Why battery-powered aircraft will never have significant range

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tspear

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Oh for goodness sakes Saville, shushhhh ! You're letting the entire vaporware world know how we older folk quickly separate BS from reality, and if the Millennials figure out how our BS filter works they might change their tactics and be harder to spot.
Millennials do not have the cash; so these endeavors are pretty much all us old folk who bring in the whippersnappers to handle the video editing.

Tim (I could not resist)
 

tspear

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Multiple propellers as redundant for winged flight are not making much sense. If you replace one prop with 4 - having the same disk and blade area, the cords are halved, and so are the Re numbers, assuming same blade speeds. At small propeller size - as the Pipistrel - this have a pretty large impact on prop efficiency.
Everything is a compromise. Multiple props, depending on the location, and thrust can simplify the failure modes which need to be addressed. If you look at the Joby Aviation video, the symmetric thrust allows for pretty the failure of any one when VTOL, and if sufficient altitude, loss of multiple and conversion to forward flight and land like a fixed wing plane. I am not saying that is the solution they have used, but it is much easier to conceive then designing a system to handle auto-rotation.

Tim
 

rv7charlie

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Multiple propellers as redundant for winged flight are not making much sense. If you replace one prop with 4 - having the same disk and blade area, the cords are halved, and so are the Re numbers, assuming same blade speeds. At small propeller size - as the Pipistrel - this have a pretty large impact on prop efficiency.
Somebody forgot to tell the Lockheed C-130. ;-)

Seriously, what tspear says is correct, but disregarding that, the primary driver is physical dimensional limits. Most a/c already swing close to the largest possible diameter prop they can, while still maintaining adequate ground clearance. In the C-130 case, as HP has been upped over the years, they couldn't increase prop diameter any more so they've resorted to more and more blades to absorb the HP. It was never physically possible to use a single prop that's large enough in diameter to absorb the total HP required for the a/c.

It's not a question of dividing the area among multiple props; it's doubling, etc, the area while living within the diameter limits.
 
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dog

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Somebody forgot to tell the Lockheed C-130. ;-)

Seriously, what tspear says is correct, but disregarding that, the primary driver is physical dimensional limits. Most a/c already swing close to the largest possible diameter prop they can, while still maintaining adequate ground clearance. In the C-130 case, as HP has been upped over the years, they couldn't increase prop diameter any more so they've resorted to more and more blades to absorb the HP. It was never physically possible to use a single prop that's large enough in diameter to absorb the total HP required for the a/c.

It's not a question of dividing the area among multiple props; it's doubling, etc, the area while living within the diameter limits.
Was it Wilbur? or Orville? who figured that out.
 

Dan Thomas

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So there may be a market for the Recharging Plane that carries a generator set and flies from airfield to airfield to recharge electric aviation without spending for infrastructure improvements, and of course, a Bush version to land on sandbars etc. to take care of the country folk. Murphy Mega Moose?
I can imagine the Mega Cost of having that airplane come to recharge your batteries. Aviation is already too expensive. Sure is a lot easier to fill the tanks so you're never stuck somewhere.
 

Dan Thomas

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Oh for goodness sakes Saville, shushhhh ! You're letting the entire vaporware world know how we older folk quickly separate BS from reality, and if the Millennials figure out how our BS filter works they might change their tactics and be harder to spot.
They'd have to be older folks themselves in order to understand how we think, and even then it would be hard to fool us. We can spot baloney in older guys, too. No fool like an old fool...
 

Dan Thomas

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Multiple propellers as redundant for winged flight are not making much sense. If you replace one prop with 4 - having the same disk and blade area, the cords are halved, and so are the Re numbers, assuming same blade speeds. At small propeller size - as the Pipistrel - this have a pretty large impact on prop efficiency.
More props means you have more prop blade tip vortices to lose energy.
 

dog

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Evtol deal anounced now, where RR is building the motors/powertrain ,Honeywell is doing flight controls ,Solvay is doing the composites and they got a billion bucks for certification,oh and Microsoft is making fleet management sofware,whatever that is.

 

BJC

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Lots of grand pronouncements, and, if it can be believed, lots of money to spend. I’ll be impressed when someone actually delivers a commercial product that meets its performance and cost projections.


BJC
 

Vigilant1

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If you replace one prop with 4 - having the same disk and blade area, the cords are halved, and so are the Re numbers, assuming same blade speeds.

Somebody forgot to tell the Lockheed C-130. ;-)
Trivia nugget: the C-130 only turns the props at about 1020 RPM. So, despite having 13.5 ft diameter props, tip speeds are a very reasonable 740 fpm.
 

EzyBuildWing

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Quietest propellers and motors ever, from Joby! see vid below. .....this is a great advancement.

Mosquito helicopter converted to electric......22 minutes of hover-time........registered as a microlight in NZ......"best thing about it is not having a noisy 2-stroke" says the builder-pilot......worth reading the full pdf story (Link below):

".....Going electric offers so many more ways to make a good taxi trainer... " quote from Dan...

Taxiing a Pipistrel consumes about 3kW....... 20 seconds or so of full power and you're at 20' altitude.....then you just chop the throttle and the regenerative braking kicks-in and a moment later you've landed straight-ahead back down on the runway, ready to practice another "taxi, take-off-hop, taxi" .....no drama at all!
Ideal taxiiing, take-off and landing practice......and quiet Joby eProp means no noise-issues with anyone. Could do this all day on one charge!


 

Dusan

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Somebody forgot to tell the Lockheed C-130. ;-)
Ha - I specifically mentioned the size. C-130 propellers diameter is over 4meters, the blade chord is large enough to have Re number around 5,000,000. Halving the Re numbers at these values has a small impact on performance, probably under 5%. Pipistrel propellers are much smaller, and halving the cord, the Re number reduces to around 500,000. The L/D of the airfoil reduces by more than 30%. This is valid for any small aircraft, especially if having reduced tip speeds to reduce noise.
 

Andy_RR

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IMO the real problem with multiple propellers if you don't stow some of them is the efficiency at low thrust, i.e. in cruise, is very poor.

I guess you could get around this by slowing down and moving to coarse pitch or even feathering unused propellers so you can wind up the efficiency of the remaining driven props but it's still a loss-making enterprise. Electric flight doesn't stand for too much of that.
 

PiperCruisin

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Trivia nugget: the C-130 only turns the props at about 1020 RPM. So, despite having 13.5 ft diameter props, tip speeds are a very reasonable 740 fpm.
That is pretty reasonable, assuming you meant ft/sec or about 504 mph or mach 0.66 at SL. Thought they might be motoring a bit faster than that.
 

PiperCruisin

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This comes up all the time. So if gasoline has about 33.6 kWh/gal, this is about 12.4 kWh/kg. A typically AC ICE engine uses only about 12% 25% (thanks Dan)of that. Now we're down to about 1.5 kWh/kg. Still, the ICE engine and fuel is not light. At the current 0.24 kWh/kg, ICE has a significant advantage unless you are talking short trips (under 1 hour vs 4). However, if the technology gets above 0.5 to 0.8, then it starts to get interesting for our realm of flight. We're not there yet, but I'm not willing to say "never", but hopeful.

Another point that is often made is you have to carry the batteries with you the whole flight. My biggest worry is takeoff when I'm full of fuel. Cruise with full fuel vs low doesn't make a big difference to me.

Coincidentally, I'm working on a hybrid/battery project. Not aircraft. To me, some of the important details would be the electrical connections (overheating, contact, fatigue...from recent experience) and thermal management. Not to mention supply of everything as the world decides to electrify everything.

Then you have cost. The batteries and equipment are far from inexpensive. However, my 1930's technology cam wear issue basically cost me $30k after 600 SMOH.
 
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