Ye Olde Rocket Forum

Go Back   Ye Olde Rocket Forum > Work Bench > Projects
User Name
Password
Auctions Register FAQ Members List Calendar Today's Posts Search Mark Forums Read


Reply
 
Thread Tools Search this Thread Display Modes
  #21  
Old 06-07-2005, 02:20 PM
CPMcGraw's Avatar
CPMcGraw CPMcGraw is offline
BARCLONE Rocketry
 
Join Date: Mar 2005
Location: Mobile, Alabama
Posts: 5,355
Default

Quote:
Originally Posted by Tweener
Craig,

I noticed that the "E" ThunderRoc Clone rocksim launch guide data says "User specified minimum velocity for stable flight: 43.9993 ft/sec". Is this something you input or does the program somehow arrive at that figure? If it was input, how was it arrived at? Just wondering because the sim says my 'D' launches shouldn't have been stable for a little over 4" past the 36" rod that I was using.

Bill,

What length rod did you use on your 'E' flight?

Excuse me if I seem a little slow, but after all this IS rocket science!


Tweener,

RockSim either calculates a value here, or there is a "pre-set" value in the program. I believe I can change that value, but I did not select that value. I've just run the simulations with mostly default values. What I did change was the temperature at launch time, the launch guide length (note, this doesn't necessarily mean a rod), and the Latitude of the launch site.

Craig...
Reply With Quote
  #22  
Old 06-08-2005, 12:08 AM
Tau Zero's Avatar
Tau Zero Tau Zero is offline
Incurable SEMROC Fan
 
Join Date: Mar 2005
Location: Twin Falls, Idaho, USA
Posts: 2,034
Thumbs up Pig(skin) Kickin'

Quote:
Originally Posted by CPMcGraw
Kick A Pig should have been posted in the other thread, but it's here for Jay...
"Heh heh, heh heh... Hey, Beavis. Let's go kick a pig!"


Quote:
My other first thoughts were to make it look like a football, with laces and everything. I might come up with a Flying Pigskin a little later...

...I've got to get that one to spin off the rod, though...

...Maybe a two- or three-motor cluster, with tilted mount tubes, and have the rod going right through the center...
Your football comments reminded me of the following Pigskin-inspired rocket designs from EMRR:

http://www.rocketreviews.com/virtual_contest5.shtml

http://www.rocketreviews.com/reviews/descon8/ncaa.html


Quote:
See what you've made me do, Jay!!???

This "thinking" stuff really is dangerous!
(modestly) Yeah, well, it's the least I can do. As a TV reporter/cameraman, I seem to have an incurable Analytical condition. --No, it has nothing to do with things gastro-intestinal.


Cheers,

--Jay
Reply With Quote
  #23  
Old 06-08-2005, 12:45 AM
A Fish Named Wallyum's Avatar
A Fish Named Wallyum A Fish Named Wallyum is offline
BP Mafia
 
Join Date: Mar 2005
Location: Ft. Thomas, KY
Posts: 6,944
Default

Quote:
Originally Posted by Tweener
Bill,

What length rod did you use on your 'E' flight?


I think ours is about a four footer.
Reply With Quote
  #24  
Old 06-08-2005, 01:33 AM
Carl@Semroc's Avatar
Carl@Semroc Carl@Semroc is offline
Junior ??? Rocketeer
 
Join Date: Mar 2005
Location: Knightdale, NC
Posts: 1,470
Default

Quote:
Originally Posted by Tweener
Craig,

... data says "User specified minimum velocity for stable flight: 43.9993 ft/sec".

That converts to 30MPH. At some point in the past, someone determined that 30MPH was the minimum velocity for stable flight. In 1961, Vern Estes designed a wind tunnel (TR-5) that produced 22 fps air flow and said it was "ideal for stability tests." G. Harry Stine in his first edition used the figures 30-40 MPH not as a minimum, but as typical.

I think RockSim is very conservative. Minimum velocity varies with the geometry of the rocket. Maybe RockSim needs a plug-in to CALCULATE the minimum velocity and launch rod length.

Another consideration for launch rod length. It should be measured from the bottom of the lowest launch lug to the top of the launch rod. Many taller rockets with launch lugs high up the side and engines raised off the blast shield only have an effective usable length of 2 feet from a 3 foot rod.
__________________
Carl McLawhorn
NAR#4717 L2
semroc.com
Reply With Quote
  #25  
Old 06-08-2005, 03:09 PM
Tweener's Avatar
Tweener Tweener is offline
Out To Launch
 
Join Date: Mar 2005
Location: Ottawa, Ohio
Posts: 281
Default

Thanks Carl,

My gut-feeling was that an over-stable design like the Thunder Roc wouldn't need much velocity at all to keep headed in the right direction - as long as it was still accelerating. I can't wait to try that Aerotech E15!

BTW, my order for a set of laser-cut fins will be in as soon as I decide what else I need/want to make at least a minimum order.
__________________
John Lance Ladd
Yoyodyne Propulsion Systems
Grovers Mill, NJ
Established 1938
lladd.netau.net
Reply With Quote
  #26  
Old 06-13-2005, 05:02 AM
A Fish Named Wallyum's Avatar
A Fish Named Wallyum A Fish Named Wallyum is offline
BP Mafia
 
Join Date: Mar 2005
Location: Ft. Thomas, KY
Posts: 6,944
Default

I built the motor mount and fin can for the Thunder Roc this weekend, but decided to order a BT-60 ejection baffle from Flis Kits to replace the tube coupler in the middle of the two uppermost BT-60 sections. This T-Roc should be quite a bit lighter than my first clone because I cut out the epoxy clay, basswood fins and huge nylon chute right off the bat. Next launch is in two weeks. (I was "under the weather" this weekend. In a completely different way than Craig was. )
I also ordered several other parts, including a "complete" set of the canted cluster mounts. They now stock them in 13mm, 18mm and 24mm for BT-50(?), BT-60 and BT-70 respectively. Not sure what project they'll become a part of at this point, but that's part of the fun. (Although that dual 24mm BT-70 mount sounds like it would make an a$$-kicking SPEV for starters.)
__________________
Bill Eichelberger
NAR 79563

http://wallyum.blogspot.com/

I miss being SAM 0058

On the build floor: Centuri Stellar Hercules, Semroc SLS Scorpion, Semroc Squire, RDC V-Max

Ready to fly: Estes Astron Farside X, Estes Astron Apogee, FRW Marauder XL, FRW Star Jart, Semroc Cherokee D
Reply With Quote
  #27  
Old 06-13-2005, 08:43 AM
Tweener's Avatar
Tweener Tweener is offline
Out To Launch
 
Join Date: Mar 2005
Location: Ottawa, Ohio
Posts: 281
Default

Quote:
Originally Posted by A Fish Named Wallyum
I built the motor mount and fin can for the Thunder Roc this weekend, but decided to order a BT-60 ejection baffle from Flis Kits to replace the tube coupler in the middle of the two uppermost BT-60 sections.

That was my thinking exactly. Kill two birds with one stone, so to speak. The added mass would only be the perforated bulkheads, since the coupler's needed anyway. The only concern I'd have is that only half the baffle is effectively anchored in the tube against the ejection pressurre. Make sure it's glued 'real good'.
__________________
John Lance Ladd
Yoyodyne Propulsion Systems
Grovers Mill, NJ
Established 1938
lladd.netau.net
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump



All times are GMT -5. The time now is 08:27 PM.


Powered by: vBulletin Version 3.0.7
Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
Ye Olde Rocket Shoppe 1998-2019