Why battery-powered aircraft will never have significant range

Homebuilt Aircraft & Kit Plane Forum

Help Support Homebuilt Aircraft & Kit Plane Forum:

Dan Thomas

Well-Known Member
Joined
Sep 17, 2008
Messages
6,050
I disagree battery+solar could give 6 + 6 hours flying time....in an efficient aeroplane....nowadays it don't have to look like Solar Impulse...as it is not soaring across the oceans.
Could. Might. Maybe. Possibly. Perhaps. Should. Lots of such terms in glowing journalistic pieces about alternative energy's advantages and capabilities. Those terms mean absolutely nothing if they're not based in solid facts. We are constantly bombarded by stuff like this in the media, written by writers who have no idea what they're talking about most of the time.
 
Last edited:

Jay Kempf

Curmudgeon in Training (CIT)
Lifetime Supporter
Joined
Apr 13, 2009
Messages
4,314
Location
Warren, VT USA
I have always said that eliminating the pink squish structures is the best overall way to simplify a design.
 

Jay Kempf

Curmudgeon in Training (CIT)
Lifetime Supporter
Joined
Apr 13, 2009
Messages
4,314
Location
Warren, VT USA
I disagree battery+solar could give 6 + 6 hours flying time....in an efficient aeroplane....nowadays it don't have to look like Solar Impulse...as it is not soaring across the oceans.
6 hours of battery and 6 hours of solar power in the same airframe? And carry a human. Well 6 hours of solar power is a HUGE amount of solar panels which is how you end up with an airframe like the solar impulse. And there is still the question of whether they really flew on solar power alone for all missions. In other words if you take off with full batteries and end with very little battery and used all the solar power that was available on the mission well then a lot of your flight was on batteries alone which is to be expected... Unless you are marketing solar flight around the world.

Again not much of a practical airplane for a reference. Pound for pound batteries are way better at putting watts per flight mile or hour than solar panels.

So how do you think you are going to get 6 hours of flight out of solar panels and 6 hours of batteries in the same practical airplane and what would you do with 12 hours of endurance? At the speeds you need to optimize around to do any endurance with electric power you end up being a spartan glider airframe and you fly just above stall so 40 knots? 12 hours at 40 knots is 480 nautical miles? Most small airplanes can do that same 480 nautical miles in two to 4 hours on not that much fuel in decent to complete comfort.
 

pictsidhe

Well-Known Member
Joined
Jul 15, 2014
Messages
8,812
Location
North Carolina
6 hours of battery and 6 hours of solar power in the same airframe? And carry a human. Well 6 hours of solar power is a HUGE amount of solar panels which is how you end up with an airframe like the solar impulse. And there is still the question of whether they really flew on solar power alone for all missions. In other words if you take off with full batteries and end with very little battery and used all the solar power that was available on the mission well then a lot of your flight was on batteries alone which is to be expected... Unless you are marketing solar flight around the world.

Again not much of a practical airplane for a reference. Pound for pound batteries are way better at putting watts per flight mile or hour than solar panels.

So how do you think you are going to get 6 hours of flight out of solar panels and 6 hours of batteries in the same practical airplane and what would you do with 12 hours of endurance? At the speeds you need to optimize around to do any endurance with electric power you end up being a spartan glider airframe and you fly just above stall so 40 knots? 12 hours at 40 knots is 480 nautical miles? Most small airplanes can do that same 480 nautical miles in two to 4 hours on not that much fuel in decent to complete comfort.
That's easy. A few little tweaks to the laws of physics is all you need.
 

Speedboat100

Banned
Joined
Nov 8, 2018
Messages
1,900
Location
Europe
6 hours of battery and 6 hours of solar power in the same airframe? And carry a human. Well 6 hours of solar power is a HUGE amount of solar panels which is how you end up with an airframe like the solar impulse. And there is still the question of whether they really flew on solar power alone for all missions. In other words if you take off with full batteries and end with very little battery and used all the solar power that was available on the mission well then a lot of your flight was on batteries alone which is to be expected... Unless you are marketing solar flight around the world.

Again not much of a practical airplane for a reference. Pound for pound batteries are way better at putting watts per flight mile or hour than solar panels.

So how do you think you are going to get 6 hours of flight out of solar panels and 6 hours of batteries in the same practical airplane and what would you do with 12 hours of endurance? At the speeds you need to optimize around to do any endurance with electric power you end up being a spartan glider airframe and you fly just above stall so 40 knots? 12 hours at 40 knots is 480 nautical miles? Most small airplanes can do that same 480 nautical miles in two to 4 hours on not that much fuel in decent to complete comfort.
It has to be very spartan airfame you are correct....good thing about batteries is that it needs no supercharger at higher altitudes....you might need some oxygen.
Even 3 + 3 would be good if the speed is right. Anyway Solar Impulse never used its whole capasity for speed..as it was charging the batteries for the night flying at daytime...it couldn't its engines were rated much smaller output than the airfame was producing electricity.
 

Jay Kempf

Curmudgeon in Training (CIT)
Lifetime Supporter
Joined
Apr 13, 2009
Messages
4,314
Location
Warren, VT USA
Your not listening.

3+3 is a simplistic way of looking at an electric/solar combo. It is going to be more like .125 + 3 solar to battery unless you have a football stadium sized solar array. No matter what you do. And that is assuming you can make a 3 hour endurance practical man carrying aircraft.

Really smart people with a lot of experience and resources are having a hard time with that. I've been up close and personal with a bunch of the practitioners, designs, analysis, yadda... and it isn't a simple problem. If you think you are going to build anything that can lift 2 humans, stay aloft at any speed more than an hour with reserve that fits in a T hangar you are in for some disappointment. Let's say the goal is 2 humans, 2 hours with reserve and it has to make it into the FAR 23 Normal Category. There's a real world benchmark. Find all that have built a 2 place airplane that have done that? Then go from there and start swapping out their components for your miracle batteries or propulsion efficiencies or your miracle structural fractions, or your miracle aero, or solar panels and see where you end up. Easy to do on paper just reverse engineering from someone else's performance numbers. Hardly requires an advanced math degree.

Then once that analysis has failed you can start increasing span, area, ????? to get there? And you end up right back at Solar Impulse with it's 747 dimensions and tiny weight budget and unique manner of defining solar around the world flight. And so it goes.
 

Speedboat100

Banned
Joined
Nov 8, 2018
Messages
1,900
Location
Europe
We'll se I am pretty far in my project and I just test the electricity..as the cells are very expensive. 10 m2 cell area ought to be able to sustain a flight....best new have 37% efficiency at high at noon that makes 5 kw continuos.

Elektra One manages to fly at 3 kw but is almost twice as heavy as my spartan ship. At high ( and I don't mean marihuana ) with suitable aerodynamics with longer wings it ought to soar at 150-200 km/h.

Where is the problem ?
 

Vigilant1

Well-Known Member
Lifetime Supporter
Joined
Jan 24, 2011
Messages
6,505
Location
US
We'll se I am pretty far in my project and I just test the electricity..as the cells are very expensive. 10 m2 cell area ought to be able to sustain a flight....best new have 37% efficiency at high at noon that makes 5 kw continuos.

Elektra One manages to fly at 3 kw but is almost twice as heavy as my spartan ship. At high ( and I don't mean marihuana ) with suitable aerodynamics with longer wings it ought to soar at 150-200 km/h.

Where is the problem ?
Could you briefly recap in one post:
1) The payload of this aircraft (mass)
2) The cruise power you will use (kw or hp)
3) The max takeoff weight of the aircraft.
4) the wingspan and wing are of this aircraft.
4) The no-lift drag (effective flat plate drag area) of this 150-200 kph aircraft.
 

Jay Kempf

Curmudgeon in Training (CIT)
Lifetime Supporter
Joined
Apr 13, 2009
Messages
4,314
Location
Warren, VT USA
So you are building a fragile single seat airplane with at least 10m^2 area and you think you are going to get 37% efficient cells that are more than your next several years salary to acquire IF and this is a big IF they exist outside of the lab and the company wants you to have them for your high profile R&D program with all the others that are in line ahead of you. And then IF you could build all that and get the structural fraction you need without and autoclave and the budget and knowledge to use it. Sure you can do it.

But it would still be a fragile impractical test craft without a market and you would end up the same price and practicality of your beloved Elektra One. Your words practical previously.

Have you ever seen an Elektra One or its solar brother? The composite guy that builds it is really quite a good practitioner. It would be hard to beat him. And I wouldn't call the Elektra One rugged or practical. It is maybe one small notch this side of spartan but probably makes the normal category with good margins. We tested one for a year. I know the design intimately. The solar panels didn't provide much in terms of range extending. Tiny fraction. And they weren't going to recharge the thing on the ground at any usable rate.

Define "far" into a project: is it one excel spreadsheet with unsubstantiated supplier data and wishful efficiencies?

TS100 rides again.
 

WINGITIS

Well-Known Member
Joined
Jun 24, 2020
Messages
449
Location
Wellington, New Zealand
Indeed it is hard to buy into the media hype as they wind into this project, BUT in their defense they certainly have the credentials!

This is one of the guys that started up Rocketlab, the company that launches satellites into space from here in New Zealand, including for the US DEFENCE department!!

So we will have to wait and see if they can actually do it.....!
 

Speedboat100

Banned
Joined
Nov 8, 2018
Messages
1,900
Location
Europe
Could you briefly recap in one post:
1) The payload of this aircraft (mass)
2) The cruise power you will use (kw or hp)
3) The max takeoff weight of the aircraft.
4) the wingspan and wing are of this aircraft.
4) The no-lift drag (effective flat plate drag area) of this 150-200 kph aircraft.
Payload is several times the craft mass...at least 150 kg so double the plane mass almost 2.5.
Cruise is 3-6 kw depending of the pilot weight.
Mtow is 300 kg...less if necessary.
Spanning 39 ft at AR of 15...yielding 9 m2 of wing area.
Flatplate area is really small ( 1-2 sqft ) as the gear is retracted..tail wheel is about 100 mm dia. Canopy is really small you can get 1 m2 solar panel area in addition to flight surfaces.

There are few points that make it tick...extremely well managed flow when engines are on...to mention one. Light weight structures are extreme...long wings are really light...yet strong.

It looks very good overall.....like something from the future.....almost a living thing....a flow machine. Reichelt planes are even more futuristic..this looks "normal" ...like something you discovered was there, but you had to spend 15 years to find it. Controls are simple...flaps 2/3 span.
 

pictsidhe

Well-Known Member
Joined
Jul 15, 2014
Messages
8,812
Location
North Carolina
The problem? In a nutshell, you can't count. 10m2 of 37% efficient cells is not 5kW anywhere on earth. That won't be your only error.

I'd also like to see how you are going to pay for 10m2 of GaAs cells, too.
 

Speedboat100

Banned
Joined
Nov 8, 2018
Messages
1,900
Location
Europe
The problem? In a nutshell, you can't count. 10m2 of 37% efficient cells is not 5kW anywhere on earth. That won't be your only error.

I'd also like to see how you are going to pay for 10m2 of GaAs cells, too.

Right...I am only saving the option for a later model..first and foremost I am building a 5-6 hr electric plane..that is fast.

Only way to test it to make it under 70 kg as it is twin engine plane I can fly it without a lisence....or it can be flown.

As under 70 kg it can only fly ½ hr tops.

Making it experimental would allow even 100 kg of batteries.
 

jedi

Well-Known Member
Joined
Aug 8, 2009
Messages
2,470
Location
Sahuarita Arizona, Renton Washington, USA
Hello!
If you planning to stay in UL (MTOM between 450-600 kg depending on EU country) than you should calculate with G forces range from -2G to +4G. That is with safety factor 1 so for airframe design you have to multiplied by min. 1,5. For new construction I would not go below safety factor 1,875 and for main parts (wing, tail surfaces etc.) better use safety factor 2-2,25.
However, if your design looks more like a glider (with with high aspect ratio) then better use range for gliders = G forces from -2,65G to +5,3G. And than again you have to use safety factor.
Finally you will find out that you have to calculate with ultimate loads a least from -5G to +10G.
Take a look here:
https://www.easa.europa.eu/sites/default/files/dfu/CS-22_Amendment 1 revised.pdf
(from page 1-C-1)
Best regards!
Martin
Or design a balloon and you only need 1.5 G strength. Better yet the anti gravity flying machine only needs 1 G for when it is unpowered,
 

Dana

Super Moderator
Staff member
Joined
Apr 3, 2007
Messages
9,931
Location
CT, USA
Why do you limit research to 118 elements. There are billions of molecules!
Because it's the chemical bond strength of the atoms in the molecules that matters. And that's something that's well understood, with no breakthroughs even remotely likely.
 

WINGITIS

Well-Known Member
Joined
Jun 24, 2020
Messages
449
Location
Wellington, New Zealand
Ok here are my initial calculations for the KEA ATMOS

It weighs 90KG including the 10KG payload

Span 32 Meters, 105 Feet

Chord is 6 Feet by my calcs off a rendered image they show.

Its max speed is 60 Knots.

At 60,000 feet, 5000 below its ceiling, it needs an airfoil/wing with an average lift of 0.275 CL across its entire span to fly level.....

That seems likely to be able to occur, more or less!

Perhaps someone should check my calculations!

KevinKEA ATMOS LIFT.pngKEA ATMOS SPECIFICATIONS.png
 

blane.c

Well-Known Member
HBA Supporter
Joined
Jun 27, 2015
Messages
4,839
Location
capital district NY
Or design a balloon and you only need 1.5 G strength. Better yet the anti gravity flying machine only needs 1 G for when it is unpowered,
Anti gravity would uncouple you from attraction to all other body's of mass in the universe, you quickly would drift aimlessly at the whim of earths air currents until reaching an altitude that would cause you to freeze solid before an eternity in the void of space. That is of course if you could get gravity to disassociate itself from time, an unlikely probability. Perhaps a gravity distortion or time machine is more likely.
 

WINGITIS

Well-Known Member
Joined
Jun 24, 2020
Messages
449
Location
Wellington, New Zealand

It's actually been designed, built and tested more than once. Higher altitudes are possible as well. The aero and power budgeting is well known for HALE aircraft and there are a few players working on that particular design point. Spent some time working for one of those players a few years back. Far from a practical man carrying corner of the flight envelope though.
Heres the Boeing Solar Eagle:


Cancelled in 2012 after many millions spent, likely actually went dark!
 
Top