# Why battery-powered aircraft will never have significant range

### Help Support HomeBuiltAirplanes.com:

#### John.Roo

##### Well-Known Member
And their numbers don't make sense. From Wikipedia:

"The 57 lb (26 kg) Siemens SP70D has a takeoff rating of 90 kW (120 hp) and 70 kW (94 hp) continuous. Utah-based Electric Power Systems provides the 92-kWh energy storage including battery modules, management and distribution."

• Crew: one
• Capacity: one passenger
• Wingspan: 38 ft (12 m)
• Wing area: 129 sq ft (12.0 m2)
• Empty weight: 1,460 lb (662 kg)
• Gross weight: 1,900 lb (862 kg)
• Powerplant: 1 × Siemens SP70D[21] electric motor with up to six lithium-ion battery packs, 115 hp (90 kW)
• Maximum speed: 135 kn (155 mph, 250 km/h)
• Endurance: 3.5 hours
• Maximum glide ratio: 20.6:1
• Rate of climb: 1,050 ft/min (5.3 m/s
How does a 92 kWh battery provide 3.5 hours endurance at 70 kW? How does a 1900-pound airplane get a climb of 1050 FPM on 120 HP? What sort of 38-foot wing gives a 20.6: L/D at 1900 pounds?

There's either some hidden magic, or a lot of mathematical deception. They built one airplane four years ago and flew it two years ago. Got 200 deposits. Are they waiting and hoping for a still-nonexistent battery a lot better than what they have? That's what the Harbour Air electric Beaver is waiting for.
I suppose that they are not planning to use max. cont. power all the time. 3,5 hours with 92 kWh battery means for example:
- Takeoff = approx 1,5-2 min. of max power 90 kW
- Climbing = 3-5 min. of 70 kW cont. power
- Cruise = 3,5 hours at 25 kW
In reality will be probably 3 hours cruise and small safety reserve.

I am just wondering what is weight of battery.
In case they use actually available cells will be 92 kWh =+-400 kg (880 lb).

So...
MTOM = 862 kg
EW = 662 kg

And in EW is included:
Battery = 400 kg
Siemens motor = 26 kg
Controller, wiring BMS... = 20 kg
Airframe... lets says = 220 kg

That looks realistically from my point of view.
EW will be probably bit higher (I would say that for pilots will be availabe +-180 kg). And during flight at MTOM 862 kg will be not easy to achieve 25 kW of power for horizontal flight, but with one light pilot....

#### Dan Thomas

##### Well-Known Member
Their estimate is based on low cruise consumption.

Their AR is just 12.....so 20,6 : 1 glide ratio may be a bit extented.

I'm trying to push my small under 70 kg planes limits and got 14,25 AR.....I might have now 20-24 L/D.
Still: where is the testing program now?

Even so, 1900 pounds on a wing of 129 square feet is 14.73 pounds per square foot, heavier than a lot of light aircraft. I don't see it flying along at very low power--25 kW or whatever (that's 33 HP) on that loading. None of the REAL airplanes I flew since 1973 ever had any performance even half of that.

And your designs are just designs, not real airplanes. Anyone can do that and come up with unrealistic figures. Unfortunately, physics ALWAYS has the last laugh. Seen that plenty of times in the last 47 years.

HBA Supporter
Flux Capacitor

#### Topaz

##### Super Moderator
Staff member
Log Member
L/D is dependent on span and equivalent drag area of the airframe. The aerodynamic performance numbers on that page are questionable or "optimistic" at best. The battery performance numbers are "unobtainium" with current technology.

#### John.Roo

##### Well-Known Member
Still: where is the testing program now?

Even so, 1900 pounds on a wing of 129 square feet is 14.73 pounds per square foot, heavier than a lot of light aircraft. I don't see it flying along at very low power--25 kW or whatever (that's 33 HP) on that loading. None of the REAL airplanes I flew since 1973 ever had any performance even half of that.

And your designs are just designs, not real airplanes. Anyone can do that and come up with unrealistic figures. Unfortunately, physics ALWAYS has the last laugh. Seen that plenty of times in the last 47 years.
Well.... I agree that TakeOff with MTOM 1 900 lb with 33 HP would be nonsence. However do you really think that to stay in horizontal flight at best L/D speed, with 33 HP and with 15 lb/ft2 wing load is not possible?

Airplane on video has wing span of 10,6 m (35 ft). MTOM 600 kg (1 322 lb). And I need far below 20 kW to stay in horizontal flight. Even with two pilots aboard (on video I fly alone).

With 15 m wing span I need 11-12 kW to stay in horizontal flight with two pilots aboard.
But that is "motorglider" configuration so it is really efficient.

Certified electric trainer Pipistrel Velis (wing area 9.51 m2 = 102.4 sq ft) needs also below 20 kW to stay in horizontal flight at MTOM 600 kg (13 lb/ft2). Honestly - when I had opportunity to test it it was take off weight over 600 kg - I am "normal" size (220 lb) pilot

#### n45bm

##### Well-Known Member
The weight and length of those extension cords will limit your altitude and range.

#### Speedboat100

##### Well-Known Member
I suppose that they are not planning to use max. cont. power all the time. 3,5 hours with 92 kWh battery means for example:
- Takeoff = approx 1,5-2 min. of max power 90 kW
- Climbing = 3-5 min. of 70 kW cont. power
- Cruise = 3,5 hours at 25 kW
In reality will be probably 3 hours cruise and small safety reserve.

I am just wondering what is weight of battery.
In case they use actually available cells will be 92 kWh =+-400 kg (880 lb).

So...
MTOM = 862 kg
EW = 662 kg

And in EW is included:
Battery = 400 kg
Siemens motor = 26 kg
Controller, wiring BMS... = 20 kg
Airframe... lets says = 220 kg

That looks realistically from my point of view.
EW will be probably bit higher (I would say that for pilots will be availabe +-180 kg). And during flight at MTOM 862 kg will be not easy to achieve 25 kW of power for horizontal flight, but with one light pilot....

I counted with Tesla batteries that to be 550 kg.

#### Speedboat100

##### Well-Known Member
Still: where is the testing program now?

Even so, 1900 pounds on a wing of 129 square feet is 14.73 pounds per square foot, heavier than a lot of light aircraft. I don't see it flying along at very low power--25 kW or whatever (that's 33 HP) on that loading. None of the REAL airplanes I flew since 1973 ever had any performance even half of that.

And your designs are just designs, not real airplanes. Anyone can do that and come up with unrealistic figures. Unfortunately, physics ALWAYS has the last laugh. Seen that plenty of times in the last 47 years.

I have an 50 years experience on designing and studied fluid dynamics at the university.

Don't bash me like you did Peter Muller.

I have a flying model of my small motorglider...and it is terrific.

#### John.Roo

##### Well-Known Member
I counted with Tesla batteries that to be 550 kg.
With standard SONY VTC6 18650 cells we achieved 35 kwh / 150 kg. It means 4,28 kg / 1 kWh. Incl. cases, but with no active cooling.
4,28 * 92 = 394,3 kg... That was year 2018.
I really hope for at least 10% better numbers in 2021

#### John.Roo

##### Well-Known Member
FES is also OK - simple, nice and low drag solution
I just like to have possibility of in flight adjustable prop because I still beleive that it can help to increase efficiency.

#### henryk

##### Well-Known Member
can help to increase efficiency.
=+30 % of thrust force...(CR Differential reductor 3: +/- 1 )

=both propellers can be "feasered"...

#### Attachments

• 472.2 KB Views: 9

#### Dan Thomas

##### Well-Known Member
I have an 50 years experience on designing and studied fluid dynamics at the university.

Don't bash me like you did Peter Muller.

I have a flying model of my small motorglider...and it is terrific.
Please state your actual aviation experience. Which pilot licenses and ratings and so on. What homebuilt projects.

Real airplanes don't have the performance of the typical model. They just can't get the same power-to-weight ratios unless they have the same endurance of about five or ten minutes or so. Besides that, there are other limitations to scaling-up that the experts in aerodynamics here can explain.

Last edited:

#### mcrae0104

##### Well-Known Member
HBA Supporter
Log Member
I have an 50 years experience on designing and studied fluid dynamics at the university.
Designing buildings is not the same thing as designing airplanes. It helps when visualizing and communicating graphically, but aircraft design includes a number of different skill sets. Please don't take this as bashing; I do the same thing for a living (though not quite for 50 years). I do agree with you that "design thinking" as a framework for problem solving is helpful and can be applied to a wide variety of endeavors. However, @Dan Thomas is right that real aviation experience does matter a lot in aircraft design.

#### Fireflyer228

##### Member
Rolls-Royce in the all electric game

#### BJC

##### Well-Known Member
HBA Supporter

Target: Last half of this decade.

BJC

#### sigrana

##### Well-Known Member
It seems to me as nobody has though about reality. Unless batteries will weigh much less than a half of the fuel load on any aircraft, their use is already unrealistic. Add to it that producing those batteries is and will cost far more than they will ever be able to recoved, Their production will need power and components mostly generated by the use of combustible fuels and oil derivates or transformations, which mean energy losses..... Even if I am aware that nearly 60% of the world pollution is generated by airliners, I do not see how it will be possible to substitute them with electrical aircraft. Do not forget as well that the batteries do not last forever and they loose capacity after every re-charge.

#### Dusan

##### Well-Known Member
It seems to me as nobody has though about reality. Unless batteries will weigh much less than a half of the fuel load on any aircraft, their use is already unrealistic. Add to it that producing those batteries is and will cost far more than they will ever be able to recoved, Their production will need power and components mostly generated by the use of combustible fuels and oil derivates or transformations, which mean energy losses..... Even if I am aware that nearly 60% of the world pollution is generated by airliners, I do not see how it will be possible to substitute them with electrical aircraft. Do not forget as well that the batteries do not last forever and they loose capacity after every re-charge.
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.

#### BJC

##### Well-Known Member
HBA Supporter
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.
Yup, studies.

BJC