RV-3 Fuel Mileage after Catto Prop

I finally got around to doing a fuel consumption check at gross weight and max continuous rpm after installing the Catto prop and here's what I came up with:

2600 RPM, 177 mph (gps), 4.8 gph (full rich) (standard slick mags)
(36.8 mpg is very nice with fuel prices at $5.50+ and rising.)

Some other numbers that I got was:
2100 RPM, 145 mph
2850 RPM, 203 mph

Many thanks to Van's for an efficient and fun airplane.
cj

Engine? Altitude?

Thanks!

Dave

engine / alt

Hi David,
The altitude was 3000ft. I guess I should have gone to 7500/8500?

The engine is an 0290-D2 which is factory rated by Lycoming for 140hp at 2800rpm for 5 min and 135hp at 2600rpm continuous.

The speed was gps verified on a triangulated course. (winds were nada, perfect evening)

Temp was comfortable around 65 to 70 deg f.

Plane was full fuel and gross weight for the RV-3

That's real nice performance.

I can't wait!

Dave
RV-3B, now building the vertical stabilizer

Catto Prop specifications ??

Grubbat, What is the dia and pitch of your prop ?

Blades?

Larry DeCamp said:

Grubbat, What is the dia and pitch of your prop ?

Click to expand...

...and how many blades does it have?

-jon

Prop spec

The Catto prop I'm running is his 2-blade design.

I believe its a 68x68. I will check tonight and repost if it isn't.

One thing that I didn't mention was the lower noise of the prop and reduced vibration. I can't tell a noise change in the cockpit but several have commented that once i take off, they can't hear me like they used to. I am running poly motor mounts (not recommended) and i can feel every vibration the engine/prop has and now the vibrations are reduced.

Also, the p-factor doesn't seem as much. Not sure if this is possible or just imagined.

grubbat said:

Also, the p-factor doesn't seem as much. Not sure if this is possible or just imagined.

Click to expand...

What kind of prop were you running before? If you were running a metal prop, mainly what you'll notice after switching to the Catto is reduced torque and gyroscopic effect due to the much reduced weight of the Catto. Can't say I noticed a difference in P-factor or slipstream effect. The rudder and stick (in pitch) feels slightly lighter due to the elimination of the gyroscopic resistance of the metal prop.

Confused...

grubbat said:

I came up with:
2600 RPM, 177 mph (gps), 4.8 gph (full rich) (standard slick mags)
(36.8 mpg is very nice with fuel prices at $5.50+ and rising.)

Some other numbers that I got was:
2100 RPM, 145 mph
2850 RPM, 203 mph cj

Click to expand...

The listed speed vs. RPMs seem very realistic; but how was the number of gallons per hour burned measured? This is the part that I can't seem to make add up in my aging brain...

According to the 0-290 Operating Manual, at 3000 ft. and pulling 2600 rpm (while full rich), the graph shows a BSFC of around .54; and the engine should produce approx. 134 hp. Therefore the fuel burn to produce 134 hp should be on the order of: .54 X 134= 72 lbs of fuel (per hour) consumed / 6.2 (lbs. per gallon)= approx. 11.7 gph burned.

With some leaning, a Lycoming should be able to get its' BSFC down to what... .42 I should think; and using this BSFC results in burning 56 lbs. of fuel per hour in order to make the listed 134 hp; which then equals 9 gph.

Looking at it another way; burning 4.8 gph = approx. 30 lbs. of fuel per hour burned (4.8 x 6.2) / .54 = 55 hp produced; and we all know the RVs are pretty efficient, but I think they would be hard pressed to be able to fly at 177 mph on just 55 hp...

"Math in public" has never been one of my strong suits, so I hope others will correct my errors and help me see what I'm missing here, since this has left me a bit confused (based on what I've learned in the past re. BSFC and its' ability to predict fuel burn vs. power produced). Of course I hope that this could somehow be true, as I'd love to see these kind of numbers on my O-290powered "3" when it finally gets airborne!

Doug Lomheim
RV-3 restoration w/O-290 "G" converted to a "D"
RV-9A/ Mazda 13B temporarily on hold...

more fuel numbers for the RV3

FWIW: I recently took a round-trip from Seattle to SanFrancisco, perfect wx, light winds. Here's some data to compare the 0-290 data with:

Engine: Lyc 0320-E2D, 7:1 pistons, MA4-SPA carb, Slick mags

Prop: Catto 3-blade, 68dia 70pitch (it's a perfect compromise climb/cruise configuration for my airplane & mission)

Using "by-the-book" leaning, two fuel stops each way:

Going there: 36gal, 5.2hrs airborne, 6.9gph

Coming back: 35gal, 5.0hrs airborne, 7.0gph

Avg en-route GPS cruise: 172sm/hr

Notes: major sore butt both ways, but well worth it to see the lovely lady posed in my cockpit in the photos (man, do I ever need another seat!)





- Steven
700+ RV3 hours
(ten more to SF and back!)

further "more fuel numbers for the RV3"

... forgot to mention:

Cruise alt: 9000'

RPM: ~2600

... and the fires around Mt. Shasta forced me up to 10500' to stay VFR (although you could easily have descended through it to a forced landing if necessary)

- Steven