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Birds that can hover (kites)

by rcgldr
Tags: birds, hover, kites
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rcgldr
#1
Jul14-13, 01:03 PM
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Splitting this off from the human powered helicopter thread since it's about birds that can hover.

Quote Quote by rcgldr View Post
At the site I was referring to, when there is no wind, the people there fly electric powered models. When there is wind, it's about 60% powered / 40% gliders, depending on the group.

As far as the kites behave versus the wind, if there's a headwind and updraft, they mostly soar with little flapping. If there's a headwind and no updraft they flap a bit more. If there's no wind, then they are flapping quite rapidly, with full swing flaps. Regardless of the wind, when "hovering", they're virtually motionless with respect to the ground (relying on vision to track a spot on the ground), which is quite impressive.

The other video I posted showed a kite hovering close to the ground (2nd part of video), where there can't be much wind, due to the small shrubs, and what wind there is appears to be blowing from behind the kite. Link to that video:

http://ibc.lynxeds.com/video/white-t...adult-hovering
Quote Quote by sophiecentaur View Post
There's little point in this conversation because I think we are talking at cross purposes and we are only differing in 'degree' and not in principle. Any video you post can't be real evidence because there are no measurements of actual wind speed (particularly not where the bird is hovering). Kites, Eagles Buzzards etc. etc, will soar on invisible thermals on a totally 'calm' day, getting their energy from the Sun.
Soaring is different than hovering. Hawks can soar very well, but they are poor fliers. I've regular see a local nesting pair of crows / ravens spot a hawk soaring above them and they can quickly fly from tree level to well above the hawk and then take turns diving at the hawk to drive it away.

Quote Quote by sophiecentaur View Post
The point is that it is very seldom 'sustained' hovering, because it is so costly.
In a no wind condition, it is costly. The local kites I see hovering in a no wind condition only do so for about 30 seconds or so before diving after prey or giving up. If there's a headwind and updraft, there's very little flapping required and they can do this for several minutes.

I don't know if the larger osprey can hover in no wind conditions, but their hovering capability is why the twin propeller aircraft capable of hovering choose Osprey for it's name (the V-22 Osprey).
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Borek
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Jul14-13, 01:31 PM
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I know you discussed some other aspects/birds earlier, but I have not followed the discussion, and most people finding this thread will not know the earlier posts as well.

I suppose we will all agree hummingbirds do hover.

What about kestrels? Do they sue the same technique kites use?
rcgldr
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Jul14-13, 01:59 PM
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Quote Quote by Borek View Post
I know you discussed some other aspects/birds earlier, but I have not followed the discussion, and most people finding this thread will not know the earlier posts as well.
I think the video from the first post in this thread is enough to demonstrate how a kite hovers.

Quote Quote by Borek View Post
I suppose we will all agree hummingbirds do hover.
Yes, and they can translate forwards, backwards, upwards, and downwards while hovering. A kite may be able to translate backwards while hovering, but I've never seen this done.

Quote Quote by Borek View Post
What about kestrels? Do they use the same technique kites use?
I haven't personally seen kestrels in action. I looked at some youtube videos, and there are a few that show the rapid flapping required to hover. However in the videos I saw, I didn't see one where the kestrel held what appears to be a fixed position (relative to ground) for more than a few seconds. The local kites I see will hold a very fixed position over the ground for 30 seconds or so in a no wind condition with a somewhat upright body position (as if they were trying to climb upwards). With a wind and updraft, they can mostly soar to hold a position, and with just a head wind, the rate and displaced angle of flapping is much less, with a more horizontal body position.

CWatters
#4
Jul14-13, 02:11 PM
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Birds that can hover (kites)

We have Red Kites in our area and I've never actually seen them hover as shown in the video of the White Kites in the first post.

Not really sure what the point of this thread is? It's well known some birds can hover in still air, others can't or just don't.
Borek
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Jul14-13, 02:16 PM
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Kestrels can keep the position over a point on the ground for tens of second if not minutes, I am observing them quite often here, over flat meadows (so no updraft over a cliff). They do apply a wing motion similar to the one hummingbirds use, but it is much slower and their wings are not stiff (I believe hummingbirds don't bend their wings during flight).

Edit: OK, I checked the kite video. This is a similar technique, but kestrel doesn't beat its wings so fast, and after some more thought I am not sure if it would be able to hover in a windless conditions (which can mean they technically don't hover, just fly very slowly).
Dotini
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Jul14-13, 02:19 PM
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The Kingfisher hunts by hovering over the water, then diving straight down into the water for his prey. I see them do this frequently.
A.T.
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Jul14-13, 04:34 PM
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Quote Quote by Borek View Post
I am not sure if it would be able to hover in a windless conditions (which can mean they technically don't hover, just fly very slowly).
Their hunting techinqe is to observe the ground at zero ground speed. And I don't think they stop hunting, just because there is no wind.
A.T.
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Jul14-13, 04:38 PM
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Quote Quote by CWatters View Post
Not really sure what the point of this thread is? It's well known some birds can hover in still air, others can't or just don't.
Sophiecentaur claimed that only very small birds can hover, which is apparently not true.
Borek
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Jul14-13, 04:55 PM
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Quote Quote by A.T. View Post
Their hunting techinqe is to observe the ground at zero ground speed. And I don't think they stop hunting, just because there is no wind.
Yes, but "no wind" is a rather rare situation. And I have a gut feeling even just a meter per second can make a huge difference.
rcgldr
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Jul14-13, 07:56 PM
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Quote Quote by Borek View Post
Yes, but "no wind" is a rather rare situation. And I have a gut feeling even just a meter per second can make a huge difference.
That translates into a 2 mph or 3.6 kph wind. Even in a "no wind" condition at ground level, there could be a light wind at higher levels, or from a thermal, although with a thermal, the direction of wind over a specific spot on the ground would change as the thermal passes over that spot on the ground.

At the radio control model site where I've seen kites hovering, there's a plateau and small parking lot near the top of a ridge where the people gather to fly their models (the parking lot is used as a takeoff and landing strip for the electric powered models), and the kites I've seen there are generally about 30 meters or so away, where there is just a slope and no plateau. Even when there's no apparent wind at the plateau, there could be a mild wind where the kites are.

Wind speed varies over time, and in the case of a light wind, if a thermal (which draws the surrounding air inwards) is upwind of a kite's hovering position, it's likely that the kite experiences zero wind or even a tail wind for short periods of time until the thermal passes by. What's impressive is that you know the wind changes speed, yet a kite compensates very quickly and manages to hold a fixed position in spite of the changes in the wind.

I do recall reading something about kites being able to truly hover in a no wind condition, but other than a test conducted inside a large building, I'm not sure how to confirm this.
CWatters
#11
Jul15-13, 02:31 AM
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This long standing claim (or similar) can be found in various places..

http://en.wikipedia.org/wiki/Bird_flight

the largest bird able to truly hover is the pied kingfisher, although larger birds can hover for short periods of time. Larger birds that hover for prolonged periods do so by flying into a headwind, allowing them to remain stationary relative to the ground (or water). Kestrels, terns and even hawks use this windhovering.
rcgldr
#12
Jul15-13, 04:48 AM
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I've since found a youtube video of kites "hovering" in a controlled environment with human trainers as part of a show. The kites translate sideways (circular arc) and even a bit backwards while following the trainers cue.

The technical term for this is "kiting". The youtube text states: Unlike a hover, the "kite" is a head-up position with the body perpendicular to the ground, but in the video, the kite's main body has a somewhat upwards lean, and the tail and the legs are dangling downwards.

http://www.youtube.com/watch?v=JnbndA0Rjfg


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