Ben
You didn't state your propeller type but I suspect its the standard
Warpdrive probably on the 912. The standard propeller is in my opinion
too small a diameter to give the best take off and climb on a Europa.
Like all things in life its a compromise. I have several customers now
who have fitted 64" props to their classic Europas and they report
improved climb without any great loss in cruise performance. When
assessing cruise performance I would not recommend simply recording the
rpm as this gives no real guide on power usage. You would have to also
know the manifold pressure or fuel consumption. I reckon that top speed
is a good measure of performance. An aircraft with a max straight and
level speed of 135 kts probably cruises more efficiently at 120 kts than
an aircraft with a top speed of 130 kts.
In my opinion there is only a small benefit in fining off the prop.
However if you were to fine off the prop and go for a bigger diameter
then you would really see some gain but loose a little top end possibly.
The front wheel guys can easily fit larger props!
On a fastishaircraft with Rotax 912 (912/S) I would normally adjust the
propeller pitch so that theengine produces 5500 rpm at full throttle in
straight and level flight. I would fine it off if itcould not reach
5500 and coarsen it if it revved past 5500. If this did not give a good
enough take off and climb I would fit a larger prop and use a finer
pitch. If the cruise was slower than I knew it could be I would try
reducing the prop diameter and increasing the pitch. Some time ago I did
a graph of what I termed apparent angle of attack against aircraft and
engine speed. If anyone is interested I have posted it on my web site
its an Excel spreadsheet. The apparent angle off attack is based on the
datum of the aerofoil which is not the underside of the blade however
you always need a little positive angle and on many blades I have found
the predicted angle equates well to the actual angle of the underside
of the blade. The graph also gives an indication of the best twist in
the blade for any given configuration.
My graphpredicts a difference of around 1.5 degrees per 10 kts at 120
kts.
url = http://www.avnet.co.uk/touchdown/pages/prop1.xls
Jerry
lts@avnet.co.uk
http://www.avnet.co.uk/touchdown
----- Original Message -----
From: Ben
Subject: Prop Settings
At present I'm operating a Classic with 912 and prop set at 15deg.in
preparation for short strip(400yds) use. This setting certainly reduces
the cruise by 15-20kts and peak revs at take off touch the red sector
(5600) but I'm not convinced the take off run is any shorter than when
at 17deg.. Anyone out there with any experience of prop settings and
their effect on take offs??
Ben G-BXGG
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