First Run 2 Aug 2002
I have a strange history of having either comical or scary "first runs" of engines, be they piston or gas turbine. Witness the radial engine, my first MW54, even the first attempts with the spot welder. I was determined to break the cycle of goofs, injuries, and general scariness this time.
|To do this, I was meticulous in the
mounting and installation of the support equipment. The
turboprop was firmly bolted to a melanine shelf board,
which clamped nicely in the ubiquitous Workmate. A lot of
the hassle associated with running a turbine for the
first time is the spaghetti nest of lines and wiring.
Since the turboprop has most of these internally, all
that was needed was to plug in a battery, fuel and
propane lines, the R/C reciever, and the ECU's LCD
display. These were all positioned well aft.
I double-checked everything. Motive power for the first run was my converted leaf blower, which at even half throttle produces starts so cold in the MW-54 straight turbine that one must be careful not to trigger ECU flameout logic. I really recommend this setup for testing rather than a starter motor, which can be tricky to use, especially if you are new to turbines or are unfamiliar with a particular turbine's behavior.
|The accessories for the run may be seen
here. The black device is a standard R/C hobby tach,
ready at hand. The fuel tank is a 1.5 liter poly tank
with a clunk. The red propane line may be seen to the
left, sneaking its payload from under the workmate.
I programmed my ECU for an idle RPM of 50,000 (a bit higher than normal) and a top RPM of 100,000 (significantly lower than normal). Max EGT for start was set at 700 C. I had every confidence that my leaf blower would not have any trouble in this regard. EGT MAX RUN was set at 700 also. The glow plug drive was set, and general ECU programming double-checked.
|The oil was added to the turboprop by
detaching the breather and injecting the oil into the
gearbox with a syringe through the breather hole,
stopping when the sight glass showed 7/8 full. I primed
the pump with the ECU, and was caught off-guard a bit
when the prime fuel really slammed into the manifold
hard. I knew I had flooded the engine, but to what extent
I could not tell. I stood the turboprop on end and made
an effort to drain it.
With some trepidation, everything was switched on, READY annunciated, and the air was applied. When the gas and ignition came on, the air was removed. No ignition. This was repeated a few times, with no luck. I increased the glow plug drive and tried again. No dice. I knew from the gas gennie's first run (only one made as a straight jet), that it was well-behaved and ignited perfectly, and with ease. Guessing that the other plug might work better (right plug when viewed from intake end), I routed energy to that plug with an alligator clip.
This time, ignition was immediate. So was some torching! At 20K RPM, I had 18" of flame shooting out the stacks. Minor torching will usually vanish if the start is continued, as the overprime depletes. In my case, since the flames were uncomfortably close due to the position of the stacks relative to the operator, it was hair-raising to say the least. Full power to the leaf blower!
Unfortunately the turboprop was not accelerating, and I figured out why when I saw the big hole melted in the air-blower hose from the right exhaust stack! Ouch! So the start was aborted. EGT never exceeded 650 C. Total run duration was about 20 seconds.
After repairing the hose, I tried again. This time there was a bit of torching but manageable in its intensity. The turbine came up to idle nicely, and there I stood for a few seconds admiring this complex and beautiful machine do what it was designed to do!
The next step was to run the turboprop up to 100K. I added throttle and the turboprop came up VERY quickly. Prop blast increased, gear noise diminished, and generally eveything was going swimmingly for about 10 seconds until the prop blast blew the R/C battery off the end of the workmate. The weight of the battery caused it to disconnect from the reciever. Instant NO R/C fault from the ECU. This particuar ECU was programmed to return the gas gennie to idle, which it did, but too abruptly. The turboprop flamed out!
Total time this run, ~ 45 seconds.
Sigh! I rigged a box, double-taped it to the end of the workmate, and fired it up again. Nice start, nice acceleration to 100K. I let it run there for several minutes. Carefully checking the sight glass, I saw that the oil pump was pumping just fine; oil level was down to 5/8 full from 7/8 full, so the gearbox was draining with ease. I had taken care to be sure the bore for the drain was adequate, and it was.
I did notice excess power turbine fuel/lube mix being ejected from the exhaust stacks. If you look very closely at the left stack above, you can see a bit of this spray, which undoubtedly contributed to the earlier torching when it was ignited. With the turbine above idle, the gas gennie's well-behaved combustion chamber keeps all the flame contained, and the fuel/lube mix to the power turbine tunnel does not ignite. So my problem was a too-open restrictor in the tunnel lube line. I went through nearly twice the normal fuel consumption of an MW54 in this 5 minute run. Please note that I did not use the Wren-supplied restrictor but engineered my own, which will have to be altered before another run.
What else can I say? More buffoonery, all my fault, but again it was a joy to see this marvel in action. More runs and measurements to come!
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