Covenant
Nice to see two very informative posts that tidy up some things that others have said – perhaps without full consideration. A couple of points regarding what you said came to mind.
Before I get to those, I must admit that I have never flown Concorde, but I was lucky enough in the mid sixties to fly both the RAE single seat aircraft (HP115 and BAC221) that were purpose designed to study the handling and performance characteristics of the projected Concorde planform. I also flew a Vulcan specially modified to look at piloting aspects of engine failure on take off as it would apply to the Concorde, as well as spent many a long hour in the Bristol Concorde simulator – then used for development and now the primary training aid for today’s crews.
This work, on behalf of the RAE boffins, left me in no doubt that the increase in drag that you refer to (when a delta flies slowly at higher angles of attack than ordinary wings can reach without stalling) is the dominating characteristic of such flight. Indeed it leads to the notion of the zero rate of climb speed (Vzrc) that is mentioned in several appropriate places in the BEA reports. If you slow down to this speed you (by definition) need full throttle just to hold that speed in level flight. One knot (or more) slower and you are in big trouble. You must lower the nose so as to reduce lift and the associated induced drag, which means you give away height in order to pick up speed. Just like the stall recovery case for conventional types. When I left that scene the boffins were seeing this Vzrc as the direct equivalent of Vs for all certification purposes. It is not a stall but it has the same effect as one and margins (1.3 or whatever) would need to be provided to keep pilots away from it just like the stall.
That I guess is neither good nor bad news. But what is very bad news is that the Vzrc is hugely dependent on the amount of thrust at your disposal. If you chop a donk Vzrc may leap up 20 or 30 knots or more depending on the aeroplane concerned. Now you are talking of a much more lethal effect than the slight increase of stalling speed that happens when thrust is lost on most aircraft.
With this in mind the linear part of the “delta wing” curve in your diagram above may not all be usable in level flight – or there again it may be possible to go right over the top and down the backside quite easily if you have monster amounts of thrust attached to your left hand (watch the Russians at airshows). But being on that part of your curve may (again depending on the design) bring about huge trim changes leading to loss of attitude control with even low levels of turbulence.
Perhaps all this is why one hears so much talk about “departures” rather than “stalls” these days. I like it when people talk about the aircraft “departed from controlled flight” because it is all embracing and not just about lift (or the lack of it).
So, months ago, when I first looked at the curves of airspeed, angle of attack and height from the accident flight, I was full of sympathy for Marty’s predicament. For what it is worth, it seems to me that he actually managed to finesse a knot or two at constant height and was initially flying quite brilliantly. Did you notice BTW that when that delicate balance was eventually lost (perhaps due to fire damage of the aerodynamic surfaces with associated change in longitudinal response) how high the aircraft shot up as the lift available at the suddenly increased angle of attack momentarily took charge?
Regards
edited for usb finger trouble
[ 01 September 2001: Message edited by: John Farley ]