An interesting read,,,,,,,,,,,,,,,,,,,,,,
First,,
Very nice to meet you Greg,,,,
Second,,
I have so much to tell you I'd ask you to call me but I prefer to type so you can refer back and not rely on memory....
First discussion,,,
Booster section,,, that's the term I use as well,, I think were supposed to call it the sustainer,,, My experience,, First,, a shock cord should not take a shock load,, if it does your e charge is too great,, separation is too violent,, or the cord is too short... Now,, that said,, I personally do not agree with the huge strength requirements some come up with as necessary for these cords..
I wouldn't go too light either.. I now use the same proportions for a 38 mm minimum diameter,, a 54 mm minimum diameter ( my Altitude Seeker ),, a 2.6 HV Arcas,, a 3" -- My Green Hornet,, and ( not built yet)
a 4" X 11 ft --"Onebadhawk"
Every one is modified extensively,
more then enough to call scratch...
Dimensions----------
Everything is all fiberglass,,, every payload section is the same length as the booster section,, I like enough room for the main chute,, every commercially designed rocket has too small of a payload section,, not enough room for the main chute...
38 mm minimum D-- 30" booster and payload...
54 mm minimum D-- 32" " "
3" -- 36" " "
4" Scratch not built yet but I have all the parts and one TAP Member----------- 48" booster and payload...
Notice all proportions are the same,, or close...
Greg,, you’re a good man,, nobody has noticed,, the strength of the material I use I just quote what it says on the reel.
You are correct,, on the reels of 1/2" Kevlar it says 2500 lbs and on the 1" it says 2000 lbs...
They are both as strong as you'd expect from Kevlar,,,,
The 1" is definitely stronger then the 1/2" plus it's so wide that I get twice the amount of stitching on each loop...
that's a very important point....
You said 55 lbs on the pad,,, that's getting there,, pretty heavy,,,
The nylon is always bulkier then the Kevlar...
Takes more room to stow...
Also,, don’t forget,, the heavier / stronger the harness you use the longer it will last.....
I'd sooner see you use the 1" Nylon,,, you could literally tow a truck with it after I sew it up,,, but it's bulky....
The 1" Kevlar would suit your purpose.....
Now ,,, length,,,,
If you have the room to stow it,,,
a longer cord ( within reason ) hurts nothing.....
On all..................
In the booster,,,
The echarge is coming from the top side of the compartment,,,
first it want to jamb everything down deep into the compartment then in the same motion separate.........
if you attach the drogue to the bottom of the av bay and the e charge try's to jamb the drogue down into the booster section it will hold back the action of separation.
Do not allow this,,,
This is why I make 3 loop cords,,, The 3rd loop is about 25% down from one end of the cord,,,
The booster has no more weight at apogee ( no propellant ) but has all the drag ( the fins ),,,, the av bay and payload has all the weight and none of the drag,,, it wants to travel away,,, let it,, don’t hold it back,,, on my 54 minimum D a 25 ft cord,,, with a 3rd loop sewn 6 ft down from the av bay,,, drogue attached to 3rd loop,,, echarge goes off,, drogue is forced down into booster without a fight,,,,,
av bay and payload,, all the rockets mass at this point in flight moves away,,, no fight,,, there shouldn't be much forward motion at this point but what there is,,, drag from fins,,,, separation and the mass easily drags the drogue out of the booster,,,,,,,,
I haven't had a fail yet..................................................
Payload / main,,,,,,,,,,,,,,
I always on all use a piston,,,,,,,
it make the echarge much more efficient,,,,
I use a piston though to stop burning my chutes,,
they're expensive and I'm cheap ,,,,lol,,,,
On top of the av bay,, on a 3 ft airframe bout 5 or 6 ft of Kevlar,,,
over the piston bout 15 ft of Nylon,,, the main is attached to the eye on the nose cone.........
This way I get the best of both worlds,,, the burn resistance of the Kevlar and a bit of give from the Nylon,,,,,,,,,
In this manor I had one fail,,, I put a bit of dog barf over the piston for burn insurance as there's no Nomex blanket used and put it in a little too tight, I inadvertently got a piece wedged between the piston and airframe wall wedging the piston in place.....
This was after many flights and I no longer put barf over the piston,,,,,
Overall,, a very good record,,,,,,,
That's why I stick to these proportions...........
By these proportions,,,,,,,,,,,,,,,,,,,
6" diameter--------
6 ft booster,,,, 6 ft payload,,,,,,,,,
between 40 and 50 ft on each side.........................................
Greg,, This reads pretty cool,,,,,,,
I hope you don't mind if I post it publicly,,,,,,,,,,,,,,,,,
Anything I can do to help,,,,,,,,,,,,,,,,,,
Ted Chernok
I'd like to order a couple of 1/2" Kevlar straps in a custom length. 
