Thread: I have a dumb question

Originally Posted by gunnut

Why are there no diesel powered piston aircraft?

There must be a very simple reason but I just don't know.

Is it because of the high rpm required? Does a pistol airplane need high rpm?

The Junkers JU-86 was a twin diesel engined bomber. Obsolete by the start of the war it served in secondary roles.

There are certainly diesel powered aircraft, such as the one mentioned by sappersgt. I was talking to an aviation mechanic last week, he's heading to Africa in a few weeks to maintain a fleet of airplanes for a missions organization, and they have several diesel airplanes. As for why there aren't more of them, I dunno. Power to weight ratio, perhaps? Your suggestion about rpm maybe close to the mark. Diesel engines are big on torque, less on hp. I might be able to ask my mechanic friend.

Originally Posted by gunnut

Why are there no diesel powered piston aircraft?

There must be a very simple reason but I just don't know.

Is it because of the high rpm required? Does a pistol airplane need high rpm?

Nothing dumb about the question. Junkers used to make diesel engines for aircraft, and fitted them to their own aircraft designs in the late inter-war period. Recent automotive diesel engine development has brought great improvements ( my Mercedes car is diesel but sounds like a petrol engine when under way ). The power and weight issues have been addressed and of course you do not have the electrical problems, so a diesel is much more reliable. In the last few years a number of European light aircraft have been retro-fitted with diesels, and new types designed for a diesel in the first place are now available. Combined with carbon fibre composites they offer unmatched speed, range and economy. I think most aircraft in future will follow suit. High rpm are not a problem as gearing can be used if necessary to reduce propeller revolutions to an optimum level.

Originally Posted by glyn

Nothing dumb about the question. Junkers used to make diesel engines for aircraft, and fitted them to their own aircraft designs in the late inter-war period. Recent automotive diesel engine development has brought great improvements ( my Mercedes car is diesel but sounds like a petrol engine when under way ). The power and weight issues have been addressed and of course you do not have the electrical problems, so a diesel is much more reliable. In the last few years a number of European light aircraft have been retro-fitted with diesels, and new types designed for a diesel in the first place are now available. Combined with carbon fibre composites they offer unmatched speed, range and economy. I think most aircraft in future will follow suit. High rpm are not a problem as gearing can be used if necessary to reduce propeller revolutions to an optimum level.

Another silly one - I suppose there's nothing to stop the same diesel engined planes running on bio-diesel?

Originally Posted by PubFather

Another silly one - I suppose there's nothing to stop the same diesel engined planes running on bio-diesel?

It can't be too silly as I do not know the answer to that! It is possible that they will have to use some additive to prevent it coagulating at the low temperatures experienced at altitude. Another possible work-round could be pre-heating the fuel before it reaches the injectors. If the USAF can run B-52s on coal-derived fuel (and they can) I am hopeful that BioDiesel can also be made acceptable to the Civil Aviation Authorities. Another possibility is to proscribe their operation above a set height level.

large aircraft is 90% jets, small aicraft relies on very few engine manufeturers, they have been building gas engines for many years, diesel development (diesel itself has been around for about 100 years) is a recent thing (variable geometry intakes, direct injection,..ect) factories need time(and money) to reorganise them to make diesel engines.also i think aircrafts themselves need to be modified for that eng.. too much to invest, imo we are more likely to see mini jets, than diesels. this is a cool little plane.

Originally Posted by omon

large aircraft is 90% jets, small aicraft relies on very few engine manufeturers, they have been building gas engines for many years, diesel development (diesel itself has been around for about 100 years) is a recent thing (variable geometry intakes, direct injection,..ect) factories need time(and money) to reorganise them to make diesel engines.also i think aircrafts themselves need to be modified for that eng.. too much to invest, imo we are more likely to see mini jets, than diesels. this is a cool little plane.

Until they can manufacture gas turbines that are as fuel efficient as the modern piston engines, I think the piston engine will prevail in the market for private owners and the diesel will take an increasing share of the lower-powered engines. Gas turbines are noisy, so not neighbour friendly. They are also very expensive. They will have a place in the General Aviation marketplace, albeit a relatively small one. To get the speed benefit from a small jet engine the aircraft wings are made as small as decently possible. A result! But also a cost in that many private strips are too small to handle the higher landing speeds, so they would be tied to paved airfields.

Originally Posted by omon

this is a cool little plane.

It is the French Cri-Cri, and it really is as tiny as it looks. I have seen one land on the roof of a moving van at an air display.

Originally Posted by glyn

( my Mercedes car is diesel but sounds like a petrol engine when under way ).

What the duece is a "petrol" engine?

Originally Posted by TopHatter

What the duece is a "petrol" engine?

It is the proper name for what you ex-Colonials amusingly (and quite incorrectly) call your 'gas' engines fitted in motor cars (which you creatively call 'automobiles').

Originally Posted by glyn

It is the proper name for what you ex-Colonials amusingly (and quite incorrectly) call your 'gas' engines fitted in motor cars (which you creatively call 'automobiles').

Hey at least we drive on the "right" side of the road.

Originally Posted by glyn

It is the proper name for what you ex-Colonials amusingly (and quite incorrectly) call your 'gas' engines fitted in motor cars (which you creatively call 'automobiles').

I never understood why they call that stuff "gas"..I mean its not even the right state of matter! And there are cars that are running on (real) gas. I mean did not the fact that their "gas" is liquid show them that there might be something wrong??

Originally Posted by Tarek Morgen

I never understood why they call that stuff "gas"..I mean its not even the right state of matter! And there are cars that are running on (real) gas. I mean did not the fact that their "gas" is liquid show them that there might be something wrong??

Gas is just a short for gasoline. I have no idea where the term gasoline came from though. Petrol you figure is from petroleum.

Whenever people say "I need to get some gas" (common expression here) I always reply "gee, that sounds like a personal problem..." )

I don't like the term gas either. I try my best to say the word "gasoline" when I mean gasoline.

Originally Posted by gunnut

Hey at least we drive on the "right" side of the road.

Literally...However, we drive on the "correct" side of the road)