# What kind of g-forces do birds feel during flight?

I was watching some videos of centrifuge training for air force pilots and I wondered about birds.

Has there been any study about typical values of g-forces birds encounter?

I was just reading about this last night. According to researcher Ken Franklin, a flight computer attached to a falcon’s tail revealed some amazing statistics.

(the following paragraph is from Thor Hanson’s Feathers, published by Basic Books, 2011)

The falcon and a lure were released at an altitude of 3000 feet; the falcon accelerated to 157mph before catching the lure and pulling out of her dive with only fifty-seven feet to spare. The gravitational force on her body at that moment was calculated at 27 G’s.
Fighter pilots risk losing consciousness at anything over 9 G’s.

OK, that’s it, his parents aren’t allowed to name anyone else ever again.

Their bodies are much less dense - especially bones - than humans so there isn’t as much mass counteracting the change in direction

Miscellaneous data point: A pilot (and everything else) in an airplane at a 60-degree bank from level feels 2 G.

(I noticed this when I was studying such stuff: The G-level on a plane at x degrees bank (or radians, whatever your measure is) is sec(x).

Huh? Isn’t this missing an acceleration?

A bank is an acceleration, because you’re changing direction.

If you fly your airplane in a curved path, with suitable bank and yaw, then absent any other acceleration forces on top of that, you will feel increased G.

Perhaps you’ve heard of the need for pilots to learn “coordinated” flying skills, which largely comes with practice. If you have just the right amount of yaw (rudder) for whatever bank (ailerons), then the increased G will be directed straight “down”, with respect to the bottom of the airplane (not “down” with respect to earth). You will not “feel” like you’re turning at all (like you would in a car), but you’ll know it because of the increased G you feel.

If the pilot doesn’t have the correct balance of yaw and bank, then the increased G will be felt as an off-center force, pushing the pilot either to the left or right (with respect to the plane). Either way, this is an inefficient turn. It may be done intentionally even while flying in a straight line, as when “crabbing” to land a plane on a runway in a cross-wind.

The pilot may monitor his turns by looking at the Turn and Bank Indicator as pictured and discussed here. If the plane is banked and turning and is coordinated, the ball will remain centered. Scroll down for picture of T&B Indicator showing a banked plane in a coordinated turn.

It needn’t be very high-tech. Gliders often have a coordinated turn indicator, consisting of a piece of string taped to the outside front of the canopy, as seen in the first picture here.

It’s been a few years, so somebody correct me if I’ve got this backwards: If you have too little bank, the plane and everything in it “falls” toward the outside of the turn, which is called a “skid”. In the extreme case, this is exactly what you experience when driving along a curve on a level road in a car. Racetracks are banked precisely to counteract this. If you have too much bank (think: airplane leaning too far over), then the plane and everything in it “falls” toward the outside of the turn, which is called a “slip”.

(Missed edit window)

OOPS: In this sentence above:If you have too much bank (think: airplane leaning too far over), then the plane and everything in it “falls” toward the outside of the turn, which is called a “slip”. I meant, of course, that everything falls toward the inside of the turn.

As for the OP: Birds, of course, know all these things.

The problem with human pilots is that they are in a sitting position. Under a high-G maneuver, the blood “wants” to migrate toward the feet, and the heart and circulatory system must work to maintain blood pressure in the head. In the F-16 aircraft, designers tilted the seatback 30 degrees away from vertical, reducing the vertical distance between heart and head by about 14% and increasing the pilot’s g-tolerance in the process. If you could figure out a way for a pilot to fly an aircraft while lying flat on its floor, he could probably tolerate quite a bit more than 9 g’s.

For a bird in a high-g turn, heart and head are pretty much on the same level; g-forces during turns and pullouts are directed from the top of the bird’s skull toward its chin. That distance is very short (just a couple of inches, even for the largest birds). In other words, the bird already is laying down while flying, just like that hypothetically prone fighter pilot.

Moreover, birds fly more slowly than fighter planes, meaning that for a given g-load, they will complete their turn more rapidly than a fighter pilot. A sparrow pulling 9 g’s at 40 MPH can do a 180-degree turn in 0.64 seconds; an F-16 pulling 9 g’s at 400 MPH will take 6.4 seconds to do a 180-degree turn. That’s enough time for the pilot to develop cerebral hypoxia and potentially black out; not so for the bird.

Bottom line? A bird’s size and speed facilitate high-g maneuvers, especially so for small songbirds (sparrows and such, as opposed to gliders like the albatross and vulture).

Great aero data in all:
Gliding flight: speed and acceleration of ideal falcons during diving and pull out.
VA Tucker
Predator versus prey: on aerial hunting and escape strategies in birds
Behav Ecol200112:150-156.
Flight performance during hunting excursions in Eleonora’s falcon Falco eleonorae
J. Exp. Biol.1999202:2029-2039.
And, lest we forget:

Courtship dives of Anna’s hummingbird offer insights into flight performance limits
Proc R Soc B2009276:3047-3052.

Highest length specific velocity of any vertebrate.

Gliding flight: drag and torque of a hawk and a falcon with straight and turned heads, and a lower value for the parasite drag coefficient Two more papers on same topic with different birds are available. Amazing stuff. Machine Elf: comments on paper?

This and all above cites but first one are full text.

Betcha didn’t know about the hummingbird, right?

Bad puns do not good names make.

If you want to see what high-speed flight looks like from the bird’s perspective, scientists have put on-bird cameras on hawks and falcons:

Here is a hawk maneuvering through a forest:

Here is a falcon doing high speed dives:
http://www.howtogeek.com/90241/on-bird-camera-shows-dizzying-flights-of-peregrine-falcon-and-goshawk/