Quantcast

Need help with Failure Analysis - Full Scale Hellfire Launch

The Rocketry Forum

Help Support The Rocketry Forum:

DMcCauley

Well-Known Member
Joined
Feb 8, 2009
Messages
177
Reaction score
0
For those of you at MDRA Red Glare V, may have seen the first launch of my Fullscale Hellfire Missile (all 60lbs of it) launched on an L-1111 which resulted in a premature separation event prior to apogee.

The full video can be downloaded here which was shot by Bob Utley.
http://www.mdra-archive.org/photos/RedGlare5/BobUtley/Full/DanielMcCauley.wmv

I'm trying to determine the cause of the failure, but can't seem to put my finger on it yet.

Basically, from what i gather and by viewing the events in slow motion. (You can do this in Windows Media by selecting >View>Enhancements>Speed Control)

1. Thrust Phase
2. Coast Phase
3. Explosive Separation between Booster and EBAY (gray plume smoke)
4. Drag separation of nosecone (25lb) and EBAY (due to booster being separated already)
5. Two distinct pops at Apogee which appear to be both altimeters firing the drogue charges
6. One distinct pop during descent which was one of the main charges going off.

Since i can hear two simultaneous pops at apogee, that makes me think that it wasn't one of the drogue separations going off. Plus, if i look at the video, when the BP charges went off, there was white smoke, not dark smoke. The smoke plume present during the premature separation was clearly dark grey, the same color as the exhaust of the motor trail at that point.

If you have a chance, check it out!

BTW, the second day, the rocket flew perfectly on an L-1080.

Thanks
 

DAllen

Well-Known Member
Joined
Jan 18, 2009
Messages
4,777
Reaction score
727
3. Explosive Separation between Booster and EBAY (gray plume smoke)
Really dumb question time...Did you drill vent holes in your booster section?

Did you have your mach delay set? I know it sounds like a looney question but you might have had a weird cross wind or strange turbulence over the altimeter vent hole to cause one of them to think it was at apogee. That doesn't explain the dual pops at apogee on the video. Even if I am going no where near mach I still set the delay for 4 seconds so I know for a fact it will not deploy during thrust. Also, don't forget audio on a video camera might be deceiving. Just because you hear 2 pops doesn't there really were 2. Sounds could have echoed off of something prior to reaching the camera microphone. Do you remember if you heard 2 pops in person?


Edit: the more I listen to it in slow mo the more it sounds like an echo.

-DAllen
 
Last edited:

cobra1336

Well-Known Member
Joined
Jan 23, 2009
Messages
949
Reaction score
1
I was there to see it. Not sure yet what happened. I'll look it over some more.
I just love the guy in the backround saying "THAT THINGS A TANK" Can't stop laughing.
 

DMcCauley

Well-Known Member
Joined
Feb 8, 2009
Messages
177
Reaction score
0
Thanks.

Yeah, that thing is a tank. About 60 lbs with a stubby nosecone that weighed 25 lbs.

Actually, there weren't vent holes (something i forgot to put, which i did correct for the next day's launch), but Fred Schumacher and I had a long discussion on this and due to the large volume of the airframe, he was absolutely convinced it had nothing to do with overpressurization.

It is a very interested problem and Bob Utley's video is really great at capturing the failure.

The rocket survived intact, even the 25lb nosecone which buried itself in the mud, but i had just bought about $300 bucks worth of new b2 skyangle chutes that morning which were all shredded to bits.
 

falingtrea

Well-Known Member
Joined
Jan 19, 2009
Messages
792
Reaction score
1
Seems to me like a main charge failure. I could hear a pop when the initial seperation happens. And there was only one main charge pop afterwards, but you could hear two distinct drogue charges. What type of electronics was being used? Did you use two different brands of electronics or two of the same units?
 

DMcCauley

Well-Known Member
Joined
Feb 8, 2009
Messages
177
Reaction score
0
Seems to me like a main charge failure. I could hear a pop when the initial seperation happens. And there was only one main charge pop afterwards, but you could hear two distinct drogue charges. What type of electronics was being used? Did you use two different brands of electronics or two of the same units?
That was a thought I had, but the initial separation was between aft and mid section (drogue). The nosecone / upper section only separated due to the drag imposed on it due to the premature separation of aft / mid sections.

Also note that during inspection, all 4 charges were fired.

The electronics being used were a MAWD and ARTS2.
 

daveyfire

Piled Higher and Deeper
TRF Lifetime Supporter
Joined
Jan 26, 2009
Messages
3,198
Reaction score
54
Location
thank u, next
Did you use any dog barf recovery wadding? That might account for the grey color of the cloud at deployment. If the main deployment charge fired first, I'd have expected to see the main chute appear; but it looks like the drogue comes out first, followed by main deployment.
 

DMcCauley

Well-Known Member
Joined
Feb 8, 2009
Messages
177
Reaction score
0
Did you use any dog barf recovery wadding? That might account for the grey color of the cloud at deployment. If the main deployment charge fired first, I'd have expected to see the main chute appear; but it looks like the drogue comes out first, followed by main deployment.
No wadding was used. Used kevlar chute protectors.

Yes, the drogue definitely separated first. The main only separated afterwards because of the extreme drag presented by the separation of the drogue under ascent. (25lb nosecone just keeps on going!)
 

brianc

Well-Known Member
Joined
Jan 18, 2009
Messages
3,220
Reaction score
1
The electronics being used were a MAWD and ARTS2.
Did you download any data from the altimeters? Any hints in the
data?

EDIT: At 18 seconds into the video, you have motor burn-out followed immediately by
drag sep of the booster. Then at 20 seconds the main separates. The first POP
I hear is the white chute shredding. This is followed by two pops of the drogue charges
(one may be an echo) later, a main charge fires.

Did you have any shear pins in play?


EDIT #2: I can't tell for sure, but the gray smoke plume you mentioned appears
to be coming out the nozzle (@19 seconds). Need to look with something better
than WMP later...
 
Last edited:

ben_ullman

Well-Known Member
Joined
Jan 18, 2009
Messages
1,509
Reaction score
0
was there a smoke grain in the motor? If so did the bulkhead used have a small pinhole in it to allow air to excape when you insert the bulkhead? I forgot to put a bolt in one of my bulkheads and the smoke leaked into that hole and deployed the parachute on the way up.

Ben
 

Bravo52

Well-Known Member
Joined
Jan 18, 2009
Messages
674
Reaction score
2
I have to agree with DAllen. I don't think there were 2 "pops" on the drogue. I saw both flights and it was my impression that the altimeter detected apogee too early and fired the drogue. Then the upward velocity caused the mechanical drag separation.

We were interested in the second flight but didn't get a real good look because we were hiding under the Suburban just in case :eek:. But the coast phase on the second flight was more nominal.

I think you've got all the answers here; just putting them in the right order is key. If you take the 2nd pop (or echo) out of the equation, it seems pretty straightforward. Now where was the grassy knoll..........
 

MaxQ

Tripoli 2747
Joined
Jan 18, 2009
Messages
4,409
Reaction score
56
Location
Central Viginia - USA
Did you download any data from the altimeters? Any hints in the
data?

EDIT: At 18 seconds into the video, you have motor burn-out followed immediately by
drag sep of the booster. Then at 20 seconds the main separates. The first POP
I hear is the white chute shredding. This is followed by two pops of the drogue charges
(one may be an echo) later, a main charge fires.

Did you have any shear pins in play?


EDIT #2: I can't tell for sure, but the gray smoke plume you mentioned appears
to be coming out the nozzle (@19 seconds). Need to look with something better
than WMP later...
"Did you have any shear pins in play?"

That was my first question after watching the video...
You claim a "coast phase" but I didn't see much of one...(1 second)

Looks like seperation almost at motor burnout...negative g's deceleration.....looked like the airframe came apart as the motor burnt out....everything else that occured electronically may have been affected by the abruptness of that event.

I would think no vent holes w/o shear pins might exacerbate the problem.
In your words..."Actually, there weren't vent holes (something i forgot to put, which I did correct for the next day's launch)," ...and when you did add vent holes...the launch went well.
 
Last edited:

MaxQ

Tripoli 2747
Joined
Jan 18, 2009
Messages
4,409
Reaction score
56
Location
Central Viginia - USA
was there a smoke grain in the motor? If so did the bulkhead used have a small pinhole in it to allow air to excape when you insert the bulkhead? I forgot to put a bolt in one of my bulkheads and the smoke leaked into that hole and deployed the parachute on the way up.

Ben
Ben..you really think a "smoke leak" through a small hole would have enough volume/pressure to deploy a parachute..?

Which rocket/flight was this?
 

ben_ullman

Well-Known Member
Joined
Jan 18, 2009
Messages
1,509
Reaction score
0
Ben..you really think a "smoke leak" through a small hole would have enough volume/pressure to deploy a parachute..?

Which rocket/flight was this?
Ill bring the pictures to the VRS launch tomorrow and show you. Thank goodness it was in a 10" diameter rocket and they didn't deploy but it burned through the nylon shockcord in 4 places and made our droug a smoldering mess.

Ben
 

DAllen

Well-Known Member
Joined
Jan 18, 2009
Messages
4,777
Reaction score
727
was there a smoke grain in the motor? If so did the bulkhead used have a small pinhole in it to allow air to excape when you insert the bulkhead? I forgot to put a bolt in one of my bulkheads and the smoke leaked into that hole and deployed the parachute on the way up.

Ben
I've never flown a rocket without the ejection charge and with a smoke charge. I thought the smoke charge just burned out the nozzle because the forward closure is plugged. I guess I am missing the reason why there would be smoke leaking into the rocket.

-DAllen
 

ben_ullman

Well-Known Member
Joined
Jan 18, 2009
Messages
1,509
Reaction score
0
I've never flown a rocket without the ejection charge and with a smoke charge. I thought the smoke charge just burned out the nozzle because the forward closure is plugged. I guess I am missing the reason why there would be smoke leaking into the rocket.

-DAllen
Some smoke bulkheads have a small 1/32" or so pinhole in the top. That way when you push the smoke grain in, it releases the air around it and cant built up pressure keeping you from pushing it all the way to the top of the bulkhead. The hole is in the center of the threaded eyebolt part on the top of the bulkhead. If you don't put a bolt in and the smoke grain leaks a little but then thats just an open hole through to the motor. If you put an eye bolt in there it seals it up and there is nothing to worry about.

Ben
 

DMcCauley

Well-Known Member
Joined
Feb 8, 2009
Messages
177
Reaction score
0
"Did you have any shear pins in play?"

That was my first question after watching the video...
You claim a "coast phase" but I didn't see much of one...(1 second)

Looks like seperation almost at motor burnout...negative g's deceleration.....looked like the airframe came apart as the motor burnt out....everything else that occured electronically may have been affected by the abruptness of that event.

I would think no vent holes w/o shear pins might exacerbate the problem.
In your words..."Actually, there weren't vent holes (something i forgot to put, which I did correct for the next day's launch)," ...and when you did add vent holes...the launch went well.
Yes, there were (4) 4-40 nylon shear pins on both the forward and aft sections.

For the 2nd launch, per one of the TRA TAP members (not sure who it was) recommended i double the number of shear pins on the upper section to (8) 4-40 pins. Which i did. I also added a few vent holes for the aft and forward sections.

However, i didn't see the video until a few days ago, so i realize now the upper section wasn't the problem in this failure, so the addition of (4) shear pins to the upper really didn't affect the outcome of the 2nd launch.

Also, i seriously doubt (as well as many other people there) that the vent holes really had much contribution. The volume of the aft section was quite large, and the rocket was moving extremely slow for a rocket and didn't hit much altitude, so i don't believe an air pressure change inside that section would have been enough to eject the aft section.

At this time, i'm leading more towards an actual ejection charge going off.
 

Handeman

Well-Known Member
TRF Supporter
Joined
Jan 18, 2009
Messages
7,721
Reaction score
316
Location
Stafford, VA
Just a thought to keep the shear pin idea alive a little.
Was the weather conditions/humidity different on the two days they were flown?
If the expansion and contractions was such that the lower BT to coupler connection was "loose" on the first flight, would it be possible the drag of the big finned bottom on the longer burning L1111 and the heavy top half sheared the four little 4-40 plasic screws? The next day the weather may have affected the connection and it was a little "tighter" and helped hold things together at burnout with the shorter burning L1100?

What was the difference in speed/drag at burnout between the L1111 and L1100?
 

MaxQ

Tripoli 2747
Joined
Jan 18, 2009
Messages
4,409
Reaction score
56
Location
Central Viginia - USA
Yes, there were (4) 4-40 nylon shear pins on both the forward and aft sections.

For the 2nd launch, per one of the TRA TAP members (not sure who it was) recommended i double the number of shear pins on the upper section to (8) 4-40 pins. Which i did. I also added a few vent holes for the aft and forward sections.

However, i didn't see the video until a few days ago, so i realize now the upper section wasn't the problem in this failure, so the addition of (4) shear pins to the upper really didn't affect the outcome of the 2nd launch.

Also, i seriously doubt (as well as many other people there) that the vent holes really had much contribution. The volume of the aft section was quite large, and the rocket was moving extremely slow for a rocket and didn't hit much altitude, so i don't believe an air pressure change inside that section would have been enough to eject the aft section.

At this time, i'm leading more towards an actual ejection charge going off.

Well, Fred knows his stuff...as do the MDRA guys.
That video sure looks like there was a seperation very close to motor burnout deceleration...

I haven't seen the Hellfire close up to know how tight the components fit together - but given what you now are saying about the shear pins (ie. yes, you had shear pins fore AND aft)...I wouldn't think that the components would seperate in that circumstance.

Bythe same token, I don't see why an altimeter would fire so prematurely so quickly when it just entered the coast for about a second...
Makes one wonder how much faith we place in electronics...doesn't it?
Ponderous...

BTW: Fine rocket project...very glad you got it back to fly again, I look forward to seeing it up close this April if you fly it at the next "BIG one"...
 

MaxQ

Tripoli 2747
Joined
Jan 18, 2009
Messages
4,409
Reaction score
56
Location
Central Viginia - USA
Ill bring the pictures to the VRS launch tomorrow and show you. Thank goodness it was in a 10" diameter rocket and they didn't deploy but it burned through the nylon shockcord in 4 places and made our droug a smoldering mess.

Ben
Sure...I kinda get the picture...this rocketry thing...full of surprises.
 

DMcCauley

Well-Known Member
Joined
Feb 8, 2009
Messages
177
Reaction score
0
Well, Fred knows his stuff...as do the MDRA guys.
That video sure looks like there was a seperation very close to motor burnout deceleration...

I haven't seen the Hellfire close up to know how tight the components fit together - but given what you now are saying about the shear pins (ie. yes, you had shear pins fore AND aft)...I wouldn't think that the components would seperate in that circumstance.

Bythe same token, I don't see why an altimeter would fire so prematurely so quickly when it just entered the coast for about a second...
Makes one wonder how much faith we place in electronics...doesn't it?
Ponderous...

BTW: Fine rocket project...very glad you got it back to fly again, I look forward to seeing it up close this April if you fly it at the next "BIG one"...
The components fit pretty snugly (not loose)

Thanks. I'd be happy to show you the Hellfire in April. Probably launch it again on an L-1080.

Guess not much more we can gather from the video. Data from both altimeters would have definitely been helpful in the diagnosis, but commuting from NJ to red glare each day (2 hour drive) and getting home late friday night after the launch wasn't conducive to downloading data from the altimeters.

Next time though!

Thanks again for all your help (everyone!)
 

DAllen

Well-Known Member
Joined
Jan 18, 2009
Messages
4,777
Reaction score
727
I absolutely agree. Great looking project. Also, this has been a fascinating thread even though I don't think anyone has made a definite conclusion.

-DAllen
 
Top