The Internet holds an amazing amount of unsuspected info; apart from the Confidential A350 purchasing contracts I dropped across yesterday. Often it's possible to unearth flight test articles, by aviation journalists. They usually quote weights etc for the flight, then V numbers used on that flight; specific to other conditions associated with that flight. MTOW, range, cruise speed, ceiling etc are widely available via manufacturers' sites. Look into the aircraft.cfg files and the designers have obviously visited the same sites. The discrepancy is that the aircraft don't, often, perform to the spec set out in the file. I can understand that with aircraft like the A340. It's more difficult to accept something like the takeoff figures for the Default A321, where MS should have a head start over third party designers. In most respects what I'm doing is indeed to forget the spec of the real aircraft and define the performance of the Fsim model; a luxury perhaps but it keeps me off the streets. In fact that's not strictly true, since I've just come back in from a 40 mile interlude on the Bonnie. I'm still surprised to find that the fully loaded Default A321 takes off at 84 kias; under any conditions! I'm even more surprised when my stall tests show that, at the same MTOW, its dirty stall speed is 110kias. So, it can take off at 25 kias below its stall speed.......odd. Still, they are moving more towards the games market.
Gerry Winskill bones wrote:
Yep - you are pushing FS beyond its limitations here. Forget real aircraft values for this exercise. The issue is with the aircraft performance file and if the designer hasn't got this locked down to the performance of the real aircraft then you aren't testing an A350 or DC10 but a mythical design - for which a full flight test program needs carrying out to find it's boundaries. Any aircraft will lift off at stall speed - because this is the minimum speed for flying and you are accelerating past this on take off. FS models the low speed performance awfully so accept that designers can't get this right all the time and that variation exists. Another thing is that you say there are discrepancies between some models and the real aircraft but where did you get real aircraft values from? The stall speed varies with a huge number of factors - weight, ISA, flap setting are the obvious ones - but it varies between aircraft fleets too as the aircraft specification may change. A Boeing 737-8AS or Ryanair will have different figures for a Boeing 737-8K7 of Austrian Airlines. That is why performance manuals are written for specific aircraft - even the two PA31 aircraft I used to fly had different figures. The best you can do in FS is to hand fly each aircraft and determine your own values - forget any book figures quoted from real manuals. bones -----Original Message----- From: jhb-bounce@xxxxxxxxxxxxx [mailto:jhb-bounce@xxxxxxxxxxxxx] On Behalf Of Gerry Winskill Sent: 02 July 2007 11:27 To: jhb@xxxxxxxxxxxxx Subject: [jhb] Re: Which Speed? What triggered off this Quest was the thought that I should rationalise the aircraft kept in my FSX Airplanes folder, so that it would hold only those I use, plus those required as AI. The others were moved to my FSX Hangar. So, I finished up with a restricted fleet of 4 GA aircraft and 8 others. The "others" were CITATION II B1900D, PDMG DASH8 Q400, Dreamwings CRJ900, POSKY A320 (BA), IFDG ERJ145, Dreamwings A350, CamSim A340-313, Aerodesigns Most had a Vspeed gauge with speeds related to published weight and V number data but I decided to run all of them through the checks I'd carried out on the A350, so that Vspeeds reflect the simulated aircraft. I also threw into the tests the Default A321. Main criteria for selecting the fleet was what seemed to be acceptably realistic performance, although the Dash8 doesn't behave as well in FSX as it did in FS9. The results showed slight discrepancies between the takeoff speeds and those of the real aircraft; with two exceptions. I do the tests at MTOW and a minmum weight, so that the gauge has a range to use. In the case of two of them I didn't bother with the lower weight. At MTOW and just the 12 degrees of flap deployed the A340 lifted off at 108 kias! Since I normally fly it with elevator trim set at 10, instead of the 80 I use for these tests, I would rotate, at this weight, at the more realistic 156 kias and not spot that it would have been able to lift off much earlier, particularly since its acceleration is what would be expected. I can't think of a simple way of altering the lift off speed, without suffering knockon effects where I don't want them. So it looks a though the A340 is heading for the Hangar. The Default A321, at max weight and just the first degree of flap set, takes to the sky at a slightly unbelievable 95 kias! It's used by AI or it would be dustbin bound. The expression "can of worms" starts to surface. Gerry Winskill I
