Brief:
Ellis Mountain makes a family of 29mm single use H and I power motors covering the 50-275 Newton average thrust range. They are reasonably priced and extremely easy to use. The photo shows (from top to bottom) an I69-10, a H275-6 (also available in 10 sec delay), a H101-4 (also available in 8 sec delay), and a H50-6 (also available in 10 sec delay). The spent casings are shown with a used AT G80-4 case for scale. They are quite long for 29mm SU motors--11" for the H101 and H275, 12" for the H50, and a whopping 16.5" for the I69.

Construction:
I have flown several of these now and they are just great. The construction of the entire family is similar: long black polymer casing that are beautifully made with propellant similar to the Ellis "Thor's Hammer" propellant which has a yellow flame and lots of white smoke, except for the H275 which seems to use a very fast burning propellant like Aerotech's Blue Thunder with a pale purplish flame and little smoke. Despite their length, I have used the H50-6 and the H101-4 in a "stubby" rocket of my own design. I had excellent flights to 2000' on both motors, although they extended from the bottom about 2". They do seem to take a bit longer to ignite than Cesaroni or AT reloadable motors, but I found ignition using either AT First fire igniters or hand dipped e-matches from Polecat Aerospace to be reliable with no failures. The delays were spot on with the H101-4 (293 N-sec total impulse) and the 5 second burn of the H50-6 (264 N-sec total impulse). I have not tried either of these motors in the longer delays.

For those who don't care for tube fin rockets, this performance roughly translates (according to simulation) to a screaming mile high 450 mph boost for a LOC Legacy on an H50-10, or a slow, majestic 7G 1200-1300' climb for a LOC Minnie Magg on the H50-6. The H275-6 is one kick butt motor--it punched a draggy, 3+lb 4" tube fin rocket built for J-power up to nearly 1000' (990' on the MicroAlt) in less time that it takes to say "Geez!" It is ideal for heavy projects, where one might consider an AT H242 or H268R. I have to say that my favorite has become the amazing I69-10 (369 N-sec total impulse). I put this motor into a tube fin rocket built from a 54mm motor tube. Cramming this 16+ inch motor into the rocket left 2 1/2" protruding from the bottom. It took a couple of seconds to come up to pressure, shot off the pad, and going nearly out of sight on that 5.3 second burn to 2970'. The delay was a good deal longer than the 10 seconds advertised. As it screamed down from apogee in a vertical dive, I could feel an "Oh no!" rising in my throat. The chute suddenly popped at that moment and the rocket landed safely with (fortunately for me) no zipper. I can't wait to do that again!

A certain amount of planning has to go into the use of a "different" motor like the long burning Ellis H50 and I69--balance checks and use of a simulator to verify the delay and thrust-weight adequacy is essential. I find these to be ideal for my fleet of tube fin rockets, which are fairly insensitive to motor weight, aft CG and wind.

For typical 4FNC rockets, you have to make sure that you're not dipping much below 7Gs on boost or on windy days which will guarantee a severe weathercock with these long burners, which means a long walk and possible too late deployment. With a typical 3"diameter 2lb (1 Kg) rocket like the LOC Forte, simulations predict a safe 11G boost to 3200' with apogee deployment. In contrast, trying a 38mm diameter PML Cirrus on the I69-10 will give a slightly early ejection at nearly 7000'--a cool flight provided you are confident of getting it back safely from this height without dual deployment. Its important with double-digit Newton average thrust, long burning, heavy motors like this to assure that the necessary ballasting for balance does not put the rocket outside of the thrust envelope for the motor. I like tube fin designs for motors like the I69-10 because the CP is so far aft that the long heavy motor case actually improves balance without ballast and moves the CG even further forward of the CP.

Finishing:
I would rate these motors a "5" except for the fact that they aren't packaged with an ignitor. I use 24" e-matches or AT FirstFire^M igniters with them.

Overall Rating: 4 out of 5