Turbines burn a huge amount of fuel.
 

Turbines have serious issues with specific fuel consumption (pounds per hp per hour). A typical small aircraft turbine will burn anywhere from 0.6 - 0.8 lbs per HP per hour, a TSIO-360 perhaps 0.5, but a diesel will burn as low as 0.3-0.35 lbs/HP per hour. That means your fuel burn at the same speed will be just about double using a turbine rather than a diesel. Even if the diesel were to weigh 500 lbs, while the turbine was at 300, you could go just as far at typical loads, and max range for the diesel would be double that of a turbine.

In addition, the specific fuel consumption of a turbine gets worse as you pull back the power. So putting in 2 750HP PT-6s would give outrageously poor fuel efficiency. Part of the reason that turbine aircraft need to fly so high to get reasonable range is that at high altitudes the engines can run at near 100% power without hitting very high IAS/CAS, which would cause a huge drag penalty. Diesels can have very high specific fuel consumption over a very large range of power settings, gasoline engines are good at lower power setting but very bad at maximum power.

I would love a diesel in my Skymaster, or Cessna 414A or anything else with a prop. The ability to use Jet-A or diesel fuel, simpler engine (no ignition system, or even a 2 stroke with no reliability issues), best possible specific fuel consumption, no icing, liquid cooling (though it could be air cooled), would all be great.

Good article in the current AOPA magazine summarizing the status of diesels for GA airplanes. The takeaway (for me, anyway) is that either (1) you'd have to do a lot of flying to ever amortize the conversion with fuel savings, or (2) love your airplane so much you don't care how much money you spend on it - read 'sunk cost.'

Appears to me that diesels in Skymasters will remain in the category of 'an interesting academic discussion' for the forseeable future.

Joe

You are almost certainly correct.
 

I just wish that some still built a small pressurized twin that didn't cost several million dollars. Come to think of it, nobody makes a pressurized piston twin at all. I know that many people are comfortable flying behind a single engine but I think I have spent too much time flying multi-engine aircraft (much of it in 8 engine aircraft) that I just get nervous with one ( at least when the weather is bad or I am over really inhospitable terrain). To be honest, I have never had an engine failure in any aircraft except my old Skymaster, but it flew on like it was a non-event.

I love turbines, and most of my flying has been in jet aircraft, but they do suck down the gas. I remember burning more fuel taxiing to the runway in a t-38 than the total fuel capacity of my Glassair. I would love a 4-6 seat diesel pressurized twin that could fly at FL350 while burning 20gph even if it didn't have the smooth power of a turbine.