[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Campbell's even crazier than a MANIAC? (archeopteryx climbing)

> We have been told about gliding helicopters on this list.
> How fast do they 
> need to go to stay above stalling speed when gliding? I
> have a hard time imagining it...

Helicopters can glide the same way autogyros can - by setting the right 
collective, they function as an unpowered autogyro.

as I said, I have video, this is an unpowered autogyro, but it is the same 
(gliding after tow begins at ~52 seconds)

Helos and autogyros can glide with zero airspeed, autorotating straight down 
safely in the event of an engine failure, and depending on the rotor, weigh, 
and other things, can manage a respectable forward glide (im thinking 5:1)
When it comes to rotary wings, they don't have a conventional stall speed, 
rather the velocity component of the air flowing perpendicular to the rotor 
disk must be above a certain rate for a given blade pitch to keep the blades 
For a given pitch the blades must be at a certain rpm, or the blades stall.

--- On Sun, 9/28/08, David Marjanovic <david.marjanovic@gmx.at> wrote:

> > I beg to disagree. I don't think finches can
> glide, and I've never seen a 
> > bat doing it (granted, my
> > experience with bats begins and ends with the
> grey-headed flying foxes in 
> > my backyard). I
> > sincerely doubt that hummingbirds can glide either.
> Oops. Bats are famous for not gliding, and I bet
> hummingbirds can't do it 
> either -- their wings are seriously tiny; except for the
> size of the hand, 
> they always remind me of tyrannosaur arms. And I had
> managed to forget that 
> the descent phases in the undulating flight of, for
> instance, small 
> passerines are purely ballistic, with the wings completely
> folded up, rather 
> than gliding.

Well, I have seen hummingbirds glide several meters between flaps, they don't 
always go "purely ballistic", and sometimes leave their wings out, or do a 
combination of the two, when traversing a distance rather than hovering of 
As others have mentioned, flying foxes in fact will thermal, which is just 
gliding in rising air, and given that this is a common form of flight, that 
means their sink rate while gliding must be rather low, else they wouldn't be 
going up.

Of course, even a human in a wingsuit can glide, and manage 1:1 or even 1:2 
glide ratios - there is no doubt a hummingbird dropped from 50 feet could cover 
a good distance without flapping, although a good flare might be needed at the 

Just because they don't do it, doesn't mean they can't, given their other 
options gliding is not preferred.
A hummingbird has tiny wings, but so does any jet fighter relative to its 
weight, and those things have glided for dozens of miles upon loosing power. 
Jet fighter= higher wingloading, lower aspect ratio wing, less efficient 
glider, still fully capable of gliding when powered flight isn't a viable