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  #1  
Old 09-10-2021, 07:14 PM
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charosenz charosenz is offline
 
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Default how many degrees when a CS prop is at cruise?

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
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  #2  
Old 09-10-2021, 07:27 PM
BillL BillL is offline
 
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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.
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  #3  
Old 09-10-2021, 07:39 PM
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Quote:
Originally Posted by BillL View Post
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....
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  #4  
Old 09-10-2021, 08:05 PM
BillL BillL is offline
 
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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.
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  #5  
Old 09-11-2021, 06:17 AM
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RV8iator RV8iator is offline
 
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Quote:
Originally Posted by charosenz View Post

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 donít pull it back until close to the airport after descent.

If my MAP equals RPM itís purely coincidental.
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  #6  
Old 09-11-2021, 07:25 AM
Northernliving Northernliving is offline
 
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Quote:
Originally Posted by charosenz View Post
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. Itís like a manual transmission in a car, but the gears(pitch) are pretty much infinitely variable.
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  #7  
Old 09-11-2021, 12:03 PM
Ralph Inkster Ralph Inkster is offline
 
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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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Last edited by Ralph Inkster : 09-11-2021 at 12:21 PM.
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  #8  
Old 09-11-2021, 12:10 PM
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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.
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  #9  
Old 09-11-2021, 07:47 PM
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charosenz charosenz is offline
 
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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.
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  #10  
Old 09-11-2021, 07:51 PM
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charosenz charosenz is offline
 
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Quote:
Originally Posted by RV8iator View Post
Well, over square is a subject for popcorn and beer.

Personally, I never run squared. Once I push the throttle up for departure, I donít pull it back until close to the airport after descent.

If my MAP equals RPM itís purely coincidental.
Ill be over for beer and popcorn tomorrow! I have been to the Saint Simons Island. My wife grew up in Savannaugh.
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