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...
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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.
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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
cap. 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.
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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.
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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
data.
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Gas
Turbine
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