Test run 17 Nov 2000 Cone off
Reeking of kerosene (mmm kerosene!) even as I type... The last week or two has been spent working on (and calibrating) the test stand with the cannibalized fish scale transducer from Wal-Mart. In the end, it was a lot of work but I beleive it was worth it. It was not a simple matter of connecting a trolley to the transducer, because unless the engine pulls on the transducer in a purely axial fashion, the weight measurement will be low. I confirmed this by mounting a tube into the stand and via a pulley arangement, loaded the tube (simulating the engine, diameters were the same) with a known 5 lb weight. With the old linkage, the 5 lb weight produced a 3.5 lb reading.
The linkage was redesigned so that when mounted on the exact engine centerline, the 5 lb weight produced a correct 5 lb measurement.
Please wait, LOTS of photos to load...
|The ground support box
in its finished state. The box carries a 12v battery for
all supporting items, and a 7.2v NiMH battery for the
pump. Seen here are the case pressure guage, white master
switch, red pump switch, the 10-turn
"throttle", the LCD readout from the
fish-scale, and a deluxe LED EGT readout.
The really sad part is that after all the work, I took the box outside for the run and discovered the EGT meter is totally washed out by the sun! I didn't even think about that. I'll need to find an LCD-powered EGT meter to replace it.
|The final test stand.
Note the spark plug, which works so well that I removed
the glo-plug from the other port and plugged it with a SS
I am using some Legris quick-disconnect micro-couplers. These are extremely slick, and function exactly like full-sized shop air tool couplers. My understanding is that Legris sells a bunch of these to dentists for their drills.
The quick disconnects are set up on the air tap (blue) and the gas tap (bottom). Lube is left, and fuel, right.
|A closeup of the thrust
measurement linkage. Buried beneath the nose of the
engine is the variable-length arm which pulls against the
thrust transducer. The big ring in the middle is a simple
clamp which can be adjusted up or down... this varies the
leverage exerted on the transducer, and allows me to
calibrate the stand.
In the foreground is a lever operated cam which allows me to remove the engine's thrust from the transducer to allow resetting the scale to zero. A flick of the lever foreward releases the carriage for thrust measurements.
|Once again, the
engine behaved perfectly, started easily, and had no bad
tendencies at all! The recordings below were done on a
cool (10C) day, unknown pressure.
Also on this run, I checked the minimum case pressure I could idle at, and found it to easily idle at 1.5 PSI. Below that, the EGT began to creep up a bit.
Earlier, I had a table of
thrusts posted here on this page which was erroneous. To
see accurate thrust measurements, click here for both cone on and cone off
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