glyn

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Semper in excretum. Solum profunda variat.

Tarek Morgen

And if you kept your nose out of our continent we would have teached them to do the same long ago!

(That is of course a joke and not meant to taken serious)

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uh I might be wrong

gunnut

I will try to refrain from telling more French jokes.

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"Only Nixon can go to China." -- Old Vulcan proverb.

Tin Man

C.I. (Diesel) engines have always been traditionally heavier than petrol engines, ie cast Iron heads and blocks. This was done to cope with the higher compression ratios in C.I. engines. Now we can build all alloy Diesel engines that are cost effective. As Omon stated, another improvement is Direct injection.

I don`t know if weight was actually the primary concern but the industry is geared up for petrol aviation engines on the whole.

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"Liberty is a thing beyond all price.

Dreadnought

Quite funny when I returned home from europe I was in such a hurry to get out and meet my brothers and friends for a few pints that night it took me a few miles or so to notice I was on the wrong side of the road but here in America I was atleast on the right side of the car.

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Fortitude.....The strength to persist...The courage to endure.

dave lukins

No No, we sit on the right side ..You sit on the left

GAU-8

Gun,

Not a dumb question at all. Short answer: Power to weight ratio. Diesels put out a lot of torque at low rpm. Historically, designers who tried to use diesels had to incorporate a gear drive to the propeller to achieve the high rpm required. This added weight put the diesel at a disadvantage to an avgas engine. But times have changed. Seeing the cost of avgas rising and some refineries looking into getting out of producing avgas, The German Thielert Group is marketing an aluminum block, water cooled, FADEC controlled aircraft engine. The engine will be available as a retrofit to existing light aircraft and comes factory installed in the Diamond Aircraft DA42 Twin Star.

AOPA Online: Diamond Aircraft DA42 Twin Star: Flying Sports Sedan

Diamond Aircraft

Centurion Engines




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When a prang seems inevitable, endeavor to strike the softest, cheapest object in the vicinity, as slowly as possible. --WW II RAF Instructor Pilot

dave lukins

Gau..What are the cost comparisons of running either engine, what about running (fuel)cost. Do you see a future in the "new" engines?

GAU-8

Hi Dave,

With the price of avgas going up (and possibly going away), it might be too soon to say. There are not enough airframes out there now to do an apple to apple comparison.

I read an in depth consumer report on the DA42 recently. (At this time the only production, state-of-the-art, aerodynamically cutting edge craft sporting diesels). Nice bird and she sips fuel, but she's slow and can't carry much. At what is normally the overhaul mark on an avgas engine (TBO), you send the engines on the DA42 back to the factory and buy new ones. So while you're cruising along at 120 kts, sipping fuel and saving money, the huge cost of buying two new engines is looming on the horizon. I'd like to see the numbers per hour in fuel savings compared to how much you will have to put aside per hour for the new engines at the end of their service limit.

I do see a future for these diesels. There is a huge market for these retrofit engines. Owners of older light aircraft will be faced with paying more and more for avgas or changing over to diesel. Once retrofitted, I'm guessing these older, less aerodynamic airframes will deliver lower performance numbers than with their original power plants.

On the other hand: With small jet engines becoming cheaper and small jet aircraft (VLJs), hitting the market, the age of the prop may be in its twilight.

I apologize for not being able to answer your cost question.
I'm afraid that answer still up in the air. (Guffaw, yuk, yuk).

glyn

.

JA Boomer

The primary reasons are that diesels engines tend to be more robust, thus heavier and larger than similar aviation gasoline aircraft engines. Diesel engines also tend to work at slower speeds (lower rpm's) than avgas engines, which is a disadvantage for a prop. Diesels also suffer from poor cold weather performance, so you can see this may be a problem in some climates and at altitude.

The MAIN reason that diesel engines have not caught on significantly though, is probably just because aviation gasoline is an institution. It was the first fuel for aircraft, and no one ever really looked back. Probably be hard pressed to find aircraft grade diesel around, where as avgas is still quite common.

I do think you will see an increase in the number of diesel powered aircraft in the coming years. Primarily because the demand for avgas is declining (has been since 1957). The primary form of avgas (100LL) and many other grades still contain lead additives, so there is also a push to get rid of it for environmental and health reasons. Also, the rising price of crude doesn't help things.

The switch to diesel powered aircraft will be made easier because standard jet fuel JET-A1 (or JET-A in the US) can be used in diesel engines. Diesel and jet fuel are similar fuels, very close to each other in the distillation process of crude oil. Jet fuel is found at almost every semi-large airport in the world now, so the supply issue really only applies to smaller airports. Perhaps we will see a standard grade of aviation diesel being produced in the near future, with the increased production and quality standards that aviation gasoline has compared with motor gasoline grades.

The current synthetic jet fuel that the USAF is using in the B-52 fleet and testing on other airframes is mainly produced from natural gas and coal, but can also be produced from biosources such as switch grass, all through the FT process. So in effect, bio jet fuel is already being used.

Perhaps it has something to do with the fact that the actually ignition and combustion of gasoline is done in a gas (vapor) phase. Toss a match into a bucket of gasoline and it probably will not light (please don't actually try this). It is the evaporating vapors from the liquid gasoline that combusts.

glyn

[quote=JA Boomer;435212]The primary reasons are that diesels engines tend to be more robust, thus heavier and larger than similar aviation gasoline aircraft engines. Diesel engines also tend to work at slower speeds (lower rpm's) than avgas engines, which is a disadvantage for a prop. Diesels also suffer from poor cold weather performance, so you can see this may be a problem in some climates and at altitude.

Slow revving is good. Most propellers are not efficient at over about 3,000 rpm. That's true even for the WW2 piston engined fighters.

The MAIN reason that diesel engines have not caught on significantly though, is probably just because aviation gasoline is an institution. It was the first fuel for aircraft, and no one ever really looked back.

Until WW2, it was ordinary 'motor spirit' (ie petrol) that was recommended in the user manuals of the time

Probably be hard pressed to find aircraft grade diesel around, where as avgas is still quite common.

Is there such a thing as 'aircraft grade' diesel?

I do think you will see an increase in the number of diesel powered aircraft in the coming years. Primarily because the demand for avgas is declining (has been since 1957). The primary form of avgas (100LL) and many other grades still contain lead additives, so there is also a push to get rid of it for environmental and health reasons. Also, the rising price of crude doesn't help things.

I wonder how successful it would be in putting a diesel engine in place of the Lycoming or Continental on the existing metal aircraft like Cessnas or Pipers? I suspect that they are generally dragmasters that need to be over-powered in able to fly at all!
.

gunnut

Here's a related but not quite question. Why don't we see more turboprops in smaller planes more? Are they not as fuel efficient or heavier?

GAU-8

Bucks. $$$

Turbines are expensive to build and maintain. Tighter tolerances and all that. One wouldn't call them "fuel efficient." They put out tremendous thrust for their light weight but they burn fuel at a high rate. If you're plodding along at low altitude, pistons are still economical. If you need to go high and fast, you'll need to pay for better equipment--turboprops or jets.

In the market for an aircraft?

gunnut

I wish.

Just curious about aviation. I know usually things are done for a good reason. I just want to find out what that reason might be. Like why not turbine hybird cars or diesel prop planes.