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  #1  
Old 09-25-2010, 02:44 PM
JohnF JohnF is offline
 
Join Date: Jan 2005
Posts: 458
Default Static RPM

I am fairly sure I am correct about this, but other inputs would be appreciated.

I had static WOT RPM at first trial setting at 5,200 +
Next trial setting gave steady RPM increase until 4,200, then added throttle began to show a reduction in RPM.

Another trial setting gave pretty much the same thing.

Time constraints made me stop; tomorrow I will try more. I suspect the reduction in RPM after 4,200 with added throttle was due to fairly heavy over pitch setting. You agree?
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  #2  
Old 09-26-2010, 06:58 AM
yankee-flyer yankee-flyer is offline
 
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Location: Dayton, OH
Posts: 838
Wink That's right

I think you need to reduce pitch a bit. I did three settings and plotted static RPM vs. Blade angle (measured with the forum's handy attachment and a digital level) then picked the setting for 4900 rpm and got 4930. I think I need to reduce pitch setting a bit since I couldn't get to 5500 in level flight but it sure climbs nice!

Wayne 143WM/120241
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  #3  
Old 09-26-2010, 11:49 AM
JohnF JohnF is offline
 
Join Date: Jan 2005
Posts: 458
Default Static RPM

I agree, Wayne. Tried this morning to reduce pitch, but cannot move the blades enough to change things. I have a total movement latitude of one space between the marks on the indicator on the prop mount. I am going to remove the prop and check the restructer plate because something is not right. My first rpm trial was 5,200 and able to go more. Now I can't get over 4,200 and then more throttle reduces rpm..I suspect something is not right with the plate because I should be able to move the indicators more than one space.
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  #4  
Old 09-26-2010, 12:16 PM
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Jetguy Jetguy is offline
 
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Location: Texas, Fort Worth
Posts: 1,231
Default Prop Adjustment

John are you using a digital level to make your adjustments?

John
RV12 N1212K
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  #5  
Old 09-26-2010, 01:28 PM
JohnF JohnF is offline
 
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Posts: 458
Default static rpm

Yes, I have a digital level and the angle mount that (I think it was) Tony's idea posted earlier...its not the sameness of the two blades that I think is the problem, it is that I cannot move the angle enough...I should be able to have a range or blade rotation as shown on the marks on the mount of more than one space...the fact that my first run gave over 5,200 rpm with more throttle yet to be used, and now can't get over 4,200 before rpm reduction with throttle advance tells me something isn't right and I am pulling the prop to inspect the restrictor plate...I should be able to move the blades a lot more.
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  #6  
Old 09-26-2010, 02:40 PM
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Tony_T Tony_T is online now
 
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Location: Lacey, WA
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Default

Quote:
Originally Posted by JohnF View Post
Yes, I have a digital level and the angle mount that (I think it was) Tony's idea posted earlier...its not the sameness of the two blades that I think is the problem, it is that I cannot move the angle enough...I should be able to have a range or blade rotation as shown on the marks on the mount of more than one space...the fact that my first run gave over 5,200 rpm with more throttle yet to be used, and now can't get over 4,200 before rpm reduction with throttle advance tells me something isn't right and I am pulling the prop to inspect the restrictor plate...I should be able to move the blades a lot more.
John,
It only takes a small movement of the blade angle to get major change in static RPM. My prop only allows about one space on the hub for adjustment, similar to yours. Please reread Scott's recommendation to change prop pitch by only 0.3° in post #15 in this thread: http://www.vansairforce.com/communit...t=59682&page=2
Also, recommend reading the RVator article on adjusting the prop:
http://www.vansaircraft.com/RVator/2...010-RVator.pdf
in that article Scott says that a change of only 0.2°-0.3° makes a measureable change in aircraft performance. Based on that article, if you move the blades to full maximum pitch, and come back 0.3° per step, using the digital level fixture you should come close to ideal.
I doubt if there is anything wrong with your propeller.

Tony
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RV-12 #202 -- Flying

Last edited by Tony_T : 09-26-2010 at 03:39 PM. Reason: corrected to "full max pitch"
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  #7  
Old 09-26-2010, 03:26 PM
BigJohn BigJohn is offline
 
Join Date: Nov 2008
Location: Gloversville, NY
Posts: 1,508
Default I haven't run my engine yet, so....

.... I probably don't know what I am talking about, but - how could more throttle possibly reduce RPM? And how could that possibly have anything to do with the prop?

This sounds like some other problem to me - throttle linkages, carb syncronization, etc.
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RV-12 N37JP 120176 Flying since 2012.
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  #8  
Old 09-26-2010, 04:01 PM
JohnF JohnF is offline
 
Join Date: Jan 2005
Posts: 458
Default static rpm

I don't know; carb sync was done with as Carbmate and was dead on at idle
(1800) at the most sensitive setting on the carbmate, and also at max rpm which at the time was 5200 rpm. Nothing on the linkage was changed, and my first run with the prop gave over 5,200 with throttle yet remaining. I moved the prop to a flatter angle and since then can't get anywhere near 5,000; the wierd thing is that rpm max'es at aroiund 4200 and then more throttle shows as reduction in rpm. I am going to pull the prop to remove any doubt that the restrictor plate is not properly in place and more or less start over. I will also recheck throttle linkages although I doubt there's any problem there, but who knows?
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  #9  
Old 09-26-2010, 05:48 PM
Mich48041 Mich48041 is offline
 
Join Date: Apr 2008
Location: Riley TWP MI
Posts: 2,651
Default Check fuel flow

Quote:
how could more throttle possibly reduce RPM?
If the prop adjustment does not fix the low RPM, the fuel pressure and flow rate should be checked. A RPM drop with more throttle could mean that there is a restriction in the amount of fuel reaching the engine. Once the engine reaches maximum RPM with available fuel, opening the throttle more creates a leaner mixture, thus causing lower RPM.
Joe
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  #10  
Old 09-26-2010, 07:44 PM
JohnF JohnF is offline
 
Join Date: Jan 2005
Posts: 458
Default static rpm

Joe, your input re fuel quantity makes sense, but I see in my notes that I was showing 4.8 psi fuel pressure at the time, tho' pressure and amount of fuel delivered might be different. I will look into this tho. thanks
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