Ejection Charges

I was thinking ( I do that now and then) Does the ejection charge (Power) change with the size motor. Say, A-C6 and C-E? Scotty Dog

Last Sunday I had an ejection charge on a 13mm motor go off like an old fashoned M-80!

Im not sure about the actual question.
but i launch a little 18mm rocket on an a8-3 for schools and it seems like there is an equal amount of energey in the ejection charge as the motor

Scotty Dog said:

I was thinking ( I do that now and then) Does the ejection charge (Power) change with the size motor. Say, A-C6 and C-E? Scotty Dog

Click to expand...

same sized motors should have similar ejection charges. In other words, all 13mm are similar and all 18mm are similar and all 24mm are similar from the same manufacturer.

Of course, this can vary a bit from batch to batch and certainly from manufacturer to manufacturer.

And the amount of powder in the motor to create the same ejection result may vary because an Estes B6, C6 has a tiny little nozzle compared to the huge 1/2A6, A8, B4 nozzle throat hole, so thos motors with a larger hole at the bottom may need more powder because more will leak out the bottom during the ejection event.

A well worded (ask exactly the question you really want the answer to) e-mail to Estes will provide you with an accurate response. We can only guess unless we were to tamper with and disassemble a bunch of motors and measure the powder for you.

The seemingly more energetic deployment charge in contemporary Estes motors (compared to those I bought in the 1960s) is not necessarily a problem. It certainly does help to get the recovery system out, especially in longer and larger diameter low power rockets. I haven't experienced any problems due to Estes motor ejection charges so far. It's rather ironic that just a few years ago there was a little research project done (possibly a NARAM R & D project) that explored the issue of getting complete ejection of the recovery system with black powder motors. Apparently there was a recurring problem with the charges either not budging anything or else blowing the nose cone off, depressurizing the upper airframe and failing to push out the device. It's hard to imagine that being an issue today.

MK

shreadvector said:

same sized motors should have similar ejection charges. In other words, all 13mm are similar and all 18mm are similar and all 24mm are similar from the same manufacturer.

Of course, this can vary a bit from batch to batch and certainly from manufacturer to manufacturer.

And the amount of powder in the motor to create the same ejection result may vary because an Estes B6, C6 has a tiny little nozzle compared to the huge 1/2A6, A8, B4 nozzle throat hole, so thos motors with a larger hole at the bottom may need more powder because more will leak out the bottom during the ejection event.

A well worded (ask exactly the question you really want the answer to) e-mail to Estes will provide you with an accurate response. We can only guess unless we were to tamper with and disassemble a bunch of motors and measure the powder for you.

Click to expand...

That was a well worded response. That part about nozzle size, ya ,I can get that. Just so ya know,Im still not used to the metric system in the rocket world. I know its been there ,I just do the BT size thing. I found out that BTsize and Airframe mm can be a bit different from each other. Meaning-some of the tubes I bought will not take a BT sized NC. And depends on what outfit made them. Scotty Dog

Scotty Dog said:

That was a well worded response. That part about nozzle size, ya ,I can get that. Just so ya know,Im still not used to the metric system in the rocket world. I know its been there ,I just do the BT size thing. I found out that BTsize and Airframe mm can be a bit different from each other. Meaning-some of the tubes I bought will not take a BT sized NC. And depends on what outfit made them. Scotty Dog

Click to expand...

I agree and I try to use "mm" to describe the motor outside diameter. I use BT and never use "mm" for body tube size or designation because a body tube that fits an 18mm tube is a BT-20 and it is *NOT* 18mm on the inside - it is larger to accommodate an 18mm diameter motor.