I have a dumb question

**dave lukins** · 08 Dec 07,, 00:18

Originally Posted by 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?

Gau, If price was not a problem, what in you opinion would be the optimum Aircraft (1) commercial (2) private..Diesel -Avgas -multifuel etc. etc. If you could choose the perfect make-up what would it be??

**JA Boomer** · 08 Dec 07,, 08:41

Originally Posted by glyn

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

Not to my knoweldge...and I guess why would there be when you can just fill up at the jet fuel pump with JET-A1. Maybe in the future, IF diesels really catch on, an aviation diesel grade might be standardized, because it would cost slightly less to produce than jet fuel, although low demand would entail high distribution and supply costs which may negate that fact.

**IflareR** · 08 Dec 07,, 11:49

aviation diesel engine has only one issue, fuel; automotive diesel fuel freezes in high altitudes and kerosine has shitty lubrication properties as it is not ment for fuel injected piston engines and lacks required additives. it causes huge wear to the fuel injection pump. and having fuel injection pump failing mid flight is NOT a good thing.

question; are you allowed to add anything to kerosine and still use it in flying things? mainly because if you mix lubricating additive('s) to kerosine it would be suitable for diesel engines. thats how polar expeditions run their land vehicles.

**GAU-8** · 08 Dec 07,, 13:46

Originally Posted by dave lukins

Gau, If price was not a problem, what in you opinion would be the optimum Aircraft (1) commercial (2) private..Diesel -Avgas -multifuel etc. etc. If you could choose the perfect make-up what would it be??

Great question Dave

Price not a problem? Wow, I'm a kid in a candy store! As a pilot, I'll always opt for the fewest moving parts. (Why I don't like helicopters). For simplicity and reliability, I'd opt for a mid to high bypass, FADAC controlled turbojet as a power plant.

As for the optimum aircraft, it would depend on the job. I can think of few places where the axiom "form follows function" is more evident than in the design of an aircraft. Personally, I miss flying fighters. If you hear of a private firm willing to pay a pudgy, gray old derelict to fly one, please forward the info. If I were hauling freight, I'd opt for one type, hauling people another. If I were operating down low, I'd opt for a turboprop. Up high, a turbojet. Aerobatics one; instructing another...

A big part of the love affair with flying is the vast diversity of aircraft. Like women, they all have their special abilities and unique beauty.

If I could choose the perfect make up? Not sure if I could settle on just one. I've flown some of these and have dreams about the others:

Piper J-3 Cub
de Havilland Tiger Moth
DC-3
Supermarine Spitfire
de Havilland Beaver (with or without floats)
F-86
F-4
T-38
A-10
de Havilland Twin Otter

Anything with an oil guzzling, blue smoke bellowing radial engine.
The list could go on forever...

**GAU-8** · 08 Dec 07,, 13:51

Originally Posted by IflareR

aviation diesel engine has only one issue, fuel; automotive diesel fuel freezes in high altitudes and kerosine has shitty lubrication properties as it is not ment for fuel injected piston engines and lacks required additives. it causes huge wear to the fuel injection pump. and having fuel injection pump failing mid flight is NOT a good thing.

question; are you allowed to add anything to kerosine and still use it in flying things? mainly because if you mix lubricating additive('s) to kerosine it would be suitable for diesel engines. thats how polar expeditions run their land vehicles.

There are common fuel additives to jet fuel (kerosine). One of the product names is PRIST. Newer jets bypass more fuel past the engine than is needed to burn. This heated bypassed fuel returns to the fuel cell and keeps it warm.

**Jimmy** · 08 Dec 07,, 16:20

That's how diesel trucks keep their fuel from gelling up during the winter, and why you always see them just idling in parking lots at gas stations and hotels and whatnot.

**GAU-8** · 08 Dec 07,, 16:54

Originally Posted by JA Boomer

Not to my knoweldge...and I guess why would there be when you can just fill up at the jet fuel pump with JET-A1. Maybe in the future, IF diesels really catch on, an aviation diesel grade might be standardized, because it would cost slightly less to produce than jet fuel, although low demand would entail high distribution and supply costs which may negate that fact.

The DA42 uses Jet A. To the best of my knowledge, all the Thielert aircraft diesels burn Jet A.

Question: Wouldn't it be more cost effective to tweak a diesel to burn Jet A than to crank up a whole production facility to supply aviation grade diesel?

**JA Boomer** · 08 Dec 07,, 18:46

Originally Posted by GAU-8

The DA42 uses Jet A. To the best of my knowledge, all the Thielert aircraft diesels burn Jet A.

Question: Wouldn't it be more cost effective to tweak a diesel to burn Jet A than to crank up a whole production facility to supply aviation grade diesel?

Yup, that was what I was trying to say. There really isn't much tweaking necessary, I've heard of people who work at airports filling up their diesel pick-ups with jet fuel. I was just thinking that if diesels really do catch on, there may be a time when the production demand warrants producing a less expensive avdiesel (would be less refined than jet fuel) that would costs less. But honestly, I don't think that will ever happen.

Using jet fuel in a diesel engine is pretty much the same as using 91 octane mogas in a 87 mogas car, or using avgas in a car. It is a more refined product, but does not make your engine more efficient or more powerful.