside * of the motor liner, with a folded insulator washer under it.

I just wanted to make sure of the details. It seems like just from my keyboard diagnostics, the light residue on the inside of the delay insulator tube would indicate to me there was a gas leakage going around the delay grain. It then ignited just as the motors pressure was dropping. This lite the backside of the delay, blowing the charge. But most importantly, provided enough gas generation to push the delay / delay tube/ spacer ring down and thru the black forward insulator disk into the liner. If the delay elements were ingested during the burn, they would have been expelled thru the nozzle or popped the motor.

Just my best guess

 

[4regt4]

I just wanted to make sure of the details. It seems like just from my keyboard diagnostics, the light residue on the inside of the delay insulator tube would indicate to me there was a gas leakage going around the delay grain. It then ignited just as the motors pressure was dropping. This lite the backside of the delay, blowing the charge. But most importantly, provided enough gas generation to push the delay / delay tube/ spacer ring down and thru the black forward insulator disk into the liner. If the delay elements were ingested during the burn, they would have been expelled thru the nozzle or popped the motor.

Just my best guess

Thanks. Greatly appreciated.

My supposition was that reduced compression of the delay O-ring would cause much of what you describe. That possibility being caused by the motor liner /insulator shrinking in length from being burned at the forward end and no longer supplying support for the insulator washer.

I plan on putting little cameras inside the motor to observe what really goes on. Just kidding....

Hans.