The age of electric flight is finally upon us
261–270 of 272 posts
Re: The age of electric flight is finally upon us
#262Earlier quoted context omitted.
>> off-field forced landing that went badly. Parachutes. They are now a very practical option for GA aircraft. More than a few cessnas have been saved. The concept of "off-field forced landing" should too be going away. https://brsaerospace.com/cessna-faqs/ " Q. How many aircraft saves are credited to a BRS Whole Aircraft Rescue Parachute System? A. As of August 2017, 376 ."
In addition to the point verelo raised about the repair/replacement cost of having used a parachute (vs. replacing a motor), I was thinking specifically of a wingtip-motor failure at takeoff (typically the worst-case scenario), possibly too low for a parachute (some figures here: [1]). This is a 9-passenger airplane, maybe too large for current recovery parachutes? (though I imagine that will change.) [1] https://www…
2 parachutes.
Re: The age of electric flight is finally upon us
#263Earlier quoted context omitted.
Compare the number of propellers on NASA’s version. They have serious backup in the event any single engine fails. Being able to take off with one engine that’s rapidly overheating, does not mean is safe to continue a flight with a single engine. Electric aircraft don’t get lighter in flight because they don’t burn fuel.
The power delivered to the rear MOTOR (not engine) is not the same for take-off and cruising. A motor that would overheat at takeoff power won't necessarily overheat at cruise and would be designed not to overheat in an aircraft application. Motor control is not just on or off.
It’s possible that that could be the case, but it’s a poor assumption that it will be the case. Especially as it’s such a useful feature they likely would have mentioned it.
Re: The age of electric flight is finally upon us
#264Earlier quoted context omitted.
In addition to the point verelo raised about the repair/replacement cost of having used a parachute (vs. replacing a motor), I was thinking specifically of a wingtip-motor failure at takeoff (typically the worst-case scenario), possibly too low for a parachute (some figures here: [1]). This is a 9-passenger airplane, maybe too large for current recovery parachutes? (though I imagine that will change.) [1] https://www…
2 parachutes.
Maybe, but that does not solve low-altitude problems, if indeed there is one. It is possible that two small-airplane sized parachutes will inflate faster than a single larger-airplane parachute, but apparently current small-airplane parachutes do not inflate fast enough to save you at low altitude.
Actually, this has me thinking: not all low-altitude situations are the same - an airplane with a downwards trajectory, such as one in a spiral dive, will need more height to save than one that is in a glide, such as after a power failure. This is why even a zero-zero ejector seat will not always save you, if you are descending rapidly at low altitude.
Even so, replacing a motor, if that is all it takes, is going to be cheaper than repairing or replacing an airframe that has undergone a parachute recovery.
Re: The age of electric flight is finally upon us
#265Earlier quoted context omitted.
Most of these discussions I see, at least on HN, seem to understand efficiency. Yeah, a lot of fuel goes into heat and not into power for the engine. People understand that. But another thing that many people don't, is that heating isn't wasted energy. It is reclaimed for heating the cabin and deicing. Which icing is a HUGE problem on aircraft. Heating is also fairly power intensive. But still, until we get into that…
Batteries also produce heat. Also -- it's pretty easy to be negative. "That's dumb, it's not going to work", etc... I really appreciate this poster remaining positive in the face of OVERWHELMING negative feedback on this thread.
Batteries don't produce nearly as much heat. And like I said, we need both camps.
And I don't think you should take my comments as "that's dumb, it's not going to work." You should take them more as "we still got a way to go but we've made a lot of progress. But don't bet all your money on this horse."
Re: The age of electric flight is finally upon us
#266Earlier quoted context omitted.
Parachute not enough?
I don't think so. You cant steer a parachute well and you don't want some bypasser to get hit by a heavy battery on a parachute. The descent speed on a parachute is very high so it will hurt or more.
Parachutes can be steered.
Re: The age of electric flight is finally upon us
#267Earlier quoted context omitted.
2 parachutes.
Maybe, but that does not solve low-altitude problems, if indeed there is one. It is possible that two small-airplane sized parachutes will inflate faster than a single larger-airplane parachute, but apparently current small-airplane parachutes do not inflate fast enough to save you at low altitude. Actually, this has me thinking: not all low-altitude situations are the same - an airplane with a downwards trajectory,…
https://www.youtube.com/watch?v=jgfG2DfPB6I
(Action starts at about 02:05)
I guess it depends on one's definition of low altitude. Rocket-deployed parachutes open very fast.
Re: The age of electric flight is finally upon us
#268Earlier quoted context omitted.
Maybe, but that does not solve low-altitude problems, if indeed there is one. It is possible that two small-airplane sized parachutes will inflate faster than a single larger-airplane parachute, but apparently current small-airplane parachutes do not inflate fast enough to save you at low altitude. Actually, this has me thinking: not all low-altitude situations are the same - an airplane with a downwards trajectory,…
https://www.youtube.com/watch?v=jgfG2DfPB6I (Action starts at about 02:05) I guess it depends on one's definition of low altitude. Rocket-deployed parachutes open very fast.
With respect to engine failure at takeoff, low altitude begins at the point where, if the engine fails, you will not be able complete a landing on a runway (or overrun area, if there is one.) With respect to my original question, if the remaining engines give sufficient performance, using a parachute would not be the standard response even if you had the height and speed for it to work.
Re: The age of electric flight is finally upon us
#269Earlier quoted context omitted.
Those tweets have been deleted, and where’s the evidence of these claims?
Yeah, I see this kind of thing repeated any time Eviation comes up. I don't believe them. The design is sound, if radical in the decision to be mostly-battery. And I think that's partly why people are so skeptical: it definitely goes counter to the industry grain. But it IS the right way to build a serious electric aircraft for regional/commuter passenger travel. Pressurized, extremely high lift-to-drag ratio, very h…
Just wanted to say thanks for the insightful comments you have in this thread. Lots of interesting musings on the state of the art.
Re: The age of electric flight is finally upon us
#270Earlier quoted context omitted.
> > improved modern materials means you can just have most of your take-off mass be battery, compensating for the poorer specific energy > Again, this can be done for any aircraft, not just the electric ones. Not only that: you burn the fuel, so for the second half of the flight you only need to carry half the fuel. But you have to carry the full battery mass (modulo E=mc^2) all the way.
Well, that’s in part a point for the batteries, though. You spend a lot of energy to lift all that fuel that you just blow out with all its potential energy up in the air, whilst the batteries provide you with that very potential energy on the way down as well. Glider planes quiet commonly are filled with water to make them heavier so they can make more use of the potential energy they gain from the externally powere…
That's not a point for batteries. I cannot imagine a circumstance where, during cruise or even descent, you'd wish that you'd be carrying more mass (except possibly to have a higher AoA and thus higher V_a if you want to fly through turbulence faster).