I still haven't quite got round to fitting my speed kit. Hopefully, it will
happen in the next
couple of weeks.
However, today the weather in Essex was beautiful for flying. It was clear
and calm (without
any noticable thermal activity). Therefore, I took the opportunity once
again to fly my
triangular course and measure straight and level performance.
The results surprised me. Yet again I'm reminded of the fact that weather
conditions can make
a significant difference to performance.
Ive set out the results below. Perhaps someone can offer an explanation as
to why the difference is so great between summer and winter. ?
******
Europa 912 Mk 1, Monowheel
Fixed pitch standard W.D. prop.
Test weight, circa 1090 lb (495 kg)
Mods: Plenum, cold air box.
Max level RPM: circa 5700.
Climb RPM: around 4900.
Test height: around 1500 AMSL.
C of G: Well aft.
Test date : 22/07/01 Temp at surface: 15C Wind at test
height:circa
290
degrees 10 knots
RPM TAS.
4800, 107 kts 123 mph
5200, 119 kts 137 mph
5500, 126 kts 145 mph
Test date : 15/11/01 Temp at surface: 7C Wind at test height:circa
290
degrees 6 knots
RPM TAS.
4700 110 kts 126 mph
5000 117 kts 135 mph
5300 124 kts 143 mph
5500 130 kts 149 mph
5700 136 kts 156 mph Max level speed
A difference of around 3-4 knots is apparent throughout the range, with the
winter figures being the better ones.
One plausible explanation might be summer thermal activity which made it
more difficult to hold an accurate track.
Another might be the effect of air density on the lift generated by the
wings.
N.B. Although the RPM figures are rounded down, in truth the FLYDAT measured
values consistently about 20 - 30 RPM higher than stated.
All the figures are arrived at by flying a triangular course at fixed
height. I then feed the values into an equation and use triginometry to
arrive at TAS. A by-product is that wind direction and strength are also
predicted. I have retained the raw data on my hard drive.
I'll probably try it all again, just once more, before fitting the new
spats.
Alan. D. Stewart
14 Goddard Way 'phone : +44 1245 264186
Chelmer Village work : +44 1245 604517
Chelmsford, Essex CM2 6UR email :
alan.stewart@blueyonder.co.uk
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