Watching a Buzzard

[Miami Mike]

I was watching a turkey vulture a couple of days ago and noticed something interesting. It seems to me that they normally fly in smooth circles within thermals as they gradually gain altitude, but this bird seemed to be flying a little differently. Through most of his circle he held about the same altitude, but every time he came around to the side closest to me, he would suddenly rise, almost as if he was climbing a step. It looked something like this:

http://www.vvsss.com/ezone/circling.gif

I wonder why he was doing that. What conditions was he flying in? Was the thermal bubble perhaps smaller than the smallest circle he could efficiently make? If so, which part of the circle had the lift? Presumably it was the section closest to me where he suddenly rose upwards. Was he deliberately pulling up in that part of the circle to slow down and increase his time in rising air, and then nosing down to speed through the sink and get back around to the lift again?

Is this a technique that's applicable to r/c sailplanes? Perhaps with enough skill a flyer could duplicate it, but I suspect it wouldn't be easy. I have enough trouble just keeping my plane flying in a circle.

[Thermaler]

That is a first, I have NEVER seen a Turkey Vulture that flew smoothly. It is always kind of shakey, kinda like us sailplane fliers.
Now a hawk or eagle, that is smooth flying.

[xtc]

mike, was the buzzard also balloooning up as he came into the wind after every circle?

i know that over the yrs i have kind of developed a kind of pumping action to try to retain and little energy while thermalling,, i tend to semi stall as i take advantage of a small core only to allow the glider to excellerate a bit getting ready for the next time i hit the core again




i might also add that full size sailplane clubs offer intro flight pretty cheap and for anyone that has never FELT a thermal ,i strongly advise it!

i would imagine the buzzard IS hitting a small core as they can be real strong at times

xtc

[Ollie]

Some Turkey Vultures are bright but others are dimwitted. ;) Some are young and some are old. Ask Thornburg (Old Buzzard’s Soaring Book). Some are heavy (full of food) but some are lean and hungry. Some have full wing feathers and some have missing wing feathers. It depends on their wing loading.

Here in FL, the Black Vultures are more common.

[Miami Mike]

mike, was the buzzard also balloooning up as he came into the wind after every circle?Careful, I never said that it had anything to do with him coming "into the wind", nor do I believe wind had anything to do with it. There really wasn't much wind at the time anyway. He seemed to be circling around the same spot.i might also add that full size sailplane clubs offer intro flight pretty cheap and for anyone that has never FELT a thermal ,i strongly advise it!I'm not sure how that relates to this, but yes, I'd advise it too. It's a great experience.

[drCarter]

Sounds like he was in a broad area of neutral to boyant air with a small core of lift. It is too small to circle in so he would blead energy when he hit the core.

I had one last sunday that allowed me to try every just about everything, with a DLG. I was about 15 feet above the ground when I entered a broad area of very light lift. I started to circle. There was one point in the circle that would knock the plane hard. i found the center of the lift and put the plane on a wing tip. I was in the center but the high G loading kept me from gaining altitude. I then switched directions and tried the other way, same result. I then set up my circle to where at one point I would cross through the center. This seemed to work out the best.

I worked the lift for about 4 mins. and only gained about 15 feet. I never had the energy to slow down when I hit the core. Your observation is very interesting and I will have to try it.

[Gliderboy]

Yep, sure sounds to me like a small strong thermal. I too have many times performed the same type of flight pattern with my unlimited class ships. They won't turn tightly enough to stay in the core without falling out. Your vulture might have sensed that.

This has happened mostly in the morning on very large temperature transient days, cold night with strong solar heating and light winds. Early the thermals are small and can be very violent near the ground. Usually, later in the day the thermals start to really pop and become much larger, then circling in them is no problem, the proverbial corkscrew elevator!

We get these type of conditions here in north Texas quite often around this time of year. However, the weather has had me grounded for the last few days. So, I am laying up a new nose skeg for the Eraser.

Happy Holidays!

[djnibler]

I second what drCarter said... a broad area of neutral air, with a small thermal core. What I find to be true many times in a real thermal is that the core is not in or even near the center, instead, the core right on the edge! The best you can do is circle through the neutral air, then hit the core and pull up.

If there IS wind (and even a 2-5mph breeze will do the trick), it seems to force the core of the thermal to the up-wind side (from my experience, and it makes sense if you think about it). This means that right as you hit the core of the thermal, you also hit the head wind. It seems like this flattens the core out and turns it into a "curtain" of lift. Too thin to circle in, but you can really go up as you hit it every 360 degrees.

Around here, most thermalling birds that I've watched fly exactly as you described. I myself fly the same way if the thermal has the properties I mentioned. In fact, I often see them LOSE altitude for 90% of the circle, only to regain it and more when they hit that spot.

[flyswithumb]

This pattern is common with free flight gliders. The diameter of their circles will often get tighter as they get closer to coring the thermal. Until then, they will fall out of it on the down wind side.

Like a free flight glider, this buzzard knew he could still climb with no control input. Lazy buzzard.

[Miami Mike]

If there IS wind (and even a 2-5mph breeze will do the trick), it seems to force the core of the thermal to the up-wind side (from my experience, and it makes sense if you think about it).Sorry, I did think about it and no, it doesn't make sense to me. Help me out here. How is the shape and orientation of a thermal, way up in the sky, affected by the direction and speed that the ground is moving way down below?

The way I see it, there is no "upwind" or "downwind" to a plane or bird flying within a moving mass of air.

[djnibler]

Let me try to explain another way (I don't know that I'm making much sense either). Forget about the up-wind/down-wind thing for now.

We all know that air is drawn into a thermal from around it to re-fill the void caused by the rising air. When you are outside of a thermal, and flying towards it, right before you hit the thermal, you may enter the air that's being sucked into the thermal and as a result, your plane speeds up. Then the nose goes down and the tail goes up as you enter the lift. Classic thermal signs.

Now in a thermal where a small, powerful core is right on the edge, the wind being pulled in will slam directly into that powerful core which will create something like a wall of lift.... almost like slope lift in a small area. Here is what would happen to your plane flying in that thermal: Lets say you are in the thermal, on the opposite edge as the core, flying TOWARDS the core on the other side. You would be sort of floating along in the light lift. Suddenly, you hit the core, and as you do, you also hit into that wind that is being drawn into that core. Now you get not only the lift from the core, but a bit of extra head wind. Your plane actually slows down and goes up, but if you keep going straight, you are now outside of the core, and the thermal entirely. You are now flying through a sinking headwind of air outside the thermal that is also being drawn into it.

This happens to me all the time. You hit that sweet spot and the glider goes up, but practically stops and hovers (relative to the ground) if you don't turn immediately, or weren't already turning when you hit it.

Perhaps I'm not explaining this correctly, or the phenomenon is not how I perceive it to be. But I think most R/Cers have experienced this kind of activity in a thermal because I've seen it hundreds of times with both my own planes and others. I just make sure I am turning when I hit that point, pull up to maximize the energy as I hit it, and try to keep my speed up in the rest of the thermal to minimize sink while not in the best lift.

[jrerickson]

The way I see it, there is no "upwind" or "downwind" to a plane or bird flying within a moving mass of air.

Not my experience. There are many vectors within a thermal. It doesn't just have an "up" component in it. I think the buzzard was either: Banking off the "hot spot" of the thermal (Fastest rising section) or there was a slight headwind condition, maybe not even perceptable at ground level.

I've seen so many hawks fly different patterns in a thermal. Sometimes if they want to range they will take the thermal up as high as they can and then split. Other times they like to stay at the same altitude (looking for food in a certain area) and they do what you saw: Just taking a bite out of the thermal, enough to stay at the same altitude.

Like everyone who has to work for a living, the buzzard was doing the least possible to get the job done
:)

John