Issue with nose cone bulkhead in ground deploy test...

The good news is that I did a successful ground deploy test of my main using a shop-vac and an RRC2-Mini.

the bad news is that the nose cone bulkhead...ummm...departed the aircraft (as the NTSB would say) well before reaching the end of the shock cord, sending the nose cone across the yard like a 16" shell heading for the Bismarck. From the slo-mo on the video, almost as quickly as it left the forward BT.

At first I thought the load was too great and my cheapie harbor Freight digital postage scale was WAY off, but after running and getting a more accurate scale I found it was surprisingly accurate. i started with a light load - the numbers said i needed 0.76g charge for the main, but this charge was only 0.5 (the HF scale only had tenths, my new one has hundredths).

Now, the bulkhead was a tight fit, in fact after inserting it past the shoulder I had to grab the U-bolt and give it a pretty good tug to pull it against the shoulder inside the NC, and it was set with 30-min epoxy. I am assuming that the charge 'ballooned' the nose cone, forcing the bulkhead forward like a piston and the resulting pressure blew it out, since it is pretty clear the shock cord had nothing to do with it.

So, what says the hive mind?

I need to clean up the bulkhead, really roughen up the shoulder and use a longer-setting epoxy with some glass fiber for added strength?

Yep, you got it, I even like to add some brass brads around the outside of the nosecone into the bulkplate, then file the heads off and prime and paint.

I would install av AV bay in the nose cone using a smaller diameter body tube. Then epoxy and pin it in place with a piece of brass from outside of the NC. I would then use a coupler to center the bulkhead, and screws to hold it in place

K'Tesh said:

I would install av AV bay in the nose cone using a smaller diameter body tube. Then epoxy and pin it in place with a piece of brass from outside of the NC. I would then use a coupler to center the bulkhead, and screws to hold it in place

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Inside the bay you could install a parachute to help recover it, should it fail again.

To be honest i think I just didn't take the due care & diligence I should have in preparing the inside of the nose cone; I washed but didn't scrub the interior and there was probably still release film there. Also, I noticed there was really no epoxy on the nose cone shoulder at all, so i need to roughen that area significantly with corse sandpaper. Also, i used a 30 min epoxy, and noticed it was quite brittle - i could snap it off with my finger tips and should should have been hard and sharp. So i will use a better quality, long-setting epoxy and will weigh it instead of measuring it.

And if that doesn't work I am getting some 1/4" lag bolts and...



But, that all said, i was actually happy with the results: I don't think the nosecone is too tight and if the bulkhead had not separated I am pretty sure that it would have been a good test even with a 30% lighter charge than called for. One step back but two steps up ain't too shabby...

K'Tesh said:

Inside the bay you could install a parachute to help recover it, should it fail again.

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A parachute for the nose cone - BRILLIANT! LOL

Actually, if the number of NCs i see separating on YouTube videos is any indication, that might not be a bad idea

There is another aspect i didn't consider yesterday: You may have noticed in the latter part of the video I have two T-nut provisions for nose cone weight in the bulkhead and those two 1/8" holes were unplugged. So the idea that, somehow, the bulkhead was blown in to the nose cone and then the resulting increase in pressure inside the nose cone blew it back out sounded logical at the time but may not be accurate.

I think the failure on my part of due diligence in securing the bulkhead properly is key, however, I think the open holes allowed the charge pressure to equalize quickly, however, and combined with the weak adhesion was also the fact that there was no internal pressure inside the nose cone to support, if you will, the bulkhead against the forces of deployment allowing it to become detached, rotate and exit the nose cone easily.

But, yes, I scuffed the heck out of it, used weighed high-quality, long set epoxy and milled glass fibers, and I plugged the weight adjustment holes. I think that should do it, but in the future, before finishing i am gonig to also install small rods, radially, to help secure nose cone bulkheads.

Live, screw up, be a warning to others & learn. I should make that my new motto

I dont think I have any advice to add beyond what's above (wash inside cone, scuff/scratch to give it tooth, etc...)

But I just watched the video and cannot go on without saying, that really was a beautiful artillery shot

Plastic nosecone, yes? If so, they are notorious for ANY glue not sticking to them...
The best glue that might work would be the ProLine 4500 that Wildman Rocketry sells.

Nytrunner said:

But I just watched the video and cannot go on without saying, that really was a beautiful artillery shot

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I know! LOL! I should have played 'Sink the Bismarck' as background music

I'm just glad i had the elevation to clear the fence

It appears you have a plastic nosecone. Besides scuffing with sandpaper, I generally use an exacto knife to score the plastic - typically cross hatching (making X marks) around where I'll be doing the epoxy. The scores allow the epoxy to really bite.

Also, I noticed you cone cleared the fence. Good thing no one was on the other side.....

les said:

Also, I noticed you cone cleared the fence. Good thing no one was on the other side.....

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Yes, still landed on the grass in my yard behind the fence, but just a tad more powder and it could have wound up in the neighbor's yard. That would have taken some explaining...

I need to rig a moving blanket as a back-stop next time.

Also, there’s enough art (vs. science) in charge weights that 2 decimal places on your gram measurements is overkill. Here are people who would think round grams are OK but they may be building R class rockets.

Curtis Enlow said:

I know! LOL! I should have played 'Sink the Bismarck' as background music

I'm just glad i had the elevation to clear the fence

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Is it too late to exclaim "He shoots, he scores!!!" Three on the board!

hey Curtis, I never trust just glue. I like to use 3/4" ply for a NC bulkhead, in the shoulder with counter sunk flat heads to hold in place. Most of my rockets need weight adjustment with different motors. This also allows you to add or remove weight in the matter of a couple of minutes.

So far. so good. Bulkhead has stayed in place through two varying charge tests. Having some minor issues with my 'burrito wrap' riding up and trapping some of the strap.

Curtis Enlow said:

So far. so good. Bulkhead has stayed in place through two varying charge tests. Having some minor issues with my 'burrito wrap' riding up and trapping some of the strap.

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That has proven to cause problems sometimes, Nomex wraps sliding up and fouling shroud lines. Tie it securely so it cannot slide up.

I always tie my Nomex into the shock cord with a square knot. That way it doesn't ride up and reef the chute.

I use the third loop to hold the nomex away from the chute.

I am using Nylon strap, so what i used was two squares of gaff tape on either side and it kept the Nomex in place.

Things went a lot better today! I didn't send the nose cone downrange

I think your 2nd test of 0.6 grams was right on. You pulled out the laundry. What else you trying to do? The 3rd test with .75 grams seems like you’re putting additional stress on anchor points that not needed.

timbucktoo said:

I think your 2nd test of 0.6 grams was right on. You pulled out the laundry. What else you trying to do? The 3rd test with .75 grams seems like you’re putting additional stress on anchor points that not needed.

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I had issues with the Nomex sliding up, which I fixed, but most importantly there were two VERY light two 1/4" bands of blue tape holding the lower Z-fold together (aft of the main connection point) that did not completely break and deploy on the 0.6g charge.

So, yes, for the Main I may leave the deploy charge at 0.6g or 0.65g since the weight of the rocket will almost certainly break any 1/4" bands of tape that remains. But, I guess the purpose of my tests (especially since it was my very first full-up deploy test) was to work out my techniques, both in placing, securing and packing the charges, and getting an idea of what it would take to get full deployment of all the components.

My bigger concern is that the final drogue charge at 0.86g (the final clip) still did not completely separate all of the Z-folds despite using much smaller tape bands than the full-width bands I have seen others using on their folds & pucks here. I am assuming that there is some dynamic in air deployment that, perhaps, I am not aware of...? One thing that I did notice (but did not address as i was pressed for time) is that with each deploy the fit of the sliding parts became somewhat tighter due to buildup of combustion products, so i will re-polish the surfaces with 600-grit and that might solve some of these issues. Also, I am going to a much lower humidity location for the actual launch, and I know that will affect things as the cardboard will change.

At any rate, a couple of different calculators gave me he same results - 0.76g for Main and 0.86g for Drogue, and given all the possible variables, broadly, I think the test went well. As one friend told me, 'Yes, it's rocket science, but it's also not rocket science.' I need to avid overthinking this stuff!

BP is dirty. I clean all surfaces after every flight and in your case I would clean after every test for the exact reason you mention.

Curtis Enlow said:

My bigger concern is that the final drogue charge at 0.86g (the final clip) still did not completely separate all of the Z-folds despite using much smaller tape bands than the full-width bands I have seen others using on their folds & pucks here. I am assuming that there is some dynamic in air deployment that, perhaps, I am not aware of...?

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The Z-folds serve two purposes:
1) - helps keep the harness neat and tangle free
2) - breaking the tape on the Z-fold absorbs some of the energy from the deployment charge.

It is NOT necessary for all of the Z-folds to break. In fact I would argue that if all of the Z-folds break than the deployment charge was too big (or you used way too little tape )

les said:

The Z-folds serve two purposes:
1) - helps keep the harness neat and tangle free
2) - breaking the tape on the Z-fold absorbs some of the energy from the deployment charge.

It is NOT necessary for all of the Z-folds to break. In fact I would argue that if all of the Z-folds break than the deployment charge was too big (or you used way too little tape )

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My views exactly Les!