Recovery system question for LPR

luke strawwalker said:

You can just tie an overhand loop in the elastic part of the shock cord between the nose cone and the rocket (or between the nose cone and Kevlar leader, if you're using one) and attach the parachute to that-- that way the nosecone has some elastic between it and the parachute. Later! OL JR

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hcmbanjo said:

Ditto!
The shock cords provided in kits are usually too short.
The rule of thumb is the shock cord should be 3 - 4 times the length of the model.

Don't tie the parachute shroud lines to the screw eye in the nose cone base.
If tied there, the nose cone will swing in and out of the shroud lines during recovery making a tangled mess.
Tie the parachute to the overhand loop 1/3 the way down from the nose cone.
At 1/3 the way down the model descends (from the top) parachute, nose cone and rocket body.

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TopRamen said:

I just use Kevlar Thread, and make it longer than I think it needs to be.
My Semroc Blue Bird Zero had the Kevlar to Elastic Set-up, and on its second Flight, managed to slam, prang, bounce or whatever they like to call it, the Nose Cone into the Muzzle of the Body Tube.
I had to fill the Dent in the Nose Cone, and have not flown it since.
Even the smaller Rockets I've built recently use just Kevlar, and lots of it. I'm talkin' like 120 Inches of 350# on my 24mm BT 60 Estes Patriot, and even 100 inches of the same on my 13mm AIM-120 AMRAAM.
The more length the better in my opinion, and getting the recovery device, Streamer or Chute' as far away from the Body Tube as Possible.
The length allows for drag to slow the Laundry upon deployment, so as not to have it just wrench itself out of where it is attached or risk "Zippering". I usually "Mindsim" my Rockets to deploy the Laundry at no greater than 20 Feet per Second of Velocity, but have farted around with Sims and done some launches where the Delay was too long. All Rockets have survived, and in the case of my TAN-SAM on 2 D12-5s, only required minimal repairs.
I've found that it is better to have the Recovery Device come out while the Rocket is still going up than to have it deploy when the Rocket is coming down fast.
YMMV.

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Micromeister said:

TopRamen:
just so you know your lengths are very reasonable but the line weight doesn't have to be so heavy to do the job and outlast the model it's installed in
Yes it is very possible to use Kevlar only for your shock cords as long as they are indeed Long enough to allow the Nosecone to slow down before hitting the end of the cord.

Normally for most of my LPR & MPR models with motor mount anchored shockcords I'll start with 36-48" of Kevlar but Not anything nearly as heavy Strength wise as suggested above, usually 70-90lb Twisted or braided for models Up to about 2.5lbs and 100-130lb braided for models 2.5 to 3.3lbs Lift off weight. To this Kevlar is overhand knotted another 36" to 42" of 1/8" Oval elastic for LPR and MPRs up to about 2.5lb or, 36" to 60" of 1/4" flat elastic on larger MPR and Clustered Upscales. So you see the overall shock-line length of 10' to 12' isn't that extreme.

If using ONLY Kevlar than 10 to 12feet of 70-90lb or 12 -15feet of 100-130 for MPR models has proven to be just about right. This give the ejected nose cone plenty of Slowing down travel time without letting the body catch up or jurk it back creating "the Dreaded ESTES Dent".

Heavier MPR or HPR models would require longer lengths.

Years ago I purchased a roll of 250lb Braided kevlar that I've never found a good Rocket use for. I think I made a horizontal teather sling with it for my UpScale BT-80 size Orbital transport but I could just as easily used the 100 or 130lb braided Kevlar.
Heavier Kevlar lines May be needed on Larger Heavier HPR models but it is just to heavy and stiff for anything I fly.

Just about all my current fleet of Micro models use Kevlar only shocklines of 50-70lb x 30" to 36". Haven't lost a Nosecone or zippered a body on any size model over the last decade or so.

Why one may ask do I still use Kevlar/Elastic combinations? Actually I'm using Stainless Leader/Kevlar/Elastic combo's on all my LPR and MPR models now but that's another story.
The reason for the combination is to allow some stretch in the line to help lessen the opening load on the recovery system. by Placing the attachment point Butterfly knot about 1/3 of the shockcord length below the Nosecone it helps greatly reduce the opening shock on the chute while allow the Body and Nose to decelerate without bounce back.

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luke strawwalker said:

You can just tie an overhand loop in the elastic part of the shock cord between the nose cone and the rocket (or between the nose cone and Kevlar leader, if you're using one) and attach the parachute to that-- that way the nosecone has some elastic between it and the parachute.

Later! OL JR

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TopRamen said:

I know I did'nt need to use such heavy weight Kevlar for LPR, but the only 100# stuff I could find I've had to order from Apogee.
I can get the 350# stuff from Amazon WAY CHEAPER as it is sold as "Spear Fishing Line", and does'nt cost $9 in Shipping and Handling alone.
Pretty sure I'll be sticking with Spearfishing Kevlar for the forseeable future. If I could get the yellow 100# stuff for my LPR Rockets at a reasonable price, in 30 or 50ft. lengths, with free shipping like I get on the Spearfishing Line, I'de gladly be using that for my LPR instead.

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Woody's Workshop said:

I don't recommend this for several reasons. 1) I have tried this and the nose cone can snap back and foul the chute. 2) If the nose cone reaches the air frame the constanly bang all the way down. 3) In even the slightest wind the nose cone will end up spinning around n around n around wrappin thing up. And if you have a camera attached the rocket it doesn't do the video an good.
Just my 2 cents.
I use kevlar at the motor mount, to a swivel to elastic to a snap swivel to the cone, and shrould lines to a snap swivel to the nose cone.

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