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
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