News, facts, and comments on the coming revolution for piston-engine aircraft.
In 1998, one diesel engine flew on a converted airplane for the first time since 1945. Today, close to 4,000 singles and twins are flying. This is the beginning of a worldwide trend which will eventually allow a rebirth of the piston-engined aircraft, around new specs and new missions.
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News of October 05, 2007
Diesel, or turbine? Propeller, or jet propulsion?
We said many times that the aero diesel will slowly take the market of piston-engined aircraft between 100 and 450HP. Why? Discussing this opens a much wider issue: the relative future of jet airplanes versus propeller airplanes.
Let me surprise you: the true turbojet engine is gone. The very common fanjet design consists in putting back on the turbine axis a geared propeller, with the difference that this propeller is captive in a fan duct and looks like a low pressure compressor. At low speeds, it increases the engine force pulling forward the plane (in a go around for instance) and reduces specific fuel consumption. The true turbojet, which still exists only on military aircraft, is a tremendous gas guzzler at low speed.
A good turboprop airplane such as the TBM 850 or the Pilatus flies at 270 to 300 knots. The new generation of mini-jets goes just a bit faster. A piston engined plane can fly as fast as a turboprop. The speed limiting factor is the propeller itself, not the engine principle. The fastest piston engined planes fly faster than 400 knots top speed (440 knots for some of them) since the late forties. A propeller airplane, whether with turboprop or piston engine, can easily be designed for a cruising speed of 300 knots.
Above 450 HP, the turbine rules. It is much lighter and much smaller, and it burns jetfuel. But it is not fuel efficient at low speeds, which is less important on a big and fast airplane with lots of fuel capacity. It is much more expensive per HP than a piston engine (because of the manufacturing complexity and cost of all turbine components and materials) but the owner can afford it: Soon he will be able to afford a business jet anyway… And he will be driven to it by tax avoidance reasons: An airplane is amortized tax-wise much faster than its real market depreciation. Since depreciation is deductible, it means that 40% of the price of an airplane is financed by the taxpayer. Which is a negligible factor on a Cessna 172, but a very big factor on a $15 million business jet.
Under 100HP, meaning for very small LSAs and Ultra-Lights, the gasoline engine rules: it is lighter than a diesel, and its fuel cost is a non issue even if Avgas goes up to $10 a gallon (and eventually it will.) And it is a small market.
In-between will be the segment where the aero diesel engine will rule. It burns jetfuel. It has all the advantages on Avgas engines which we have discussed many times, which are more important for smaller planes. And the public still doesn’t realize what a twin-diesel with two 450HP engines will look like. (Think of the German TT62 prototype, or an Adam push-pull). It will be much less expensive than a jet of similar capacity and useful load. It will have a much longer range. Flight management will be far more flexible. Its maintenance costs will be much lower. And it will cruise at 300 knots.
Now, if the US and other administrations decide that it is time to extend the amortization time span of all aircrafts and if the disguised tax subsidy gradually fades out, it will be more and more difficult to justify moving VIPs around in a 30 million plane. VIPs may consider that, if President Eisenhower was satisfied in the fifties with flying at 170 knots in an Aero Commander 520, its modern, 300 knots diesel equivalent might be good enough for them?
posted at 4:18 AM
Cessna and Thielert Team to Offer Skyhawk Turbo Diesel 155HP Option
After an extensive market survey and flight test, Cessna Aircraft Company announced at the AOPA Convention in Hartford CT that it will offer the new Thielert turbo diesel engine in its Skyhawk 172S aircraft with deliveries set to begin in mid-2008. The Skyhawk TD (turbo diesel) will feature a Full Authority Digital Engine Control (FADEC) equipped Thielert Centurion 2.0 liter engine. The DOHC (double overhead camshaft) in-line four-cylinder turbocharged engine develops 155 horsepower, is certified to operate on Jet-A fuel, is liquid cooled and drives a composite three-blade constant speed propeller. "The Skyhawk is already the best-selling, most-flown airplane ever with more than 43,000 delivered, and this option further expands the market due to the worldwide availability of Jet-A fuel," said John Doman, Cessna vice president of worldwide propeller aircraft sales. Thielert has a supplemental type certificate (STC) for the Skyhawk, allowing Cessna to offer a factory-installed Thielert engine. The engine features low specific fuel consumption, electronic engine control systems and improved hot-and-high engine performance. "With the Skyhawk TD, we will incorporate standard aircraft design changes to ensure simple installation and full STC integration," Doman said. "Pilots will enjoy a number of benefits in addition to lower fuel cost, such as simplified engine management and exceptional reliability." With increased range and endurance, the Skyhawk TD will offer an ideal solution for special mission applications like flight training, forestry patrol, wildlife conservation efforts, pipeline/power line patrol, traffic reporting and airborne law enforcement. Cessna and Thielert Aircraft Engines GmbH made the announcement at the annual Aircraft Owners and Pilots Association (AOPA) Expo, running Oct. 4-6 in Hartford, Conn. At the static display at Hartford-Brainard Airport, Cessna features the Skyhawk TD, Skylane, Stationair, Grand Caravan, Citation Mustang and Citation CJ2+. In the exhibit hall, Cessna showcases a mock-up of the SkyCatcher. (Thielert 10/4/07)
DieselAir Comment: This constitutes another major breakthrough on the aero diesel market. Until now the main problem with the 172 Thielert was that it was somewhat underpowered at low altitude. With 155HP we can expect the new 172 Thielert to show comparable performance to an Avgas run 172 upto 4,000 ft, and much better at higher altitudes including a much higher ceiling, since this is a turbo. On top of that, Cessna is formally entering the market, tiny until now, of OEM diesel airplanes. Let us wait with interest for the first test flight, and for the impact Cessna will now have on the US and world market...
posted at 2:30 AM
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Every month: news, facts, and comments on the coming revolution for piston-engines aircrafts between 130 and 400 HP: Retrofitting a diesel engine to run on Jetfuel or Kerosene, reduce Gallons/Hour by some 30%, eliminate ignition systems (magnetos, spark plugs) and their problems, eliminate mixture control, increase TBO to 2,400-3,000 hours, increase performance between 6,000 and 12,500 ft., and drastically reduce Operating Costs.
The letter is intended for piston engines aircraft owners, manufacturers, fleet operators and FBOs, re-manufacturers of engines for these aircrafts, manufacturers of engine components and ancillaries, and all professionals acting in decisions of engine exchange or refitting at TBO, in North and South America, Pacific Rim, African continent, and all parts of the world were Avgas, Mogas, Kerosene and Jetfuel are available.
The DieselAir Newsletter is a confidential publication available only as printed material sent by mail (airmail for overseas), to fully identified individuals or businesses involved in General Aviation. Forums and online content may be printed at discretion of the publisher.