HED parachute configuration on a large rocket?

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AllDigital

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For a very large bipropellant rocket we are doing head end deployment (HED) of the drogue and the main. The rocket is an 8" airframe, 180 pounds (dry) and will use a seven foot drogue and a 26 foot main. The nose cone is ejected using a spring (solenoid) latch mechanism releasing the drogue. The Main is held in with another solenoid latch, until 2K feet. This is a big rocket (BFR) and a lot of chute to get out the tube. We have been debating the best harness configuration for a successful deployment. Below are two configurations, A&B. The A configuration assumes the main is pulled up by the base of its shroud lines and rides to the side of the drogue and the nose cone. Configuration B assumes the drogue acts as a pilot and pulls the main out from the apex, but this appears to create high risk of entanglement with a now deflated drogue and a nosecone spinning around.

I figured this group wouldn't be shy with opinions and alternatives. Thoughts?

Mike

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Cameron Anderson

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B

Just make sure the bridle attaching the drogue to the main is sufficiently long so it won't impact main chute inflation and it'll just drift off to the side.
Also make sure the bridle attachment point on the main can handle the weight of the rocket and the tugging force of the drogue.
Would consider a deployment bag essential for this as well.

"A" is unfeasible due to the fact that the rocket won't be falling fast enough under drogue to get a good, clean, reliable inflation of the main - 26 feet is a lot of silk to fill.
 

OverTheTop

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Personally I have used option A and found it to work well. My L3 project used an AARD release to keep the main in the airframe till it was needed.

I do mine a little differently nowadays. The NC blows off at apogee and has a drogue attached to its base. A harness goes back to the main rocket body to keep everything together. The main is in a deployment bag and connected to the airframe by its own harness. It stays in the airframe until the altimeters in the airframe eject the bag out into the airstream. The main has its own pilot chute that catches the air when the bag gets into the wind and pulls the main out of the DB. The deployment bag is tethered to the main harness, just outside the airframe.
 
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cerving

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B, but have the nose cone attached to the shock cord below the main chute, so it doesn't interfere with its inflation.
 

jderimig

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Consider a freebag config. Drogue pulls deployment bag off main chute. Nosecone and bag descend under its own chute. The drogue is the NC chute.
 

AllDigital

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Thank all!

Consider a freebag config. Drogue pulls deployment bag off main chute. Nosecone and bag descend under its own chute. The drogue is the NC chute.
I like this line of thinking, but how to get the main fully pulled out vs just pulling the bag off. Also, it still seems to me (as in option B) that there is some risk that the nose and drogue could come down dead center to the canopy and tangle. The nose is about 8 pounds. I also thought about just releasing the nose by itself on its own chute, but apogee is about 22K feet, so the nose is going to float far away while the rocket falls fast under drogue.
 

AllDigital

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B, but have the nose cone attached to the shock cord below the main chute, so it doesn't interfere with its inflation.
Thanks Cris. This could take some creative rigging, especially with latches, but it is likely the safest option.
 

jderimig

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Thank all!


I like this line of thinking, but how to get the main fully pulled out vs just pulling the bag off. Also, it still seems to me (as in option B) that there is some risk that the nose and drogue could come down dead center to the canopy and tangle. The nose is about 8 pounds. I also thought about just releasing the nose by itself on its own chute, but apogee is about 22K feet, so the nose is going to float far away while the rocket falls fast under drogue.
This is a proven technique. Generally the main chute is free to come out of the tube. Pulling on the bag pulls the chute out of the tube. When the main harness is fully extended then the bag will come off. Since the main is not inflated at this point the main will fall away from the nosecone quickly. You attach the NC chute close to the base of the nosecone. Zero chance of entanglement.
 

Handeman

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Thank all!

I like this line of thinking, but how to get the main fully pulled out vs just pulling the bag off. Also, it still seems to me (as in option B) that there is some risk that the nose and drogue could come down dead center to the canopy and tangle. The nose is about 8 pounds. I also thought about just releasing the nose by itself on its own chute, but apogee is about 22K feet, so the nose is going to float far away while the rocket falls fast under drogue.
I'm not using head end deployment, but when my nose cone is ejected, it pulls out a pilot chute. That pilot pulls out the deployment bag. The main shrouds are zig zagged into elastic loops on the d-bag and pull out first, then the d-bag is pulled off the main and it opens after the shroud lines are all pulled straight.

The thing I did was make sure the main and rocket descended at about 15 - 17 ft/sec and the nose cone and pilot with the d-bag descended at about 11-13 ft/sec. I then attached a small line (150 lb Dacron) between the inside of the d-bag and the top of the main.
The slower decent rate keeps the pilot and nose cone above the main, but the line keeps them attached so they land together.

If you can do something similar with the nose cone and drogue and control when the d-bag gets released and pulled off, it should work for head end deploy too.

Good luck.
 

Rocketjunkie

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I put the nose ejection at the tip and let it push out the chute.
 

AllDigital

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In re-running numbers on option B, it seems like the drogue and nose would naturally stay high, above the main, as long as there is a sufficiently long tether to allow it to stay inflated. A seven foot drogue with an 8 pound nose is going to fall at a rate of 10fps (very rough) and the rocket under main is going to fall at about 22 fps, so shouldn't the drogue/nose stay high and get pulled down from the main/rocket?

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