I eventually got around to examining the effect of increasing the landing flap angle, on the TB21GT. It worked!

Before trying the mod I did a series of tests to check the actual stall speeds, at 30 deg and 45 deg, with the gear down. Under the same temperature conditions repeats show that it stalls at 56 kias and 52 kias, for the two settings.

I then increased the Landing Flap angle to 60 deg. The first pleasant surprise was, seen in spot view, that the angle did indeed increase. Equally surprising was that the increased angle was supported by the deployment brackets etc.

A repeat of the Stall checks showed the 30 deg figure to be unchanged but the 60 deg flaps reduced the stall speed by 3 kts, to 49 kias. I'd thought it might increase drag, without increasing lift.

Next to see what difference it made to landing attitude. With a landing completed, with power slowly pulled back during the hold off, a landing was completed, then played back. On Short Finals the attitude was slightly flatter. In the hold off the AOA increased realistically, before it greased itself on with no tendency to get close to a tail strike, as it had before.

A far better result than I'd expected. Although there was no crosswind to complicate matters, I had it set with no headwind either.

It's going to be worth trying on the other  couple of the of GA aircraft that I use and it might confirm my impression that the Lionheart TB21GT is above average.

Gerry Winskill


bones wrote:

Slow speed handling in FS is especially rubbish if you don't fiddle with the
values properly.

The average aircraft wing stalls at 15 degrees AoA (forgetting supercritical
sections and flaps). As you rightly observe some FS aircraft adopt much
higher nose up attitudes before the stall occurs which means the wing is
still flying at crazy AoA's. There's not a lot you can do about this unless
you want to rewrite the Section 404 data.

Your idea of adding more flap drag is a work around but you have to be
careful as both lift and drag values create pitch moments. I'm surprised
that drag coefficient is a fixed figure across all flap settings though -
where are you finding this value and what are you editing it with?

Don't forget that you can cheat by altering the flap selection settings in
the cfg file by stating higher deployment angles than in real life. If the
default values are 0, 10, 20, 30 you could change this to 0, 15, 25, 40 or
even 0, 15, 25, 60 (or more).

Note that in the .air file in Section 320 there is a Max Flap Angle value in
radians. I've no idea what this is for or whether it is now redundant.

bones

-----Original Message-----
From: jhb-bounce@xxxxxxxxxxxxx [mailto:jhb-bounce@xxxxxxxxxxxxx] On Behalf
Of Gerry Winskill
Sent: 08 September 2007 07:39
To: jhb@xxxxxxxxxxxxx
Subject: [jhb] Re: Pireps


Because I include the Vspeed gauge in my commercial aircraft, together
with a Plaque giving Vref and throttle settings for various weights,
I've had to carry out the exercise you describe, for about half a dozen
aircraft. I soon discovered that the stall warning is a dodgy FS
parameter and adopt your other suggestion, of using altitude drop. My
multipage check list gauge allows me to watch for the point at which
rate of descent starts to increase.
It becomes an enjoyable exercise in its own right, even though quite
time consuming.

The overall time required is greatly reduced if, in each case, a
situation is saved, so that you can recover to that situation, rather
than starting from scratch. For instance I might save a situation with
max landing wt, gear and flaps down and already within about 20 knots of
expected stall speeds, at my test altitude. With one data set aquired I
recover to the saved situation and start again.

I do the same sort of exercise with the takeoff regime, to get some idea
of required thrust v TOW. It's easy to just apply max thrust but with
low TOW for a short sector, a decent bizjet model would have you off the
ground in an unrealistically short time and extremely pushed to get it
down to 250 kias without climbing vertically. Your raising the matter is
going to force me to stop overlooking the effect of temperature. I do
hope my SWMBO doesn't bear you too much animosity!

Once the approach is adopted then I admit the workload just escalates.
Because of the variation in thrust settings, I was forced to make a
percent throttle setting gauge, etc, etc.

Another area where I've started to do a bit of fiddling is GA aircraft
landing speeds. In some, as delivered, it's quite difficult to land by
the numbers. Sometimes the stall speed proves to be significantly lower
than stated. Even worse, if you look from the outside, you find that
holding off to the stall always results in a tail strike because the
change of attitude doesn't produce an acceptable speed reduction..
Sometimes this can be improved by increasing the flap drag. Which is
where another limitation of FS surfaces. You can't increase the drag of
one flap setting, in isolation. So it's possible to get the landing
speed down to a realistic level, overcoming the equally unrealistic
slipperiness of something in the Spam Can bracket, only to find that the
first stage of Take Off flap increases the take off run to unacceptable
levels. I tried increasing the aircraft drag instead, but this requires
the available engine power to be taken beyond realistic levels, to
maintain correct cruise performance.

If you chuck this on top of the other bits in which we get involved,
then getting up at 0600 becomes essential. For no pay, you ask? The
blokes a nutter! I suppose we also forget how little we pay and what
flight dynamics accuracy we can expect to recieve, for the money.

Gerry Winskill



bones wrote:

 

Wind and speed - two of the most important factors on the approach and
landing.

A 10kt headwind can reduce landing run by 20% or more and because this
sort of wind is about normal for the UK most pilots get used to the
short landing it produces. A zero wind landing can still come as a
shock for the length of runway it uses up, the apparent lack of
deceleration after touchdown and the sloppy control reactions.

Speed is more critical. I've already mentioned this in respect to
Gerry's farm strips but it applies to all aircraft regardless of size.
Excess speed on the approach is going to result in excessive landing
distance. Speed is mostly relative to weight, which is why airline
pilots calculate the approach speed for EVERY approach. It is also
relative to other factors like flaps, temperature and pressure so a
complex graph is used to determine the right speed (or the FMS on
posher aircraft).

For light aircraft the published approach speed is usually a single
value and based on the maximum weight the aircraft is authorised for.
Technically this means you are safe at any weight (you won't stall if
heavy) but the lighter the aircraft is from MAUW the lower the stalling
speed and the more you will float on flaring the aircraft.

A PA28 181 has a flaps down stall of 49kts. Approach speed is 1.3 x
Stall so this is 63.7kts (usually rounded up to 65kts). This book
figure is based on the MAUW of 2550lb. With just one person on the
aircraft and 10 gal fuel the weight is down to 1800lb - a good 750lb
lighter - and this drops the stall speed by 7.8kts to 41.2kts. At this
weight an approach could be flown at 55kts safely. The important point
is that if the approach is flown at 55kts at 1800lb it results in the
same landing run as flying at 65kts at 2550lb - because the lift
generated on the approach is the same in both cases.

If you don't adjust for weight and fly at 65kts on the approach at
1800lbs then you are too fast. In flaring the aircraft it has to
decelerate from 65kts down to 41kts before the wing no longer generates
lift to fly and that eats up a huge chunk of runway.

It may be hard to apply this learning in FS because you need to know
the MAUW and the flap down stall speed of the aircraft you are flying
and this isn't always available. If it is then, as a rough guide, for
every 100lbs you are below MAUW subtract 1kt from the stall speed. Your
approach should be made at 1.3 x Stall.

Airliners are far more complex and the approach speed can vary hugely
with weight. I doubt many FS pilots use anything other than a nominal
book figure for approach speed but it would never work in real life.
Excess speed in an airliner on landing has far more serious
implications.

Even on big jets the same basic rule applies - approach speed is
determined as 1.25 x stall. If you are used to banging in the same fuel
amount on a jet each time you fly you can see from the above that a
short flight of 30min is going to need a faster approach speed (little
fuel used so heavier aircraft) than taking the aircraft across the pond
on a 7 hour trip. Which leads to a nice little exercise in FS for you..

Take your favourite jet and prepare it for flight as you might normally
do. If you never fiddle with fuel amounts so much the better. Before
you start this trip write down the normal speed you use for the
approach. Now get airborne, fly a circuit round to a 10nm final on the
ILS and settle on the approach in normal landing configuration at your
normal approach speed.

Set the Alt Hold to 500ft so the aircraft levels off at this height.
DON'T touch anything - keep the gear and flaps in approach settings.
Now, slowly start reducing the speed on AT so that the aircraft slowly
slows down - it has to be slow for a good reading. Forget that you have
overflown the airport as that was only to get you settled into correct
landing configuration with flaps and gear down. As you bring the speed
back watch for one of two things - either the stall warning or the
aircraft starting to lose height. One or the other will happen first -
it's a mark of how well the perf file has been written. Make a note of
the speed at which this occurs.

This exercise should show (roughly) the stall speed of the aircraft at
your normal loaded fuel weight. OK you may have spend 20 min doing this
so you could say it would represent a short flight. If you multiply the
observed speed by 1.25 this should be your approach speed AT THAT
WEIGHT - and it would be interesting to see if it is anywhere near the
speed you normally use.

I could ask you to repeat the exercise except this time you take the
aircraft for a pretty long run so a lot of fuel is burnt off. It may be
easier just to dump fuel using the menu. Regardless, if you repeated
the exercise but with a great deal less fuel on board (and maybe an
emptier
cabin) then when you come to reduce throttle to get the aircraft to stall
you may be very surprised to find that the figure is substantially less
  

than
 

when you flew with a lot more fuel on board.

For 90% of our flying we don't do any of this in FS and that is where
the division starts to break down between FS and real world flying. FS
is good for showing us system management of aircraft but it's pretty
much goldfish when it comes to teaching airmanship. Very few FS pilots
learn to appreciate the relationship between weight, speed, angle of
attack and approach handling.

One thing I may have misread from Mike's post but you should never vary
approach speed with wind strength. The only time you EVER do this is in
gusty conditions when you should add 50% of the difference between Max
and Min wind speeds as given by ATC.

bones

-----Original Message-----
From: jhb-bounce@xxxxxxxxxxxxx [mailto:jhb-bounce@xxxxxxxxxxxxx] On
Behalf Of Mike Lucas
Sent: 07 September 2007 12:31
To: jhb@xxxxxxxxxxxxx
Subject: [jhb] Re: Pireps


Something I discovered landing a F100 at EGNS last night.  Bones had
given me "Winds calm"; I had the approach set up perfectly, usual
speed, full flaps ... but it just felt wrong coming over the threshold.
I have never experienced a medium jet going "floaty" on me, but that's
the only way I can describe it.  Fortunately I had enough margin to
plonk it down after using rather more of the runway than usual, and I
stopped before the end - but only just; I had to backtrack for Taxiway
B.  I could/should have knocked 10 kts off my final approach speed.

Mike L

bones wrote:



  

Wind is your friend - with a 10kt headwind your
landing run is greatly reduced but pilots get used to this. Landing
with no wind eats up more runway but this is exceptional in the UK and
so pilots don't realise what the normal landing performance is - they
become accustomed to windy conditions and it affects their perception
of landing distances.