head end deployment problems

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watermelonman

watermelonman

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When I got my first batch of new Wildman nose cones, I was real excited at the prospect of deploying mains from the nose cone. It gives me so much more flexibility with construction and payloads to loft, rather than payloads that are needed for operation of the rocket.

However, after a single successful separation, I have been having nothing but problems. Three times in a row now I have failed to get full separation between the nose cone and avbay. Thankfully the awesome strength of this fiberglass and injected fillets means my rocket is fine, but boy do I feel silly watching it hurdle towards the ground on a pathetic little drogue. It is bound to fail outright at some point, too.

The worst part, by far, is that each of these failures is preceded by successful ground tests. Each time I have upped the powder charge, despite ground test success, in hopes of a little extra being what it takes to work properly. I strongly suspect that the drogue deployment forces are causing the nose to go cockeyed on the avbay, which in turn will now require much more force to separate. Ironically after hitting the ground it seems to loosen up, not that it does any good at that point. I rebuilt a brand new avbay, being extra careful to sand smoothly around the circumference, and tried a new nose cone too. Nothing is working for me. I suppose the roundness could still be better, but if that is the issue I apparently lack the skill to get it that perfect. I was about as careful as I could have been this last time, and sanded down the avbay lid too.

At this point I am considering eliminating the head end deployment in favor of a baby payload bay. Is anyone else having these problems? It is driving me nuts.
 
I have 3 Wildman rockets all with Head Deployment and all with multiple flights and all successful main deployment. My biggest charge on a 4" V2 is 1.5 grams BP for the main. My Punisher & Wildman use a little less. Im using 3 shear pins on each and I also shove the shock cord in the NC ahead of the chute to help aid pull the chute out.
When you say you don't get "full separation", how much are you talking about? Details please!
 
Are you using shear pins? Is the launch causing the av bay to go too far into the nosecone putting it in a bind?
 
Sorry yes, three shear pins exactly like CJ describes in the original Punisher build.

When I say incomplete separation, I mean that the nose cone does not come completely off the avbay. I am also careful to pack the shock cord in before the parachute but when it never opens that part does not matter. Usually after crash landing it is about a millimeter or two off the vent band, sometimes with a shear pin or two still in place partially.

I had it all flush when drilling shear pin holes, so pushing into the nose cone seems unlikely but could be possible.
 
I have had dozens of successful flights and only one or two failures. Here are the key things to make sure are right:

Apogee shock cord length....make it long.

Shear pins in the nose.....don't forget them.

Main chute ejection charge.....get it right and then add a bit more.

I have also had good luck with placing the main ejection charge forward of the parachute (stick them way up into the nose)

Many others will chime in here. My advise is only based on my personal experience. Not something I heard or saw.
 
Assuming your vent band is properly glued on the AV bay that slides into the nose cone, I don't think there's a problem with it getting rammed up into the nose cone and that being a problem. I also don't think the drogue charge would be causing any issues with the nose cone not being properly fitted on the AV bay, since you're holding it in place with shear pins and you said you ground tested, so I think you'd have to have a massively oversized apogee charge to cause enough force that you'd deform the nose cone's shear pins and cause problems of the nose cone no longer fitting properly on the AV bay. If anything, the force of a hard landing on the nose cone would be what could cause it to get "cockeyed" on the AV bay coupler.

What size rocket are you working with? I have one of Tim's 6" V2s that I have yet to have any head end deployment problems with. I will say, though, that I use comparatively large charges compared to some of my other rockets. The nose cone is about 1/4 to 1/3 filled from nose weight epoxied in and then topped off with 2-part foam. After I pack in an 84" Fruity Chute and the tubular nylon along with nomex blankets to protect everything, there's not much room at all left in there for space. I'm using 2.5g of FFFg for both apogee and the main to make sure I get main chute deployment. I have two shear pins in the nose cone and two in the body, which consistently shear with ease.

If you're noticing that it's barely off the vent band when it comes in under the drogue, I have to ask the question: are you sure your main charge is firing? If you keep using larger charges and not seeing any results, either your charges aren't firing, they are incredibly undersized (wouldn't make sense if you're ground testing and it's separating), or somehow the powder charge isn't holding together at the end of the ematch and maybe you're not getting full burning of the powder.

Best of luck,
Joe
 
GRIFFIN said:
I have also had good luck with placing the main ejection charge forward of the parachute (stick them way up into the nose)
Click to expand...

I have not done a HED yet, but have a rocket or two in the build pile where this would make a lot of sense. I've contemplated the same thing, with putting the separation charge for the nosecone/av-bay at the nose tip, as it seems you are describing. How did you contain it, or did you do the latex glove & ematch thing? Did you just put the charge in first and the pack on top of it, or did you tape/hot glue the charge at the tip somehow?

I would think a Marsa54L with the remote pyro module would be useful for this, either way it is setup.
 
That seems weird to me. If you pick up the rocket by the cone will it come off easily? I polished my coupler so that it comes off easily. How big of a charge are you using? My 3" Saab uses the same cone as the Punisher. It has 1.5lbs of weight added. I'm using 4x nylon rivets for shear pins. I wound up using 2g of powder for the main charge.
 
schneijt said:
Assuming your vent band is properly glued on the AV bay that slides into the nose cone, I don't think there's a problem with it getting rammed up into the nose cone and that being a problem. I also don't think the drogue charge would be causing any issues with the nose cone not being properly fitted on the AV bay, since you're holding it in place with shear pins and you said you ground tested, so I think you'd have to have a massively oversized apogee charge to cause enough force that you'd deform the nose cone's shear pins and cause problems of the nose cone no longer fitting properly on the AV bay. If anything, the force of a hard landing on the nose cone would be what could cause it to get "cockeyed" on the AV bay coupler.

What size rocket are you working with? I have one of Tim's 6" V2s that I have yet to have any head end deployment problems with. I will say, though, that I use comparatively large charges compared to some of my other rockets. The nose cone is about 1/4 to 1/3 filled from nose weight epoxied in and then topped off with 2-part foam. After I pack in an 84" Fruity Chute and the tubular nylon along with nomex blankets to protect everything, there's not much room at all left in there for space. I'm using 2.5g of FFFg for both apogee and the main to make sure I get main chute deployment. I have two shear pins in the nose cone and two in the body, which consistently shear with ease.

If you're noticing that it's barely off the vent band when it comes in under the drogue, I have to ask the question: are you sure your main charge is firing? If you keep using larger charges and not seeing any results, either your charges aren't firing, they are incredibly undersized (wouldn't make sense if you're ground testing and it's separating), or somehow the powder charge isn't holding together at the end of the ematch and maybe you're not getting full burning of the powder.

Best of luck,
Joe
Click to expand...

my point about the apogee charge was to make sure it was enough to separate, but not to force the nose to the end of a (short) shock cord, causing the cord to hyperextend and pulling the nose off the av bay prematurely.
 
Here's a question I haven't seen yet...

Did the BP for the flight come from the same container as the powder used for the ground tests? The exact same container?
 
Are you wiping the BP grit/residue off the coupler & inside the cone after every flight?

The fit is so close that one must usually do a bit of wet sanding on the coupler [only the side/half that fits into cone. I used 600 & only barely sanding to get it to fit perfect. Over-sanding is really easy to do with these. If you do that, there is wobble induced into the fit from A un-even sanding or B go too far and making the fit to loose. [check by the wiggle test]. Out of 4 cones 3 needed wet sanding. [less than 5 minutes to good fit & that's nothing, we are supposed to be BUILDING not assembling rockets, right guys? Well old timers anyway]

In any case, grit from residue will make it bind when charge fires.

Another possible issue. I use 1/4 Kevlar on mine [around 15ft for main]. Sometimes edge of cord or nomex will get between the lip inside cone & end of coupler BP, making for a tight fit on last 1/4in when seating the coupler/avbay. Luckily I caught it when installing as I alway push in & pull out to be sure it goes smoothly both directions before installing shear pins.

When all is working correctly...........My vents are 3/16th [3] charges are 1.2 apogee & 1.4 ish main. Shock cord is put IN FRONT of parachute to insure pulling it out. Charges are always on the bulk plate. I have 17 flights on the 3 rockets with Nose cone DD & every one worked perfectly. Punisher------Jimbo 4in. Jart------ V-2 4in.

I suspect if I had a hands on look, I would figure in out in a minute.
Biggest problem folks have, is how they fit the parts. Rarely will 2 guys do it the same, so the charge needed may be more or less than in a thread you read, depending on how tight/loose the fit.
 
Thanks WILDMANRS and blackjack2564; I was hoping one of you would chime in but both is a bonus!

With this much sanding I have a tough time seeing it being too tight. Powder, I am using enough to scare all my neighbors and make the nose cone explode off when I am on the ground. It is 3F pioneer, though, not 4F black, and maybe getting moved or upset during flight. The apogee charge is the same and works great, though. I am using cut plastic glove fingertips, by the way, stolen from Tony Alcocer.

I think CJ is on to it with the coupler being too loose and too dirty. He was talking about 600 grit for five minutes. I did 80 grit for more like an hour. The charge is probably offset to the side, and the apogee forces must be further cockeye jamming the connection. I am quite careful to make sure there is no shock cord catching the lip.

Between this and questionable stability on my motors of choice, I think the best plan of action is to add a baby payload tube to my beloved Punisher. My current idea is to epoxy a new coupler into the nose cone, then epoxy a short airframe segment onto that coupler. This will both bring the CG forward as well as eliminate the coupler to nose transition that I have been unable to make correctly. I will probably use a longer avbay as well, since that had previously been a concern for lateral forces as well as deployment.
 
Can you explain what you mean by "Pioneer"? Is it a BP substitute? If so, latex glove fingertips won't work reliably. There are numerous threads about containing BP substitutes to get desirable results. For many reasons real BP is preferred. Before heavily modifying your rocket, only to learn the results are still poor, obtain some BP from a fellow flyer.
 
If you are saying that you are using Pioneer (as in Jim Shockleys American Pioneer Powder BP Subsititute)....... STOP - DON'T USE IT

In my Black Powder rifles, Pioneer will produce about 2/3 of the muzzle energy as the same amount of Goex Black Powder, and it leaves MORE residue.

If you are ground testing, make sure that you wipe out the inside of the nose cone AND outside of the coupler with a damp rag. Windex is an even better cleaner.

Methinks the problem lies in a mix of not as much ooomph as BP, and more residue.
 
Last edited:
Hah, CJ called me back and set me straight! I am going to get some 4FG, non substitute, real black powder for the next run, and will consider putting it up in the nose tip instead of the avbay bulkhead although that scares me a little.
 

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