Author: "wv4i" <callsign@...> Time: Sat Nov 6, 2004 11:55 am PST Link
In reply to an email I sent the following which I thought others might
benefit from reading:
I went from a Sensenich metal fixed pitch prop to a Hartzell constant
speed, available from Van's. I also got the MT governor and associated
controls, spinner, plates, etc. from Van's. Prop drive pad and oil
tube came from a private party as did 7/16" prop bushings, had 3/8"
before. The Sensenich was a 80" pitch, so more of a cruise prop to be
sure. The static rpm on takeoff was about 2200, or basically a 45% HP
reduction. Most rpm I saw in level flight was about 2550, and max on
that prop is 2600. My Van's tach reads about 75 rpm low at 2200 rpm,
so these are corrected numbers. At 2550 rpm sea level std day, I got
about 150 kts. Van's gets into a lengthy discussion re fixed vs
constant speed props in the builder's manual so won't repeat here any
further.
The first thing you need to determine is if your engine has a hollow
crankshaft. Mine is an O-320 D2B and does of course. I don't know if
just the model suffix can tell you, so better to just pull the prop
and look if you don't know. If so, there will be a front and rear
plug, and the rear should have a hole in it for fixed pitch prop
application. If it does not, you're in biz. Otherwise, need replace
rear plug and I'm told this is a hassle. Front plug stays out of
course. There are numerous other mechanical issues that I can relay to
you if you decide you're going to make this change.
As to performance, with the c/s prop, you're now taking off with rated
engine power, not a 45% reduction. Ditto for climbing. Basically, I
barely get an instrument scan at power up while I'm raising the tail,
and I'm in the air. This is on grass! This time of year in South FL, I
can easily hold 85mph and 1400+ fpm climb to 3-4k', at abt 1600 lbs.
Speaking of weight, the c/s prop change will also move your empty CG
fwd, and now my RV-6 computes within aft CG limit at 1800 lbs. Empty
CG is abt 1/2" aft of fwd limit. I have a lighter, vfr equipped, no
frills airplane with an empty weight of 1014. Looks like at cruise I'm
seeing less than 8 gph at 150ktas with 23" and 23-2400 rpm at
6-8,000'. I don't have oat at the moment so guessing at TAS, but
probably very close.
So, it's more money and complexity, may be worth it for some but not
others, etc.. Sort of like where do you stop with steam gauges vs
EFIS, VFR or IFR, 160 or 180 hp, etc....
Link
RV-6
N42GF
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