h a l f b a k e r yA riddle wrapped in a mystery inside a rich, flaky crust
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Doing some surfing today, I stumbled upon the site of
Moller International (not for the first time). Moller, who
has been talking about his flying car for almost as long as
I've been alive, has now -- somewhat embarrassingly, if
you ask me -- taken to Indiegogo to fund his "untethered"
flight
-- something that he's been otherwise promising to
do for about a decade, and this despite, or perhaps
because, Moller International is a penny stock.
This sorry exercise got me to thinking: why is it that we
don't have flying cars yet? I'm sure I'm not the first one on
this site to think about this subject. And then I realized:
They are solving the wrong problem. They are all trying to
make cars fly. Well, wtf? Cars are meant for driving.
Why do you need cars to fly, when planes are perfectly
reasonable at 2D locomotion. What they need to fix are
the roads, and the airports, not the cars!
So, the driving plane. It's already in your neighborhood
airplane store. Now all you need is slightly wider highways,
more local airports, and perhaps to convert your 4 car
garage to a hangar -- it's totally worth it.
There you go, problem solved. Now, give me something
hard to work on.
Moller International
http://moller.com
[theircompetitor, Nov 10 2013]
The above mentioned Indiegogo project
http://www.indiegog...skycar-into-history
[theircompetitor, Nov 10 2013]
Roadable Aircraft
https://www.google....q=roadable+aircraft
The phrase you didn't use, but others are using. [Vernon, Nov 10 2013]
multi modal drones
http://www.wired.co.../transformer-drone/
it flies, it dives [theircompetitor, Nov 11 2013]
[link]
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Many light aircraft will lift off the ground at
70 knots IAS. Even in benighted places where
the typical speed limit is a treacly 55 mph,
the addition of a mere 15 knot headwind will
be enough to reduce the load on the
undercarriage to the point where nosewheel
steering and main gear braking become
significantly less effective. |
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Using spoilers to kill the lift massively
increases drag. |
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The big whirly fan thing on the front is going
to do wonders for any wayward pedestrians.
And everyone behind is going to be
constantly worried about FOD. |
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An airscrew is an inefficient way of
propelling a ground vehicle, and is only
resorted to (sleds, airboats, hovercraft) when
no traction to the supporting surface is
available. |
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Oh, and it's been done. A workable plane
with removable wings that could be driven
on normal roads was demonstrated some 40
of your years ago. |
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[+] if and only if you edit the idea to include amphibious /submersible capability. |
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[8th] I am fully aware. The idea was mostly a
reaction to seeing the absurd indiegogo campaign.
Next no doubt we'll start seeing crowdfunding
campaigns for fusion power. |
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//Using spoilers to kill the lift massively increases
drag.// |
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That's sort of farce about ace. If you turn an aircraft
upside down, it will have the same drag as right way
up, but the lift is now glueing you to the road. So,
all that's needed is a trim setup that accomplishes
this. |
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Moller (and a handful of Halfbakers, no names of course)
would benefit from reading 'Where's My Jet Pack?' by Daniel
Wilson. |
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// If you turn an aircraft upside down, it will have the same drag as right way up, // |
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No it won't, because aircraft designers are by nature unimaginative traditionalists (except for the spiky-haired gibbering loons who "design" helicopters) and therefore tend to have only one set of wheels, which is placed on the side of the aircraft intended to be next to the ground. Boring, but true. |
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The net result is that if you turn an aircraft upside down, drag increases massively. |
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// but the lift is now glueing you to the road. // |
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Only if you're going fast enough for the airfoil to generate aerodynamic forces. What are you intending, tractor pulling or something ? |
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// So, all that's needed is a trim setup that accomplishes this. // |
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Thrust, lift, drag, weight. |
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Small aircraft don't tend to have aileron trim tabs, relying more on a slight dihedral on the mainplane. If you trim up the elevator to provide downforce, the tail will lift and the plane will ground-loop, or become unstable because of the excessive force on the nosewheel. |
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It would be possible to modify the flight controls for that sort of ground running, but the profile of the wing is meant to generate lift; cancelling that completely on the ground is non-trivial. Tilting the whole wing at the root might be practical, but would have a large weight penalty. |
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And even with slight negative lift, the whole vehicle would still be vulnerable to crosswind gusts. |
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[8th] old bean, I cannot help but arrive at the
tentative but
unavoidable conclusion that you may have not
failed to
misunderstand my meaning. |
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Your contention was that the spoilers necessary
to stop an
aeroplane from taking off at highway speeds would
add massively
to the drag. |
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My response was that, with a suitable trim of the
wings, a
substantial downforce can be generated with no
more drag than if
the aeroplane were configured for flight. |
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It's not necessary to tilt the wing at the root. A
simple tailwheel,
deployed only when in car mode, which holds the
tail high, will
be adequately sufficient. The wings will then
have a negative angle of attack. Admittedly
you're working against the aerofoil profile, but to
be honest I've never really believed in that
nonsense - most of the wing's lift just comes from
pointing it upwards (or downwards). |
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Or perhaps I have been remiss in my undertaking
to apprehend
the nature of your apparent misunderhension. |
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There are two separate flight control mechanisms under discussion here. |
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Let us confine our attention to single-engined single-wing light aircraft like the Cessna 172 and the Piper PA-28, as that limits the complexity. |
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These aircraft do not have spoilers. They have balanced ailerons, and trailing-edge flaps. |
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In a "clean" configuration (no flap deployed), as forward airspeed speed increases, so will lift. |
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How, then, to prevent the aircraft taking off ? |
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Spoilers disrupt the airflow over the upper surface of the wing, creating massive drag and preventing the wing from functioning as it should. Ice accumulation will do the same thing. But spoilers waste energy in turbulence; they are used on landing to ensure the aircraft doesn't float back into the ground effect while it still has flying speed, and to get the weight of the aircraft down onto the maingear so the brakes can take effect without skidding. |
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Ailerons control the aircraft in roll. To produce aerodynamic downforce, both ailerons would have to move downward in synchrony, which would require a small modification to the flight controls, but would be practical to do. |
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The question the remains as to whether the relatively small area of the ailerons compared to the total wing surface in general would be sufficient, or whether it would be necessary to also reverse the flaps. |
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A high tailwheel is not practical since most modern light aircraft have no tailwheel; they have tricycle undercarriages with nosewheel steering and differential braking on the port and starboard maingear. |
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Further, a nose-down attitude would present a serious risk that, under even moderate braking, your bag of fish and chips will slide off your lap and go all over your trousers. |
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// How, then, to prevent the aircraft taking off ?// |
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See -- we need more of that kind of thinking :) |
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