I’ve always loved the Peregrine Falcon; whenever somebody asks ‘what is your favourite animal’, I would reply ‘the peregrine falcon’.
I’ve heard numerous different reports as to what its top speed is, claims from 200 km/h to 200 mph are not uncommon.
I know that the speed recorded depends on various factors such as dive height, wind speed, angle, etc etc, but there would need to be a maximum that the PF could endure physically, I would assume.
So, does anybody have the straight dope on what the maximum speed a Peregrine Falcon could realistically attain without appreciable injury?
“Falcons are strong, fast fliers with great aerial agility. They seldom soar in the manner of hawks. The peregrine has been clocked at 290 km/h (180 mph) in a stoop, or dive. This speed and agility make falcons successful hunters of birds, reptiles, and small mammals.”
Is there a reason why it’s top speed wouldn’t be its terminal velocity? I can’t think of anything organic that would break because it went too fast, especially on something as streamlined as a hawk. You’ll have to wait until someone who knows how to calculate drag coefficients and terminal velocities to come along to answer your question entirely.
I saw on a TV show a test to find the top speed of a PF; they hooded it, took it up in a hot air balloon quite high, tempted it with a piece of meat, then jumped out. They measured the time it took for the falcon to catch up and calculated it’s velocity from that, it was 180mph ish. Then it just hung around the skydivers, toying with them until they opened their parachutes. The program makers say speeds of 200mph seemed plausable seeing as it took so little time to catch up.
The falcon is attaining speeds far in excess of its terminal velocity, which is achieved when a falling body reaches equilibrium with air resistance and ceases to accelerate further.
Terminal velocity for a falling human is about 200 km/h, or 124 mph. A peregrine’s own terminal velocity is much much smaller than that, since its weight is much smaller in relation to its surface area.
Peregrines reach these speeds through a power dive; their powerful musculature coupled with a high degree streamlining enable them to overcome air resistance.
Falcons can’t “power dive”, there is nothing for their “powerful musculature” to push against in midair. (Except their wings, which would slow them down, not speed them up.) They are not equipped with rockets.
They just fold their wings against their bodies and fall. They are sufficiently streamlined that they encounter very little air resistance. Low air resistance leads to higher terminal velocity, so they do get moving pretty fast. By the end of the fall, they can hit pretty hard.
How, exactly would a falcon “attain speeds far in excess of its terminal velocity”?
Assuming the 157ms[sup]-1[/sup] figure is accurate, that comes out to ~351mph. A mathematically-ideal falcon could achieve even higher speeds.
This is all based on modelling and estimates, of course, since no-one has ever actually recorded a falcon diving in excess of 300mph. But it does seem plausible, and more importantly, survivable.
You don’t seem to understand basic aerodynamics. What they are pushing against, of course, is the air.
Nonsense. Have you ever seen a falcon execute a power dive? To attain their fastest speeds, they first pump the wings vigorously to accelerate. Then they fold their wings to take advantage of their streamlining. A falcon’s fastest stoop is not a “gravity only” drop.
Note that in my post, I was using “terminal velocity” in the sense of the final speed acquired in free fall, without a previous powered acceleration. Falcons achieve speeds greater than what they would by simply dropping out of the air in free fall.
There are a pair called Frodo and Frieda who nest on a building about a hundred yards from my office. I see them (very briefly) outside my office window all the time. They move, even in level flight, like you are seeing speeded up film. I have seen them stoop (on pigeons) only a couple of times, and then their pace is like no other bird you have ever seen.
For pictures see here. Pictures 3 and 4 from the Photo Gallery are pretty much the view out my office window.
I will admit that I didn’t know that they pre-accelerated their dives. Thanks for the info.
This still does not, in my mind, meet the definition of “powered dive”. The first phase is accelerated by wing power, yes, but then the bird folds its wings and allows gravity to take over. Which (to me) means it is dropping, not power diving.
So, did you use “terminal velocity” to mean “final velocity” (i.e. the velocity at the end of the dive)? Maybe I’m missing something here but I understood that terminal velocity was:
This velocity is not dependent on previous acceleration. The fact that falcons may accelerate first only means that they will hit their terminal velocity sooner in the dive.
My understanding of the situation is this (and if I’m wrong, I’m willing to be educated): In the start of a dive, a falcon is moving relatively slowly. It starts flying actively (powered dive) downward to push its initial acceleration up. At some speed, the added air resistance of having its wings open cancels out the acceleration it can provide with wingpower. So, it folds its wings into the most streamlined form it can, and allows gravity to continue to accelerate it (passive drop). Gravity will continue to accelerate it until the acceration of gravity is canceled out by the increased air resistance, which would be when the bird hits terminal velocity. The bird cannot go faster than this.
If this is correct, than the point of the initial wing-powered boost is so that the bird can hit terminal velocity (or at least a high velocity) in the space between it and the ground - which is not infinite.
So, feel free to educate me on basic aerodynamics.
Consumer Sovereignty, here’s a link to a web cam on a tall building in downtown Indianapolis, Indiana, USA. A pair of peregrine falcons has raised four chicks this year.
I stand corrected on a falcon’s terminal velocity. Darwin’s Finch’s information indicates that it is higher than I expected relative to that of a human. Given a falcon’s higher surface-area to mass ratio (because of its much smaller size) I would have expected its terminal velocity to be lower. This site indicates that the typical terminal velocity of a human skydiver spreadeagled (maximum air resistance) is about 120 mph. The record achieved at normal elevations without special equipment by minimizing air resistance is listed at 321 mph. It surprises me that a falcon’s terminal velocity could exceed this, since it is only about 1/35 the weight of a human. Clearly, its streamlining relative to a human clearly has a very large effect.
Well, it’s called a power dive because it is, in part, powered. Its not the quite the same as a dive-bomber, which may be applying power throughout the dive, but the falcon is certainly doing more than simply dropping like a stone.
There are various definitions of terminal velocity, but the most common one is the velocity reached when acceleration due to gravity is matched by air resistance. A more general definition is the second one on the list, which is “The velocity at which the driving forces are cancelled out by the resistive forces,” in which driving forces could include those other than gravity (e.g. wing propulsion). In my first quote above, what I had in mind was distinguishing the first definition from the second.
Yes, that is basically correct, except that if Darwin’s Finch’s figure is right, birds rarely if ever achieve terminal velocity.
My basic point is that the falcon achieves a faster speed at any point in time during its dive by using powered flight during the first phase than it would by using gravity alone. Compare it to a bobsled, say, in which one that receives a powerful push by its crew on takeoff will get to the end of its run faster than one which is merely nudged over the edge, despite the fact that it is only powered by gravity through most of its run. (Not a strict analogy, since we are dealing with contact friction rather than air resistance; however, I think the point holds.)
As the first link in my post indicates, Kittinger evidently reached 9/10 the speed of sound, but did not exceed it. The reason he was able to achieve such a high speed was the virtual absence of air resistance at such altitudes. He did not “freefall to Earth,” but only for about 7,000 feet of his descent.