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View Full Version : Always just around the corner


Stephen Furner
10th Oct 2009, 21:21
Sabaru have for a few years now had a diesel boxer engine available for their cars yet the aviation community is still without a good Jet A1 boxer engine for its aircraft as an alternative to the popular petrol Lycoming or Continental. What happened to the promise of cheap clean quiet low maintenance (at least 2000 hours between overhaul) piston diesel aero engines that seemed to be just around the corner 5 years ago? Low cost Jet A1 for everybody and perhaps ordinary car/lorry fuel bought from the garage forecourt for those that wanted to use it. It seemed like only a question of a couple more years of LL100 and we would all be moving over to Jet A1 for the average spam can such as a Cessna 150, 172 or PA28. However, they still seem to be just around the corner and not getting any closer.

Pilot DAR
11th Oct 2009, 00:33
One of the many reasons for the slow progress in the certification of diesel engines for GA use, is the doubled affect of the cost. First you have to type certify the engine, and within that, the propeller, a hugely costly effort. Then, you have to certify that enigne propeller combination in each aircraft type, one by one. All of this on top of the immense development and design costs. There is just not enough need for the aircraft out there to justify this. I worked on and off for a year with a company who were planning to type certify the Subaru diesel for aviation use. I was just to costly, and complicated to document the quality control and traceability of an automotive engine, when the eninge manufacturer did not support this effort. The rather limted choices of suitable propellers for diesel engine's torque characteristics does not help the matter much either.

More recently I was involved in the STC approval of the DA42 back to gasoline engines. The DA42 diesel is a delightful and simple aircraft to fly, but challenges with the engines are well documented. The Lycoming IO-360 is tried and true. A gas gobbler, well, yes, compared to a diesel. But dollar for dollar to operate the gasoline engine is still cheaper overall, and pilots are continuously whining about the cost of flying.

If pilots and owners were saying, here industry, is gobs of money for developement of diesel powered aircraft, we'd be getting the new techology. Pilots and owners (with the exception of the DA42 and Thielert STC'd aircraft owners, are not) so here we are.

Of the six vehicles/machines I own, only the plane and the ATV are gasoline powered. The ATV used to be available diesel, but they discontinued it the year before I bought (I guess they had their reasons). The plane only sees MOGAS, so the saving of diesel would not really get the operating cost lower enough to be worth the up front cost. Gasoilne should be a fuel of the past for aircraft, but that just is not going to be the case for a very long time. The will just is not there for the development of long term economical diesel for aircraft. Here in North America, we can't even get car owners to embrace it!

Pilot DAR

englishal
11th Oct 2009, 08:25
Diamond got the DA42 NG engines certified in pretty quick time though?

Most of them are Audi / Merc blocks and to be honest, sometimes I'd feel happier flying with an Audi engine up front with FADEC to protect it, liquid cooled than with a lycoming. The DA42 dipstick is the same as I have in my Audi A4.

The Avgas DA42 is a travesty, all that modern technology thrown out of the window with a dodgey throttle quadrant stuck in.....such a shame.

Still the NG should be a real go places plane. I was chatting with a DA42 owner who took his from the USA to Brazil and back, something that logistically would be pretty tough with an avgas powered aeroplane.

1800ed
11th Oct 2009, 08:59
GA is much bigger business in the USA. They don't seem to have much of a problem with Avgas there, so there isn't the pressure to spend the cash developing a new diesel engine.

bjornhall
11th Oct 2009, 09:02
One thing that concerns me is who is going to be around to support and maintain those modified Audi/Mercedes engines in 40, 30 or even just 20 years? Let alone build them?

With car manufacturers' product cycles being quite a few decades shorter than the life span of a GA aircraft, isn't it rather probable to end up with lots of perfectly good aircraft with no new engines available? Especially if, as I have understood, the current breed of diesel engines (and gearboxes, and clutches, etc) are actually replaced rather than overhauled at TBO (or well before...).

Another concern, which may or may not be founded, is that the fuel economy displayed by some diesel engined aircraft is in no small measure due to a less powerful engine. Take a clean design, put a 135 hp engine in it, and say "look at our cruise speed! The ancient 180 hp spam cans don't have a chance against our fantastic diesels! Buy one you too!". Sure, but that clean design isn't nearly as helpful in a low speed climb, making both takeoff and
landing performance suffer. Install a 160 hp diesel, and the fuel economy is nowhere near as good anymore. Keep the 135 hp and you can't operate out of many shorter grass fields.

Poor short-field performance in new aircraft is already a big problem IMHO; a C172S already has significantly worse landing performance than a C172N, and many people don't even know it... :sad: With even worse performance, we will either see more landing accidents or people will eventually wake up and have to move away from most grass strips. What many also do not realise is that near sea level, on grass, with less than maximum weight, landing performance is usually limiting, especially when adding the recommended (or mandatory, where I fly!) 1.43 safety factor. Hence they don't even bother checking landing performance, assuming takeoff is more limiting. Then they run off the far end on wet grass (somone just broke our Archer II that way). But that's another story...

Add to that reliability concerns that are not just teething troubles, but fundamentally due to the fact that it is necessarily a much more complex engine with many more things that can go wrong.

It's problematic. I hope they get the diesels right, sooner rather than later, but in the meantime I expect to stick with Lycomings and Continentals (or even Rotax... :oh:) for quite a while.


: Less power -> less ability to climb with full flaps -> flaps can not be as draggy -> flaps most likely less effective -> higher landing speed -> longer landing distance.

englishal
11th Oct 2009, 09:25
Although a 135HP turbo diesel will develop the same power at 10,000' more or less, so I'd be happy to take a Twin Star into an 8000' airfield but NOT a seneca 1.....

Modern FADEC aeroplanes with liquid cooled engines protect the engine from the pilot. Reading the Flyer article on the Mooney a while ago, descent planning was extremely important so as not to break the engine. Conversely in a DA42 if you have a problem, you slam the throttles shut, drop the gear and pitch 30 degrees nose down and you come whistling down....and the engine is fine.

Swings and roundabouts, but it is time to get away from old air cooled engines IMHO in the new gen slippy aeroplanes.

vee-tail-1
11th Oct 2009, 10:26
Anyone have an up-date on the Gemini diesel? It is based on the highly successful German WWII Junkers design. Power/weight seems similar to a petrol burner. See: www.ppdgemini.com (http://www.ppdgemini.com)

Stephen Furner
11th Oct 2009, 14:47
Very interesting to hear that there has been an attempt to migrate the Sabaru technology into light aircraft. I must admit this was the first thought that came to mind when I first heard about it.

At the first London Fly show I saw the Wilksch AIrmotive Jet A1 engine and heard Wilksch talk about the design and testing. As I recall the design team had even tried it out with red diesel since it might be have agricultural applications but were concerned about filter blockages from biological contaminants. To me the engine appeared to be ready for or very close to serial production.

My impression is that there are now proven technical designs for true aero engines – not just converted car blocks with their associated problems of gearbox, wear life, size, shape and weight - but they are not being taken forward into serial production by the major or even small specialist manufactures.

Is the absence of a good Jet A1 piston engine a market research problem rather than a technology barrier? The commercial case is not at the moment part of the public debate. I don’t see easy answers to even very basic question such as how many units a manufacture could expect to sell each year and what a reasonable retail price might be.

For the average owner if a replacement Jet A1 engine came in at the same price as an overhaul of an existing Continental or Lycoming petrol unit then I believe – assuming moving to Jet A1 did not raise ongoing maintenance or other costs of ownership – most people in Europe would swap out to a diesel unit.

Given the social benefits of moving from an engine fuel that contains lead there may an argument here to claim back some of the tax paid by the GA community to assist in the transition in infrastructure areas such as engineer training and conversion of LL100 pumps and storage over to Jet A1.

In the absence of a realistic understanding of the economics of a GA transition to Jet A1 as its primary fuel it is difficult to see how a manufacturing company could justify setting up a production line.

bjornhall
11th Oct 2009, 17:44
Given the social benefits of moving from an engine fuel that contains lead

There is already unleaded Avgas available in some parts of the world, suitable for most engines that run on 100LL.

Stephen Furner
11th Oct 2009, 20:38
There are also some interesting accounts of research into biomass based fuels that can replace LL100 and of course there is a production version of the Embraer Ipanema which runs on ethanol. Embraer EMB 202 Ipanema - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Embraer_EMB_202_Ipanema).

I have heard that in Sweden there is a group who have started a limited manufacture of the older version of avgas without the led additive. It is claimed that older engine designs still in use today were originally intended to run on this fuel and will operate better with it and suffer from less plug fowling and other problems.

Moving away from LL100 to Jet A1 reduces cost in the supply chain since Jet A1 benefits from a larger scale of production and lower tax than LL100. The use of Jet A1 for European GA isn’t only motivated by ecology but also by costs. These two issues come together for this particular fuel option. The belief is that it offeres a cleaner technology that operates at a lower cost than LL100.

Pilot DAR
11th Oct 2009, 22:07
Hmmm...

The Avgas DA42 is a travesty, all that modern technology thrown out of the window with a dodgey throttle quadrant stuck in.....such a shame.

How have you formed this opinion?

I hope the throttle quadrant is not truely "dodgey", as I am the person who made the finding of design compliance for the Canadian STC for the aircraft. I can say that the Diamond crew's design and execution of the DA42 L360 throttle quatrant is the best designed, highest quality, and most artful light aircraft quadrant I have ever flown.

The IO-360 engine installation is masterful. I have never flown better cowled engine installation, in terms of cooling. I was one the pilots who did the testing of it's characteristics, and I made the findings of design compliance for the STC. I have never flown a more shock cooling resistant installation. I was the pilot who slammed the throttles closed, and started down, watching the temps very carefully. Amazingly stable temps. I could not have been more pleased. I found design complance with a wide margin of satisfaction.

I'm not knocking the diesels. I flew the standard DA42, and loved it. I just would not want to pay the maintenance costs, or suffer the down time for the engine maintenance. The fact that I pilot must learn to properly operate the IO360's on a DA42 L360, is not a travesty, it is part of a pilot's responsibility to understand as many different aspects of aircraft operation as possible. I certainly learned a lot about the simplicity of the Thielert diesel in the standard DA42, as I had to check myself out in the aircraft when I flew it. It was even easier that the turbines I have flown. So I suppose that any plane the DA42 pilot will fly next (other than a sailplane) will require more engine managment skills!

The IO 360 STC for the DA42 was a much needed solution to an unfortunate situation, and Diamond is to be wholey commended for stepping up, making a big investment, and providing this solution for their DA42 customers. The result is a great twin, with very well understood engines, that any engine shop in the world can repair or overhaul, and with a huge spare parts base.

If there are DA42 L360 owners out there who are unhappy with that aircraft, as modified by the STC, I would be very interested in hearing the details of their unhappiness, so I can consider these aspects in my future certification work...

Pilot DAR