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  #1  
Old 05-18-2021, 05:21 PM
00Dan 00Dan is offline
 
Join Date: Nov 2016
Location: Atlanta, GA
Posts: 223
Default How much RPM gain would I get from upgrading to PR wheel pants?

As the title implies, I have a fully faired airplane but with the old one-piece wheel pants and the two-piece aluminum leg fairings. I recently purchased a second hand three blade Catto and found it to be rather cruise pitched for my plane - my static RPM is approximately 2090, and it winds up to 2150 in the takeoff roll. My WOT RPM at 7500í is 2640.

In speaking with Nicole, it seems I could benefit from a repitch for more static and climb out RPM. In the process of this, I inquired if the additional airspeed from the newer wheel pant design would make up any of the difference; she wasnít sure.

So thatís my question. Will upgrading my wheel pants let my prop spin up to the magic 2700 RPM as currently pitched? Similarly, while it obviously wouldnít affect static, would the takeoff run and climb RPM be improved at the same airspeed? If yes, may it prove sufficient or is the static RPM still just a tad too low?

For reference, the prop is a May 2016 production (Iím not sure if thatís second or third gen.) on a 150 HP RV-4.
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  #2  
Old 05-18-2021, 09:09 PM
blaplante blaplante is offline
 
Join Date: Jan 2010
Location: Southern California
Posts: 294
Default 3-5 mph

In an article in the 2000 2nd RVator (200 mph on 160 hp) they saw 3 to 5 mph gain by changing to the newer wheel pants and also said 'as advertised'. So I guess someone back then was saying 3-5 mph and they confirmed it.

Oh, BTW, this was on RV-6A's
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  #3  
Old 05-18-2021, 09:18 PM
Kyle Boatright Kyle Boatright is offline
 
Join Date: Aug 2005
Location: Atlanta, GA
Posts: 4,634
Default

I bet you'll get most of the 60 RPM increase at 7,500' and a few more MPH.

On takeoff and climb, you'll probably get a very, very modest performance increase, but I think it would take a gen-u-ine test pilot with a kneeboard, a stopwatch, a flightsuit, and maybe a few epaulets to actually measure the improvement.
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Marietta, GA
2001 RV-6 N46KB
2019(?) RV-10
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  #4  
Old 05-19-2021, 06:30 AM
Scott Hersha Scott Hersha is offline
 
Join Date: Jan 2005
Location: Cincinnati, OH
Posts: 1,956
Default

Quote:
Originally Posted by Kyle Boatright View Post
I bet you'll get most of the 60 RPM increase at 7,500' and a few more MPH.

On takeoff and climb, you'll probably get a very, very modest performance increase, but I think it would take a gen-u-ine test pilot with a kneeboard, a stopwatch, a flightsuit, and maybe a few epaulets to actually measure the improvement.
I agree with Kyle. It seems like your prop is almost perfect right now. If you re-pitch the prop for higher static, youíll probably overspeed if you are trying not to exceed the 2700 Lycoming recommended limit. The wheel pants will give you more RPM at higher speeds because of less drag rise, but not so much when slow. The one piece gear leg fairings wonít make any difference at all, unless the two piece ones you have now are in bad shape or not aligned properly.
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RV6/2001 built/sold 2005
RV8 Fastback/2008 built/sold 2015
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RV8/2018 built/Sold(sadly)
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RV6/Used kit purchased 2021 building
Cincinnati, OH/KHAO
JAN2021
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  #5  
Old 05-19-2021, 06:52 AM
lr172 lr172 is offline
 
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 6,539
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On the prop, be sure to think through your typical flight habits. My 320 has a moderately under pitched prop and fits my style perfect. I get better climb and at 8000', I could get a bit over 2800, if I ran ROP. However, I almost never cruise ROP. At 8000, I get 2730 RPM at 8 GPH and that is perfect for me. I can also get 2690 at 13000' at peak or slightly ROP. If I had more pitch, I would probably get similar cruise performance (at a lower RPM), but could go faster with more fuel without hitting 2800, however, my climb rates would be lower. Its all about finding the right compromise with FP props.

Remember, lycoming's RPM limits have tach error factored in, as back in the day, the old mechanical tachs often couldn't get any closer than that. Lycoming allows + or - 5% accuracy on the tach, I believe. The means that ultimate limit is really 2835, if you have a trustworthy, modern electronic tach. I do most of my cruising around 2720-30 and engine has done well fo 700 hours. I am not in the camp that thinks the engine will grenade at 2701 RPM, though I do respect the other camp that does. We each have to form our own opinions and limits. I should add that I would not be so cavalier with the RPM if I didn't have a tach that I trusted to be +/- 10 RPM.

Best to think through the options.

Just another opinion to consider.


Larry
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Last edited by lr172 : 05-19-2021 at 07:03 AM.
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  #6  
Old 05-19-2021, 09:11 PM
jrs14855 jrs14855 is offline
 
Join Date: Apr 2008
Location: Lake Havasu City AZ
Posts: 2,592
Default RPM

In the era of the Pitt's with fixed pitch prop and parallel valve engine, the engines usually were overhauled at 12-1400 hours because 1200 was the recommended TBO for aerobatics. every aerobatic flight in that era was 3300 to 3500 rpm depending on prop pitch.
The geared Lycomings from the 400 series to the 541 all turned up in the 3500 range. TBO's were in the 1200 hour range.
To have any concern about 2800 or even 2900 rpm is ridiculous.
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  #7  
Old 05-20-2021, 10:53 AM
00Dan 00Dan is offline
 
Join Date: Nov 2016
Location: Atlanta, GA
Posts: 223
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The prop is designed for 2750 RPM on a 160 HP engine. Iím not too worried about the 2700 RPM limit based on what Iíve read, Iím more using it as a baseline for determining over/under pitched.

I ordered the new fairings, so Iíll see how far that gets me before I make a non-easily reversible change like a repitch. Of course, I could also just consider the prop as is future-proofing me when I eventually redo the engine and go 8.5:1.
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  #8  
Old 05-20-2021, 01:50 PM
MK77 MK77 is offline
 
Join Date: Apr 2013
Location: Evanston, IL
Posts: 138
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My Catto 3-blade prop is pitched a little bit lower than I thought I'd like at first (WOT at 8000 DA is around 2830 RPM, 2250 static). To Larry's point, although I've considered re-pitching it to hit 2700 RPM at WOT, I find that with my typical flight profile I enjoy the higher climb rate and faster acceleration from my prop. I do fly cross-countries where I wish I could run WOT at a lower RPM, but I honestly don't fly XC that often compared to local fun / acro / breakfast runs.

That said, I feel if I were you, I'd definitely want to have it re-pitched so that I could get more RPM out of it. 2700 at least. Seems like you'll gain top speed and climb performance with that change.
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  #9  
Old 05-21-2021, 06:59 AM
RVDan RVDan is offline
 
Join Date: Jun 2012
Location: Frederick, MD
Posts: 940
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Quote:
Originally Posted by MK77 View Post
My Catto 3-blade prop is pitched a little bit lower than I thought I'd like at first (WOT at 8000 DA is around 2830 RPM, 2250 static). To Larry's point, although I've considered re-pitching it to hit 2700 RPM at WOT, I find that with my typical flight profile I enjoy the higher climb rate and faster acceleration from my prop. I do fly cross-countries where I wish I could run WOT at a lower RPM, but I honestly don't fly XC that often compared to local fun / acro / breakfast runs.

That said, I feel if I were you, I'd definitely want to have it re-pitched so that I could get more RPM out of it. 2700 at least. Seems like you'll gain top speed and climb performance with that change.
Just a heads up on overspeed limits and inspections. If you have a Lycoming engine with a 2700 RPM redline, anything other than a momentary excursion above 2835 requires an overspeed inspection. I know we are exp. but this is for safety. See Lyc SB 369S. You also need to consider any prop RPM limits. In my days of doing engine overhauls, I saw overspeeds result in real damage.
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  #10  
Old 05-21-2021, 10:40 AM
MK77 MK77 is offline
 
Join Date: Apr 2013
Location: Evanston, IL
Posts: 138
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Quote:
Originally Posted by RVDan View Post
Just a heads up on overspeed limits and inspections. If you have a Lycoming engine with a 2700 RPM redline, anything other than a momentary excursion above 2835 requires an overspeed inspection. I know we are exp. but this is for safety. See Lyc SB 369S. You also need to consider any prop RPM limits. In my days of doing engine overhauls, I saw overspeeds result in real damage.
Thanks for the info Dan. I don't run above 2700 other than when I tested the WOT max RPM of the prop / engine combo. I usually run at 2650 or less in a X/C cruise setting. In this case, I do have to pull the throttle way back which is why I debated re-pitching the prop.
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Garmin G3X
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