Hjelmco is certainly fighting the good fight in that regard.

Which brings up the point of the availability of Avgas worldwide.

I had an aeroplane ferried from the UK to Australia, via the middle east and asia. Avgas, with engines only certified to use the leaded variety, was extremely hard to find and extremely expensive through much of the region. I have a photo of the aircraft being refuelled in India via hand held funnel and two gallon cans.

This also means that many of the NGO and small relief aircraft which used to be active in those areas are no more.

Still plenty of JetA1 available, but one needs a totally different engine for that.....

Last time I looked, few years ago it seemed the long term solution was to switch to diesel. Diesel has some advantages, higher efficiency means lower fuel consumption, energy per gallon is higher, but lower per pound. And also diesel is safer to handle.

Probably modern materials allow for reliable diesel aircraft engines that are lower cost over the life of the aircraft. But difficult though since the pace of development in the light aircraft industry is very slow and there is little money in it.

I wonder why there's no effort to make affordable turboprop engines in the power range required for typical GA usage. Sure, small turbines take an efficiency hit (boundary layer friction and whatnot), but still? And what makes them so expensive compared to piston engines?

But yeah, maybe small diesel engines are a better approach, shrug... And some of the designs look neat, e.g. opposed piston two-stroke like ye olde Junkers engines.

There's also efforts to create and certify an unleaded replacement for 100LL. Probably won't solve the price and availability issues with avgas, but at least it doesn't contain lead (which in addition to the environmental issues is a PITA for refineries ) and I guess it's a hedge against that last TEL-producing factory on the planet going bankrupt and grounding the fleet..

Primary training aircraft at least have big potential in electric propulsion.

Hybrid Electric aircraft are kinda interesting when you start running the numbers.

The weight of the batteries of course reduces the amount of fuel the aircraft can carry. However increased efficiency reduces the amount of fuel you need to carry. There are a bunch of other advantages which would improve safety.

In particular better throttle response. A problem with turbine engines is when an aircraft is hit by wind shear during landing you need more power right now, and turbines have lag. And also when you shutdown an engine in a multi-engine aircraft you have a serious thrust imbalance. Hybrid electric would allow power to be routed evenly to each fan as needed.

Traditionally you deal with the lag with variable pitch propellers. But with electric motors you can have a lot of immediate / momentary torque and power and instead vary the propeller speed.

I think what is aimed at with electrics is you get a lot simpler aircraft with far lower operating costs and higher reliability and availability.

No engine maintenance, no variable pitch propeller, no fuel systems (you do have batteries but they should be self contained man changeable systems). No huge checklists with warmup etc procedures on the ground.

It's worth it to just have 30-60 minutes of flight time, because you still get to train takeoffs and landings.

Maybe the instructor and student can first swap the new battery with 5x20 kg units or so, take off, do a few touch and go:s, land, then let the next guys do the same.

The nice thing with a diesel aviation engine is that it can run on kerosene (Jet fuel). Jet fuel is available at pretty much every airport.

Yeah's the big driver otherwise it'd be moot.

I think most everyone that tried introducing diesel aero engines in the early 2000's went bankrupt. Which actually isn't the end of things as long as the business is sound.

The QUEST Kodiak is filling in for many of the larger NGOs. I believe it was designed for that express purpose (taking over where the small avgas powered planes could no longer operate due to the price or availability of avgas).

Unfortunately Turboprops come with a whole new set of maintenance requirements but otherwise it's an excellent aircraft and working out quite well.

I think the Quest Kodiak is a great aeroplane, and very comparable to the Cessna 208. Both have many advantages over the Cessna 206s and 210s which were fulfilling these types of roles over the previous 40 years.

The biggest issues with both of these is the cost to buy and also the cost to maintain. Both are well in excess of the older Cessnas.