Death of the Diesel?
Avoid imitations
Join Date: Nov 2000
Location: Wandering the FIR and cyberspace often at highly unsociable times
Posts: 14,581
Received 438 Likes
on
231 Posts
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.
Not forgetting that one day they will be filling the fuel tanks with renewable bio/vegetable oil.
Join Date: Sep 2003
Location: Oxford
Posts: 91
Likes: 0
Received 0 Likes
on
0 Posts
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.
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.
Join Date: Jun 2003
Location: EuroGA.org
Posts: 13,787
Likes: 0
Received 0 Likes
on
0 Posts
SAS
YES.
But power is not some artificial concept, no more than "10" is a "made up figure" by multiplying "2" and "5"
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.
So basically IO you are saying that power is a made up figure from torque and engine speed!
But power is not some artificial concept, no more than "10" is a "made up figure" by multiplying "2" and "5"
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.
Guest
Posts: n/a
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
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.
Look interesting: http://www.centurion-engines.com/c40/c40_start.htm
Join Date: Sep 2002
Location: Savannah GA & Portsmouth UK
Posts: 1,784
Likes: 0
Received 0 Likes
on
0 Posts
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
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
Join Date: Mar 2000
Location: U.K.
Age: 46
Posts: 3,112
Likes: 0
Received 0 Likes
on
0 Posts
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.
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.
Official PPRuNe Chaplain
Join Date: Apr 2001
Location: Witnesham, Suffolk
Age: 80
Posts: 3,498
Likes: 0
Received 0 Likes
on
0 Posts
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.
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.
Join Date: Jun 2003
Location: EuroGA.org
Posts: 13,787
Likes: 0
Received 0 Likes
on
0 Posts
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
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
Join Date: May 2003
Location: Essex, UK
Posts: 616
Likes: 0
Received 0 Likes
on
0 Posts
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.
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.
Join Date: Dec 2004
Location: Sweden
Posts: 208
Likes: 0
Received 0 Likes
on
0 Posts
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!
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!
Join Date: Mar 2000
Location: U.K.
Age: 46
Posts: 3,112
Likes: 0
Received 0 Likes
on
0 Posts
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!!
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!!
Join Date: Jun 2003
Location: EuroGA.org
Posts: 13,787
Likes: 0
Received 0 Likes
on
0 Posts
Back to college
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....
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....
Thread Starter
Join Date: Apr 2003
Location: Midlands
Posts: 2,359
Likes: 0
Received 0 Likes
on
0 Posts
“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
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
Join Date: Mar 2000
Location: U.K.
Age: 46
Posts: 3,112
Likes: 0
Received 0 Likes
on
0 Posts
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!
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!
Why do it if it's not fun?
Join Date: Jul 2001
Location: Bournemouth
Posts: 4,779
Likes: 0
Received 0 Likes
on
0 Posts
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
-------------
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
-------------
Join Date: May 2003
Location: Essex, UK
Posts: 616
Likes: 0
Received 0 Likes
on
0 Posts
IO
You are quite right and I only mentioned it as I thought you said:
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.
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.
Join Date: May 2002
Location: West Sussex, UK
Posts: 220
Likes: 0
Received 0 Likes
on
0 Posts
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.
Designer called Phil Heward-will try and get a link for more details but it sounds promising.
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.
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.
Join Date: Apr 2000
Location: UK
Age: 54
Posts: 106
Likes: 0
Received 0 Likes
on
0 Posts
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.
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.
Last edited by 100LL; 23rd Feb 2005 at 22:14.