Scott, Aerotech delays come in S (short), M (medium, and L (long). There isn't a generic S-M-L delay; it depends on the propellant. All reloads come with M delays. I'll send you two files that can help you decide which one is the long for a J420. Looked it up. For a J420 the 14 second delay is the 14+, and for a J350 the 14 second delay is a 15+. Tim Thomas has these at every launch.

Scott,

The iffiness of motor ejection delays was what lead me to electronic deployment. I found instances where Rocksim says you need 12 sec and AT comes in 10 or 14, both of which lead to 100+mph deployments. There is a delay adjustment tool that lets you remove some of the delay charge to shorten the timing, but no method to increase the delay of the longest delay.

I have also found that several things can lead to spectacular deployment failures with electronics, such as 1) forgetting to turn them on, 2) improper settings of the mach delay, 3) high horizontal velocity at apogee due to weathercocking into the wind, and 4) connections becoming disconnected at launch to name a few.

I was sitting here looking at this motor specs and was wodering how long of a ejction delay an (M) was? When I looked it up (10 sec.) I guess the "M" delays are standard packaging.
I decided that it wasnt going to work. Rocksim has a 5 lb Rocket (before motor) on a J420 still traveling about 150 fps when this ejection fires.

The big question is how many Zippers have the newbies had, because,
they didnt know???!!! This happen to any one here?

If you tied a 5 or 6 foot chute to your wrist, and threw it out the window of a car moving 100mph, would it rip your arm off? (or maybe just dislocate it)

I think I'll have to get a 14 sec. element , and maybe another 1/2 Lb in the nose to burn up some extra newts.

Does any of this sound right to you more expierianced guys (or gals)?

Scott e

Scotte,

Some Key things about Rocksim.. It will be the most accurate if you have dead on accurate weight. When I do my sims I weigh each part and all the epoxy and measure their placement on the airframe. I make sure each part has the correct values. If not you will get a sim thats off. It could be off slightly or quite a bit. So your sim may be off some. I tell you who is the magic man on Motor ejection delays. Is Dave Hanson. All you have to do is hand him the fully loaded rocket with motor in it and let him feel it. Then out pops the delay size.. Its like magic.. LOL Im not kidding actually he does have a talent for it..

But anyhow. When I flew my L2 rocket on a J350. It was a PML 4" endeavour. Weighed in close to 6 or 7 lbs. Rock Sim told me to use a long 13sec delay. Dave advised me to use the medium. I did and it was spot on. So for whatever its worth.. You may have a sim thats off.

I just weighed the whole thing on a postage scale. I know Rock sim aint perfect, but I think 14 is going to be closer than 10. I also tested a couple of ejection charges.

I used a bag of Ice melt (damn winter weather) to catch the nose cone and chute.(about 10 feet away)
The first was 1/2 gram of 4f, kinda weak but it came out. Tiny hole in the bag.
The next was, uh, about .8 grams, Nice strong ejection, nice pour hole in the Ice melt bag. 3/4 gram probly about right.

Seeing how Nice and strong that ejection was. Im convince the last flight with the 2 grams of powder, last month, too strong for quantum tubing, probly blew the sides out off the rocket. Oh well. One Month later Im a lot smarter. 😉

scott e

Oh well. One Month later Im a lot smarter

That's the way it goes in this hobby. Theory will only get you so far - actual practice is necessary to determine what actually works. I learned the hard way and so does everyone else if they stay in this hobby. There ain't a one of us with more than a few flights under our belt who hasn't learned the hard way.

Warren

Truth be told - we learn more from mistakes - ours and others - then we do from our successful launch and recoveries.