VansAirForceForums  
Home > VansAirForceForums

- POSTING RULES
- Donate yearly (please).
- Advertise in here!

- Today's Posts | Insert Pics

  #1  
Old 09-10-2018, 10:50 PM
pilotyoung pilotyoung is offline
 
Join Date: Jan 2018
Location: Birmingham, AL
Posts: 41
Default Fuel Burn

I bought my RV-12 in February. I have flown it about 60 hours and I am getting between 5 and 6 gallons per fuel burn. I seem to remember than Van's says you get 4.5 hours.

I flew from Birmingham, AL (KEET) to (KLUX), then to Triple Tree this weekend. I stopped for fuel at KLUX before going on to Triple Tree. I flew home straight from Triple Tree, without adding fuel at Triple Tree. I averaged between 5.5 and 6 gallons an hour of fuel burn for this trip.

One other observation from the trip is that the fuel guage reads about 1 gallon low. I landed at KLUX, the fuel guage said 5 gallons, but I only put in 13.95 gallons to completely fill the tank. When I landed at KEET, the fuel guage said 4 gallons, but I only put in 15 to competely fill the tank.

So I am worndering if something is not set correctly and I am burning more fuel than I should. The aircraft runs fine, it trues in the 115 range with thewheel pants off. Twice this weekend it seemed everythig fas fine except I shold hve ben burning 45 gal per hour instead of hte higher figrel.

So this is my experiencel I m wondeing what others are experiencig with fuel burn nubers in he standard 912 ULS engine?n
Reply With Quote
  #2  
Old 09-11-2018, 12:08 AM
dpemmons dpemmons is offline
 
Join Date: Apr 2017
Location: San Francisco, CA (KDVO)
Posts: 16
Default

I’ve seen related issues on a 2010 rv12 I recently bought. See my thread from a few weeks ago. Still figuring it out, but now know my prop was massively over pitched and that likely contributed.

What altitude were you at and what was your indicated manifold pressure and rpm? Were you at full throttle?
__________________
2018 Donation ✔
Reply With Quote
  #3  
Old 09-11-2018, 05:25 AM
BigJohn BigJohn is offline
 
Join Date: Nov 2008
Location: Gloversville, NY
Posts: 1,538
Default

If you were seeing 115 TAS with wheel pants off, you had to be running at near WOT. In that case 5.5 - 6.0 GPH is normal. 4.5 GPH can be obtained, but at a reduced power setting.

You do not say which fuel gauge you are looking at. Assuming it is the guage driven by the float in the tank, you may want to recalibrate.
__________________
John Peck, CFII, A&P, EAA Tech Counselor, Flight Advisor.
“Master Pilot” Award, UFO Member.
RV-12 N37JP 120176 Flying since 2012.
One Week Wonder Build Team, OSH 2018.
VAF paid through 10/2018.
Reply With Quote
  #4  
Old 09-11-2018, 07:10 AM
rejnovca rejnovca is offline
 
Join Date: Feb 2005
Posts: 53
Default

The fuel flow shown on the EFIS is total fuel flow to the engine and does not account for the flow in the fuel return line to the tank. To get accurate fuel burn use the fuel add and total hours flown numbers when you refuel. You should find these in the 4.5 gal/hr or less range.
Reply With Quote
  #5  
Old 09-11-2018, 08:05 AM
pilotyoung pilotyoung is offline
 
Join Date: Jan 2018
Location: Birmingham, AL
Posts: 41
Default Fuel Burn

I based my numbers on having the aircraft full before I took off, and the amount of fuel I added when I landed 2 1/2 hours later. I was flying at 5500 feet into a 10 kt headwind at about 5400 rpm.

I have learned that when I land and the fuel guage reads 5 gallons or 4 gallons, it really has 1 more gallon. I don't want to land with less than 4 gallons.

What rpm do you guys fly with to get 4.5 gph?
Reply With Quote
  #6  
Old 09-11-2018, 08:34 AM
rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 7,749
Default

Quote:
Originally Posted by rejnovca View Post
The fuel flow shown on the EFIS is total fuel flow to the engine and does not account for the flow in the fuel return line to the tank. To get accurate fuel burn use the fuel add and total hours flown numbers when you refuel. You should find these in the 4.5 gal/hr or less range.
This might be true for some RV-12's if they have never had the fuel flow indication calibrated.
If the Kfactor is adjusted based on actual fuel used vs indicated fuel used, it can get the fuel flow indication quite accurate. Even though some fuel is always being returned to the tank, if the fuel pressure is relatively constant, the return fuel flow will be constant as well, and this can be calibrated out of the actual fuel flow reading.
It is not perfect, but it will very close.
__________________
Any opinions expressed in this message are my own and not necessarily those of my employer.

Scott McDaniels
Hubbard, Oregon
RV-6A (aka "Junkyard Special ")
Reply With Quote
  #7  
Old 09-11-2018, 08:47 AM
rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 7,749
Default

Quote:
Originally Posted by pilotyoung View Post
I based my numbers on having the aircraft full before I took off, and the amount of fuel I added when I landed 2 1/2 hours later. I was flying at 5500 feet into a 10 kt headwind at about 5400 rpm.

I have learned that when I land and the fuel guage reads 5 gallons or 4 gallons, it really has 1 more gallon. I don't want to land with less than 4 gallons.

What rpm do you guys fly with to get 4.5 gph?
The fuel flow and fuel level indications on the EFIS require calibration.
It is possible yours was not done properly, or that something has changed slightly since it was.

The indication for fuel level is quite accurate if the calibration has been done properly, and it could be redone.

Regarding cruise power fuel flow of 5.5 - 6 GPH..... There are a lot of factors that can have an influence on this. One of the primary is propeller pitch. Since it is adjustable there is no way of knowing what influence your propeller pitch setting is having compared to other RV-12's.

115 kt TAS with no wheel pants, at lower altitudes like 5500 will likely produce fuel burn in the range you are seeing, but more info would be required (such as throttle position / manifold pressure, etc.)

With a proper propeller pitch setting and flight at higher altitudes, very good true airspeeds are attainable with good fuel economy.
__________________
Any opinions expressed in this message are my own and not necessarily those of my employer.

Scott McDaniels
Hubbard, Oregon
RV-6A (aka "Junkyard Special ")
Reply With Quote
  #8  
Old 09-11-2018, 09:23 AM
DaleB's Avatar
DaleB DaleB is offline
 
Join Date: Sep 2012
Location: Omaha, NE (KMLE)
Posts: 1,894
Default

I've consistently seen higher fuel burn in mine (completed in 2011, now with a little over 400 hours) than others I have talked to. A friend on field will walk away from me in cruise while burning almost a full gallon per hour less fuel. Of course he also installed the HACman mixture control, so all comparisons are now skewed by that as well. But even comparing notes with others at Oshkosh, it's been obvious we're burning more gas than others have been.

The prop was significantly over-pitched when I bought it, with the static full-throttle RPM set at about 4700 until I fixed it. Correcting that helped some with speed and fuel consumption. I was still burning over 6 GPH in cruise -- wheel pants on, 5300-ish RPM, 4500-6500 MSL typically. EGTs have also always been a little low, below 1250 almost all of the time.

During the CI we just finished, I did the carb inspection. Replaced the needle jet and jet needle, O-rings, all that. Didn't replace diaphragms or floats, they're still good. But I did set everything dead on factory spec. It's still early, but the fuel consumption seems to have changed for the better. EGTs over the weekend were just a little higher, but we know we have a little bit of a starting carburetor (AKA choke) issue due to a bad cable, replacement is on the way. It was also a LOT easier to set the carburetor balance, and they're extremely closely balanced now from idle throughout the RPM range. We may have also corrected a minor rigging problem; it's too soon to tell if that's having an effect since the wheel pants aren't on yet.

So, from experience I can think of a few reasons for 6 GPH or higher fuel burn. Over-pitched prop. High RPM operation, meaning over 5300. Mis-adjusted or worn carburetor parts.
__________________
Dale
Omaha, NE
RV-12 # 222 N980KM "Screamin' Canary" (bought flying)
Fisher Celebrity (under construction)
Previous RV-7 project (sold)
-=VAF=- 2017 dues paid
Reply With Quote
  #9  
Old 09-11-2018, 10:08 AM
tomkk's Avatar
tomkk tomkk is offline
 
Join Date: Apr 2014
Location: Port Orange, Fl
Posts: 779
Default

Quote:
Originally Posted by BigJohn View Post
If you were seeing 115 TAS with wheel pants off, you had to be running at near WOT. In that case 5.5 - 6.0 GPH is normal. 4.5 GPH can be obtained, but at a reduced power setting.
Without wheel fairings, I regularly get 116 kts TAS at 5400 RPM with 5.1 GPH on the Dynon readout at about 3000' DA. 113 kts at 5300 with 4.9 GPH. At my prop pitch, I get 5680 RPM WOT at that altitude. Chock to chock I'm abouit exactly to 5.0 GPH (Fuel actually burned/Hobbs time).

I've got a bit over 500 hrs on my -12 and spent quite a bit of time calibrating the K-Factor but, to tell the honest truth, I rarely pay it much attention. My fuel gauge is extremely accurate and I pay more attention to that than the fuel flow.
__________________
Tom
Port Orange, Fl
RV-12 N121TK ELSA #120845; first flight 06/10/2015
RV-12 N918EN ELSA #120995 Eagles Nest Project
Reply With Quote
  #10  
Old 09-11-2018, 06:17 PM
pilotyoung pilotyoung is offline
 
Join Date: Jan 2018
Location: Birmingham, AL
Posts: 41
Default Fuel Burn

Thanks for all the information. I am going to check the prop pitch and see what rpm I get wot at altitude on the next flight.

The fuel computer is not calibrated correctly so I will be working on it also. The fuel gauge seems to be 1 gallon high which is OK with me.

While I am new to the RV-12, I have been landing with 5 gallons of fuel.
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 05:20 PM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.