Convair MX-774 Hiroc fins?

[blackshire]

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/dusrm/app1/rtv-a-2.html
http://www.spaceline.org/rocketsum/atlas-program.html
http://www.astronautix.com/lvs/hiroc.htm
http://www.postwarv2.com/mx774/flyingkits/flyingkits.html
http://www.postwarv2.com/mx774/flyingkits/centuri_mx774.html
http://www.postwarv2.com/mx774/mx774.html
http://www.semroc.com/Store/scripts/ClassicParts.asp?ID=495
http://www.spacemodeling.org/jimz/ka-3.htm

[hcmbanjo]

I think the best scale information you'll find would be here:
http://www.nasm.si.edu/research/arch/WebPDF/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.

[blackshire]

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!

[rocketguy101]

Hello All,



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:


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

[blackshire]

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 sizeDavid, 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).

[rocketguy101]

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.

[blackshire]

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...")

[blackshire]

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!

[bradycros]

Semroc has it listed as #8 at 5.5 inches.

[blackshire]

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.

[rocketguy101]

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!
I measure 4.5" on the nose. I am measuring from the edge of the boattail to the front edge of the tube. The boattail is 1.25" long.

It is a short tube---makes packing the recovery system challenging!

[blackshire]

I measure 4.5" on the nose. I am measuring from the edge of the boattail to the front edge of the tube. The boattail is 1.25" long.

It is a short tube---makes packing the recovery system challenging!Thank you, David! That would be "crowded" for a 'chute. :-) Since Semroc lists that tube length as 5.5", I wonder if Centuri may have changed the length sometime during the MX-774 kit's time in production? I vaguely recall reading somewhere (maybe in one of Peter Alway's books or articles) that the full-scale MX-774 was built in two different lengths.

[rocketguy101]

Thank you, David! That would be "crowded" for a 'chute. :-) Since Semroc lists that tube length as 5.5", I wonder if Centuri may have changed the length sometime during the MX-774 kit's time in production? I vaguely recall reading somewhere (maybe in one of Peter Alway's books or articles) that the full-scale MX-774 was built in two different lengths.
Yes, in ROTW, the third flight incorportated a 34" long instrument compartment, which at 1/33 scale, would be about 1" long.

The MX-774 has a rounded (ogive?) boattail that starts above the fins. Centuri changed this to a straight body with a conical (straight) boattail.

BTW the G. Harry Stine drawings available from NASM (link above somewhere) are excellent with interesting details (antennas, vents, etc).

[blackshire]

Yes, in ROTW, the third flight incorportated a 34" long instrument compartment, which at 1/33 scale, would be about 1" long.Ah yes, that's what it was! (I didn't think they would have built two MX-774 main airframe "marks" in the eventual production batch [out of the 10 rockets planned] of just 3 vehicles.)The MX-774 has a rounded (ogive?) boattail that starts above the fins. Centuri changed this to a straight body with a conical (straight) boattail.Good--I *wasn't* "seeing things" in the photos of the full-scale rockets--that rear curved taper *was* really there! :-)BTW the G. Harry Stine drawings available from NASM (link above somewhere) are excellent with interesting details (antennas, vents, etc).As for myself, I'll stick with the Centuri kit (but I thank you for pointing that out for the more ambitious scale modellers among us). I had gotten away from scale model rockets for a number of years because I contracted "accuracy fever"--if a model wasn't within a hair of perfect (in terms of available scale documentation as well as actual construction) I couldn't build it, and as a result I built very few scale model rockets. :-) By enjoying the "just to Centuri (or Estes) standards" scale kits such as the MX-774, I can enjoy scale model rocketry again without risking another bout of "accuracy fever."

[blackshire]

By the way, here's the catalog "fleet group photo" showing the MX-774 in the 1972 Centuri Catalog: http://www.ninfinger.org/rockets/nostalgia/72cen024.html .

[dwmzmm]

Great thread!! I have the Centuri kit too, and it does fly very high, even on a Quest A6-4 engine. I've been planning on building a larger scale MX-774 so as to incorporate a cluster of four engines like the real one. Thanks for all the links!

[rocketguy101]

Great thread!! I have the Centuri kit too, and it does fly very high, even on a Quest A6-4 engine. I've been planning on building a larger scale MX-774 so as to incorporate a cluster of four engines like the real one. Thanks for all the links!
Dave, what is your tube length? I am curious to see if Centuri did change it during the production run.

[dwmzmm]

Dave, what is your tube length? I am curious to see if Centuri did change it during the production run.

David, I think it's 4.5" too. The particular kit I had has the plastic red nosecone instead of the balsa. I didn't like the plastic one, as the tip is rounded instead of sharply pointed. I've only flown it once (at NSL-2004) as I was surprised as to how high it flew on a Quest A6-4.

[blackshire]

David, I think it's 4.5" too. The particular kit I had has the plastic red nosecone instead of the balsa. I didn't like the plastic one, as the tip is rounded instead of sharply pointed. I've only flown it once (at NSL-2004) as I was surprised as to how high it flew on a Quest A6-4.Dave, does your MX-774 have a blow-molded PNC-89 nose cone, or is it injection-molded? Centuri switched to a blow-molded version of the PNC-89 in the MX-774 kit during the company's later years (see: http://www.postwarv2.com/mx774/flyingkits/centuri_mx774.html ). If this was the case with your MX-774, then the 4.5" long body tube remained constant from the early production runs of the kit to the later ones.

[blackshire]

From Reply #16: Great thread!! I have the Centuri kit too, and it does fly very high, even on a Quest A6-4 engine. -SNIP-and...From Reply #18: -SNIP- I've only flown it once (at NSL-2004) as I was surprised as to how high it flew on a Quest A6-4.Dave, the MX-774 also flies well on 13 mm mini motors (using a friction-fitted motor adapter mount, of course). The "Recommended Engines" chart in the 1979 Centuri catalog (see: www.ninfinger.org/rockets/nostalgia/79cen062.html ) lists the 1/2A4-3M and A4-4M Centuri mini motors for the MX-774. The recommended maximum rocket lift-off weights (including motors) for these motors are 2 ounces and 2.5 ounces, respectively (see: www.ninfinger.org/rockets/nostalgia/79cen042.html ) The Estes near-equivalents of these motors are the 1/2A3-2T and A3-4T (both have a 2 ounce maximum lift-off weight, see: www.ninfinger.org/rockets/catalogs/estes74/74est54.html ). The A10-3T should also work well in the MX-774.

[dwmzmm]

Dave, does your MX-774 have a blow-molded PNC-89 nose cone, or is it injection-molded? Centuri switched to a blow-molded version of the PNC-89 in the MX-774 kit during the company's later years (see: http://www.postwarv2.com/mx774/flyingkits/centuri_mx774.html ). If this was the case with your MX-774, then the 4.5" long body tube remained constant from the early production runs of the kit to the later ones.

The nosecone to my MX-774 looks like injection mold, as it's pretty thick. It came in two parts; the cone and the base/adapter section that had to be glued with plastic cement. As I said, I was disappointed when I saw the plastic nosecone as I really wanted one that was sharply pointed. Maybe one of these days I'll get an equivalent balsa cone from SEMROC to compensate.

[dwmzmm]

and...Dave, the MX-774 also flies well on 13 mm mini motors (using a friction-fitted motor adapter mount, of course). The "Recommended Engines" chart in the 1979 Centuri catalog (see: www.ninfinger.org/rockets/nostalgia/79cen062.html ) lists the 1/2A4-3M and A4-4M Centuri mini motors for the MX-774. The recommended maximum rocket lift-off weights (including motors) for these motors are 2 ounces and 2.5 ounces, respectively (see: www.ninfinger.org/rockets/nostalgia/79cen042.html ) The Estes near-equivalents of these motors are the 1/2A3-2T and A3-4T (both have a 2 ounce maximum lift-off weight, see: www.ninfinger.org/rockets/catalogs/estes74/74est54.html ). The A10-3T should also work well in the MX-774.

Yes, I think I recall seeing those recommended engines (the 13 mm ones) in those later Centuri catalogs. Coupled with the sleek style and boat tail the MX-774 has, I knew it'll be an easy high flyer. That's why when I flew her at NSL-2004 (Hearne, TX) I used the Quest A6-4 (I was just getting back into model rocketry then after a 22 year absence) to keep it low, but those Quest engines ejection charges shot a lot of black soot that marred the white finish to the upper body tube of my model. But you're right, I think the 1/2A's 13 mm from Estes should be a good choice.

[blackshire]

The nosecone to my MX-774 looks like injection mold, as it's pretty thick. It came in two parts; the cone and the base/adapter section that had to be glued with plastic cement. As I said, I was disappointed when I saw the plastic nosecone as I really wanted one that was sharply pointed. Maybe one of these days I'll get an equivalent balsa cone from SEMROC to compensate.Yep, your MX-774's two-piece PNC-89 nose cone is the earlier injection-molded version. The later blow-molded version (see: http://www.postwarv2.com/mx774/flyingkits/centuri_mx774.html ) was thinner-walled and considerably lighter, and its tip appeared to be more rounded than that of the injection-molded version.

If Semroc doesn't already make it (they *do* make a balsa copy of the injection-molded PNC-89 for their Centuri Spartan kit, see: www.ninfinger.org/rockets/catalogs/centuri75rt/75rt8.html ), they (or Sandman) could make a custom sharp-pointed BNC-89 for your MX-774.

[blackshire]

Yes, I think I recall seeing those recommended engines (the 13 mm ones) in those later Centuri catalogs. Coupled with the sleek style and boat tail the MX-774 has, I knew it'll be an easy high flyer. That's why when I flew her at NSL-2004 (Hearne, TX) I used the Quest A6-4 (I was just getting back into model rocketry then after a 22 year absence) to keep it low, but those Quest engines ejection charges shot a lot of black soot that marred the white finish to the upper body tube of my model. But you're right, I think the 1/2A's 13 mm from Estes should be a good choice.Thank you. The 1/2A6-2 (one of the MX-774's original recommended motors) should also yield pleasing flights, and the Estes A8-3 should give flight profiles very similar to those of the Quest A6-4, minus the soot. :-)

[dwmzmm]

Thank you. The 1/2A6-2 (one of the MX-774's original recommended motors) should also yield pleasing flights, and the Estes A8-3 should give flight profiles very similar to those of the Quest A6-4, minus the soot. :-)

If I use the A8, I'd go with the A8-5 delay. I know they're hard to find in most retailers, but we have a local mail order vendor who has an excellent selection of Estes/Quest/AT engines that I can order from and get extra fast service (http://www.launchpad2000.com/). By local, I mean here in the Houston area where I live, but they take orders from anywhere......

[rocketguy101]

The nosecone to my MX-774 looks like injection mold, as it's pretty thick. It came in two parts; the cone and the base/adapter section that had to be glued with plastic cement. As I said, I was disappointed when I saw the plastic nosecone as I really wanted one that was sharply pointed. Maybe one of these days I'll get an equivalent balsa cone from SEMROC to compensate.
Mine is the two piece, orange nose/white shoulder as well.

[dwmzmm]

Mine is the two piece, orange nose/white shoulder as well.

The one that came with mine was all red, including the base and base plug.....

[blackshire]

If I use the A8, I'd go with the A8-5 delay. I know they're hard to find in most retailers, but we have a local mail order vendor who has an excellent selection of Estes/Quest/AT engines that I can order from and get extra fast service (http://www.launchpad2000.com/). By local, I mean here in the Houston area where I live, but they take orders from anywhere......You're right--the MX-774 only weighs 1.1 ounces without a motor installed, so like the Estes Viking (and Centuri Viking) and Wizard, it should use an A8-5 due to its low mass and low drag. Thank you for providing the LaunchPad2000.com vendor link--A8-5 motors are also scarce "on the rack" here in Fairbanks!

[blackshire]

Mine is the two piece, orange nose/white shoulder as well....contrasted with...The one that came with mine was all red, including the base and base plug.....Judging by the Centuri kits I've seen, red seemed to be the most common color of their plastic nose cones. The plastic nose cones sections in Centuri catalogs said that they were "molded in bright colors," however, and I have seen examples of other nose cone colors in Centuri kits. These include blue injection-molded PNC-89s in Screaming Eagle kits and blue (as well as red) PNC-54s in Star Trooper kits. Also, I once saw a yellow #7 size injection-molded nose cone in an eBay auction that I failed to win. All of the blow-molded Centuri nose cones I've seen (in a Twister kit and in the online photo of the MX-774 kit) were red, but two kits are admittedly a very small "sample" on which to base a conclusion--they might very well have been blow-molded in other colors.

[rocketguy101]

Bumping an old thread I know...

First, I have been comparing the G. Harry Stine MX-774 drawing to Pete Alway's ROTW drawing and have a question. I think I am mis-interpreting the ROTW drawing: is the end of the cylindrical body/start of the ogive at STA 174.15, or is that just showing the end of the cable channels? G. Harry's drawing seems to indicate the top of the cylinder is the top of the black stripe (which would translate to STA 154.1 if I did my math right :) )

Second, while searching for some higher resolution pictures to answer my question above, I came across a thread on nasaspaceflight.com about gimbaling engines, and somebody posted a nice article on the early Atlas history from Spaceflight magazine. The article is in this link (http://forum.nasaspaceflight.com/index.php?topic=31053.msg1010313#msg1010313) -- I have contacted the author about availability of any hi-res pics, especially on the launch pad.

[GregGleason]

Attached is what I think is a color pic of the MX-774 (along with a V-2) from an old Popular Mechanics.

Greg