HEDD Question

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Budro0

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I'm a head end first timer and I ground tested my charges this weekend. I just noticed the damage in the pic, but after reviewing video I think my charge was incorrectly placed/too hot.

This is a WM Punisher SS (54mm airframe) and I started at .3g (4f BP), which gave me a quick snap, but didn't shear all three pins. Charge was in a centrifuge vial at the top. Bumped up to .4g and got good shear, but it did seem almost too energetic. I got full extension on the 8 ft shock cord (nosecone is tight...). And now I notice the damage about where my charge was.

For those of you with experience with this kit or other HEDD rockets, did I place the charge too far forward? Too much for the little nosecone? Should I go back to a canister on top of the av-bay? This is an easy enough repair but I'd rather only do it once.

PXL_20220223_071853759.jpg
 
I normally use aluminium charge canisters that face the blast axially up the airframe so damage has never occurred in my big birds. I did use a small charge once that was just packed into the airframe and it put a hole in the cardboard airframe.

I have used centrifuge vials but had them sitting in an aluminium canister to prevent the vial floating around and doing unpredictable things. Nowadays I just use canisters on their own.

Here is an example of one of my bays with "submerged" canisters fitted.
AltsCompleted.JPG
These take up less room in the laundry area.
 
OverTheTop said:
I normally use aluminium charge canisters that face the blast axially up the airframe so damage has never occurred in my big birds. I did use a small charge once that was just packed into the airframe and it put a hole in the cardboard airframe.

I have used centrifuge vials but had them sitting in an aluminium canister to prevent the vial floating around and doing unpredictable things. Nowadays I just use canisters on their own.

Here is an example of one of my bays with "submerged" canisters fitted.
View attachment 505989
These take up less room in the laundry area.
Click to expand...

You always have the coolest rocketry components . . .
 
For a 54mm airframe, I only use 2 shear pins and all my rockets with HED deployment have charges on av bay and like over the top, I also use canisters. For what it’s worth, I hate thin walled fiberglass.
 
timbucktoo said:
For a 54mm airframe, I only use 2 shear pins and all my rockets with HED deployment have charges on av bay and like over the top, I also use canisters. For what it’s worth, I hate thin walled fiberglass.
Click to expand...

Why do you hate thin wall fiberglass?
 
timbucktoo said:
I have had many tubes splinter/fracture from even mild landings. Saw it again in another guy’s rocket last Saturday.
Click to expand...
One of my Drago's had that happen. I have to get a piece of coupler to glue inside to fix it... thanks for the reminder!
 
It seems like the anecdotal advice I received about charges on top to throw the laundry may be less reliable. I appreciate all the advice.

I'll switch to a canister on top and retest charges tonight.
 
Budro0 said:
It seems like the anecdotal advice I received about charges on top to throw the laundry may be less reliable. I appreciate all the advice.

I'll switch to a canister on top and retest charges tonight.
Click to expand...
I've seen the "blown it down from the top" work many times, I think it really depends how your BP is contained, how large of a chute you are using, and how bulky your recovery cords are. My view (preference) is for a less bulky chute (such as a top flight recovery standard), and smaller tubular kevlar cord. You are on the right track with retesting the charges and get it right on the ground.

Best,
 
I'm also going to be building a head-end deployment rocket for the first time (a composite warehouse 4" Pink Lady) and had a couple of questions.

1. How do you attach one end of the main harness to the inside of the nose? I was thinking of just pouring some some epoxy down the nose and holding the end of the harness in it as it cures, but I was wondering if there were some more elegant and less permanent ideas.

2. To ensure the parachute comes out of the nose, is it just a matter of attaching the main parachute down low on the harness so that the harness pulls the parachute out as the nose goes flying off? I'm also hoping for something more elegant for this as it seems like the long harness end holding the nose on would be prone to tangling with the drogue harness as they both dangle during descent.
 
Here is an example of blowing it down from the top. This gets my 3D-printed ABS nosecone off and pulls out the drogue. That is mostly how I fly. These were an early version of the canisters, without a groove for o-ring to hold the tape down, and I did stuff up by not leaving much space between the canisters here. Still works though.
NCRear.JPG
 
I have two harnesses, one from lower airframe to NC with drogue attached, and the other just airframe to the main. Main resides in a deployment bag in the airframe.

NC blows off at apogee and pulls out drogue. Main altimeters (below recovery compartment in airframe) blow out the main deployment bag into the airstream at the required time. The flap on the deployment bag opens in the air, pilot chute inflates and pulls the main out of the bag. That's mainly how I fly.
 
Antares JS said:
I'm also going to be building a head-end deployment rocket for the first time (a composite warehouse 4" Pink Lady) and had a couple of questions.

1. How do you attach one end of the main harness to the inside of the nose? I was thinking of just pouring some some epoxy down the nose and holding the end of the harness in it as it cures, but I was wondering if there were some more elegant and less permanent ideas.

2. To ensure the parachute comes out of the nose, is it just a matter of attaching the main parachute down low on the harness so that the harness pulls the parachute out as the nose goes flying off? I'm also hoping for something more elegant for this as it seems like the long harness end holding the nose on would be prone to tangling with the drogue harness as they both dangle during descent.
Click to expand...

I'm probably not the expert you wanted, but I'll chime in. Of course on my punisher, it has a metal tip and came with an eye bolt, so I just attach to that with a quicklink. If yours doesn't, you could rig up something similar with an eyebolt and nut/washers or carriage bolt in epoxy.

I agonized over where to attach the chute quite a bit, but finally determined that if at full extension my parachute was 36" long, I needed to attach it to the harness about 36" from the nose end. I don't remember exact measurements right now, but my logic was even with a 12" nosecone, that would put some nylon in the wind to pull the rest out - should the apex get hung up in the nose. I am only using an 8' shock cord, so I am pretty close to the middle of the cord.
 
Antares JS said:
I'm also going to be building a head-end deployment rocket for the first time (a composite warehouse 4" Pink Lady) and had a couple of questions.

1. How do you attach one end of the main harness to the inside of the nose? I was thinking of just pouring some some epoxy down the nose and holding the end of the harness in it as it cures, but I was wondering if there were some more elegant and less permanent ideas.

2. To ensure the parachute comes out of the nose, is it just a matter of attaching the main parachute down low on the harness so that the harness pulls the parachute out as the nose goes flying off? I'm also hoping for something more elegant for this as it seems like the long harness end holding the nose on would be prone to tangling with the drogue harness as they both dangle during descent.
Click to expand...

Does the Pink Lady have a removable tip? Assuming not, and if that is the case, ideas here in post 1: https://www.rocketryforum.com/threads/amw-red-fibermax™-kit-with-head-end-dual-deploy.141700/

Anything glued in, don't glue in the long length of cord, make a short "lead" with a sewn loop or quick link so you can remove/service the longest piece(s).
 
Budro0 said:
Took me an extra night, but got home early enough to test the new setup. Ended up going up to .5g - not sure why it needed the extra 1/10. Anyway. Works well, and you can see the chute comes out nicely still in a tight wrap.
Click to expand...

Charge on the bulkhead now?

Nomex and parachute connected to the same point on the recovery cord? If so, I would move them apart a little.

What is your intended main altitude deployment height?
 
I use a little tape packet on the end of the ematch. This goes all the way to the tip of the nose cone so it blows behind the main and pushes it out. I do not trust the momentum of the altimeter bay to pull the main out of the nose cone. My smallest HED ejection is a 3" Punisher and requires a nomex blanket. Not enough room for dog barf. This is how I did it with my 7.5" Goblin before HED kits were available https://www.rocketryforum.com/threads/almost-a-goblin.8709/
 
rfjustin said:
Charge on the bulkhead now?

Nomex and parachute connected to the same point on the recovery cord? If so, I would move them apart a little.

What is your intended main altitude deployment height?
Click to expand...

Charge is on the bulkhead now. I do normally have the nomex attached to the av-bay (short kevlar tether to the eyebolt), but I was rushed for time last night - I was more worried about shearing pins that anything else. I haven't fully figured out where I want to be at deployment, but I am using a Quark on this one, so I think that limits me to 800, 500, or 300. We'll see how deployment goes on test flights, but I see no reason I can't use 500.
 
Budro0 said:
Is that because there is something different about a head end deployment? Honestly curious, I think on most of my other DD I use 500 or so.
Click to expand...
Combination of experience and best practices. Its not worth eating up critical altitude if the chute needs just a little more time to fully inflate. Even on a small rocket popping fins or stressing tubes isn't fun.
 
Rocketjunkie said:
I use a little tape packet on the end of the ematch. This goes all the way to the tip of the nose cone so it blows behind the main and pushes it out. I do not trust the momentum of the altimeter bay to pull the main out of the nose cone. My smallest HED ejection is a 3" Punisher and requires a nomex blanket. Not enough room for dog barf. This is how I did it with my 7.5" Goblin before HED kits were available https://www.rocketryforum.com/threads/almost-a-goblin.8709/
Click to expand...
I do not believe there is any overall advantage outing the ejection charge underneath the chute. You run a large increased risk of chute and connecting lanyard damage for a very small gain in ejection capability.
 
RocketScientistAustralia said:
I do not believe there is any overall advantage outing the ejection charge underneath the chute. You run a large increased risk of chute and connecting lanyard damage for a very small gain in ejection capability.
Click to expand...
The space in the nose cone is tight, especially in smaller rockets. Relying on the momentum of the nose cone is asking for trouble.
 
timbucktoo said:
I have had many tubes splinter/fracture from even mild landings. Saw it again in another guy’s rocket last Saturday.
Click to expand...

A lot of that has to do with the resin system that the maker used and the wind angle. You can change up the crosslinking and angle so that they are more compliant to impacts. Less curative (slightly less crosslinking) and higher wrap angle makes for a slightly more compliant part.
 
Rocketjunkie said:
The space in the nose cone is tight, especially in smaller rockets. Relying on the momentum of the nose cone is asking for trouble.
Click to expand...
That depends on how you pack your gear. I attached the nomex to the bottom third of the recovery cord in smaller HED cones, that way the burrito does not travel far before the whole enchilada is pulled out easily.

My .02.... YMMV
 
Think of it like this. Ejection charge goes pop. Hot gasses have to get past your chute to pressurise the fuselage before breaking your retaining shear pins. At that point there is no real high pressure wave behind your chute to push it out. The cannonball chute you think you're trying to push out has already had the ejection gasses bypass it. Your chute on the other hand has just had a very hot day on the beach as has your deployment bag.
This has been discussed before. I'll let you do the research. It's your rocket. YMMV.

Test it. Do what you test. Also bear in mind that a charge behind your chute could result in a softer load being applied to your shear pins.
Good luck with the flight. If you've tested your methodology and it works for you. All good.
 

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