L3 Post Mortem - Flight of the Terminator

Your charge wells are almost the same volume as the ones I'm using. Yours should be more constrained. The only thing I can think of that would make them act as you describe is if the ematch head was below the powder in the charge well and some of the BP is getting blown out of the well before it has been lit.

I've used masking tape with equal success, 2 of my 3 flights just used a strip of 3/4" masking tape over the end of the well. I doubt that was the problem. If the charge wells were build and packed as you describe I can't imagine that the tape would have made that much difference.

Worsaer said:

Chris, my home made T6061 containers are 0.5" ID, and roughly 1.75" tall. After adding BP and the ematch, I pack firmly with dog barf and seal with masking tape (criss-cross, then around the perimeter good and tight.
My gut tells me I should have used electrical tape or duct tape, several layers.

If I think in terms of burn surface area, my next ones will likely be larger diameter. I will be doing several tests to quantify the difference.

Click to expand...

????????????
I was certain you were going to say the harness balled up...
Wow,,, this ones a real stumper..
I'll tell ya one thing,,
it's a really good thing you took that vid of the ground test...
That looked exactly like I try to achieve but doesn't always happen on the first try,, perfect...

Wow Bill,,, You've really got me stumped..

Teddy

Couple things to consider (total spitballing on my part here):

1- Temperature difference from ground test to flight causing tubes to fit tighter (the Raven records temp; might be informative to look at that data?)

2- Inside of BT & outside of coupler dirty and causing more binding that the 'virginal' ground test (did you clean the mating surfaces real good before flying?)

3- Were the EXACT same kind of screws used for the shear pins?

Again, sympathies.

Another thought. There are loads in the cone due to air moving on it that are not present during a static test.

cvanc said:

Couple things to consider (total spitballing on my part here):

1- Temperature difference from ground test to flight causing tubes to fit tighter (the Raven records temp; might be informative to look at that data?)

2- Inside of BT & outside of coupler dirty and causing more binding that the 'virginal' ground test (did you clean the mating surfaces real good before flying?)

3- Were the EXACT same kind of screws used for the shear pins?

Again, sympathies.

Click to expand...

All good questions. I will check temps. I have that available from several devices for comparison.

Coupler was clean - I clean them well after testing for this exact reason.

Yes, exact same screws, from the same lot. And for those that didn't ask, same BP from the same can as the test.

markkoelsch said:

Another thought. There are loads in the cone due to air moving on it that are not present during a static test.

Click to expand...

Good point Mark, and something to bear in mind.

Worsaer said:

Thanks John.
I will be doing some interesting testing, measuring containment in the same charge wells with different types of tape, and wells of greater length, optimizing for full burn of the BP.

I'm reminded of muzzle loaded rifles designed for BP. Barrel lengths were quite long, giving more time for the BP to burn before being expelled.

Click to expand...

Bill I know your tests and data recording is thorough.

I would be interested if you can duplicate the problem by trying less containment not more. Find out what you would have to do to have a failed BP charge. As many of us find it hard to believe that BP can be underconstrained with normal practices.

I was doing some calculations. 3 #4 nylon shear pins could have a strength of up to 70lbs each (high end of strength estimates). So this might require at least 210 lbs of force. 2g of BP in that volume should generate about 300#. That gives you about 100# of margin on paper. What could decrease this margin, more friction or binding on the nosecone shoulder? Does 2g of BP generate the same pressure at 12K feet + ground MSL? Could the first charge disrupted the second charge canister spilling its BP?

Just thinking out loud.

Nick had a similar problem in that I told him to restrain his charges well
so he restrained them so well that the PVC charge canisters let go / blew up....
One more thing,,
When I pack a charge canister I put the e match on the top of the powder as opposed to the bottom
feeling that it's more likely to light all of the powder as it has nowhere to scatter in the down direction ( into the canister )....

Another thing I learned from always fling pistons..
If the shoulder or piston cocks in the airframe your done,, nothing will move it until it's uncocked...

That is my vote so far...
The nose cone shoulder ( or av bay shoulder ) cocked as it was trying to leave on the primary charge.....

Teddy

I just sent Nick an email link to this thread...

Teddy

The key to black powder is containment. The OP's method sounds like it was well done - a metal canister sealed with electrical tape has been 100% reliable for me. I don't see how the BP could have broken the tape seal without fully igniting unless it wasn't 3F or 4F powder.

I think that your charges were undersized based on total volume. Here's how I came to that conclusion: Your AV volume listed above is of the closed container. But of course as the AV bay starts to separate you have an increasing volume which the gas needs to keep pressurized. Using your L3 drawing I measured your total volume (the space between the plate where the canisters sit and the bulkhead of the coupler when the pieces are at maximum extension before separation) as 19" long. 2 grams of BP only produces 200 lbs of force into that area. You may have had enough initial pressure to break the shear pins but not enough residual pressure to fully deploy the chute.

I have always used the fully extended volume to calculate my charges on larger diameter rockets.

Also, have you tried lighting the unburnt powder to see if it will burn as normal gunpowder?

I'm glad your electronics survived but I bet it was very painful watching the Fruity Chute get destroyed. But at least it helped save the rocket so that's a lot better than losing the chute and everything else.

Good luck getting to the root cause,


Tony

Three 4-40 shear pins on the drogue bay seems excessive to me. What loads were you expecting and why do you think that they are as large as the drogue deployment loads on the main?

I use two 2-56 shear pins in a 6" airframe with 2 gram primary and 3 gram backup charges. The main gets two 4-40s with the same charge size.

jderimig said:

Bill I know your tests and data recording is thorough.

I would be interested if you can duplicate the problem by trying less containment not more. Find out what you would have to do to have a failed BP charge. As many of us find it hard to believe that BP can be underconstrained with normal practices.

Click to expand...

Thank you John.

Your point is well made. Using a salvaged section of airframe, I will attempt to recreate my initial ground test with intentionally smaller BP charges, gradually scaling up until I repeat the result of my original ground test. Additionally, I will repeat the tests with a couple of different types of containment for comparison.

It will take time to get the testing right, but eventually I will learn something, and will share it here. I won't be flying again until next year, so the timing is good.


You ask another thought provoking question:

Does 2g of BP generate the same pressure at 12K feet + ground MSL?

Click to expand...

I don't know. It may produce the same volume of gas, but perhaps not as quickly? Same volume, less pressure? If I need enough combustion gasses to get to ground level pressure (comparing with the ground test) then more for shearing the pins, volume of BP needed will increase with altitude.

My working assumption and reason for 3 #4 shear pins was 1) following motor burnout the inertia of the heavy nose cone would induce separation; 2) The air pressure at 12k feet would be measurably less than inside the sealed airframe, also exerting pressure to separate the nose from the body.

I know it's not a true sealed container, but i planned for worse case conditions. I don't really know what the atmosphere if pressure was inside the payload tube, but it's possible it was greater than ambient pressure at 12k'.

Perhaps someone smarter can school me.

My 4" all glass scratch "SteamPunk" is alway loaded in the exact same way,,
from the charges to the chutes..
It has been on 1800 ft flights ( low and slow ) and now holds my personal best altitude record,,
I was hoping for 3 miles and made 14,400 ft...

It always seems to deploy the same.......

Teddy

Worsaer said:

...My working assumption and reason for 3 #4 shear pins was 1) following motor burnout the inertia of the heavy nose cone would induce separation...

Click to expand...

Maybe I missed it earlier but did your ground test include the full weight of the rocket as flown? If not, how much difference was there between the tested weight and the flown weight?

But I just can't let go of the unburnt powder. I think I understand the dynamics of firearms propellent pretty well and have several black powder firearms in addition to regular firearms. Most people mistakenly believe that the powder completely burns in the charge holder. It does not. Guns have barrels for two reasons - to stabilize the bullet and to allow the powder to completely burn. No matter where you put the e-match once enough pressure is generated the container will burst and much of the BP will burn as it travels away from the container. That's why using a tube for containment is a good idea - it forms a strong flame front to ignite the airborne powder.

Here are several other things to consider: is there anyway that things moved during flight so that a quick link or other recovery component could have punctured or otherwise torn the masking tape? That could account for the unburnt powder.

Another thought came to mind. Is it possible that the canister burst and ejected the remaining unburnt powder so it was deflected to the side of the of the charge canister and protected from the flame front? If the powder was blown off the the side and especially behind the canister and the flame front was not able to completely heat and pressurize the area the powder may not have ignited. Maybe the arrangement of the shock cords or chute protector somehow inhibited the BP from burning.

Finally, I can't tell from your L3 doc or your previous description if your tubes are open on both ends and how they are retained to the bulkhead. If they are open on the end that is against the bulkhead is it possible they were knocked free and the powder escaped out the back? You don't say if the charge holders were recovered intact against the bulkhead or at least not that I saw.

Just my thoughts.


Tony

Worsaer said:

Thanks Stan.

For round two, I will either do another Terminator ("I'll be back"). That's the stubborn side of me saying I won't fail on a project, it just may take longer than expected. However, my second choice is the 5" version of the Broken Arrow. The upside is that it can also handle 98mm hardware, giving me more flight options over time...

I'm in no hurry - for me designing & building them is as much fun as flying.

Click to expand...

Another consideration would be a conventional DD with charges fore and aft on the ebay with a tracker nosecone or a "hardened" GPS tracker on the apogee shockcord? Ditch the wireless communication requirement, do a simple and straight-forward
project, obtain the L3 and then pursue your wishes with less stress and duress?

Yeah, I'll dodge the rotten fruit thrown my way by those who say you should make it as hard and as impressive as possible but doing a basic cert flight doesn't make anyone "less" of a flier. If you have a lot mentally invested in this and are certain you'll sort it out and be successful, by all means continue but if there's a second cert failure how bad will you feel? You pull off a basic L3 cert with success (ducks here:duck revisit this project and then fail at it
you may go shoot and give it up or may still go on and pursue it. The difference is you will have the L3 already in hand and not have to worry about a third attempt in trying to "get" the cert. Just a thought from a K.I.S.S. person who rushed the L2 as
fast as possible so I would be able to fly certified motors at an "Ex" launch in the old days. I didn't fly a J for a very long time after that and was scared that I pulled off my first L motor with one altimeter and a tracker failure with a successful main chute and recovery. (Landed within sight at the limit of vision)
Gives me the "willies" to think about that now. All that rocket coming in ballistic scares me and it's going to be modified to a tracker nose and two deployment computers for future flights. Hope the second try has the sweet burned APCP smell
of success for you. Kurt Savegnago

ksaves2 said:

Another consideration would be a conventional DD with charges fore and aft on the ebay with a tracker nosecone or a "hardened" GPS tracker on the apogee shockcord? Ditch the wireless communication requirement, roject, obtain the L3 and then pursue your wishes with less stress and duress?

Click to expand...

That part worked perfectly and was not a factor in the mishap....(as JD picks up a overripe tomato and winds up....)

manixFan said:

Also, have you tried lighting the unburnt powder to see if it will burn as normal gunpowder?

Click to expand...

manixFan said:

But I just can't let go of the unburnt powder. I think I understand the dynamics of firearms propellent pretty well and have several black powder firearms in addition to regular firearms. Most people mistakenly believe that the powder completely burns in the charge holder. It does not. Guns have barrels for two reasons - to stabilize the bullet and to allow the powder to completely burn. No matter where you put the e-match once enough pressure is generated the container will burst and much of the BP will burn as it travels away from the container. That's why using a tube for containment is a good idea - it forms a strong flame front to ignite the airborne powder.

Click to expand...

These post remind me of the experiments Jim Jarvis performed in order to gain some knowledge on the effect of altitude on BP. Pulling the altitude part out of the equations, Jim collected and weighed all apparent BP residue post test and tried to ignite it as a crude but effective test to validate that it was in fact un-burnt BP and not just residue.

One other conclusion Jim came to was that containing the BP in a longer barrel had an appreciable affect on the effectiveness of the BP, albeit more in relation to the extreme altitudes that Jim flies but none the less there may be a lesson in that to applies here.

Worsaer said:

Chris, my home made T6061 containers are 0.5" ID, and roughly 1.75" tall. After adding BP and the ematch, I pack firmly with dog barf and seal with masking tape (criss-cross, then around the perimeter good and tight.
My gut tells me I should have used electrical tape or duct tape, several layers.

If I think in terms of burn surface area, my next ones will likely be larger diameter. I will be doing several tests to quantify the difference.

Click to expand...

Bingo, post 47 is close. You need more room for your BP to totally burn. Go to 3/4 ID and make your canisters a little longer. At 1/2 ID and 1.75" long that 3 gram charge just about fills that canister up, right?? I know been there. The size your canisters are at right now should be good for 1.5 grams and under, after that you will get un burnt powder. Just think the powder burns in all directions. Got to spread the stuff out a bit rather than pile it up. Don't tamp the dog barf down hard on top the stuff either, just enough to keep it in place. You want BP granules just hugging each other, not compressed to tightly together.

onebadhawk said:

I just sent Nick an email link to this thread...

Teddy

Click to expand...

Thanks Teddy much appreciated, I've been reading and trying to think of things as well and have PMd the Op. Sounds like Worsaer has done his homework, Hate to read of his misfortune. Also I've moved to syringe charges for my L3 and double tested both drogue and main charges - extending harness approx 80%.

rcktnut said:

Bingo, post 47 is close. You need more room for your BP to totally burn. Go .

Click to expand...

Why did it work on the ground?

Sorry to hear about the failed attempt. Learning a lot by reading this thread.

Hope you'll be able to get it on your next attempt, and that you won't have long to wait for the chance.

jderimig said:

Why did it work on the ground?

Click to expand...

No idea, one would think a good ground test would mean a good flight that's why we do ground tests. I'm positive with his experiments using a bigger canister for a charge that size will show a more complete burn of the BP. That should solve the un-burnt BP problem. Maybe the charges for the flight were packed to tight/ tighter??

rcktnut said:

No idea, one would think a good ground test would mean a good flight that's why we do ground tests. I'm positive with his experiments using a bigger canister for a charge that size will show a more complete burn of the BP. That should solve the un-burnt BP problem. Maybe the charges for the flight were packed to tight/ tighter??

Click to expand...

As per my post, there is evidence from Jim Jarvis' test that BP effectiveness is diminished with alt, and a longer "barrel" has an appreciable effect to counteract this. If you accept this then the question is does 12,000' alt make enough difference to be a contributing factor.

I didn't see it mentioned, what type of e-match did you use? I ask because I have had two failures with Quest ignitors. Resistance measured fine when prepping on the ground, but never lit in flight or when voltage was applied after the flight. I now only use them when I have two in series.

Hopefully this will help.

This shows the AV bay removable bulkhead post flight, before opening the bay. The shorter charge holder has an effective depth of 1.75", and the longer one 2.25". What looks like holes are actually sealed with epoxy, acting as a foundation for the screws. To explain the photo, I slid the protector back and out of the way, so the ematch head was fully in contact with the BP. With these lengths, there was substantial dog barf in each one, well compacted, and taped.


The charge holders are not damaged or impaired in any way. FWIW, the nose cone has three similar canisters for the Main chute, in much closer proximity, and were all packed the same way with masking tape.
One fired as designed at 1,000 ft, and the adjacent charges were not affected. They remained intact and undamaged. The point being I don't think one drogue charge damaged the other. And it still doesn't explain why the test worked fine on the ground, but the same charge was insufficient or ineffective in flight.





Outside of the nose cone, here's what the configuration of the three charge holders looks like. Conventional medium size BlastCaps on a 3" buklhead. This is a construction photo, just for reference.





And here's the zippered body tube as found in the field. My first 'zipper' of fiberglass - technically it didn't unzip, it sort of crushed and unraveled.

manixFan said:

Also, have you tried lighting the unburnt powder to see if it will burn as normal gunpowder?


Tony

Click to expand...

Good question - I actually did. I wasn't certain if it was burned or unburned residue. I collected what I could, but it didn't burn. It may have been burned residue.

jderimig said:

That part worked perfectly and was not a factor in the mishap....(as JD picks up a overripe tomato and winds up....)

Click to expand...

Understand the feeling.:blush: Kurt

UhClem said:

Three 4-40 shear pins on the drogue bay seems excessive to me. What loads were you expecting and why do you think that they are as large as the drogue deployment loads on the main?

I use two 2-56 shear pins in a 6" airframe with 2 gram primary and 3 gram backup charges. The main gets two 4-40s with the same charge size.

Click to expand...

The nose cone assembly with the Main and Aux AV bay in the coupler weighed in at roughly 7 lbs. I had the same ( 3x #4 shear pins) on the nose cone main, and it deployed properly on 2 grams, albeit with slightly less volume in the nose cone'

jderimig said:

Why did it work on the ground?

Click to expand...

That's the $64k question that puzzles. I used 3.3 grams of Swiss 4F in a stretched Wildman rocket I made with a longer upper bay that had a tight main chute pack. I worked up to 3.3 grams on 3 ground tests which technically was quite high a charge. The energy was expended just as the NC reached the end of the harness. Worked fine in flight but I didn't see the deployment event. Yeah it was a main chute event.

One would think with the nice ground test Bill had (and I presume it was with four shearpins of the same type used during the flight) it should have been a ringer flight. The primary charge blew and the backup with more powder blew and no success.
Kurt

ksaves2 said:

Another consideration would be a conventional DD with charges fore and aft on the ebay with a tracker nosecone or a "hardened" GPS tracker on the apogee shockcord? Ditch the wireless communication requirement, do a simple and straight-forward
project, obtain the L3 and then pursue your wishes with less stress and duress?

Yeah, I'll dodge the rotten fruit thrown my way by those who say you should make it as hard and as impressive as possible but doing a basic cert flight doesn't make anyone "less" of a flier. If you have a lot mentally invested in this and are certain you'll sort it out and be successful, by all means continue but if there's a second cert failure how bad will you feel? You pull off a basic L3 cert with success (ducks here:duck revisit this project and then fail at it
you may go shoot and give it up or may still go on and pursue it. The difference is you will have the L3 already in hand and not have to worry about a third attempt in trying to "get" the cert. Just a thought from a K.I.S.S. person who rushed the L2 as
fast as possible so I would be able to fly certified motors at an "Ex" launch in the old days. I didn't fly a J for a very long time after that and was scared that I pulled off my first L motor with one altimeter and a tracker failure with a successful main chute and recovery. (Landed within sight at the limit of vision)
Gives me the "willies" to think about that now. All that rocket coming in ballistic scares me and it's going to be modified to a tracker nose and two deployment computers for future flights. Hope the second try has the sweet burned APCP smell
of success for you. Kurt Savegnago

Click to expand...

I understand your perspective Kurt, no tomatoes. I'm not in a hurry to get my L3 cert - I want a satisfying project that teaches me something, and of which I can be proud.
In this case the array of electronics didn't make it more difficult, in fact, I knew pretty much what was happening throughout the flight in real time. I never lost GPS lock, watched it reach apogee at one second intervals, and had the disheartening feeling of watching it descend at high speed - all without being able to see the rocket.

John's altimeters and gadgets performed flawlessly. I spent sufficient time testing it all together, giving me confidence in the integrated system well before the flight.