Motor Mount length

[ActingLikeAKid]

Are there any "rules of thumb" for how much of a motor casing needs to be inside the mmt tube? At least half? All of it? Most of it? I'm scratch-building this Estes Vector Force upscale ... I'll probably fly it mostly on H and I, but I'm thinking I might put a little J in to get L2. The motor casing would protrude above the mmt tube... is that problematic, as long as most of the motor is inside the casing and everything is well-secured?

 

[ActingLikeAKid]

With a J motor in it....

 

[rharshberger]

Are there any "rules of thumb" for how much of a motor casing needs to be inside the mmt tube? At least half? All of it? Most of it? I'm scratch-building this Estes Vector Force upscale ... I'll probably fly it mostly on H and I, but I'm thinking I might put a little J in to get L2. The motor casing would protrude above the mmt tube... is that problematic, as long as most of the motor is inside the casing and everything is well-secured?

The motor tube can actually be fairly short, one pic you posted in your second post it could be cut down to the top of the tabs for the forward small fins and the centering ring moved up to the top of the tube. Some people have even suggested and built rockets with no motor tube just some centering rings and a thrust plate at the bottom of the airframe (I have yet to actually see one of these rockets but the idea is one I intend to try soon). Some of the motor adapters for like 75mm to 54mm are very short.

 

[TopRamen]

I make all of my MMT's as short as possible to lessen tail weight. As long as they are stout and well designed they should be fine.

 

[ActingLikeAKid]

Thanks, all!

 

[NateLowrie]

Thanks, all!

Unless you need that forward centering ring for the forward fin set, you could scale the MMT all the way back to the centering ring right in front of the fins.

 

[75Grandville]

Now see if a Loki 1200 (38mm J/K) will fit (you need more than 24")...

Wink wink nudge nudge...

:wink:

 

[ActingLikeAKid]

Unless you need that forward centering ring for the forward fin set, you could scale the MMT all the way back to the centering ring right in front of the fins.

Don't *need*, but I thought it would help strengthen it and besides, it's already super-stable, so a little weight back there wouldn't hurt much.

 

[ActingLikeAKid]

Now see if a Loki 1200 (38mm J/K) will fit (you need more than 24")...

Wink wink nudge nudge...

:wink:

Barely. If I really wanted to go there, what I'd probably do is replace the 38mm "lower-upper" section with one a bit longer (to hold a 'chute), build an altimeter setup, etc etc.

Am I the only one who gets a wicked glint in their eye when OpenRocket's only warning is "Body calculations may not be entirely accurate at supersonic speeds"?

 

[ActingLikeAKid]

Now see if a Loki 1200 (38mm J/K) will fit (you need more than 24")...

Wink wink nudge nudge...

:wink:

When I go for my L2, it's probably going to be with this and either an Aerotech DMS J or a CTI 6GXL J. The latter comes close to Loki numbers.

 

[75Grandville]

When I go for my L2, it's probably going to be with this and either an Aerotech DMS J or a CTI 6GXL J. The latter comes close to Loki numbers.

Based on my limited experience, I'd suggest the smallest J possible when you go for your L2. When I got mine, I used a small J (J315 - 747 Ns total) in a 10 lb rocket, which went to 2000'. It was all about proving I could build a rocket that would fly on a J. Now, that rocket has since flown on a K, and has an L waiting for it. But I kept it as simple as possible for the L2 flight.

I flew a Loki J650 Spitfire in the 1200 case in my Darkstar Jr. on the Salt Flats this summer. The case was so long I had to go drogueless, and barely fit the shock cord in the rocket. That rocket had already proved itself to be darn-near bulletproof when the chute got hung up on a rail button screw and it plummeted from 1300' without breaking (OK, I had to cut 1/4" off a coupler and and replace a bulkplate). More simply put - please don't use the 6GXL for the first flight.

I've been watching your main build thread, very cool looking rocket.

And yes, I know what you mean about that glint... Just wait until you start playing with clusters! Just for fun, I ran a sim with 3 x K627 motors in a LOC TriStar clone that I am building. 11,000 AGL and Mach 1.8. :grin: Pretty sure it would re-kit itself, but fun to think about.

 

[ActingLikeAKid]

Based on my limited experience, I'd suggest the smallest J possible when you go for your L2. When I got mine, I used a small J (J315 - 747 Ns total) in a 10 lb rocket, which went to 2000'. It was all about proving I could build a rocket that would fly on a J. Now, that rocket has since flown on a K, and has an L waiting for it. But I kept it as simple as possible for the L2 flight.

I'm with you. I got my L1 on an Argent with a "just over the line" H in it... apparently "I JUST GOT MY L1, LET'S GO NUTS!" is a thing; instead, I flew a custom MPR rocket on an Estes F BP motor. All things in good time

I flew a Loki J650 Spitfire in the 1200 case in my Darkstar Jr. on the Salt Flats this summer. The case was so long I had to go drogueless, and barely fit the shock cord in the rocket. That rocket had already proved itself to be darn-near bulletproof when the chute got hung up on a rail button screw and it plummeted from 1300' without breaking (OK, I had to cut 1/4" off a coupler and and replace a bulkplate). More simply put - please don't use the 6GXL for the first flight.

Duly noted Hey, this saves me from dropping $$ on a new case, too. First flight in this may be a 29mm motor with an adapter. It's better for things to go a little south with an H than VERY VERY WRONG with a J.

I've been watching your main build thread, very cool looking rocket.

And yes, I know what you mean about that glint... Just wait until you start playing with clusters! Just for fun, I ran a sim with 3 x K627 motors in a LOC TriStar clone that I am building. 11,000 AGL and Mach 1.8. :grin: Pretty sure it would re-kit itself, but fun to think about.

Thanks! Yeah, I thought L1 would be "it" and now....well...L2 is just like L1 with a test....and....
Biggest hurdle going higher would be trying to justify dropping the $$$$$ that L3 would take.