Scratch Built Speed Demons

The other thread going has gotten me thinkkng and lead to some questions.

1. If a person got a coupler for 38mm tubes to use as a mandrel for an all CF frame, would they need to add a couple of wraps of something to add just a smidge to the diameter to give room for the motor to actually slide into the airframe?

2. (I know this could vary widely, but...) what kind of wall thickness is common per layer of CF?

3. On a minumum diameter rocket, what do you do about the rear closure of the motor that extends beyond the OD of the BT?

Attached is a file that I came up with tinkering around.
The BT "ring" at the rear is to simulate that knurled rear closure on AT motors.
Of course, I simmed it using a Cessaroni.
Depending on whether I kept it at minimum weight (mass) for speed or optimal weight for altitude, I think I got good numbers either way.
It'd probably shred, but that's why one does it in RS; costs less money.

Answers to the questions or ideas on the rocket would are sought,

Greg

Originally posted by 11Bravo
The other thread going has gotten me thinkkng and lead to some questions.

1. If a person got a coupler for 38mm tubes to use as a mandrel for an all CF frame, would they need to add a couple of wraps of something to add just a smidge to the diameter to give room for the motor to actually slide into the airframe?

2. (I know this could vary widely, but...) what kind of wall thickness is common per layer of CF?

3. On a minumum diameter rocket, what do you do about the rear closure of the motor that extends beyond the OD of the BT?

Attached is a file that I came up with tinkering around.
The BT "ring" at the rear is to simulate that knurled rear closure on AT motors.
Of course, I simmed it using a Cessaroni.
Depending on whether I kept it at minimum weight (mass) for speed or optimal weight for altitude, I think I got good numbers either way.
It'd probably shred, but that's why one does it in RS; costs less money.

Answers to the questions or ideas on the rocket would are sought,

Greg

Click to expand...

1. They would need to add something to get the CF to release from the mandrel. This would server that same purpose. Two wraps of wax paper does the job for me. Comes very clean off the mandrel. Off the ID, not so easy. Takes some work, but work it does. But that's the price of cheap.

2. Best I can say (no calipers) is "about like Kraft paper". Nosecones fit the ID fine and there's no lack or excess on the OD any worse than with the variations in Kraft tube. This is all single layer. Don't know if double layer is twice, more or less. BTW, I've never used any shrink tape, vacuum, or heat curing on mine. I also tend to use plenty of outside coating, so they may be coming out thicker than otherwise (ie. might be less than paper 'naked').

3. I use a Slimline with larger RMS and minimum diameter , so that's not an issue, but it does shift the lip issue up to the top of the Slimline. I fillet that with JB Weld. One smaller (24 and 29mm) ones I use a motor hook and tape/friction fit with SU motors. Not willing to risk RMS on very high perf flights. You could use either JB Weld or epoxy putty to build a motor block around the base of the tube. In any case, be careful of the lugs/buttons/rail guides. They'll need to stand off so as not to catch on the motor lip or other device.

Crap; forgot about the buttons needing to clear the closure.
Crap.

Greg

Originally posted by 11Bravo

1. If a person got a coupler for 38mm tubes to use as a mandrel for an all CF frame, would they need to add a couple of wraps of something to add just a smidge to the diameter to give room for the motor to actually slide into the airframe?

2. (I know this could vary widely, but...) what kind of wall thickness is common per layer of CF?

Click to expand...

1. No, your tolerances should be ok. Because you are using the OD of the coupler, the ID of your tubing should always work ok. May have some thermal effects to deal with between the phenolic and carbon, but you can always sand down the phenolic a little bit.. And like Dynasoar your ID of the carbon tube will be about 5-10 mils off from the coupler due to your release.

2. One layer of 5.8 oz/yd2 (standard weight carbon or 3k) or 2" Carbon Aerosleeves should be somewhere in the .015"-.020"range. With any type of tape or bagging layup can reduce to probably .010" or so. 2 layers of CF for a 38mm should be sufficent for "standard" rockets, no J350 or J570 min diameters, etc.. For something "non standard" 3-4 layers or more.

By the way, be sure to check out Aerosleeves new Tutorial. It contains a lot of new info an good techniques for design and making composite tubes.

https://www.aerosleeves.com/tut.php

Nick Anderson

Nick-
I saw the new tutorial last week when I placed my order.
I ordered on Wednesday night I believe and got the stuff on Mondya, great fast shipping.
One question on the sleeves- when one removes the taped ends how does one stop them from unravelling?
AAAAGGGGHHHH!
Also, what would be a good way to cut them to length?
With them fraying so fast I would think scissors would not be optimum; how well do those roller cutters work?
Can't wait to actually try galssing, whenever I can get my buddy to drive the 2.5 hours up here to help.

Greg

More tape! Thats why we ship them with taped ends. Otherwise by the time you get them, half the sleeve would unravel during the shipping process.

We use the easy release blue painters tape. You may be able to soften up the adhesive with heat and possibly pull it off. I would just cut prior to sliding it over. We include enough "extra" per yard to account for losses you see at the end.

Should have gotten to on saturday, but our internet was down on thursday and couldn't print USPS labels online.

Nick Anderson