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albertaflyer

Active Member
I have an o360 a1a carb, fixed pitch prop. On a trip today of 410 sm I burned 19.9 gallons. Started with both tanks to filler caps and refilled to same when I got back. It took me 2.9 hrs to fly it at 2400 rpm. When I do the math it just doesn't seem possible. I lean fairly aggressively. It works out to 6.9 gallons an hr.
 
You'd be amazed how low a fuel burn you can actually get. My -4 has an O360A1A with an Ellison throttle body...I can burn 11.5 to 12 at 2700 RPM and 175kts TAS or drop it down to 135kts and burn about 6..or drop it down to 115kts and burn just a hair over 4 :)
 
That is with a climb prop and 2400 rpm. That's with takeoff and landing twice so that is why the average speed is lower.
 
albertaflyer said:
I have an o360 a1a carb, fixed pitch prop. On a trip today of 410 sm I burned 19.9 gallons. Started with both tanks to filler caps and refilled to same when I got back. It took me 2.9 hrs to fly it at 2400 rpm. When I do the math it just doesn't seem possible. I lean fairly aggressively. It works out to 6.9 gallons an hr.
Click to expand...

Tony, I see that you have that engine in an RV-6. Just for a data point, I recently installed a red cube fuel flow transducer coupled to my EI UBG-16 engine monitor for fuel flow monitoring. I did the same test as you yesterday (same plane, engine, carb and prop except mine is a cruise prop at 85 pitch). Filled tanks and flew 1 hour at 8500' DA on right tank (after takeoff on left tank). 2500 rpm burning 8.5/hr. I lean the old fashion way, pull until rough, enrich until smooth.

I know from my flight test phase 1 and several trips that the engine burns 8.5/hr at that rpm ( I get about 160 kts/185 mph TAS at that rate/altitude)
I wanted to confirm that the engine monitor fuel flow is reliable based on actual use. It was and I filled 8.5 after landing.

I also know that during phase 1 testing I confirmed that at 2350/2400 rpm I burned 7.0/hr going 148 kts/170 mph. I figured that to be roughly 55 percent power, which matches closely what you demonstrated.

Like Dan suggested, I also burn around 10+ something going at 2700 rpm and 175 kts/200+ mph TAS at 8500'. I just like to run around the 8.5/hr rate. I'm usually not in that much of a hurry, I'm retired. :D
 
Another reference point

I too have an RV-6 with carb O-360A1A. I typically travel long distances at approx 60% power (2400 rpm, ~22 MP). I will see 150 kts TAS and 7.2 gph fuel burn. These are not precise numbers, but are representative of what I have seen.
 
Thanks for the responses. My result of course wasn't scientific and I'm sure I'm out a bit, but I was just surprised at the numbers. It's intrigued me a bit too! I've started re-reading speed with economy along with these forums.
 
I have an O-360-A1A, FP (Sensenich 72FM8S9-1-85 cruse prop), on a 6A with Sam James cow. I have just installed a red cube fuel flow meter, and have not checked it's calibration; however, @ 2,400rpm, 21MP, 140KTS, 5,500 feet I am seeing more like 9.7GPH. 100 degrees ROP.
 
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A well set up O-360 with no leaks, good plugs etc etc. will burn WOT fixed pitch in the cruise at altitude about 7.8 GPH.

And that will be LOP.

If you are less than that you are incredibly LOP or you have the throttle closed too much. Open her up a bit :) You don't build a fast plane to go slow!


pa38112
At such a low power setting why are you wasting fuel at 9.7GPH and 100ROP. That does nothing good for your engine in fact it is doing less good. 2GPH wasted compared to the numbers I have shown above. At $12 an hour plus more deposits in the engine and way more carbon monoxide generated (should you get a leak into the cabin) this is less than optimal.
 
I have updated my prop specs in my first post.

I lean according to the recomendation from the power wheel app. I don't know if that fuel flow is acurate until I check the calibration, but I tend to believe it.
 
Fuel log

You might want to consider a simple fuel log. If you have a notebook in the plane, it's easy to jot down tach/Hobbs time and fuel added each time that you service the plane. This will allow you to do a couple of things. First, it will give you reliable long-term data, and second it will allow you to spot anomalies that could be the result of a fuel leak, carb malfunction, etc.

This requires no instrumentation or in-flight engine management technique whatsoever, just the discipline to record the data at the conclusion of each flight or when you service fuel.

Obviously, if your "average" fuel flow works out to 7.0 GPH, this is only a reference number, actual fuel burn is a function of SFC, which really translates to the percent of power you're developing as the other folks have noted in this thread. As they also pointed out, you'll be pleasantly surprised at how efficient RV's are!

Cheers,

Vac
 
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