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Re Static RPM

 
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rexjan(at)bigpond.com
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PostPosted: Thu Jan 19, 2006 4:23 pm    Post subject: Re Static RPM Reply with quote

Hello List,
Quote:

I have the 3-Blade GSC Wood Prop coupled to a C-Box (3.47:1) and 582. GSC
states that static RPM should be about 6200...the previous owner had
static
RPM way up at about 6500. I'm awfully tired of fine-tuning this thing -
whats the best static RPM in your opinions? BTW, right now I'm lucky to
push
6200 in climb-out.

Thanks!

Andrew
KF3

Hi ! Andrew,
I 'm not sure I am qualified to comment but I thought
mentioning my figures won't hurt. I have a MKIV 1200. It has a 582 blue
head, an "E" box 3:1 ratio. The prop is a 3 blade ground adjustable IVO. I
live in Australia in an area called the Riverland in South Australia. We
have a mild winter and fairly hot summers like currently we are have having
days around 40 to 45 degrees Celsius. I can get 6,200 static where my prop
is adjusted and I never change that although the previous owner changed
between summmer and winter. He was probably right and I'm probably wrong.
Now I haven't actually checked my static on these very hot days. I
suspect it would be down though. We are at 115 ft AMSL. When temperatures
were around the mid 20's C with 2 x 90Kg pilots on board I checked maximum
straight and level at about 1,500 ft and it wound out to 7,000 RPM and 108
knots Vne before I throttled back. I'd say it was not going to do much more
anyway but as it was already slightly over RPM and at Vne I figured that was
enough.
Now on the other end of the scale in 40 deg C with 2 x 90 Kg pilots the
other day on rough grass about 12" high I could not lift off first attempt.
There was a very light cross wind. Normaly it lifts off just fine with us 2
x 90 pilots even on the grass and this was my only experience to the
contrary. Solo it lifts off like a rocket at any time.
After the above aborted take-off I thought about reducing the pitch and
this might be the correct way to go in the hot weather but if I don't have
to I don't want to chop and change as the weather changes. Also due to
normally getting 6,200 static. [ In fact it always is although I don't even
try when it's very hot.] and 7,000 S&L as stated I am not inclined to reduce
pitch. My take-off is not really a problem
Strangely I may only see 5,800 in climb out despite 6,200 static. I'm
guessing but I figure static the prop is slipping but with some speed in
climb out it is efficient and not slipping. I relate this to my experiences
racing on water with a propeller in a 5 litre hydroplane. I would pull 6 to
7,000 until the prop grabbed at about 45 mph then it would drop to 4 to
4,500 and from there the revs and speed very quickly built up again.
So Andrew I just think no matter what you do unless you change pitch for
every occassion there is always a compromise. I would suggest if you are
normally getting 6,200 static and you are not having other problems then
accept that. Perhaps consider changing your setting summer and winter if you
must. My fuel burn is between 15 and 18 litres per hour in cruise.
By the way I use Mogass. Sometimes Regular and others Premium. I do notice
a difference in EGT's and feel their is a slight change in power. My water
temp always seems to sit on 170 no matter what basically except going down a
little on a long descent perhaps. When I first got the plane we were doing a
lot of fast taxi-ing and did tend to go over 180 then in the heat of the
summer.
I hope all this is of interest and/or help,
Rex.
rexjan(at)bigpond.com


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