Convair MX-774 Hiroc fins?
 

Hello All,

Below are several links to photographs (and other scale data) and historical information on the Convair MX-774 Hiroc, which pioneered several technological innovations (pressure-rigidized "balloon" propellant tanks, a separable nose cone, and gimballed thrust chambers) that Convair later incorporated into the Atlas ICBM.

I have a couple of polyurethane resin duplicate Centuri PNC-89 nose cones from Sirius Rocketry's ( www.siriusrocketry.com ) "Moldin' Oldies" product line, the injection-molded (and later, blow-molded) originals of which were used in Centuri's MX-774 scale kit. Unfortunately, the scan of the die-cut balsa fin sheet on JimZ's web site ( http://www.spacemodeling.org/jimz/ka-3.htm ) doesn't have a scale to indicate the fin size.

Does anyone here have a .PDF scan of the Centuri MX-774 fin sheet or the fin dimensions (including the fin sheet thickness)? Many thanks in advance to anyone who can help, and here are the other MX-774 Hiroc links:

http://www.designation-systems.net/...p1/rtv-a-2.html
http://www.spaceline.org/rocketsum/atlas-program.html
http://www.astronautix.com/lvs/hiroc.htm
http://www.postwarv2.com/mx774/flyi...flyingkits.html
http://www.postwarv2.com/mx774/flyi...turi_mx774.html
http://www.postwarv2.com/mx774/mx774.html
http://www.semroc.com/Store/scripts...arts.asp?ID=495
http://www.spacemodeling.org/jimz/ka-3.htm

I think the best scale information you'll find would be here:
http://www.nasm.si.edu/research/arc...DF/prepsets.pdf

On the fourth page, you'll see the MX-774 drawings by G. Harry Stine.
The plans are not too expensive.

I'm doing a kitbash of the MX-774 from the Estes Bull Pup kit on my blog right now.
www.modelrocketbuilding.blogspot.com

This is only a sport scale model, but will still capture the feel of the MX-774.
It's based on an article by A. William Wilfong at:
www.spacemodeling.org/JimZ/mx-774.htm

In his article he suggests 1/16" thick airfoiled fins. I don't know what thickness the Centuri kit had. For strength, I went with 3/32" thick balsa.
The Centuri kit was only 11" tall. My kitbash is based on the BT-55 and will end up around 16 1/2" tall.

Chris, I apologize for not being more specific. I'm interested in re-creating the Centuri MX-774 kit using the resin PNC-89 nose cones I have--"building a scale model of a scale model," so to speak. That's why I'm looking for the fin dimensions and the balsa fin sheet thickness from the Centuri kit.

Nonetheless, I'm glad that you posted those links and I thank you for doing so! Using them, *real* scale competitors (which I most definitely am *not*) can produce accurate scale models of the MX-774 for NARAM and International scale competition. If the performance of the Centuri kit is anything to go by, the MX-774 (built to the Centuri kit's or other scale factors) might even be a contender in Scale Altitude competition!

I have a Centuri MX-774 that I built a few years ago. I did not trace the pattern before building the rocket :(

I converted the JimZ tif to a pdf @ 100%, printed it off @ full size, and it compares pretty close to my as-built fin. I had rounded all the edges, and for some reason the sharp edges of the fin are rounded too, but tracing around the fin, using a straight edge to recreate the sharp corners, it is pretty darn close!

My fin thickness measures 0.1" which is close to 3/32".

Here is the pdf print it at full size

David, I thank you very much for converting the JimZ fin scan to a .PDF file! If you're interested in building another MX-774 (to save your original Centuri one from damage or loss), Semroc makes a balsa version of the PNC-89 (used in their reproduction Centuri Spartan kit), and Sirius Rocketry has the polyurethane resin duplicate PNC-89 nose cone in their "Moldin' Oldies" line (not all of their duplicate Centuri and Estes plastic nose cones are listed on their web site).

Thanks for the clone info! She is showing some battle scars...and you are right about altitude, this little rocket really screams! I put a streamer on it.

You're welcome, and thank you for posting the picture of yours! Other than in the "group picture shots" in the 1972 & 1973 Centuri catalogs, I've never seen a photograph of a built MX-774 kit.

According to the kit instructions, it could even use nose-blow recovery safely for flying from small fields or on windy days, but I'd use a streamer on mine as well. (The English model rocketeer Stuart Lodge wrote in his book "The Model Rocketry Handbook: 21st Century Edition" that "it's a shame" that streamers are only used for the smallest and lightest rockets "...because streamers are safely able to recover rockets over 50 g in weight and will normally keep the device within the confines of the field...")

David, if I could ask your indulgence just one more time, how long is the Centuri MX-774's ST-8 body tube? The written-up documentation page that accompanies the plans on JimZ's web site gives the length (the author's guess) as 4.5 inches.

Many thanks in advance for your help!

Semroc has it listed as #8 at 5.5 inches.

Brady, thank you for posting this. The 4.5" body tube length did seem rather short.