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Posted: Mon May 17, 2010 3:18 pm
by PyroJoe
Here is something I put together just for fun, it is a FMX-4 with two Kraken engines. FMX-5 probably has cleaner lines, but haven't found dims for that one.

Re: FMX-4

Posted: Tue May 18, 2010 11:09 pm
by Bruce Simpson
Having two engines, each significantly displaced from the center-line of the airframe will produce *major* problems if one of those engines stops for any reason. The result will be an immediate spiral due to the offset thrust.

Also, looking at the drawing you posted, that will *not* be a very fast aircraft -- too much wing area for the amount of power available.

If you mount the two engines closer together then you'll also want to add a separator plate between their exhausts or you can get an anti-phase situation where one engine ingests the exhaust of the other because one's sucking while the other is blowing. That produces very erratic running and a lack of power.

I had these problems with the 320lbs-thrust twin pulsejet dragster I built -- until I fitted a separator between the intakes of the lockwood engines used.

Re: FMX-4

Posted: Wed May 19, 2010 1:58 pm
by PyroJoe
The engines would need to be individually ducted/insulated and gradually shifted inboard to gauge the "pilot roast" factor. The outlet ducts could better set the exhaust flow to the centerline to some measure.

Top speed is not one of the critical factors as much as stall speed, spin resistance and low landing speed. It has been written the FMX should be a good fit for low time and infrequent pilots. The concept is scaleable so it can go bigger or smaller.

Re: FMX-4

Posted: Wed May 19, 2010 4:57 pm
by PyroJoe
Guess pilot roasts are nothing new to the craft:

: Why didn't you paint it black?
A9: With all the window area, and no air conditioning, we considered planting geraniums in the Facetmobile. As our test pilot, Peter Lert observed, "if you painted the Facetmobile black, you could measure the appropriate flight times by waiting for a turkey timer inside the pilot's navel to pop out"