Every time I hear of an all electric aircraft of any size, I always wonder what they’re going to do about landing weight.
Every modern transport category jet has a higher takeoff weight than landing weight, because of the simple unavoidable fact that landings are rougher than takeoffs. Taking off, the load gradually comes off of the landing gear, on landing it’s suddenly applied. Jets burn tons, literally tons, of fuel enroute, so they’re considerably lighter on approach. It’s why aircraft have dump valves to jettison fuel overboard in case of forced landing early in the flight.
Batteries don’t get lighter as they’re discharged, so…?
The same way we make bigger aircraft with higher landing weights: beefier landing gear and structural reinforcement. Airliners don’t have a lower max landing weight than takeoff because they have to, they do it because it’s cheaper and more efficient. Add some more structural weight and you lose some payload, but if the efficiency gains from fuel cost savings make it worthwhile, then manufacturers will make them.
That’s true regardless, batteries will never power intercontinental wide-bodies (short some major new developments in battery design). This will probably reduce the maximum aircraft size where batteries remain viable, but they are obviously very viable for short hops in small jets, the point where they cannot compete is somewhere but it’s not “never”, even with this limitation.
That all said, maybe someone will explore just dropping batteries along the way? It sounds ridiculous, but it also sounds like something we have the tech to solve…
It’s a bigger deal on bigger aircraft, but on mid-size narrow bodies it’s not as much of a problem. A 737, depending on the model, only has a difference of about 20-30k lbs between MTOW and MLGW and no fuel dump capability. An overweight landing isn’t really a big deal in one, just a quick maintenance inspection. Closing the gap so MTOW and MLGW are equal is doable. It’s hard to overstate how huge of an expense fuel is to an airline, if they have to lose some passengers and cargo they would absolutely do it if it got rid of the fuel expense.
Of course all that is contingent on having batteries with enough energy density to get somewhere close to current MTOWs while having something of a useful range.
Blown wings are basically powered lift. You’re planning on bringing a civilian passenger plane down final approach at a speed it can’t glide at if the power plant fails?
I could see that for a carrier based aircraft where STOL is a factor but no you’re not doing that in airline operations.
You can rethink the engineering with electric motors.
One of the other limitations is that you’re stuck with propellers if you’re using electric motors, so your top speed is going to be significantly slower than jets. Unless you do the Tu-95 thing with contra-rotating props whose tips exceed the speed of sound, and then you have monstrous noise problems.
That’s ridiculous. No one on final gives a crap about take-off weight. What you need is a ride in a glider or parachute. Learn to land on your ride’s minimal weight. Dropping stuff is only an extra measure if possible, not a necessity.
Every time I hear of an all electric aircraft of any size, I always wonder what they’re going to do about landing weight.
Every modern transport category jet has a higher takeoff weight than landing weight, because of the simple unavoidable fact that landings are rougher than takeoffs. Taking off, the load gradually comes off of the landing gear, on landing it’s suddenly applied. Jets burn tons, literally tons, of fuel enroute, so they’re considerably lighter on approach. It’s why aircraft have dump valves to jettison fuel overboard in case of forced landing early in the flight.
Batteries don’t get lighter as they’re discharged, so…?
JETTISON ZE PACKS!! PREPARE FOR LANDING!!!
The same way we make bigger aircraft with higher landing weights: beefier landing gear and structural reinforcement. Airliners don’t have a lower max landing weight than takeoff because they have to, they do it because it’s cheaper and more efficient. Add some more structural weight and you lose some payload, but if the efficiency gains from fuel cost savings make it worthwhile, then manufacturers will make them.
You’ll hit a point where the payload is so poor it isn’t worth operating.
That’s true regardless, batteries will never power intercontinental wide-bodies (short some major new developments in battery design). This will probably reduce the maximum aircraft size where batteries remain viable, but they are obviously very viable for short hops in small jets, the point where they cannot compete is somewhere but it’s not “never”, even with this limitation.
That all said, maybe someone will explore just dropping batteries along the way? It sounds ridiculous, but it also sounds like something we have the tech to solve…
It’s a bigger deal on bigger aircraft, but on mid-size narrow bodies it’s not as much of a problem. A 737, depending on the model, only has a difference of about 20-30k lbs between MTOW and MLGW and no fuel dump capability. An overweight landing isn’t really a big deal in one, just a quick maintenance inspection. Closing the gap so MTOW and MLGW are equal is doable. It’s hard to overstate how huge of an expense fuel is to an airline, if they have to lose some passengers and cargo they would absolutely do it if it got rid of the fuel expense.
Of course all that is contingent on having batteries with enough energy density to get somewhere close to current MTOWs while having something of a useful range.
You can rethink the engineering with electric motors.
The planes you are describing are designed assuming they will be lighter on landing because of fuel. So why design them for take off weight?
Electric motors are condusive of blown wing design for example, and would have a unique landing profile. (The plane can land at much slower velocity)
Edit: yeah they’ve moved the engine shroud which allows for lower speeds. Given the same runway you would be able to trim vertical speed.
That ain’t gonna happen on a civilian airliner.
Blown wings are basically powered lift. You’re planning on bringing a civilian passenger plane down final approach at a speed it can’t glide at if the power plant fails?
I could see that for a carrier based aircraft where STOL is a factor but no you’re not doing that in airline operations.
Why couldn’t it actually be safer since you could have distributed power centers, across multiple motors?
You could also have hybrid approaches - there is space between not being able to glide and smashing your landing.
I’m just getting at it being a different system so some old assumptions can be reexamined.
Bigger challenge than landing is energy density.
Regardless it’s a very interesting space.
Multiple redundant motors are heavy.
Batteries are far heavier. There’s going to be as many motors are there are propellers, it really doesn’t make sense to do otherwise.
One of the other limitations is that you’re stuck with propellers if you’re using electric motors, so your top speed is going to be significantly slower than jets. Unless you do the Tu-95 thing with contra-rotating props whose tips exceed the speed of sound, and then you have monstrous noise problems.
You can do ducted fans, which is what a turbofan minus the turbine is.
Fun fact, batteries DO become lighter when they discharge. But obviously not like fuel. But it’s still a fun fact.
FYI 1 kg battery when fully discharged loses about 10⁻¹² kg of its rest mass …
You mean because of e=mc²? That’s true but basically unmeasurable. Air batteries do get mesurable heavier.
That’s ridiculous. No one on final gives a crap about take-off weight. What you need is a ride in a glider or parachute. Learn to land on your ride’s minimal weight. Dropping stuff is only an extra measure if possible, not a necessity.
when r/fuckcars thinks they know anything about aviation.
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I’m a CFI.