Dual Deployment Quandary

[Tinker]

Hello all,

I have built a dual deployment Estes Star Orbiter and I have a bit of a quandary. When I run sims on the rocket, there is no single use Aerotech motor that Apogee carries that has a long enough delay for this rocket. Every motor I sim really wants another half a second more than the maximum provided. I had always envisioned the motor charge as redundant for the apogee ejection charge, but should I set the EasyMini so that the apogee charge fires 1-2 seconds after apogee assuming the motor ejection charge indeed fires slightly prior to apogee?

Thanks,
Tinker

P.S., I haven't made the commitment to RMS in 29mm yet.

 

[dhbarr]

A few things that would help: motors you've simmed, your total weight, and the sim itself.

 

[Tinker]

A few things that would help: motors you've simmed, your total weight, and the sim itself.

Rocksim is the application. The motors I have simmed are the F50t-9, the G74W-9 and the G78G-10 and the Estes F-15-8. The weight as calculated is ~9oz but the actual weight is at about 8oz (without motor). So far the Estes comes in at 7 seconds at apogee, so that would work as envisioned, but the previous three all sim at ~+.5 seconds longer than the delay (which is max for the motor).

I hope to add a cargo bay in the future for a tracker, but the trackers are out of stock. I was hoping that extra weight would tip the scales.

Tinker

 

[dhbarr]

Cool beans. A half second isn't going to kill you, as there's a natural variation in delay burn-throughs anyway.

Remember that more mass can yield a higher-but-slower flight equating to a longer coast phase.

thrustcurve.org suggests several other possibilities, you should check out the motor guide.

 

[Tinker]

So do I run the EasyMini in standard mode for the F-15 and have the apogee charge on a 2 second delay for the composites? (I essence letting motor be the primary with the apogee charge as redundant)

 

[Steve Shannon]

NFPA 1125 allows motor delays to vary from the label value by +/-1.5 seconds or 20%, whichever is greater but not to exceed 3 seconds. If you look at the certification letter for the motors you're looking at you'll see how they tested, including delay times.


Steve Shannon

 

[markkoelsch]

I would just use the electronics, and remove the powder from the motor.

 

[MikeyDSlagle]

I would just use the electronics, and remove the powder from the motor.

I agree.

I would ditch the motor ejection all together. It may be fine but if it pops way too early you'll have problems.

I've seen more damage from imperfect motor delays than anything else. Most of my birds are rigged for electronic apogee events, and all new builds are.

 

[djs]

FYI- I rigged up my Wildman Interceptor to have a nose cone AV bay with an Eggtimer quark in there to pop the main at apogee. Normally I use it for EX motors, but it also works in this instance. The nice thing about this setup is that it wasn't that expensive, and it's only single deploy- less hassle than working with DD if you're not used to dealing with the setup on it.

 

[Tinker]

I agree.

I would ditch the motor ejection all together. It may be fine but if it pops way too early you'll have problems.

I thought the same when I got the sim results, but with this bird, even if it shreds the chute with an early ejection, I am probably ok as it is the drogue chute and I am probably only really screwed if I get no separation at apogee. I wish the electronics had an option to blow the main if velocity hit a certain value, to act if the apogee event failed. I would be nervous forgoing the motor charge since I am a novice at so many elements of DD, from e-match construction, to charge size to loading chutes with nomex cloth. At least if the motor charge fires I am likely not completely screwed as the bird is light.

I am hoping by wrapping the apogee charge in a wadding sheet, I can prevent that charge firing due to the motor charge ejecta if it fires first.

Tinker

 

[ttabbal]

I wish the electronics had an option to blow the main if velocity hit a certain value, to act if the apogee event failed.

Get an Eggtimer Quantum. It has that option.

 

[Bat-mite]

If you go with altimeter ejection only (i.e., plug the motor), make absolutely sure you continuity test your e-matches and don't trust any that have a funky resistance reading. If you use the chip-style e-matched, no harm in wiring two together in series to increase your odds. Do not wire in parallel, or else the increased current might fry the altimeter. I do this all the time, even when I have dual altimeters.

 

[Handeman]

I thought the same when I got the sim results, but with this bird, even if it shreds the chute with an early ejection, I am probably ok as it is the drogue chute and I am probably only really screwed if I get no separation at apogee. I wish the electronics had an option to blow the main if velocity hit a certain value, to act if the apogee event failed. I would be nervous forgoing the motor charge since I am a novice at so many elements of DD, from e-match construction, to charge size to loading chutes with nomex cloth. At least if the motor charge fires I am likely not completely screwed as the bird is light.

I am hoping by wrapping the apogee charge in a wadding sheet, I can prevent that charge firing due to the motor charge ejecta if it fires first.

Tinker

Ground test, Ground test, Ground test, and Ground test some more. Once you determine the size of the charges you need, start using vacuum on the av-bay to have the altimeter blow the charges. By the time you finish all that, you won't be such a "a novice at so many elements of DD".

Just go and play with the DD, all aspects of it. I did my first DD with my L1 cert rocket. I ground tested so many ways with the altimeter, various methods and placements of charges, etc. that by the time the cert launch rolled around I was a lot more nervous about the motor assembly then I was about the DD.

Drop the motor charge and go with the altimeter. They really are much better at deploying right at apogee.

 

[Banzai88]

Ground test, Ground test, Ground test, and Ground test some more. Once you determine the size of the charges you need, start using vacuum on the av-bay to have the altimeter blow the charges. By the time you finish all that, you won't be such a "a novice at so many elements of DD".

Just go and play with the DD, all aspects of it. I did my first DD with my L1 cert rocket. I ground tested so many ways with the altimeter, various methods and placements of charges, etc. that by the time the cert launch rolled around I was a lot more nervous about the motor assembly then I was about the DD.

Drop the motor charge and go with the altimeter. They really are much better at deploying right at apogee.

Yeah, pretty much that. I think I had 20 or more ground level DD charge and altimeter tests like Handeman says before my first actual vertical DD flight! I was so convinced that the motor was gonna CATO because I was so sure of the DD set up and operation. Luckily CTI are pretty foolproof.

 

[Bat-mite]

Make sure your ports are big enough, correctly spaced, and drilled clean.

 

[Zeus-cat]

You could add some weight to the rocket to get the motor ejection charge to occur before apogee.

Since you are new to DD, let me explain something. You will have two ejection events and you seem to think deploying the main is the important one. Wrong, firing something at apogee is far more important. I have had an apogee event failure with a main deployment. It was ugly. The nose and the fin can survived, but nothing else. I have seen other people do the same and it was always ugly. The rockets were destroyed or severely damaged. On the other hand, rockets that have an apogee event, but no main event, can survive with little or no damage.

 

[T-Rex]

If you will post the rkt file you have, then we can look at it and help you. There may be an error in your sim file somewhere. For example I always have to remember to change the finish on all my sims to "regular paint" from the default "polished" (I use Open Rocket). You would be surprised at the difference that little bit makes.

 

[Handeman]

You could add some weight to the rocket to get the motor ejection charge to occur before apogee.

Since you are new to DD, let me explain something. You will have two ejection events and you seem to think deploying the main is the important one. Wrong, firing something at apogee is far more important. I have had an apogee event failure with a main deployment. It was ugly. The nose and the fin can survived, but nothing else. I have seen other people do the same and it was always ugly. The rockets were destroyed or severely damaged. On the other hand, rockets that have an apogee event, but no main event, can survive with little or no damage.

+1 on this one. I've had several main failures for various reasons but never damaged the rockets. The apogee failure resulted in the main deploying at 300 ft and 300 mph. The chute, nosecone and payload/av-bay were fine, but the fin can hit the ground at an estimated 150 mph. The ground won!

 

[Zeus-cat]

Duplicate post

 

[Zeus-cat]

Here is a photo of the remains of the rocket that had a main deployment, but no apogee deployment.


This is the recovery of the lower section of someone's half scale Patriot. Again, no apogee event, but the main deployed. The main ripped away instantly and didn't slow the rocket at all. The rocket hit the ground about a quarter mile from the crowd and it hit so hard that we felt the impact with our feet. Neither of the guys in the photo owned this rocket. The nose was recovered by the owner and it appeared in good shape. This photo is from 2007.


And here is the eyebolt that the parachute was attached to for the above Patriot.

 

[Steve Shannon]

+2. It's not preached as loudly as it should be. The apogee event is the most important part of dual deployment.

 

[cerving]

+3. If your drogue fires and the main doesn't, the damage is usually minimal. If the drogue doesn't fire, bad things happen.

 

[r66astro]

I use 2 alts. 2 charges, set one alt 1 sec delay and 2 Jolly Chute releases in series.

 

[Buckeye]

I like the idea of motor backup, but only if the delay is much longer that the optimal. Anything +/- 2 sec of the optimal delay runs the risk of an early deployment and damage. I learned this the hard way. My DD skills are good enough that I will start eliminating the motor charge altogether.

 

[Buckeye]

I use 2 alts. 2 charges, set one alt 1 sec delay and 2 Jolly Chute releases in series.

4 electronics for one dual-deploy flight?

 

[Handeman]

I use 2 alts. 2 charges, set one alt 1 sec delay and 2 Jolly Chute releases in series.

why not just use the 2 alts and 4 charges, set one for a 2 sec. apogee delay and 100 ft lower main deploy. That is pretty much the required setup for L3 cert flights.

 

[dhbarr]

The advantage of 2xCRs is in simplifying the AVbay, wiring, harness, & packing. Pop the nose, hang out the laundry, no more pyro.

 

[Handeman]

The advantage of 2xCRs is in simplifying the AVbay, wiring, harness, & packing. Pop the nose, hang out the laundry, no more pyro.

So you're not really doing dual deployment. You're using JLCR with electronic apogee charges instead of motor eject.

Frankly, I wouldn't be surprised if that basic set-up becomes the norm for L1 and smaller L2 rockets. I think it will be one altimeter and one JLCR of course, most folks won't bother with dual devices until they get to the larger L2 rockets.

 

[dhbarr]

So reefing of any cablish-kind isn't "real" dual deploy; but as long as you're keeping it wadded w/ tube & bulkheads for both phases, that's "real".

Just want to make sure I draw the line correctly. I presume deployment bags & co2 makes it DD2.5?

 

[Handeman]

So reefing of any cablish-kind isn't "real" dual deploy; but as long as you're keeping it wadded w/ tube & bulkheads for both phases, that's "real".

Just want to make sure I draw the line correctly. I presume deployment bags & co2 makes it DD2.5?

If i use the wrong definitions or distinctions I'm really sorry.

Why don't you publish what is 1.0, 2.0 or whatever variations you feel are needed so we don't get confused and use the wrong ones in the future.