Reference info on first MPR

[Sandy H.]

I am about to build my first scratch MPR (a few kit and scratch LPR's complete) and wanted to make sure I was on track.

I am building a 42"-ish BT-80 rocket with a 24mm mount. I ran a wRASP simulation for the rocket with an F39, which is the max I am planning on running it with and got a result of mach .39, 23G's. I think I am well within the window of 3/32 basswood and TTW fins with no other measures, but wanted to check in with the pro's to see if I am missing something simple. Once sure that this configuration is correct, I'll run the calculations for CG, CP and start the build.

I am using standard Estes type thin BT-80 (36"), a Phoenix nosecone, (4) 15 in^2 clipped delta fins and a 24mm mount with up to an F39 reload. I used the stock cd of .6 in wRASP, as I this seems conservative for this configuration.

Thanks for any help!

Sandy.

 

[ben]

only one thing wrong with it,







MMT is too small!!!!!!!!!!!!! I have a 38mm inmy Estes Phoenix made for DD. I think that thing could handle a 29mm with an adapter. Remeber you can always adapt down

thanx, Ben

 

[BAR0051]

I think it should not be a problem, but I would put a 29mm motor mount in it, you can always adapt it down to 24mm. I have flown my bashed Estes Canadian Arrow
https://i45.photobucket.com/albums/f77/BAR0051/ArrowLight.jpg
on a G64, though it flys better on F40 motors. It has basswood fins & plywood centering rings but is the Estes BT80 tubing.
Hope this helps.

 

[loopy]

Sounds fine! My Phoenix uses the standard Estes body tube with all basswood fins, and handles 24mm reloads just fine.

I think the 24mm is a fine choice for motor mounts, just don't use an Estes type motor tube, as it will not last as long as something like a LOC motor tube because of the higher heat generated by the APCP reloads.

Have fun and keep us posted!

 

[Sandy H.]

Thanks for the replies. It turns out that doing a search first was, for once, the wrong thing to do. Just a few threads down is this one, which addresses the issue as well.

https://www.rocketryforum.com/showthread.php?s=&threadid=28781

Doh! I relied on the search only and didn't browse this forum, as I tend toward LPR. I think I'll go with basswood and surface mount fins, sanding the glassine off of course. If it needs a rebuild later, so be it.

I have mixed luck with motor mounts. . . I apparently put small ones in (Fat Boy, Big Daddy) some and big ones (24mm in Quest Harpoon. . . ) in others. I bet you're right that a 29mm is the right call, as an adapter is easy. I did buy an E motor mount kit (heavy tube with ply rings for BT-80) from BRSHobbies and figure I'll use that for now.

The project is an interesting one. Myself and a work buddy are building similar rockets as far as main components go. We both are using 36" BT-80 and PNC-80K, but that's where the designs change. He's going with a triple 24mm canted mount (Estes only: 3 D's on paper, but might get 3 E's at a sanctioned launch) and I'm going with a single 24mm with F-ish reloads. He sims higher with wRASP, but its all for fun, right. I almost think an F reload (Black Jack or White Lightning) might get a bigger response, even if it comes up 300 ft short.

For kicks, should I be considering a stuffer tube? I did one on my upscale (BT-60) 1906 Sizzler and it runs great, but I'm wondering if the volume to be pressurized on this one might be critical. I have no frame of reference for what a reload does with the ejection charge. I'm pretty sure that 3 shots from a BP motor will get his cone away with no problem. . .

Thanks for the advice. I'll post a picture here of what I come up with.

Sandy.

 

[Stymye]

With the aerotech loads,don't worry, popping the cone won't be an an issue .
with a d-12 I would run the motor tube up to the chute bay.
thats just insurance to me