What would it look like.

[zav6a]

There is a lot of traffic on fuel economy these days. I fly an 182L occasionally and it is quite apparent (when hitting the pumps) that fuel was relatively cheap when that design was generated.

While the Vans designs are inherently efficient, it is fun to think about a Vans style, ground up design focused on economy of operation.

You care more about economy on long trips so it would have to comfortably roomy for two.

How about a tandem with -9 wings. If less concerned about short field performance, lower drag, lower lift wings would work. (don't know how the pitching moment works out) Could be lighter all around if max speed is held to 150kts or so. Maybe an O-240 optimized for economy. Cowl etc. optimized to reduce cooling drag for the smaller engine. Maybe some wind tunnel work to really cut out airframe drag.

What other design elements could contribute to big economy?

[Mike_ExpressCT]

-A very high aspect ratio wing (think sailplanes or the U-2)
-Very small frontal area
-as light as possible
-minimal drag (laminar flow wing and fairings, retractable gear, etc.)
-diesel engine

With the current stuff Van has, I'd agree...a -4 fuse. with -9 wings, taildragger, optimized for a smaller engine (light weight).

Although, most people on here would say the most efficient planes are the 200 h.p. ones at very low power settings.

[Mike S]

This. By the way, it is side-by-side, not tandem.

http://www.mcp.com.au/pipistrel-usa/

Won 5 of 7 classes in the NASA/PAV competition.

[AlexPeterson]

Sinus? They might need to re-think that name. Might as well call it Loogey.

Reminds me of a US perfume company that decided to market their "Spring Mist" product in Germany. Didn't do so well, since Mist means manure in German.

BTW, a -9 will do 120 knots with a fuel burn around 3.5 gph (Pete, is that right?). My 6A will do 120 knots TAS at 4 gph.

[zav6a]

The Vans are pretty impressive. Not much more fuel consumption (.5 gph) than the Venus/Sinus planes if you want to slow down to 120 kts but still have the potential of hitting 170 kts and do acro. And, 300 lbs heavier. Apparently there is not much more economy to be gained at 120 kts in spite of those fat stubby wings.

Maybe the challege ought to be designing for low fuel consumption at 150 or 160 kts. Mine is good for that at 7.5 gph. Any aero engineers out there? What would the flat plate area have to be to get 160 kts out of say 5 gph at .39 lb/hp-hr? What is the flat plate area of the current -8?

That improvement would save about $10,000 over the first 1000 hours. Does not sound like much considering how much everything else costs for 1000 hours (guessing about $70,000 with cost of capital). Probably would not give up all of the versatility for the difference!

It would be interesting to see the flat plate area of the high end formula class planes they run at Reno. Those are some slick looking planes.

[Ironflight]

You pose some interesting questions, and the fact is, yes, you can build a more efficient airplane than an RV. Ad you can build one that handles better, lands shorter, flies faster, or does just about anything else better....

But....

In my opinion, the amazing thing about the RV's is that they do so many things very well. They aren't number one in any category, but as I've said here before, if you place second in EVERY NASCAR race in a season, you're probably walking away with way more total points than anyone else. Yes, you can optimize an airplane for a particular parameter - but always at the expense of something else.

Take the Gossamer Condor or Albatross - they flew with exactly One Human Power - a whole lot less than a Horsepower. but they couldn't fly in anything more than a small breeze, or pull more than a fraction of a G above normal - and they had no maneuverability at all. Extreme case, for the purpose of illustration, yes - but the point is that if you optimize an RV in any direction, you'll give up in others, and probably enjoy the total package less....

Sorry for the lecture....just got me thinking again about just how incredible a job Van did with the overall package. Total Performance is the motto, and he seems to have gotten it pretty close to right.

Paul

[n2prise]

I have to agree with Paul. My RV-9A is classic with a 160 HP carbureted O-320-D1A, Hartzell C/S prop, 1 mag/1 LSE Plasma III, and about 100 pounds overweight compared to Van's prototype.

I fly at 140 knots (160 MPH) and get 25 MPG at 10,000 to 12,000 MSL. Flat out down low, full throttle, the 193 MPH (167 knots) is real, but the fuel burn goes up to 11 gallons-per-hour instead of my normal cruise of 5.5 to 6 GPH.

It does a lot of nice things for me and is a great cross-country airplane. Fly high, fly cool, cruise a long way... 238.5 hours on the Hobbs meter since June 9, 2005.

[Jaypratt]

the long ez is good on mpg, not so good on short field.
i will keep my RV8, does good when i need it