Nose cone too tight?

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Well-Known Member
May 23, 2004
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I am just finishing up a PML Tethys and I was test fitting the nose cone in to the Qunatum tube when I noticed that I could not get it in much past the first ridge. I do have a vent hole below where the shoulder is, so it is not a pressure problem. Even with the nose cone inserted 1/2 way, I could easily pick up and shake the rocket (which is at about 10 pounds) with no slippage from the nose cone. It absolutely would not go past the second ridge, even with some force. I had protected the inside of the QT with masking tape while finishing, there is no residue inside the tube. In fact, the piston slides in and out with no problems or hangups.

The only way the nose cone would even fit into the BT was to remove both ridges completely from the shoulder. Since I have not yet entered world of HPR yet (the Tethys will be my L2 attempt), and I am not familiar with the ejection forces from the Pro38 J285 I plan to use, I would like to know how tight is too tight on an HPR? With both ridges gone, the nose cone slides in easily, but now seems a little loose. I can turn the rocket upside down and the nose cone slides out about 1 inch - not all the way. Is this acceptable or should I added a little masking tape for a somewhat tighter fit?

It's mainly a feel thing, but now that you've removed those ridges, when you are at the field, pick the rocket up by the cone and shake it. If the rocket comes off before you can even get the nose cone off, add tape. It should come all the way off with a nice shake or two, if it doesn't, remove some tape. Usually one wrap will do it, but if that's too much, I sometimes use just small pieces of tape around the shoulder to hold it on better.

Wait till you get to the feild, you never no the differences in humidity (contracting and expanding) of Germany and Orangeburg:D
It's probably the Quantum tube that is a bit small. My first HPR was a Tehtys and everything fit nice. I am now building a PML Eclipse and the forward Quantum BT is smaller than the other two pieces of airframe in the kit. The nose fits in my forward tube the same as you described, but the nose that came with the Eclipse fits fine in the Tethys. The nose for the Eclpise fits fine in the other two section of BT as well. So I know PML has some smaller/tighter fitting BTs. I've cleared it deep for burrs and it still fits tight as heck.
Follow the previous suggestions to get a good fit.
Good luck w/ your L2.
I'll echo what the others are saying, and say it again: when you get to the field, do a fit check. I've found that a good fit is when you can hold the (loaded) rocket by the nose cone and it doesn't come off, but if you shake it a little bit, the rocket begins to slide apart. Shim the fit with masking tape as needed, and let 'er rip. The J285 is a great motor for the Tethys!
Thanks for the tips, I think this will work. I was hoping I could use masking tape to adjust the fit if needed. I have to think HPR, not LPR, but I am glad to hear that tricks on the little stuff can still work on the big stuff!

Now the fun part, trusting the rockets to the Postal Service so they will be waiting for me when I arrive in Orangeburg for the Freedom Launch over Labor Day weekend! If they survive the mailing, they will survive the launching!
Originally posted by joepolicy
Thanks for the tips, I think this will work. I was hoping I could use masking tape to adjust the fit if needed.

High power rocketry would not exist without masking tape :D
Originally posted by karatekicker271
Have you mailed them?

Today is the day I give my rockets up the the Postal Gods - no relation to the rocket Gods... :)
Originally posted by joepolicy
Today is the day I give my rockets up the the Postal Gods - no relation to the rocket Gods... :)

Or so you think.... They are probably in cahoots....

Good luck at Orangeburg!