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Why battery-powered aircraft will never have significant range

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John.Roo

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For aircraft that the mission flight time is under an hour, there are studies showing the electric propulsion system, even with current battery technology, could be even lighter than the piston internal combustion system. I agree, in current aviation that is a very small niche (some training perhaps, or short fun flying), but that can change as electric propulsion enables much easier development of VTOL configurations, and a personal VTOL aircraft could replace the car as commuting vehicle.
Sorry, I know I will repeat myself...

Electric propulsion actually makes sense in aerodynamically efficient airplanes (like gliders). We can also call it "short fun flying" - especially when weather is not perfect or pilot has no experience with gliding :) Unfortunatelly VTOL airplanes are far from "efficient construction". You need A LOT of power to lift vertically weight of airframe, propulsion (motor, controller, batteries etc..) and crew.

"Short fun flying" = flight arround 1 hour. But in real life this means to have capacity of batteries for at least 80-90 min.
Why?
Because:
1) you don´t want to have 0% reserve when you landing = safety
2) you want to have as long as possible lifetime of your bateries = economy.

Small glider like looking airplane will need battery with capacity arround 12 kWh (approx. 50 kg weight). Max. power for takeoff 24-30 kW (32-40 hp) will keep discharge rate on reasonable value of 2-2,5C. This is also good for battery life and no need for battery active cooling systems. For horizontal flight you have to stay at +-8 kW power.

With this parameters you can make "affordable" nice small electric one-seater for fun flying.

I am not experience with VTOL airplanes, but I am sure you need MUCH more energy to achieve 60 min. endurance = MUCH bigger battery, probably more motors and controllers and props and active battery cooling (large discharge rates). I would also recommend reasonable safety reserve. During takeoff (when batteries are fully charged) is all OK, however during landing = lower battery voltage also lower available power = more stress and very limited time to repeat landing.

That is my actual point of view ;)

Best regards!
Martin
 

Dusan

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Sep 15, 2014
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Canada
Unfortunatelly VTOL airplanes are far from "efficient construction". You need A LOT of power to lift vertically weight of airframe, propulsion (motor, controller, batteries etc..) and crew
You don't need A LOT of power for vertical lift if you have a lot of rotor disk area. If you don't care about the L/D than just have the design with oversized rotors, and the power reduces almost to nothing, fact demonstrated by AeroVelo Atlas, the first to win the Sikorsky Human Powered Helicopter Competition.

The problem is not hovering for an hour on a battery powered aircraft, it is very possible with the right design, but combining high hovering performance without affecting cruise performance, and that is very hard.

The problem with any VTOL aircraft design is that has conflicting requirements for the parameters that drives cruise and hovering performance: L/D drives the performance in cruise and that means large aspect ratio wings, low wetted area, careful design to minimise drag, and a small propeller size. On the other hand, hovering performance is driven by low disk loading and no flow interference, and that means large rotors and no wings.

The recent electric VTOL designs are getting wing-borne fast, sometimes under a minute, to minimise the time in hover and reduce energy needed for flight. Also you can have more laxed reserve restrictions if you can land anywhere.
 

John.Roo

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"If you don't care about the L/D than just have the design with oversized rotors, and the power reduces almost to nothing, fact demonstrated by AeroVelo Atlas, the first to win the Sikorsky Human Powered Helicopter Competition."
I understood we are discussing about 60 minutes electric flight outside of hangar ;)

You have probably some idea of "personal VTOL design" - that is OK.
Just think about the power you need for "...under a minute vertical takeoff..." and time necessary for "vertical landing procedure". Max. power you need + time will define capacity of batteries. Necessary capacity of batteries = some expected weight. You mentionned "with current battery technology" so you can calculate with +-200 Wh / kg.
And don´t underestimate power reserve. As I wrote - lower voltage = lower available max. power. I have personal experience with that.
"...more laxed reserve restrictions if you can land anywhere" - sounds like good example of last sentence before death :cool:

Please don´t take my comments like as a critique.
My point of view is a lot affected by 9 years of flying with electric propulsion. I really, REALLY like flying machines able to fly even if propulsion does not work ;)
Pole.jpg
 

Dan Thomas

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Sep 17, 2008
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5,555
I agree, just studies.
We've been fed a lot of bogus data from "studies" of all kinds. Studies are easy to commission by people who have something to gain from the right sort of results, and the studiers are often eager to produce the right sort of results. It can pay really well. At my age I inisist that the folks involved produce the real thing, not another study. We've been lied to far too often.
 

Noeson

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Sep 27, 2020
Messages
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Ontario has 250,000 lakes, and they are all within range of the amphibious e-Lazair 😀 It's on the first page of the Lazair owner's manual: DESIGNED AND CREATED IN AND FOR THE FLATLANDS OF ONTARIO.

We only how many lakes there are in Ontario because of the legendary Canadian Vickers Vedette - another good candidate for electrification and which, interestingly, was once owned by the Electric Boat Company!

Pic is of Ontarian flying Ontarian plane in Ontario.

ae-monohull.jpg
 

rbarnes

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Aug 28, 2015
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318
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Texas
We've been fed a lot of bogus data from "studies" of all kinds. Studies are easy to commission by people who have something to gain from the right sort of results, and the studiers are often eager to produce the right sort of results. It can pay really well. At my age I inisist that the folks involved produce the real thing, not another study. We've been lied to far too often.
 

Dan Thomas

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Sep 17, 2008
Messages
5,555
Some promising alternatives if any of us live long enough.
As usual, that article has a lot of "mights" and "coulds" and "long ways to go(s)." And 40% or 70% improvements. Yes, advances are being made, but they're still relatively small. We need advances in orders of magnitude, as we've seen in information storage. It will probably happen but, as both you and the article's author state, it might not be in our lifetimes.

I sure do appreicate the lithium batteries, though. I grew up with carbon batteries powering incandescent flashlights that were seldom more alive than dead. Cordless tools were unimaginable. Now I have cordless drills that lasted me a week of aircraft inspection panel removals and installations and other maintenance stuff, all on one charge. LED flashlights that run a LONG time on a pair of AA cells and have awesome light for my old eyes. Wonderful stuff.
 

Dan Thomas

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Sep 17, 2008
Messages
5,555
I assume we can fly 6 hrs with an electric plane that costs 20 k in two years.
Assumptions never built or flew anything. Two years ago we already saw some man-carrying quadcopters. Two years ago we could by an electric airplane. What makes you thing that another two years will bring a massive leap forward that produces a 6-hour range for a tenth of the cost of what we have now?

Battery technology has moved out of the realm of the backyard handyman and into the multimillion-dollar labs staffed by professional engineers and doctorates. There's a lot of pressure to come up with something spectacular that will make gobs of money, and yet it's slow progress. There's a reason for that, and assumptions won't fix it.
 
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