The Mighty M840 bonding grains

Shop deals on ebay
shop deals on amazon
rocket sok
the rocketry show
The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
Wayco said:
I have never heard of an XL nozzle, where would I find that? Maybe that's why it's melting the bottom edge.
Thanks for bringing that to my attention, I just contacted CTI asking about it.
Click to expand...

If you look at the pro75 dimensions https://pro38.com/pdfs/Pro75_dimensions.pdf it shows the difference between the regular and XL nozzles. On the second page it has the boat tail dimensions and the note about using XL nozzles only. It does look like you toasted the end of your boat tail
 
Good eye, I have looked at that drawing several times today and never noticed the markings for the XL nozzle. I measured how far in my nozzle is from the back of the boattail and it is .675". Not an XL nozzle, obviously. Probably true with the other motors I have flown in this rocket. L995, L1115 and L395. This long burn M won't be doing it any good either, so I'm taking it off and installing the threaded ring. I really don't think this part is helping much anyway.
I did send an email to CTI asking which motors have the XL nozzle, if I get a reply, I will post up here. If anyone else knows the answer, please let me know.

Edit. I see where MarkH. as already answered most of my question:
MarkH said:
If it is an XL nozzle, the bottom of the nozzle would be nearly flush with the end of the boattail. With the M840 9 second burn yeah I think you could get some melting. The M2245, M2250, and K2000 have the longer nozzle among others.
There is a note about using the boattail with XL nozzles only, on the pro 75 dimension drawing on the CTI site.
Click to expand...
 
Last edited:
I think Jeroen posted a list of motors with XL nozzles before, but I can't find it. Basically the high average thrust motors
2000N or so have the longer nozzle.
 
Last edited:
I've flown an M840 before, but it didn't come with the glue you mention...? So I used Gorilla Glue and a 3/4" wooden dowel as a mandrel - both worked perfectly.
Flown the M650W as well, but the cores weren't perfectly aligned as the mandrel I used was a bit too small. No issues there, either.

Wayco said:
It's a pretty rocket, I left the carbon fiber exposed, there are no decals. Here it is with the M840:
Click to expand...
Nice looking bird! What's your expected altitude on the 840?
 
All this M840 talking got me excited. I had to build one!! Bringing it to Air Fest as a "last minute" grab.
 
AlnessW said:
I've flown an M840 before, but it didn't come with the glue you mention...? So I used Gorilla Glue and a 3/4" wooden dowel as a mandrel - both worked perfectly.
Flown the M650W as well, but the cores weren't perfectly aligned as the mandrel I used was a bit too small. No issues there, either.


Nice looking bird! What's your expected altitude on the 840?
Click to expand...

I'm getting sims around 25k, but all previous flights have exceeded sims, so I'm hoping for 28k. Guys like Griffin, who have more experience with this motor, seem to think it will go higher....

GRIFFIN said:
All this M840 talking got me excited. I had to build one!! Bringing it to Air Fest as a "last minute" grab.
Click to expand...

Must be nice to grab a 75mm "M" motor out of your stash and fly it on a whim. I've been planning this flight for almost a year. I'm excited though, this is our biggest launch each year. :w:
 
Wayco said:
Must be nice to grab a 75mm "M" motor out of your stash and fly it on a whim. I've been planning this flight for almost a year. I'm excited though, this is our biggest launch each year. :w:
Click to expand...

Don't forget who's the guy on the other end of the phone on Black Saturday!! Don't give me the "must be nice" LOL!!! I see what you order!!!!
 
Wayco said:
I'm getting sims around 25k, but all previous flights have exceeded sims, so I'm hoping for 28k. Guys like Griffin, who have more experience with this motor, seem to think it will go higher....
Click to expand...
Sweet, good luck on the flight! Wish I could be there to see it...
 
Wandering around on the forum today, I found this old thread. I did fly my carbon fiber Mongoose 75 on the "Mighty M840" at the TRA/PHX Eagle eye launch last November. Here is all the proof I have:


It flew to 28,905 ft. and was recovered 3.5 miles South of the launch. Eggfinder data was lost during boost, but started receiving packets well before it reached apogee. Drove South about three miles and walked right to it with the Eggfinder LCD and an Android phone running Rocket Locator. Not an easy recovery though, it was stretched across a mesquite tree and cats claw!
IMG_6471.jpg


IMG_6472.jpg
 

Similar threads

Richardx
AeroTech 75/2560 liner length
Replies
16
Views
507
rfjustin
rfjustin
davidshewitt
Grain Bonding an M1550R
Replies
19
Views
2K
Steve Shannon
Steve Shannon
kramer714
Bonding Bulkheads - with Worms
Replies
0
Views
129
kramer714
kramer714
M
Aerotech RMS J275W - Loose Grains Forward to Aft - This is not good right?
Replies
28
Views
1K
3stoogesrocketry
3stoogesrocketry
UPscaler
K455 Flying Case
2
Replies
40
Views
3K
StreuB1
StreuB1

Latest posts

Back
Top