Chris Blake December 2, 2010 12:16 PM If I were Bill Gates, I\'d pay for one of these up-front. SWEET!! Arthur Hu December 8, 2010 01:31 PM 800 mph would be supersonic. .95 mach at altitude is somewhere in the neighborhood of 650 mph, about the same as the B-52 or F-86 PeeCeeBee December 13, 2010 09:00 PM Glad it wasn\'t just me thinking ....800mph...subsonic..???..!!! 800mph is Mach 1 at -15000ft - a bit tricky to achieve!! lol! This link shows what it should be: http://www.aerospaceweb.org/question/atmosphere/q0112.shtml So that leaves - how fast is this aircraft? If it is 800mph, then it is a really serious piece of kit? But.. ...much more likely, somebody has divided the speed of sound by the 0.925 performance, instead of multiplying it!! So the actual speed is probably just under 700mph, still not too shabby!! Dan K December 24, 2010 03:36 PM The speed of sound is EXTREMELY variable, with temperature, pressure altitude, etc... 800mph is entirely feasable as mach .95 Richard Mathie January 19, 2011 07:49 AM the fastest civil aircraft ever was concord or the TU 144, they were both civil aircraft and cruse at about Mach 2 or 1334 mph mommus January 26, 2011 11:02 AM 650mph is about the avearage speed of sound at ground level. At 40,000ft the air is thinner and the speed of sound is higher, though I suspect 800mph (ground speed) would only be possible with a strong tail wind, such as the jet stream. Fosteve February 1, 2011 05:28 PM LSS is calculated by temperature not altitude. Altitude is irrelevant as one day at 20,000 feet it can be -25 C (ISA) and with a temperature inversion it could be -10 C Formula for LSS: Temperature in C 273 Kelvin (Square root the answer) x 38.94 = LSS in Knots x 1.15 = LSS in MPH i.e. at 40000 feet its -56.5 -56.5 273 = 216.5 (Sq root 216.5) = 14.71 x 38.94 = 572 Knots x 658 MPH Gabriel Jones March 11, 2011 12:26 PM Speed of sound gets slower as altitude goes up. It is related to the density of the medium through which it is traveling. speed of sound is = to the sqrt of the C(coefficent of stiffness)/p(density)... Facebook User April 11, 2011 03:15 PM Fosteve is right. .925 Mach is nowhere near 800MPH. At ANY altitude or temperature, but I\'m sure the jet could hit 800 in a dive.... We\'ve all heard of \"vaporware\" software... this is what\'s called a \"Vaporcraft\" Roger Bamkin April 15, 2011 06:30 AM Fast ever it says in the headline .... apart from the Concorde that is. I see its correct in the article so maybe a different author?