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.)