Questions from a Dual Deploy Neophyte

[Knundrm]

I am nearing completion of a Blue Tube custom rocket, modeled after a stretched Estes Executioner, which I am building for dual deployment. After reading a plethora of articles and watching countless videos, I'm down to a few "how to" DD questions I can't reconcile and would value the sage counsel of the forum members, replete with anecdotal humor of course, on how to resolve the issues:

1. Drogue chute deployment: My build will have the drogue chute deploying from the aft end of the rocket. If I use the altimeter to ignite an ejection charge to deploy the drogue chute at apogee, do I remove the ejection charge that comes with the motor? If I do not remove the motor ejection charge, will it effect/impede the performance of the deployed drogue chute, as it will have already been deployed by the altimeter ejection charge? Or do I simply leave the motor ejection charge in place to function as a redundant, "fail safe" system? I suppose I could forego an altimeter charge for the drogue chute, relying only on the motor ejection charge, but I'm not real comfortable with the accuracy of drilling out the delay to adjust the timing of the charge to coincide with apogee.

2. With the altimeter ejection charge affixed to the bottom of the electronic bay, above the drogue chute, how do you protect the chute from the ejection charge? Will the Kevlar chute protector be sufficient, without the benefit of dog barf, etc. between the charge and the chute? And is the Kevlar chute protector still placed below (closest to the motor) the drogue chute on the recovery harness?

With the advent of the Jolly Logic Chute Release, I suppose I could forego all of these machinations by using that simple solution but, I fear that would not serve to "slay the windmill" of what has become my Don Quixotesque DD obsession!

Thanks in advance for any insights!

 

[markkoelsch]

Nomex chute protectors on drogue and main will be adequate.

I would not use the motor ejection.

I am not entirely convinced on the chute reefing devices- I have seen several tangle up.

 

[djs]

I leave in the ejection charge, but leave the delay "long" as an emergency backup charge. The caveat to this is if the delay is not long enough for the planned flight- then I leave the delay in for tracking smoke, but take out the charge.

 

[BrAdam]

I leave in the ejection charge, but leave the delay "long" as an emergency backup charge. The caveat to this is if the delay is not long enough for the planned flight- then I leave the delay in for tracking smoke, but take out the charge.

+1 on this.

 

[Bat-mite]

I do a simulation to get the recommended delay, then add 2 seconds to it and drill to that number. That way I don't risk the motor ejection going off simultaneously with the apogee charge.

 

[noffie79]

I leave in the ejection charge, but leave the delay "long" as an emergency backup charge. The caveat to this is if the delay is not long enough for the planned flight- then I leave the delay in for tracking smoke, but take out the charge.

+2.

 

[Igotnothing]

The OP asked:
"...how do you protect the chute from the ejection charge?"

Wrap the chutes in the protective blankets like a burrito so that the chute is protected from both the motor charge and the altimeter charge.

And test that the deployment charge will separate the rocket and drag the chute out into free air.

 

[Zeus-cat]

I leave in the ejection charge, but leave the delay "long" as an emergency backup charge. The caveat to this is if the delay is not long enough for the planned flight- then I leave the delay in for tracking smoke, but take out the charge.

+3.

 

[CzTeacherMan]

1) -what DJS said
2) Nomex is good enough. Some use dog barf as extra, it helps, but not needed. Yes still place the Nomex below the drogue chute.

One thing you haven't mentioned... I started DD using redundant altimeters immediately. I recommend you do, too. On one flight, my main altimeter never fired, and that would've been an expensive problem. Glad I had two altimeters. Since I'm used to it now, it's never been a problem... More expensive up front, but cheaper than replacing a fully loaded rocket.

 

[jeff_j_black]

+1 on dual altimeters and dual charges for each deployment.

I use the charge canisters that are on the end of a wire lead, so I can place the charges below the chute, or at least wherever I want them.

Like these:
https://www.apogeerockets.com/Eject...Canisters/Standard_Capacity_Ejection_Canister

 

[Knundrm]

All,

Thank you for the information. Very helpful!

One more question: I know Recovery Harnesses are recommended to be 3 to 4 times the length of the rocket. Does that guidance apply with DD as well or would the recovery harness length be adjusted to 3 to 4 times the length of the two sections of the rocket?

Many thanks!

 

[djs]

Longer is always better, so probably 3-4 times the length of the rocket is good- especially if you are using kevlar.

 

[CzTeacherMan]

All,

Thank you for the information. Very helpful!

One more question: I know Recovery Harnesses are recommended to be 3 to 4 times the length of the rocket. Does that guidance apply with DD as well or would the recovery harness length be adjusted to 3 to 4 times the length of the two sections of the rocket?

Many thanks!

Harnesses should be at least as long as the tallest tree your rocket might land in. :lol:

 

[rharshberger]

Generally for my DD in HPR rockets the harness are 20' or more long and z-folded for shock attenuation. The attached picture is of my OneBadHawk harnesses for my L3 project, the z-folds are shown the one harness is 25' (rolled up one) and the other (z-folded) is a 30' custom harness with a built in Y-harness (it actually has 4 total connection points). The important thing with harnesses is to get them long enough and manage how they stretch out by using the correct ejection charge, too much and the harness or attachment points get stressed/damaged no enough and deployment failure occurs.

 

[djs]

Harnesses should be at least as long as the tallest tree your rocket might land in. LoL!

good thing your rockets never end up in trees!

CZTeacherman makes a point though. My opinion is, the longer your harness is, the more your rocket is "spread out" when on the ground, in a tree, etc. When you're flying DD, you're likely to go higher, and despite DD probably drift farther than a rocket on an Estes motor. The more the rocket is spread out, the easier it is to find when looking for it as it covers more space.

 

[rharshberger]

Harnesses should be at least as long as the tallest tree your rocket might land in. :lol:

There is some truth to that indeed!

 

[webtech]

for the motor deployment charge.. depends on the flight, if it will go off after apogee then I will leave it.. but if it's sure I will plug it.

protection, I use nomex and dog barf ..

don't for get to do lots of ground testing before throwing it up in the air.

 

[Knundrm]

Thanks!