Why the dearth of faster piston-powered planes?
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Why the dearth of faster piston-powered planes?
There aren't very many fast piston airplanes in production. By "fast" I mean, if you look back in the early to mid 20th century, before turbines won out, there were lots of piston airplanes in production that pushed the practical velocity limit of propeller-driven aircraft, cruising 360+ knots in military planes, sometimes as fast as 330 knots in commercial airliners. And this was with a terrible understanding of aerodynamics and piston engines compared to today.
Today, for both singles and twins, the fastest speeds around aren't much higher than 200 knots. ~240 knots in the case of the very fastest couple available airplanes like the Cessna 400 and fastest Mooney.
There are indications that with modern materials and engineering, much faster speeds can be achieved using piston engines already available. The Cobalt CO50 Valkyrie design claims to push a spacious 4 person cabin up to 260 knots with a single 350hp engine. The recently-certified Diamond DA-62 can move a spacious 7 passenger cabin at ~200 knots using only a pair of 180hp engines.
Why aren't there more faster piston airplanes available? Would the market not be interested in piston powered planes that could do 300 knots? Shouldn't you be able to make almost those speeds for a very small plane powered by a single commonplace 350hp engine? Shouldn't you be able to make those speeds in a more spacious plane with a pair of commonplace 350hp engines?
My understanding of the marketplace is that the #1 reason people choose piston is cost. And isn't the cost of operating piston engines, even two piston engines versus a single turboprop, much much lower? How much does a 350hp turbocharged piston engine cost brand new, $50k-$60k? So even buying a pair of them is $100k-$120k. And then how much does a single comparable turbine engine cost? ~$800k with proportionately higher rebuild costs per flight hour? Plus 20%+ higher SFC than a piston?
Basically, I see the Piper M600 listed at $2.8M, or the TBM930 listed at $3.9M, and I don't understand why it would be hard to achieve nearly the same performance for a fraction of the price using a pair of cheap piston engines. For example the Piper M350 has the same 6 passenger cabin as the M600 and also includes pressurization, and with a single 350hp engine makes over 210 knots on a very old airframe with a list price of under $1.2M. If you basically built the same airplane but reoptimized for twin engines and using modern materials and aerodynamics, shouldn't you be able to achieve near 300 knots by adding another piston engine? And shouldn't you be able to sell the resulting airplane for well under $2M, and with a significantly advantaged SFC (and therefore range and payload) than the M600?
Today, for both singles and twins, the fastest speeds around aren't much higher than 200 knots. ~240 knots in the case of the very fastest couple available airplanes like the Cessna 400 and fastest Mooney.
There are indications that with modern materials and engineering, much faster speeds can be achieved using piston engines already available. The Cobalt CO50 Valkyrie design claims to push a spacious 4 person cabin up to 260 knots with a single 350hp engine. The recently-certified Diamond DA-62 can move a spacious 7 passenger cabin at ~200 knots using only a pair of 180hp engines.
Why aren't there more faster piston airplanes available? Would the market not be interested in piston powered planes that could do 300 knots? Shouldn't you be able to make almost those speeds for a very small plane powered by a single commonplace 350hp engine? Shouldn't you be able to make those speeds in a more spacious plane with a pair of commonplace 350hp engines?
My understanding of the marketplace is that the #1 reason people choose piston is cost. And isn't the cost of operating piston engines, even two piston engines versus a single turboprop, much much lower? How much does a 350hp turbocharged piston engine cost brand new, $50k-$60k? So even buying a pair of them is $100k-$120k. And then how much does a single comparable turbine engine cost? ~$800k with proportionately higher rebuild costs per flight hour? Plus 20%+ higher SFC than a piston?
Basically, I see the Piper M600 listed at $2.8M, or the TBM930 listed at $3.9M, and I don't understand why it would be hard to achieve nearly the same performance for a fraction of the price using a pair of cheap piston engines. For example the Piper M350 has the same 6 passenger cabin as the M600 and also includes pressurization, and with a single 350hp engine makes over 210 knots on a very old airframe with a list price of under $1.2M. If you basically built the same airplane but reoptimized for twin engines and using modern materials and aerodynamics, shouldn't you be able to achieve near 300 knots by adding another piston engine? And shouldn't you be able to sell the resulting airplane for well under $2M, and with a significantly advantaged SFC (and therefore range and payload) than the M600?
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Turbines are more reliable and believe it or not cheaper to run - AVTUR also much cheaper than AVGAS (even taking into account turbines' higher fuel burn) and also much more widely available. This is the main reason why in recent years all the golden oldies such as Cessna 310s, Navajos etc. have all been fast disappearing.
Also there is the safety aspect. A jet is easier to operate, more reliable and if the is an EFATO, there is no prop to feather. An un-feathered prop has a huge amount of drag and has been responsible for many deaths.
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Insurance and Pilot Capabilities
I suspect one of the reasons you don't see "fast" pistons is the cost of certification and insurance.
As mention above, Jets are easier to fly, and Twin Turboprops give a higher margin single engine, but piston twin proficiency requires constant practice.
The difference between a Professional (Doctor/Entrepreneur etc) who flies, and an Professional Pilot is huge, the investment in time and money to achieve the same level of proficiency is more than most "busy" people are willing to spend.
So there's no demand, and the price of each item goes up to the point that it's cheaper to buy a used TBM than a new piston-powered 350HP rocket ship.
Been there, done that.
As mention above, Jets are easier to fly, and Twin Turboprops give a higher margin single engine, but piston twin proficiency requires constant practice.
The difference between a Professional (Doctor/Entrepreneur etc) who flies, and an Professional Pilot is huge, the investment in time and money to achieve the same level of proficiency is more than most "busy" people are willing to spend.
So there's no demand, and the price of each item goes up to the point that it's cheaper to buy a used TBM than a new piston-powered 350HP rocket ship.
Been there, done that.
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Not much to go wrong, in all honesty.
Unlike piston engines, in turbines everything is constantly rotating in one direction, not back-and-forth with stopping in between. Turbines are much simpler and more reliable in operation because there is less to go wrong and there is less stress on the components involved.
Think of the components in a piston engine. Big end bearings, little end bearings, crankshaft, balancers, pistons, con rods, camshaft, valves, pushrods, springs, all starting and stopping multiple times per second and moving in different directions whilst in operation.
In a turbine there are a series of turbine rotors all on one shaft constantly rotating and all in one direction. Much smoother and simpler and the reason why these engines are much more reliable.
Unlike piston engines, in turbines everything is constantly rotating in one direction, not back-and-forth with stopping in between. Turbines are much simpler and more reliable in operation because there is less to go wrong and there is less stress on the components involved.
Think of the components in a piston engine. Big end bearings, little end bearings, crankshaft, balancers, pistons, con rods, camshaft, valves, pushrods, springs, all starting and stopping multiple times per second and moving in different directions whilst in operation.
In a turbine there are a series of turbine rotors all on one shaft constantly rotating and all in one direction. Much smoother and simpler and the reason why these engines are much more reliable.
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I have been told that, all else equal, for a given airframe which is assumed to have a relatively constant coefficient of drag across speeds until it gets into the transonic regime, doubling the available power should increase maximum speed by 26%. The Aerostar twin that could make 260 knots from a pair of 350hp engines was built during an era when the fastest single-engine comfortable four-seater planes sporting a single engine could make, what, 220 knots? MAYBE 230 knots? Whereas today, with modern technology, they can built a 350hp single with a big 4+1 passenger cabin that can do 260 knots. It seems to me that leveraging those same advances in materials and aerodynamics, they should be able to build an Aerostar-like pressurized 6 seater that could do ~280 knots. And they should be able to sell it for about half the price of turboprop singles.
Turbines are more reliable and believe it or not cheaper to run
Thanks
Yes! Exactly like that. I have read that late versions of the Aerostar could break 260 knots. If a similar plane was being designed from scratch today, using modern composites and related design techniques, using the latest updated piston engines or possibly new piston diesels if they meet the hype, shouldn't they be able to build a "modern Aerostar" that could do 280 knots?
I have been told that, all else equal, for a given airframe which is assumed to have a relatively constant coefficient of drag across speeds until it gets into the transonic regime, doubling the available power should increase maximum speed by 26%. The Aerostar twin that could make 260 knots from a pair of 350hp engines was built during an era when the fastest single-engine comfortable four-seater planes sporting a single engine could make, what, 220 knots? MAYBE 230 knots? Whereas today, with modern technology, they can built a 350hp single with a big 4+1 passenger cabin that can do 260 knots. It seems to me that leveraging those same advances in materials and aerodynamics, they should be able to build an Aerostar-like pressurized 6 seater that could do ~280 knots. And they should be able to sell it for about half the price of turboprop singles.
That's the real b
tch.Building a new, certified twin from scratch is a massive financial undertaking. And what's the market for it?
Not big enough, I'm afraid.
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Tuna HP - Mx costs might be higher but turbines require less Mx (Generally run on-condition rather than a specified TBO).
Fuel burn is everything, the much lower cost of AVTUR sees to that, in some places its a quarter of what AVGAS costs, quite a significant saving even taking into account increased burn.
Fuel cost is the biggest single running cost facing any operator over the lifetime on an airframe.
Fuel burn is everything, the much lower cost of AVTUR sees to that, in some places its a quarter of what AVGAS costs, quite a significant saving even taking into account increased burn.
Fuel cost is the biggest single running cost facing any operator over the lifetime on an airframe.
In most commercial GA applications even turbines have mandatory TBOs. Not necessarily so in private ops (depending on your regulations) but I'd argue commercial use tends to be the demand driver of the cabin class & larger GA aircraft.
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The typical GA flight is no longer the long-haul vacation trip of the 80-90ies, but the tour round the corner for a coffee. You don't need fast aircraft for that. Even further, look at the fast small aircraft - they all have to climb high to uncomfortable altitude to be fast, even a Mooney Acclaim at 5000ft is not really fast ... Not to forget the 250kn max limit below FL100, so the current fast aircraft are pretty close to that.
Last edited by ChickenHouse; 10th Aug 2016 at 10:08.
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I stand corrected Tinsaffl regarding turbine TBOs, my apologies. I was aware of private ops not needing TBOs in some cases and I incorrectly assumed this also applied to CAT.
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Give it a few more years, perhaps five (?) and a new generation of hybrid Jet A1/Bio-fuel/Diesel (whatever can be bought cheapest) compatible engines - i.e. multi-fuel capable, combined with a very powerful, but lightweight electrical motor and super-capacity battery packs will be available.
People are already getting about 5 kilowatts per kilogram I think, like Siemens, out of some new light electric motors with superconductors.
Prodrive - the motorsports gurus in the UK are developing just such an engine with 300HP from the reciprocating 'diesel' engine and a further 300HP from the electric engine where one can back-up the other in emergencies (so effectively a 'twin') and 600HP is available when you might want it, for take-off for example. It is the same size and form or weight as a typical six-pot Lycoming or Continental equivalent including the battery pack.
Safer than a single turbine solution, possibly cheaper and easier to retrofit and as technology improves, may have ever-greater power to weight ratio over time.
If you gave Elon Musk the task of refining that technology and the batteries, in due course you'll get the powerplants you might want with the power you need to drive any little pocket-rocket aircraft over the 300 knots cruise boundary at a relatively sensible price. One day, maybe not tomorrow.
The safety side though is a no-brainer, if reciprocating engine fails, you have an electric back-up to keep you going until you can find a safe landing spot - or vice-versa depending on how the hybrid is utilised. And in a 'single' centreline configuration, no handling issues.
People are already getting about 5 kilowatts per kilogram I think, like Siemens, out of some new light electric motors with superconductors.
Prodrive - the motorsports gurus in the UK are developing just such an engine with 300HP from the reciprocating 'diesel' engine and a further 300HP from the electric engine where one can back-up the other in emergencies (so effectively a 'twin') and 600HP is available when you might want it, for take-off for example. It is the same size and form or weight as a typical six-pot Lycoming or Continental equivalent including the battery pack.
Safer than a single turbine solution, possibly cheaper and easier to retrofit and as technology improves, may have ever-greater power to weight ratio over time.
If you gave Elon Musk the task of refining that technology and the batteries, in due course you'll get the powerplants you might want with the power you need to drive any little pocket-rocket aircraft over the 300 knots cruise boundary at a relatively sensible price. One day, maybe not tomorrow.
The safety side though is a no-brainer, if reciprocating engine fails, you have an electric back-up to keep you going until you can find a safe landing spot - or vice-versa depending on how the hybrid is utilised. And in a 'single' centreline configuration, no handling issues.
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From an insurance perspective, a new HP piston is a scary thing, hence high premiums, if the standard insurance companies would even write it at all. As mentioned, the complexity of a recip engine, turbocharged, high compressions, etc. is not something insurance companies get excited about.
They're thinking- "owner flown, just stepped up from a C-172, ie: non professional pilot, 4-6 seats filled with friend who are moderately high net worth individuals, something happens, maybe mechanical, maybe the pilot/owner gets behind the aircraft, plows it into a field in IMC. The estates of the dead WILL sue, and now the insurance company is paying out millions upon millions, and possibly the OEM who always get sucked into lawsuits too. The Bonanza was called the "Doctor Killer" because of this, and frankly it still is. I've been at those crash scenes in the last couple of years, and now the SR22 is supplanting the Bo at this. Imagine a piston with more power and more speed. Dr. Fantastic or Business Man Amazing gets one right after training in a Cessna to blast around with his friends.
Well, this is the way it goes in litigation happy America anyway. So big powerful pistons are a no no, and commercial operators use turboprops. PC-12 will win out over a twin piston every time. PC-12 is certified, supported, good track record, one engine. No need for a twin piston.
They're thinking- "owner flown, just stepped up from a C-172, ie: non professional pilot, 4-6 seats filled with friend who are moderately high net worth individuals, something happens, maybe mechanical, maybe the pilot/owner gets behind the aircraft, plows it into a field in IMC. The estates of the dead WILL sue, and now the insurance company is paying out millions upon millions, and possibly the OEM who always get sucked into lawsuits too. The Bonanza was called the "Doctor Killer" because of this, and frankly it still is. I've been at those crash scenes in the last couple of years, and now the SR22 is supplanting the Bo at this. Imagine a piston with more power and more speed. Dr. Fantastic or Business Man Amazing gets one right after training in a Cessna to blast around with his friends.
Well, this is the way it goes in litigation happy America anyway. So big powerful pistons are a no no, and commercial operators use turboprops. PC-12 will win out over a twin piston every time. PC-12 is certified, supported, good track record, one engine. No need for a twin piston.
My relatively uninformed view is that the limiting factor on speed is primarily airframe drag, and that twins win out over singles not because they have more horses, but because they are certified with higher stall speeds so can have smaller wings.
Hybrids hold out the promise of v/stol with small wings and a faster, more efficient cruise. In-between, I can't see anything much changing. There are plenty of fast homebuilt designs available.
Hybrids hold out the promise of v/stol with small wings and a faster, more efficient cruise. In-between, I can't see anything much changing. There are plenty of fast homebuilt designs available.