K650 pink delay

[watermelonman]

How is it that the K650 pink has the longest motor delay Cesaroni makes? Strangely enough it is a solid 2s more than any other motor I see. Also the K780 and K635 grains that it is apparently composed of both have significantly lower max delays.

I happen to have one and got myself into a situation where it might make sense for motor deployment tomorrow.

 

[dhbarr]

AFAICT there are really only a few delay grain compositions, and they burn at different rates depending on the motor they're capping.

I could be very wrong, and welcome a detailed correction. Bonus points if someone's burned each of the AT grains in open air

 

[tbonerocketeer]

How is it that the K650 pink has the longest motor delay Cesaroni makes? Strangely enough it is a solid 2s more than any other motor I see. Also the K780 and K635 grains that it is apparently composed of both have significantly lower max delays.

I happen to have one and got myself into a situation where it might make sense for motor deployment tomorrow.

It's all about chamber pressure.

 

[watermelonman]

It's all about chamber pressure.

Interesting. I feel like I should have known that but did not. Thanks!

 

[tbonerocketeer]

Interesting. I feel like I should have known that but did not. Thanks!

It's how much burning occurs during the motor burn based on pressure which will leave x amount of seconds.

 

[mpitfield]

It's how much burning occurs during the motor burn based on pressure which will leave x amount of seconds.

Is burn time part of that equation as well, thinking specifically of the Vmax motors delays? As an example the E75 has a 17 second delay which is the longest of all the 24mm motors. Unless the Vmax has a relatively low chamber pressure, I really do not know. However intuitively I would of guessed that it would be on the higher end of the spectrum?

 

[tbonerocketeer]

It does, but due to the extreme short burn it almost doesn't. The delay burns faster while the motor burns, with the burn rate being higher as the pressure goes up. Maybe Bob or Scott will chime in with a better explanation.

 

[Reinhard]

Is burn time part of that equation as well, thinking specifically of the Vmax motors delays?

Yes. As long as the pressure is increased, the delay is consumed at a faster rate. How much faster, depends on the pressure and the exact composition of the delay. For example, on ATs 38mm motors, the delay burns roughly 6 times as fast during motor burn (about 0.146"/s vs. 0.031"/s). A slow burning BlackJack reload will have consumed about 0.45" of delay at burnout, whereas a faster Redline reload will only have consumed 0.22".

Numbers for ATs delays can be found here:
https://www.aerotech-rocketry.com/c...Flyers_Data_Sheets/aeroTech_delay_lengths.pdf

Reinhard

 

[KennB]

I know of a college team that wanted to ground test their rocket for motor ejection. I don't recall which brand of reload they were using but they loaded only the delay and ejection and left the fuel grains out. The igniter was fired and smoke started to trickle out of the nozzle. The delay was supposed to last in the mid-teens of seconds but without the chamber being pressurized, it smoldered for over one-and-a-half minutes before the ejection charge fired.