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
  #61  
Old 01-01-2011, 12:11 PM
rocketguy101's Avatar
rocketguy101 rocketguy101 is offline
frustrated aero
 
Join Date: Sep 2006
Location: Duncan, OK
Posts: 833
Default

About the fin dimensions...I did some searching on rec.models.rockets and found a couple threads discussing the fact that it appears Estes issued two different fin patterns for this model. Kurt did a lot of detective work on this issue!

from http://groups.google.com/group/rec....7bfa950df986464

Quote:
Indeed. Bill e-mailed me, and it appears that there are *two* patterns "out there" for this kit. Bill's fins have the following dimensions:

Root edge: 2 7/16"
Leading edge: 3 9/16"
Leading tip: 1 3/4"
Trailing tip: 1"
Trailing edge: 2 5/16"

And, he says it flys stable with this geometry. Anybody know about why there might be two patterns?

and from
http://groups.google.com/group/rec....146892e1b43b770

Quote:
There was (and continues to be) confusion over the fin size, shape, and geometry, with accompanying confusion over the height of the fin ring. I hear from (I think Buzz) that he has an original kit with 2 7/16 inch root-length fins. I have a set of plans from Bob Craddock that show a fin with a root length of about 3 inches. The ones on Jim Z's site are longer.
I ended up using the 3" root-length fins that I had, mainly because I had already cut them before I discovered the other sizes. Bottom line is that it was stable in flight, probably would have been with the smaller fins too, and the small length of ring and fins that extends below the bottom of the body tube was absolutely no problem.


I created RockSim files and I think I see why Estes increased the fin size. Using the Barrowman equations, the original 2-7/16" root length fin (dimensions from the RMR post), and C6-5 engines, the static stability margin is .77 (using the RockSim equations yields 1.17). Increasing the fin size (3" root, rear overhang) yields a stability margin of 1.37 (Barrowman) or 1.65 (RS). Kurt's fin pattern offers a stabiliby margin of .86/1.27.

Attached are the RS files for both Kurt's fin and the 3" fin from JimZ. The nose is modified per my model. If anybody want to model the original BT-20/BT-60 internal structure, you are welcome to it!
Attached Files
File Type: rkt GeminiTitan_K21_KurtFin.rkt (75.0 KB, 103 views)
File Type: rkt GeminiTitan_K21_BigFin.rkt (75.1 KB, 92 views)
__________________
David Stribling
NAR 18402 SR
But it is rocket science!
Get yer Barrowmans here
Reply With Quote
  #62  
Old 01-11-2011, 07:09 PM
kurtschachner's Avatar
kurtschachner kurtschachner is offline
Master Modeler
 
Join Date: Mar 2005
Location: Southeastern Wisconsin
Posts: 1,243
Default

The drawing I did was from an actual kit, where I scanned in a ring and drew it up from that. The only thing that was changed was the pattern for the engine bells, the ones from the kit were way, way off and were unusable. IDK how that happened but it was.


Quote:
Originally Posted by Royatl
It's been my *opinion* that the holes in the aft ring are farther apart than Kurt's drawing, but a little narrower than your drawing. However, in the attachment, which is a slightly blurry photo of an actual kit part, it appears to be closer to Kurt's drawing.



The engine bells do extend past the aft former ring on the engine tubes, and they do touch, or almost touch, depending on how loose or tight the builder has made the shrouds.
Reply With Quote
  #63  
Old 01-11-2011, 09:13 PM
kurtschachner's Avatar
kurtschachner kurtschachner is offline
Master Modeler
 
Join Date: Mar 2005
Location: Southeastern Wisconsin
Posts: 1,243
Default

Wow, 1997. A lifetime ago

Actually, a career ago...

Quote:
Originally Posted by rocketguy101
About the fin dimensions...I did some searching on rec.models.rockets and found a couple threads discussing the fact that it appears Estes issued two different fin patterns for this model. Kurt did a lot of detective work on this issue!

from http://groups.google.com/group/rec....7bfa950df986464


and from
http://groups.google.com/group/rec....146892e1b43b770
Reply With Quote
  #64  
Old 01-30-2011, 05:36 PM
rocketguy101's Avatar
rocketguy101 rocketguy101 is offline
frustrated aero
 
Join Date: Sep 2006
Location: Duncan, OK
Posts: 833
Default

I see many GT models painted w/ a yellow strip at the top of the booster tube. The Estes instructions don't call out a yellow stripe, and ROTW show the top of the tube to be silver. I searched NASA's website to find launch pictures of all the manned Gemini missions, and only GT-3 seems to have a stripe -- all the others are silver. I can't find a really hi-res image of GT-3, but that color almost appears to be the goldish-anodized aluminum color similar to some of the images of the Titan II in the missle tube. I have attached a montage (L-R GT-3 to GT-12).

Anybody know why the yellow stripe is on many models?
Attached Thumbnails
Click image for larger version

Name:  GeminiLaunchMontage.jpg
Views: 117
Size:  123.7 KB  
__________________
David Stribling
NAR 18402 SR
But it is rocket science!
Get yer Barrowmans here
Reply With Quote
  #65  
Old 01-30-2011, 06:28 PM
jharding58's Avatar
jharding58 jharding58 is offline
Master Modeler
 
Join Date: Apr 2007
Location: Kennesaw, GA
Posts: 1,936
Default

It is only on a GT-3. If you look at the serial number on the airframe it must be 12558 if it is manned. The Grissom/Young mission was the only manned airframe which carried the marking. Gemini 1 and 2 also had the band, but GT-3 was the last to carry it. David Weeks has it on his drawings from RealSpace, but I am not sure how he documented the band. I long thought is was a radio transparent section much like a radome. I replicate the band using a 1/2" stripe of Microscale Dark Dulux (TF-39)
Attached Thumbnails
Click image for larger version

Name:  DSC_7138.JPG
Views: 132
Size:  195.9 KB  Click image for larger version

Name:  pg.jpg
Views: 128
Size:  86.7 KB  
__________________
Gravity is a harsh mistress
SAM 002
NAR 91005
"The complexity of living is eminently favored to the simplicity of not."

Last edited by jharding58 : 01-30-2011 at 06:52 PM.
Reply With Quote
  #66  
Old 02-27-2011, 04:42 PM
rocketguy101's Avatar
rocketguy101 rocketguy101 is offline
frustrated aero
 
Join Date: Sep 2006
Location: Duncan, OK
Posts: 833
Default

Finished painting the GT--I used an ink-jet decal for the interstage detail and "United States". Its not perfect, but I am pretty happy with it!

I used Kurt's recommendations about the fins, used Lexan from Tower Hobbies, and Weldon #16 to glue it all together.
Attached Thumbnails
Click image for larger version

Name:  GTII_woFins.jpg
Views: 154
Size:  109.5 KB  Click image for larger version

Name:  GTII_w_Fins.jpg
Views: 143
Size:  107.1 KB  Click image for larger version

Name:  DSC_2914MR.jpg
Views: 159
Size:  135.9 KB  
__________________
David Stribling
NAR 18402 SR
But it is rocket science!
Get yer Barrowmans here
Reply With Quote
  #67  
Old 02-27-2011, 07:12 PM
Bill's Avatar
Bill Bill is offline
I do not like Facebook
 
Join Date: Sep 2008
Location: North Tejas
Posts: 3,087
Default

Quote:
Originally Posted by rocketguy101
Finished painting the GT--I used an ink-jet decal for the interstage detail and "United States". Its not perfect, but I am pretty happy with it!

I used Kurt's recommendations about the fins, used Lexan from Tower Hobbies, and Weldon #16 to glue it all together.



I don't know what you are talking about; it looks very good to me.

How thick is your Lexan? How did you cut it? Score and break?


Bill
Reply With Quote
  #68  
Old 02-27-2011, 07:49 PM
rocketguy101's Avatar
rocketguy101 rocketguy101 is offline
frustrated aero
 
Join Date: Sep 2006
Location: Duncan, OK
Posts: 833
Default

Quote:
Originally Posted by Bill
I don't know what you are talking about; it looks very good to me.

How thick is your Lexan? How did you cut it? Score and break?


Bill

Thanks...the "tube" is 0.02 in. thick, and the fins are 0.04 in., just like Kurt recommended in one of the links I posted above. I used a piece of 2.25" dia metal barstock to wrap the 0.02" and bake it to stress-relieve.

Yes, scoring and breaking worked really well. I originally was going to use a bandsaw, but thought I would try s&b first, and liked it.
__________________
David Stribling
NAR 18402 SR
But it is rocket science!
Get yer Barrowmans here
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 06:13 PM.


Powered by: vBulletin Version 3.0.7
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Ye Olde Rocket Shoppe © 1998-2024