Help with ejection charge

[Luke-H11]

Hi,

I am brand new to this forum, so huge apologies if I have posted this in the wrong place.

I am a member of a new university team (based in the UK) and we are planning to launch a solid-state rocket.

One issue that we are encountering is the parachute deployment and trying to understand motor specs. Does a motor like the G80-7 (https://wizardrockets.co.uk/product/g80-7-or-10/) contain an ejection charge, and if it does, does the delay indicate the amount of time it takes before it is discharged? If this is the case, is there anywhere that we can find the statistics for the strength of this charge? We are most likely not going for this motor (as it is very powerful), but I am not sure if this is not possible. If an ejection charge is not in the motor how would you go about doing the release mechanism it appears to be very difficult to obtain the black powder in the uk.

Any help will be greatly appreciated.

Thank you!

 

[David Schwantz]

It has an ejection charge. The -7means it will fire 7 seconds from ignition. Don't quote me on this but I think it has 1.4 grams of BP in it. You can use Altimeters like this for electronic deploy.

https://eggtimerrocketry.com/home/altimeters-av-bay/

 

[tfish]

Here's a link to a series of NASA videos that are about High Power Rocketry.



 Tony

 

[MarsLander]

The -7means it will fire 7 seconds from ignition.

The delay time is measured from when the propellant is burned up (completely consumed) and stops producing thrust, to when the ejection charge fires to push out the parachute.

Don't quote me on this but I think it has 1.4 grams of BP in it.

Aerotech G motors have .7g of ejection charge.

Aerotech Motors (per email):

• 24-29mm single use - 0.7 grams of FFFFg
• 29-38mm reloads - 1.4 grams of FFFFg
• 54mm reloads - 2.1 grams of FFFFg

You want something 10-15psi for your ejection. The best way to determine the charge need is to test.

The second best way is to use a tool like this:

https://rocketrycalculator.com/rocketry-calculator/bp-estimator/

Put in your open space body tube length and diameter and desired psi (start with 10 or 12). It will tell you the required charge. You can compare that to the .7 grams that are included in the motor. If .7 isn't enough, you will want to add more.

 

[David Schwantz]

Sorry, on a composite motors, delays starts to burn at ignition, that is why you push the ignitor all the way into the motor. Delay lights at the same time as the motor. BP motors delay starts to burn after propellant is done.

https://d11fdyfhxcs9cr.cloudfront.n...ages/g80t_new_su_in_21003-1_1642626256946.pdf

 

[Titan II]

Even on composite motors, the delay "time" indicated by the manufacturer is after burnout.

https://www.rocketryforum.com/threads/when-does-the-time-start-for-delays.16575/

 

[MarsLander]

Sorry, on a composite motors, delays starts to burn at ignition, that is why you push the ignitor all the way into the motor. Delay lights at the same time as the motor. BP motors delay starts to burn after propellant is done.

https://d11fdyfhxcs9cr.cloudfront.n...ages/g80t_new_su_in_21003-1_1642626256946.pdf

From the link you posted, under motor classification:

The next number of the code shows the time delay in seconds between propellant burn-out and the firing of the ejection charge.

Yes, the delay may start to burn at ignition, but the -7 is from motor burn out to ejection event...

 

[Coast Phase]

For making an external (to the motor) explosion for parachute ejection, has anyone tried "flash cotton" rather than BP? This stuff is available from a magician's supply house and cleaner to deal with. A small amount of this stuff wrapped around an igniter, and placed within a small, 35 mm film type canister with pop-off lid (available from Amazon) makes an 'ejector'. The igniter wire is run thru a small hole drilled in bottom of canister, then sealed with hot glue. When igniter is fired, lid of canister is explosively opened and rocket body tube containing canister will be pressurized, same as with BP, ejecting nose cone & parachute.

 

[Titan II]

For making an external (to the motor) explosion for parachute ejection, has anyone tried "flash cotton" rather than BP? This stuff is available from a magician's supply house and cleaner to deal with. A small amount of this stuff wrapped around an igniter, and placed within a small, 35 mm film type canister with pop-off lid (available from Amazon) makes an 'ejector'. The igniter wire is run thru a small hole drilled in bottom of canister, then sealed with hot glue. When igniter is fired, lid of canister is explosively opened and rocket body tube containing canister will be pressurized, same as with BP, ejecting nose cone & parachute.

Yes. As with BP, you need to test on the ground.

Start at post #74:
https://www.rocketryforum.com/threads/4f-black-powder.63926/page-3#post-1937657

Its use is also discussed in this thread:
https://www.rocketryforum.com/threa...lternatives-to-bp-for-ejection-charges.64061/