[jhb] Re: Pirep Grrrr!
- From: "Fossil" <fossil@xxxxxxx>
- To: <jhb@xxxxxxxxxxxxx>
- Date: Tue, 27 Apr 2010 18:47:26 +0100
You can still get caught out in real life. If we had a reasonable load to
fly over a short distance (say IOM to BPL) we still required the diverted,
holding and taxi fuel - and that would still put you over MLW on arrival. I
think we worked out that the shortest sector length we could fly to stay
below MLW on arrival was 42 minutes but it only took 30 min to get to
Blackpool, Liverpool, Dublin or Belfast..
bones
bones@xxxxxxx
-----Original Message-----
From: jhb-bounce@xxxxxxxxxxxxx [mailto:jhb-bounce@xxxxxxxxxxxxx] On Behalf
Of Gerry Winskill
Sent: 27 April 2010 16:58
To: jhb@xxxxxxxxxxxxx
Subject: [jhb] Re: Pirep Grrrr!
Fiddling the contents to get it something like, after modifying some
parameters, is quite satisfying, so I shouldn't really complain.
The Gulfstream mods also highlight the need to fly by the numbers.
Having recorded the dirty stall speed, at a variety of weights, I have a
plaque that lists them. One of my instruments also displays current
total weight, so I can pick the correct landing Vref. With this
aircraft, that makes a big difference. for the landing weight at
Capetown the weight dictated 105kias. If I pick the Vref for a higher
weight, then the attitude to attain that speed is definitely too nose
down. At the correct 105 it's a more realistic attitude and the flare
and touchdown easy to handle.
To go with that, the data on fuel burn, for taxi, climb, cruise,
descent, hold and divert are in a Lotus spreadsheet. I enter Distance,
cruise altitude, tax time guess for departure and arrival and it gives
me the required fuel load. I cobbled that together a couple of years ago
and have the data input for a dozen aircraft. The spur for creating it
was leaving with full tanks, only to find I'd be well above Max Landing
Weight on arrival. Before making the spreadsheet I dealt with that by
designing in a fuel dump valve, opened and closed by a GF button. I
eventually realised I was becoming more non green than Jeremy Clakson,
so stopped using it and switched to leaving with a calculated fuel load.
All helps keep the few remaining grey cells stirred slightly...
BTW, still no sign of the overdue Langness Report?
Gerry Winskill
Fossil wrote:
> The difficulty for aircraft designers is that they need skills in too many
> areas these days. Most start out just wanting to design a nice aircraft so
> they get to grips with GMax or FSDS and eventually (after much torture)
end
> up with a very nice visual model. That alone can take months - it did for
my
> Tiger - but then FS created Virtual Cockpits so the poor designer now has
to
> create the instrument panel and gauges - and partly build the cockpit
> internal detail too.
>
> Next step is to find out about texturing (another learning curve) as it
can
> be tricky wrapping textures to part of the aircraft that are compound
> curves. Texture wrapping nearly had me throw the whole project away.
>
> Next comes sounds but these are complex to record and to apply in FS so
most
> farm out this work to sounds guys like Mike Hambly. Even after he sent me
> the Tiger sound set and I looked at the CFG file values I still couldn't
> make sense of what he'd written.
>
> Now you finally have a nice looking (we hope) visual model with working
> instruments and decent sounds - but the hardest part hasn't yet begun.
> Turning the grounded aircraft into something that remotely flies like a
real
> aircraft requires two disciplines. First is that, in the designing of the
> aircraft, you set the empty Centre of Gravity in the right place. Oddly
> enough this is embedded in the GMax file and if you've got it wrong when
> designing the aircraft it is a right pig to change. In fact you can't move
> it as it is the reference point for the visual model and the only solution
> is to move the whole aircraft model around it.
>
> The .air file and the aircraft.cfg file then need to be built to reflect
the
> handling and performance of the aircraft. Given that the .air file is a
> shadow of the earlier FS98 data set and is now quite crude the first shock
> for a new designer is that even if they have all the necessary book
figures
> to type into the aircraft.cfg file the sad fact is that the aircraft will
> not fly anything like the real aircraft. In truth you start off with the
> book figures and see how the FS aircraft flies and then slowly start
> adjusting all the parameters to get the aircraft as close to the real
thing
> as you can get.
>
> The trouble here is that you really need to know something about the real
> aircraft and the way it flies otherwise your changes are guesswork. With
the
> Tiger the first changes were in basic stability - get the aircraft in
level
> flight and then see what happens with a brief control displacement. This
is
> crucial because if you don't have correct response in yaw, pitch or roll
> displacement the aircraft will never handle correctly. This test has to be
> run through the full speed range of the aircraft too so it can take some
> time.
>
> Once this is determined the next step is to tune the aileron, elevator and
> rudder responses. Again this must be done across the whole speed range -
but
> slow speed testing has to be treated with caution as FS is awful in this
> area. Sadly FS isn't good at high AoA lift/drag calculations because it
> models both wings as a single surface and the result is an aircraft with
> very docile handling compared to the real thing. Only Real Air have pushed
> this boundary back but only by careful manipulation of the .air and config
> values.
>
> Once basic handling is tuned the designer can move on to gear and flap
> operation, tuning these for correct drag and pitch effects. Next is engine
> power changes on pitch and yaw but before doing this the correct power
> output has to be checked in case the FS model is over or underpowered.
> Whilst on the engine the fuel burn at various altitudes must also be
checked
> as this will have an impact not only on burn rate but also on range and
rate
> of climb/descent.
>
> And so it goes on, checking every config value and testing again and again
> because some changes will impact on other values already tested. It's hard
> work and you sometimes find the changes result in unacceptable behaviour
and
> you have to start all over again.
>
> I know a lot of designers are quite good at the external model and panel
> design but spare a thought for performance. Some of the config settings
are
> serious aerodynamic theory and a lot of people will quickly get well out
of
> their depth. A decent aerodynamicist might make a good stab at a design
but
> even here it needs some actual knowledge of the real aircraft's handling
to
> get it anywhere near being accurate.
>
>
> bones
> bones@xxxxxxx
>
>
> -----Original Message-----
> From: jhb-bounce@xxxxxxxxxxxxx [mailto:jhb-bounce@xxxxxxxxxxxxx] On Behalf
> Of Gerry Winskill
> Sent: 27 April 2010 11:50
> To: JHB Restricted
> Subject: [jhb] Pirep Grrrr!
>
> Just come back into the room, after hanging a couple of pictures for
> SWMBO. I'd landed at FACT at1037 our time. Back in to receive a fizzer
> saying I'd been idle too long, so days times cancelled.
>
> Anyway, the flight was to check the changes I'd made to the Gulfstream
> 550. It now flies as it should and covers the claimed 8000 nm, instead
> of its out of the box 6000 nm.
>
> It's difficult to justify criticising Freeware designers but I sometimes
> feel they are happy to produce a nice looking aircraft, with the correct
> numbers entered into its Aircraft.cfg. Flying the things, better still
> getting someone else to test it, seems to be overlooked. Pity because
> the Gulfstream 550 looks more like a commercial airliner than most
> bizjets, whilst having great range and performance.
>
> Whilst up in the loft, looking for frames, I came across a mini TV, that
> we used to use on the canal boat. Since it's analogue, it's merely a
> candidate for the bin. Pity but that's progress foryou.
>
> Gerry Winskill
>
>
>
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