Here's another burning question in my ongoing Tau Zero saga.

Sure, the outside diameter of a Semroc HTC-7 is 0.715". But how much is the INSIDE diameter?

http://www.semroc.com/Store/Scripts...p?idproduct=206


On a related note, what's the *official* (average?) Outside Diameter (O.D.) of an 18mm Estes motor?

Anybody got some digital calipers?


Inquiring minds want to know. CenturiGuy and BARCLONE are feverishly trying to figure out how to retain Estes motors inside Centuri/Semroc ST-7 tubes *without* using engine hooks, which can make Really Big Gouges in minimum-diameter tubes.


Thanks in advance,

__________________
Jay Goemmer
"Centuri Guy"/"Tau Zero"
YORF Member 28
Semroc SAM #0029
NAR 86131


"I think about organizing things all the time. Never seems to happen. I find something that piques my interest and I'm off on a quest. Or a Centuri. "

--Bill Eichelberger, 02/22/2022


“Centuri fret buzz in an updated form.”
Bill “Wallyum” Eichelberger re: Estes Flutter-By
03 Sept 2014

From the P.O. - .673 ID X .713 OD X .020 Wall 1.000" Long Fishpaper


From another PO - 2.75" LG X .500" ID X .688" OD PT HIGH BURST VIRGIN KRAFT

The .688" is the beginning tube diameter as it goes into "the machine." The sleeve is nominally 11/16" (.6875") but gets larger with wear over time. Also, depending on the moisture and compression strength, the motor can "grow" after it is ejected from the sleeve. It is not uncommon for motors to be larger than .710" when they have "cured." That is one of the reasons we always used the ST-7 size (.715") instead of the BT-20 size (.710"), because it would work with more motors. The BT-30 size was better, because it would work with ANYTHING! The nominal size as reported over the years was .690", but it is rare to find one that small.

__________________
Carl McLawhorn
NAR#4717 L2
semroc.com

Thanks for your "zippy" response, Carl!

(heavy sigh) Okay, so that's Not Gonna Work.

Next?


Cheers,

__________________
Jay Goemmer
"Centuri Guy"/"Tau Zero"
YORF Member 28
Semroc SAM #0029
NAR 86131


"I think about organizing things all the time. Never seems to happen. I find something that piques my interest and I'm off on a quest. Or a Centuri. "

--Bill Eichelberger, 02/22/2022


“Centuri fret buzz in an updated form.”
Bill “Wallyum” Eichelberger re: Estes Flutter-By
03 Sept 2014

After hashing it out offline with Carl and Craig BARCLONE McGraw, it looks like we may have to settle for using a Semroc HTC-7B connector:

http://www.semroc.com/Store/scripts...p?idproduct=207

...to firmly anchor the engine hook to the Tau Zero's ST-7, even though that means slightly reworking the inner fins' root edge to allow for the 1" long exterior coupler.

The Centuri "Bandito" used a similar technique, although the fins were folded paper:

http://www.ninfinger.org/~sven/rock...a/72cen020.html

http://www.dars.org/jimz/ka-7.htm


"--Velcome to Rocket Shyenshe."


SCIENTIST 1: "At least we're not starting from scratch."

SCIENTIST 2: "And a good thing, too, since we're fresh out of it."


Cheers,

__________________
Jay Goemmer
"Centuri Guy"/"Tau Zero"
YORF Member 28
Semroc SAM #0029
NAR 86131


"I think about organizing things all the time. Never seems to happen. I find something that piques my interest and I'm off on a quest. Or a Centuri. "

--Bill Eichelberger, 02/22/2022


“Centuri fret buzz in an updated form.”
Bill “Wallyum” Eichelberger re: Estes Flutter-By
03 Sept 2014

Jay,

Wanna avoid the gouge from an engine hook being pulled by the motor trying to kick? Try a line of glue down half the length of the engine hook, begining at the end inserted into the body tube slit, and then setting the hook into it. Once the glue dries, smear another layer of glue over it and glue a layer of paper over it so it overlaps the body tube.

Another option. Use an engine hook for an E engine. Buy coupler stock from BMS. Cut to length and install as a long engine block.

Don
NAR 53455

Don,

Once again, you are a rocketeer and a gentleman. I especially appreciate the "line of glue" technique, which I think will most likely make it into the Tau Zero instructions.

*Thank you!*


Cheers,

__________________
Jay Goemmer
"Centuri Guy"/"Tau Zero"
YORF Member 28
Semroc SAM #0029
NAR 86131


"I think about organizing things all the time. Never seems to happen. I find something that piques my interest and I'm off on a quest. Or a Centuri. "

--Bill Eichelberger, 02/22/2022


“Centuri fret buzz in an updated form.”
Bill “Wallyum” Eichelberger re: Estes Flutter-By
03 Sept 2014

Jay,

You know this is a step found in some of the earliest Estes models which used hooks, even on the internal motor tubes, and which I'll bet many of us never bothered to do?

__________________
Craig McGraw

BARCLONE Rocketry -- http://barclone.rocketshoppe.com
BARCLONE Blogsite -- http://barclone.wordpress.com
BARCLONE Forum -- BARCLONE Forum

BARs helping BARs

SAM 0044
AMA 352635

I'm blushing right there with ya, buddy.

But I guess this is all part of rediscovering rocketry, right?


Even if that means reinventing the flying wheel. ("Hey, Zeke! Get a load of *this!*")


Cheers,

__________________
Jay Goemmer
"Centuri Guy"/"Tau Zero"
YORF Member 28
Semroc SAM #0029
NAR 86131


"I think about organizing things all the time. Never seems to happen. I find something that piques my interest and I'm off on a quest. Or a Centuri. "

--Bill Eichelberger, 02/22/2022


“Centuri fret buzz in an updated form.”
Bill “Wallyum” Eichelberger re: Estes Flutter-By
03 Sept 2014

What? Is someone not "read a step, do a step"?

Don
NAR 53455

I've come across many Estes motors that had a bulge in them at the ejection end from the machine ramming the powder in. Those are the worst for trying to fit into BT-20.

__________________
Scott D. Hansen
Ye Olde Rocket Shoppe - Your One Stop BAR Shoppe!
Ye Olde Rocket Plans - OOP Rocket Plans From 38 Companies!
Ye Olde Rocket Forum
WOOSH NAR Section #558