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-   -   mile for mile (https://vansairforce.net/community/showthread.php?t=9578)

BillyBob 07-27-2006 03:47 PM

Your Time?
 
Did you factor in your time driving at $100/hour?? ;)

cobra 07-27-2006 04:44 PM

Seems to me the following somehow need to be figured in:

Cruise ground speed- power setting, fuel/air mixture
Some allowance for time saved (quality of companions...)
Head/tail winds
Weather limitations, diversions
Type of fuel used (big advantage to mogas)
Hanger/storage fees
Fun factor- who really wants to drive anyway??? :D

gorbak 07-27-2006 05:45 PM

PRKAYE brings up an interesting point
 
How does the gph of a 118hp compare to a 160hp lycoming?

Now that is an interesting idea (especially since I am building a RV9-A with the Lycoming o235 L2C 118 hp engine with a Catto two bladed prop).

Extrapolating Van's numbers for the 118 hp engine (and checking the Lycoming Engine Manual) we get an estimation that follows:

Full power 173 mph 4.53 flight hrs 7.5 gal/hr
(assuming 34 gal. usable..start/taxi/takeoff...)
75% power 166 mph 5.27 flight hrs 6.45 gal/hr
55% power 150 mph 6.90 flight hrs 4.92 gal/hr

I drive from Ozark, MO to Wichita, KS often. 257 miles 4 hours 15 minutes and get barely over 20 mpg with my Jeep Grand Cherokee for a total fuel consumption of 12.85 gal at $2.89 per gal equals $37.14

Lets use full power RV9-A (using AeroPlanner.com)
full power 229 sm 173 mph 1.32 flight hrs 11.9 gal used (2 gal. for start/taxi/takeoff/altitude @6000 ft.)
75% power 166 mph 1.38 flight hrs 10.9 gal used
55% power 150 mph 1.53 flight hrs 9.5 gal used
Assuming 100LL is $4 per gal........
Full power would cost $47.60 :o
75% $43.60 :)
55% $38.00 :D

The 0235 118 hp engine isn't looking so bad after all. Of course, only true flight will tell us how close the extrapolated numbers really come but it is an interesting exercise with fuel prices rising. I can't wait to get this bird in the air.
Pat Garboden
Ozark, MO
RV9-A 942WG (reserved) 0235 L2C 118 hp
RV9-A 942 PT (reserved) 0320 E2A 150 hp

Bryan Wood 07-27-2006 06:33 PM

10 gph?
 
Quote:

Originally Posted by Brian130
Assume 10gph in an average RV and 150 KTAS. That's 2.37 hours = 23.7 gallons. Assume $4.00/gall 100LL (and that's low probably). $94.9 each way in 100LL.

. :D

10 gph to do 150 knots in an RV is way on the high side! On long trips my 9A will easily do 8gph running it hard, and at higher altitudes the block times (fuel burns for a given trip including take off, climb, cruise, decent) will come out right at 7gph with speeds around 157-160 knots. About 2 months ago my wife and I flew from San Jose, CA to Oklahoma for our sons basic training graduation and made several stops. Six weeks later we duplicated the trip to bring him his car with the final destination in Northern Texas about 40 miles from the Oklahoma location. On both trips we overnighted at Laughlin, except the RV got us there in about 3 hours burning just under 21 gallons. The same leg took 8 hours by Cobra Mustang and used 23 gallons. The rest of the trip was similar.

While a smaller engine seems like it should burn less gas we repeatedly are reminded that the planes running the bigger engines powered back do as well or better. The injected 200hp RV's running LOP seem to use the least amount of fuel in any group when flying together. Just another opinion, but go with the biggest engine that can be used for your plane. I'd be prepared to spring for a coke if your not happy after a year or so.

Regards,

N941WR 07-27-2006 06:34 PM

Funny you were running these numbers because I was doing the same over the weekend only I was comparing my O-290 powered RV-9 to Corey Bird's 240 knot Symmetry.

Lots of SWAGS were used but here is what I came up with.

RV-9 w/ O-290-D2
75% power = 101.5 HP
7.1 GPH
175 MPH
24.6 GPM
200 mile trip = 1:10 minutes +/-
1:10 minutes * 7.1 GPH = 8.1 gallons * $4 = $32.46

Symmetry w/ IO-360
75% Power = 150 HP
12 GPH (I'm guessing here)
240 knots / 276 MPH
23 MPH
200 mile trip = 45 minutes +/-
45 minutes * 12 GPH = 8.7 gallons * $4 = 34.78


Quote:

Originally Posted by gorbak
How does the gph of a 118hp compare to a 160hp lycoming?

Now that is an interesting idea (especially since I am building a RV9-A with the Lycoming o235 L2C 118 hp engine with a Catto two bladed prop).

Extrapolating Van's numbers for the 118 hp engine (and checking the Lycoming Engine Manual) we get an estimation that follows:

Full power 173 mph 4.53 flight hrs 7.5 gal/hr
(assuming 34 gal. usable..start/taxi/takeoff...)
75% power 166 mph 5.27 flight hrs 6.45 gal/hr
55% power 150 mph 6.90 flight hrs 4.92 gal/hr

I drive from Ozark, MO to Wichita, KS often. 257 miles 4 hours 15 minutes and get barely over 20 mpg with my Jeep Grand Cherokee for a total fuel consumption of 12.85 gal at $2.89 per gal equals $37.14

Lets use full power RV9-A (using AeroPlanner.com)
full power 229 sm 173 mph 1.32 flight hrs 11.9 gal used (2 gal. for start/taxi/takeoff/altitude @6000 ft.)
75% power 166 mph 1.38 flight hrs 10.9 gal used
55% power 150 mph 1.53 flight hrs 9.5 gal used
Assuming 100LL is $4 per gal........
Full power would cost $47.60 :o
75% $43.60 :)
55% $38.00 :D

The 0235 118 hp engine isn't looking so bad after all. Of course, only true flight will tell us how close the extrapolated numbers really come but it is an interesting exercise with fuel prices rising. I can't wait to get this bird in the air.
Pat Garboden
Ozark, MO
RV9-A 942WG (reserved) 0235 L2C 118 hp
RV9-A 942 PT (reserved) 0320 E2A 150 hp


John C 07-27-2006 06:38 PM

mpg
 
I have an RV-9A and an O-320 fixed pitch prop rated at 160 hp. At 8000 feet and 75% I get 185 mph true and 21 mpg. At 55% I get 165 mph and 25 mpg. At 65 mph, my S-10 Blazer gets 21 mpg. At $3/gal, the car get 7 miles/$. At $4/gal, the airplane gets 5-6 miles/$. The 118hp at 75% is about the same as the 160hp at 55%.

Tom Green had a nice write-up in the recent RVAtor on the relative costs of bicycle, car, and RV. Tom used 175 mph and 22 mpg for the RV. Meals, motels, time on the road are all factors. Speeding tickets, insurance, hangar rent, etc. Of course, I spend about $2k a month to garage my car, but my wife and I stay free in the house. Regards, John.

Bob Axsom 07-27-2006 08:21 PM

When the CFO isn't looking
 
Dayton, Ohio to Fond Du Lac, WI via Sterling Rock Falls and Rockford, Illinois ~483 statute miles, 45.7 gallons 100LL, ~2.5 hrs, $178.23 (@ $3.90/gal), O-360-A1A. Driving not an option.

Bob Axsom

AlexPeterson 07-27-2006 09:40 PM

I've flown round trip from Minneapolis to Fort Myers FL about 5 times in my O360 FI, EI RV6A. It is 1214 n.m. straight line, or 1400 s.m., and I typically use 120 gallons round trip. That equates to 23.3 statute miles per gallon (at 185 statute miles per hour). We've driven the route also, and it is 1750 s.m., so comparing apples to apples the RV's mileage would be 29.

The mpg performance numbers for RVs probably varies more than any single other parameter, since the fuel flows vary so widely. For that reason alone, I am very glad I have FI and EI, both of which contribute appreciably.

Tom McCutcheon 07-27-2006 10:22 PM

118 HP VS 160 HP
 
Consider this. Go ahead and put the 160 HP Lyc in and when prudent throttle back to a fuel burn of the 118 HP engine. I realize that would take a lot of self control, but when you really need the power for those high density altitude take-offs you would have it. When you really want to conserve just throttle back. Also, you would get to altitude a lot sooner where you could really save (assuming no winds).

Tom

RScott 07-27-2006 10:48 PM

On average, flying distances are about 80% as far as driving distances. So an RV getting 22 MPG (180 mph burning 8 gph, rounding down) would be equivalent to a car getting 27.5 mpg.

The poster listed a 150 HP RV-9, which could burn mogas (I know, we had that discussion a couple days ago), so fuel per gallon need not cost more than gas for a car if he doesn't have to refuel at an airport. If you have to burn avgas, around here it is about 30% more than mogas, so that gives you effectively 19.5 mpg (27.5 x 0.7).

RV is much faster & more fun, but you have to rent/borrow a car when you get there. Cars rarely get delayed for weather. RV's rarely get tied up in traffic.


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