Lawn Dart Dissection - Mega Derp Red Max

So this is what happens when grease meets delay grain:


I augured in this MDRM on its maiden voyage on an Aerotech G77 Redline LMS. Boost was nice, straight, and fast. So was the recovery.

I've since built another, and successfully flown it on an L1 cert flight, so I figure I can move on to the next stage of grief - fascinated dissection. It's been an interesting piece of desk art for a few weeks, but I got curious and wanted to see the guts, and maybe find out if anything could be salvaged.



It turns out that 900 ft. nose dives take off a bit of length. The white bit poking out like a broken bone is the bottom of the nose cone.

A close up.


The other side. Note a few inches of fresh Arizona dirt, as well as the divot where the upper rail button got sheared off by the cone shoulder (I never did find it).


View from the top. The white hunk of plastic in the hole in the cone tip is actually a chunk of the nose cone base. The red is the chute protector, all of the laundry having been shoved up into the tip of the cone.

The crash left the nose pretty well welded into the fin can area, so I needed to trim away the shredded body tube to extract it. The fin can looks pretty intact - no damage to the fins and two of the centering rings are still in place. Perhaps it can be the base of a resurrected rocket?

Step 1 was to trim away the broken tube:

An interesting look...

Next was to rip off that chunk of nose cone shoulder. As you can see, the shoulder took out the front centering ring, shearing it into three pieces on the fin tabs. But the motor mount tube was surprisingly intact:

Dog barf everywhere.

With the messed up cone section off, the rest of the cone came free, holding the still burrito-wrapped 'chute and shock cord:


After a bit of clean up, the fin can seems remarkably unscathed. Perhaps a future for these parts after all?


No cracks on the fins, rear two centering rings unharmed, fin tabs a little nicked up but in good shape, even the motor tube is unbent.

I laid out all the parts crash investigation style, including the casing for the motor that set it to its demise:


This was actually surprisingly fun. I'm thinking of building up from the fin can with a 4" tube, the transition from the LOC Expediter, and a 3" upper section. Probably put provisions for electronic recovery (maybe even redundant...) in the transition.

While it's never good to see that kind of damage to a rocket, I have to admit, I found the dissection fascinating.

Best of luck on it's resurrection.

With some creative cutting, the damaged nosecone could become a tailcone.

Very interesting

terryg said:

With some creative cutting, the damaged nosecone could become a tailcone.

Click to expand...

I hadn't thought of that, but that's a great idea. Would make a nice V2 type boat tail...

Oberon said:

I hadn't thought of that, but that's a great idea. Would make a nice V2 type boat tail...

Click to expand...

Or use it for a scratchbuilt design.

Oberon said:

So this is what happens when grease meets delay grain:

Click to expand...

I have a question, and not to embarrass you,
but that looks like a single use engine (I could
be mistaken); how did grease get in it?

That would be one big Arapahoe! Maybe call it the "Thunderbird" and give it an Air Force T-birds paint scheme...

On the other hand, making a big retro style silver rocket with swoopy fins is appealing too. Lots of good uses for a big boat-tail.

Shade said:

I have a question, and not to embarrass you,
but that looks like a single use engine (I could
be mistaken); how did grease get in it?

Click to expand...

OP noted that this is an LMS...you assemble and install the delay with that type:
https://www.aerotech-rocketry.com/c...uctions/MR-LMS_Loadable/g77r_lms_in_20201.pdf
"1-2. Fig.-1: Chamfer both inner edges of the delayinsulator with your fingernail. Assemble theRMS-Plus™ delay element, delay insulator,delay spacer and delay o-ring..."
"1-3. Fig.-2:Apply a light film of grease to the innercircumference of the delay cavity (but not theforward end of the cavity)."

Yep, an LMS. They go together pretty much like an RMS, but the case and closure are plastic and you epoxy the front closure in place. They may literally be unassembled single use motors, they look identical.

LMS motors are a bit cheaper than SU, they can have their delays drilled with the RMS drill tool, and they ship non-HAZMAT.

Based on some gunk in the port from the delay grain to the charge well, my guess is that some grease got pushed up onto the front surface of the closure and soaked into the delay and/or clogged the port. It looked clear when I put the black powder in, but I did that the night before a morning launch, it was hot, so the grease may have migrated. I definitely used quite a bit more than I do now on my RMS cases.