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  #11  
Old 07-01-2019, 04:28 PM
rv7charlie rv7charlie is offline
 
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Location: Pocahontas MS
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Perusing the Lycoming power/altitude charts for a stock engine, I find that at roughly 8500', standard day, it takes wide open throttle *and* 2700 rpm (or the rpm for rated max HP) to generate 75% power. There may be a couple of HP above 75% due to reduction in pumping losses on the nomographs, but not much. Electronic ignition (modded engine) might buy another couple of HP.

The Lyc nomographs for stock engines also show a *best* BSFC of around .43 pounds per HP per hour (at 2400 rpm; not 2700). Doing the math, most HP/fuel burn numbers seen on the interwebs look a lot like fish stories, to me. :-)

Now, modded engines, or above 8.5-1 compression, obviously should give *slightly* better numbers.

Point is, I'd take the plane to 8500' DA, and run it full throttle and rated full-power rpm. If it over revs, it's underpropped (and slower than it should be). If it under revs, it's over propped, or the engine is weak, or the airframe is draggier than it should be for that engine and the proper prop for that airplane (and slower than it should be).

Of course, if it's a Sensenich metal prop on 160 HP, you're out of luck; can't be done (safely).
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  #12  
Old 07-01-2019, 06:56 PM
moosepileit moosepileit is offline
 
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Location: Floyds Knobs, IN
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75% of 160hp =120 hp
8.3gph x6#/gal= 50 #/hr
50/120=.4 BSFC, normal for air cooled, carb'd, fixed timing lawnmowers, VWs, Lycs and others.

Looked like 75% power to me.
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  #13  
Old 07-01-2019, 07:29 PM
rv7charlie rv7charlie is offline
 
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I was really addressing the OP's question, but forgot to include the significant point of 'properly leaned for best power'. My bad; I've seen this stuff for so long I sometimes forget details.

Best I can tell you is to look at Lycoming's performance charts.
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  #14  
Old 07-01-2019, 08:23 PM
moosepileit moosepileit is offline
 
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Yes, similarly I took the OP's points, asked for the relevant details and offered up my numbers as an example.

I then double / reverse-checked that I was at 75%. The Sens fixed pitch has some compromises, but it does give "Vans" numbers. I static over 2300 rpm, where many prefer more cruise speed and accept less static rpm.
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  #15  
Old 07-02-2019, 08:16 AM
gwav8or gwav8or is offline
 
Join Date: Apr 2009
Location: Durant, Ok
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Thanks for all the replies, guys. I appreciate all the info. The 6 I'm looking at indeed does have a Sensenich prop. However, I have decided to pass on the opportunity. It's a wonderful looking aircraft but I have other responsibilities at this time so I don't think the timing is right.

[Text deleted due to violation of VAF rules; S.Buchanan]

Last edited by Sam Buchanan : 07-02-2019 at 09:41 AM.
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  #16  
Old 07-02-2019, 03:57 PM
Boyd Birchler Boyd Birchler is offline
 
Join Date: Sep 2014
Location: IN
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One year ago the wife and I flew our RV7 rotating legs as PIC, around the perimeter of the lower US. The trip was 10,700 NM. We averaged 7.5 GPH (LOP)/155 knots per hour (179MPH), block to block, including all maneuvering, climbs and descents.
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  #17  
Old 07-03-2019, 12:07 PM
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DeeCee 57 DeeCee 57 is offline
 
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retired pilot using typical settings of 19/2000 returning a 130TAS at <21 l/hr (<5.5 USG/h), >6 hours endurance, and a very quiet environment

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O-360 A3A with MTV-12 3 blades
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  #18  
Old 07-27-2019, 04:55 PM
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gmcjetpilot gmcjetpilot is offline
 
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Quote:
Originally Posted by DeeCee 57 View Post
retired pilot using typical settings of 19/2000 returning a 130TAS at <21 l/hr (<5.5 USG/h), >6 hours endurance, and a very quiet environment O-360 A3A with MTV-12 3 blades
Yep slowing down (especially with a tail wind, can be nice and save fuel... and as you say more time for sightseeing and less engine noise. 5.5GPH is pretty good.... 750 Stat miles in 5 hours with 1 hour reserve... Makes sense and saves time if it saves fuel stop... Everyone is geared to fly as fast as they can... sometimes that is the way to go... but the joy of slow flight (not that 130Kts TAS is slow).
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  #19  
Old 07-29-2019, 09:49 AM
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thompsonbr87 thompsonbr87 is offline
 
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Location: Smyrna, TN
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Quote:
Originally Posted by gmcjetpilot View Post
It sounds like he has it throttled back. To compare apples and apples you should fly it FULL THROTTLE at Sea level and ALSO at 8,000 feet WOT. These are typical standard bench marks.
This was my experience. It could be that the owner is relating the numbers he typically sees based his personal flying, not the full performance capabilities of the aircraft. I used to see speeds that people posted and was disappointed thinking I had bought a 6A that was super slow. Eventually, I looked closer at the numbers I realized that my normal flight profile was not 8000' @ 75%. My cruise is usually more like 55%, and the numbers are reasonably close. I know there are probably a dozen things I could do squeeze out a few more knots if I really want them (wing root fairings, wheel pants, exhaust, etc.).
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  #20  
Old 07-29-2019, 11:56 AM
lr172 lr172 is offline
 
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Quote:
Originally Posted by Sam Buchanan View Post
That is close to what I see with my 1999 RV-6 that has similar equipment.
same here. I get 160 kts true at 8000-9000 on 8.1 or 8.2 GPH. IO-320 with balanced injectors, one EI and Catto prop.

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