Death of the Diesel?

[Rod1]

The European finance ministers have asked the European Commission to look into raising a tax on aviation fuel (JetA1). Apparently the idea was brought up by the UK at a recent meeting of the G7!

If the tax came in it would remove the advantage in price and interest in JetA1 powered light aircraft will drop significantly. In the US there is very little interest as the price difference is not large.

Rod1

[High Wing Drifter]

But diesels are so much more efficient, so they still have a distinct advantage. The recent Diamond TwinStar non-stop crossing of the Atlantic provides some evidence to support this.

http://www.avweb.com/newswire/10_35a/briefs/187987-1.html

Anyway, I doubt jet fuel will be taxed to the same degree as 'lesuire' fuel. Also, to me, this was inevitible.

[A and C]

The tax for me is not such an issue it is the 30% increase in SFC and the fact that the turbocharging will keep 75% power up to and above FL100.

[ShyTorque]

Plus the advantages of no mixture control (just a "power" lever, which varies the amount of fuel injected) and no chance of carb ice. Not forgetting - no magnetos either.

Still the way forward. ;)

[IO540]

Does a diesel engine provide a lot more range per kg of fuel carried? I don't know, but it's a question worth asking. The fuel has a different SG, IIRC.

A 30% gain (if it is that) in range isn't worth paying the huge retrofit fee for, given that some SEPs can already do 10hrs endurance at best-range power. Neither would be a 30% gain in flow rate for a given IAS.

The DA42 making it across the Atlantic West to East doesn't in itself mean a lot because a) it is a very aero-efficient design; b) there is no petrol version to compare with; c) they must have had good tailwind :O

FADEC and turbos can be equally applied to a petrol engine.

I do think this will limit the diesel market to new aircraft; in effect it will kill it off because new aircraft sales are very low.

The real question is how the EU is going to get around their treaty obligations for tax free jet fuel.

I've heard it mentioned that some EU states provide tax free jet fuel only to AOC holders. That is an obvious anti-private flying discrimination measure which is likely to raise very little money for the foreseeable future, but it's one way.

[ShyTorque]

I agree about the retrofit dilemma, but today's old aircraft won't be around indefinitely. Certainly most of the ones I learned on have gone to the scrapheap......

However, the future of AVGAS as a viable fuel isn't certain either. As it is seen as environmentally bad, it may be phased out altogether or made even more expensive. Even today, not every airport stocks it and then the range problem has another significant factor in the equation - a pilot may have to go well off a straight line track to find his next tankful.

Less than twenty years ago people said that diesel powered cars would never catch on in any great numbers - but look what's happened.

I'll guess that AVGAS has another twenty years at most. :8

[Skylark4]

Shy Torque is right.
Avgas is rare in Africa aparrently.
Had a talk at the Oxford PFA a year ago about avgas, very interesting. One point made was that there is only one manufacturer of Tetra-Ethyl-Lead in Europe.
In my opinion diesels are better for several reasons. Fuel is safer, engines are more efficient, engines are more reliable( no ignition and no carb ) and the normal diesel power curve fits a propellor application superbly.

Mike W

[Circuit Basher]

Having been involved with a group where we looked at a diesel aircraft last year, I was quite surprised to learn that the Thielert diesel was on a total replacement periodicity of 1000 hrs. I just checked the Centurion Thielert web site and I could find no easy reference to this and there was just a Maintenance Data Sheet (http://www.centurion-engines.com/pdf/datasheet_maint.pdf) showing a 1000 hr inspection.

On another part of their Web Site (http://www.tae-service.de/doc-download/manuals/TMTAE1250001Rev1LifeTime.pdf), it states 'The entire aircraft engine TAE 125-01 has a proved lifetime of 1000 flight hours or 12 years whichever occurs first. For safety reasons it is strongly recommended to replace the entire aircraft engine after 1000 flight hours or after 12 years whichever occurs first.'

I don't know the current CAA certification status, as I know Thielert were working to increase the TBR to 2000 hrs. The replacement is pretty well everything forward f the firewall (including wiring looms, ancillaries, etc).

[Mike Cross]

As far as I am aware diesel engines have a lesser power-weight ration than gasoline engines.

Turbo and injection can equally be applied to gasoline engines.

Gasoline engines have a long proven record as light aircraft power-plants.

The reason for developing diesel as a light aircraft power plant appears to be to take advantage of tax breaks on fuel - not a good safety reason.

Mike

[Say again s l o w l y]

I would always rather have a diesel or turbine engine in an a/c rather than a rotten old piece of 30's technology.

Mike just to make a point, in the event of an accident where a fuel line or tank is ruptured, which is more likely to combust, Dielsel or petrol? In an accident, I'd rather have pools of diesel than petrol any day of the week (not that I would like to see either of course!)

So as safety goes, there is a case for a diesel engine.

Petrol engines have got a long record for powering light a/c, but that is more down to the fact that there has been no alternative rather than their inherent suitability for the task.

If Lycoming or Continental had put some effort into developing their ancient products, then we might have some competition between the Diesels and petrol engines. As it is, eventually Avgas will be wiped away due to it's cost, current environmental impact and the reducing availability of the stuff.

It is inevitable that Diesels/Avtur powered engines will overtake their Avgas rivals, it is just a matter of time.

[ShyTorque]

All the arguments against diesel engines also applied to the increasing number of road vehicles so powered...... but the case FOR diesels is becoming overwhelming.

In my youth, diesels were noisy, smelly, sluggish things that were only fit for lorries and railway locomotives. However, once the road-going diesel engine was given more research and development, because the market had accepted it as a concept, the output and sophistication increased markedly. There is absolutely no doubt that the type has become very widely accepted, even though in UK the road fuel is actually MORE expensive than petrol.

A diesel can run on a wide range of fuels, all of them cheaper to produce than petrol. A spark ignition / petrol engine needs a very specialised fuel quality to make it work, especially in the relatively large cylinders required for aero engines. Without such a high octane fuel, the power output has to be reduced. If the use of tetra-ethyl lead is completely banned (there is speculation that it might be), it would quickly signal the end of the line for the petrol aviation engine as we know it because there is no viable replacement suitable for aero engines.

Having read the preceding posts, one thing that perhaps needs clarification - modern aero diesels run on Jet-A1, NOT the diesel fuel (DERV) used by road-going vehicles. This means that the fuel is already very widely available at aviation oulets.

I speak as a self-declared petrol head, definitely one who doesn't enjoy driving diesel cars. However, if I was in a position to choose a brand new light aircraft, it would definitely have a diesel powerplant.

[Rod1]

“end of the line for the petrol aviation engine as we know it because there is no viable replacement suitable for aero engines”

I think Rotax, the largest European aero engine manufacturer, would disagree with you! Their 4 stroke specific aircraft designed engines are based around Mogas, which is the obvious alternative to Avgas for most of GA. Almost non of the small airfields I visit have JetA1, but some have mogas by PPR. A modern Rotax engine has most of the advantages of a Diesel, but with much less weight. Weight is a problem in a car, but it is a huge problem in an aircraft. It is only in comparison with 1930’s engines that modern diesels can compete on weight, a modern mogas engine like a Rotax will win every time unless there is a big difference in the cost of the fuel.

Rod1

[ShyTorque]

I know the sound argument for small engines like the Rotax but MOGAS is not such a viable proposition for higher performance aircraft that operate at altitude, nor allowed for commercial operations or in twins.

There are obviously other known safety concerns with the use of MOGAS, such as an increased likelihood of carb icing and fuel vapour lock at high ambient temperature.

[Say again s l o w l y]

Mogas isn't a viable solution to the problem. Look at the extreme reluctance of the regulators to it's use.

A diesel or to be more correct a compression ignition engine will always be at a disadvantage when the argument is purely about power to weight ratios, but how about a power to torque ratio, that is probably more important.

One argument is, that due to the increased efficiency of a Diesel is that you can reduce the amount of fuel you have to carry for a certain sector, therefore the difference in TOW between an Avgas or Avtur powered a/c would be reduced.

To me, reliability is still the most important issue in aviation and lets face it, a Diesel is inherently a more reliable powerplant than any petrol engine.

Bring 'em on I say.

[IO540]

Shy torque

today's old aircraft won't be around indefinitely

I really really wish you were right. I wish that the whole of the present-day c. 1970 fleet was scrapped and made way for modern designs, composite, aerodynamically efficient and with modern navigation kit. GA could then move forward into the 20th century (let's not be too ambitious :O )

But the money to replace it just isn't there. The desire to do so isn't there either, because GA is packed with people who see nothing wrong with these old heaps.

There is a virtually limitless supply of old Cessna/Piper heaps in the USA; plenty to keep Europe going for decades.

There is no indication that new aircraft sales will take off anytime soon. This means the diesel market is going to remain mostly retrofit, and the figures for that don't add up unless one is doing hundreds of hours a year.

If the tax break was taken away, the figures would not add up in any GA situation I can imagine, which is why there is next to zero interest in diesels in the USA.

Avgas will go away eventually but it's going to create a huge upheaval when it does. It will be like mandatory Mode S transponders but 20 times worse, and that's assuming that a usefully reliable diesel has been developed by then. Nobody has done it yet, certainly not Thielert. I hope somebody does it before it's too late.


SAS

how about a power to torque ratio

I think that's a misconception. Power = torque x RPM.

You can get an engine to deliver lots of torque at a low RPM but it will be big, with big cylinders. It won't be able to rev high because the big heavy parts won't have the strength. So you end up with a Lycoming-type engine. A diesel doesn't in itself deliver higher torque than a petrol engine.

[Flyboy-F33]

Say again slowly

Your argument about being able to carry less fuel due to diesels being more efficient doesnt stack up. You are not taking account of the fact that Avtur is 12% heavier than Avgas.

Apart from that....I look forward to the day when a 300HP Diesel is available

[Say again s l o w l y]

So basically IO you are saying that power is a made up figure from torque and engine speed!

Torque is basicall turning force, what is an engine trying to do? Turn a prop. To my eyes is it just as if not more relevant than power.

O.K so Avtur is 12% heavier, how much more efficient are Diesels than Petrol engines? If it is more than 12 % then the argument is valid, if minor. Though it is a point worth noting.

Actually, I think I meant to type a weight to torque ratio rather than a torque to power ratio!

[High Wing Drifter]

A diesel doesn't in itself deliver higher torque than a petrol engine.
I believe that diesels tend to produce a flat(er) torque curve than petrol engines. If this is the case, then the 'power' is in a more useful location in the rev range. By that I mean that more torque is possibly being generated at 50% power than the equivelent petrol engine would of the same max HP. This in turn means that diesel engines can be of a lower capacity, which in turn means that they probably drink less for the same effective force produced.

Does that sound right?

[revilo_rehsif]

The European union are also looking to triple the tax on Red diesel for motorboats. when will tony Blair take charge of his own country and stop being bossed around by others.:* :*

[TD&H]

Torque:

The 2 litre diesel engine in my car produces 50% more torque at significantly lower revs than the 2 litre petrol engine.

D=330 nm at 2000 rpm versus P=210nm at 3500rpm.

So you don't need a larger diesel than petrol to produce torque which is the most important element of driving a propeller.

[ShyTorque]

Diesels give better torque at lower RPM because of the benefit of the much higher compression ratio and higher volumetric efficiency. Put a turbo or supercharger on a diesel and you can have as much torque as the engine will stand, at propellor friendly speeds and not lose the economy. It isn't necessary to use a prop reduction gear assembly, unlike with some bigger piston engines, which somewhat offsets the higher weight of the unit.

Not forgetting that one day they will be filling the fuel tanks with renewable bio/vegetable oil.

[Algirdas]

I think I'm right in saying that diesel engines do use less kg of fuel per hour for a given output - but they also do weigh more.
If you call the weight of the engine (EW) + fuel weight (FW), and use the prefix D for diesel and P for petrol, then for a short trip, (DEW+DFW)>(PEW+PFW), and for a long trip (DEW+DFW)<(PWE+PFW).
The breakeven journey time obviously varies with the plane/engine combo.
So perhaps it's more a question of what type of flying do you do which determines the best choice for you....
As for reliability, the Rotax 912 and variants are supremely reliable - and with the huge numbers in use out there, the development curve is solid. As of today, diesels are in far less common usage, and no doubt they do theoretically have the potential to be more reliable, but I'm not aware of any data that proves that today's available engines actually are - they may be less reliable.

[IO540]

SAS

So basically IO you are saying that power is a made up figure from torque and engine speed!

YES.

But power is not some artificial concept, no more than "10" is a "made up figure" by multiplying "2" and "5" :O

Power = torque x RPM

Also, power directly equals thrust. A prop which absorbs X HP (at a reasonable blade AOA) will deliver Y newtons of thrust. I can't recall the multiplier but assuming say 85% prop eff. it is just a number.

Also, fuel flow equals power. Again, a straight formula, X GPH gives you Y HP - assuming stochiometric combustion.

IF you have the option of a gearbox (so no need to compromise the engine design because the prop tips mustn't get anywhere near mach1) and IF you have a VP prop (so the engine can run at a narrow RPM range for both takeoff and cruise) then any old engine delivering X HP will do the same job. Torque doesn't come into it.

The Lycos are designed (compromised, but everything is a compromise) to avoid a gearbox, so they run at a low rpm. Obviously an engine rated at 250hp at 2500rpm needs to deliver double the torque of another 250hp engine that does it at 5000rpm. The problem with the latter is that a 5000rpm prop is a problem (efficiency and extreme noise, and would have to be of a small diameter to remain subsonic).

Turboprops have a gearbox because a turbine cannot possibly be compromised enough to rev low enough.

If an engineer came into this from scratch, he may choose a 5000rpm engine (petrol or diesel) because such an engine is going to be a lot smaller than a 2500rpm engine of the same HP - even though the gearbox will weigh a lot, and won't be reliable unless it is expensively robustly engineered (which isn't going to happen).

Or he might choose to copy a Lyco (avoiding a gearbox) but design it better, with better heat transfer and FADEC. It could be a diesel too, although that doesn't change the basics (except diesels hammer the gearbox more).

If you start with a car engine (Thielert) you won't get any useful power out of it at 2500rpm, so you are stuck with a gearbox.

I am no engine designer but did loads of this at college+univ, and I would bet that the best GA engine would be something big and slow, burning jet fuel, without a gearbox, with electronic ignition+management, and air cooled.

Air cooled, because unless one does spacecraft-quality plumbing (which won't happen) it will leak and if it leaks you have an near-immediate engine failure.

Advanced materials could be used because the budget is huge - a new IO540 for example is about 25 grand. The cost of materials doesn't even feature on the costing.

I am sure this has been discussed here before.

[High Wing Drifter]

I think I'm right in saying that diesel engines do use less kg of fuel per hour for a given output - but they also do weigh more
Does anybody know how much a modern diesel weighs compared to an equivelent ancient Lycoming lump?

Air cooled, because unless one does spacecraft-quality plumbing (which won't happen) it will leak and if it leaks you have an near-immediate engine failure.
Good point. However, the diesel engines in question are liquid cooled; I guess because of the car origins.

Look interesting: http://www.centurion-engines.com/c40/c40_start.htm

[Mike Cross]

The tax regime is inherited from marine bunkering. Unless every state imposes the same tax you just get fuel tankered around from where it is cheapest.

What HMG would no doubt love to do is tax fuel for domestic use while keeping it tax free for international use.

We already have the daft situation where the export of your spending power to your holiday home in Spain is subsidised with tax-free fuel whereas the trip to your holiday home in the UK by car is heavily taxed.

Mike

[Say again s l o w l y]

This brings in all the problems associated with reciprocating engines. None of them are particularily efficient, but a Diesel is a lot better in this respect than a petrol lump.

I normally sit (Just) infront of a couple of fairly large turboprops (PT6's) and unless the things are knackered (which most of them are!) we are usually limited by the amount of torque the gearbox can handle, rather than other limits such as ITT. This says to me that having a vastly complex and expensive piece of kit like a gearbox stuck on the front of a dainty and highly efficient engine is a total pain, so a nice slow revving but torqey engine would be ideal.

"Modern" avgas engines are still totally in the dark ages when it comes to efficiency, their HP/litre figures are utterly laughable for example a new yamaha R1 produces nigh on 160 HP at the back wheel from a one litre engine, now look at an O-360 of similar output. It probably weighs in at the same as the whole bike and the R1 is liquid cooled.

Now obviously these are totally different beasts designed to completely differing briefs, but it shows what can be done with a petrol engine, but you have to rev the damn thing to almost 14,000 RPM to get the power from it. So again we want a nice slow revving diesel producing big dollops of torque from as low an RPM as possible.

All engines produce heat as a by product and unless the engine is as efficient as a turbine, then aircooling isn't really a satisfactory way of controlling temperature. Modern engines are much more dependant on controlling the temperatures better (ally blocks and heads tend to warp a bit more than old stuff made out of pig iron) so water or some form of liquid cooling is vital. Is it heavier? Yes and no. You can run an engine harder with water cooling since you can control temps better, so you can get away with more. Mind you how many Diesels are made of Ally? Not many if any at all.

There is nothing mythical about the plumbing needed for a water cooled system. How often do you get problems with your car unless it is donkey's years old?

Aircooled engines are dinosaurs and about the only place you'll find them being used with any regularity is in aero engines and lawn mowers. In fact my lawn mower even has electronic ignition and oil cooling so my Briggs and Stratton is more advanced than most Lyco's!

I still think that the best light engine is a small turbine with a gearbox, with enough of them sold to let the economies of scale bring the price down. It just needs a leap in production processes and the price of unobtainium to drop.

[Keef]

It's a long time since I was involved in engine design, and diesels have come a long way in the past few years.

My present 2L diesel car engine produces over twice the torque of the previous V6 petrol, and about 75% of the BHP. It weighs almost exactly the same.

Max RPM is much lower - which is ideal for aero use. It achieves 42mpg average where the V6 did around 27 mpg - both the way I drive them.

Diesels also produce far less "waste" heat than petrol, so I don't see why a purpose-designed diesel for aero use couldn't be air-cooled.

The problem is that the sales volume would never justify the R&D it would take - I know what it cost to develop one all-new car diesel. It would scare you.

[IO540]

SAS

I think you will find that your PT6 uses considerably more fuel (kg, litres, whichever) per HP than an old Lyco. Small turbines are powerful for their weight but like your 14000 rpm Yamaha they are not fuel efficient.

This is why when people do piston-turbine conversions they find their range has dropped about 1/3.

One can reduce the difference by flying at 25k+ feet but even there a turbocharged piston would deliver more HP per fuel flow than a PT6.

But turbines are great. A single turbine is several times less likely to have to land due to engine failure than a piston twin.

If I had loads of money (a million or so spare) I would buy a single unpressurised turboprop. It would do everything my present SEP does, go a bit faster, use less takeoff distance.

It would drink a lot more fuel per mile but the fuel is (presently!) tax free which more than compensates, and it is available throughout the world.

However when one looks at the very expensive maintenance (HSIs etc), of turbines one probably spends one's fuel cost savings entirely on the turbine maintenance.

Nobody has yet found a way of making a turbine at a low enough price for GA piston replacement. The money isn't there in GA and even if there was, most people would not pay the premium for the reliability. Those that will pay it, can have it already: your King Air, TBM700, various small turboprops, etc

[bar shaker]

IO

Being pedantic, Power=torque x rpm/5250

Take a look at any graph showing both power and torque, you will see that they always cross at 5250 rpm.

Think of a gearbox as a torque multiplier. The R1 has a top gear equivalent to 2nd gear in most cars. If our cars could rev to 14,000rpm, they would be lively too. An F1 car produces very little torque, but revs to 18,000 and also a 6th/7th gear equivalent to 2nd in a Mondeo.

The requirement for a prop to turn slowly makes diesels ideal for a/c. Vibration is the only real problem.

[ThePirateKing]

So why not get rid of reciprocation and go rotary? (After all, it works for Mazda!)

TPK:ok:

[deice]

Mmmm, yes, except they want lots of fuel. The main problem with rotarys seems to be that fact and the problem of keeping them sealed properly over time (the rotor that is).

Comparing "diesel" (i.e. the Thielert) to the Rotax 912 is not apples to apples. The Rotax only puts out 100hp and as such is comparable to a Lycoming O-200 which incidentally has almost the same FF for the same power... (That's just plain thermodynamics I guess) So much for evolution... Benefits are lower wieght (?) and liquid cooling among other modern design techniques which should have been applied to all our ancient material ages ago.

What's really interesting is the amount of thrust from a certain power/prop combo. The Thielert can replace the Lyc320 of a PA28 or C172 and produce the same or better thrust (certainly at altitude due to Turbo) and also at the same weight. But, it adds lower FF, single lever power, optimized thrust throuh VP-prop etc. It is nothing short of a revolution.

Could the same have been done with a Avgas engine? Most certainly. And it will come. The question is if there will be fuel for it?
Personally I'd love the new Thielert V8 in our Commander 114, if not for power just for the sound! At 310 hp and Turbo it would make it go like stink! :ok:

[Say again s l o w l y]

Deice has brought up a good point. Modern engines aren't really better at converting fuel to power, they just lose less of it along the way.

Small turbines in GA is a pipe dream, but you never know, one day we may be able to get the costs down far enough. Long way off though.

At our high speed cruise of 190 kts we work on a figure of 18L per minute, giving a flow of 1080L per Hour. This is in an aircraft with a MTOW of 12 tonnes, we have around 3000HP so get a figure of 2.77L per hour per HP. Now divide this by 12 gives you 0.23L per Hour per HP per tonne.

A bit gash, but what do you expect here!!

[IO540]

Back to college :O

Power = torque * revs

If one chooses the correct units then there is no other multiplier.

Most people measure power in HP but often it is in kW.

Most people measure rotational speed of engines in RPM. One could use radians per second, too.

As for torque, NM, lb-ft, various other things.

All these different units require different fudge factors, but nothing changes the fact that power=torque*rotational speed. A gearbox just trades torque for revs.

Too many comparisons here aren't applicable. Motorcycle engines are terribly inefficient - all those tiny pistons banging away at 14000rpm. I've done my time on 2 wheels, too. Most of today's "superbikes" average about 25-30mpg, which is appalling given the low weight.

Most car engines spend most of their time developing very little power - if they spent most of their time at say 65% of max rated power (that's about 120mph for a car which can do 140mph) I am sure the reliability profile would be very different.

Even stationary engines like generator sets don't normally do 65% power continuously.

I've had several "engine failures" on cars due to coolant loss; even one on a Toyota. The plumbing on an aircraft engine would have to be very good indeed for this failure mechanism to not be the prime feature in forced landing statistics. It can be done because it's already done with oil, but oil is noncorrosive and the flow rate is a lot less that it is on a water-cooled engine.

As for fuel efficiency, I haven't seen any figures yet suggesting that an old Lyco is any less efficient (in cruise) than any other Avgas engine, no matter how recent and no matter what electronic controls it has. One is indeed stuck with thermodynamics....

[Rod1]

“The plumbing on an aircraft engine would have to be very good indeed for this failure mechanism to not be the prime feature in forced landing statistics.”

The 912 range is water cooled and has the best reliability of any engine in its class. It has other modern advantages like solid-state ignition etc. coolant problems are very low on the problem list most have been related to bad coolant mix, rather than pipe failure. Trust me, if I can install one it can not be that hard! Rotax are also working on a range of large hp engines, which will also run on mogas.

Rod1

[Say again s l o w l y]

I still can't understand the reticence about water cooled engines. For a start it would remove a huge number of problems such as cylinder cracking due to shock cooling. How many engines a year are killed by that little issue?

With the levels of maintenance that is carried out on your average GA machine, how much of a problem would it be to keep a water system operational?

With regard to the fuel consumption of a superbike, when on a track and caning the life out of it, you will struggle to see 30 MPG, but then again you are using full throttle for much of a lap with lots of accelerating and braking thrown in again using massive amounts of fuel. (some might say unnecessarily!) Take the same bike on to the motorway and cruise at 70-90 mph and I personally get nearer to 55-60 mpg with no problems. Whilst a bike may not be very heavy, they are not exactly aerodynamic, especially with a lump like me on the back!

Bike engines are amongst the most efficient petrol engines on sale today, but again they are designed for a totally different use than a horrible great Lycoming. You put a lot less fuel in and go almost, if not faster than most light a/c!! Not very good at aero's though!

[FlyingForFun]

Re. the Rotax as a reliable water-cooled engine:

I can't speak for other variants, but certainly the 914 in my aircraft is still partly air-cooled - specifically, the heads are air-cooled while the cylinder walls are water-cooled. In the event of a coolant leak, the engine will still run for a finite amount of time - can't remember exactly how long it says in the manual, but it's long enough to get to an airfield unless you're somewhere pretty remote.

FFF
-------------

[bar shaker]

IO

You are quite right and I only mentioned it as I thought you said:
Power = torque x RPM

;) ;)

I did qualify by mentioning my pedantic mood.

I also agree with your points regarding outputs, although modern ECUs can achieve an economy that we cannot achieve with the same safety margin.

A modern ECU will be adjusting for optimum lean thousands of times a second, dependant on all factors (temps, fuel quality, air density ec). We can get it about right, but either we aren't as close as we could be or we are into the danger zone of predetonation.

The modern diesel engine is the perfect example of this. Diesels ten years ago were awful. Now they are the engine of choice, in everything except racing. Its the engine management that has dramatically changed, not the mechanical parts.

[ETOPS773]

I have heard that a company based in cambridge has a small,GA orientated turboprop running.Its based on a 100 BHP turboshaft (think it was called a HF100) and I believe it will be flight tested on a Piper Cub sometime soon.

Designer called Phil Heward-will try and get a link for more details but it sounds promising.

[bookworm]

If the tax came in it would remove the advantage in price and interest in JetA1 powered light aircraft will drop significantly. In the US there is very little interest as the price difference is not large.

AvGas at Cambridge is (was late last year) £1.04/litre, of which £0.28 is duty. That leaves about £0.76 as the base cost of AvGas. That compares with £0.49 for Jet-A1. At larger airports, I imagine the difference would be much greater.

The European market for AvGas is so much smaller than for Jet-A1 that the price can be hiked mercilessly, with little effect on sales volume. (Indeed a few years ago, before the suppliers apparently cottoned on to this, AvGas was cheaper than MoGas with duty included -- just a little more as a base cost.)

Even if a tax on Jet-A1 were introduced, it seems unlikely that it would be anything like the 28p/litre on AvGas.

[100LL]

FlyingForFun think you got that the wrong way round, The heads are watercooled and the cylinders are air cooled. The Rotax 912/914 is a very reliable engine if maintained correctly for some strange reason there are people out there who still cant read the maintenance manual.

As for the Centurion, yes the TBR (time between replacement) still stands at 1000 hours but the manufacturer says that the life time should go up to 2400Hrs. See Here (http://www.centurion-engines.com/sales/sales_prorata.htm).

[GTOTO]

Interesting discussion on Aero Diesels with lots of points covered and many miss conceptions.

As a recap there are about 8 Diesels in development with 3 on the market.

Thierlert
4 stroke, 4 cylinder modified car engines, liquid cooled, reduction gear box and harmonic damper.
135hp. Fast to market design. V8 300hp plus to come.

SMA, 4 stroke, 4 cylinder, new design, air cooled, high cooling drag,
low power to weight ratio. Due to high strength require to hold it together
because of the large power pulses and reverse torque from the prop.
Not really a sensible design from an engineer point of view. 235 hp

Wilksch, 2 stroke, new design, liquid cooled, novel ball joint little end in the piston,
through flow, air flow design, with poppet exhaust valves,
Inverted inline design. 3 cylinder is 120 hp. 4 cyl 160hp. 5 cyl 200hp.

Delta Hawk, V 4 2 stroke, piston ported intake and exhaust. Liquid cooled with 60% limp home mode on coolant lose.
160 and 200 hp models. Due on the market in 2005.
This engine is probably the most significant engine as it competes head on with an IO360
is a US design and cost less than the Lycoming.
It weight almost the same as an IO360, goes 25% further on similar fuel loads, full power to 14,000ft.
An SR20 with the 200hp version would be the plane for the 21st century. £10 an hour for fuel with no tax. 1000nm range

Diesel Air, 2 stroke, opposed piston, 100 hp. Flying in airships. Good power to weight ratio.
Compact design with twin crank shafts. Liquid cooled.
They have a big order for UAV aircraft engines.

Zoche, 2 stroke, piston ported, radial, air cooled engine, with no electrics needed for starting and operation,
The 8 cylinder 300hp unit runs like an electric motor, perfectly balanced with very smooth power delivery, low frontal area.
Probably the best design of the lot, only trouble it seems to be in perpetual development.

Basically the best Diesels are 2 strokes, there are lots of advantages, both in smoother power delivery, cooling,
higher power output for the capacity and lower harmonics. All the 2 strokes have a combined turbo/supercharger unit
and standard plain bearing bottom ends. Not to be confused with 2 stroke lawn mower engines.
They can go from idle to full power in 1 second as well.

Note the most powerful fuel efficient engines in the world, are Marine 2 stroke diesels, about 100,000 hp.

[Rod1]

"Forget diesels, say goodbye to those 1950's avgas burners, the future has one moving part:"

http://www.innodyn.com/aviation/products.html

Aquired from another place.

Rod1

[deice]

I can't believe I've missed this. It sounds almost too good to be true, but why not, it's 2005 after all. If they can live up to the low maintenance claims together with the high TBO and low price (it's dirt cheap for a turbine!) this could well be the next technical leap in aviation development.

Hope we get there before I sprout my own wings.

[FlyingForFun]

FlyingForFun think you got that the wrong way roundOops - but it doesn't really alter the point.....

FFF
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[E1453]

I would love to believe that mogas can be the future, but it can´t.
For a reason: the mogas varies from country to country.

GA would still depends on a specific fuel, a special mogas.

For example: here in Brazil the Rotax engines cannot use mogas, because it contains 25% of ethanol. We would need a special no-ethanol gasoline. I know it also happens in other places.

The only worldwide stardarized fuel is QAV, so it's the way to follow.

As there are just a few engine supliers, and it would be impossible to build a spefic version for each marketplace or resptrict an aircraft to a specific region, I can't see the future with a fuel that is not worldwide stardarized.