In reality no business jet will be fitted with autothrottle. Airliners have
them because there can be a huge variation in weight on bigger aircraft with
the aircraft, effectively, being grossly overpowered at light weights.
There isn't any harm in sticking an AT on an FS bizjet but the effectiveness
depends a lot on the quality of the performance file. The figures you give
would seem to suggest the aircraft is overpowered but there may be a reason
for this.
An AT will never give you bags of thrust when you dial in a higher speed or
ROC - just sufficient power to meet the new targets it has been set. I've
seen other aircraft that suffer a 10kt target loss but all I've done is add
10 to the required speed.
From your description below it seems as though the target ROC is being
achieved but with a shortfall on IAS. I presume you dialled in 340KIAS at
low level because at height it would have been pushing the aircraft along at
close to supersonic speed.
bones
-----Original Message-----
From: jhb-bounce@xxxxxxxxxxxxx [mailto:jhb-bounce@xxxxxxxxxxxxx] On Behalf
Of Gerry Winskill
Sent: 30 May 2007 08:48
To: jhb@xxxxxxxxxxxxx
Subject: [jhb] Autothrottle
In many of my modified panels I have a gauge to display the percentage
thrust lever setting.
On quite a few aircraft I've noticed that they are reluctant to climb,
on A/P, at dialled in rate of climb ans speed. The thrust gauge shows
that this is due to the A/P's niggardly use of Thrust.
At the moment I've just taken off in a Citation. It's climbing at 1800
fpm and not quite making the dialled in 240 kias. When I increase set
speed to 270 kias, it uses no more than 50 % and it doesn't make better
than 263 kias. If I then increase ROC to 2200, the thrust still doesn't
exceed 53%. If I make a bigger speed increase, to 340 kias, it initially
increases to 80% before dropping back to 53%, at which setting it
doesn't exceed 340 kias.
If I use manual throttle, I can get much better acceleration but have to
be careful not to pass my target speed by a large margin.
Any ideas folks?
Gerry Winskill
