Forget electric flight propulsion for a minute. Electric *taxiing*???

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henryk

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-off top=
=I was exploating thri CITROENs AX 1.5D....>400 000 km each ...

=NEVER oil (not syntetic) change, ONLY fulfil sometimes !
 

BBerson

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pfarber

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Lots of erroneous statements / incorrect info being posted here.

Here is what the experts say about engine oil: https://www.lycoming.com/sites/default/files/SI1014N Lubricating Oil Recommendations.pdf

See page 15 for minimum engine temperature for takeoff https://www.lycoming.com/sites/default/files/(L)IO-360-M1A Oper & Install Manual 60297-36.pdf


BJC
Did you read table 1?

It recommends 20W50 for 0c to 32c 50weight!!! Thats like running tar for oil. A modern car uses 0w-20 or 5w-30 at most. A 2020 F150 runs 5w-30. 20W50? Thats molasses. An a main bearing clearance in a Lycoming is the same .001-.003 as a car motor.

I've never sat and waited for oil temp to be in the green. Most oil temp guages are just a green bar and the pointer in GA AC, and there is no way to control oil temp.. you get what you get. Even 'page 15' basically says.... 'as long as the engine is working, the oil temp is fine!'
 

Dan Thomas

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Did you read table 1?

It recommends 20W50 for 0c to 32c 50weight!!! Thats like running tar for oil. A modern car uses 0w-20 or 5w-30 at most. A 2020 F150 runs 5w-30. 20W50? Thats molasses. u get. Even 'page 15' basically says.... 'as long as the engine is working, the oil temp is fine!'
You obviously do not understand the function of multigrades.

A 20W50 oil is an SAE 20 oil with viscosity modifiers. It's an SAE 20 at low temperatures. 15W50 is an SAE 15.

A car engine IS NOT an airplane engine. I've lost count of the times I've had to say that. The car engines of today have very small clearances, and bearing clearances of .003" would be a worn-out engine. Furthermore, aircraft engines are air-cooled, and cylinder wall temps and oil temps get a lot higher than in a car. Typical max oil temp is about 275°F. A car's will never get near that. The aircraft engine runs at 65 to 100% power, all the time. A car will seldom see even 75 or 80%, and then only for a few seconds. The aircraft engine's clearances are larger. You start putting lightweight auto oils in an aircraft engine and it will soon beat itself to death.

Get used to it. It's the way things are in aviation.
 
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wsimpso1

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My training has been:
  • 50W needs sump above 60F for start;
  • 40W needs sump above 30F for start;
  • If the needle is off the peg and the engine responds to the throttle, you are good to go.
I and partners operating that way for over 2000 hours on our engine, looked great inside when a cylinder had to come off.

As to electric taxi, I thought about it a while back. While I suspect it is doable by putting a motor on a wheel, there are drawbacks:
  • The motor and its control system adds weight, control system, and failure modes to the airplane;
    • If the motor is direct drive, it will be pretty substantial as it will be a low speed motor;
    • If the motor is geared to drive the wheel while running higher motor rpm, the motor can be smaller, but that adds weight, inertia, complexity and more failure modes to manage;
  • Landing has to spin up the wheel with the motor - force tire tread patch is not less than 25% of downward force on tire (old FAR Part 23 appendices C & D). The motor and other rotating hardware add substantial inertia to that wheel and thus add substantial braking effect at the wheel at touchdown;
  • Existing landing gear structures include these spin-up reactions for the existing wheel and tire. Increase the landing loads your gear legs with added inertia, and the gear legs may no longer be adequate to handle landing loads;
  • You most likely can not tolerate a asymmetric install because of the braking effect. Nose wheel or both mains…
  • Can we disconnect for landings?
    • We can stick a little one way clutch in, but then it will only drive forward - you lose the ability to back into parking, and some new landing inertia is still added to the wheel, and now you have more failure modes to manage, like asymmetric dis-engagement by the OWC;
    • We can put in a little clutch in to disconnect for landings, but a clutch of adequate capacity adds some weight, inertia, landing reactions, and such, so still has to be calculated and tested;
    • Then there are all of the failure modes that must be managed: locked motor/gearbox; seized clutch; electrical faults; etc.
This whole scheme seems like a net loser in GA, but might be worth the trip for larger airplanes. It would have to be very thoroughly examined and tested and maintained... I can see the NTSB hearing after a loaded bizjet veers off a runway and burns: "So what level of risk did you consider "acceptable" for the failure effect of asymmetric wheel lockup during landing?"

Billski
 
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Aesquire

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Electric taxi seems logical for an Airbus. Big turbines burn lots of fuel at idle.

Silly & dumb for a RV -x or Kitfox. Most reasons already listed above. Better to add pedals and a chain. still silly.

As to oil... Cylinder wall clearance on air cooled engines, with big diameter pistons, like a Lycosaur or Harley require a bit thicker lube than the small liquid cooled pistons on a 2 litre car engine. My Rav-4 uses 0W-16... B, no less, the newer later spec.


And 0W08 is coming! Faster warm up with engines that start & stop at EVERY STOP & even more often for hybrids. At a steady 60 mph on hilly upstate NY roads the IC engine shuts off and restarts every rise & fall.

Combine an engine that may be started, run for under a minute, then shut off, then restarted under a minute later, hundreds of times a day, with low tension/low drag rings & direct injection and you have a radically different environment for oil than my Cyclone ( 74 cubic inches air cooled, 100 hp ) with a carburetor.

Apples and oranges, indeed.
 

Aesquire

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Btw, after driving a Toyota Hybrid a few thousand miles, I'm both impressed by the clever programming used to save fuel, & convinced that the concept is a total waste of mass and money in a light plane.

An electric motor propelled airplane with a "range extender" or serial hybrid with IC or turbine engine, like a Diesel Electric Locomotive , might be useful if the Electric motors are used in a "non traditional" way. Like multiple motors or in a Mini-Imp pusher design with a motor instead of a heavy long drive shaft, or ...

And perhaps as a range extender for a "conventional" battery powered current generation plane, like the Pipistrel electric trainers, but that's a kludge of complexity and extra weight to "fix" a range problem imposed by our still primitive technologies. Possible. But probably unwise. ( except for getting funding... )
 

tspear

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I disagree, range extender has many positive attributes to it.
1. Allows development of many other parts of the electric power train system. Including engines, prop including pitch control (if needed), battery management systems
2. Helps solve chicken and egg of when do you install chargers? No one buys a plane before there are places to charge it, no one installs a charger until there are planes needing it...
3. Allows usage of mass produced engines and practically eliminates vibration and other issues (think Billski's long explanations on torsional dampers).
4. Because the genset is somewhat (or should be) self contained, easier to design as a replacable unit if fuel requirements change (e.g. avgas to jet-a to biofuel).
5. The prop does not need a large cross section just behind the prop to hold the large ICE engine. Electric motors have much smaller cross sections.

There is probably more. But I think you get the idea. The downside, is a loss in efficiency, and depending on intent, sacrificing performance in some manor.

Tim
 

Dan Thomas

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The downside, is a loss in efficiency, and depending on intent, sacrificing performance in some manor.
And weight gain. Significant weight gain. That cuts into utility as well as performance. Then there are the multiplied failure points that reduce reliability and safety.

Complexity has to be intelligently managed, or it will manage you.
 

Tiger Tim

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What would happen with snow on the ground?
What do you do when you want to fly a Piper Cub but there’s a thunderstorm over your airport? It’s not the right time to use it so you don’t. Maybe motorized wheels never have a right time but a single case of inconvenience shouldn’t be enough to shoot down an idea.

I can’t imagine a practical case for you or I to have an electric-taxi out system but I suppose if someone wanted to be ‘that guy’ they could claim a lot of media space by being the first.
 

Aesquire

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Going to a very different power plant offers unique benefits if you design around the perks. Possibly the best example is the small diameter of the electric motor, allowing less frontal area or better streamlined cowl. Much like V12 engines vs. Radials in the fighters from the 1930-1945 Era.

Less common in flight, so far, but everywhere in "brochure fantasy electric flying car buzzword" planes, including pretty pictures from NASA, is the Other perk for electric motors, the multi motor & remote propeller ( no long driveshaft & torsional vibes ) designs that are impossible or Very hard with gasoline engines.

Otoh, just replacing an IC engine with electric, while VERY SMART FOR DEVELOPMENT, ( see Pipistrel ) is suboptimal for efficiency and performance.

Philosophy might say use appropriate tech.

Thus an airliner likely to sit in ground traffic for hours ( not deliberately but it's too common ) is a perfect candidate for the extra mass and complexity for electric taxi. But a RV-12... not so much.
 

tspear

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And weight gain. Significant weight gain. That cuts into utility as well as performance. Then there are the multiplied failure points that reduce reliability and safety.

Complexity has to be intelligently managed, or it will manage you.
Depends on the compromises made. e.g. if normally you need 300 HP for takeoff, and cruise at 60% which is 180HP. An IO390 producing 200HP turbo normalized, with a generator weighs a lot less than an IO-540. (I am assuming a roughly 20HP efficiency loss converting to electric and back to mechanical, and only carry enough battery for climb to altitude and maybe a little reserve, with no recharge in the air at normal cruise).


Tim
 

Dan Thomas

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Depends on the compromises made. e.g. if normally you need 300 HP for takeoff, and cruise at 60% which is 180HP. An IO390 producing 200HP turbo normalized, with a generator weighs a lot less than an IO-540. (I am assuming a roughly 20HP efficiency loss converting to electric and back to mechanical, and only carry enough battery for climb to altitude and maybe a little reserve, with no recharge in the air at normal cruise).


Tim
An IO-390, depending on model, weighs a few pounds either side of 300. The IO-540 models range from about 370 to 448 pounds. Now, how much does a generator capable of producing 200 HP weigh? And how much do the batteries weigh? And how much does the electric motor weigh?

In the end, if we figure on 90% efficiency for the generator, we get only 180 HP out of it, a long way from the 300 HP that the 540 can give us. And we lose efficiency at the motor as well, shoving in 180 HP and getting less than that our of it. One needs to put more than 200 into it to get 200 out. It's not 100% efficient. So the batteries need to supply more than 100 HP for some time. Significant battery weight, I'd say. And how do we recharge them in flight if we're using all the power from the IO-390 just for cruise?

Not apples-to-apples at all, is it? If we want 300 HP and have the aircraft weight that needs 300 HP, then we need 300 HP, and have to suffer all the hybrid-system losses that go with that.
 
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rv6ejguy

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I believe Airbus evaluated an electric motor driven nose wheel a few years back and it may be implemented on future designs. Ground emissions and fuel savings make this attractive. Airbus used a powered nose wheel on their electric E-fan.
 

Aesquire

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This isn't the "I want to put a Locomotive generator with a P&W turboshaft in my Firefly, and will ignore the 3200 pounds of heat exchanger needed to keep it from melting" or the "I look forward to the dilithium crystals that have been promised for next year for the last 6" or the "Electric planes might not annoy my neighbors so much, and I have realistic expectations about the technology" thread.

It's "can I save money, pollution, and noise by electric taxi?"

Like many things, Electric ground propulsion for an airplane is a matter of scale. A portable drill motor, a cable, handle, some brackets, and a skateboard wheel might work fine for rolling your Firefly out of the hanger and down the mile to the end of the runway and save you enough fuel to give an extra margin of safety on that "$100 hamburger run". A battery pack and motor out of a Tesla might be just the ticket for that 737 to wait out the long line at O'Hare during the Thanksgiving rush to pay for an executive bonus in fuel saving. ( and there's going to be a memo on using the APU to run the interior lights and AC more than 5 minutes an hour while the plane waits )

Neither of the above will make a good choice for a RV-12. The first is too slow, the second too heavy.
 

Tiger Tim

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I’m changing my stance. If you want to save fuel getting an airliner to and from the runway you may as well use an electric tug. Large tugs are often in the 50 ton-range and towbar-less examples already exist that can universally pick up the nose wheel of anything, which in turn saves on ground crew. Leave the batteries, motor, and driveline on the ground.
 
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