Will low oil pressure affect how a CS prop works? On a plane I have been flying the oil pressure is a little low ~47psi and I'm just curious if that could be causing the prop to not adjust to full fine pitch. The engine builder said running the engine with 47psi oil pressure won't hurt anything. If it were my plane I'd adjust the relieve valve so the pressure is where it should be but it isn't and the owner doesn't want to change anything.

You may remember my post about not reaching max rpm on takeoff, I'm still chasing that issue and am wondering if the low oil pressure could be the cause. I adjusted the governor but nothing changed. As I've become more comfortable in the plane I have realized that when I first apply full power on takeoff the engine revs to about 2650 then as the plane accelerates the rpm back off to ~2600.

Engine is a Lyc O360, prop is a 78" Mac C214, governor is an MT.

Whee, Not sure as it has been awhile since I adjusted Hartzell on my M6 but have you adjusted the stops on the prop?
Good luck.

Haven't adjusted the stops on the prop yet. That is another thing the owner doesn't want to do...

Whee, There will be many more knowledgeable posts on the subject of C/S props, but I believe that low or no oil pressure will cause the prop to "go to fine pitch" in most applications. There are some aerobatic props that work the opposite, So, with this info, I would also think that the fine pitch stops on the prop are in need of adjustment. Also, there is an adjustment on the prop governor that could affect the achievement of max RPM on takeoff.
Enjoy the day
John

Hey Whee,

The surge as you apply full power is pretty common, even in my brief experience I've seen it in Husky's, Maules, etc before. Obviously it's caused by the governor responding to the over-rpm condition as the engine winds up. The responce time may not be as fast as possible with lower oil pressure, beyond a certain low point - above that certain pressure, it should be roughly linear - and that point will be related to the smallest orifice size (restrictor) in the oil supply (including governor), and not something which could be discussed without being a real expert and knowing your exact setup. Caveat is I'm no expert, just a casual observer.

Interesting to hear that the governor adjustment did nothing - how much did you adjust it?? From memory, each turn on the stops should change about 25RPM or so, depending on your model of governor. If you did a few turns on the stop screws and RPM didn't change, something may be wrong. Given the above paragraph, the governor sounds liike it's working to steady the rpm at full power. In that case, you would expect some change in RPM upon adjusting the governor, because it seems the prop isn't resting on the stops at T/O.

On a different note....
Have you considered hooking up some industrial scales you your truck with a tow rope, and hooking the other end to the plane? That way you could measure the static thrust at T/O power, and compared it to the expectations - that would be a kind of proxy for horsepower and prop effectiveness combined.

quote="Superpacer"]Whee, There will be many more knowledgeable posts on the subject of C/S props, but I believe that low or no oil pressure will cause the prop to "go to fine pitch" in most applications. There are some aerobatic props that work the opposite, So, with this info, I would also think that the fine pitch stops on the prop are in need of adjustment.[/quote]

I was thinking the same but didn't know for sure and couldn't verify.

Battson wrote:
The surge as you apply full power is pretty common, even in my brief experience I've seen it in Husky's, Maules, etc before. Obviously it's caused by the governor responding to the over-rpm condition as the engine winds up. The responce time may not be as fast as possible with lower oil pressure, beyond a certain low point - above that certain pressure, it should be roughly linear - and that point will be related to the smallest orifice size (restrictor) in the oil supply (including governor), and not something which could be discussed without being a real expert and knowing your exact setup. Caveat is I'm no expert, just a casual observer.

The surge is pretty quick and the reason I mention it is because at this point is seems that the prop isn't hitting the fine pitch prop stop.

Interesting to hear that the governor adjustment did nothing - how much did you adjust it?? From memory, each turn on the stops should change about 25RPM or so, depending on your model of governor. If you did a few turns on the stop screws and RPM didn't change, something may be wrong. Given the above paragraph, the governor sounds liike it's working to steady the rpm at full power. In that case, you would expect some change in RPM upon adjusting the governor, because it seems the prop isn't resting on the stops at T/O.

I only adjusted it 1.5 turns, I didn't know how sensitive it was. Next time I have the chance I'll turn it 4 or 5 times and see what that gets me. I'll have to adjust the cable too because it won't travel that far. The prop runs nice and smooth in flight. the only time it surges is on initial takeoff when full power is applied.

Lack of oil pressure for most non-aerobatic props for singles will cause them to go to fine pitch, i.e., higher rpm, so whatever your prop issue is, it isn't caused by the lower-than-normal oil pressure. Guaranteed that's what happens, because when my engine lost all oil pressure, the first indication after the gauge read nada was the prop over-speeding.

Although frankly, 47 psi isn't all that far off of Lycoming's 50-55 psi minimum for economy cruise power, I would want it higher if it were mine--somewhere between 55 and 90. FWIW, my O-360 normally runs around 80-85, even when hot.

Mine will surge if I move the throttle too quickly. I avoid the surge by cranking in only a little throttle (mine's a vernier control) until the airplane gets moving with a few inches of MP, then pushing the button and firewalling it smoothly. My full throttle rpm is between 2650 and 2700.

One other thing to be aware of, that the tach may not be accurate--many are off.

I'm not understanding the owner's reluctance to have things adjusted correctly. Is he shorting other maintenance items as well?

Cary

Have you checked the rpm with an optical tach? Like Cary said the tach could read low, we see it all the time.

Surges in bigger engines are the result of adding power too quickly, we train to bring the power up very slowly until on the governor and then pour the coals to it.

Macs and Hartzells on the lycoming are at the low or fine pitch while at rest. Oil pressure drives them away towards high or coarse pitch, that's why engines overspeed when the governor is lost.

Sam

Cary wrote:I'm not understanding the owner's reluctance to have things adjusted correctly. Is he shorting other maintenance items as well?

I don't really get it either but it is not mine so... There really isn't any other Mx items yet, the plane is basically brand new and looks good.

Haven't checked the tach yet but I need to. It is a brand new electronic tach with an analog readout but still it could be off.

whee wrote:I only adjusted it 1.5 turns, I didn't know how sensitive it was. Next time I have the chance I'll turn it 4 or 5 times and see what that gets me. I'll have to adjust the cable too because it won't travel that far. The prop runs nice and smooth in flight. the only time it surges is on initial takeoff when full power is applied.

With some governors, you can also turn the whole "head" on the governor body - using the manufacturer's instructions of course. Handy to know if there's not enough threads left on the rod-end bearing.