Orcas Electric Aircraft

August 18, 2012

In 1997 the Toyota motor car company delivered the first commercial, consumer hybrid battery / gasoline vehicle. By combining the benefits of high torque, highly efficient electric motors and small gasoline motors, Toyota proved to the world that there was a market for a high mile per gallon hybrid electric vehicle.

Now the Nissan Leaf and Chevy Volt are all electric driven cars. Wow. In just a 15 years Detroit has made an electric car! If early interest is any indication, its going to be a winner. With fuel costs at $5 a gallon on Orcas Island, fuel efficiency is attractive.

General Aviation has taken a dive recently. Since gasoline prices skyrockets past 6 dollars a gallon to $6.70, pilots are deciding there’s an cheaper way to get around and leaving the aircraft behind.

At the Fly-in this year, I promoted an exciting idea. Building a hybrid aircaft.

While Experimental planes have taken to exotic 1.3 million dollar carbon fiber 300 Knot pressurized high performance kits, like this one in AOPA Magazine, I’m thinking Island Hopping needs an electric aircraft and I’ll explain why and how.

In the Grumman Cougar I owned with my two partners, we could load up 118 gallons of usage av-gas and fly 1100 nautical (1265) miles. Two Lycoming 0-320 gasoline engines provided 160 HP each to a constant speed prop that provided the thrust needed to cruise at 155 knots. It remains one of the best crafted light twin engine aircraft ever. Originally designed to handle IO-360s, for 80 more horsepower, the Cougar might have attained 190 knots.

This has always been intriguing. But with a fill-up that once cost $200, now over $600, its not attractive to think of how to *increase* horsepower and gasoline consumption.

The puzzle has been, how can I put 200 HP x 2 and *cut* my gasoline consumption. The gasoline engine has an efficiency of about 30%. So only about 1/3 of my 114 gallons of gasoline’s energy is turning the prop. So about 38 gallons of gasoline energy is all I use. That’s not much of a deal.

There’s a much more efficient way to convert stored energy into mechanical energy, and its in that Prius and Leaf and Volt. An electric motor can convert chemically stored energy at about 90% efficiency. Wow. ya hey. That’s more like it. But the trouble is, converting gasoline to electricity isn’t very efficient, so we can’t really boost out power plant overall efficiency that way.

Do I need to fly 1250 miles? ever? no. Anything over 3 hours without a break / landing and I’m not happy. With 118 gallons of fuel, I’d have about 716 lbs of gasoline with me. The O-320 engine was first certified in 1953. Hmmm..

The O-320 weighs about 250 pounds with the crankcase oil included.

The tesla roadster’s electric motor weighs 70 lbs and has a peak HP of 288. Saving 180 pounds per engine, or 360 pounds while adding 12O HP * 2, and gaining 90% efficiency is sounding pretty good.

Let’s run some numbers. Gasoline stores 40:1 energy gasoline to battery. Since electric motors are 90 % efficient and gasoline is 30%, we need 3 times less stored energy than a gasoline aircraft. So how much energy can we store in the same weight as gas? Well, if we take 716 lbs of fuel and add the weight saved in the engines 320 lbs we can top up 1036 lbs of batteries. That’s about 50 % more weight of stored energy. Assuming we have about a 13:1 storage challenge, at max weight of 716 lbs, and a range of 1300 miles, it looks like about 100 miles, but we’re going to add 50% to that, because of the weight saving for the engines. 150 miles!

Now that’s interesting.

Since gas engines convert gasoline’s energy to mechanical thrust, at 30% efficiency, and electrics do so at 90% I can say I nee

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