With the right gearing, a car could easily get such mileage. My car gets 25mpg (US miles, US gallons) consistently at about 110 mph (on the autobahn). It's a 3.2L gas engine which makes about 320bhp, no turbo, seats 4 comfortably, and it has far from optimal gearing (80mph is almost 4,000 RPM!). A diesel with good gears could likely do much much better.

An RV10 with a deltahawk twincharged diesel engine (still waiting on certification ) will do 193kts on 8.5 GPH, a 100LL Mooney can do 160kts on 10gph... Both will seat 4.

Both of those blow this "awesome super-efficient turbodiesel cessna" out of the water for less than 1/4 of the cost.

 

Um, if you get 25mpg at 110mph, you must get about 100mpg at 55...right?

 

Negative, it's about 39-40.

 

I'm skeptical of this "magical" car of yours, but in any event- at those speeds, hearing has little impact on your fuel burn. If your statement about your car's performance was true, better gearing doing the rpm down to 3000 rpm would have a very minor effect on mileage, if the engine could even maintain the load at that rpm. People overestimate the effect of gearing, especially at high speeds in automobiles.

Comparing a rv10 to a certified airplane is not fair, I guarantee the rv stall speed is greater than the 61 knots that the faa requires for certificated single engine pistons. That diesel rv is impressive, but unless regulations are relaxed, no certified airplanes will be able to compete on a speed per horsepower basis.

 

As Rick hinted a few posts ago, it's not fair comparing airplanes to ground vehicles because the latter are not after the same set of optimization goals. Cars will always win the efficiency game if going from point A to point B without using much energy is the goal, because they stay in ground effect and do not fight gravity in so doing.

 

Gearing has EVERYTHING to do with fuel burn in a car, and has an almost exponential effect on your fuel burn as speed increases.

When I raised my final drive ratio by .15 (a noticeable, but small change), fuel mileage at higher speeds dropped by about 7 mpg. Drag does play a significant factor, but gearing in a vehicle is much more of a factor than you account for.

I'm almost curious to see what would happen if I dropped my final drive down by .45, I might even have the proper unit in my garage, but it would rob my acceleration by a noticeable factor.

RV10 published stall speed is 57 mph statute, which equates to under 50mph nautical. You could certify the RV10 yourself if you wanted, you'd just have to shell out the clams to buy a few kits and build them all the same way and then get a type certificate from the FAA.

As for airplanes vs cars, theres no doubt you can make cars more efficient. Several of the newer diesels are capable of more than 100mpg if driven properly, however airplanes can be made comparably efficient. Klaus Savier did a 1985 sm transcon in his two seater VariEze, using only 25.8 gallons, that's about 77mpg, he's been known to hit almost 100 mpg in competitions as well.

 

I agree with everything here, just not the 25mpg at 110mph. I got 27mpg in my big V8 a few weeks back on a 750mi trip (one day), 26.6 the next day over 650mi the next day. People are usually amazed I can get that out of this brick of a car, but it's a combination of the 6th gear ratio and really knowing how to squeeze the mileage out (minimizing stops and starts, using the car's 1-4 gear skip shift feature, avoiding unnecessary accelerations, etc). It turns 1700rpm for about 70mph, and yes, that does make for decent mileage. On the flip side, I've owned a few "fast" cars now, any time you get to speeds like what you posted, you burn a TON of fuel, I also know people that own the same car that I do that can't figure out why they get more than 13-15mpg. I've gone fast in a big V8, a much smaller 4cyl turbo, and a few in between. When you "cruise" at those speeds, you can almost watch the fuel gauge move the entire time. If your gearing is such that you can cruise at 70mph at the rpms I listed, it can be difficult to accelerate to those speeds (in that gear). The drag going from 70, to 80, to 90, to 100 and then faster is huge. It's not linear, as we know, so it's not going to cost 2mpg for every 10mpg over 70, it has a huge effect at 110mph in a car.

 

You can drive any chemical reaction backwards if you throw enough energy at it in the form of heat and/or pressure. This new fuel therefore sounds like huge waste of electrical power, making a small amount amount of liquid fuel from a massive amount of input electricity. At best it sounds like a way to store energy in places where there is a lot of wind/water power and no way to get it to the grid.
-----------------------------------------------------------------

Scientists turn fresh air into petrol

(S. Connor, The Independent, 10/19/12) A small British company has produced the first "petrol from air" using a revolutionary technology that promises to solve the energy crisis as well as helping to curb global warming by removing carbon dioxide from the atmosphere. Air Fuel Synthesis in Stockton-on-Tees has produced five litres of petrol since August when it switched on a small refinery that manufactures gasoline from carbon dioxide and water vapour. The company hopes that within two years it will build a larger, commercial-scale plant capable of producing a ton of petrol a day. It also plans to produce green aviation fuel to make airline travel more carbon-neutral. Tim Fox, head of energy and the environment at the Institution of Mechanical Engineers in London, said: "It sounds too good to be true, but it is true. They are doing it and I've been up there myself and seen it. The innovation is that they have made it happen as a process. It's a small pilot plant capturing air and extracting CO2 from it based on well known principles. It uses well-known and well-established components but what is exciting is that they have put the whole thing together and shown that it can work." Although the process is still in the early developmental stages and needs to take electricity from the national grid to work, the company believes it will eventually be possible to use power from renewable sources such as wind farms or tidal barrages. "We've taken carbon dioxide from air and hydrogen from water and turned these elements into petrol," said Peter Harrison, the company's chief executive, who revealed the breakthrough at a conference at the Institution of Mechanical Engineers in London.

"There's nobody else doing it in this country or indeed overseas as far as we know. It looks and smells like petrol but it's a much cleaner and clearer product than petrol derived from fossil oil," Mr Harrison told The Independent. "We don't have any of the additives and nasty bits found in conventional petrol, and yet our fuel can be used in existing engines," he said. "It means that people could go on to a garage forecourt and put our product into their car without having to install batteries or adapt the vehicle for fuel cells or having hydrogen tanks fitted. It means that the existing infrastructure for transport can be used," Mr Harrison said. Being able to capture carbon dioxide from the air, and effectively remove the principal industrial greenhouse gas resulting from the burning of fossil fuels such as oil and coal, has been the holy grail of the emerging green economy. Using the extracted carbon dioxide to make petrol that can be stored, transported and used as fuel for existing engines takes the idea one step further. It could transform the environmental and economic landscape of Britain, Mr Harrison explained. "We are converting renewable electricity into a more versatile, useable and storable form of energy, namely liquid transport fuels. We think that by the end of 2014, provided we can get the funding going, we can be producing petrol using renewable energy and doing it on a commercial basis," he said. "We ought to be aiming for a refinery-scale operation within the next 15 years. The issue is making sure the UK is in a good place to be able to set up and establish all the manufacturing processes that this technology requires. You have the potential to change the economics of a country if you can make your own fuel," he said. The initial plan is to produce petrol that can be blended with conventional fuel, which would suit the high-performance fuels needed in motor sports.

The technology is also ideal for remote communities that have abundant sources of renewable electricity, such solar energy, wind turbines or wave energy, but little in the way of storing it, Mr Harrison said. "We're talking to a number of island communities around the world and other niche markets to help solve their energy problems. "You're in a market place where the only way is up for the price of fossil oil and at some point there will be a crossover where our fuel becomes cheaper," he said. Although the prototype system is designed to extract carbon dioxide from the air, this part of the process is still too inefficient to allow a commercial-scale operation. The company can and has used carbon dioxide extracted from air to make petrol, but it is also using industrial sources of carbon dioxide until it is able to improve the performance of "carbon capture". Other companies are working on ways of improving the technology of carbon capture, which is considered far too costly to be commercially viable as it costs up to £400 for capturing one ton of carbon dioxide. However, Professor Klaus Lackner of Columbia University in New York said that the high costs of any new technology always fall dramatically. "I bought my first CD in the 1980s and it cost $20 but now you can make one for less than 10 cents. The cost of a light bulb has fallen 7,000-fold during the past century," Professor Lackner said.

 

The Navy is looking at a similar scheme to turn seawater into Jet-A.

But in their case it makes sense...available reactor power is unlimited (at least for 20 years or so) so Jet-A storage and at-sea resupply ends up being the limiting factor for sustained carrier flight ops.

 

I read that story over dinner tonight...and made fun of it.