Electric planes

[MontyFloyd]

Not only fighters are limited in frontal size. Airliners are sized to an optimum frontal plane themselves.

Ever consider why passenger aircraft are a tube is because it is the best design for a pressure vessel?

There are plenty of non circular fuselage designs that worked just fine.

@Earl showed great examples.

Another great example it is for pressure the fuselage is round.
Boeing 377 Stratocruiser is a "double bubble", that dimple in middle not effect its performance, but allowed for pressurized comfort.

 

[wooter]

Ever consider why passenger aircraft are a tube is because it is the best design for a pressure vessel?

And when we have electric planes, they're not pressurised anymore?

 

[wooter]

I can show you some with no body - everything is in the wing.

Sure, but none of them transported passengers or cargo.

Then there are these:

View attachment 1017497

View attachment 1017500

Although one can argue how successful some of them were.

Check the front profile.

The front is what the air sees, and the more space the front takes, the more air needs to move out of the way, and the more energy it requires to move through the air.

The same principle that makes a Model X less efficient than a Model Y, and an Y less efficient than a Model 3 on the highway is at play here: the greater the air displacement, the more energy is required.

 

[UkNorthampton]

Electric planes will nibble at the edges for a while (perhaps freight & cheap to run trainer - especially in UK or other places where there are high fuel taxes),

I think about Heathrow, it has limited operating hours due to

1. Noise from arriving/departing passengers vehicles on nearby roads
2. Aircraft noise
3. Pollution from above

Landing slots are in short supply.

I'm not even sure that freight is a big part of Heathrow operations, but it serves to illustrate for other locations.

1. Freight can be delivered to airports within existing time limits, preferably a little earlier. A few large HGVs (trucks) are less noise/pollution than dozens of ICE buses & cars. Heathrow is within London's ULEZ - ULEZ and eventually might be subject to specific congestion zone charges or restrictions.
2. Electric planes should ideally be quieter than combustion aircraft for take-off & landing (aerodynamic noise, ducted power).

Due to less annoyance to residents, a compromise might be reached where the last few landing slots become electric only plus extending slots a little longer (electric only). As electric planes become more capable, this electric-only quieter zone can be extended - economically favouring electric.

So, I'm suggesting that electric planes should emphasise quietness (propulsion & aerodynamic) initially. This probably means a slower takeoff/landing, slower cruise speed. I'm hoping that the economic benefits including cheaper and extended slots helps adoption. The slower cruise speed may be less of a problem with freight, again possibly helped by more slot availability.

Weight limits on electric probably means that low density, high value cargo is best suited such as packaged mobile phones. Heavy phone, little booklet, plenty of padding. There are even better use cases.

Power required to take off seems to be a limit. At slow speeds - are electric motors driving the wheels better for the first part of the acceleration (and doubling as secondary brakes/less brake wear)? Certainly quieter than a ducted fan at the start of takeoff. This might allow the in-flight propulsion to be optimised a little better (more aggressive angle of attack on propellers or fans). I'm assuming that driven wheels would consume less power than propellers/fans.

Now we get to lower cruising speeds - better aerodynamics would help, removing passenger windows & other features probably allows optimisations. Otherwise, electric would probably make sense overall in many cases, but the slower transits would be a drag on economics otherwise.

 

[EVer Hopeful]

Well, once they changed the ejection seat to go upwards . . .

 

[fhteagle]

And when we have electric planes, they're not pressurised anymore?

The 787 uses electric compressors to provide cabin pressurization and conditioning. So the tech is ready. Boeing claims increased efficiency from this setup as well, versus standard turning engine bleed air + air cycle machine conditioning systems.

Why does the Boeing 787 use Cabin Air Compressors (CACs)?

What are the advantages of this new air conditioning system compared with the traditional engine bleed systems? More engine output power, or easier adaption to future aircraft design?

aviation.stackexchange.com

Biggest issue right now is the electric planes that are actually for sale are too small to be able to afford the weight of the compressor, conditioning, let alone the seals and pressure vessels. As the expansion upwards into 6-20 passenger sized craft occurs, the pressurization trade offs start to pay off more. For example, Bye Aerospace eFlyer 800 advertises a ceiling of 35000 feet, which most certainly requires pressurization.

Bye Aerospace Unveils 8-Seat All-electric eFlyer 800 - Bye Aerospace

Bye Aerospace Unveils 8-Seat All-electric eFlyer 800 Safran to Support Propulsion Design DENVER, Colorado – April 22, 2021 – Bye Aerospace has announced an eight-seat all-electric twin turbo-prop class airplane, the eFlyer 800™, in response to growing demands for regional all-electric airplanes...

byeaerospace.com

 

[wooter]

Adding electric motors to the wheels is adding more weight. Does the acceleration gained from direct traction on the ground offset the weight penalty?

I like to think out of the box but flying is all about mass, drag and energy, together with long standing rules. Current electric airplanes are for instance not allowed to regenerate energy, so they're still stuck with air brakes and wheel brakes, or to use the rudder and ailerons to slow down. But how much energy can be recuperated by regenerating?

 

[wooter]

The 787 uses electric compressors to provide cabin pressurization and conditioning. So the tech is ready. Boring claims increased efficiency from this setup as well.

True, but the claim was that the tubular design was because it's the most practical way to pressurise a vessel, and I questioned then if electric airplanes didn't need to be pressurised anymore. Of course they will, and that will also be a driver in the shape of the airplane.

 

[Etna]

Power required to take off seems to be a limit. At slow speeds - are electric motors driving the wheels better for the first part of the acceleration (and doubling as secondary brakes/less brake wear)? Certainly quieter than a ducted fan at the start of takeoff. This might allow the in-flight propulsion to be optimised a little better (more aggressive angle of attack on propellers or fans). I'm assuming that driven wheels would consume less power than propellers/fans.

Powered wheels are indeed beneficial in electric aircraft for taxi operations, because the propellers have very poor efficiency at those low power levels, and wheels can regen from multiple stop and go's. The energy savings obtained from powered wheels yield a corresponding battery weight saving that is higher than the system weight, thus a winning trade. Operationally they also provide key advantages such as safe pushback from confined spaces without fear of propwash FOD.

For takeoff there is no benefit. The system weight would be orders of magnitude higher due to the higher power requirements. Moreover, acceleration on contaminated runway surfaces will be problematic. For quiet takeoff operations, the propellers can operate at lower rpm and be very quiet, and electric motors can still provide a lot of power at lower rpm contrary to turbine engines. Takeoff distances will still increase substantially but since a turboprop aircraft typically uses a fraction of the available runway distance, it won't be a limitation at most airports.

 

[fhteagle]

Tube fuselage does spread pressurization loads fairly well, that's true. But it's also popular due to manufacturing simplicity, ease of modifying the design with a stretch plug, etc. Airport terminals are optimized for the low width of the nose near the building, and would have to be completely rethought to handle flying wing or blended wing body (BWB) designs.

Aerodynamically, tube and wing is not the most efficient out there, not by a long shot. I saw posts in this thread a bit back trying to argue that it makes the least frontal area, but that's only one factor in aerodynamic efficiency. How smoothly the cross sectional area increases and decreases ("area rule geometry") matters at least as much, if not more than, total cross sectional area seen in a front view.

Blended wing body (BWB) is more efficient for subsonic flight, despite the higher front view area. BWB does suffer from more "wetted area" skin friction drag, but because more of that area is contributing to lift it more than cancels that downside out. The biggest reason you don't see them produced by Boeing, Airbus, Bombardier, etc yet is that BWB is much harder to manufacture cheaply.

As fuel costs will continue to rise, at some point someone will have to break open the BWB design to get the efficiency they've been leaving on the table.

 

[Earl]

Sure, but none of them transported passengers or cargo.

Sure, but the ones you showed weren't electric powered. The point you're missing is that, if electric propulsion is impossible with the current design paradigm, they may require different design decisions.
I don't proclaim to know what decisions may work, and certification lock-down may not permit any great excursions from the norm so we may be out of luck, but we should be open minded.
I'll also add that, while wings need to be thin for low drag, they do have some thickness. Today, that is used to carry fuel but, with flying wings, it would carry payload as well.

 

[MontyFloyd]

Sure, but none of them transported passengers or cargo.

Sorry to prove you wrong. CBY-3

There was also an experimental cargo glider version, the XCG-16

 

[wooter]

Sorry to prove you wrong. CBY-3

Burnelli CBY-3 - Wikipedia

en.wikipedia.org

Despite a trouble-free test program and glowing accolades from the press and industry observers, no production orders resulted

All the arguments why flying tubes are most interesting for airlines and airports still hold. The most successful electric airplane will be the one that fits in these parameters, just like the most successful electric car fits within the world of cars with combustion engines, and the most successful autonomous driving car will be the one that fits within a world of cars with human drivers.

 

[MontyFloyd]

All the arguments why flying tubes are most interesting for airlines and airports still hold.

It will be the one that offers the lowest operating cost, shape is meaningless.

Probably will see the Short Sherpa return in electric version for short haul flights. This design is perfect for a conversion.

 

[jerry33]

It will be the one that offers the lowest operating cost, shape is meaningless.

Probably will see the Short Sherpa return in electric version for short haul flights. This design is perfect for a conversion.

Have you ever ridden in the rear seat of one of those? Permanent turbulence. No, I didn't require the bag, but it wasn't for lack of trying on the plane's part. The seats rotate around the wing's axis.

 

[MontyFloyd]

Have you ever ridden in the rear seat of one of those? Permanent turbulence. No, I didn't require the bag, but it wasn't for lack of trying on the plane's part. The seats rotate around the wing's axis.

Ever rode in a DC-3?
OTOH, what about the slab sided B-24?

Happen to know what altitude the Sherpa flight was at?

 

[jerry33]

Ever rode in a DC-3?
OTOH, what about the slab sided B-24?

Happen to know what altitude the Sherpa flight was at?

Sorry, it was over 25 years ago.

 

[ThomasD]

I had the pleasure or torture of flying in a C 130 once.

 

[bxr140]

I had the pleasure or torture of flying in a C 130 once.

The electric one?

 

[ThomasD]

Thet were like these