More HP = more RPM?

[bret]

Question, So my IO 360 A1A angle valve and Hartzell CS prop came out of a Mooney, in the logs I see the governor being removed and worked on, so I am assuming they had it set up for a max 2700 RPM. So now it has a full dual EFII setup, when I do a practice launch, ( 3 seconds full power down runway, < 40 Knots ) I see 2850 RPM. I have searched and read where folks dial in the fine pitch stop on the prop 1.5 to 2 turns in, to have the prop slightly more course pitch. Is this what I need to do to bring the RPM down? I am trying to understand the science behind this, Also I am doing this at 4720 MSL, does density altitude-altitude play a part in this max RPM issue? Thanks,

[BobTurner]

Originally Posted by bret

Question, So my IO 360 A1A angle valve and Hartzell CS prop came out of a Mooney, in the logs I see the governor being removed and worked on, so I am assuming they had it set up for a max 2700 RPM. So now it has a full dual EFII setup, when I do a practice launch, ( 3 seconds full power down runway, < 40 Knots ) I see 2850 RPM. I have searched and read where folks dial in the fine pitch stop on the prop 1.5 to 2 turns in, to have the prop slightly more course pitch. Is this what I need to do to bring the RPM down? I am trying to understand the science behind this, Also I am doing this at 4720 MSL, does density altitude-altitude play a part in this max RPM issue? Thanks,

Did your governor come out of the same make and model engine as your current IO360A1A? Different engines have different gear ratios driving the governor (often the governor is NOT at 2700 RPM when the prop is). The fine pitch stop can be adjusted on the governor; but I'm not sure if there's enough range for 150 RPM adjustment.
Many people set the PROP pitch stop to limit the RPMs to 2690 when the plane is not moving, no wind, sea level. That sort of gives the max possible protection (which isn't really that much) should the governor fail.
I strongly urge you not to operate at 2850 RPM.

[RV Jerry]

Are you flying yet or only high speed taxi? Just curios

[bret]

Only high speed taxi, not flying yet.....waiting on our not so efficient FAA aeromedical department. The governor is the one that came with the engine-prop combo.

[Larkrv10]

Bret I would highly suggest setting your rpm at something less than maximum fine until you get a couple of takeoffs under your belt. This means you should be operating from a minimum 4000' runway. Your RV should have all sorts of take off performance to easily fly long before you get anywhere near the runway end. I had an MT prop governor destroy itself from a poorly engineered internal bushing that resulted in a prop over speed, and ultimately a crank shaft replacement. Had I had the rpm dialed down sufficiently, I may have saved myself a lot of trouble. I know my IO-540 with just me in it will easily takeoff at lower rpm settings, just takes more runway. Just make sure you talk over your plans with an experienced fellow RV'er who know the performance of your type of aircraft.
Also a higher density altitude does have an affect on engine performance, but I doubt it will make much difference on rpm (not 100% sure on this though).
Rick
#40956
Southampton, Ont

[cajunwings]

Bret: You need to adjust the low pitch stop to limit the max rpm to 2700 on the take off roll(add some more pitch). This is easily done on most Hartzells with the threaded stem & locknut on the nose of the prop. The Hartzell owners manual explains how to do this. I get home Monday night and can send you a copy of the procedure.

Don Broussard
RV9 Rebuild in Progress
57 Pacer

[bret]

looks easy enough, lock nut and Allen screw in to go more course, what rule of thumb does one turn in, relate to as far as decreasing RPM? no worries with runway to play on, 7400 X 100

[cajunwings]

I wouldn't go more than 1 full turn at a time. May take a couple of runs to get it right.

Don Broussard
RV9 Rebuild in Progress
57 Pacer

[paul330]

There are steps to fix this.

Firstly, you need to adjust the prop fine pitch stop. At sea level, you should get something in the order of 2600rpm on a static full power run. At your sort of pressure altitude, you should aim for something slightly lower - say 2500 - 2550.

Now, when you accelerate, the RPM will increase. This is where the governor comes in and you should limit the RPM to just below 2700 using the high stop screw on the governor.

[bret]

What limits the RPM, is it oil pressure against the prop return spring + dynamic load of the prop blade, and will viscosity of the oil have any affect on these adjustments, ( should I stay with the same wt of oil ) summer to winter time delta of 100 deg here.......