[jhb_airlines] Re: Another Diversion

  • From: Gerry Winskill <gwinsk@xxxxxxx>
  • To: jhb_airlines@xxxxxxxxxxxxx
  • Date: Sun, 14 Aug 2005 19:27:02 +0100

I've been trying to find a way of reconciling the B1900D numbers, listed with the PDMG version, with some variation on Mike's formulae. I've not managed it. PMDG quoted figures are

WEIGHT       FLAPS      V1        Vr      V2
17120               UP        115      116     123
                        17         103      106     112
16000                UP       110      111     120
                         17        100      102     109
15000                UP       107      107     117
                         17        100      100     107
14000                UP       104      104     114
                         17        100      100     107
13000 &<          UP      103       103     113
                         17        100      100     108
Do they fit in with your spreadsheet?

Gerry Winskill

Bones wrote:

Not only are the figures aircraft specific they are also configuration
specific too - different values for each flap setting.

I've been playing around with this and you can almost do away with squares
and square roots. A basic play with Excel showed that if I tap in an AUW and
stall speed my readout for stalling at various actual weights can be very
closely approximated using Mike's /x +y formula.

Take an aircraft with an AUW of 6000 and stall of 88. If I use (actual
weight)/92 +45 it gives me fairly accurate results between a weight of 3000
and 6000. Only a 1.6kt error to real stall over the whole range.

For a 2400lb aircraft at 60kt stall my trial and error gives me (Actual
Weight)/55 +31 to give only a 1kt error between 1200lb and 2400lb.

For a 2400lb aircraft at 45kt stall (say with flaps down) the figures change
quite a bit to (Actual Weight)/91 +19 - giving only a 0.5kt error.

The values obviously change for each flap setting and also the speed you are
after. Actual stall speed for a given weight and the approach speed for that
weight require differing values. For the above 2400/60 example the approach
speed determination works if you change the values to (Actual Weight)/68

To make these figures work you must have actual known aircraft values for
Max AUW and the stalling speed for every aircraft flap configuration. Only
then can you start working out the simpler formulae for the figures. It's
possible Mike has an easier way of working these out but it's not obvious to
me yet.


-----Original Message-----
From: jhb_airlines-bounce@xxxxxxxxxxxxx
[mailto:jhb_airlines-bounce@xxxxxxxxxxxxx] On Behalf Of Gerry Winskill
Sent: 14 August 2005 17:35
To: jhb_airlines@xxxxxxxxxxxxx
Subject: [jhb_airlines] Re: Another Diversion

I think the most obvious comment on Mike's formula is that it must be specific to the F100; though it has also to be said that it doesn't agree with the V numbers produced by the other gauge. When used in the B1900D it produces V numbers almost 30 kias below the real figures, despite picking up the correct gross weight.

Gerry Winskill

Bones wrote:

For light aircraft pilots are taught just the two stalling speeds for
the aircraft - flaps up and flaps down - which are based on the max AUW
of the aircraft. The thinking here is that most light aircraft don't
have a great speed or weight range and so it isn't necessary to over
complicate the issue with deeper explanations. The ASI is also marked
with these two speeds - the bottom of the green and white arcs - and
this should be the end of the matter.

In truth though we all know that stalling speed is relative to several
variables - especially weight. Higher weight means higher stall speed
which means higher V1, V2, Vr and approach speeds. For airliners the
difference between almost empty and full weights is considerable and
therefore the stall range is too great to have one fixed value. Pilots
therefore have to work out the speeds based on actual aircraft weight.

Once I was taught this I actually worked out the figures for the light
aircraft I flew and found that even a PA28 had a 10kt stall variation.
It doesn't sound a lot but on the Archer it means the difference
between landing on the numbers and floating halfway down the runway as
speed decays. Approach speed is nominally 1.25 x Stall so the variation
compounds. In the case of an aircraft with a Max AUW approach speed of
75kts it could easily, when almost empty, fly the approach at 62.5kts
and still have the same safety margin over the stall.

The formula I use isn't as simple as that below as it involved square
roots. I'll have to see if Mike has found an alternative calculation
that avoids them.


-----Original Message-----
From: jhb_airlines-bounce@xxxxxxxxxxxxx
[mailto:jhb_airlines-bounce@xxxxxxxxxxxxx] On Behalf Of Gerry Winskill
Sent: 14 August 2005 13:45
To: jhb_airlines@xxxxxxxxxxxxx
Subject: [jhb_airlines] Re: Another Diversion

Another gauge, also within the PF100 Panel package, is CRJ_REF.cab, by Mike Worley. This looks more attractive and has pages for Pre Takeoff, Cruise and Landing. Looking into its .xml file, the approach to the V number calcs seems less sophisticated, as follows

V1 at Flaps  8    (Tot Wt / 500) + 42
V1 at Flaps 20   (Tot Wt / 556) + 41

Vr at Flaps   8   (Tot Wt / 500) + 47
Vr at Flaps 20   (Tot Wt / 556) + 46

V2 at Flaps   8   (Tot Wt / 625) + 78
V2 at Flaps 20   (Tot Wt / 556) + 55

Vref at Flaps  0    (Tot Wt / 610) + 96
Vref at Flaps  8    (Tot Wt / 610) + 84
Vref at Flaps  20  (Tot Wt / 641) + 83
Vref at Flaps  30  (Tot Wt / 610) + 74
Vref at Flaps  45  (Tot Wt / 610) + 66

I can't find a logical thread here, particularly since the max gross wt
of the CRJ600 is about 45,000 lbs.

Any shafts of insight?

Gerry Winskill gwinsk@xxxxxxx

Gerry Winskill wrote:

For UK FPI flights I often use the Project Fokker F100. One of the
gauges accessible gives the V1, Vr and V2 values. It also links them
to unacceptible flap postitons, etc. Better yet, it offers the option
of call outs. A quick check shows it to be a CAB file gauge. Looking
at the .xml file reveals it's designer is Doug Dawson and that he has
inserted instructions on how to make bespoke versions, specific to
other aircraft types.
Quite a small gauge but a complex .xml file.
I may be gone for some considerable time. Who was it started off this
need to look into .xml gauges................

Gerry Winskill

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