below an interesting report from Edward - 60 plus sec burn time?
"Today I've been corning Rapier propellant of red gum base, lightly misting the premix with 91% isopropyl alcohol and forcing it through a coarse screen before it dries. When then compressed in the nearly-dry state, it forms a rock-hard grain of high density that burns very slowly, < 0.09-in/sec.
Then I fully dried a corned batch, and compressed it at 10,000-psi into a 3/8" bore carbon-fiber composite tube 6" long, and fitted an end plug and clay nozzle of 1.75-mm. That motor, with a grain of nearly 6" length, burned at full thrust for a whit longer than 65-seconds.
One thing for certain, on a free-flight model there would be a serious shift of CG while under power. Heavy when loaded, that CF motor is feather-weight when empty. Taped to a thin bamboo stick, that motor would have sailed out of sight into the wild blue.
This is what retired solid propellant engineers do on Saturday afternoons, while the Blue Angel pilots are unwinding at a watering hole somewhere nearby". My comments below:
1. There is a greater weight change during burning for Rapiers than for metal cased Jetex motors. This is why we put Rapiers around the horizontal CG - which means moving them back a bit on the old Flying Scale models.
2. Edward doesn't state the thrust he was getting, but if it was say 150 mN we have a motor suitable for 'micro R/C applications. This would keep the model from flying away!
3. The motor sounds perfect also for tethered models - especially hydroplanes.
For myself, I am much more interested in free flight models, so 30 sec is about the limit for my flying site and 66 year old legs!
I look forward to Dr Ed's further reports. Seriously, if we have a motor the R/C guys would be interested in, the commercial possibilities become much more attractive.
Held in Germany make rockets for R/C boost guide applications, but Edward's motor would be very attractive for 'micro R/C jets' where previously the only option was micro (or nano) EDF.
The following user(s) said Thank You: jetexpropulsionlab, actonw5
The thrust didn't quite reach 150 mN, and I'm just now deciphering the data from this Mickey Mouse test stand. Thrust rose very gradually from ~10-gm (~ 100 mN) and progressed slowly to near 12-gm for the duration, with a bit of "chuffing" during the finals seconds (perhaps zinc slag condensing down the long motor tube, intermittently blocking the nozzle). The test rig is too sensitive, it turns out, and at +/- 0.5-gm it needs dampening of some sort. I'll switch to the third candidate load cell next week for trials.
As a footnote, that nice, newly-built, simple test stand was blown to bits on the second or third test last week. Like a Phoenix, it's again back in service, though the 1000-gm load cell was tweaked. Usually overpressure will eject the clay nozzle, but on occasion the entire motor tube lets go, bursting through 1/8" walls of the 5/8" OD tube. I don't run tests before 0800 AM any more, and wind things up at dusk. There are neighbors, even in Mojave.
60 seconds of 10 - 12g grams is indeed very useful, too useful for us free flighters though!!!
30 seconds of 20-24g would be fantastic but 25 seconds of 24- 28g would be fabulous, that is just in the ball park that I need to make my heavier KK models like the Swift or Easybuild Mig 15 perform out of this world.
Anything over 20 seconds is actually very desireable compared to say the 15 seconds we have been getting used too, and a bit more umph without going up to the weight and size of an L3 is very attractive. More than 30 seconds burn time starts to look a bit too long unless you have endless flat acres and a recovery motorcycle to go find it. As Roger says 60 seconds is into the R/C realm and I am no longer into that.
Just been reading about the L3 motors. As you know I only use L3s in my boat models and up to date I have not had any blow outs, how ever I do find the cases do go very brown from the burn heat, to stop
end blow out I fill the case with slow cure epoxy glue. My motor tubes are made from carbon fibre with high temp laminating epoxy. after full cure I cut cooling slots length wise to keep the motors cool during the run.