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Old 06-26-2011, 01:24 PM   #11 (permalink)
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re: 140 miles
per FAR 91.151, planes cannot take off without 45 minutes reserve flying time beyond their destination at night (30 @ day but we should look at worst case). That is for VFR. So assuming the lower limit of 90 minutes flight time (@ 70mph) you should plan on being at your destination within 45 minutes of flying, even if you are landing where you started. So that you could go 26 miles out and 26 miles back if you leave late in the day. Even if you assume 30 minutes reserve for daylight and VFR, that is still 60 minutes on the inside of flying time or 35 miles out and 35 back. Forgive my hyperbole of 10 miles.

I understand the local applications of this, and there is certainly some envelope of operation where it could make sense, but it is competing directly with potentially more efficient/affordable ground transportation at these distances, not for commuting in the general sense certainly.

But I am very concerned that john Q. public (and the folks looking for startup money) will not understand those limitations and think that we are on the verge of replacing all liquid fueled aircraft with batteries. 99.9999% of the public thinks of airliners when they think of airplanes, and of closing large distances in a small amount of time, because that is what they use when they buy passage on an airplane.

I also appreciate the reliability/durability concerns, and I hope that brushed motors are not on the table for the same reason. But a turboshaft could close the gap fairly well too and still offer high energy/weight and high energy/volume, both of which equate to more payload for way more miles.

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Old 06-26-2011, 02:15 PM   #12 (permalink)
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Make no mistake, I would love to have one and a backyard big enough for it if it were handed to me, but if I'm getting in a plane it is usually to go a considerable distance (i.e. significantly over 400 miles). And propellors can still make quite a racket.
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Old 06-26-2011, 05:03 PM   #13 (permalink)
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Making a large passenger plane that is all electric is a rather silly idea, just like it's silly to try to build an all electric semi truck or school bus, but for light duty use an electric plane is really tempting, I didn't know about the 45minute rule so that does cut back on the usefulness but I'm sure there are still people out there where this would be the correct tool.
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Old 06-26-2011, 05:31 PM   #14 (permalink)
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...and, now, reversing roles for a moment and playing the "Angels' Advocate":

How about a solar-powered airliner, that uses batteries for "reserve & emergency" power? Coat ALL the upper body and wing surfaces with solar-cell material instead of paint!
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Old 06-26-2011, 05:47 PM   #15 (permalink)
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There have been a few flimsy solar powered aircraft, and it wouldn't hurt to put them on here either if you are flying 45 miles away somehow to no power and can wait a few days for it to recharge, but I don't expect much contribution for the duration of a "normal" flight, unless you slow down to the speed of a bicycle or something and have one not-too-heavy passenger and no payload.

All timeframes above are complete swags.

Here is another one, I forget how fast, maybe 25mph or something on a slight decline...
http://www.wired.com/autopia/2011/05...tional-flight/ Initial scan of the comments seems to be in agreement with what I'm trying to say. 100+ million dollars for 25mph?
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Old 06-26-2011, 06:20 PM   #16 (permalink)
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Quote:
Originally Posted by dcb View Post
Here is another one, I forget how fast, maybe 25mph or something on a slight decline...
Solar Airplane Attempts First International Flight | Autopia | Wired.com Initial scan of the comments seems to be in agreement with what I'm trying to say. 100+ million dollars for 25mph?
You're still trapped in the box of thinking of the airplane as a way to get from A to B. There are both practical & recreational reasons why you might also want aircraft that would do something different. As for instance this solar powered one: park it at 30,000 feet and it could circle for years (with robotic pilotage) doing surveillance or acting as a cell phone relay.

Or again, the recreational market. I don't suppose that in all my sailplane flying, I ever got much more than about 10 miles from my starting point, so fuel/battery capacity is pretty irrelevant, as long as it's enough to launch and get into a thermal.
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Old 06-26-2011, 06:38 PM   #17 (permalink)
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You're still trapped in the box of thinking of the airplane as a way to get from A to B.
Lol, you want me to consider your special case where you always fly back to where you started and you call me trapped? THAT is funny... If this isn't about efficiency then it belongs in another forum, i.e. the lounge.
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Old 06-26-2011, 10:52 PM   #18 (permalink)
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Quote:
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What I find funny about that video is the RC jet guys are lucky to push 360mph
Are you kidding me? Have you ever tried to fly something with a five foot wingspan going that fast? You can only fly straight for a second or so before you need to turn around so you don't lose it. That's not even fun anymore. The AMA in the US won't insure anything over 200mph.

Pretty cool video.
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Old 06-27-2011, 01:31 PM   #19 (permalink)
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Quote:
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Lol, you want me to consider your special case where you always fly back to where you started and you call me trapped? THAT is funny...
OK, so how much time have you logged in sailplanes, or in a single engine aircraft? I have a couple of hundred hours sailplane time, a bit under 2K total, and have owned my own (well, 4-way partnership) Piper Cherokee for going on 20 years.

With sailplanes, you mostly do return to your starting point, unless you're doing some sort of competition. Similar with small planes: if you're just flying for fun (or for training), you might go up for an hour or so, then return to where you took off from. You can argue all you want, but that's simply the way it is.
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Old 07-06-2011, 02:12 PM   #20 (permalink)
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A speed record in a (tiny) electric airplane:


(click on image for link)

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