Flying for max fuel efficiency

[chrisk]

I was looking in the manual of a 1967 M20F and noticed it specified an operating point of 1950 RPM and 16.9 MP. It gives a range of 1300+ NM and 11 hours of endurance @7500 MSL. Obviously true air speed isn't great, but gets a little better if you fly higher.

I'm just curious how many people fly with these settings?

[Hank]

I've played with it in my C (1950 & 20") but it's too slow for traveling. If you need to loiter, it will give you a long time; if you want to wait for fog to lift, use it. Personally I would divert if possible and wait on the ground, but that's not always possible and sometimes forecasts are not accurate.

Note that there are two definitions of 'fuel efficiency': 1) the furthest distance; 2) the longest time per gallon of fuel. This power setting gives the longest time. More people are interested in the former than the latter.

[carusoam]

Search for Carson's speed. Nice place to fly for efficiency.

Are you building time?

Best regards,

-a-

[Awful_Charlie]

Have a read of http://www.db.erau.edu/research/cruise/piston.frame.html

I've tried it, and in the Bravo as I was loaded at the time (a couple of hundred lbs under MTOW) V_mr was so slow as to be uncomfortable (wallowing around, nose high, below autopilot control speed) V_lrc was a bit better of course, but it would require a very special mission for me to operate there

Ben

[jetdriven]

V_MR (106 KCAS) and V_LRC (113 KCAS) are both way too slow for cost efficient flight. They also dont take into account the value of your time, The lower efficiency of the engine below 50% power, nor the non-fuel costs of the airplane. Carson speed will (except engine efficiency), and was calculated by Testwest at 123 KCAS.What I have found is that around 130 KTAS is a good compromise airspeed for the extra 1-2 gallons per leg used.

The M20J has a very low C_d of only .32 and does not save fuel as much by slowing down as a more draggy airplane such as a 182, 210, or a Lance. In fact, Carson speed (123 KCAS) can net you 20 NMPG, but 142 KTAS running 15 LOP is 18.3 NMPG.

An even simpler way, taken from Jim R. is "climb to 60 degrees, set the prop to 2400-2500, fuel flow to 8 GPH and forget the rest". There's your 60% power and 130 KTAS. Thanks, Jim.

[1964-M20E]

Fly above 6k feet at wide open throttle find the best tail wind or less of a head wind and run LOP. This will get you there as quickly and efficently as the plane is capable. If you are just building time and burning holes in the sky 1950 and 16.9 not a bad way to go this will get you a low GPH rate but little speed as well. When I just goofing off like that I generally go about 20"mp the plane seems to handle a little better. IMHO

[chrisk]

Actually what got me thinking about this was the other thread about flying to Cancun across the gulf. It's something that I would probably not do, but even if I were to fly over land, I would want to avoid stopping in Mexico as much as I could.

[meddesign]

I do it when going no-where just around the patch or going for the $100 hamburger. 19" 1900 RPM 6.3 GPH ROP indicate 120kt. about 2500 feet. all numbers are approximate. makes me realize just how great and versatile our birds are. Wish I had charts for these power settings.

[Riq]

Im super happy pulling 23/25@fl17.5@10gph with my old and ugly 63C. Best ive seen is 219knts on the gps.

Yet, If I wanted fuel economy Id be in a diff game. I fly to fly fast. With a turbo on my old c I get the best of both worlds....But as an old motor-head, there is no replacement for displacement, and id love to have a rocket.

[DrBill]

This past weekend I flew from Charlotte to Okeechobee Fl. 620sm. I flew at 10K down, and 11K up. Going down I made it in 3.5 hrs and used 32 gallons. That's 177MPH average and 19.375 MPG.

Coming back it was 3.8 hrs but I did not fill up. That's still 163MPG average. This is at 2420 RPM and WOT (wide open throttle) at 21 inches. See the picture of my tach/MP gauge in my gallery.

To me, this is fast and economical.

Bill

[Riq]

163MPG!

Im at a loss for words.

Im always better then my expedition on any "expedition" with my mooney. I do far less in my cherokee at any burn rate.

[gregwatts]

This past weekend I flew from Charlotte to Okeechobee Fl. 620sm. I flew at 10K down, and 11K up. Going down I made it in 3.5 hrs and used 32 gallons. That's 177MPH average and 19.375 MPG.

Coming back it was 3.8 hrs but I did not fill up. That's still 163MPG average. This is at 2420 RPM and WOT (wide open throttle) at 21 inches. See the picture of my tach/MP gauge in my gallery.

To me, this is fast and economical.

Bill

163 MPG avg? Wow.....that is incredible! Must have been flying LOP.

[201er]

In my unscientific experience I have found that on the upward side of 130 knots is more efficient for covering distance whereas the 100-120 knot range is better for spending time. Basically below 130 knots the mpg goes up less drastically yet the duration increases a lot. Although 130 knots might be more efficient, I find 140-145 knots to be a lot more tolerable.

I flew from Linden NJ to Wichita Kansas nonstop in 8 hours with 85 gallons on board. Cruising at 6000ft, I started out doing 15LOP 2500RPM WOT ~10GPH and worked my way back to 2330RPM 8.4GPH which boosted my arrival reserve from 5 gallons to 14 which was a lot more comfortable. Only lost 10 knots and about 15 minutes but saved a 40+ minute fuel stop enroute. However, bringing the speed back to something like 120 or less would have been ridiculous because it would have taken to long to make my destination. Another thing to remember is that headwinds affect slower cruising speeds more than faster ones (as a percent of speed - 40 knot headwind in 80 knot plane doubles trip time).