Question about Dr Rocket motor casings.

I am new to high-powered rocketry and want to learn everything I can about it before I start buying stuff. I've read "Modern High-Power
Rocketry" cover to cover and curiously the quesiton I have was never mentioned. On Dr. Rockets casings (and others that use screw-in end closures I assume) the end closures are somewhat larger in diameter than the casing itself. I guess I have two or three questions. 1. Is the "38mm" on a 38mm motor for instance, the diameter of the case, the end closures, or the reload? 2. On some of the casings it looks like the head-end closure is larger than the casing but the nozzle-end one is not. How do you keep the motor in alignment with the airframe? I'm sure you could build some sort of adapter but as I've never seen anything of the sort mentioned I'm guessing I must be missing something. Any help would be appreciated.
-Scott Ferrin
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Scott Ferrin wrote:

Scott,
What you're likely seeing as the nozzle end is probably the forward delay/ejection well.
What you're calling the "head-end closure" is the aft closure. Its oversize outside diameter keeps the motor from sliding up though the rocket. Basically, the motor imparts thrust to the rocket via this ring. It's essentially the engine block. The nozzle is disposable, and will protrude aft thru this closure when the motor is assembled.

38mm is the nominal outside diameter of the motor case and the nominal inside diamter of the rocket's motor mount tube. An actual number is 1.525" inside diamter for some of the common 38mm MMT's. The 38mm motor case will be slightly smaller than that.
HTH. Doug
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wrote:

Yep that's exactly what was happening. I *was* thinking "damn that a small nozzle on the M1939 :-)

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If you have a chance, go to Aerotech's web site, and download their assembly video of the 29/40-120. It's not a high power case, but assembly is basically the same. It will answer many questions you might have.
David

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The problem is they use Spyware Quicktime for their videos. I get a pop-up from SpySweeper catching a configuration program from Quicktime that has loaded into my startup file WITHOUT asking my permission.
Sysweeper has detected new programs that will start when Windows starts. ...
Quicktime task: assessment unknown
Aerotech needs to change their video format.
--
...The Bit Eimer NAR 84054
"My goal in life is to be the kind of person my cat thinks he is"
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On Mon, 1 Nov 2004 08:35:46 -0700, "bit eimer"

More than likely, it's just trying to download a CODEC. I can play the videos & the spyware checkers haven't detected anything.
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bit eimer wrote:

I think SpySweeper is full of it -- I don't get those kinds of alarms on my system, and nothing I run complains about QuickTime being "Spyware".
-Kevin
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<snip>

I have since searched around and it appears that the main issue with QT is that it tries to "take over" file extensions in the system. Anyway, I've found an alternative - conveniently called QuickTime Alternative - which has no such issues.
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bit eimer wrote:

There's an option in QuickTime (just like in many programs) that lets you tell it whether or not you want it to notify you if something else tries to take over file associations. MOST (but not all) programs have this; I tell most of them NO, and they behave quite nicely. Including QuickTime.
-Kevin
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On Mon, 01 Nov 2004 19:36:01 -0600, Kevin Trojanowski

What I find humorous is that he wants to keep the association to the program that DOESN'T work.
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wrote:

Believe it or not I've read the assembly instructiions in "Modern High-Power Rocketry" several times. I figured since I'd never read anything about a problem fitting motors or dealing with what I *thought* was the head end flange that I had to have been mixed up somewhere. Thanks for the link (another individual emailed it to me too). That's exactly what I needed.

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