Mongoose 75 motor hardware

CTI just came out with a 75MM tapered rear closure.

Put a forward bulkhead in to accommodate the longest motor you plan to fly. For shorter motors, use allthread, with jam nuts on the forward closure end. Have the allthread pass through the forward bulkhead and used an eyenut on the end of the allthread with fenderwasher under the eyenut. I think the forward motor tap is 3/8".

Yes, I have the 98 version. 75 works the same, replaces the standard rear threaded closure ring, BUT you must also buy the extended threaded ring.

Works like this: normally you screw threaded ring into rear against nozzle carrier, flush to rear of motor tube.

To use the tapered closure you screw the extended threaded ring into case against nozzle carrier. There will now be threads extending out the rear of case. The tapered boatail screws over these & is now flush with case & rear of airframe.

Wayne, since you're such a nice guy, I dug out mine and took some pics. Much easier to understand:

Standard ring with extended



When screwed in tight to nozzle carrier threads extending out back [ realized after taking pic, I put on forward end of case, put on rear, next to thrust ring for final shot, it's flush with thrust ring]



Extended adapter is clearly stamped on one side [next to standard ring]


whole shebang slid into airframe


a wrap of ALUMINUM duct tape covers joints and smooths them

blackjack2564 said:

Yes, I have the 98 version. 75 works the same, replaces the standard rear threaded closure ring, BUT you must also buy the extended threaded ring.

Works like this: normally you screw threaded ring into rear against nozzle carrier, flush to rear of motor tube.

To use the tapered closure you screw the extended threaded ring into case against nozzle carrier. There will now be threads extending out the rear of case. The tapered boatail screws over these & is now flush with case & rear of airframe.

Click to expand...

Why am I not surprised you would have one? Because you have all the neat stuff! Any chance you would be bringing it to Airfest? I would like to get a look at how it all goes together before we build the Mongoose.

MarkH said:

Put a forward bulkhead in to accommodate the longest motor you plan to fly. For shorter motors, use allthread, with jam nuts on the forward closure end. Have the allthread pass through the forward bulkhead and used an eyenut on the end of the allthread with fenderwasher under the eyenut. I think the forward motor tap is 3/8".

Click to expand...

My plan was similar, but I like yours better. I think the tricky part will be getting the allthread to pass through the forward bulkhead, and making the allthread the right length to tighten down with an eyenut. Thanks for the info.
Now I must search for a 3/8" eyenut. Fastenal maybe?

Ok Wayne, here is the down & dirty cheap way for positive motor retention.

In the pic you see a 1.5 in section of coupler, bulk plate, eyebolt & motor forward closure.

Secure the eyebolt through bp on top of coupler and into front of motor.

Slide motor into airframe. I had green tube, so could see where to mark coupler from outside. Since you have carbon, you'll need to slide a measuring tape down from top of airframe and get measurement.

I used 3 #8 stainless set screws, drilled hole through airframe and coupler then screwed in setscrews flush. puttied over them. [If for some reason you need to move/remove you can....glued your toast]

Of course use the longest motor to be flown, do NOT glue BP. Leave it removable. Now you can make up threaded extensions with coupler nuts for flying smaller motors and screw them into eyebolt. Run eyebolt through BP then into rod extensions, drop on top of coupler and screw motor in.

simple...cheap.... and works. To tighten eyebolt with extensions make a tool with PVC pipe. cut notches in end, that will fit over eyebolt to tighten.

To use..... stand motor on end, slide fin can over motor, drop in BP with treaded rod & eyebolt, recovery attached, it will lay alongside, so you can tighten. It should self-center, since it's vertical.

Tighten with home made tool...works for me

I got my eyenuts from Mcmaster, but Fastenal probably sells them too. If you're using this method, you probably also want to put a nut on top the allthread after securing the eyenut, to keep the eyenut from backing off (If you can fit your fingers inside a 3inch tube to do so)

To size the allthread, mark it a little long, then cut it. Test fit with the eyenut, and take more off as needed. I cut mine with a Dremel and cutoff wheel

As for -forward- retention, I did this on mine...

https://www.rocketryforumarchive.com/showpost.php?p=574560&postcount=31

https://www.rocketryforumarchive.com/showpost.php?p=574566&postcount=32


It's been 6 years since I built mine--
https://www.rocketryforumarchive.com/showthread.php?t=47440&highlight=mongoose+75

Kaycee said:

As for -forward- retention, I did this on mine...

https://www.rocketryforumarchive.com/showpost.php?p=574560&postcount=31

https://www.rocketryforumarchive.com/showpost.php?p=574566&postcount=32


It's been 6 years since I built mine--
https://www.rocketryforumarchive.com/showthread.php?t=47440&highlight=mongoose+75

Click to expand...

Thanks Kevin, that's exactly what I have been looking for. Have you done any more CF layups? Would you change anything you did back then? That is one beautiful rocket. Funny how many names I recognize that are on this forum now. Even Stickershock!

Wayco said:

Would you change anything you did back then?

Click to expand...

Hi Wayne-
If I had a Mongoose kit today there is only one thing I would have done differently--my forward retention method. If you use an eye-bolt as I did, you might
consider using something additional to suppliment your shock cord mount--either anchor the eye-bolt to the bulkhead using safety wire or use a swivel.

At LDRS 30, the winds were blowing pretty strong. I launched my Mongoose out of a tower on a Gorilla M745. Apogee @ 16,002'. The rocket was drogueless due
to the wind, and after a ~3+ minute tumble back to earth the eyebolt that was double-nutted -and- LocTited unscrewed a few thousand feet over the field on
the way down. Upon recovery, the 20' of 1/2" Kevlar on the booster section was twisted so much it was only ~5' long.

These days I use swivels on all my builds. Untwisting shock cords sucks.


https://www.youtube.com/watch?v=zqRhupuQz4A

Kaycee said:

Hi Wayne-
If I had a Mongoose kit today there is only one thing I would have done differently--my forward retention method. If you use an eye-bolt as I did, you might
consider using something additional to suppliment your shock cord mount--either anchor the eye-bolt to the bulkhead using safety wire or use a swivel.

At LDRS 30, the winds were blowing pretty strong. I launched my Mongoose out of a tower on a Gorilla M745. Apogee @ 16,002'. The rocket was drogueless due
to the wind, and after a ~3+ minute tumble back to earth the eyebolt that was double-nutted -and- LocTited unscrewed a few thousand feet over the field on
the way down. Upon recovery, the 20' of 1/2" Kevlar on the booster section was twisted so much it was only ~5' long.

These days I use swivels on all my builds. Untwisting shock cords sucks.


https://www.youtube.com/watch?v=zqRhupuQz4A

Click to expand...

This is great info. Kevin. It identifies a critical component that needs to be addressed in my build. When I saw how you used two sections of coupler with a bulkhead it cleared up a question I had about the components provided with the kit. Now I am looking at ways I can improve on what you did. I'm thinking a U-bolt with a swivel for the drogue shock cord anchor, and a 3/8" nut epoxied into the top of the bulkhead. The entire coupler/bulkhead assembly will be retained at the highest point with flat head screws into pem nuts attached inside the couplers. The motor will be retained with a piece of all thread cut the correct length for that size casing, and the entire motor, all thread and coupler slid up into the fincan with the shock cord already attached.

Thanks for adding that video, it shows how fast even a long burn M will accelerate off the rod with the Mongoose. Very impressive. Do you attend any of the other Kloudbusters launches in Argonia?

Wayne, that's exactly what I would do for motor retention!

As for other Kansas launches no, but this year will be the 4th year in a row we've spent Labor Day weekend with the Kloudbusters. As always we're looking forward to it.

Wayne, here is an on-board video of my Mongoose flight at LDRS XX. There was a piece of tape flapping around in front of the lens, but I think you'll get an idea of just how violent the descent was and why I now use swivels on every rocket I build.

https://youtu.be/njSxPdv49Gw

Kaycee said:

Wayne, here is an on-board video of my Mongoose flight at LDRS XX. There was a piece of tape flapping around in front of the lens, but I think you'll get an idea of just how violent the descent was and why I now use swivels on every rocket I build.

https://youtu.be/njSxPdv49Gw

Click to expand...

That is some ridiculous spin. I'd have never thought something could spin that fast during descent.

The good news is that the payload section & NC was recovered under chute ~100yds to the south of the flight line, and the booster came in ~100yds farther out. After 16k up, 300 yards away made for an easy recovery. Unfortunately the booster and camera were destroyed upon impact but thankfully I was able to salvage the flight data. The booster looked like a Slinky, but the motor and all 3 fins were recovered in good condition.