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  #11  
Old 05-16-2016, 09:28 AM
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tbzep tbzep is offline
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Really nice, John! I'd love to build one some day so be sure to do a kit or plan pack with wraps!

The reason the engines look that way is because he had to use BT-5 for the motor mounts.

As for finless stability, think bottle rocket. CG in front of CP. It doesn't matter whether it's "pushed or pulled". If that was all that mattered, bottle rockets would swap ends at burnout.
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  #12  
Old 05-16-2016, 03:29 PM
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Quote:
Originally Posted by johnpursley
...was nearing completion, they are not of the completed model

Didn't catch it this morning. JediBoss, you have to get some updated pics of the completed model up here!!!
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  #13  
Old 09-25-2016, 11:16 PM
leftover leftover is offline
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Default Awesome skins and guidance from John Pursley

Recently reached ounto John to get a set of skins for a k-21 clone but, with TONS of help from him, I decide to build a t BT-80 version of my Favorite Space craft.

As a BAR and a child of the space race I Always loved the Gusmobile and the titan that launched them into space. It was never as flashy as Apollo or as romantic as Mercury, as an Air Force Brat living on Patrick AFB in the ealry days of Mecrury and Gemini and then Ellington for Gemini and Apollo, Gemini just seemed to be "the one that got it done"

I ordered the wraps from John and they are super detailed and will really make the rocket pop.

John even provided me (even after numeours question from me and several issues with my email not showing the attachment) detailed plans for the engine mount and rocket setup. He also tailored my skin set to include the interstage section from shapeways.

I have since bought several more skins kits from him

Thanks John for all your help look forward to buying alot more from you.
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Last edited by leftover : 09-26-2016 at 05:17 PM.
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  #14  
Old 09-26-2016, 01:28 AM
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georgegassaway georgegassaway is offline
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Regarding finless, in 1971 I made a finless egglofter for a North Georgia Regional Meet (NGRM) in Atlanta.

It used a CMR egg capsule, and 18" of BT-50. The liftoff CG was about 1 to 2” behind the capsule, so there was 16-17” of BT-50 behind the CG (I THINK it was 1" behind the capsule)

The main idea was to use it launched “inside” of a plugged Centuri #10 body tube, for a simple “Closed Breech launcher”, as pistons had not come into use, or were not well known at least, in 1971. The model worked, but did not fly very well, a rod-launched model with 12” of BT-20 and fins would have flown a lot higher. Hey, it was my first contest, I learned a lot.

Years later I duplicated the design just to fly it as a novelty. It was notable in that when it flew, it would very slowly wobble back and forth. The lower part of the body had to “stick out” into the airflow at a significantly visible angle of attack to finally stop the pitch or yaw motion and get pushed back the other way where the slow oscillation cycle repeated a few times. I have never seen a finned model do anything like that. It would have been interesting to have replaced the large diameter egg capsule with a say a 4-5” long BT-50 payload section and add the weight of an egg inside, or whatever was needed for the 1-2” CG below the top of the 18” BT-50, just to see if it would wobble as much or wobble a lot less (likely the latter).

Would also make for a pretty neat “surprise” 2-stage rocket, like A8-0 to B4, or full blown C6-0 to C6, when with a finned booster it would look like a single stage rocket.
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Last edited by georgegassaway : 09-26-2016 at 06:15 PM.
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  #15  
Old 09-26-2016, 02:18 PM
johnpursley johnpursley is offline
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My very first "real finless" model was back in '69, I think. It was a BT-20 payloader with a slightly larger payload section (this was also in the pre-"dirt loft" days). I had seen an article about closed breech launchers in Model Rocketry Magazine, then discovered the ARCAS was a CBL vehicle, and THEN got all excited about cutting drag as much as possible.

The launcher was built around a tubular shower curtain "rod" or possible shower curtain rod that I got somewhere. It had in inside diameter of just about exactly 24mm...a AR-2050 (or was it RA?) was a nice slip fit inside. So I built the model with a "faired" 2050 ring on the rear (I probably gained more base drag from that ring on the model than drag that I lost by omitting the fins...but it didn't matter...I mainly wanted to try out a CBL launcher!). I went across the street and flew the thing 3 times in rapid succession until, as I recall, the heavy payload section whacked the body on recovery. It flew arrow straight each time (it was very long [for a so-called competition model] measuring in at probably around 24" long). After that I recall the launcher gathering dust in my dad's workshop until I lost track of it when I moved away from home some years later. I still remember almost exactly how I built it and could probably "replicate" it today...flaws and all!

"Coning" is typical of most finless models that I have seen fly. I flew a 1/100 scale Saturn V that had finless upper stages and the second stage always "coned." I suspect that the coning for rockets that are "short and fat" would have a tendecy to be more severe than long and skinny models. I also suspect that they can more quickly reach the "point of no return" in pitch and yaw than a finned rocket. I further suspect that evey very small fins...possibly amounting to no more than "tabs" would go a long way to minimizing-eliminating coning and keep the model within a safe pitch/yaw envelope...but then it wouldn't be a "finless" rocket any more!

John Pursley
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  #16  
Old 09-26-2016, 02:27 PM
johnpursley johnpursley is offline
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Quote:
Originally Posted by leftover
Recently reached ounto John to get a set of skins for a k-21 clone but, with TONS of help fom him, I decide to build a t BT-80 version of mu Favorite Space craft...


I appreciate the kind words Jon!

Months ago I mentioned I would get the Gemini wraps on eBay or available direct. I've had so many irons in the fire and twists in my life that it wasn't until recently that the Gemini Titan skins have been "revived."

Again, if anyone wants Gemini Titan skins for just about any body tube up to about BT-101, contact me. I can instantly send GT skins for BT-80 models. Also, unless things change, all my skins from this day forward are on a new more conformal, thinner, whiter and lighter material that has a gloss finish rather than the matte finish of previous skins.

John Pursley
johnpursley@accur8.com
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  #17  
Old 10-05-2016, 09:27 PM
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njrick njrick is offline
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that Gemini is beautiful! WOW!
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  #18  
Old 12-02-2016, 10:12 AM
dtidmore dtidmore is offline
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Join Date: Sep 2016
Posts: 46
Default and all the GT discussion...

as I was always a big fan of Gemini due to the way that it really screamed that it was a "piloted" vehicle as opposed to the man-in-a-can look, I have regretted that I never built either of the Estes kits. Well, all this talk and the availability of JP's skins I have decided to roll a scratch GT based on a BT-80 tube with Shapeway parts for the Gemini, interstage, and engine nozzles. As I have a an extensive set of things that I did with the BT-80 core in my heavily modded Estes #2001 SV, I am going to bring as much of that over as makes sense.

As I have a an Estes 2176 MR to be built and the SV nearing completion, the GT and eventually the Mercury/Atlas will make make the set complete.
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