A 7 foot tall Teratorn skeleton found in Argentina, Its flight feathers would have been 5 feet long. California Teratornis Meriami, found in the La Brea Tarpit. It's 1/3rd larger than the largest California Condor. 1.333=2.35 X 23 lbs Condor weight = Merriam's Teratorn weight of ~54 Lbs. (But this weight calculation ignored the Square-Cube Law and was incorrectly made just by proportion increase.— Swordmaker)
Calculations have been done by Ornithologists working with Aeronautical Engineers on the power the Argentavis magnificens had available to it under modern conditions (the only one's the team of scientists who did the calculations even considered — Swordmaker) to maintain level flight under 1G. They found that the Teratorn would require 600 Watts of continuous aerobic power just to maintain level flight... but they calculated the theoretical maximum power the bird could generate with its muscles (using extremely conservative estimates for its mass, and extremely liberal estimates for its wing area and flight muscle mass) was only 170 Watts. (Oops. It couldn't sustain level flight under 1G conditions! — Swordmaker)
In addition, it was calculated that their ideal Argentavis magnificens' stall speed for landing was 39 Mph... far too fast for a safe landing... and its take off speed with no headwind required the bird, whom ornithologists say was not well designed for running, to run at 39 mph... for ~100 feet down a 10º slope to gain air speed and lift and then hope it finds an 300 foot diameter continuous updraft of at least 3 feet per second to use to climb before it crashes back to the ground. Of course if our hypothetical bird were lucky, and if found an obliging headwind, it could run a bit slower or for a lesser distance. An alternative method to get into the air required the bird to climb up a >65 foot tree or cliff and jump off into a 5 mph head wind and hope to level off before hitting the ground... and THEN, again, find an large updraft. . . All the while avoiding hungry, ground based predators.
Strangely, while some Argentavis magnificens skeletons have been found in the Andes, the majority have been found on the Pampas... flat, level, treeless plains. (Again, oops... how does it get airborne? Sounds to me like an awful lot of luck and ideal conditions was needed to get this over sized, over weight bird into the air.— Swordmaker)
Other scientists were able to get the Merriam's Teratorn, a much smaller bird, into simulated flight... but to do it they assumed that the bird, 1/3rd larger then the California Condor, also weighed only 1/3rd more than the Condor! That is totally ignoring the Square Cube Law—which they are apparently familiar with—because they DID multiply the wing area of the Teratorn by the square of the size multiplier but didn't multiply the mass by the CUBE of the size multiplier... Why not? Did they think that the Teratorn's muscles and bones were 2.35 times lighter or more efficient than a Condor's? Most likely they fudged because that's what it would take to keep the mass only 1/3rd more. In other words, they cheated.
Procedings of the National Academy of Science, U S A. 2007 July 24; Volume: 104(30), Pages: 12398-12403.
Published online 2007 July 3. doi: 10.1073/pnas.0702040104. PMCID: PMC1906724 - Copyright © 2007 by The National Academy of Sciences of the USA
The aerodynamics of Argentavis, the world's largest flying bird from the Miocene of Argentina
Sankar Chatterjee, Department of Geosciences, Museum of Texas Tech University, Box 43191, Lubbock, TX 79409-3191; R. Jack Templin, retired aeronautical engineer, formerly with the Canadian National Research Council in Ottawa, 2212 Aster Street, Ottawa, ON, Canada K1H 6R6; and Kenneth E. Campbell, Jr., Department of Ornithology, Natural History Museum of Los Angeles County, 900 Exposition Boulevard, Los Angeles, CA 90007
Edited by Steven Vogel, Duke University, Durham, NC, and accepted by the Editorial Board June 6, 2007
Author contributions: S.C. designed research; S.C. performed research; R.J.T. contributed new analytic tools; K.E.C. studied the fossil; S.C. and R.J.T. analyzed data; and S.C., R.J.T., and K.E.C. wrote the paper.
Received March 5, 2007.
ABSTRACT
We calculate the flight performance of the gigantic volant bird Argentavis magnificens from the upper Miocene (~6 million years ago) of Argentina using a computer simulation model. Argentavis was probably too large (mass ~70 kg) to be capable of continuous flapping flight or standing takeoff under its own muscle power. Like extant condors and vultures, Argentavis would have extracted energy from the atmosphere for flight, relying on thermals present on the Argentinean pampas to provide power for soaring, and it probably used slope soaring over the windward slopes of the Andes. It was an excellent glider, with a gliding angle close to 3º and a cruising speed of 67 kph. Argentavis could take off by running downhill, or by launching from a perch to pick up flight speed. Other means of takeoff remain problematic.
You can read the paper here:
The aerodynamics of Argentavis, the world's largest flying bird from the Miocene of Argentina