Fuel Efficiency
Dave,
I love your motorcycle analogy. Bigger is not always better, to some of us, so don't give up quite yet on the 0-235.
First of all, the RV-9 was purpose-built for the 118 HP Lycoming engine. The longer wing, fowler flaps, larger tail were all combined to make lower-powered flight possible. The RV-9 prototype was built with an 0-235, and received glowing write-ups for efficency and eze of handling. But before the prototype could be emulated by new builders, it was destroyed in an unfortunate weather accident in Arkansas on the way to a fly-in in 2000.
(Van doesn't like instrument flying, and doesn't allow gyros to be installed in factory aircraft). The second prototype was built with an 0-320, for reasons I don't fully understand in light of the glowing reports on the first prototype.
Now you see guys putting 180 hp Lycomings and 200 hp Subarus in the 9. I don't understand it, and it makes Van very uneasy to see his airplane cruising
above it's Vne. Which I'm sure is rather baffeling to a newbie like yourself trying to make a safe and sane engine choice.
To understand this logic, you need to understand that many homebuilders are like hotrodders. Speed is the alter on which many worship. Heck, there are guys putting 6 cylinder Lycomings on RV-7's........because they can! That's the beauty of experimental aviation......you can push the envelope until something breaks. And if that's not enough speed, you can move up to a Harmon Rocket and go even faster. Not fast enough, install a Chevy V-8 like some fellow here in Phoenix did and cruise way over the redline and design gross weight. Turbines are also available so you too can experience the joy of seeing 30 gph fuel flows!
Now having said all this, the 0-320 is a wonderful engine, and would only give you a 1-3 gph fuel penalty. Better high altitude performance if you want to go to ABQ in the afternoon, and about 50 percent better climb rate. Only about 15 kts more speed though, for about 3 more gph.
I have flown Stearmans, Supercubs, Luscombes, Champs and Grummans with
bigger engines than the designer intended, and not one was any more fun to fly. They just burned more fuel. You get to where you are going a little bit faster, but like you so wisely stated "I'm not in a hurry to have a good time". I have a strong suspicion that the RV-9 will be just the same.
I want to do some long distance flying with my plane, so the maximum fuel efficency is very important to me. I've been through my "hair on fire" stage, about 30 years ago, so now it is more important to me to arrive at my overwater destination with fuel in the tanks. Now days I only care to impress myself, and I find 34 mpg the 0-235 will deliver to be very impressive.
There is one guy here that claims to get 35 mpg from his IO-360, but he won't submit proof of sustained performance, only a snapshot of an engine instrument. Fact is, all internal combustion engines produce their best sfc's
at rated horsepower. Throttling back a large engine just won't match the efficiency of a purpose-built airframe/engine combination.
Please though, don't take my word for any of this. Contact Stan Shannon in
Lubbock Texas and ask him why he has installed the 0-235 on the last 3 RV-9's he built. ( Now just sit back and watch all the hotrodders and tuners flame me for liking small engines! Comes with the territory I guess!)
John Ragozzino
RV-9 QB / 0-235
Phoenix, Az
