Ejection on burnout; H148R

[Flyingiazzi]

Dad tried for level 1 at The Plains, Va, on Dec. 11. He flew an EZI-65 on an H148R. The motor was supposed to have a 10 second delay, but the ejection charge fired on motor burnout. It shredded the parachute, and the rocket landed hard, breaking off all the fins and damaging the body tube. Does anyone know how this could of happened?

 

[llickteig1]

Without seeing the flight or examining the wreckage post mortem, there are a few possibilities:

1) Ejection charge didn't really fire at that point but the rocket drag seperated because the nosecone was too loose;

2) Ejection charge didn't really fire at that point but the rocket pressure seperated because a pressure bleed hole wasn't used; or,

3) Blow-by where the seal around the delay grain didn't hold due to assembly error or foreign material on the o-rings.

If there are no signs of excessive buring inside the airframe 3) is unlikely. I doubt that 2) happened, but it is possible, too, if the nosecone was really loose.

You should be able to pick-up the rocket by the nosecone and have it hold firmly.

HTH, --Lance.

 

[lalligood]

Originally posted by llickteig1
You should be able to pick-up the rocket by the nosecone and have it hold firmly.

When the rocket is fully loaded with motor (pre-flight ready). It should take a couple up-n-down shakes when held by the nosecone/payload tube to separate.

HTH,

 

[North Star]

Originally posted by lalligood
When the rocket is fully loaded with motor (pre-flight ready). It should take a couple up-n-down shakes when held by the nosecone/payload tube to separate.
HTH,

Amen to that - and if you have a lump of lead in the tip of the nosecone, like on my Minnie Magg and Warlock, the speed of separation is quite something

It's called the learning curve. I learnt about it with the MM so it doesn't happen on the Warlock.

 

[Flyingiazzi]

The payload section/ nose cone was on tight. It was the ejection charge that seperated the rocket. However, we bought the motor from some friends who shortened the delay 2 seconds (1/6th of an inch) for an 8 second delay, which was simulated to be perfect for our rocket. It ended up at less than 1 second. (Quite a sight, a 3 foot chute opening at 280 mph). Maybe that had something to do with it.

Is it possible that the delay burned extra-fast?

 

[llickteig1]

#1 - You should not have adjusted the delay on the motor. Aerotech motors are not certified with adjustable delays. For shame. Double that sentiment for a certification flight. BTW, you said earlier the motor had a 10 second delay, which now appears to be false; it is much easier to try to diagnose problems if accurate information is given the first time.

Having said that, I believe that in general Aerotech delays burn at 1/32" per second. I stand corrected if it is different for the Redline delay kits. If the delay was a medium (10 seconds) and you indeed drilled out 1/6", then you could well have gone deeper than a short delay which could have blown through early. If you were off by an extra 1/32" or 1/16" then it is even more likely. The delay element helps hold pressure in the motor until the end of the burn. You're probably a little lucky you didn't damage the forward closure or your motor. The correct adjustment would have been 1/16", I believe, which I am not condoning or recommending.

--Lance.

 

[n3tjm]

Redline delays have been known to burn short. My guess is Redline takes a long time to start... during that time the delay is burning... the longer the time the motor takes to start, the shorter the delay time after burnout.

If you can get the reload new, it starts pretty much right away... but after a few months, it quickly oxidizes, taking forever to ignite. One of the reasons I don't like em. I usually stick a piece of BT in the core, and use single fold Magnelite to get them started, and even with that, it can take a while.

 

[UhClem]

The burn rate catalyst used in Blue Thunder and Redline reloads is incompatible with the delay grains. If the delay is stored with the propellant the result will be a much shorter than expected delay.

This is why the delay is segregated from the propellant.

You might have noticed the press release from Aerotech stating that they were working on using a new catalyst that didn't have this problem but was much more expensive.

 

[Flyingiazzi]

Sorry, I meant 1/16 of an inch!!!!

Even more sorry I trusted someone who was level two certified to cut my delay without my permission, and then assure me that it would work better that way. I did not want to modify the delay in the first place but was told that 10 seconds would be too long.

 

[Donaldsrockets]

Originally posted by UhClem
The burn rate catalyst used in Blue Thunder and Redline reloads is incompatible with the delay grains. If the delay is stored with the propellant the result will be a much shorter than expected delay.

This is why the delay is segregated from the propellant.

Yep, if stored for awhile, the catalyst will interact with the delay element and when the motor is fired, the delay element will burn faster than normal resulting in a shorter than expected delay.

In other words, this catalyst is meant to increase the burn of Redline and Blue Thunder propellants but it also increases the burn of the delay element.

 

[North Star]

Originally posted by Flyingiazzi
I did not want to modify the delay in the first place but was told that 10 seconds would be too long.

Indeed it would, but the chance of surviving a late deployment would be much better (especially if you build strongly) than deployment at burnout; which a quick 'wrasping' gives as 416 fps .. phew

Were there no vendors on site who could have supplied an appropriate delay grain? Had you simmed the flight prior to attending the launch?. Please don't think I'm getting at you but this was L1 cert attempt and the result so far is, the rocket is lost and so is confidence in your L2 friend. I have RSO'd a few L1 and 2 attempts and the flier has always known the flight profile on the motor/delay being used.

 

[Todd Knight]

Amoung the issues mentioned above, RL burns at a higher core pressure. Higher pressure will cause the delay element to burn faster and or push the flame front around the o-ring. It could have been combination of all the above. Was the motor a pre-AT fire? I know there were issues with blow by in the early batches of RL.

Lesson learned? Don't give up. Mistakes happen and you learn. Motors fail and you fly another one. Rockets crash and you build a new one. Sorry it was your first HPR flight but guess what, you get to due it again.

Even I screw up once in awhile. Forgot an o-ring in an EX K motor. Blow torched the inside of a brand new booster. They threatened to take away my Level 3 card.

photo coutesy of https://www.blacks-ink.com/

 

[bobkrech]

Hopefully you learned a few things.

If you're flying HP, you alone are responsible for your flight. It's your responsibility to know what your rocket is going to do.

You are obligated to use only certified motors at NAR launches. Using a shortened Aerotech delay on a certification flight is an automatic disqualification, even if the flight is otherwise uneventful. You also put the club at risk because you nullified the insurance coverage for the club for that flight by flying an uncertified motor. If anything bad happened, you, the RSO, the LCO and the club would bear the entire cost and consequences of the flight.

Review your motor assembly technique. It is quite possible that the motor/delay was not properly assembled and that is the reason for the early deployment.

Make sure you use an appropriate ignitor for the motor. A commercial ignitor supplied by the manufacturer or another vendor is preferred to a homebrew ignitor. (I get flack for this, but that's how it is.) A chuffing motor doesn't lift of promptly and if the delay catches first, you're going to get an early deployment.

Learn from your mistakes. Everyone makes mistakes, that's how we learn. Just don't repeat them.

Good luck on the next attempt.

Bob Krech