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  #1  
Old 06-22-2021, 07:45 PM
airguy's Avatar
airguy airguy is offline
 
Join Date: Oct 2006
Location: Garden City, Tx
Posts: 5,546
Default The amazingly efficient wing on the -9

It's been a while since I did a really good cross country, I've made a few that qualified as XC since Sun 'n Fun, but nothing really good. Today everything lined up and I decided to go fly a bit. It's absolutely amazing what $100 of fuel can do.

I'm based in west Texas on a private strip, and decided to continue some efficiency testing that I've had in progress for a while, to get good numbers for transoceanic hops on a RTW trip. With that in mind, I topped off my tanks (67 gallons in the wing) and did a round robin tour from home, around the White Sands Missile Range, and back to home.

https://flightaware.com/live/flight/...20210622/1844Z

I wish there was a way to embed photos with descriptions in the body of a post without a file sharing site, but you'll just have to look at the attachments I suppose.

My route was 742 nautical miles, home-MAF-INK-SFL-ELP-KLRU-LAYEN intersection - TCS-ONM-CNX-CME-HOB-MAF-home. That kept me comfortably outside the restricted areas and MOA's.

In the interest of true efficiency testing, I took off and immediately reduced power to 2500 rpm, 21" map, and went lean of peak and added 4 degrees of timing to my ignition. Then I set my climb rate to 500fpm and activated the flight plan. As I climbed I added more throttle to keep 21", and I played with the mixture to keep my hottest cylinder between 390-400 - always lean, but rich enough to produce climb power. Around 12,000' I was out of throttle and dropped the climb rate to 400 fpm, and at about 15,000' I had to drop down to 300fpm for the rest of the climb - but keep in mind that at takeoff I was right at 1750 pounds and I was climbing at low power lean of peak. I settled in at 16,500 for the west bound leg and did a few mixture sweeps and adjusted my cylinder fuel flow trims (SDS injection) and get them all lined up happy, and then just proceeded to enjoy watching the scenery roll by. At 16,500' I was burning 6.0gph (about 40-50 LOP, Air-Fuel ratio in the low 16's) and showing consistently 143-144 ktas, with a DA of 18,568.

After making it west past El Paso and turning north, just before Truth or Consequences NM at LAYEN intersection I turned into the first half of the compass rose and climbed up to 17,500' for the remainder of the flight, at 300fpm. Temperature there was 28F and DA was 19,665. I was burning 5.8gph and making 143-144 ktas consistently. I turned east at Socorro and then southeast at Corona, and back home.

Total trip was 5 hours 8 minutes from crank to shutdown, including taxi. I covered 742 nautical air miles on less than 30.7 gallons of fuel - and that was burning automotive 93E10 from Walmart, all blood guts and feathers. Less than $100 actual fuel cost. That an average of 24.5 nautical miles per gallon, significantly better than my pickup. On my screenshots, the standard inboard tanks are bottom left and my outboard tanks (15.5 gallons each) are bottom right.

I took one screenshot at top-of-descent, and it shows range remaining in my tanks of 952 nautical miles, after having flown 5 hours and 742 nm. Another shot was taken of the screen at shutdown to show the flight timer and fuel remaining. It just absolutely blows my mind what this wing airfoil can do and how much it loves the high altitude.

Thanks again, VAN!
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Greg Niehues - SEL, IFR, Repairman Cert.
Garden City, TX VAF 2021 dues paid
N16GN flying 850 hrs and counting; IO360, SDS, WWRV200, Dynon HDX, IFD440, G5
Built an off-plan RV9A with too much fuel and too much HP. Should drop dead any minute now.

Last edited by airguy : 06-25-2021 at 08:10 AM.
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  #2  
Old 06-22-2021, 08:38 PM
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BlackhawkSP BlackhawkSP is offline
 
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Awesome !!! This should be front page on the website next update, for sure :-)......
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  #3  
Old 06-22-2021, 09:01 PM
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emsvitil emsvitil is offline
 
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How did your bladder last that long?

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  #4  
Old 06-22-2021, 10:04 PM
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Brdog42 Brdog42 is offline
 
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Greg, That Is Impressive!

RTW? Ive missed that intention in your posts. That will be fun to follow.
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  #5  
Old 06-22-2021, 10:57 PM
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rv6ejguy rv6ejguy is offline
 
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Great post Greg and yes, the -9 is an awesome design.
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Turbo Subaru EJ22, SDS EFI, Marcotte M-300, IVO, Shorai- RV6A C-GVZX flying from CYBW since 2003- 449.8 hrs. on the Hobbs,
RV10 95% built- Sold 2016
http://www.sdsefi.com/aircraft.html
https://www.youtube.com/channel/UCiy...g2GvQfelECCGoQ


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  #6  
Old 06-23-2021, 01:31 AM
KayS KayS is offline
 
Join Date: Jul 2009
Location: lake constance
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this is a great post! thank you for sharing.

i wonder if you could further increase your gas milage with lower RPM. Don't know if you had 2500 RPM also at cruise. I experimented a bit with my 7 and lower RPM makes LOP easier and you come closer to carsons speed with the engine still being in the efficient power setting range.
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  #7  
Old 06-23-2021, 03:35 AM
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Ed_Wischmeyer Ed_Wischmeyer is offline
 
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Agreed on the efficiency, but the ride in turbulence... not so wonderful. One very knowledgeable source says that the RV-9 "rides like a buckboard."
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  #8  
Old 06-23-2021, 03:53 AM
Cth6 Cth6 is offline
 
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Location: Central Florida
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Quote:
Originally Posted by Ed_Wischmeyer View Post
Agreed on the efficiency, but the ride in turbulence... not so wonderful. One very knowledgeable source says that the RV-9 "rides like a buckboard."
I know sacrilege, but if you slow down the ride to spam can speed it is so much smoother then that of a Piper Warrior or 172 IMO. My copilot requests that flight profile when the puffies are building fast down here.
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  #9  
Old 06-23-2021, 09:31 AM
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Carl Froehlich Carl Froehlich is offline
 
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Greg,

You might want to get data when not so deep LOP. At altitude I find just 1020 degrees LOP yields a nice operating point. Here I suspect power is dropping faster than fuel burn as you go further LOP.

Carl
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  #10  
Old 06-23-2021, 02:56 PM
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FORANE FORANE is offline
 
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Having the extra fuel onboard makes a huge difference. I wish I could carry more. When we had our 9A I didn't have extra fuel and was always afraid to run a tank to empty (or even close to it). The result is I could not have made that flight non-stop.

I completely agree with the comments regarding the ride in rough air. There were a couple flights we made in the 9A that were rough at altitude, but on the edge of dangerous when trying to land. How ironic that the plane that was so easy to fly became harder (for me) to land than my Lancair in gusty WS conditions.
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