Gerry,
I was always taught that a general figure for Vr would be 1.1 x the
aircrafts stall speed with flaps retracted.
I actually downloaded the A350 yesterday and have started doing a
repaint for it, but haven't yet flown it. In your opinion is it a
"goer" as they say?
Alex
Gerry Winskill wrote:
Having decided not to make assumptions about Vr, I ran a series of
tests, at max and minimum takeoff weights, to find the takeoff speeds
at the various permissable flap settings. I ran the tests hands off,
with elevators trimmed up at 60%. I've got decent rpeatabillity, so.....
I know it's nowhere as simple as a linear relationship but is there a
reasonable difference I can apply to the takeoff speeds, to get to Vr?
V1 and V2 are not, I guess, capable of being arrived at by rule of
thumb.
Gerry Winskill
Gerry Winskill wrote:
A couple of days ago I downloaded the FSX version of the wide bodied
Airbus A350. It looks good and flies well.
One advantage of the Airbus familly, to users of Fsim, is that
commonality of panels etc is a real aircraft feature. That left me
needing to modify the Vspeed gauge, to reflect the A350's weights
and V numbers. I've not managed to unearth any V number data but
weights and performance are available, from the Confidential sale
contract conditions that have found their way onto the Net..
For Vr I'm assuming that the numbers won't be far off those for the
rest of the familly.
Producing Vref data should be straightforward, since all I have to
do is determine the dirty stall speed, at the same altitude and with
zero wind, for a set of All Up Weights. Only it wasn't
straightforward. The aircraft.cfg gives the dirty stall speed as 124
kias, without reference to any weight. In fact there seems to be no
Aircraft.cfg facillity for varying stall speed with weight.
The difference between the stall speeds I determined and the
Aircraft.cfg figure were big, to enormous! At Max Permissable
Landing Weight of 400,000 lbs it stalled at an indicated 99 kias,
with the Stall Warning following a few knots below that. At the
bottom end of the weights, with just the minimum permissable fuel
reserves, it stalled at 80 kias.
As if that isn't bad enough there was a discrepancy between the AIS
/ Map indicated speeds and the Ground Speed recorded in my Checks
gauge. When ASI read 99 the GS was 110. With ASI at 80, GS was 88.
Where does that leave me? It seems reasonable to take the actual
stall speeds recorded, as the route to calculating the Vref figures
for the simulated aircraft, but should I use the ASI or the higher
GS figures?
In passing, the figures for dirty stall speed in most of the
aircraft I fly seem to be higher than the actual speed at which the
stall occurs. Which explains why I can seldom hold off enough to get
the Stall Warning klaxon to sound, when landing. Which makes it seem
likely that the actual stall speed data is held somewhere other than
the Aircraft.cfg. The fact that there is an actual variation of
stall speed with weight seems to bear this out, since that ain't
possible from the data held i the Aircraft.cfg. This is a serious
limitation of FSX and its predecessors, since lapses of
concentration allowing the speed to fall to the stall don't produce
the wake up effects of a real life lapse!
Gerry Winskill
--
Alex Barrett
Turbine Sound Studios
(+44) 0121 288 3195
alex@xxxxxxxxxxxxxxxxxxxxxxx
http://www.turbinesoundstudios.com
