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.
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
Landing 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 gwinsk@xxxxxxx