Jaypratt

Jaypratt

Well Known Member
Mentor
RV Pilots,

Question, What kind of MPG are you getting?
I have just short of 2000 RV hours and until recently have not tried to get an accurate MPG for my RV trips. I have not cared much until now about this. $5 + per gallon

This OSH 2008 trip, I saved the gas receipts and have the time but not the accurate mileage, I dodged WX etc.

Straight line miles was 1701 NM
add some WX zig zags 100??? NM
100 LL used 107.23
Divide 1800 NM by 107= 16.822 MPH?

I thought RVs got better mileage? I was low, 1500ft, some of the flight. 8500ft some of the time. Dodging WX and off course some too. so mileage is not possible to get accurate.

What or how, do you guys figure MPG.

Thanks
 
I departed OShkosh on Tuesday with full tanks (38 gallons, minus a little bit). After clearing the airspace at Osh, I climbed directly to 11,500' and set course for VPC, which is just NW of Atlanta. I stayed at that altitude until roughly Chattanooga, TN, where weather forced me lower.

The total distance coverd was about 620 nautical miles. Fuel consumption was 29 gallons based on full tanks at engine start and 9 gallons remaining when I arrived home (I defueled the airplane to get an accurate quantity remaining.). From engine start to shutdown was right at 4 hours.

So, my fuel burn was 7.25 GPH. My block speed (engine start to shut-down) was 155 knots. And fuel mileage was 21.4 nautical miles per gallon or 24.6 statute miles per gallon.

I have a 160 hp RV-6 with a cruise pitched Aymar Demuth prop. My cruise setting was just under 2400 rpm and just over 19" of MP. Both the power charts from Lycoming and the fuel burn indicate that this was around 60% power at 11,500'.
 
I've made the trip from Minneapolis to Fort Myers, Florida 6 or 7 times. I typically use 120 gallons +/- 5 for the round trip. It is about 1250 n.m. each way, so this breaks down to about 21 miles per n.m. or 24 mpg statute. I fly at around 22", 2300 rpm, around 7.2 gph. This give me at tas of about 156 to 160 knots. During cruise, I get about 22 miles per n.m., and on the long trips the take offs and descents seem to not affect it much.
 
Nautical and statute

Jaypratt said:
Straight line miles was 1701 NM
add some WX zig zags 100??? NM
100 LL used 107.23
Divide 1800 NM by 107= 16.822 MPH?
Click to expand...

Remember to convert to statute if you want to compare the numbers to an automotive reference. 16.8 = 19.4 MPG.

John Clark
RV8 N18U "Sunshine"
KSBA
 
AlexPeterson said:
I've made the trip from Minneapolis to Fort Myers, Florida 6 or 7 times. I typically use 120 gallons +/- 5 for the round trip. It is about 1250 n.m. each way, so this breaks down to about 21 miles per n.m. or 24 mpg statute. I fly at around 22", 2300 rpm, around 7.2 gph. This give me at tas of about 156 to 160 knots. During cruise, I get about 22 miles per n.m., and on the long trips the take offs and descents seem to not affect it much.
Click to expand...

Is that all the faster these things are? I thought the 8, I'm building was faster than that, like at least 180 kts. My 450hp Cessna 195 cruises at 157 kts TAS while burning 22 gph. ****, what have I done!

At least my mpg between the two will more than double, maybe even triple, last check the big motor 195 was around 7 mpg. Sure is fun,,,,,till you pull up to the pump! Another plus of the Gaaaasss hog. Good shade under the wing, sitting in a chair. Where do you sit when at the RV?

Oh well, never met an airplane I did'nt like. Some of them you just don't want your friends seeing you in........Like some other nameless things.
 
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My 135 HP -9 with a climb prop works out to run 20.9 MPH.

The MPG can go up if you use the miles that you would drive, if you took your car.

What was I thinking? My original post was in error, way in error.

My total distance driven (both ways) would have been 2176 miles according to MapQuest and my total fuel burn was 96 gallons, giving me 22.6 MPG. Still a lot better than my truck but not as good as my car but still not the 40 some MPG's I was dreaming of.
 
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Comparison

You got me to wondering about the costs associated with my trip to OSH.

I steered clear of the Class B around ORD the flight up and back was 564 NM each way. (564NMx1.15=648SM)x2=1296SM round trip.
Google maps shows the fastest way to drive up and back of 881sm each way, or 1762sm round trip.
I have a VW diesel Jetta and at the speeds I drive I get 43 MPG on the highway. That works out to about 20.4 gallons of Diesel each way or 40.8 @ $4.79/gal which is $195.43. Then plan on about 15 hours in the car each way, probably a hotel each way and meals and snacks. So 200 for fuel, 200 for hotels, 50 for meals and 30 hours on the road. About 450 bucks round trip.

OR

3:25 in the RV8 going up (low altitude for winds, 4500MSL) with a burn of 32 gal. @ 4.90 ($156.80)and 3:10 on the way back (11,500 for winds and economy) with a burn of 29 @ 5.12, ($148.48)no meals, no hotels, no hassle and lots of fun is $305.28.

The way I figure it, I got 18.49 NM (21.26SM) per gal. in the plane and saved 24 hours driving time over the VW. Granted I did use 20.2 gallons more 100LL than I would have used Diesel.

As stated in a couple other post about camping and visiting and being at OSH..

Priceless!
 
RV's are good, but come on guys, the laws of aerodynamics and stuff still apply. You get better fuel burn than the Cessna 210 I came back in... but not per seat. If you really want efficient, you could get a VeryEZ... but that has it's own set of limitations.

And to the guy building a -8 that doesn't know how fast it goes... what are you doing dude? Keep the 195 :), much higher cool factor.... at similar speeds.
 
Of course not

CE196 said:
Is that all the faster these things are? I thought the 8, I'm building was faster than that, like at least 180 kts. My 450hp Cessna 195 cruises at 157 kts TAS while burning 22 gph. ****, what have I done!

At least my mpg between the two will more than double, maybe even triple, last check the big motor 195 was around 7 mpg. Sure is fun,,,,,till you pull up to the pump! Another plus of the Gaaaasss hog. Good shade under the wing, sitting in a chair. Where do you sit when at the RV?

Oh well, never met an airplane I did'nt like. Some of them you just don't want your friends seeing you in........Like some other nameless things.
Click to expand...

Yes it will do 180kts..no problem...You just won't do it at 7.2 GPH thats all..:)

Frank
 
Just looking at cruise mpg, without factoring in the climb, most RVs can be set up to return mid-20's statue-miles-per-gallon. Cessna 172s are typically in the teens, but you can twist the overall economy factor by factoring in the number of seats and computing seat-mpg.

At any cruise altitude above about 7,000' my RV-3B, when leaned out, will do 32 mpg (statute) or better. My EFIS fuel computer provides real time mpg. It has amazed even me, I wish there was some sort of efficiency contest I could enter with it, I think I could do well. Check the lower left corner for mpg, and TAS is at the bottom of the airspeed tape. The little engine display shows how much each cylinder is LOP...

SS051506.jpg
 
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osxuser said:
RV's are good, but come on guys, the laws of aerodynamics and stuff still apply. You get better fuel burn than the Cessna 210 I came back in... but not per seat. If you really want efficient, you could get a VeryEZ... but that has it's own set of limitations.

And to the guy building a -8 that doesn't know how fast it goes... what are you doing dude? Keep the 195 :), much higher cool factor.... at similar speeds.
Click to expand...

Yea, I'm going to keep the big motor 195, and glad to hear the 8 will cruise at 180 kts, true I hope. The 8 will add alot of fun for the local type flying as well as cross country. Just can't take much stuff with us!!!! You should see what will fit into the 195. :D
 
Pull the power back...

I prefere to cruise at 10,500 to 12,500 MSL at full throttle with a Hartzell constant speed prop at 2,300 RPM. My O-320-D1A with carb and one Plasma III and one Slick mag gets 25 MPG at 160 MPH true air speed. I lean to near equal EGT's and get a smooth running engine at 5.5 to 6 gallons per hour. At lower altitudes, I pull the power back to maintain 150 MPH TAS and still get the same fuel flow rate.

This first photo is coming home from Pennsylvania after Oshkosh 2005. You can see I am up high at 12,500 MSL. Look closely at the Dynon D10-A and you will see it is showing TAS of 143 knots. The GPS is showing 157 MPH ground speed or about a 7 MPH headwind (143 knots = 164 MPH).
DSCN0015.JPG


The second photo is northbound along the Florida East Coast looking for minimum headwinds at 4,500 MSL. In this one, the D10-A is set to display statute miles per hour on the TAS of 153 MPH. The GPS is showing a ground speed of 146 MPH.
DSCP0316.JPG
 
Here is some data to illustrate the mpg vs ias vs mixture (egt) settings at my typical cruise settings for MAP and RPM.





Note that the mpg on the second chart is indicated, not tas or even cas. These two charts show nicely that, although airspeed drops sharply LOP, the mpg peaks around 50 to 75 LOP.
 
Alex, now you're making me feel guilty for not compiling all the data that I should for my POH. Obviously you have done that. Converting to TAS though is the only real mpg metric, you're doing yourself a disservice by not taking that final step. Looks like mid-20s just doing a thumbnail.

Good work!
 
randylervold said:
Alex, now you're making me feel guilty for not compiling all the data that I should for my POH. Obviously you have done that. Converting to TAS though is the only real mpg metric, you're doing yourself a disservice by not taking that final step. Looks like mid-20s just doing a thumbnail.

Good work!
Click to expand...

Well... Randy, thanks, but you don't need to feel guilty. POH? Don't have one. I just like learning more about these contraptions, and data is the only way to be sure. There is a fair amount of BS floating around, and I don't want to contribute more than I already have! I didn't record the baro pressure that day it appears, so it would be mumbling to do the conversion now. Guess a test flight is in order!

But, as you suspected, based upon quite a bit of note taking over the last 7 years, the mileage is right around 24 to 25 statute mpg at my normal cruise settings. What is worth pointing out is that this mileage is when I'm around 50 to 75 LOP. If I were to run around 100 ROP, the mileage would be less than 20. Yes, I fly slower, but I could also push more MAP in and run a bit faster. The curves would look similar, but at a higher fuel burn/lower mpg. The only time that 6 or 7 knots even registers is when I do the 1250 n.m. run to south Florida. Even then, it is only about 20 minutes difference!
 
Some more mpg data!

Well, I collected a little data today on a nice 45 minute trip back from northern Minnesota. I ran two settings of MAP and rpm, and varied the fuel burn. I set the fuel burn, allowed 10 or 20 seconds for speed to stabilize, and recorded the indicated airspeed. I brought this data home, and converted the speeds to CAS and then to TAS. This chart shows the results for the two settings:



Discussion:
1. Looking just at the TAS lines, it can be seen that they cross near the left side. I was really a long ways LOP on the 23.4/2400 settings, and, while the engine was still smooth, it was really losing power.
2. It can be seen, that for most fuel burns, the mileage at the higher MAP/rpm is better. This is likely because of two things - first, the throttle is wide open (minimal pumping loss) and second, the charge is further LOP than the same setting at the lower MAP/rpm.
3. Peak egt would be about at 7.5 gph for the lower and 8.5 for the higher MAP/rpm settings. I didn't record them for this run.
4. I didn't record (nor have time to allow them to stabilize) cht's, but they would have been sub 300 towards the left side of this chart.
5. It is a coincidence of scaling that all the curves cross at the one point! It happens that I typically run right there, about 7 gph and 160 knots.
6. For the 21.9"/2300 (about my typical cruise), I give up about 5 knots speed from peak power to 50'ish LOP. However, my mileage goes from about 22.5 to 26 statue mpg (fuel burn from 8.5 down to 7.0)

I will get the cht/egt data as well the next time I get a chance.
 
RV-10 Gas Mileage

On Sunday I flew down to Redlands California nonstop from my home airport in Bountiful UT.
Here is the data from my trip. I converted the numbers from nm to miles just for comparison to driving.

Flying was 550 miles, 32.2 gallons was used which equals 17.08 mpg
Total flight time was 3 hours 22 minutes = 163.7 mph
In cruise my average TAS was 160 knots or 184 mph.
I had an 8-10 mph headwind most of the flight as well.
I was flying at 25 deg. lean of peak at 12,500 at 18.5 inches and 2360 RPM burning 9.2 gph.
The fuel at Redlands was $5.22. So my fuel cost was $168.08.

If I were to drive it would have taken over 10 hours.
Driving would be 632 miles, (35.5 gallons, estimated of Nissan Titan @ 18 mpg)
The cost for driving at an average of $4.00/gallon would be $142.00

I'm always impressed with this plane.

RV-10 Spot Tracking
350149980_TJNpJ-L.png


Driving
350149919_LomVk-L.png
 
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Some more data for whatever its worth

I looked at my most recent flights - mostly $100 meal runs - and summed it all up.

5 round trips or ten flights
6.1 hours
43.1 gallons (per fuel flow meter/GRT)
Avg. gph about 7
788 NM
129 kts GS average.
18.2854 NM/g = 21 mpg.

I normally run the engine at about 7.2 gph LOP which translates to about 60% and gives a TAS around 150 kts. If I go faster, the mpg is less and I suppose it would be better if I went slower, but this is a nice speed for my tastes and the trips are so short there's not much point in going faster. Some of these flights were below 7 gph. These numbers are total for the trip including climb and descent, etc. I always have headwinds - OK, mostly anyhow. Most of the flights were at density altitudes below 6,000 and sometimes as low as 3,500 MSL (not DA) so climb was not a big factor. I think 4500 MSL was the hightest for any of them. I usually climb at about 110 kts indicated and slow down about 5 miles out for the pattern. I burn an indicated 15 gph at full power but I often reduce power and begin leaning even for the climb, once safely up there. That still gives me between 500 and 1000 fpm.
 
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