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how many degrees when a CS prop is at cruise?

charosenz

Well Known Member
I am curious what the (typical) pitch is of a constant speed prop, when set to max cruise speed. I know that it will vary, but I am looking for some examples. I would be happy to know the results in either degrees, or in inches.

I know the general rule of thumb is to run at squared, MAP vs RPM. I.E. but of course that does not tell me the actual pitch in degrees or inches.

Thank you in advance to the person who can answer this.

Charlie
 
i'll look at my data Charlie. I will look to be sure the numbers are correct, but my Hartzell composite hits the max pitch stop at 165-170 kts at 2300 rpm. Let me confirm the max pitch, speed and rpm. I think you need all of these.

You might not get any other answers as I would not know the pitch if it did not hit the stop. Maybe the best source of good pitch data are people with a fixed pitch and similar speed and power to yours.
 
i'll look at my data Charlie. I will look to be sure the numbers are correct, but my Hartzell composite hits the max pitch stop at 165-170 kts at 2300 rpm. Let me confirm the max pitch, speed and rpm. I think you need all of these.

You might not get any other answers as I would not know the pitch if it did not hit the stop. Maybe the best source of good pitch data are people with a fixed pitch and similar speed and power to yours.

Bill,

Yes, I think you are right, in that most will not know, or need to know the pitch (at travel limits) for their use.

I was just thinking there would be some inquisitive minds out there that felt they just had to put a protractor or digital pitch gauge on their prop on the ground at the limits of pitch travel just to because they wanted to know....
 
Charlie, yes each prop has a book specification for the max pitch and the Hartzell aluminum BA's are much larger than my composite. This means at cruise they can really crank down (drop the governed RPM) the pitch, but can not because as long as it drops the RPM it has not reached the stop. So, at WOT, if one can keep dialing back the rpm and the engine keeps dropping, then the pitch is still increasing. I can not go below 2300 as it hits the pitch stop. It took me a wallet of money and time to understand that, but there it is.
 
I know the general rule of thumb is to run at squared, MAP vs RPM. I.E. but of course that does not tell me the actual pitch in degrees or inches.

Charlie

Well, over square is a subject for popcorn and beer.

Personally, I never run squared. Once I push the throttle up for departure, I don’t pull it back until close to the airport after descent.

If my MAP equals RPM it’s purely coincidental.
 
I am curious what the (typical) pitch is of a constant speed prop, when set to max cruise speed. I know that it will vary, but I am looking for some examples. I would be happy to know the results in either degrees, or in inches.

I know the general rule of thumb is to run at squared, MAP vs RPM. I.E. but of course that does not tell me the actual pitch in degrees or inches.

Thank you in advance to the person who can answer this.

Charlie

I think the pitch would different for every airframe, prop, RPM and HP configuration. I would also conjecture DA would be a contributing factor. It’s like a manual transmission in a car, but the gears(pitch) are pretty much infinitely variable.
 
An old time prop guy once told me that re-pitching a fixed pitch prop for better cruise vs climb performance usually resulted in about 25RPM drop for every inch of pitch twisted out. So if a 80" pitch was twisted to 82", static and initial climb out RPM if originally was 2200RPM would now be 2150RPM.

(1" pitch increase = 25RPM reduction, 4" increase = 100RPM reduction, so for 200RPM reduction would need 8" courser pitch in theory according to the old guy)

Now that is at the lower RPM/HP power bands and probably doesn't really relate well to higher RPMs/HP outputs at cruise. Just for the exercise of following that thought - a typical O-360 fixed pitched RV prop with 85" pitch that normally produces 2700RPM WOT in level flight - would need about 93" of pitch to wind it down to 2500RPM WOT.
Note this gibberish is in inches of pitch, not degrees of pitch.

Those that know of what they speak - please chime in!
 
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When I first got my 8 it had an angle valve IO360, 200 hp Lyc and a Prince 74x93 prop. Static rpm without adjusting the mixture back was 1900. Long roll for an RV, say 800 feet, but once it got going it was fast. WOT at 8500 ft about 2600 and north of 180 true. Knts.
 
I appreciate the answers and comments and examples.

Just to clarify my question, I am wondering if anyone knows the degrees or inches of pitch when it is set at minimum (climb) and maximum (cruise). For example, if your minimum is - say - 76" what is your pitch at its max travel limit for cruise 100"??

I do understand this may be difficult to determine (with oil controlled set ups) as it takes oil pressure to move the pitch and that is a bit of a challenge with the engine off.....

I only asked because I suspect there may be someone out there who knows the numbers.
 
Well, over square is a subject for popcorn and beer.

Personally, I never run squared. Once I push the throttle up for departure, I don’t pull it back until close to the airport after descent.

If my MAP equals RPM it’s purely coincidental.

Ill be over for beer and popcorn tomorrow! I have been to the Saint Simons Island. My wife grew up in Savannaugh.
 
Pretty sure there is no one out there that knows the numbers, because there are too many variables, this includes Hartzell. For an experimental amateur built airplane there are too many variables.
You originally asked for the pitch setting for max cruise speed. This would be the setting when the engine is at its max power setting for the density altitude you are at - usually 2700 Rpm, full throttle, (although on some engines it’s limited to 2600 RPM depending on prop selection). If you have your throttle firewalled and your governor, or fixed pitch selection is set up to protect the engine RPM limit (usually 2700), and you are at approximately 8,000’ DA (very variable), then you are at your max power setting (2600-2700 RPM). You can gain fuel efficiency and decreased engine wear with you constant speed prop down to 2300-2400 RPM, but this won’t give you max cruise speed

I appreciate the answers and comments and examples.

Just to clarify my question, I am wondering if anyone knows the degrees or t theinches of pitch when it is set at minimum (climb) and maximum (cruise). For example, if your minimum is - say - 76" what is your pitch at its max travel limit for cruise 100"??

I do understand this may be difficult to determine (with oil controlled set ups) as it takes oil pressure to move the pitch and that is a bit of a challenge with the engine off.....

I only asked because I suspect there may be someone out there who knows the numbers.
 
Pretty sure there is no one out there that knows the numbers, because there are too many variables, this includes Hartzell. For an experimental amateur built airplane there are too many variables.
You originally asked for the pitch setting for max cruise speed. This would be the setting when the engine is at its max power setting for the density altitude you are at - usually 2700 Rpm, full throttle, (although on some engines it’s limited to 2600 RPM depending on prop selection). If you have your throttle firewalled and your governor, or fixed pitch selection is set up to protect the engine RPM limit (usually 2700), and you are at approximately 8,000’ DA (very variable), then you are at your max power setting (2600-2700 RPM). You can gain fuel efficiency and decreased engine wear with you constant speed prop down to 2300-2400 RPM, but this won’t give you max cruise speed

Scott,

I guess what I really should have asked is if anyone knows the amount of degrees of pitch that their constant speed prop allows when compared between the minimum pitch to the maximum pitch. (My guess is that it is somewhere in the ball park of 15-20 degrees or 40-50 inches).

In other words, if you were to test the unit on the ground, with the engine off and just using oil pressure, given: if your minimum pitch is - say - 76 inches, what is the maximum pitch your particular set up allows (when full oil pressure is applied ? 100"? 120".

I understand this sorta falls in "(dont) need-to-know" category. I do appreciate the replies....

Thank you.

Charlie
 
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Charlie,
I read your last question above as being much different than the question that started the thread.

Minimum pitch on any non aerobatic prop can be measured on the ground with the engine stopped. That will be the pitch for 2700 rpm while not moving.

Similarly, the max pitch can be measured too. It requires a lever to manually twist the prop to max pitch. A common method is a pair of wood studs and some clamps to create a lever that is easy to move.

This has nothing to do with pitch at hypothetical cruise since that value is controlled by the prop gov somewhere between the 2 hard limits measured above.
 
You can get the min-max info off the Hartzell web site. For a large number of their props designed for 260 HP, top speed around 200 knots, airplanes, their prop’s minimum and maximum pitch are like 10 and 30 deg, respectively, measured at some particular station. e.g., the variation is 20 deg.
 
Charlie,

Minimum pitch on any non aerobatic prop can be measured on the ground with the engine stopped. That will be the pitch for 2700 rpm while not moving.

This is only true if the low pitch stop has been adjusted to the correct position. Many CS props haven't been set correctly and in the event of a governor failure the engine over revs when the prop goes to fine pitch (on the ground or in the air)
 
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You can get the min-max info off the Hartzell web site. For a large number of their props designed for 260 HP, top speed around 200 knots, airplanes, their prop’s minimum and maximum pitch are like 10 and 30 deg, respectively, measured at some particular station. e.g., the variation is 20 deg.

Bob,

Perfect! Thank you!

Here is a screen shot of the pitch settings for a 160 engine application from the Hartzell manual. Just in case there were any other gear heads out there who were interested....
 

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My apologies for my poorly worded original question but I have the numbers I was looking for....

thanks.

Charlie
 
Charlie has some of the info.

My Hartzell prop for an O-320 came with an "Assembly Inspection Check-Off Record" and lists Low Pitch 11.1-degrees and High Pitch 38.8 degrees / 38.9 degrees.

Have not seen this data in the TCDS or other Hartzell info that I have looked at. I am sure there is a Hartzell manual somewhere that lists the setting for the low pitch and high pitch stops. Please share a link to the document if anyone knows.
 
Charlie has some of the info.

My Hartzell prop for an O-320 came with an "Assembly Inspection Check-Off Record" and lists Low Pitch 11.1-degrees and High Pitch 38.8 degrees / 38.9 degrees.

Have not seen this data in the TCDS or other Hartzell info that I have looked at. I am sure there is a Hartzell manual somewhere that lists the setting for the low pitch and high pitch stops. Please share a link to the document if anyone knows.

Gary,

That is spot on with the info I found on the Hartzell site. I attached (in previous post) a page from their manual and highlighted the min and max pitch travel limits. It may be hard to see given it is quite small. Of the dozen or so various engines for the RV series it varies from a min pitch setting between (roughly) 11 to 13 degrees and the max varies between 27 to 35 degrees. Just what I was looking for. Of course the actual pitch will vary greatly for any given engine, aircraft, DA, and much more.

ADDED: Hartzell prop document. The Vans Aircraft pages are about 1572 or so.

https://hartzellprop.com/MANUALS/159-0000-A.pdf
 
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Charlie, my Hartzell composite stops are set to 10 deg fine, 27 deg coarse. That means that at 8000DA, 163KTAS, and 2300 RPM my prop is set 27 degrees.

The actual pitch will change somewhat with efficiency, or the airspeed.

I hope some of this helps.
 
Charlie, my Hartzell composite stops are set to 10 deg fine, 27 deg coarse. That means that at 8000DA, 163KTAS, and 2300 RPM my prop is set 27 degrees.

The actual pitch will change somewhat with efficiency, or the airspeed.

I hope some of this helps.

Bill,

That is very helpful. Good information. I gives me encouragement that the variable pitch prop I am ordering should provide a noticeable gain in top speed, especially that I have a turbo for added benefit at higher altitude.....

Charlie
 
This is only true if the low pitch stop has been adjusted to the correct position. Many CS props haven't been set correctly and in the event of a governor failure the engine over revs when the prop goes to fine pitch (on the ground or in the air)

Yep, and they are flying approach with excess rpm to maintain speed. Then will have a lead sled if they loose oil pressure.
 
This is only true if the low pitch stop has been adjusted to the correct position. Many CS props haven't been set correctly and in the event of a governor failure the engine over revs when the prop goes to fine pitch (on the ground or in the air)


Since my Hartzell BA was spot on from the factory and I have heard of zero instances of builders in my area needing to adjust the fine pitch stop, I think the number is lower that you intimate. Overspeed in the air due to gov failure has nothing to do with fine pitch stop.
 
Since my Hartzell BA was spot on from the factory and I have heard of zero instances of builders in my area needing to adjust the fine pitch stop, I think the number is lower that you intimate. Overspeed in the air due to gov failure has nothing to do with fine pitch stop.

I'm not exactly sure what your saying here but If you have a constant speed Hartzell and you haven't adjusted the low pitch stop on the prop, the governor is controlling your RPM on takeoff.

If your climbing out at 2700 and the governor fails with a correctly set low pitch stop you wont notice any RPM change until you reduce the climb rate or gain speed both of which will increase RPM.

On the other hand, If your climbing out and the governor fails and you haven't adjusted the low pitch stop, the engine over revs and can destroy itself.

My new hartzell was so far off in adjustment if my governor would have failed the engine would have potentially been close to 3800 RPM in the climb. I cant imagine what the RPM could climb to in cruise at that setting with a governor failure but I'm betting if you dont catch it in time the engine is junk.

The low pitch stop is an easy adjustment and I believe it's recommended in the manual for all new installations
 
I'm not exactly sure what your saying here but If you have a constant speed Hartzell and you haven't adjusted the low pitch stop on the prop, the governor is controlling your RPM on takeoff.

If your climbing out at 2700 and the governor fails with a correctly set low pitch stop you wont notice any RPM change until you reduce the climb rate or gain speed both of which will increase RPM.

On the other hand, If your climbing out and the governor fails and you haven't adjusted the low pitch stop, the engine over revs and can destroy itself.

My new hartzell was so far off in adjustment if my governor would have failed the engine would have potentially been close to 3800 RPM in the climb. I cant imagine what the RPM could climb to in cruise at that setting with a governor failure but I'm betting if you dont catch it in time the engine is junk.

The low pitch stop is an easy adjustment and I believe it's recommended in the manual for all new installations

What atmospheric conditions should be used to set the stop? And, isn't it only good for a zero headwind speed? After all, as one gets to 30-60-90 kts that pitch will allow the engine speed to rise (overspeed) anyway. Isn't that what happens to a fixed pitch prop, they don't start with 2700 rpm at power application.

All meaning, it is well and good to set for static run-up, so rapid throttle does not outrun the ability of the governor to advance pitch and maintain RPM. But - after 50kts we are depending on the governor anyway to advance the pitch and govern the set RPM. If I am climbing out and the governor fails, having set the fine pitch stop is not going to protect me from an excess RPM.
 
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I was surprised when I looked a the Hartzell manuals how low the minimum pitch numbers were in many cases. I.E. 11, 12, 13 degrees seems - in my very limited knowledge, considerably low pitch. While never having owned a constant speed prop, I suspect that the minimum pitch stops settings are more a course pitch than these numbers.

I do have a ground adjustable prop and I started at 20 degrees and increased it to 22 degrees. I have to admit I have never done any testing below 20 degrees. I did some napkin math and I calculated that a 12 degree setting came out as a 46 inch pitch on a 72 inch diameter prop as measured at the 95% blade radius mark.
 
If your climbing out at 2700 and the governor fails with a correctly set low pitch stop you wont notice any RPM change until you reduce the climb rate or gain speed both of which will increase RPM.

This is absolutely incorrect. Unless, of course, you are willing to accept less than 2700 rpm at the start of the takeoff roll.
 
Right. In theory, "perfect" setting of the low pitch stop will allow YOUR engine to turn 2700 RPM static at SL, standard conditions. ANY forward motion/relative wind would see the governor pull the blade off the stop and increase pitch to maintain 2700. This why you often hear the surge early in the TO roll.

That said, some of us do set our low pitch stop a little more course than that and I do not see 2700 until liftoff. I might not see much of an overspeed if the governor failed at liftoff, but it would certainly go past 2700 at my normal 135 knot climb. In my case this is a slight hedge against a governor failure/over speed event early in the flight, but won't save me in cruise (been there, done that). Such a setting certainly adds a few feet to the takeoff roll, but its a Rocket, so I'm still off in 300 feet if needed. The trade is worth it to me.
 
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As Bob said, the comment about low pitch stop controlling takeoff climb rpm is incorrect.

The low pitch stop controls static rpm only. Meaning the max RPM while the craft is not moving. As soon as the plane is moving, such as take off roll, the governor increases pitch to control RPM. Governor failure on any properly set non-aerobatic prop will cause an rpm increase in flight since oil pressure loss will allow the prop to go to fine pitch.

I do not argue that the low pitch stop is hard to adjust. I argue that it is not needed if it is correct from the factory. Low pitch stop adjustment in my area is so rare as to be non-existant. I attribute this to Hartzell knowing what they are doing when they sell a standard recommended prop to a VANS builder using a common engine.

With your 3800 rpm failure scenario, what was your static rpm? What performance feedback did you use to adjust your fine stop?


I'm not exactly sure what your saying here but If you have a constant speed Hartzell and you haven't adjusted the low pitch stop on the prop, the governor is controlling your RPM on takeoff.

If your climbing out at 2700 and the governor fails with a correctly set low pitch stop you wont notice any RPM change until you reduce the climb rate or gain speed both of which will increase RPM.

On the other hand, If your climbing out and the governor fails and you haven't adjusted the low pitch stop, the engine over revs and can destroy itself.

My new hartzell was so far off in adjustment if my governor would have failed the engine would have potentially been close to 3800 RPM in the climb. I cant imagine what the RPM could climb to in cruise at that setting with a governor failure but I'm betting if you dont catch it in time the engine is junk.

The low pitch stop is an easy adjustment and I believe it's recommended in the manual for all new installations
 
I do remember well a Lyc 360/190 HP on a Falco,2 bld hydraulic prop sized 74" model GT2-V29 had 26/28° 175 kts . Measures were recorded by a special equipment homade that we still positively use on different planes/engines/ tests combo .

https://www.facebook.com/GtProp/photos/1203278443110230

Hope this can help.

K regards Alex

www.instagram.com/gtpropellers/

This is very interesting. I looked at the link but cannot find the pages that have the pitch data. Can you provide a link to that? Either here or PM.

Thanks.
 
I'm not exactly sure what your saying here but If you have a constant speed Hartzell and you haven't adjusted the low pitch stop on the prop, the governor is controlling your RPM on takeoff.

If your climbing out at 2700 and the governor fails with a correctly set low pitch stop you wont notice any RPM change until you reduce the climb rate or gain speed both of which will increase RPM.

On the other hand, If your climbing out and the governor fails and you haven't adjusted the low pitch stop, the engine over revs and can destroy itself.

My new hartzell was so far off in adjustment if my governor would have failed the engine would have potentially been close to 3800 RPM in the climb. I cant imagine what the RPM could climb to in cruise at that setting with a governor failure but I'm betting if you dont catch it in time the engine is junk.

The low pitch stop is an easy adjustment and I believe it's recommended in the manual for all new installations

The Hartzel manual has a procedure for confirming that the low pitch stop is set correctly, but it only needs to be adjusted if that check shows that it is not within spec (This should be checked on every new installation). I think I have only had to adjust one propeller out of many installations on RV's... they are usually spot on.

As others have said, the test / adjust procedure is setting the stop relative to a static RPM. Once the airplane begins to gain airspeed the RPM would increase if it was only the low pitch stop controlling RPM in climb (just like a fixed pitch prop does). Because of that, it is not the low pitch stop regulating the RPM once the airplane is moving. That is handled by the gov.
 
The Hartzel manual has a procedure for confirming that the low pitch stop is set correctly, but it only needs to be adjusted if that check shows that it is not within spec (This should be checked on every new installation). I think I have only had to adjust one propeller out of many installations on RV's... they are usually spot on.

As others have said, the test / adjust procedure is setting the stop relative to a static RPM. Once the airplane begins to gain airspeed the RPM would increase if it was only the low pitch stop controlling RPM in climb (just like a fixed pitch prop does). Because of that, it is not the low pitch stop regulating the RPM once the airplane is moving. That is handled by the gov.

Thanks Scott....
 
With your 3800 rpm failure scenario, what was your static rpm? What performance feedback did you use to adjust your fine stop?

The static RPM before adjustment was 2710 ( the governor was doing it's job) It took 5 full turns on the low pitch stop to reduce the RPM to 2600 static. Hartzell and lycoming have different specs out there from 2600-2650 static for a constant speed, I've also seen a couple as high as 2690.

I choose to be more conservative at about 2550 static which gives me 2700 at VX. It's possible the governor is having an influence even at that speed
 
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The static RPM before adjustment was 2710 ( the governor was doing it's job) It took 5 full turns on the low pitch stop to reduce the RPM to 2600 static.
I choose to be more conservative at about 2550 static which gives me 2700 at VX. It's possible the governor is having an influence even at that speed

Per the Hartzell manual, 1 turn should have changed rpm by 200 rpm. Something isn’t right here.
As to ‘being conservative’: True, you’ve lessened the risk of an overspeed if the governor fails and you’re at Vx (How much time do you spend there?). But you’re starting every takeoff with 5% less than full power. I’m not sure which is a greater risk.
 
I see that you have chosen to operate the prop as a fixed pitch unit from takeoff to Vx. As you are the first person i have talked with to choose that route, i had not considered it in the previous operation comments. To each his own. I prefer the improved TO acceleration of full CS operation.
 
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