Great BALLS of Fire 2.0

AlnessW said:

Thanks! I was planning on leaving both stock. Your thoughts?

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My M2245 flight had stock tube, you just have to know how to fit your couplers and where/how to drill your holes. I would be more worried about that stubby gel coat cone though. In any case, I think you should fly the M2245 and I think you'll be just fine :wink: I think with that motor you'll get pretty close to your 38K estimate. Good luck!

4kids49 said:

Bummer. I guess that he is out.

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He is indeed. But like I said, he still has inventory to sell off and could probably offer you a good deal. (He gave me 30% off retail for the Rocketman chute.)

mannyskid said:

My M2245 flight had stock tube, you just have to know how to fit your couplers and where/how to drill your holes. I would be more worried about that stubby gel coat cone though. In any case, I think you should fly the M2245 and I think you'll be just fine :wink: I think with that motor you'll get pretty close to your 38K estimate. Good luck!

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Good to know - thanks for stopping by, Manny! If your rocket held together then almost certainly mine will... What are your thoughts on vent holes?

I am pondering a Von Karmon nosecone... TBD.

Cleaned my shop first like I said I would - whew! Now that wasn't so bad. Anyway, back to business.


Here we have the mostly-assembled altimeter sled. Used an L-bracket on each side to attach the the sled to the bulkpate for extra strength. Both altimeters fit on there quite nicely.


Then the 9V batteries are attached on the other side. I'll add an extra cable tie to each, as well...


First, we tack the screws in place with hobby epoxy.


To secure them, I use Kevlar strips soaked in West Systems epoxy. After it cures I always add a second layer of Kevlar/West Systems for extra strength.

I just ordered at CTI M840 longburn from Bay Area Rocketry which he should have for me at BALLS. Not sure yet if I'll fly it in this rocket or the Competitor 4 as it would do very well in either... TBD. I wanted to fly the CTI M2245 in this rocket but I just couldn't afford it.

I did the second layer of Kevlar on my nosecone anchors only to discover that my altimeter sled wouldn't fit in there anymore. I must have mis-calculated the inside diameter of the nosecone shoulder with the screws in place, or something. Harrrrrruuuumph!

But the good news is that it was an easy rebuild with a design that I, quite frankly, was much happier with.


Second layer of Kevlar "layup" on the nosecone anchors. This is now the second time I've used this design on a nosecone and I'm totally sold on it. Bulletproof.


Tada! My "2 hour wonder" - Completely redesigned and rebuilt altimeter sled.
Manny - I heard through the grapevine once that you put together an entire G10 sled in one night at Bruno's not too long ago??


Much better than the old one, too. Complete with push on-push off buttons for arming switches (my standard) and 9V batteries on the back of the sled.


This time, it fits in the nosecone perfectly.


More good news! My airframe arrived today. Upon arrival I realized it had came from New Hampshire (Hawk Mountain) via FedEx Ground, hence the longer wait.


Clean, washed, and scrubbed down with isopropyl alcohol.


I practiced putting the fin can together today, as well (no threadlocker yet). I must say, this thing is pretty high on my list of "sexiest rocket parts I've ever used!"
Admittedly I had a bit of difficulty at first, until I realized I was putting the screws in wrong.

How are you accessing PB switches when they are in the nosecone?


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dixontj93060 said:

How are you accessing PB switches when they are in the nosecone?


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Probably through the NC shoulder/AF via a hole that has been drilled and maybe even utilizing a vent hole located in the shoulder/AF… seeing as he has baro based flight computers.

A5tr0 An0n said:

Probably through the NC shoulder/AF via a hole that has been drilled and maybe even utilizing a vent hole located in the shoulder/AF… seeing as he has baro based flight computers.

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Well yes, but NC sampling ports and Mach+ flights don't mix well.

dixontj93060 said:

Well yes, but NC sampling ports and Mach+ flights don't mix well.

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That is true, the pressure can throw off the computer. I know that the SL100 (which he has) will do fine. I have taken that to M2.5 with it housed inside the nose cone and vented via the shoulder/AF. The soft mach lockout tends to work decently well, it appears. Also I know that Nic and Mike both used the SL100 on their M3+ flight with no reported issue. The data might be a little off though in certain spots. I cannot speak for his other computer however.

dixontj93060 said:

How are you accessing PB switches when they are in the nosecone?

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A5tr0 An0n said:

Probably through the NC shoulder/AF via a hole that has been drilled and maybe even utilizing a vent hole located in the shoulder/AF… seeing as he has baro based flight computers.

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Yep, vent/access holes in the nosecone shoulder. (In conjunction with the airframe.) I need holes there, anyways...

A5tr0 An0n said:

That is true, the pressure can throw off the computer. I know that the SL100 (which he has) will do fine. I have taken that to M2.5 with it housed inside the nose cone and vented via the shoulder/AF. The soft mach lockout tends to work decently well, it appears. Also I know that Nic and Mike both used the SL100 on their M3+ flight with no reported issue. The data might be a little off though in certain spots. I cannot speak for his other computer however.

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This was a concern of mine as well. However, I believe that with the flight computers I am using I will be in good shape. (Especially the Stratologger, like you mention.) The RRC2+ is also mach-immune.

AlnessW said:

View attachment 181403
I practiced putting the fin can together today, as well (no threadlocker yet). I must say, this thing is pretty high on my list of "sexiest rocket parts I've ever used!"
Admittedly I had a bit of difficulty at first, until I realized I was putting the screws in wrong.

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That's the first time I've heard of that. What were you doing wrong so we can maybe address that in the instructions?

Binder Design said:

That's the first time I've heard of that. What were you doing wrong so we can maybe address that in the instructions?

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Probably just me being a dingbat but I was installing the screws backwards - that is, I was putting them into the threaded side of the hole first.

AlnessW said:

Probably just me being a dingbat but I was installing the screws backwards - that is, I was putting them into the threaded side of the hole first.

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That is a good one! The threaded side is a press nut aka pem nut. According to a mechanical engineer, when a nut is utilized as a fastener, the materials being fastened go between the bolt head and the nut.

I might add something in the instructions to show the orientation.

Binder Design said:

That is a good one! The threaded side is a press nut aka pem nut. According to a mechanical engineer, when a nut is utilized as a fastener, the materials being fastened go between the bolt head and the nut.

I might add something in the instructions to show the orientation.

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Exactly! When you said you had never heard of that I figured it was a simple step I was overlooking... Given that I'm no mechanical engineer, not a real surprise I didn't think of "the materials being fastened go between the bolt head and the nut." Although... I get it now.

Speaking of which, how do those press nuts work, exactly? Are they embedded into the sheet metal?

AlnessW said:

Speaking of which, how do those press nuts work, exactly? Are they embedded into the sheet metal?

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They are pressed into the metal. Pem nuts have teeth that dig in to the perimeter of the hole. They are used in thin sheet metal where threads in the material would not be structural enough, and regular hex nuts may not be accessible for tightening.

They are used in the fin cans because they provide a lower drag profile then regular nuts and you don't have to try to put a wrench on them while tightening a screw. One drawback...They are expensive. The nuts for the 4" fin can run ~ $10 per can. Regular nuts would be under $1 per 4" fin can.

Binder Design said:

They are pressed into the metal. Pem nuts have teeth that dig in to the perimeter of the hole. They are used in thin sheet metal where threads in the material would not be structural enough, and regular bolts may not be accessible for tightening.

They are used in the fin cans because they provide a lower drag profile then regular nuts and you don't have to try to put a wrench on them while tightening a screw. One drawback...They are expensive. The nuts for the 4" fin can run ~ $10 per can. Regular nuts would be under $1 per 4" fin can.

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Interesting stuff! Thanks for sharing and I can't wait to fly this thing.

Did some ground tests last weekend. The drogue charges will be housed in nitrile glove fingertips, so they will not be affected by lack of oxygen at 30K. Ground tested and determined that 3 grams is perfect to cut the 3 x 4-40 nylon screws on the nosecone. I may add more since I have a long harness and will want to make sure I have enough pressure for separation. Oh yeah, and a big backup charge...

I also did a static test of the Tender Descender/main chute release system. It worked perfectly. Now I just need to make sure my ematch wires won't get pulled loose on drogue descent. 4 days and counting...

30k isn't high enough to matter, but "glove fingers" won't provide sufficient containment at high altitude.
Current BKM is to use surgical tubing and glue/wire-ties to close.

FredA said:

30k isn't high enough to matter, but "glove fingers" won't provide sufficient containment at high altitude.
Current BKM is to use surgical tubing and glue/wire-ties to close.

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How so, exactly? I know surgical tubing is preferred for higher altitudes, but is it because it's heavier duty material?

AlnessW said:

How so, exactly? I know surgical tubing is preferred for higher altitudes, but is it because it's heavier duty material?

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You can more completely seal it using hot glue.

AlnessW said:

How so, exactly? I know surgical tubing is preferred for higher altitudes, but is it because it's heavier duty material?

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Surgical tubing will likely be better than the glove finger because there will be at least some containment. For 30K, I would increase the BP by 30% or so, but using 4 grams with surgical tubing is difficult because the charge gets too long. You should really be using some sort of hard-sided container.

By the way, for high altitude, surgical tubing is by no means BKM.

Jim

By the way, for high altitude, surgical tubing is by no means BKM.

OK Jim, teach us what you consider the [hobby] BKM for high altitude -- say 100k AGL....

FredA said:

By the way, for high altitude, surgical tubing is by no means BKM.

OK Jim, teach us what you consider the BKM for high altitude -- say 100k AGL....

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Better Known Method, perhaps, is sealing the entire parachute bay at ground level pressure... no need for any more containment than you do on a low altitude flight. But that requires designing the whole rocket around that principle.

FredA said:

By the way, for high altitude, surgical tubing is by no means BKM.

OK Jim, teach us what you consider the [hobby] BKM for high altitude -- say 100k AGL....

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I guess the surgical tubing (or maybe CO2?) might be the best known method, but it isn't (IMO) the best of the known methods.

Assuming you're asking for my opinion of the best method, I can start by telling you what I do at high altitude, which is described in the attachment. This was a Rockets Magazine article in June 2011, which I updated to reflect the method I currently use. My apologies for posting this for the nth time.

I'm pretty sure my method isn't the best of the known methods because it is too energetic. I refer to it as deployment by shotgun because every spec of BP burns (really fast). Then again, about 1.5 grams of BP will open up a 4" rocket at 100K, and I'm pretty sure that a surgical tubing charge won't work there. I suspect there are methods using a sealed, hard-sided container that more optimized than what I do, and might not be much different from what a lot of guys do now.

Jim

View attachment Article on high altitude deployment charges_May 2013.pdf

sorry for the video in the middle of your build thread. I can't seem to post just the link....


AeroPac's 100K project went to 104K. Recovery was via it's back up charges. The back up charges were 2 grams 4F in surgical tubing. The main charges, CO2, failed to puncture the CO2 cylinders. In the video you can hear the primary charges fire, but nothing happens.

Found the video...deployment is at 2:10 [video=youtube;krNFHr2YZBY]https://www.youtube.com/watch?v=krNFHr2YZBY[/video]

Ryan an David went to 63K at Mudroc. Those charges were 3 grams IIRC and we used 2 zip ties on each end. The tube we used was https://www.mcmaster.com/#5234k99/=tcun2z

Tony

My belief with the surgical tube method is that if you increase the size of the charge, and if the tube and recovery equipment is packed tightly (which it typically would be), you can get enough of the powder to fire to separate the rocket even if all the powder doesn't burn. The problem I have is that you have to guess those factors and you cannot ground test to verify the setup.

Jim

Interesting stuff, but... I ask again: Why is surgical tubing preferred to glove fingertips? Stronger?

I'm only going 14K this weekend and am using 3 grams for the drogue, with a 6 gram backup charge...

AlnessW said:

Interesting stuff, but... I ask again: Why is surgical tubing preferred to glove fingertips? Stronger?

I'm only going 14K this weekend and am using 3 grams for the drogue, with a 6 gram backup charge...

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More stretch = less containment with the glove.

dixontj93060 said:

More stretch = less containment with the glove.

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Interesting!

AlnessW said:

Interesting stuff, but... I ask again: Why is surgical tubing preferred to glove fingertips? Stronger?

I'm only going 14K this weekend and am using 3 grams for the drogue, with a 6 gram backup charge...

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Wilson, I'm kind of curious about the sizes of the charges you are using. In my 3" rockets, I don't believe I've ever used more than about 1.3 grams of BP in any of them. I assume you've ground tested your 3 and 6-gram charges (glove finger charges?) and that they give appropriate deployment for your rocket? If yes, I wonder if you're actually getting all of the powder burned? Or, perhaps you're just a member of the "blow it out or blow it up" club.

Jim