Why battery-powered aircraft will never have significant range

Homebuilt Aircraft & Kit Plane Forum

Help Support Homebuilt Aircraft & Kit Plane Forum:

S

SvingenB

I compared 2 power-plants, similar power, electric vs internal combustion engine (ICE). The result I condensed in the following graph:

View attachment 68958

The electric motor weight is only a fraction of the weight of the ICE. The graph sows that for short trips the weight of electric motor + batteries is smaller than for the ICE + gas. It seems that for aircraft specifically designed for short trips, under an hour, it makes sense to go fully electric.

I used values for real batteries you can buy and weight data from engine and motor datasheets. The future batteries I expect to be better in the specific energy department so it makes sense to start investing in an electric power plant. The fact that an electric motor does need only a fraction of the cooling compared to an ICE, so reduced cooling loses and the fact that cowling can be more aerodynamic, reducing drag is not taken into consideration, and only can help.

I did this for a study on personal VTOL aircraft that could be used for commuting. For a VTOL aircraft there is a big difference in how much power is needed in hover/transition versus cruising. In this case an electric motor have also the advantage to be highly efficient even when needs to output only a fraction of it's maximum power.

More details about my project here: aliptera.com
That's interesting. As a glider tow pilot I have long been wondering about making the ultimate tow plane. With a range of 10-15 minutes, it should e possible to do 10+ tows in one charge. With an easy battery cartridge system, replacing the used battery with a fully charged one is done in seconds. The plane has to be purpose built for glider towing, max L/D at the right speed etc, and 2-300 hp or more. Up to 5-600 hp should be no problem, but probably overkill. The aircraft will of course charge on the way down, as a small-ish bi-effekt of steep descent, and will off-set some of the battery weight. It would be fun to optimize this concept.

The "proof of concept" have already been done by Siemens and Extra, although the Extra 330 must be a very un-optimal airframe.

[video=youtube_share;R4T7LZaMxI8]https://youtu.be/R4T7LZaMxI8[/video]
 

Dusan

Well-Known Member
Joined
Sep 15, 2014
Messages
166
Location
Canada
I don't get "lip wing". The Hiller duct is a duct, not a wing. The lip on the duct can increase lift somewhat, but usually the added duct weight is about the same so no gain.
The Hiller duct produced 40% of the lift. Considering that the weight of the VZ-1 Pawnee is 250 Kg, the duct produced 100Kgf lift. I do not know how much the duct weights but I think it is somewhat less than that. The problem with ducts is that they can be optimised only for a very limited speed range. This is because for certain airspeed, duct diameter and power setting the intake air stream has a certain convergence that needs to be matched by the intake shape. For example the Hiller VZ-1 duct is having a big bell-mouth shaped inlet designed to take advantage of the inlet high air convergence and so to provide as much static thrust as possible.

For a VTOL aircraft that transitions, and having a much larger speed range, the duct cannot have a big bell-mouth shaped inlet as it will have a lot of drag at higher speed. The lip wing changes the geometry of the inlet, having such a shape to extend the surface of the duct's inlet, creating a bell-mouth surface when it is placed adjacently to the duct, for the exact purpose of augmenting thrust in hover, similar to the big inlet of the Hiller platform. It is called a wing because during transition and horizontal flight it changes its relative orientation, to maintain an optimum angle of attack, to follow the reduction of intake air convergence as the aircraft speed increases, and creating lift as any regular wing does.

Hopefully this explains how the lip wing works and creates lift even in hover.
 

BBerson

Light Plane Philosopher
HBA Supporter
Joined
Dec 16, 2007
Messages
15,245
Location
Port Townsend WA
Ok, I see how the wing rotates up to duct. But it only wraps half way around.
I would caution. NACA/NASA found some tricky airflow around such wing and ducts at high angles in forward transition.
 

pictsidhe

Well-Known Member
Joined
Jul 15, 2014
Messages
8,812
Location
North Carolina
The lipwing looks like it will have a very aft centre of lift in hover. The fan will likely need moving forward quite a bit, which rather complicates where to put the crew with a single fan.

Renderware!
 

ToddK

Well-Known Member
HBA Supporter
Joined
Jan 13, 2016
Messages
512
Location
Shweaty Texas
On "The Grand Tour" Hammond crashed Rimac Concept One that promptly burst in the flames. For the next 5 days it would randomly catch fire. Had something to do with the damaged battery packs. Apparently this can and does happen with damaged electric vehicles. The batteries in an electric airplane should be easily removable for inspection and testing in the event of an occurrence that might have damaged them. It would really suck to go down hard in a field, drag your plane back to the hanger for repairs, then come back the next day to a smoldering heap of rubble.
 

pictsidhe

Well-Known Member
Joined
Jul 15, 2014
Messages
8,812
Location
North Carolina
Lithiums are a little touchy with how they are treated. Mechanical damage as well as incorrect charging/ discharging can cause conflagration.
 

karoliina.t.salminen

Well-Known Member
Joined
Oct 7, 2008
Messages
407
Location
Finland
This is reply to 5 min to launch, it takes less than minute to launch VTOL.
5 mins would involve hovering that the VTOL must not do, for safety and energy consumption reasons. In fact only 30 seconds could be enough to launch above the trees for transition to horisontal flight.
 

karoliina.t.salminen

Well-Known Member
Joined
Oct 7, 2008
Messages
407
Location
Finland
To continue, with electrics, the differential for cruise power and VTOL power can be high. Launch could be 700 hp and yet the cruise would be under 100, preferably no more than 50 hp. With electric motors this is not difficult, but normal, very much like Tesla which is cruised at low power, but insane amount of power is available for acceleration. I knew what to expect when test drove Tesla, but it still surprised me and left a grin that did not want to wear off. Similar power ratio is very much the case for a VTOL.
 

BBerson

Light Plane Philosopher
HBA Supporter
Joined
Dec 16, 2007
Messages
15,245
Location
Port Townsend WA
I would want to take off into a five foot hover, check the systems then climb vertically at 500 feet per minute to a minimum of 1000 feet agl before any forward transition to avoid overflying other properties while below 1000 feet. That would require about 2.5 minutes of high power. Then another 2.5 minutes should be reserved for an emergency descent and return to original home VTOL pad if needed. So 5 minutes of high power available needed, more or less.
 

cheapracer

Well-Known Member
Log Member
Joined
Sep 8, 2013
Messages
6,394
Location
Australian
On "The Grand Tour" Hammond crashed Rimac Concept One that promptly burst in the flames. For the next 5 days it would randomly catch fire.
So what, tens of thousands of electric cars on the road now not bursting into flames. While this is a fact, it's very rare and belongs in the anti-electric, crying wolf category, and nullified by knowledge.


I own a Tesla driven daily, I own a 110hp Geely EV driven daily, I own a local distributorship of various brand EVs and my after hours hobby is designing and building an EV of my own.

Here's some random facts.

Heavy use of electric motors burns energy at a fantastic rate, far more exponential than ICE. Last night I drove home at around 180 kmh for almost 20 minutes and used over 250kms of range for 50kms and the heat it produced had all the fans on the Tesla screaming away when arrived at the toll booth.

The range numbers car manufacturers quote is rubbish for real world driving and should not be used as a guide for your calculations. Generally if you get 2/3rds with normal driving you are doing well, 1/2 if you are a lead foot, and then there's the reduction of safety allowance for finding your next charge point (or landing point).

Pipistrel EP have about the right balance currently, no doubt they spent a lot of time and money researching their facts. So about 40 minutes real time plus landing plus safety margin is about it at the moment in a 'normal' 2 place aircraft. If they wanted more range then the battery weight, with the airframe weight to support the extra weights of both increase at a no gain sum, maybe even a loss.

Notice I said "normal". I believe you will see manufacturers eventually turning to delta/twin wings/biplane/flying wings etc to go electric. This enables carrying capacity and wing loading.

In SvingvenB's case of a tow glider, this is a more realistic use and I would be looking at a more powerful, cheaper aircooled DC motor, controller and batteries arrangement rather than a watercooled AC setup for short powerful events. Same for an ultralight also. DC rules for outright power bursts needed for take offs and climb. It's also a lighter package.

AC is best for normal car driving applications, don't be fooled it's best for aircraft use, there are clear advantages and disadvantages for both systems.

The biggest hurdle for anyone considering it is the obscene price of batteries, even in China the best I can do is around $300 USD per KWH. That's why there's lines of people wanting to buy used Nissan Leaf, Tesla and Chev Volt battery packs from crashed cars for their homebuilt projects.

EV West have a complete conversion kit including 25KWH of batteries for old VW Beetles, probably similar components to the Pipistrel setup, for $19,000 USD. 60% of that price is the batteries alone.

Quoting motor weights without batteries is patently ridiculous.
 

tspear

Well-Known Member
Joined
Feb 12, 2014
Messages
987
Location
Outside Boston
@cheapracer

I asked my brother who had a Nissan Leaf for three years, and switched to a Chevy Bolt. When he drives, he often gets very close to the "advertised" range. Usually within a mile or two; but then he often is doing basic cruising. Compared to his wife, who has a little bit of a lead foot. She often only gets about 2/3 of the advertised range....

Tim
 

BBerson

Light Plane Philosopher
HBA Supporter
Joined
Dec 16, 2007
Messages
15,245
Location
Port Townsend WA
The range of a Nissan Leaf also depends on the age. Could be 80% or less for an older Leaf. I looked into buying an older used one. But determined a new battery would far exceed the per mile cost of my old Honda CRX that still gets 50mpg and never needs parts beyond a tune up or occasional $80 CV joint that I replace myself.
 

cheapracer

Well-Known Member
Log Member
Joined
Sep 8, 2013
Messages
6,394
Location
Australian
@cheapracer

I asked my brother who had a Nissan Leaf for three years, and switched to a Chevy Bolt. When he drives, he often gets very close to the "advertised" range. Usually within a mile or two; but then he often is doing basic cruising. Compared to his wife, who has a little bit of a lead foot. She often only gets about 2/3 of the advertised range....

Tim
The 3 EVs I have now owned can only achieve advertised figures by quite gentle acceleration and staying under 50 mph/80kmh. I can't do that, I just don't have the patience.

But I was trying to relate it to aircraft use, you don't have a choice there, you have to be a leadfoot, relative, to get airborne and/or climb.
 

Doggzilla

Well-Known Member
HBA Supporter
Joined
Jun 2, 2013
Messages
2,352
Location
Everywhere USA
The 3 EVs I have now owned can only achieve advertised figures by quite gentle acceleration and staying under 50 mph/80kmh. I can't do that, I just don't have the patience.

But I was trying to relate it to aircraft use, you don't have a choice there, you have to be a leadfoot, relative, to get airborne and/or climb.
In the US we had to change our laws to more accurately represent the efficiency, which naturally reduced them by a significant margin. But still lightyears ahead of the competition, except the few small diesel cars available here, and only on the highway.
 

henryk

Well-Known Member
Joined
Mar 8, 2010
Messages
6,209
Location
krakow,poland

Doggzilla

Well-Known Member
HBA Supporter
Joined
Jun 2, 2013
Messages
2,352
Location
Everywhere USA
A limited production of 250 units began by mid 2013 and pricing starts at €111,000 (~ US$146,000). The Volkswagen XL1 plug-in diesel-electric hybrid is available only in Europe and its 5.5 kWh lithium-ion battery delivers an all-electric range of 50 km (31 mi),[2] has a fuel economy of 0.9 l/100 km (260 mpg‑US; 310 mpg‑imp) under the NEDC cycle and produces emissions of 21 g/km of CO2.[5] The XL1 was released to retail customers in Germany in June 2014.
How in the hell did I miss that? Very impressive car. Hopefully they will produce more in the future.
 
Top