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Discussion in 'Flight Following' started by Ventucky Red, Nov 17, 2020.
But not when you’re quoting efficiency as gallons per hour.
True, but gallons per hour are meaningful only at low altitudes, where the changes in volume are minimal (that's why we piston pilots use it as a lazy shortcut). Otherwise, pounds (or kilograms) per hour is the actual measure that doesn't vary with pressure altitude.
Me too. History doesn't repeat itself (that's a dangerous misconception), but one can still look for analogies. Back in 1890, for example, it was easy to dismiss the automobile as an apparently-useless toy for rich people or hobbyists, with little practical application (though it could be fun for a short drive in the country, as long as you didn't mind stopping to make repairs once or twice during each trip). By 1920, the personal automobile was an in-demand item for the growing middle class, while oil companies set up chains of gas stations and cities refactored their roads to accomodate it.
Most new technology ideas fail, so it's reasonable to be cautious --- and electric vehicles have suffered for decades from being overhyped by people with more enthusiasm than understanding --- but they really are starting to prove themselves practical for many of the lower-demand applications we currently use internal-combustion engines for.
In general aviation, I don't think all-electric planes will make it further than trainer levels of performance, but that represents a huge amount of flying --- we all start in trainers (a large majority of takeoffs and landings at my home airport are student pilots and instructors), and many of us find they'll do for us and stick with them for life: just ask any J3 Cub owner.
I understand but I was replying to a post referring to gallons per hour by @Tantalum
^and that was in appreciation of the DA62 hitting 170 KTAS on two engines carrying a 5,000 lb plane. At 13 gph that's burning substantially less than any comparable twin I'm familiar with, and less than most single engines. Can you get a Cirrus or Bonanza to true at 170 on <14 gph? At 8K I can get an NA SR22 pretty close but not quite there.
There’s some studies that say it depends on the company and their plant types. Because... maintenance shutdowns have to happen sometime.
Very company dependent whether they actually want the demand curve flattened.
For some it means they need new plants so they can do maintenance if the grid is busy all night. And they’d prefer nuclear. But they can’t get licensing nor investors. Or they have to buy power from competitors.
I plan on it! I'm looking forward to flying a proper "big" plane and appreciate its rugged nature. My DPE logged a few thousand hours in an Aztec and had only good things to say about it. They lost an engine over the mountains of South America with 6 people on board. They managed to stay at 9K and make it 2 hrs to an airport.
Flatten, not table-top flat. Even if it were table-top flat they'd still need excess capacity for maintenance, failures, time of year (more demand in summer than winter) and growth (takes years to build a new plant).
Right now they have big sine wave curves that peak during the day and dip low at night. They would love those peaks and troughs to not be as large.
Some would, some wouldn’t.
Look into how much energy is wasted to manage heat. Depending on the plane as much as 70 percent of the drag is due to managing the engine cooling.
Electric effectively eliminates all or most of this drag. Makes it much more attainable.
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Exactly. In terms of battery use as primary power on small aircraft we are still orders of magnitudes away. Our great-great grandparents' 1930s Lycoming engine tech plus fuel still takes us farther at the half the weight.
Well, this looks promising...
Car, 300 mile range, 10 minutes to recharge.
I wonder how much is marketing fluff? Do you get all 300 miles in 10 minutes?
Agreed. There are lots of optimisations (energy recovery from a windmilling prop, eliminating a big chunk of the 200–300 lb ICE engine and mount weight to buy more load for batteries, more-streamlined fuselage, etc) that get bring us a bit further than just the improvements in battery tech, but I'm factoring those in when I write about getting to a PA-28-140 performance level some day with electric planes. Of course, we can make tradeoffs — more speed for less load or range, etc. But even with optimisations, right down to solar panels on wings, I don't think it's even theoretically possibly to get close to the speed+load+range combination of a Bo or SR22 with an all-electric plane.
Articles like this appeal to people who have no knowledge of electricity. The article gives NO numbers regarding kWh or anything else. So one has to make some educated guesses:
Suppose the car uses 20 HP while moving it at 60 MPH for 300 miles. That's about 15 KW per hour, or 75 kWh for the five-hour trip. To recharge that battery in ten minutes requires a flow of 450,000 watts for that ten minutes. At 220 volts, that's 2,045 amps. And that's assuming 100% efficiency, which is a fantasy.
2045 amps would need a cable about as big around as a pop can.
Can anyone say "brownout?"
Am I missing something here?
Physics is really inconvenient sometimes.
You probably are missing something. That's why I asked, if for example, you got the full range out of that charge. And they didn't say how long it would take to go 300 miles. I seem to remember that max range for most cars is around 40-45 mph because the drag is much lower than 60 mph. But isn't horsepower and wattage already expressed as units of time, as joules/second? You may want to check your math again.
I did ask how much was marketing fluff
Edit- the math looks fine. Tesla V3 superchargers give 250 KW, and they are looking at 350 KW and more, presumably at higher voltages to keep the current down.
I doubt there is much energy to be had from a "windmilling" propeller. Any recovery amount more than a few kW will stall the propeller, and since electric airplanes will, as you noted, be used mostly for training, the duration of descents will be measured in minutes.
I couldn't think of a worse training plane, than an electric one. Why bother teaching pilots at all, just toss them the keys to the king air 360, and tell them to have a fun time, without a single lesson.
The windmilling prop is my favorite of all the silly reasons electric is awesome for aircraft. I mean, who doesn’t want to slow down at the end of their flight so they can shorten the recharge time from 18 hours to 17 hours 59 minutes? Rotfl
The really smart electric fanatics like to fantasize about a generator designed into the aircraft so that the batteries are charging the entire flight.
Why is that? I never had issues with learning with a gasoline engine- it was the mechanics of flying, such as keeping on a centerline in a crosswind, while maintaining airspeed with pitch and throttle, that I had to learn. Flying an electric plane will be similar to flying a fuel-injected FADEC engine powered plane except less noise.
You still need to navigate in three dimensions with wind, as you do with any trainer.
You will avoid the same weather conditions as you do in any trainer available now.
The flight controls will work the same.
You still need to keep track of long the energy storage will last (either battery or fuel)
In either case, some peckerwood's gotta get the thing up. And some peckerwood's gotta land the son of a *****. And that "peckerwood" is still going to be called a "pilot".
Me thinks you are reading clickbait. No one seriously will incorporate that into a design. You know- the first and second laws of thermodynamics. The most "efficient" of those ideas is to tap into the tip vortices for recapturing energy. You get more gains in efficiency in greatly reducing vortices.
"GM aims to end sale of gasoline, diesel-powered cars, SUVs, light trucks by 2035"
Not sure how much of that work will be applicable to aircraft.
Since electric motors can also be used as generators, it wouldn't add significant weight to implement, but it would really only charge the battery during descent.
I think you missed my points.
You forget about such things as Angle of Attack on that propeller's blades. In a power-off glide, the AoA is extremely negative, striking the front side of the blade at a steep angle, absolutely the most inefficient way to drive any blade. Further, an ICE keeps the prop turning at idle, reducing that negative AoA; an electric motor would be shut off, making the AoA much steeper and totally useless. The drag of the propeller would steepen the glide so much that you'd have to keep the power on longer in order to reach the airport, negating any gains.
The top figure shows AoA when the prop is producing thrust. Look at the AoA in the bottom picture, a power-off glide. The prop blade's airfoil is flying inverted, and since it's not a symmetrical airfoil, we have a LOT of drag.
Don't be so sure of that..
https://www.flyingmag.com/hybrid-tech-electric-airliner/ our famed Peter Garrison notes it as a viable way to charge batteries (although at least he acknowledges the descent rate trade off)
The Washington State DOT put this out https://wsdot.wa.gov/sites/default/files/2019/07/15/ElectricAircraftWorkingGroupReport-June2019.pdf where on page 16:
Let me put the descent charging into perspective another way since what seems so obviously foolish to me is not so obvious to others.
You have to slow down your groundspeed to charge. Now, in some aircraft, that isn't an issue if their Vne is low enough, but in many aircraft, that's just wasting time. Time that won't be regained in charging faster (see the next point below)
The amount of charge you can get in 5 or 10 minutes of descent is nothing compared to what you'll get on a 220 volt charger. It wouldn't even be a measurable difference in time to recharge.
It's completely idiotic if you think about it for any amount of time at all. We don't have stop lights and stop signs, and mountains to climb and roll back down over and over again during the trip like you do in a car. In a car you're extending your range with all these micro-charges. But in an aircraft in descent, you aren't extending your range. Your trip is over already. IT DOES NOT MAKE ANY SENSE AT ALL.
And if I have to explain why running a generator off wind power for the entire flight is idiotic, well, I just give up on you.
haha.. it's extremely foolish to me too. But idiots (and sometimes even "smart" people, as I quoted above) tack it on as a "gain" of electric/hybrid aircraft
I completely agree with you
Well, you've proven your point and convinced me it isn't only clickbait with this stuff. I think some people add that to the marketing to get investors. I hope that whoever provides that information simply didn't think it through, but you won't have to work hard to show me they are deliberately misleading people.
Who are you replying to? I don't think anyone here is disagreeing with you.
I don't have the reference anymore, but I read an article from the Honda engineers that originally worked on their regenerative braking system, and it basically said that it really didn't do much to extend range relative to the extra complexity in the system. I believe the motor / generators are considerably more expensive, and more heavy also? But it's too good a selling point to pass up, and it might help in some corner case trips.
Do you have people on ignore? or are you just willfully ignoring those that are posting this stuff? I didn't build a straw man, it's been mentioned in this very thread multiple times.
Pilots won't learn how to take care of an engine, check oil, gas up, lean the mixture or anything else. And so now you have a license and no clue how to operate a plane with a gas engine or engines, and that is the plane they will have a 99.99% they are flying after flight school. So why teach on an electric plane. Also after each student the plane needs a lengthy recharge, so a school would need 4 electric planes to replace each gas plane they have now. So yes an electric plane is the worst idea for a school there is.
And the pilot would have to not only be 100% power off, but so high and fast, he needed extra drag. I generally don't come in stupid high and fast on final, and if i did it would be 15 seconds of actual charging. I plane my approaches to be stabilized, not 500 feet to high, and 15 knots too fast. I call that pilot error!
You are making assumptions that will not be true. You are assuming the same batteries that are currently used in cars. Those literally won't fly outside of some testing. It may be marketing fluff, but see the post about the Toyota car with the solid state battery. More range off a short charge. Something like that, or one of the other batteries that may come along, will be used.
I still fly the same sort of planes I trained in. C-150, C-152, C-172. If Liberty Aircraft had been successful, a lot of students would be flying behind a FADEC engine so they would have only learned about mixture and leaning in a theoretical sense. I believe that Rotax engines handle mixture for the pilot. Fueling a plane isn't that much different than fueling a car- do you really think it is so difficult? The only real differences are the grounding strap and checking for water- the sump locations are different on different planes. I commonly see pickup trucks with four tanks, so dealing with multiple tanks isn't an impossible task. If you follow a pre-flight list (you do that, don't you?), it reminds you to check fuel, oil, brakes, etc. I haven't flown a different plane yet anyplace without a check-out, and they'll help a new pilot with the differences in a new plane.
Every pilot I've ever met does.
Who are you hanging around that doesn't?
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No, I remember @David Megginson asking about using the prop that way, but I thought he was asking. He may have been making a suggestion. But you set him straight. You are setting @Palmpilot straight. Perhaps I didn't state my position clearly- no one serious about designing these planes will expect much from regeneration. The people in this thread aren't such people.
I think he is lamenting that if electric planes become used as trainers, they can't possibly learn to check the oil and such on a gasoline powered plane.
Yes, I mentioned energy recapture via a windmilling prop under potential tiny tweaks that could add a bit, but not enough to make a significant difference past the hard chemical limit of battery capacity. I'm a bit puzzled at all the angry reactions you and I are getting, but the whole idea of electric vehicles — even in a neutral discussion like ours (neither of us is claiming they'll be able to replace all ICE planes, etc etc) — seems to be a huge emotional trigger for part of the population.
I'm puzzled that you interpret laughing as anger. That's pretty odd.
Interesting. By the same token, if pilots start training in piston aircraft with ICE engines, I assume they'll never be able to move on to airline jobs and turbines. And we'd best not start teens on gliders (like Air Cadets does in Canada).
FWIW, you didn't come across as laughing to me, either.