Will we all be flying diesels?

We have had so many “diesel” threads here…

The trouble with diesels is the same blindingly obvious stuff which is responsible for Product X not selling regardless of what business you are in.

Take my TB20 with 250HP. SMA “had” an engine with 230HP. So, we have

• Less power. Who wants LESS power? Precisely absolutely zilch, zero, nobody on earth. Every plane, possibly short of an F16 or such, is horribly underpowered.
• New technology. Anybody who can type http:// into a browser will have noticed that most new products have problems.
• The “Thielert accounting experiment” has p1ssed all over the diesel bonfire, for years
• A ridiculous retrofit cost – of the order of two brand new Lyco engines, or one brand new Lyco and avgas for the rest of your actuarial life
• Socata played with it and dropped it (reported reasons vary – hard to know who can be believed… my contact at Tarbes reported “too much vibration”).
• The main selling point is the fuel, but in ~ 90% of the world’s market (the USA) this advantage is zero – unless you buy into the “avgas end fear” and old timers in GA soon get bored with that

To make something sell, you cannot start with such a long list of negatives, and hope against hope that people will throw money at you at the end of it. It’s like trying to sell a Xmas tree which is shorter than average for 2x the average price.

Aero Friedrichshafen is always showing engines which have a “great future”, and it’s like that every year.

To sell something, it has to offer a decisive advantage – it has to be a no-brainer. So you need

• An IO540 sized engine with 300HP+ (or IO550-sized, 350HP+ for an SR22)
• Loads of field testing, reliability data, and very obvious manufacturer committment by a strong company
• Retrofit cost similar to an overhauled engine (say 30-40k €)

Then it will sell. Until then it won’t.

Peter wrote:

Take my TB20 with 250HP. SMA “had” an engine with 230HP.

That is somewhat moot since what you loose at takeoff you will gain up high where your 250 HP will be reduced to 50% at FL180 while the diesel will still output 90% thanks to the turbo.

The engine vibrations, or rather the more powerful acceleration at each stroke, is a challenge that all diesel manufacturers need to address and is one of the reasons why the diesel engines are fitted with scimitar propellers rather than aluminum, as well as clutches with vibration dampeners.

That is somewhat moot since what you loose at takeoff you will gain up high where your 250 HP will be reduced to 50% at FL180 while the diesel will still output 90% thanks to the turbo.

True but the perception is what matters

Also 20HP less translates to a lot worse takeoff (runway) performance. Nobody wants that, because there are so many marginal runways. Zell am See is one of many in Europe.

Completely agree, Peter. Too many negatives and the positives are not big enough over the existing stuff. Innovations must be hugely better than what they replace in order to be successful.

Over at the Aerostar forum there was a huge following for the still in development EPS 350hp engine. They’re making some good process, and it’s even produced 450hp in test bench. I wasn’t skeptical of the technology, but I was skeptical of the future pricing. They didn’t say how much it would cost, but they hinted at $250K+ for an engine. Even if it gets certified, which might take another 10 years, then someone is going to have to develop an STC for each airframe, which will take mother 5 years. On top of that, you’re now looking at a minimum cost $600K for a twin, for a virtually unproven engine with probably lower TBO. That’s going to take a lot of fuel savings to get back. You could run a turbine for less money for years.

So, unfortunately, I’m not very positive of the diesel future anymore. I actually think electric or hybrid/electric will develop faster than diesel.

I am very confident that the new TCM 6-cylinder diesel will deliver what we want – except a low price. The power range, they say, will be between 300 and 350 hp, and the base engine is so smooth and has so little vibration that it might work. I am driving that engine since 2011. It delivers a very high torque of 520 NM at 1800 rpm already. We’ll see …

One of the biggest trade-offs for the turbo-diesels (and least talked about) is the cooling drag – significantly more than a gas engine and that is always going to handicap the TDs and ruins any efficiency gains.

And the reason for potentially increased cooling drag, in spite of higher engine efficiency, is that the fluid from which you are rejecting heat (the coolant and the radiator fins touching it) is at lower temperature than the fins of an air cooled engine. Therefore you need more surface area to reject the heat to the air.

The biggest trade-off for me is that to the best of my knowledge every TD aircraft engine program has been wrapped around a sole source for engine overhauls and for parts. That loss of freedom and inevitably increased cost is something I would never sign up for, ever.

Michael wrote:

One of the biggest trade-offs for the turbo-diesels (and least talked about) is the cooling drag – significantly more than a gas engine and that is always going to handicap the TDs and ruins any efficiency gains.

I do not really understand that. Is it an air-cooling versus liquid-cooling thing?

In my experience the problem with diesel engines in cars it that it is difficult to get them warm enough in cold temperatures and in cold countries diesel powered cars require an additional diesel burning heater for creature comfort.

@Aviathor, the first paragraph of my post #119 was in response to your question. Yes, it is a liquid cooled versus air cooled thing.