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3 hours ago, Ah-1 Cobra Pilot said:

You would be trading a gearbox for a generator and a motor.  I suspect the weight of the two would be more than the weight of the gearbox; plus, the efficiency losses would make it undesirable.

You may be surprised how small the weight difference is. Modern permanent magnet motors can be made amazingly light. Just look at the new starters. The same would apply to the generator.

The reason aircraft gearboxes are so problematic is because of torsional resonance between the engine and the propeller. This causes the gears to bang back and forth constantly instead of constantly loading one side of the gears. This is why the Thielert Diesel engine had such a short TBO on its gearbox. That gearbox also had a clutch to allow the drive to slip a bit during the peak of the torsional oscillations. This is the main problem with putting Diesel engines in airplanes.

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33 minutes ago, jaylw314 said:

The weight of a transmission is not trivial.  My subaru WRX transmission weighs about 350-400 lbs.  The Tesla sedan brushless electric motor weighs 70 lbs.  I'd trade 350 lbs for 140 lbs any day.  Also, gearbox efficiency is not 100%--depending on load, it can vary between 50-80%.  That's comparable to the 60% I guesstimated above for the generator-battery-motor efficiency.

The gear box in a GO-300, for instance is over 90% efficient and weighs about 30 lb., (if memory serves me).  It only needs to reduce the rpm from about 3200 to 2400.  Those worse figures are probably from turbo props or other high-percentage reduction.

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31 minutes ago, Ah-1 Cobra Pilot said:

No, just as in aircraft, you have several friction/drag curves and the engine has its own efficiency curve.  Where these curves meet, essentially, is the best speed vs. fuel burn.

I don't understand.  Above best glide speed, there is not another faster speed that somehow gives you better range? Or above Carson speed, there is not another faster speed that somehow gives you more knots per gph? 

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3 hours ago, jaylw314 said:

I don't understand.  Above best glide speed, there is not another faster speed that somehow gives you better range? Or above Carson speed, there is not another faster speed that somehow gives you more knots per gph? 

Technically your best range “speed” is defined off of an angle of attack.... which means that weight actually changes the speed.  As is you max endurance (longest time airborne for the fuel).

it all goes back to your lift vs drag curves, which define where the most “efficient” flight profile exists.  They (max range/max endurance) are defined off an angle of attack that corrisponds to the intersections of the L/DMax curves.

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1 hour ago, M016576 said:

Technically your best range “speed” is defined off of an angle of attack.... which means that weight actually changes the speed.  As is you max endurance (longest time airborne for the fuel).

it all goes back to your lift vs drag curves, which define where the most “efficient” flight profile exists.  They (max range/max endurance) are defined off an angle of attack that corrisponds to the intersections of the L/DMax curves.

Exactly.  Total Drag comprises parasite drag, induced drag, etc.  Some are greater at high speeds, some greater at lower speeds.  Cars have similar/analogous forces acting upon them, too.

Forgive me for not previously spelling everything out in the interest of conserving words.

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14 hours ago, jaylw314 said:

You wouldn't need a clutch, the motor could simply be directly connected to the main motor and the prop..  Today's brushless electric motors can run throughout the range of propeller RPM's without a problem, and the power controller can be set to "freewheel" the motor when no output or input power is used.  Teslas and some other electric cars use one brushless electric motor with no gearbox--the motor runs through the entire range 0-155 mph in one "gear". 

Yes the electric motor can go through the RPM ranges with no problems.  MY thoughts were that in the event of an engine failure the sprag clutch would allow the prop to freewheel same as on a helicopter if the engine fails the rotors freewheel without the drag of the engine.  The electric motor could then power the prop for a short distance without having to turn the engine to extend glide range or avoid an obstacle.  Oh and the electric motor might be able to double a the starter saving some weight there as well.

Some have touted the diesel electric type model where you have a generator powering the electric motor with a battery backup.  The generator can always run at its most efficient speed and the electric motor with a limited battery backup could provide good takeoff and acceleration power with no density altitude consequences.  However, you do get a weight penalty for the extra batteries and the extra generator. 

To get 150HP continuous at the electric motors you will need an engine to produce 150 to 180HP and a generator to produce 150kW.  This system wold have a weight penalty.

A true hybrid would use the direct drive engines we currently use a small battery for energy storage to assist in acceleration and climb 10 to 15 min.  Once at cruise the electric motor would be along for the ride.

Now a fuel cell and electric motor or motors arranged in a pancake set up and prop  that would weigh about the same as our current engine and props that would get you to an all electric powered aircraft.  The question is does such a fuel cell exist?  Also what would the physical size of the fuel cells be?

fuel cell Fuel: methanol, ethanol or gasoline hydrogen storage at high pressure would be too much weight, liquid hydrogen too expensive

fuel cell Power density: 150kW to 200kW output 2 or more individual cells

fuel cell weight: 200 to 300 lbs

Battery: sized to run  for 10 minutes  at 50% power

electric motors:  150kW to 200kW output (utilize 2 or more motors stacked for added redundancy) this would be for J type performance

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On 2/16/2018 at 2:41 PM, jetdriven said:

The biggest one there I could find was 74HP gross intermittent, which says not continuous duty. And it weighs 650lb and it’s CRDI and turbocharged which means complex. Make the block of aluminum and it won’t last as long, either. Tractor engines are reliable and long lived because they are massively overbuilt for their job  

 

http://www.kubotaengine.com/assets/documents/Brochures-Engines Tier 4/2016 June/07/v3307_cr_te4b_tie4b.pdf

Ya I kind of came to the same conclusion so then I always go back old school to the diesel radial.   https://en.wikipedia.org/wiki/Packard_DR-980

If you put some modern Electronic injection on it and tightened up the tolerance and a decent exhaust system it should do well.

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On 2/14/2018 at 1:38 PM, N201MKTurbo said:

IThere is very little you can do to our engines to make them more powerful, efficent or reliable. 

 

Ah yes, the circa-1930 tractor engine. Known for its ultra efficiency with a carburator older than my grandpa and with less power than a modern subcompact car.

I really do think a diesel-powered, direct-injection, water-cooled engine with FADEC would be the most powerful and most efficient engine to stick into an airplane. If not and sticking with gasoline air-cooled, to at least go with double electronic ignition, new exhaust, injected engine, with a complete makeover of the intake/cooling system (ala David's research but with R&D budget from Lycoming) in carbon fiber or kevlar.

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7 hours ago, Raptor05121 said:

Ah yes, the circa-1930 tractor engine. Known for its ultra efficiency with a carburator older than my grandpa and with less power than a modern subcompact car.

I really do think a diesel-powered, direct-injection, water-cooled engine with FADEC would be the most powerful and most efficient engine to stick into an airplane. If not and sticking with gasoline air-cooled, to at least go with double electronic ignition, new exhaust, injected engine, with a complete makeover of the intake/cooling system (ala David's research but with R&D budget from Lycoming) in carbon fiber or kevlar.

So let's take these claims one at a time.

"less power than a compact car" Most auto engines never make their rated power. The only way to do it would be to pull a heavy trailor up a steep hill at sea level. Full power requires full throttle at redline RPM at sea level barometric pressure. Most cars and trucks would overheat making 100% power for more than a short time. Most auto engines operate at about 10% power or less in normal operation.

"Electronic fuel injection" what can this do other than change the fuel/air ratio? We have the ability to adjust that to a fine degree using the red knob. The only thing EFI would do is make it easier, not better. Making a car driveable and efficient is a very different task than operating an engine that runs at a constant high power setting in a very narrow range of RPMs and manifold pressures and has no requirement to accelerate rapidly.

"Electronic ignition" this can only change the spark advance. Auto engines normally operate between 500 and 7000 RPM. With constant excursions through this range especially with lead footed drivers. The optimal spark advance is an ever changing value. An electronic ignition system does a great job of keeping the spark where it needs to be. We operate our aircraft engines between 2300 and 2700 RPM at a constant fuel air ratio. There is an optimal spark advance for those conditions and that is where our mags are set. Electronic ignition has very little to offer to improve the performance of our engines.

"Air Cooling" air cooling is the lightest and most reliable method of cooling our engines. That was proven during WWII the water cooled aircraft engines were more susceptible to battle damage and other normal failures. Adding water cooling to our engines would make them heavier by adding the jackets around the cylinders, the coolant hoses, the water pump, thermostat, radiator, expansion tank and the coolant. It also adds a lot of failure points to the system. Can you say you have never had a blown or leaking radiator hose or had a water pump go out? Imagin that happening at night IFR over a huge area of icing. I'll stick with air cooling.

"Direct injection turbo diesel" you can buy a certified one right now. The Continental Centurian Diesel engine. It has proven to be very expensive to maintain and people are removing them and replacing them with Lycomings.

The bottom line is all these things you are talking about have been thought about and tried. Most decades ago. They offer very little advantage to our engines. If they did, they would have been incorporated a long time ago. Do you honestly think you are the first person to think of this?

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Diesel aircraft engines have been in development and testing for about 90 years now.  

I don’t see many incentives strong enough to compel a widespread switch from gasoline to diesels  - except perhaps this one:   If in the USA 100LL becomes unavailable and no suitable fuel replacement is on hand then Diesel alternatives may be attractive enough for a  fairly widespread conversion.  

Within the PA46 community there is also on-going discussion of finding a Diesel  replacement engine for the 350 hp turbocharged Lycoming.  

The difference for the PA46 family compared to Mooney is there exists an STC alternative—the PT6A.  About a third of the eligible fleet has converted already.   

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Jerry,

What is the typical source for somebody hanging a PT6A on the front of their plane? Are they buying them brand new from Honeywell? Or overhauling a particular engine from a fleet of planes that have gone offline for some reason?

a small advantage of diesel comes in its available energy per gallon.  More energy fits in the same tank. Oil density vs. gasoline density.  Unfortunately, more weight as well...

Best regards,

-a-

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Yetti,

On their TurboProp page they convert to the KW to HP, and give limitations for T/O and continuous operation....

http://www.pbsvb.com/customer-industries/aerospace/aircraft-engines/tp-100-turboprop-engine

241hp max...

214 hp cont...

188 hp cruise...

Would work pretty well with an M20C behind it...   :)

I was looking for some comparisons of the RR500.  The 2008 Mooney/Rolls project... somewhere around 350 - 400shp....?

Best regards,

-a-

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15 hours ago, N201MKTurbo said:

So let's take these claims one at a time.

"less power than a compact car" Most auto engines never make their rated power. The only way to do it would be to pull a heavy trailor up a steep hill at sea level. Full power requires full throttle at redline RPM at sea level barometric pressure. Most cars and trucks would overheat making 100% power for more than a short time. Most auto engines operate at about 10% power or less in normal operation.

"Electronic fuel injection" what can this do other than change the fuel/air ratio? We have the ability to adjust that to a fine degree using the red knob. The only thing EFI would do is make it easier, not better. Making a car driveable and efficient is a very different task than operating an engine that runs at a constant high power setting in a very narrow range of RPMs and manifold pressures and has no requirement to accelerate rapidly.

"Electronic ignition" this can only change the spark advance. Auto engines normally operate between 500 and 7000 RPM. With constant excursions through this range especially with lead footed drivers. The optimal spark advance is an ever changing value. An electronic ignition system does a great job of keeping the spark where it needs to be. We operate our aircraft engines between 2300 and 2700 RPM at a constant fuel air ratio. There is an optimal spark advance for those conditions and that is where our mags are set. Electronic ignition has very little to offer to improve the performance of our engines.

"Air Cooling" air cooling is the lightest and most reliable method of cooling our engines. That was proven during WWII the water cooled aircraft engines were more susceptible to battle damage and other normal failures. Adding water cooling to our engines would make them heavier by adding the jackets around the cylinders, the coolant hoses, the water pump, thermostat, radiator, expansion tank and the coolant. It also adds a lot of failure points to the system. Can you say you have never had a blown or leaking radiator hose or had a water pump go out? Imagin that happening at night IFR over a huge area of icing. I'll stick with air cooling.

"Direct injection turbo diesel" you can buy a certified one right now. The Continental Centurian Diesel engine. It has proven to be very expensive to maintain and people are removing them and replacing them with Lycomings.


The Continental CD135 and CD155 are starting to become very popular. I am closely following two projects in a 172 and a Piper Archer. Granted both are overseas and being used in a flight school environment, initial testing is giving them 5-10 kts faster on the order of 5.5-6.0 gph. I believe the TBR on the gearboxes are now over 2,000 hours, and they can burn diesel ($2.90/gal right now near me) and JetA ($3.30/gal) versus $3.90+ for 100LL. Mooney was also using these engines in the M10 project.

-EFI as you know would allow for more efficient leaning. Less spread on the injectors. This isn't new

-Electronic Ignition is more precise compared to mags which can drift in timing which reduces power and increases fuel consumption. Do any search on people doing EI swap and they're claiming lower CHTs, more power, higher climb rates, etc etc.

-Air cooling is simple and reliable, but I believe technology has gotten to the point that other methods can be made *as* reliable. My F-150 is 20 years old. I've *NEVER* changed the water pump. It is a factory unit, as it rolled off the assembly line in 1997. It has 600,000 miles on it. I have replaced the radiator, only to an accident. You claim you don't want to fly at night at IFR due to a radiator or liquid line bursting, but you're flying behind one of those right now- an oil cooler. Losing either one of those would result in the same ending.

Combine all of these factors and it makes for an efficient engine. There is 0 reason the technology of the modern automobile industry cannot be applied to general aviation.

The Diamond DA62 is also a strong contender to this. The twin Astro diesel engines at a measly 180 hp can loft seven people, or a useful load of 1,600 pounds, up to 160kts on 12gph TOTAL. High cruise speed is 190KTAS at 17GPH. Its a Baron 58 on steroids with the economy of a Mooney. On even cheaper fuel! Those numbers wouldn't be anywhere using an air-cooled gasoline engine without huge big-block 300hp+ TIO-550s sucking 20+ a side. The Astro's have a TBO of 1800hrs. I'm not familiar with Continentals, but a quick google search says the 550s TBO is 1700hours. The only downside to these new engines is the massive price.

I had very high hopes for the M10 injecting much needed capital into Mooney. If I had unlimited funds, I think a M20 with a ~180hp diesel engine would be an amazing combo.

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15 hours ago, N201MKTurbo said:

 

The bottom line is all these things you are talking about have been thought about and tried. Most decades ago. They offer very little advantage to our engines. If they did, they would have been incorporated a long time ago. Do you honestly think you are the first person to think of this?

No the reason they haven't been incorporated is because the FAA and lawyers ruin it for the rest of us. If aviation was cheaper, the Porsche Mooney would have been a viable if it were competitive in the market. Imagine if development would have continued from 1988 to today at an exponential pace without blossoming finances ruining it- we'd all be behind FADEC engines, but alas, we're stuck behind tractor engines that have less moving parts than a woman's vibrator but cost $50,000.

I'm no engineer, I'm no economist. I'm just a low-time, young private pilot with a passion for aviation just getting mad watching our industry wither away due to silly reasons while the auto industry is blossoming with laser headlights and hologram dash boards for the same price as a flying relic from the 50s.

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