We now have 61 hours on GK Whip. 26 hours on the Arplast PV 50 in flight
variable pitch prop. Max speed at 2,500 ft is 135 kts, compared to 130 kts with
the Warp Drive set at 17.5 deg pitch (at the tip). Both speeds at 5,700 rpm.
We like the Arplast although I feel it has more to give yet. Optimisation of the
blades might get us nearer the 145 kts claimed by Walter Binder. Anyone know
what height he achieved that speed? The Arplast has been removed for checks.
There is no apparent wear of the mechanism. Jerry Davies has gone to France for
discussions with Arplast as to the next step.
The cooling has been no problem at all, neither have we had any sign of fuel
vapourisation. I'd have been worried if we had, in view of the fuel purge line
fitted to GK Whip. In spite of the fact that the oil never exceeds 90 deg C and
water 110 the mechanical fuel pump has reached 71 deg C. presumably heat soak
---From the gearbox. We once saw very low fuel pressure for a few seconds
starting
the engine 1/2 an hour after landing. Seems to indicate that the fuel purge
works. The bleed back is even smaller than the .3 mm Rotax recommend.
My feeling is that we have some extra cooling drag due to the increased airflow
through the cowls. Next winter, or when we get bored flying !:-? whichever is
the sooner I plan to make a new cowl more on the style of Walter Binder's
design. I think the cleaner exit for high speed air behind the prop disk has to
give some benefit. A single radiator might also reduce the cooling drag.
Graham
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