This isn't a problem Mike and I can easily accomodate you on this, however be aware that this makes the motor officially "uncertified" and while NCR usually doesn't make an issue of these things other clubs may do so.

Warren

Warren is correct, by doing what you want to do with the closure then any motor using that closure is officially "modified" and is no longer a certified motor. Research launch only, NCR and TC have plenty of them. Those are TRA rules.

Art

I understand the sentiment here, and for my TRA records I never used modified closures. In fact, in retrospect, there were no "closures" as they were single use motors. I have flown tailcones on some other rockets.

That aside, I wonder... did Rouse certify tapped and untapped forward closures? Plugged vs. unplugged? (i.e. closures suitable for motor ejection). My guess is that Rouse, Dr. Rocket, etc. did NOT certify all closures. If they didn't, then I don't see why an aft closure that is smoothed down should be tossed out.

Along the same lines -- If you fill the knurling with putty (so it is smoothed out and creates less drag) is it "modified"? I don't know. It would be an interesting question of TRA.

You might give Mr. Rouse a call. I thought I read something on TRF about him doing an aft closure with the OD matching the tubing, specifically for staged projects, but it didn't go to market. I'll try to find the thread.

Ken

I contacted Tom Rouse and he said they make flush rear closures and they are currently in stock and do not affect the certifications.

I also contacted Robert DeHate at AMW about removing their aft thrust ring and that is OK as well.

So... the need for this thread no longer exists, other than as a reference for others that are wishing to do the same thing. I don't need any special machining or exo-couplers at this time.

Thanks for everyone chiming in.

By the official rules, ANY modification of a motor casing or closures is forbidden. This means that the many flyers who have drilled and tapped plugged forward closures for eyebolts or who have had custom rear closures made or turned down from factory closures are essentially flying "illegally".

If a manufacturer makes the part, it's OK - if you make it, NOT OK. That said, no one is checking on such things and the rule is in place to make Tripoli's and NAR's insurance companies happy.

However, such things as custom rear-closure tailcones, while not a problem at NCR launches can be a big problem at other launches if the RSO is a stickler for the rules and if used in the context of a contest, might cause some grumbling from those flying without such an advantage. I would expect this to be a particular problem with NAR contests.

Again, all that said, I will gladly turn down the knurling on rear closures or center drill and tap plugged forward closures for eyebolts.

Warren

Happy to have helped out. Thanks Mike.

I emailed Tom Rouse to see if I can get some flush aft closures in 38mm. They would be not only good as a sustainer coupler, but should help with base drag in altitude shots.

With a flush aft closure, it should also be possible to make a miminum diameter rocket with an integrated tailcone, into which the motor is loaded from the front. 🙂

Instead of front loading, wouldn't it be easier to turn down the retainer to a tailcone and then fly it on a research day?

Edward

If I had a lathe, I might be tempted. But mostly I'd like to use a certified motor so that I can set a record. I think the I and J records are do-able with our launch site and existing 38mm motors.

Tom said that What's Up hobbies has the flush rear closures in 38mm. They're not on their website so I'm emailing them.

Update: What's up hobbies does not have them. I bounced the question back to Tom. We'll see if these are made of unobtanium or if it's a real product that someone can in fact purchase.

turning an aft closure flush to the AF does not make a motor "not certified". As long as you do not do anything to the temper of the AL and do not change anything can change the way a motor works you are fine. I think that some of the NAR rules get caught up in others rules and things get polluted. You can not do anything that could weaken the motor case or closures. An example would be welding fins on to a case. If you have the machine and the skills then change you aft closure, if not let someone that does.

I don't know if he reads the forums or not, but Dennis Billings would be the one to talk to.

I have precision lathe capabilities up to 8" diameter and 13" long. I'm more than happy to turn factory closures down. Not so happy to make one from scratch since I've haven't learned how to thread things yet..

Personally and not to dispute James, my understanding is that any modification of the motor case or either front or rear closures makes the motor uncertified and therefore not legit. I may be wrong, but I'd like to hear a member of the BOD or Paul Holmes tell me that before I was sure. Definitely not trying to dispute James, but the way I read and hear the rules is that if you mod a motor case and closures in ANY way, they're uncertified. My logic says it ain't right, but many clubs apparently take it exactly that way.

...fortunately, NCR ain't one of 'em. I'd do that if I were you and just make sure it don't blow up in TOO spectacular a manner when the media are about.

W

I don't know if he reads the forums or not, but Dennis Billings would be the one to talk to.

Not sure who Dennis is but the person that makes the call on things like this for TRA is Paul Holmes and if there is any question then it would go to the BOD or maybe the TAP.