Early ejection?

Hello,

Flew a bunch of rockets the other day. It seemed that the ejection charge was firing early. A couple rockets came down with the parachute wrapped around the fins. It was about 15 degrees cooler then most other launch days. Does temperature or thermals play a role in how long rockets coast? I couldn't figure it out because I was using the recommended motors but the rockets weren't reaching apogee before the ejection charge went off. Any ideas?

Brian

 

[powderburner]

Doctors have new medications and techniques to help you with this problem . . .

(sorry, I just HAD to do it, or else someone else would have)

Temperature changes would cause negligible variations in delay charge burns, certainly less than the motor-to-motor variations that already infect small BP motors.

Thermals could affect the descent rate, but would not significantly affect the ascent rates/speeds/durations.

What you are probably experiencing (parachute wrapped around the rocket) is a cold parachute that doesn't want to fully open. Did you pre-flight the model by opening and dusting the 'chute?

As far as the recommended delay not matching the actual coast-to-apogee, the manufacturer's recommendations are 'close' but are seldom perfectly timed. There just aren't enough selections in delay timing available to achieve an optimum delay for each model. Some are gonna pop a bit early, some are gonna go a little late. And any motors you shoot can vary by something like +/- 0.5 seconds from the labeled delay time, especially if you use motors from different production batches.

 

Can you get treatment online. lol

I dusted the parachutes with baby powder and carefully folded them. For whatever reason the nose cone was popping off while the rocket was still going up. Then the parachute went down and got tangled up on the fins. This happened on two different rockets. I was joking with my Dad that maybe Estes produces some bad batches of motors to increase rocket kit sales. lol

Brian

 

[Justin Horne]

Im not sure about LPR, but in mid and HPR there is a thing known as pressure separization. This MAY be your problems.. It has to do with the rocket going up, and the different pressures making the nosecone pop off. Although it could be the charge, " For whatever reason the nose cone was popping off while the rocket was still going up." that sounds exactly like pressure sep. if it is, dill an 1/8 hole and you should be fine.

 

[powderburner]

It is also possible that you had a batch of (low power) motors that all failed to operate properly.

If the motors are stored under the wrong temperature conditions (exposed to changes in temp, day-to-night heating and cooling) it is possible that the propellant grain would begin to separate from the inside of the motor case. If so, at ignition the combustion in the main chamber would quickly squirt through the side of the motor and pop off the NC (and eject the 'chute). This would happen almost immediately after ignition.

Does that sound more like the problem you had?

 

[rocketsonly]

That's interesting. A few days ago when my TARC team built a tripe direct stage rocket, the last stage, a C6-7, seemed to have an ejection charge of 0. The rocket didn't seem to go TOO high, maybe 500 feet or so, is that enough to cause a pressure seperation?

 

[Justin Horne]

Uh.. I really don't know... I bet it could if it got tere fast and you had a loose cone.. It might have.. I really dont hear too much about pressure sep on low power birds, so that might mean it doesn't happen.. That may be because they don't get too high?

 

Everything appeared normal until the rocket got close to max. altitude. I didn't see that much tracking smoke and then the nose cone just popped off. I wonder if the rocket engines are going bad. Every launch I bring most of my rocket engines in a plastic tub. I usually don't use all the engines that I bring to the launch site. Do you think exposing them to the heat a couple of times before I actually use causes the engines to go bad?

Brian