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  #1  
Old 11-13-2013, 06:34 PM
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Solomoriah Solomoriah is offline
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Default Sprinting to the past...

So I have an Estes Sprint that dates back to the late 1970's, and a Quest Flash that I built back in 2006. Looking around Ninfinger's site, I discovered that FSI had a Sprint as well, and I've decided to clone it.

But... I have a four position launch stand. So, does anyone know of any other companies that made rockets called Sprint?
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Old 11-13-2013, 08:55 PM
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Quote:
Originally Posted by Solomoriah
So I have an Estes Sprint that dates back to the late 1970's, and a Quest Flash that I built back in 2006. Looking around Ninfinger's site, I discovered that FSI had a Sprint as well, and I've decided to clone it.

But... I have a four position launch stand. So, does anyone know of any other companies that made rockets called Sprint?

You said that you have a Quest Flash. Did you mean Sprint? I have a Quest Sprint.
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Old 11-13-2013, 09:06 PM
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Quote:
Originally Posted by Solomoriah
So I have an Estes Sprint that dates back to the late 1970's, and a Quest Flash that I built back in 2006. Looking around Ninfinger's site, I discovered that FSI had a Sprint as well, and I've decided to clone it.

But... I have a four position launch stand. So, does anyone know of any other companies that made rockets called Sprint?


Yep. Martin Marietta. Zero to mach 10 in five seconds!





.
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Old 11-13-2013, 09:09 PM
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Quote:
Originally Posted by Solomoriah
So I have an Estes Sprint that dates back to the late 1970's, and a Quest Flash that I built back in 2006. Looking around Ninfinger's site, I discovered that FSI had a Sprint as well, and I've decided to clone it.

But... I have a four position launch stand. So, does anyone know of any other companies that made rockets called Sprint?

There's always the new Astron Sprint XL,
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Old 11-13-2013, 10:22 PM
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Duh. Yeah, I meant Quest Sprint. I have a Flash still in the bag also, but the Sprint is built.
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Old 11-14-2013, 07:13 AM
Scott6060842 Scott6060842 is offline
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There is the Centuri Magnum Sprint ...

http://www.ninfinger.org/rockets/ca...i83/83cen4.html
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Old 11-14-2013, 10:04 AM
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Hmm. Was hoping for a different take on the name, rather than an upscale. I guess there were only three.

Cloning the FSI Sprint

I got the "Early" and "Late" plans somewhere, can't recall if it was from JimZ or here, but the most useful thing for cloning the Sprint is the diagram in the 1970 FSI catalog here:

http://www.ninfinger.org/rockets/ca...fsiflyer12.html

It contains measurements for some of the components, a great boon to the cloner.

I've noticed, looking through photos from various sources, that the FSI Sprint changed shape several times during the production. In particular, I've found photos of Sprints with longer lower tube sections than the 3" indicated in the 1970 diagram. So I don't feel like I have to slavishly follow the plans in this case.

The upper tube is 30mm in diameter; the diagram doesn't say if that's ID or OD, not that I care (as noted above). The closest modern tubes are Quest T-30 and Centuri ST-11; since I source my parts from Semroc for the most part, we'll go with ST-11. That tube is 5.75" long in the diagram, and Semroc has a 6" piece of ST-11 on the price list, so that's the one I'll use.

The lower tube is 21mm; the closest modern tube is Estes BT-40. I simmed the rocket with BT-40, and the engine tube is a really close fit. Even though it's a bit bigger, I think I'll go with ST-8 tube for the lower section.

The diagram shows 3" of the lower tube exposed. The FSI kit used a balsa transition, hollowed out, but I'll use a paper transition instead; this means I need another 2" of tube (1" for the transition plus 1" up in the ST-11). That is, of course, a total of 5" of tubing; Semroc sells a 5.5" long piece, so we'll go with that.

To be clear, I'm not going to cut either tube, I'm just going to use them the size they come from Semroc.

Using strictly Centuri-sized parts means I won't have to make my own centering rings; I'll need two CR-811 rings and two CR-78 rings.

... gah. CR-811 rings don't apparently exist. So I guess I will have to make my own. At least the CR-78 size is available.

I find it's easier to deal with a paper transition if you have a coupler between the rings. Semroc sells a coupler for ST-11 that is 1.25" long; that will eat up half or a bit more of the "error" in the lower tube length. In fact, depending on how thick the upper centering rings end up, I might be right on the number; using OpenRocket defaults gives me a 3.05" exposed lower section.

As far as the nose cone goes, the one in the diagram is a 3.5" long ogive. Semroc does, in fact, sell a ST-11 sized, 3.5" long ogive nose cone, so that was easy.

The fins are one part that apparently varied a lot. While all versions claim to have birch plywood fins, the shape appears to have varied several times; the shapes shown in the Early and Late plans are different from each other, and neither one matches the catalog photos or diagrams. After doing some looking I decided I liked the Early fins better, so I've reproduced them in my OpenRocket file.

... and I just discovered that OpenRocket 13.11 does not let me change the dimensions or materials for some existing components. I noticed I was using an Estes-sized rather than Centuri-sized thrust ring, but OR 13.11 won't let me change it. Gah. So back to 13.09.1.

Ah, much better now.

My simulation shows the Dv being just a bit hot with the best B and C engines, namely the Estes B6-4, Estes C6-5, and Quest C6-5, all being around 20-24 ft/sec. The Quest engine sims to the highest altitude, 1148 ft. with a Dv of 20.7 ft/sec. With an Estes A8-3 the Dv is just 2.74 ft/sec, quite nice, at an altitude of 212 ft.

The rocket has a 1.18 caliber margin of stability with an Estes C6-5 loaded.

If all goes well, I'll probably do my own decal for one fin as with several of my other rockets, since, like the design, the decoration of the FSI Sprint varied over the years also. A roll pattern might be nice as well.

So here's my airframe shopping list for Semroc:

BC-1135 Balsa Nose Cone #11 3.5" Rounded Ogive - $4.30
CR-78 Centering Ring #7 to #8 (Pkg of 6) - $1.50
HTC-11 Tubing Coupler #11 1.25" Long - $0.65
ST-1160 Body Tube #11 6.0" Long - $1.55
ST-730 Body Tube #7 3.0" Long - $0.55
ST-855 Body Tube #8 5.5" Long - $1.35

I have the thrust rings, engine hooks, launch lug, etc. in my stock already so I don't need to order them.

I've attached my quick-and-dirty OpenRocket simulation file, in case anyone is interested.
Attached Files
File Type: ork FSI Sprint Clone.ork (193.2 KB, 30 views)
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  #8  
Old 11-14-2013, 03:47 PM
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Quote:
Originally Posted by tbzep
Yep. Martin Marietta. Zero to mach 10 in five seconds!





.


Unbelievable! Here is some very impressive footage of the Sprint and Spartan...........

http://www.youtube.com/watch?v=5vq4mWyYl2Y
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Old 11-14-2013, 09:52 PM
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Wow. Cool footage. Those missiles really get down. Very impressive.
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  #10  
Old 11-15-2013, 10:03 AM
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One of the things that has always been a problem for me in scale model rocketry is that, for the most part, the launches aren't scale. Model rockets need enough speed to be stable by the time they clear the launch rod, so scale liftoffs of a Saturn V or 1B, Mercury-Redstone or Gemini Titan, forget it.

Sounding rockets are good for scale launches.............they leave the pad in a hurry, just like the big ones.

Building a scale model of the Martin Marietta Sprint, loading it up with a large fast burn engine and letting her rip would be an impressive launch.

Joe
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