VansAirForceForums  
Home > VansAirForceForums

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

- Today's Posts | Insert Pics

  #1  
Old 04-27-2019, 09:41 PM
mikesmithstormlake mikesmithstormlake is offline
 
Join Date: Aug 2012
Location: storm lake ia
Posts: 13
Default High fuel flow

Yesterday while flying my first cross country flight my fuel flow was 5.4 gph at 5500 ft at 5350 rpms. When I climbed to 7500 ft my fuel flow was 7.5 gph at 5350 rpm. I descended back to 5500 ft and flow showed 5.4 gph again. Couldn't really be burning 7.5 gph could it?? Any ideas .
Reply With Quote
  #2  
Old 04-28-2019, 06:00 AM
AlexPeterson's Avatar
AlexPeterson AlexPeterson is offline
 
Join Date: Sep 2005
Location: Maple Grove, MN
Posts: 2,184
Default

Quote:
Originally Posted by mikesmithstormlake View Post
Yesterday while flying my first cross country flight my fuel flow was 5.4 gph at 5500 ft at 5350 rpms. When I climbed to 7500 ft my fuel flow was 7.5 gph at 5350 rpm. I descended back to 5500 ft and flow showed 5.4 gph again. Couldn't really be burning 7.5 gph could it?? Any ideas .
Could be fuel vapor bubbles going through the fuel flow transducer.
__________________
Alex Peterson
RV6A N66AP 1600+ hours
Maple Grove, MN
Reply With Quote
  #3  
Old 04-28-2019, 07:07 AM
John-G John-G is offline
 
Join Date: Jan 2012
Location: Northeast Ohio
Posts: 589
Default

Mike -

Were you burning mogas??? If so, perhaps a little experimenting would shed light on the issue. Assuming you are running mogas ... it would be interesting if you can repeat the high ff readings at 7500 ft then land, siphon out the mogas and replace with 100LL and climb back to 7500 ft and see if there is a change in the ff readings.

Of course, in order for the testing to be remotely meaningful, you would want to test on a day that is around the same temperature as the day you experienced the issue.

If the switch to 100LL makes a notable improvement, you may want to consider running a blend of mogas and 100LL between now and June 1 when the mogas switches over to the summer blend ... which has a lower RVP (Reid vapor pressure). As it gets warmer between now and June, I routinely blend around 30% 100LL with my mogas .... seems to really help reduce vapor issues as the days get warmer but the summer blend of fuel is not yet available.
__________________
John
www.dogaviation.com
RV-12 Wings, Empennage, Fuselage, Finishing, Avionics and Powerplant kits all completed
Now Flying!!

Dues paid until September 2020
Reply With Quote
  #4  
Old 04-28-2019, 09:50 AM
DHeal DHeal is offline
 
Join Date: Sep 2006
Location: Windsor, California
Posts: 824
Default

There is an interesting report regarding a recent accident involving a Czech SportCruiser (Rotax 912 ULS) at KSMO -- see:

http://www.kathrynsreport.com/2019/0...ed-to-and.html and https://dms.ntsb.gov/pubdms/search/h...E53086BF684941

In the report, the following is noted:

"According to technical representatives from FloScan, the introduction of air into the fuel supply lines can cause the unit to read higher than normal fuel flow rates.

According to technical representatives from Electronics International Inc. (EI) (who manufacture the FT-60 fuel flow transducer, installed on later models of the SportCruiser), when air inadvertently enters a rotor style flow transducer through the fuel lines, the rotor is free to spin at the velocity of the air that passes over it. This velocity is higher for air than it is for fuel, and as such "vapor lock" is often represented as spikes in fuel flow. Additionally, with air in the system, pulses of air from the fuel pump can cause the rotor to spin back and forth in both directions. Under these conditions, the pickup still measures flow irrespective of direction, resulting in "jumping" fuel flow readings."

While there are a number of significant design difference between this specific SportCruiser and our RV-12s (e.g., no fuel return system, FF module, etc.), I found the above information to be interesting.
__________________
David Heal - Windsor, CA (near Santa Rosa)
EAA #23982 (circa 1965) - EAA Technical Counselor and Flight Advisor; CFI - A&I
RV-12 E-LSA #120496 (SV w/ AP and ADS-B 2020) - N124DH flying since March 2014 - 825+ hours (as of Sep 2019)!
VAF donation through June 2020.
Reply With Quote
  #5  
Old 04-28-2019, 10:08 AM
Piper J3's Avatar
Piper J3 Piper J3 is offline
 
Join Date: Nov 2014
Location: Hinckley, Ohio
Posts: 1,494
Default

Quote:
Originally Posted by mikesmithstormlake View Post
Yesterday while flying my first cross country flight my fuel flow was 5.4 gph at 5500 ft at 5350 rpms. When I climbed to 7500 ft my fuel flow was 7.5 gph at 5350 rpm. I descended back to 5500 ft and flow showed 5.4 gph again. Couldn't really be burning 7.5 gph could it?? Any ideas .
Was electric fuel pumping running continuously? Some folks have added a switch to shut off electric fuel pump, which in my opinion, is bad idea.
__________________
-
Jim Stricker
Hinckley, Ohio (1OA2)
EAA #499867
PPL/ASEL 1970 - Sport Pilot since 2007
80 hrs Flying Aeronca Chief 11AC N86203
1130 hrs Flying 46 Piper J-3 Cub N6841H
RV-12 E-LSA #120058 AWC July 2012 N633CM
RV-12 Bought Flying Oct 2015 with 48TT - Hobbs now 490

LSRM-A Certificate 2016
Special Thanks... EJ Trucks - Crew Chief A-4 Skyhawk
MJ Stricker (Father & CFI) - 1st Lt. Captain B-17H
Reply With Quote
  #6  
Old 04-29-2019, 06:13 AM
bobnoffs bobnoffs is offline
 
Join Date: Jul 2012
Location: n. wi
Posts: 635
Default

this as just a fwiw. my jab had a mechanical pump and an electric backup which i used for takeoffs and landings. whenever i would forget and leave the electric pump on, in straight and level flight, fuel burn would show 25-35% higher.
just to cloud the issue.....
__________________
Bob Noffs
n. wi.
dakota hawk/jab 3300 built and flying. sold 6/18.getting serious about the 12.
RV-12 kit as of 9/13
Reply With Quote
  #7  
Old 04-29-2019, 08:23 AM
pilotyoung pilotyoung is offline
 
Join Date: Jan 2018
Location: Birmingham, AL
Posts: 124
Default High Fuel Flow

Jim,

I am interested in your opinion. Will you share why you think a switch and turning the pump off in cruise is a bad idea?

Thanks.

John
__________________
John D. Young, RV-12 Owner
Serial Number 120022, N6812Y
Bought it as a flying airplane in Feb. 2018
Just passed 140 hours flight time in RV-12, and 10,000 hours mostly in corporate jets. I am a CFI; CFII; MEI; and a advancd Ground Instructor, CFIG; and hoping to be able to help new RV-12 owners by doing some transition training for new builders and owners in RV-12's.
Reply With Quote
  #8  
Old 04-29-2019, 11:22 AM
JosephineJ79 JosephineJ79 is offline
 
Join Date: Jul 2010
Location: OSH WI
Posts: 12
Default

Here are good reasons for shutting off the electric fuel pump.
1. When the mechanical pump fails, you will find out immediately that it is not working. Why have to wait until the next pre-flight run up?
2. Shutting off the electric pump is a good way to test the vapor pressure of non-leaded gasoline. Fill the tank with your favorite brand of automotive fuel. Shut off the electric pump soon after takeoff and climb until the engine sputters. Note the altitude. Land, then repeat the test with other brands of fuel.
3. Save electricity.
Reply With Quote
  #9  
Old 04-29-2019, 12:34 PM
Piper J3's Avatar
Piper J3 Piper J3 is offline
 
Join Date: Nov 2014
Location: Hinckley, Ohio
Posts: 1,494
Default

Quote:
Originally Posted by pilotyoung View Post
Jim,

I am interested in your opinion. Will you share why you think a switch and turning the pump off in cruise is a bad idea?
If a switch is added there is a possibility to have switch in off position for critical phase of flight e.g. – takeoff. Ask yourself how many folks have taken off with elevator trim set incorrectly. Switch is also an added point of failure.

Anything to mitigate vapor lock should be religiously adhered to. Rotax 912 with carbs mounted up high on engine, and nearby hot cylinders, is known to have vapor lock issues. Having cool fuel constantly recirculate through the fuel distribution hoses under cowling with return line to fuel tank is correct design for reducing vapor lock.

Electric fuel pump assures constant source of low pressure “cool” fuel is always presented to carbs. If fuel boils in a hot carb bowl – “cool” fuel is immediately available to replenish.

Van’s recommends electric fuel pump running 100% of time. That, in and of itself, is good enough endorsement for me.

Per thread above… I don’t think I would tempt vapor lock in flight as an experiment. Enough things can go wrong on their own without purposely causing vapor lock/engine stumble. Best to have as much going in your favor at all times.
__________________
-
Jim Stricker
Hinckley, Ohio (1OA2)
EAA #499867
PPL/ASEL 1970 - Sport Pilot since 2007
80 hrs Flying Aeronca Chief 11AC N86203
1130 hrs Flying 46 Piper J-3 Cub N6841H
RV-12 E-LSA #120058 AWC July 2012 N633CM
RV-12 Bought Flying Oct 2015 with 48TT - Hobbs now 490

LSRM-A Certificate 2016
Special Thanks... EJ Trucks - Crew Chief A-4 Skyhawk
MJ Stricker (Father & CFI) - 1st Lt. Captain B-17H
Reply With Quote
  #10  
Old 04-29-2019, 03:21 PM
PilotBrent PilotBrent is offline
 
Join Date: Dec 2011
Location: Hackettstown, NJ
Posts: 454
Default High fuel flows

I was having a series of misc. equipment failures last fall (fuel tank leak, ...then a heavy float, and failing volt. regulator & finally a bad oil pressure sensor) After resolving all of them I went flying and found high fuel flow readings (very high!) sometimes above 10. Very concerning and stupid of me for not draining out the stale mogas from my tank after having the aircraft grounded for several weeks.

After syphoning out most of it and adding 100LL, the fuel flows were lower, but not entirely back to normal for me. I think the old mogas was clearly the primary cause.

At my recent annual at 5 years I replaced both the facet and the Rotax engine driven fuel pumps. Fuel flow with fresh mogas is now completely back to normal and idle fuel pressures are noticeably higher than prior to the new pumps. Maybe my old facet pump was beginning to fail, can't be sure but clearly stale mogas needs to be avoided.

I generally try to avoid using 100LL for local flights, but I'm much more diligent than ever in using fresh branded mogas.
__________________
---------------
Brent Connelly
Hackettstown, NJ
RV-12, N913BC
http://www.mykitlog.com/brent45

Check out & subscribe to my Youtube channel for latest RV-12 flying videos...
https://www.youtube.com/channel/UCxQ...Px2I7jmazGdLqg

Last edited by PilotBrent : 04-29-2019 at 03:49 PM.
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 09:33 AM.


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.