Jet A1 - a strange world come to think of it
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Jet A1 - a strange world come to think of it
For a change Europe has taken an innovative initiative. Diesel engines are more fuel efficient, are quieter, and are likely to last longer. Presumably all good for the environment.
Undoubtedly the lower price of diesel has encouraged their development.
Moreover, they are manufactured in Europe, rather than in America, and therefore both create jobs at "home" and avoid the need to ship units half way around the world.
What a success story for the United States of Europe .. .. ..
.. .. .. until we manage to spoil it by hiking up the price of diesel.
Strange world really. If I were Diamond I wouldn’t be voting for my "local EMP" that’s for sure.
Undoubtedly the lower price of diesel has encouraged their development.
Moreover, they are manufactured in Europe, rather than in America, and therefore both create jobs at "home" and avoid the need to ship units half way around the world.
What a success story for the United States of Europe .. .. ..
.. .. .. until we manage to spoil it by hiking up the price of diesel.
Strange world really. If I were Diamond I wouldn’t be voting for my "local EMP" that’s for sure.
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With regard to relative running costs, I believe it is principally on fuel price difference. AVGAS of any Number, ULGAS and commercial DIESO (DERV) have Duty and Tax loaded on them but AVTUR and agricultural DIESO doesn't. Of course they will wait until we've spent all the effort and money on replacing light petrol donks with heavier diesel ones before they review the tax alignments. You've all noticed how the duty on DERV is magically higher than it is on Petrol?
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Fuel consumption is typically 40% lower on the diesels than the equivalent Avgas Lycoming - so there is still a saving to be had.
Thielert Centurion equipped PA28s also have a 100 hour check, not 50 hour, so there is also a maintenance saving.
Thielert Centurion equipped PA28s also have a 100 hour check, not 50 hour, so there is also a maintenance saving.
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Not sure it is 40% by the time you allow for the much lower HP.
Somebody with a brain and decent training could fly any old PA28 and get a 30% fuel saving off the fuel flow which a typical PPL will be getting, just by correct leaning. And by doing a lot more stuff like gentle cruise climbs rather than doing all climbs full-bore one could save more.
There is still an "MPG" saving with a diesel but it's nothing like 40%, AFAIK.
Most of the case for diesels is currently from the tax difference.
How come there are no more 50hr checks on the airframe?
Somebody with a brain and decent training could fly any old PA28 and get a 30% fuel saving off the fuel flow which a typical PPL will be getting, just by correct leaning. And by doing a lot more stuff like gentle cruise climbs rather than doing all climbs full-bore one could save more.
There is still an "MPG" saving with a diesel but it's nothing like 40%, AFAIK.
Most of the case for diesels is currently from the tax difference.
How come there are no more 50hr checks on the airframe?
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According to the published figures, the Thielert's fuel flow in a Piper Warrior is just a little more than half of the fuel flow of a Lyc 0-320 and it produces 20% more thrust. That is impressive.
Presumably part of the reason is the amount of fuel used by Avgas engines for cooling. Diesels are water cooled.
There are other advantages. Whilst not proven, the engines are expected to last longer. They are on the whole full FADEC, so the waste of fuel that occurs through incorrect operation of Avgas engines does not occur. In the real world, whilst pilot should be trained to lean engines properly, they are not, and even if they were, most of the fleet does not have any engine monitoring kit fitted. Incorrect leaning can cause more problems in the long run than no leaning at all, including to your wallet! There is of course no added lead in the fuel. I believe there is less pollution associated with the production of Jet A1.
These all seem to be factors that contribute to the use of diesel in aviation making a significant contribution to reducing the impact on the environment of GA.
Presumably all a mystery to the government and its advisors in the pursuit of raising more taxes.
Presumably part of the reason is the amount of fuel used by Avgas engines for cooling. Diesels are water cooled.
There are other advantages. Whilst not proven, the engines are expected to last longer. They are on the whole full FADEC, so the waste of fuel that occurs through incorrect operation of Avgas engines does not occur. In the real world, whilst pilot should be trained to lean engines properly, they are not, and even if they were, most of the fleet does not have any engine monitoring kit fitted. Incorrect leaning can cause more problems in the long run than no leaning at all, including to your wallet! There is of course no added lead in the fuel. I believe there is less pollution associated with the production of Jet A1.
These all seem to be factors that contribute to the use of diesel in aviation making a significant contribution to reducing the impact on the environment of GA.
Presumably all a mystery to the government and its advisors in the pursuit of raising more taxes.
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There's also a reduction to the risk of fire to consider.
OTOH, diesel is denser than petrol. Not sure about avtur, but I'd imagine that is the same - they both come from the same fraction.
Edit: Actually, diesel oil is a slightly heavier fraction than kerosene, if anyone is interested, see here.
OTOH, diesel is denser than petrol. Not sure about avtur, but I'd imagine that is the same - they both come from the same fraction.
Edit: Actually, diesel oil is a slightly heavier fraction than kerosene, if anyone is interested, see here.
Last edited by Son of the Bottle; 31st Jan 2007 at 20:07.
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Fuji
the Thielert's fuel flow in a Piper Warrior is just a little more than half of the fuel flow of a Lyc 0-320 and it produces 20% more thrust. That is impressive
On the basis that thrust = horsepower, I am certain the above is a thermodynamic impossibility. There is no way to get ~ 2.2x more HP from the same volume flow rate of diesel than avgas.
I have too seen the "more thrust" claims but they can't be right. Prop efficiency doesn't vary that much (assuming VP of course) and one thus cannot get away from the direct relationship between thrust and HP. People also say diesels produce more "torque", but that's equally meaningless; all that matters is the HP.
The old Lycos are thermally poor designs (thin metal sections, etc) to save weight in every department and for simplicity, but once leaned to peak or LOP in cruise they are converting the chemical energy in the fuel just as well as anything else burning the same fuel.
The diesels are all turbocharged which means that even if starting with 2/3 of the HP of the avgas machine, the diesel starts to win at about 8000ft+ (very roughly) which is how they get the great figures for range. If you put say a 150HP turbocharged engine in a TB20, and took it up to FL150, it would undoubtedly have more range than the standard TB20. But the low level performance would be lousy - just like a DA40Tdi.
It's hard enough to compare figures for two common avgas planes, e.g. a TB20 and a SR22. Most of the published data is either incomplete or deliberately misleading. Comparing the efficiency of an avgas machine with say a DA40Tdi is harder still because so many variables are not specified.
the Thielert's fuel flow in a Piper Warrior is just a little more than half of the fuel flow of a Lyc 0-320 and it produces 20% more thrust. That is impressive
On the basis that thrust = horsepower, I am certain the above is a thermodynamic impossibility. There is no way to get ~ 2.2x more HP from the same volume flow rate of diesel than avgas.
I have too seen the "more thrust" claims but they can't be right. Prop efficiency doesn't vary that much (assuming VP of course) and one thus cannot get away from the direct relationship between thrust and HP. People also say diesels produce more "torque", but that's equally meaningless; all that matters is the HP.
The old Lycos are thermally poor designs (thin metal sections, etc) to save weight in every department and for simplicity, but once leaned to peak or LOP in cruise they are converting the chemical energy in the fuel just as well as anything else burning the same fuel.
The diesels are all turbocharged which means that even if starting with 2/3 of the HP of the avgas machine, the diesel starts to win at about 8000ft+ (very roughly) which is how they get the great figures for range. If you put say a 150HP turbocharged engine in a TB20, and took it up to FL150, it would undoubtedly have more range than the standard TB20. But the low level performance would be lousy - just like a DA40Tdi.
It's hard enough to compare figures for two common avgas planes, e.g. a TB20 and a SR22. Most of the published data is either incomplete or deliberately misleading. Comparing the efficiency of an avgas machine with say a DA40Tdi is harder still because so many variables are not specified.
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The deisel conversion burns just under 5 US gals p/h compared to just over 8 US gal p/h for the standard avgas at the same IAS. I make that around 40% less fuel flow. The basic empty weight goes up by around 150 lbs and of course Jet A1 is heavier (has greater mass) than Avgas but you need less of it to get the same distance so loading isnt a great deal different. They are however a little under powered at MSL so wouldnt like to try a short grass strip at MAUW but once above 2000ft or so the performance is a little better due to being turbo.
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Mmmmmm.......
Why not look at what's best for the job?
Petrol engines have a better power-weight ratio and have been proven over many years. The R101 which crashed at Beauvais in 1930 killing the Secretary of State for Air and the Director of Civil Aviation was an early example of the use of diesels.
Let me put it this way:-
We take an engine that was never designed to run on Jet Fuel and that has an inferior power-weight ratio to what is currently in use.
We take a fuel that was never designed for use in reciprocating engines.
We modify the engine to cope with the fuel. We don't modify the fuel at all.
Why do we do this?
Because it will make a more capable or safer aviation powerplant?
Or simply because the Tax Regime means Jet Fuel is cheaper?
I have difficulty in reconciling the idea that engineering gymnastics for the purpose of Tax Avoidance is a major advance in safety or efficiency.
One could argue that removing the cost differential contributes to safety.
Mike
Why not look at what's best for the job?
Petrol engines have a better power-weight ratio and have been proven over many years. The R101 which crashed at Beauvais in 1930 killing the Secretary of State for Air and the Director of Civil Aviation was an early example of the use of diesels.
Let me put it this way:-
We take an engine that was never designed to run on Jet Fuel and that has an inferior power-weight ratio to what is currently in use.
We take a fuel that was never designed for use in reciprocating engines.
We modify the engine to cope with the fuel. We don't modify the fuel at all.
Why do we do this?
Because it will make a more capable or safer aviation powerplant?
Or simply because the Tax Regime means Jet Fuel is cheaper?
I have difficulty in reconciling the idea that engineering gymnastics for the purpose of Tax Avoidance is a major advance in safety or efficiency.
One could argue that removing the cost differential contributes to safety.
Mike
Mike,
The reason that JetA1 is chosen for diesel engines is merely one of logistics. It is the only fuel readily available in the aviation marketplace that is capable of being run in a diesel engine. Also, by adopting JetA1, you benefit from the economies of scale. (one of the primary reasons that AVGAS is so expensive is because the volumes are so small)
The reason you choose a diesel cycle engine is because it can be made much more efficient over it's entire operating range, when compared to an AVGAS fuelled piston. Additionally, it makes a mockery of any turbine in terms of fuel consumption (turbines win in power-weight though)
Diesel aero engines could be as power-weight competitive to AVGAS piston engines if they are suitably designed. The Thielert engines are all conversions, which means they start life compromised. Bespoke aero engines like the WAM and the Deltahawk show that power-weight can be very competitive, however the economies of scale within the aviation industry weigh heavily against the success of these engines, unfortunately.
Taxation issues aside, on a level playing field and starting from square one, an aero engine designer these days would choose JetA1 and the diesel cycle over AVGAS and the otto cycle. It's the historical legacy that hinders making this choice today.
and BTW, a diesel aero engine doesn't need FADEC. The WAM proves this very successfully.
A
The reason that JetA1 is chosen for diesel engines is merely one of logistics. It is the only fuel readily available in the aviation marketplace that is capable of being run in a diesel engine. Also, by adopting JetA1, you benefit from the economies of scale. (one of the primary reasons that AVGAS is so expensive is because the volumes are so small)
The reason you choose a diesel cycle engine is because it can be made much more efficient over it's entire operating range, when compared to an AVGAS fuelled piston. Additionally, it makes a mockery of any turbine in terms of fuel consumption (turbines win in power-weight though)
Diesel aero engines could be as power-weight competitive to AVGAS piston engines if they are suitably designed. The Thielert engines are all conversions, which means they start life compromised. Bespoke aero engines like the WAM and the Deltahawk show that power-weight can be very competitive, however the economies of scale within the aviation industry weigh heavily against the success of these engines, unfortunately.
Taxation issues aside, on a level playing field and starting from square one, an aero engine designer these days would choose JetA1 and the diesel cycle over AVGAS and the otto cycle. It's the historical legacy that hinders making this choice today.
and BTW, a diesel aero engine doesn't need FADEC. The WAM proves this very successfully.
A
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Taxation issues aside, on a level playing field and starting from square one, an aero engine designer these days would choose JetA1 and the diesel cycle over AVGAS and the otto cycle. It's the historical legacy that hinders making this choice today.
I drive a diesel car and while the fuel's a few pennies more than petrol it delivers around 42 mpg compared with the 30 or so I'd expect from its petrol equivalent. It delivers 115 bhp with a turbo compared with 145 bhp for the same capacity petrol without the turbo. Its performance is lower and its weight higher than the equivalent capacity petrol engine.
It's noisier, less responsive, and emits more particulates than the petrol equivalent.
What's so special about aero diesels that frees them from these drawbacks?
In the end it's a compromise, I chose to give up some of the advantages of petrol to gain the advantages of diesel.
While there are advantages to diesel, there are also disadvantages and ultimately the market makes the decision. I suggest that it's better if that decision is not artificially influenced by inequalities in taxation.
Mike
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The deisel conversion burns just under 5 US gals p/h compared to just over 8 US gal p/h for the standard avgas at the same IAS. I make that around 40% less fuel flow
With the avgas engine running with the red lever all the way to the stop, the above is about right. Then, about 30% of the avgas goes straight out of the exhaust, unburnt.
With the avgas engine running with the red lever all the way to the stop, the above is about right. Then, about 30% of the avgas goes straight out of the exhaust, unburnt.
Surely, given a fresh start, designers would opt for a small turboprop with a FADEC single lever engine/prop control rather than a turbocharged reciprocating engine?
A road vehicle needs a more rapidly responding engine than does an aeroplane - which is probably why road gas turbines will never replace piston engines except in large trucks. 'Part time' turbochargers improve performance, as do clutched superchargers. But neither do much for economy - when my supercharger engages, the engine takes on an Oliver Reed thirst! But it ups the power from 215 bhp to 354....
The clunking old combine harvester engines of the 1950s which still power most light aircraft have surely had their day. Future light aircraft should have small turboprops and have the fit and finish of a decent car.
And GPS, of course!
A road vehicle needs a more rapidly responding engine than does an aeroplane - which is probably why road gas turbines will never replace piston engines except in large trucks. 'Part time' turbochargers improve performance, as do clutched superchargers. But neither do much for economy - when my supercharger engages, the engine takes on an Oliver Reed thirst! But it ups the power from 215 bhp to 354....
The clunking old combine harvester engines of the 1950s which still power most light aircraft have surely had their day. Future light aircraft should have small turboprops and have the fit and finish of a decent car.
And GPS, of course!
Mike,
The advantages for aero diesel over road diesels is because it's not required to meet the stringent levels of emissions of road vehicle (and rightly so) as well as them being largely a constant speed application.
Also a diesel engine works optimally at low speeds (due to injection pressures and burn rates), whereas a gasoline engine is compromised in its efficiency at low speeds (due to knock limits and compression ratios). A reduction drive can improve things in favour of a gasoline (Rotax?), but adds weight and complexity.
The best BSFC of a gasoline engine will be around the 250g/kWh mark but will degrade rapidly from this operating point, whereas a diesel engine can readily achieve less than 200g/kWh and still has a fairly flat characteristic away from this optimum point.
While I somewhat agree about the undue influences of taxation, I think the gasoline engine is unduely influenced by history and legacy too - in the ideal world. What I am saying is that if you had a clean sheet - you might possibly choose a JetA1 burning diesel over any gasoline burning SI engine.
BEagle - turbines do not scale at all well. As you reduce the size of a turbine the maximum achievable efficiency drops pretty dramatically. A 150-200hp turboprop would have a horrendous fuel consumption - even if it were cheap JetA1
A
The advantages for aero diesel over road diesels is because it's not required to meet the stringent levels of emissions of road vehicle (and rightly so) as well as them being largely a constant speed application.
Also a diesel engine works optimally at low speeds (due to injection pressures and burn rates), whereas a gasoline engine is compromised in its efficiency at low speeds (due to knock limits and compression ratios). A reduction drive can improve things in favour of a gasoline (Rotax?), but adds weight and complexity.
The best BSFC of a gasoline engine will be around the 250g/kWh mark but will degrade rapidly from this operating point, whereas a diesel engine can readily achieve less than 200g/kWh and still has a fairly flat characteristic away from this optimum point.
While I somewhat agree about the undue influences of taxation, I think the gasoline engine is unduely influenced by history and legacy too - in the ideal world. What I am saying is that if you had a clean sheet - you might possibly choose a JetA1 burning diesel over any gasoline burning SI engine.
BEagle - turbines do not scale at all well. As you reduce the size of a turbine the maximum achievable efficiency drops pretty dramatically. A 150-200hp turboprop would have a horrendous fuel consumption - even if it were cheap JetA1
A
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Ah! So FA need have no worries about the hike in the price of diesel then! People will continue to buy them because they are better, not because the fuel's cheaper. (where's the emoticon that says I'm deliberately stirring?)
You have a good point.
However, surely one of the purposes of tax incentives is to encourage a particular trend or development within the community because it is perceived to be good for the community.
In this case the lack of duty on Jet A1 was not introduced as an incentive, it has always been that way. It would seem to be more the case that any form of fuel eventually becomes a tax target.
However, the lack of duty did encourage the development of these engines, notwithstanding that they have other advantages.
The Government has a track record of taxing any form of fuel that becomes popular so the tax hike should not come as a surprise.
Should legislative changes be introduced in the way they have resulting in an "overnight" increase in the price which has no commercial basis - that I doubt. I suppose our Government has resisted these changes - if their heart is really in it?
You have a good point.
However, surely one of the purposes of tax incentives is to encourage a particular trend or development within the community because it is perceived to be good for the community.
In this case the lack of duty on Jet A1 was not introduced as an incentive, it has always been that way. It would seem to be more the case that any form of fuel eventually becomes a tax target.
However, the lack of duty did encourage the development of these engines, notwithstanding that they have other advantages.
The Government has a track record of taxing any form of fuel that becomes popular so the tax hike should not come as a surprise.
Should legislative changes be introduced in the way they have resulting in an "overnight" increase in the price which has no commercial basis - that I doubt. I suppose our Government has resisted these changes - if their heart is really in it?
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If the aircraft is maintained on LAMS it will still have a 50hr check regardless of the engine requirements. It may need servicing every 100hrs but at least on a Lycoming you don't have to change the crank balance dampers, strip the fuel pump down, change the cambelt...
The PA29 conversion with the Centurion (was 1.7 Merc, now their own 2.0 supposedly), weighs about 120lb more, cruises 5kts slower and has a poorer take-off and climb to 2000ft than a standard Lycoming version. Oh, and all with the help of a CS prop. What an excellent mod. Not....
Fuel costs are only one small part of the cost of running an aircraft. Perhaps when the Americans use diesel in everyday life rather than just huge trucks then the market might open up - oh and perhaps if the reliability improves, that might help to.
Not just Centurion. Allegedly there was the case of a 30p resistor failing in a SMA powered C182 FADEC recently which put the engine at max chat on start-up. A van stopped it eventually (aircraft beyond economic repair apparently) and lucky the hangar doors had just been closed before it went in there. Bit embarrassing, it being the demonstrator....
The PA29 conversion with the Centurion (was 1.7 Merc, now their own 2.0 supposedly), weighs about 120lb more, cruises 5kts slower and has a poorer take-off and climb to 2000ft than a standard Lycoming version. Oh, and all with the help of a CS prop. What an excellent mod. Not....
Fuel costs are only one small part of the cost of running an aircraft. Perhaps when the Americans use diesel in everyday life rather than just huge trucks then the market might open up - oh and perhaps if the reliability improves, that might help to.
Not just Centurion. Allegedly there was the case of a 30p resistor failing in a SMA powered C182 FADEC recently which put the engine at max chat on start-up. A van stopped it eventually (aircraft beyond economic repair apparently) and lucky the hangar doors had just been closed before it went in there. Bit embarrassing, it being the demonstrator....
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Turbines are OK at 450HP+ but still about 20-30% worse than the old Lycos.
If you look at the specs of the Grob 140 (most likely a defunct design due to Grob working on their VLJ) and look at the range they get out of their fuel payload, it's not at all bad. That's a 450HP Allison heli engine. At the right price, I'd buy one tomorrow.
The problem is cost. A turbine (Allison or the PT6) doubles the cost of a typical IFR tourer, from say 250k to 500k. There is a perception (probably correct) that anybody with 500k has got a lot more so why not give it to them.
There is also the practical flight planning issue that with such an engine - as with a turbo Lyco - you want a 25k+ operating ceiling to get into VMC above most (non-CB) cloud tops, and that is not practical on oxygen, so a pressurised hull is required, and that jacks the price of your turboprop from 500k to close to 1M. Then, you can't market a 1M plane with the "simple" avionics of a 250k IFR tourer, can you? So you stick a load of kit in there to make it look worth the money. Some of this, like radar, is very good mission-capability stuff but soon you are at 1.5M.... which brings us to a TBM type of thing.
The Grob 140 was going to sell for close to 1M GBP, which is too much, since a Piper turboprop can be had for that much and is pressurised. Not as versatile of course; a decent light 450HP turboprop has a fantastic short field capability, with 200m takeoffs from grass.
But I suspect the group of pilots who want short field capability and who do serious long trips is just too small. In Europe especially since an IR is a must to get the altitude which is desirable for IFR routings and economy, and the JAA IR is so hard to get very few people have it.
So a lot of the drive is not technology; it's marketing.
If you look at the specs of the Grob 140 (most likely a defunct design due to Grob working on their VLJ) and look at the range they get out of their fuel payload, it's not at all bad. That's a 450HP Allison heli engine. At the right price, I'd buy one tomorrow.
The problem is cost. A turbine (Allison or the PT6) doubles the cost of a typical IFR tourer, from say 250k to 500k. There is a perception (probably correct) that anybody with 500k has got a lot more so why not give it to them.
There is also the practical flight planning issue that with such an engine - as with a turbo Lyco - you want a 25k+ operating ceiling to get into VMC above most (non-CB) cloud tops, and that is not practical on oxygen, so a pressurised hull is required, and that jacks the price of your turboprop from 500k to close to 1M. Then, you can't market a 1M plane with the "simple" avionics of a 250k IFR tourer, can you? So you stick a load of kit in there to make it look worth the money. Some of this, like radar, is very good mission-capability stuff but soon you are at 1.5M.... which brings us to a TBM type of thing.
The Grob 140 was going to sell for close to 1M GBP, which is too much, since a Piper turboprop can be had for that much and is pressurised. Not as versatile of course; a decent light 450HP turboprop has a fantastic short field capability, with 200m takeoffs from grass.
But I suspect the group of pilots who want short field capability and who do serious long trips is just too small. In Europe especially since an IR is a must to get the altitude which is desirable for IFR routings and economy, and the JAA IR is so hard to get very few people have it.
So a lot of the drive is not technology; it's marketing.