Constant speed VS. fixed pitch

[rcarson]

Can anyone tell me if there is a sufficient performance difference in an O320 with a constant speed VS a fixed pitch prop (160hp). I realize there will be some difference but is there any emperical data showing the differences. I am trying to make the determination and if the top end is not significantly different I would be hard pressed to go with the higher priced, higher maintenance constant speed prop. I don't need to squeese out every bit of speed, just something reasonably close to the stated performance goals. Its time to order the finish kit!!!

 

[vic syracuse]

You are not going to see a dramatic difference in cruise flight with a constant speed propeller vs. a fixed pitch, especially with some of the newer, more efficient fixed-pitch propellers on the market. After all, a constant speed propeller is really a fixed pitch while in cruise flight. OK, for all of the purists, it is never really fixed, and in bumps will actually be making constant pitch corrections, but the difference is really negligible for this discussion. Some of the advantages of a constant speed propeller are the availability to use all of the rated horsepower for takeoff and climb, perhaps a little more directional stability due to the gyroscopic effects of the larger mass, the ability to run at slower rpms in cruise, and the ability to slow down faster and use the braking effects of the propeller when landing.
The disadvantage are higher intital costs and complexity, ongoing maintenance, and of course they are much more expensive to repair if damaged.
If you get a chance to fly behind one, the difference in take-off acceleration usually causes one to forget about costs and practicality.

Vic

 

[videobobk]

This is a very basic answer, but I hope it is helpful. If you are looking for best cruise, a fixed pitch prop set up for cruise may actually be a bit faster than a CS, but not by much. The real difference will be in takeoff and climb numbers. Talk to Craig at Catto Props and tell him you wants/needs. Also research some of the threads already on this forum on this topic. There is a lot to learn. Engine size makes little difference in the relative results. A 320 will have lower numbers in all cases than a 360, but proportional.

Bob Kelly

 

[RVbySDI]

Can anyone tell me if there is a sufficient performance difference in an O320 with a constant speed VS a fixed pitch prop (160hp). I realize there will be some difference but is there any emperical data showing the differences. I am trying to make the determination and if the top end is not significantly different I would be hard pressed to go with the higher priced, higher maintenance constant speed prop. I don't need to squeese out every bit of speed, just something reasonably close to the stated performance goals. Its time to order the finish kit!!!

Don't get hung up on the top end speed (cruise performance) of fixed vs constant speed as that is not where the real difference will be seen. The differences that will be noticeable will be on the takeoff performance and braking performance (slowing the plane down to land) you will see. This will be where you will have to make your decision as to whether the extra expense and weight is worth it.

 

[Jerry Cochran]

Get a ride...

In a FP and CSP preferably similar RV's in other respects. The takeoff alone should make a believer one way or other. I did that 6 yrs ago, sure made me one and would never go back to FP.

YMMV, .02, etc.


.

 

[terrye]

CS vs. Fixed Pitch

I'm not an expert, and am still building my RV-9A, but my research indicates:
PRO C/S
Better initial acceleration on takeoff
Better climb rate
Better deceleration for landing
Better fuel economy, especially in cruise
CON C/S
Heavier
More expensive (but see better fuel economy)
More maintenance

PRO F/P
Cheaper
Lighter
Same cruise speed (if optimized for cruise) but at higher engine RPM

CON F/P
Worse initial acceleration
Worse climb rate
Worse fuel economy
Sensenich RV props have a barred speed range which means they have a harmonic vibration peak in the engine operating range. To me this is unacceptable.

As a result I am planning to use a Hartzell C/S propeller

 

[n5lp]

Where's Larry Adamson when you need him???

(Mel and I are satisfied with our fixed pitch props)

 

[pierre smith]

There are faster props..

.... To me this is unacceptable.

As a result I am planning to use a Hartzell C/S propeller

..than a Sensenich.

I flew a -6A for 5 years with a Catto three-blade, which can turn up to 3200 and consistently beat Van's numbers. It was pitched for max cruise and turned 2750 WOT,

Best,

 

[Sam Buchanan]

Sensenich RV props have a barred speed range which means they have a harmonic vibration peak in the engine operating range. To me this is unacceptable.

The restricted range for the Sensenich FP prop on an O-320 is rpm in excess of 2600 (the O-360 doesn't have this restriction). It is true this means the engine will never see rated power but I doubt most O-320's see >2600 rpm except for takeoff. I've flown the Sensenich FP on the O-320 for nearly 1000 hours and never considered 2600-2700 rpm to be a significant portion of the engine operating range.

That said, the CS prop is definitely the way to go for maximum takeoff performance. But the FP prop is a fine performer if budget and non-maintenance are high priorities, especially for operations at modest density altitudes.

I can not believe Larry hasn't jumped all over this thread yet.............

 

[n5lp]

...
Sensenich RV props have a barred speed range which means they have a harmonic vibration peak in the engine operating range. To me this is unacceptable...

Just a note that this RPM restriction applies only to the Sensenich for the O-320.

 

[apkp777]

I don't know how to throw this into the mix, but what about the ground adjustable prop from Sensenich. Where do you think this falls?

 

[rv7boy]

FP vs CS

...and don't certain models of the Hartzell constant speed prop on certain lycomings have an RPM range to avoid at certain power settings? I don't think it's true for the blended airfoil props, but rather for some of the older Hartzell CS props. The details escape me now.
There's a lot to know in this area before one makes a good decision. Do lots of homework.

 

[Rick6a]

The restricted range for the Sensenich FP prop on an O-320 is rpm in excess of 2600.....

Sam brings up a fair point and as usual, is absolutely correct. To give you an idea of what that means in the real world, consider this: My Sensenich prop is bolted to an O-320, thus the prop RPM limitation exists. Since the O-320 engine develops 155 H.P. at 2600 RPM, we seldom approach anything near max engine RPM so it follows we enjoy pampering our engines automatically.

As for real world performance, I've showed skeptics over and over again with flight demonstrations. Just give me a modest tailwind component to work with and GPS measured groundspeed easily flirts with and often generously exceeds 200MPH. That is what I call efficiency on a blue collar budget.

 

[Ron Lee]

180 HP or better engine

CS prop

 

[kevinh]

My 7A O-360 has a constant speed prop. I just got back from flying a friends RV with an O-360 an a fixed pitch prop (I was flying solo to do the 'acro' checklist items he wanted on phase I).

Yes, the constant speed is awesome. However, the fixed pitch is still a great plane. His plane climbed way better than any spam can I've flown. So if the cost and maintenance is a turn-off, you might want to avoid the tempation to spend extra money (especially if lots of mtn flying isn't in the cards).

As for slowing down, it isn't a big deal - it just requires a little bit of planning.

 

[MauiLvrs]

... The differences that will be noticeable will be on the takeoff performance and braking performance (slowing the plane down to land) you will see. This will be where you will have to make your decision as to whether the extra expense and weight is worth it.

Very true on both counts.
With just me on a cool morning with 20 deg flaps the takeoff roll can't be much more the 150 feet.

No problem getting it slowed down either.

Now if the engine quits, that would be a different set of trade offs....

 

[L.Adamson]

I don't know how to throw this into the mix, but what about the ground adjustable prop from Sensenich. Where do you think this falls?

I think it will just end up at the most compromised setting...........most of the time. It won't be a climb prop like a C/S, won't have the braking ability of a C/S, and you won't being pulling the rpms back in cruise for quieter flight, as is done with a C/S.

Pulling the spinner everytime to change prop settings, seems like a bit of hassle to me. I just see this prop as being a compromise depending on the conditions..............and not adjusted all that often.

L.Adamson --- RV6A/ Hartzell CS

 

[rvator51]

ground-adjustable prop

For a person looking for a fixed pitch prop, I think the ground-adj prop has some advantages. You would be able to dial it in for best performance for your RV and you could decide what "best performance" is for you. Maybe if you are doing a lot of local flying, you might set it up for higher climb rate and if you were doing a long trip or two, you could set it up for best cruise at a certain altitude. Certainly not as simple as a C/S, but if you werent going to buy a C/S anyway, that might be the way to go.

 

[apkp777]

I think it will just end up at the most compromised setting...........most of the time. It won't be a climb prop like a C/S, won't have the braking ability of a C/S, and you won't being pulling the rpms back in cruise for quieter flight, as is done with a C/S.

Pulling the spinner everytime to change prop settings, seems like a bit of hassle to me. I just see this prop as being a compromise depending on the conditions..............and not adjusted all that often.

L.Adamson --- RV6A/ Hartzell CS

That's what I am thinking. I see myself just having a more expensive fixed pitch prop that once in a while I tweak for a particular flight or two.

 

[N941WR]

The question is, what is acceptable climb rates?

With my old fixed pitch prop on an 135 hp O-290, I could climb at 1800 FPM on a hot day, solo. Load up the plane at gross and it would "only" climb at around 1000 FPM. Oh bummer!

Granted, the CS prop will push you into the back of the seat when you push the black knob forward.

For me, it has been about useful load, fast cruise, and acceptable climb. Thus a FP Catto prop is my choice.

Notice how this is written, "I", "for me", "my choice". Your requirements may be different; however, no FP O-320 powered RV is a dog in climb or cruise, except when compared to another RV with a CS prop.

 

[Ron Lee]

No FP O-320 powered RV is a dog in climb or cruise, except when compared to another RV with a CS prop.

That is where you will see the delta and lament the 160 HP engine and FP prop. So do not fly with other RVs if you go with 160 HP/FP prop.

Yes I am opinionated.

 

[Sam Buchanan]

That is where you will see the delta and lament the 160 HP engine and FP prop. So do not fly with other RVs if you go with 160 HP/FP prop.

Yes I am opinionated.

Well Ron, you just messed up my whole flying world.

I've been flying with a pack of RV's for eleven years, many of which have CS props. I failed to get the memo that I am supposed to feel inferior and intimidated because my old RV-6 has a little motor and FP prop.

Guess now I'll have to let the gang go without me and maybe I can sneak into breakfast without any of them seeing me.

 

[jclark]

It depends ...

Can anyone tell me if there is a sufficient performance difference in an O320 with a constant speed VS a fixed pitch prop (160hp). I realize there will be some difference but is there any emperical data showing the differences. I am trying to make the determination and if the top end is not significantly different I would be hard pressed to go with the higher priced, higher maintenance constant speed prop. I don't need to squeese out every bit of speed, just something reasonably close to the stated performance goals. Its time to order the finish kit!!!

I have flown the SAME RV6 with Sterba, MT and Catto (3-blade) fixed pitch props as well as Hartzell CS prop. I have also flown RV6A and RV9A with Sensenich FP and one of those RV9A's with Catto (3 blade).

With all of that I say it depends ...

The Sterba was most economical. Worked fine (have to slow down in rain though), was smooth. The MT and Catto gave better rain protection and each was dialed in for a slightly different RPM. For each of those props I was able to exceed 170kts true airspeed, given willingness to go wide open throttle. I tested them past 2800 RPM but afterwards never flew them that hard.

The weight with them all was a wash.

My acceleration was slow **compared to some RV's*** but it was just fine. My cruise was fine.

I changed to the CS for Formation Flying. (For the Team RV airshow group now, don't show up without one. ). Although my acceleration and deceleration is significantly better, my cruise speed is not significantly better.
There is more weight on the nose although in my case, with other changes, it amounted to about an additional 10 lbs I think.

Long-winded response to say her is MY opinion ....

1. Get a hollow crank engine for sure.
2. Start with an Ed Sterba if you want the "most economical".
3. Start with a Catto 3-blade if you want a nice, smooth, efficient prop and "3-blade sex appeal".
4. Start with a Sensenich if you want the benefits of metal (don't be bothered by the 2600 RPM restriction as I have had planes OUTRUN ME(!!) with those props as they really are tuned to the RVs.)

5. When you have a lot of additional $$ to spend or MUST do formation big time or need MORE climb performance, swap out the FP (sell it) and bolt on the $CS$ + some other $$tuff.


James

 

[Greg Arehart]

FWIW, I'm very happy with my FP Sensenich on an IO360 (this is in a 9) set up for cruise (87 inch pitch). Sure, my takeoff performance at 5000 ft here in Reno is "anemic" (~800-1000 FPM) but still fantastic compared to most other small airplanes. And I get very economical cruise, which is where I personally spend most of my time.

greg

 

[LifeofReiley]

I'm flying a Catto three blade with my modified 320, my friend running a IO360 200HP, blended airfoil hartz, we're in the pattern at the breakfast airport at the same time both pushing to get there. I weigh 1059, he weighs 1175... It's all about your mission, my build was light and extremely affordable, his well... we won't go there.

 

[dhall_polo]

aerobatics with cs and fp

For those who've flown RV's for aerobatics with both, care to chime in?
For the -7, it ain't all about straight and level.

You have have my blue vernier when you pry it from my cold dead hand.

Don

 

[Mel]

I regularly fly acro with my Catto 3-blade, and before that, did it with a Sensenich wood. Absolutely no complaints.
I have also flown acro in several RVs with C/S. No problems either way.

 

[ronschreck]

For those who've flown RV's for aerobatics with both, care to chime in?
For the -7, it ain't all about straight and level.

You have have my blue vernier when you pry it from my cold dead hand.

Don

I would feel comfortable doing sport aerobatics and formation flying with a FP prop. But, if you are talking competition aerobatics or formation aerobatics the CS is the hands-down winner. I have not seen a reference to high RPM limitations in this thread and the CS takes this limitation out of the equation. Long down-lines in competitive aerobatics would likely require you to exceed the 2700 RPM limit. We typically use 165 KIAS as the entry speed for formation loops. We have one team member with a FP prop and we have instructed him to resist looking at his RPM at that speed. He ain't going to like what he sees!

For those who don't need a CS for formation or aerobatics there is one very nice perk that hasn't been mentioned: on a cross-country trip you can descend from 10,000 feet at 500 fpm with cruise power and enjoy twenty minutes of 190+ knots in the descent. With a FP you would be pulling back on the power to avoid an overspeed.

For the flying that I do the CS is a must. YOU must determine the type of flying that YOU will do in your RV and make the choice that suits YOU best.

 

[rcarson]

cs VS fp

Thanks for all of the opinions. The flying I have done for years was in a Cherokee 180 FP and it was more than sufficient performance in climb and take off. Most of what I am after is cruise speed without the additional maintenance and complexity in an IFR situation. Keeping it simple is the key for the type of flying I normally have done and will continue to do. The reason I went to the experimental category was to do my own maintenance, modification, etc without the mother may I with the FAA and the outstanding performance of more modern design. An RV will still out climb the old Cherokee by at least double at gross with an FP. This forum has helped me more than you all know. Thanks again.

 

[rzbill]

Amen

There is one very nice perk that hasn't been mentioned: on a cross-country trip you can descend from 10,000 feet at 500 fpm with cruise power and enjoy twenty minutes of 190+ knots in the descent. With a FP you would be pulling back on the power to avoid an overspeed.

Hartzell is under the bench awaiting install. Looking forward to smoking downhill even better than the Arrow I rent during this build. (yes yes, I know about TAS Vne). This was my #1 reason for CS, not climb or decel.

 

[sahrens]

FP vs CS

I have been going round and round on this issue. FP, no CS, no FP, no really CS. Thanks for making the decision easier... FP it is!

 

[L.Adamson]

I have been going round and round on this issue. FP, no CS, no FP, no really CS. Thanks for making the decision easier... FP it is!

In California with sea level altitudes..............you might do okay...

Up here in the Rockies of the western US..........it's just no contest between a fixed pitch & constant speed. The C/S can do everything the F/P can't....

The C/S was one of the first items I ordered, at the expense of a few other priorities I would have liked. I'd do the same, again.

L.Adamson --- RV6A

 

[apkp777]

I have been going round and round on this issue. FP, no CS, no FP, no really CS. Thanks for making the decision easier... FP it is!

Would you consider the new Sensenich ground adjustable? I am giving it some thought?

 

[David-aviator]

Would you consider the new Sensenich ground adjustable? I am giving it some thought?

One of my friends saw one at OSH and has gone ga-ga over it. Evidently, it is a thing of beauty inside and out, and very easy to adjust.

 

[apkp777]

One of my friends saw one at OSH and has gone ga-ga over it. Evidently, it is a thing of beauty inside and out, and very easy to adjust.

Yes, it looks really nice. However, do you think it's worth $3700. My Catto needs to be re-pitched and my options are sell the Catto, go with the GAP or re-pitch the Catto.

 

[PCHunt]

The obvious advantage of the Ground Adjustable prop is that you can have several different FP props at your disposal without having to remove and reinstall the prop.

Cruise prop setting for long X/C from long runways in winter. Come summer, and you need better climb performance for a shorter hop from a shorter runway, you merely adjust the pitch of the prop accordingly.

If you need that capability, the GA prop makes sense.

I think Whirlwind makes a Ground Adjustable prop, as well.

 

[rvbuilder2002]

In California with sea level altitudes..............you might do okay...

Up here in the Rockies of the western US..........it's just no contest between a fixed pitch & constant speed. The C/S can do everything the F/P can't....

The C/S was one of the first items I ordered, at the expense of a few other priorities I would have liked. I'd do the same, again.

L.Adamson --- RV6A

The question builders need to each answer for them selves is...do they need the added performance ?

Larry is correct. The CS prop gives an RV the maximum performance it is capable of with any specific engine.

In 17 years and 1300+ hours of flying RV's (both FP and CS), I have never, ever, found my self sitting at the end of a runway with the throttle in my hand, wishing I was in an RV that had a CS prop on the front (nor have I ever completed a takeoff and afterwords vowed to never do that again in a fixed pitch RV).

I have flown RV's in the Rocky mountains a lot. I just completed a trip to OSH and back with my 180 FP RV-6A. There is not a single airport in all of the Rocky's that I wont land at, but would if it had a CS.

I will admit there are times I somewhat wish I had a CS. I can cruise at the same speeds as someone with a CS at most any altitudes people usually fly RV's; I just have to do it at higher RPM's. It is a little bit noisier and more fatiguing but I feel it is a worthwhile trade off for the big difference in cost, maint, and slight difference in weight. The other trade-off is that the higher RPM's result in very slightly higher CHT's and oil temps, but in all operating modes it is not a factor.
I always come back to being satisfied with the performance I get considering the big difference in cost.

Choosing a FP prop in no way makes for a substandard RV, and it will not effect the utility/usefulness of the airplane. This is assuming the use of a metal Sensenich. The wood and composite props also have great performance but limit the airplane utility somewhat because they result in an empty C.G. position that reduces baggage capacity slightly (just the opposite of a constant speed where the airplane actually has better handling with some weight in the baggage compartment).

It is a big decision...
The great thing is that regardless of which way you choose, you get a great performing airplane either way.

 

[Mike S]

Well said Scott.

Scott, that is one of the best statements concerning props I have ever seen.

Thanks.

 

[n5lp]

...In 17 years and 1300+ hours of flying RV's (both FP and CS), I have never, ever, found my self sitting at the end of a runway with the throttle in my hand, wishing I was in an RV that had a CS prop on the front (nor have I ever completed a takeoff and afterwords vowed to never do that again in a fixed pitch RV).

I have flown RV's in the Rocky mountains a lot. I just completed a trip to OSH and back with my 180 FP RV-6A. There is not a single airport in all of the Rocky's that I wont land at, but would if it had a CS...

Very well said Scott. I have flown with a lot of RVs in a lot of places and at high altitudes. The fixed pitch prop has never caused me to not be able to keep up and has never caused me to not land someplace. The performance is terrific.

The picture below was snapped at 17,500 MSL in the middle of summer. If I am reading the instruments correctly the density alitude was over 19,000 feet. 120 knots indicated for a true of about 164 knots (GS of 206 knots). I think that is pretty good altitude performance.

The main thing I miss about a constant speed is the acceleration during the takeoff. That is fun for a few moments. I actually prefer the way a fixed pitch airplane acts during the landing.

 

[Daver]

wood fp cg

just got done weighing my -9A with the Sterba wood prop.

I was worried I was too light in the nose to carry much behind the seat without exceeding the aft CG limit.

To my surprise, I couldn't exceed the aft CG with almost any combination of fuel, passengers or bags. Two 200 lb "bubbas", 30 lb of fuel and 100 lbs of bags and it still did not exceed the aft limits.

BTW, my total weight was 1044 and the nose had 262 lbs.

Dave
-9A ground testing

 

[elippse]

There is an assumption in this discussion that a cruise prop cannot be a climb prop. This is based on old, outdated technology and is simply not true. The three blade prop on my plane has over 90% efficiency in cruise at over 200 mph and at least 82% efficiency in a climb at only 105 mph IAS. My plane has only 125 hp and a wing with only 77 sq. ft., but it will climb at over 1500 ft./min at 1350 lb and 2400 rpm, which is 86% of the available power. No existing propellers can claim that kind of efficiency in cruise; I know, for I have run tests on many different types. Efficiency is what turns horsepower into thrust. You must resign yourselves to the fact that this saying is no longer true. It's like saying that a car that gets great gas mileage on the highway gets poor mileage in town. The higher the peak efficiency, the higher will be the efficiency all along the curve below peak. If a propeller has high cruise efficiency, it will also have high climb efficiency. High efficiency is high efficiency and that's all there is to it!

 

[rvbuilder2002]

just got done weighing my -9A with the Sterba wood prop.

I was worried I was too light in the nose to carry much behind the seat without exceeding the aft CG limit.

To my surprise, I couldn't exceed the aft CG with almost any combination of fuel, passengers or bags. Two 200 lb "bubbas", 30 lb of fuel and 100 lbs of bags and it still did not exceed the aft limits.

BTW, my total weight was 1044 and the nose had 262 lbs.

Dave
-9A ground testing

Is this with an O-320?

 

[Daver]

fp weight

Yes, Scott, the engine is an O-320E2A (150 HP). Its a few lbs lighter than the 160 HP versions

Dave
-9A ground testing

 

[handkas]

180 HP or better engine

CS prop

why is that? I was told that a FP will never exploit max power of -360, but sensenich does make props for this engine (85") don't they?

considering the cost and all you said here, i also think a FP will be enough for my cross-country flying, but I am still wondernig which engine to use

I know the rpm limitations of props for -320 and I'll be satisfied with perfomace. Does -360, FP make a diffrence?

also, do you know anything about GT propellers (wood-composite)? I use one on my remos G3. I love the costs and maintainance.

 

[Sam Buchanan]

What do you folks think would be the pros and cons of choosing between fixed pitch and constant speed, particularly 160 HP fixed pitch and 180 HP C/S? Performance differences?

Brian,

Use the Search feature of the forum to find a ton of info concerning your question, it gets asked often. Here are some threads to get you started:


http://www.vansairforce.com/community/showthread.php?t=61183&highlight=constant+speed

 

[MauiLvrs]

In love with our C/S on our 9

What do you folks think ...

I think, no, I know, that we are in love with our C/S on our 9 .... Because...
On a nice cool morning....
Flaps 20
Mixture forward
Prop forward
Roll onto runway and line up
Throtle 1/4 ... nose comes off
Throtle 1/2 ... plane get light
Throtle full ... plane jumps off the runway
Around 150 feet

And when we come blasting over the airport at 150 kts, it is no problem getting down to 70 kts on final after a break to downwind

Has anyone lately said how great Van's aircraft are

 

[Mile High Relic]

My advisor says...

I have been working with someone as I look for planes. I had found a really nice plane, but it had a fixed pitch prop. I'm in Denver, and my advisor said "I really think you will be happier in the long run if you buy an RV with a 180 HP engine and a constant speed prop. In Colorado, on take off, you are only pulling 24" of manifold pressure, and with a fixed prop, only 2250 RPM, which is about 60-65% power on take off. With a constant speed, you will pick up an extra 10% plus in power for take off and climb, cruise will not be much different."

If I still lived in the midwest I'd have gone with the fixed pitch, because for me, simple is good. A fixed pitch prop is stupid simple, both from a flying and maintenance perspective.

After talking to my advisor and some local builders, I have decided that I will hold out for a plane with a C/S prop.

 

[flyboy1963]

I think, no, I know, that we are in love with our C/S on our 9 .... Because...
On a nice cool morning....

Flaps 20
....etc

Hey Dave,
as a -9a driver with little time on type, I am trying to assemble the correct operational data.

why 20 degrees of flap for takeoff? Have you tested this as the best lift for the wing? If so, that can't be easy to do, so I'd like to do the same for myself, and wonder how to go about it exactly.
I asked Van's what the best lift flap setting was, and they referred me to John Roncz. If I recall, he said that he expected best lift at somewhere between 15 and 20, ( I had guessed 10!) but that this should be verified. ( for the individual aircraft, CG , loading condition etc I assume)

sorry to hijack this thread, but if you or anyone knows, obviously it could be very important to use the right setting for critical obstacle clearance & hot & high ops.

regards,

 

[HBpilot]

What does the extra maintenance for a CS involve ? (cost and work)

 

[Jamie]

What does the extra maintenance for a CS involve ? (cost and work)

Lube at each annual and follow overhaul procedure (which can vary for each manufacturer or even prop model). Most Hartzell manuals say to overhaul every five years.