Motor ejection charge failure

So I flew my first dual deployment flight last week and it almost went as planned.
I flew with the intention to use the motor ejection charge as back up charge for my drogue. However after the flight when I take a look at the motor I discover that the delay grain never lit and the motor ejection charge failed to go off, this was a CTI -I800 motor. The motor worked but not the motor ejection, good thing I was set up for DD!

Has anyone experienced this?

Cheers

spyfly said:

So I flew my first dual deployment flight last week and it almost went as planned.
I flew with the intention to use the motor ejection charge as back up charge for my drogue. However after the flight when I take a look at the motor I discover that the delay grain never lit and the motor ejection charge failed to go off, this was a CTI -I800 motor. The motor worked but not the motor ejection, good thing I was set up for DD!

Has anyone experienced this?

Cheers
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Has not happened to me but ask Jim Jarvis about his experience and observations on the Vmax.

spyfly said:

So I flew my first dual deployment flight last week and it almost went as planned.
I flew with the intention to use the motor ejection charge as back up charge for my drogue. However after the flight when I take a look at the motor I discover that the delay grain never lit and the motor ejection charge failed to go off, this was a CTI -I800 motor. The motor worked but not the motor ejection, good thing I was set up for DD!

Has anyone experienced this?

Cheers
View attachment 272107View attachment 272108

Click to expand...

Please report the failure even though it didn't cause your rocket to crash. As your experience shows, it is a very good idea not to depend on the ejection charge in Vmax motors. Unfortunately, this does not seem to be something that the powers-that-be are willing/able to address, but report it anyway.

Jim

JimJarvis50 said:

Please report the failure even though it didn't cause your rocket to crash. As your experience shows, it is a very good idea not to depend on the ejection charge in Vmax motors. Unfortunately, this does not seem to be something that the powers-that-be are willing/able to address, but report it anyway.

Jim

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spyfly, here is the site you can use to report the ejection charge failure.
You should also let the vendor who supplied the reload know about this.
I'm glad your electronics worked for your recovery.

This is typical of both CTI vmax and Aerotech warp 9. The burn so fast, and shutdown so rapidly that it tends to snuff the delay grain. I would not rely on motor ejection for either propellant.

Sorry to ask (and good to bring up for others), but you're sure you didn't get any grease on the delay, right?

KenECoyote said:

Sorry to ask (and good to bring up for others), but you're sure you didn't get any grease on the delay, right?

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Yep, sure.

I also heard of "a pocket of gas" getting "trapped" at the top and thus preventing the delay element from burning. This SAME thing happened to me with an AT G76-7G reload. I opened it up and the delay looked like new and never burned nor had any marks on it....weird. I did not have grease on it. That is when this guy told me of the "pockets of trapped gasses" (??????)

Rapid depressurization of a motor casing is the only reliable way to shut off a solid rocket motor and is used in ballistic missile upper stages to shut the solid motor down when the target bus velocity obtained. Once surface burning has started, it is sustained by conductive, convective and radiative energy transfer from the hot gases leaving the surfaces back to the surface. If the pressure above the surface drops extremely fast, the combustion sustaining energy flow back to surface is rapidly reduced and the energy transfer can stop and even reverse, cooling the surface to a temperature below the combustion temperature and quenching the combustion.

Warp9 burns so fast at any temperature that a delay column is extinguished when the motor burns out. V-max burns fast, but slow enough that under it rated operating temperature, the dP/dt is not rapid enough to extinguish the delay column. Apparently under certain environmental conditions, the limit is crossed and the delay column is extinguished.

I'll speculate this is occurring with Vmax on hot sunny day in dark painted rockets that have been sitting on the pad for a long time, pushing the propellant temperature above its maximum rated temperature. Hot propellant burns faster than at the certification temperature of 70 F, and as a result of the propellant temperature, the motor shuts off faster and at higher chamber pressure, and at burnout, the higher depressurization rate extinguishes the delay column.

Paining the airframe around the motor white, and keeping your motor storage container in the shade should keep the motor cool enough so this does not happen.

Bob

Bob, not to derail too much but I have a question about the paint thing. Say you have a black rocket and leave it on the pad for 10-15 minutes or so on an 80 degree day. In a 38mm load, how much would you expect a delay grain to be sped up? I ask because I had an early delay in a G67. Just trying to gauge if that could have contributed.

grouch said:

Bob, not to derail too much but I have a question about the paint thing. Say you have a black rocket and leave it on the pad for 10-15 minutes or so on an 80 degree day. In a 38mm load, how much would you expect a delay grain to be sped up? I ask because I had an early delay in a G67. Just trying to gauge if that could have contributed.

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Think about the inside of a car on a hot day in full sunshine.....the air gets hot fast, but the objects inside have heat capacity to it takes time for them to get in equilibrium with the air temperature.

The maximum temperature rise could be to 160 F after 15 minutes, but in reality it would probable be less, but 120F would not be out of the question. That would increase the burnrate somewhat but there are no published values I am aware of. If I had to guess, the temperature rise might increase the burn rate by 5%-10%. That would decrease the delay time by at least 5%-10% and possibly more as the delay burns from ignition.

This is an educated guess and not cast in propellant....:wink:

Bob

If CTI added a BP slug in front of the delay grain would that help? Just thinking...