Rule of thumb for ejection charge, apogee eject questions.

Wondering if when I start getting into high power the proper way to determine the amount of ejection charge.

If rocket has a body diameter of 4" and a length between nose cone and top centering ring of 12". Figure in area taken up by chute and chute protector. Wondering how all that works.

Also would using an altimeter to apogee eject over motor eject help with learning about the charges and electronics needed? Could be a good stepping stone to dual deploy.

So much to learn.

See ya,
Rod

For the ejection charge calculator, try this.

RodRocket said:

Wondering if when I start getting into high power the proper way to determine the amount of ejection charge.

If rocket has a body diameter of 4" and a length between nose cone and top centering ring of 12". Figure in area taken up by chute and chute protector. Wondering how all that works.

Click to expand...

See: https://archive.rocketreviews.com/tool_black_powder.shtml

Also would using an altimeter to apogee eject over motor eject help with learning about the charges and electronics needed? Could be a good stepping stone to dual deploy.

Click to expand...

I think this is what you are describing ... using a delay in the motor that's a bit too long along with an altimeter and ejection charge set to fire at apogee. If so, that's a good way to test your altimeter and skill at setting everything up. If the altimeter works right, you'll see the 'chute deploy right at apogee. Then, a second or two later, you'll see a puff of smoke from the motor's ejection. If you only see the 'chute deploy a little late, then something was wrong with the altimeter or the way you are using it.

As an altenative, you could try full dual deployment the first time, but again include an ejection charge in the motor with a slightly too-long delay. That way the motor will deply the drogue 'chute if the altimeter doesn't work right. You can use a slightly larger drogue than required so that everything will come down safely if the main 'chute doesn't deply.

-- Roger

Rule Of Thumb:

• Body Tube Dia:
• 1.53" - 0.5g per 36" of length
• 2.15" - 1g per 36" of length
• 2.56" - 1g per 25" of length
• 3.00" - 1g per 18" of length
• 3.90" - 1g per 11" of length
• 5.38" - 1g per 6" of length
• 6.00" - 1g per 6" of length
• 7.51" - 1g per 6" of length

Thanks guys! That is what I am after.
Level 1 in 2013. Look out wallet!

See ya,
Rod

RodRocket said:

Thanks guys! That is what I am after.
Level 1 in 2013. Look out wallet!

See ya,
Rod

Click to expand...

Glad you got what you needed. Just a note on that, if you start flying larger MPR like the GForce or other 4" rockets on Hobbyline motors, you may want to supplement the powder in the ejection charge a little. The reverse of that is if you fly H motors in your larger MPR. You may need to reduce the charge some. I've got one rocket in particular that I use half the supplied powder when flying H motors.

A rule of thumb I would recommend, if the supplied amount of powder in the reload is significantly different then what your calculations say is needed, ground test before the first flight! Also remember, baffles, pistons, etc. effect the amount of powder needed for ejection.