Aluminum tubing for coupler?

[SolarYellow]

I am planning a build that will be MPR/HPR H/I power with LT-125. That's 1.25" ID and 1.34" OD. No coupler material is currently available for that. It's probably possible to cut down some BT-55 coupler (split and reglue). However, I'm pretty sure I have some 1.25" OD, 0.035-wall 6061 tubing sitting in a box in my garage that will likely never get used for anything else. It's strong enough and light enough and the right size without doing any more work except cutting it to length.

We use aluminum for motor cases. Would a 3-inch long section of this tubing used as a coupler/ebay without any pressure containment trespass on the safety code prohibition against metal airframes/nosecones/fins/etc.?

 

[Steve Shannon]

It would violate NFPA 1122, the Safety Code for model rockets. It would probably be allowed for high power use. But it’s easy to make your own by rolling up craft paper or turning a piece of balsa. Think old school.

 

[OzHybrid]

Throws up the interesting question "is an aluminium cased motor a violation of the LPR code?"..........Are we just using an approved motor or is the casing part of the construction?........

 

[tsmith1315]

I am planning a build that will be MPR/HPR H/I power with LT-125. That's 1.25" ID and 1.34" OD. No coupler material is currently available for that.

T52H/29mm motor tube is 1.210" OD. IIRC, LPR coupler is typically .003" smaller than the body tube ID. That should be close enough to work.

 

[DigBaddy]

T52H/29mm motor tube is 1.210" OD. IIRC, LPR coupler is typically .003" smaller than the body tube ID. That should be close enough to work.

That plus a wrap of paper and it should be basically perfect, and nothing to worry about materials-wise.

 

[jhill9693]

LT-115 works as a coupler. It’s the tubing used for 29mm motor mounts. Build it up slightly with masking tape.

Or, go balsa. I’ve done it with that tube. Works great!

 

[SolarYellow]

Might do that. Would make a 0.055-wall coupler (same as 38mm MMT), which would be nice and beefy for a 0.045-wall tube. I've been looking at wrapping other components this week; once I pick materials and methods, I can branch out.

Might also just 3D print an ebay and use that for a coupler.

 

[Rob Campbell]

Throws up the interesting question "is an aluminium cased motor a violation of the LPR code?"..........Are we just using an approved motor or is the casing part of the construction?........

No. Motor cases are made from aluminum because in the event of an overpressure failure, an aluminum tube will split and not fragment and send shrapnel flying.

 

[OzHybrid]

No. Motor cases are made from aluminum because in the event of an overpressure failure, an aluminum tube will split and not fragment and send shrapnel flying.

The LPR not HPR code states that only cardboard or plastic etc shall be used....... Then you get the aluminium cased 24 and 29mm reloadables from Aerotech.
The HPR code allows ductile metal as required for strength.....

Motors are excluded from the rocket construction definition. It's in one of the NFPA docs. Then you get the Tripoli rules that prevent the use of steel in a motor, unless it's a sugar motor and it's for the NOZZLE ONLY and the Nozzle is recessed into the aluminium motor tube..

All rules must be read together. etc etc.

 

[kjhambrick]

I am planning a build that will be MPR/HPR H/I power with LT-125. That's 1.25" ID and 1.34" OD. No coupler material is currently available for that.
It's probably possible to cut down some BT-55 coupler (split and reglue). << snip>> ...

@SolarYellow --

For the record, LT-115 or BT-52H ( aka 29mm motor mount tubes ) and a little tape work pretty well as couplers / av-bays / motor mount tubes for the LT-125 airframe.

I am curious though ... What are you doing for a nose cone ?

Thanks !

-- kjh

 

[SolarYellow]

I have a pack of PNC-56s. Might cut the shoulder off and print a new shoulder/ebay or just reverse-engineer the shape and print an all-new cone. And there's another shape that will definitely be printed because it's NLA in RealSpace.

 

[David Schwantz]

M2050 X uses a stainless steel forward seal disc in the motor.

 

[David Schwantz]

Aluminum and copper may be used in construction of the airframe and it is left up to the builder to decide.

 

[cwbullet]

Aluminum and copper may be used in construction of the airframe and it is left up to the builder to decide.

Good info thanks.

 

[David Schwantz]

It is in the safety code under metal in airframe . But alas, I cannot log in as it states my password is bad. I was going to post it again. Chuck, feel free to do so if you want to. Thanks.

 

[kalsow]

But alas, I cannot log in as it states my password is bad. I was going to post it again.

Posting your password won't make it any better.

 

[David Schwantz]

https://s3.amazonaws.com/ClubExpres....0.pdf&Signature=dRoGwMfVeeJKUReQIUT5B/wJ06g=

 

[David Schwantz]

OMG Bill, I thought you had my password and I was just going to ask you for it")

 

[kalsow]

OMG Bill, I thought you had my password and I was just going to ask you for it")

Geez, I suppose you'd want your bank account and credit card numbers too....

 

[David Schwantz]

If you would please!!!!!!

 

[SolarYellow]

https://s3.amazonaws.com/ClubExpres....0.pdf&Signature=dRoGwMfVeeJKUReQIUT5B/wJ06g=

Link looks to not be working. At least it takes me nowhere.

 

[David Schwantz]

works when I click on it. It might be that you need to be logged into your Tripoli account as it is in member info. Give that a try.

 

[bad_idea]

Metal in Rocket Construction

 

[Rschub]

Guess I should start buying Aluminum all-thread.

 

[David Schwantz]

Yup, that's gonna strip

 

[Titan II]

Guess I should start buying Aluminum all-thread.

Why?

 

[SolarYellow]

So it looks like I would be cool at a TRA HPR launch to use some of that old 0.035-wall, 1 1/4-inch tubing that is left over from a Miata coolant reroute to make a coupler for my LT-125, if it is "necessary." On the other hand, I'd also have to be able to make a case that it satisfies mission requirements significantly better than fiberglass, c.f., or a 29mm MMT wrapped with a couple more layers of paper. Which is a potentially hard sell for 29mm motors that don't go above I impulse.

It also doesn't really support decorative actually-aluminum fin bracket scale details on a really cool IQSY Tomahawk model. Can't really come up with a good argument why those couldn't be polystyrene, except that my inner geek likes the idea of fabbing scale details from "real" material. Unless I can sell that they are not structural, just cosmetic.

None of it would be likely to get the green light at an NAR launch and it would put me in "HPR" category even with an F motor.

 

[Rschub]