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Thu, May 05, 2005

A Diesel Primer

Putting Diesels In Airplanes Isn't A Bad Idea

By ANN Contributor Patrick Puckett

Since I do the engineering and oversee and manage the maintenance of about 70 various items of equipment (most of it diesel) and our shop handles almost every bit of maintenance including complete overhauls. And, oh yes, I am the company pilot... which now brings us to diesel powered aircraft.

To begin with: most people need to understand that the term. "Horsepower" is actually a measurement of time, but it's become such a common term beginning with Henry Ford's desire to replace the "HORSE" drawn buggies, that everyone has used it, and it has therefore become a huge selling tool to this very day. But now that diesel powered pickups are just "flat" out performing their gas engined counterparts, and more and more sales advertisements are now touting the true name of power of any engine -- namely, "torque."

Simply put: Torque is the amount of force -- or power -- measured in pounds of force at a certain distance. For example: let's say that you have a TSIO-550 B swinging, (hypothetically speaking, of course) a 20-foot diameter propeller. That means that 10-feet of it extends from either side of the hub. Since the torque of a TSIO-550 is not published, we will use the formula of: HP x 5252 divided by the RPM will equal 680 pounds of force at the crank at MSL.

Now, here's why that prop is so long. If you divide it by the length of the 10-foot prop you get 68 pounds per foot, or pound/foot. Simple, eh? If you were able to put a scale at the end of the 10-foot prop, you would see 68 pounds. Multiply that by 10-feet and there you have it.

Okay, here's horse power simply put. "How fast will that engine accelerate?" That's it. It's just a measurement of time. Drag racers, (yup we did that too), like as much Horse power as is INSanely possible. Why? Just in case you didn't get the above, the answer is: acceleration.

Putting it all into perspective, a particular version of a 12 liter Detroit Diesel-powered Freightliner develops about 350 horsepower, but it makes about 1,400 lb/ft of torque. It'll pull an 80,000 pound load up to and over 70 mph, burning a gallon of fuel every five to seven miles. Now take out that engine and replace it with a gas burning 350 hp V8 engine, and you might get it up to 10 mph (before it burns up), while using two to three "gallons" per mile -- not miles per gallon.

Here's what we're aiming at: The soon to be certified, (spring 2005), Centurion 4.0 liter diesel engine makes 698 lb/ft of torque -- but only 310 hp. The Continental TSIO-550-B produces 350hp, but only about 680 lb/ft of torque, (power). What this means is: it will take an extra two or three seconds to accelerate to full RPM. But, because it produces more power -- it will outclimb -- and cruise faster -- than the 550 will. And it will do so using less than half the fuel, and because the Lapse rate is far less than the 550, it will also make more power at altitude. That's how you get higher cruise numbers for a fraction of the operating costs. What this means is that your go fast six-pax single that really could never carry more than two or three souls with full tanks, can now load all 6, while carrying less than half the fuel, and go gobs more miles.

Good news to us GA guys, eh? Bad news to gas burner manufacturers. This is also really bad news to a certain 450 hp turbine engine that has a particularly high lapse rate, as the diesel will run off and hide from the turbine at FL 200 for an exceptionally deep and wide reduction in costs. But if you have a problem with how fast the diesel will rev up, then hold your brakes, -- push that "single lever" all the way forward and wait an extra 3 seconds before launching, you will lift off in the same distance or less (unless you have Al Bundy's mother in law on board).

Speaking of Al's mother in law, what happened to the weight of the old diesel? To answer that question, we have to go to how the fuel was formerly delivered. Since compression is what ignites diesel fuel and the old mechanical system would squirt in a measured amount (depending on where the throttle was set) into the cylinder where the compressed air was so hot and rich in oxygen that when the fuel hit it -- it ignited, -- actually more like an actual explosion. And we're not talking just any kind of explosion here. We are talking about a really "Big Bang." And when that bang occurs, it rattles all the way down the piston, connecting rod, crankshaft, out the engine block and -- voila! The famous diesel rattle.

About seven years ago, General Motors went over to its Izusu diesel division and developed a way to introduce fuel in a controlled way via computer that literally changed the industry. Now the fuel is introduced in stages and basically it starts the flame front with just a miniscule amount -- builds it up to the amount required -- then tapers out.

No more "Big Bang," (go stand next to an idling Duramax, or 6.0 Ford and see for yourself), and therefore no longer requires massive amounts of steel to absorb that sudden impulse of power. The side effect is that now today's diesel's makes more power and uses even less fuel.

Since that time, people are learning that gas engine technology has maxed out and diesel technology is just beginning. Honda is currently testing a family sedan in England that will do 133 mph while getting 92 miles per gallon. It's just the beginning fellow pilots, and I'm not even close to covering all that is currently involved in aircraft diesel's, and diesel's in general.

(Pat Puckett is a pilot and engineer for American Steel in Las Vegas, NV. The company engineers and manufactures metal buildings. Pat also designed and engineered the company's own one piece hydraulic "HyMatic" hangar door. After starting American in 1981, Pat started doing extensive research on diesel engines, and now have an extensive library of facts starting with diesel powered German aircraft of pre world war existence.)

FMI: www.dieselpub.com


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