[jhb] Re: Which Speed?
- From: "bones" <bones@xxxxxxx>
- To: <jhb@xxxxxxxxxxxxx>
- Date: Sun, 1 Jul 2007 20:14:43 +0100
V1 and V2 are computed for runway length and density altitude conditions. As
they are go/no-go speeds they are, essentially computed from runway distance
remaining. Assuming normal acceleration an aircraft should use x feet of
runway to reach a position from which it cannot stop again. Pilots can't
measure runway used so this is converted into a speed value. Of course a
quick look at this system can see awful flaws in it but it is the best we
can use.
bones
-----Original Message-----
From: jhb-bounce@xxxxxxxxxxxxx [mailto:jhb-bounce@xxxxxxxxxxxxx] On Behalf
Of Gerry Winskill
Sent: 01 July 2007 19:38
To: jhb@xxxxxxxxxxxxx
Subject: [jhb] Re: Which Speed?
I agree. The recorded figures are correct, having been reproduced
several times. The effect of the weight variations on stall speed, ie
the reaction of the model, isn't credible.
BTW, am I correct in assuming that V1 values have available runway
length as a component? If so the Vspeed gauge doesn't require it so
can't calculate it.
Gerry Winskill
bones wrote:
>If you can vary the weight between 246,000 and 400,000lbs then your
>stall speed figure variation of just 18kts is seriously wrong.
>
>bones
>
>-----Original Message-----
>From: jhb-bounce@xxxxxxxxxxxxx [mailto:jhb-bounce@xxxxxxxxxxxxx] On
>Behalf Of Gerry Winskill
>Sent: 01 July 2007 18:42
>To: jhb@xxxxxxxxxxxxx
>Subject: [jhb] Re: Which Speed?
>
>
>But at Actual All Up Weights varying between 400,000lbs and 246,000
>lbs, depending on fuel loaded, which is quite a large variation. It's
>just payload, not fuel, that can't be reduced, though it can be
>increased.
>
>Gerry Winskill
>
>bones wrote:
>
>
>
>>Except that will explain why your speeds are so narrow - the aircraft
>>is always operating at max payload weight.
>>
>>bones
>>
>>-----Original Message-----
>>From: jhb-bounce@xxxxxxxxxxxxx [mailto:jhb-bounce@xxxxxxxxxxxxx] On
>>Behalf Of Gerry Winskill
>>Sent: 01 July 2007 17:33
>>To: jhb@xxxxxxxxxxxxx
>>Subject: [jhb] Re: Which Speed?
>>
>>
>>The Max AUW is the same as quoted by Airbus. I'd guess he's just aken
>>the fuel wt from MAUW and put the rest in as aircraft weight,
>>including an unspecified load weight. It handles and performs so I'm
>>not too bothered about his shortcut.
>>
>>Gerry Winskill
>>
>>bones wrote:
>>
>>
>>
>>
>>
>>>If it is overweight with just full fuel and no payload then he's
>>>either got fuel capacity wrong or the Max AUW.
>>>
>>>bones
>>>
>>>-----Original Message-----
>>>From: jhb-bounce@xxxxxxxxxxxxx [mailto:jhb-bounce@xxxxxxxxxxxxx] On
>>>Behalf Of Gerry Winskill
>>>Sent: 01 July 2007 16:32
>>>To: jhb@xxxxxxxxxxxxx
>>>Subject: [jhb] Re: Which Speed?
>>>
>>>
>>>That was the first and obvious route I tried to take. To my surprise
>>>the FSX Payload Settins menu just has a single Staion 1 slot and that
>>>contained a default value of zero. Which didn't leave much scope for
>>>reduction. A check on a Default A321 shows it has a six slot
>>>variation capabillity, with a Default total passenger load of 14340
>>>lbs. At least the A350 designer hasn't just used a default model, as
>>>many do.
>>>
>>>Gerry Winskill
>>>
>>>bones wrote:
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>>Surely it would have been better to reduce passenger payload? Or was
>>>>the aircraft over MAUW with no pax on board?
>>>>
>>>>bones
>>>>
>>>>-----Original Message-----
>>>>From: jhb-bounce@xxxxxxxxxxxxx [mailto:jhb-bounce@xxxxxxxxxxxxx] On
>>>>Behalf Of Gerry Winskill
>>>>Sent: 01 July 2007 13:50
>>>>To: jhb@xxxxxxxxxxxxx
>>>>Subject: [jhb] Re: Which Speed?
>>>>
>>>>
>>>>Definitely!
>>>>I've just made one change to the aircraft.cfg. If full fuel loaded
>>>>it exceeds MTOW, so I've reduced the centre tank capacity to
>>>>correct.
>>>>
>>>>Gerry Winskill
>>>>
>>>>Alex Barrett wrote:
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>>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
>>>>>
>>>>>
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