[simpits-tech] Landing aircraft

[Justin Messenger]

Brian,

for info on what the F-4 is like to fly you might want
to check out this webpage
www.geocities.com/cap17.geo/FlightPerformance.html
I think the F-4 has a much more sophisticaed flight
control system than other jets of the time, such as
the F-104, F-105, or F-106. When the F-4's Automatic
Flight Control System is out of rigg the the pilot is
not to fly agressivly, and is to land ASAP. I heard a
story of an F-4 flying low to the ground at highspeed
when the A.F.C.S. malfunctioned. The Fighter suddenly
rocked up and down out of control, pulling up to 20g.
Th pilot regained control and safely landed and the
F-4 had to have a serious overhaul before flying
again. here is the section I have that deals with your
question.

Q.Does the pilot feel anything in the stick when 
he taxi, icluding any difference with front wheel
streering 
engaged/disengaged? 

A. Stick stays in a neutral position (2 degrees down
for takeoff)
with/without steering button engaged. Nose wheel
steering button is
held depressed and rudder pedals used to steer.

Q. While in the air, does the hydraulic system take
out any feel of the 
pressure on the flight controls? Lets say the aircraft
is out of trim 
and wants to go in a nose down attitude, do you feel
any pressure on 
the stick when you try and hold the aircraft in a
level attitude? 

A. There is an artificial feel system in the aircraft
(bellows intake is
on the vertical stab). Stick forces change with
airspeed, flap
changes, etc, and you constantly need to trim the
pressure out --
except in situations like formation flying where you
can get more
precise control while having resisting stick pressure
from  some nose
down trim. Thumb that operates the trim button is one
of the most worn
areas of the right glove!

Q. How do you tell you are out of trim? 

A. Airplane wants to go up/down or left/right (and in
some cases yaw -
rudder is also trimable)

Q. Is there anything unique in the feel of the stick
at anytime in the F-4's flight 
envelope that I need to know about for my simulator?

A. Trim change most dramatically when raising/lowering
flaps, and when
going from supersonic to subsonic (for example, you
need more stick
supersonic, and if you then go subsonic with the same
back pressure
during the transition, you'll get "Mach Tuck" as the
stab becomes more
effective (around .85 I think..or .92...can't
remember). Easy way to
over G the aircraft. Lots of trim changes also while
refueling as
Center of Gravity shifts and Angle of Attack
increases.

Q. When you start the engines, do you feel any kind of
vibrations 
through your seat and in the cockpit? 

A. Yes, but not very much.

Q. I guess when in the air in level flight it has a
smooth ride. I know 
at high angles of attack the flight gets rough. One of
my F-4 videos 
shows an in the cockpit view while the pilot follows
an F-5, and it 
looks like the thing is going to shake apart.

A. High speed at low altitude generally gives a bumpy
ride. As for high
AOA -- the F-4 gives plenty of warning starting with a
slight "burble"
and going to a full wing rock before departing
controlled flight.
Trick is to know the optimum rumble corresponding to
the optimum AOA.
There is also a tone and a visual AOA indicator, but
seat of the pants
allows  focus on what you are chasing/dodging.

 At optimum AOA, the aircraft is turned with back
pressure and rudder
-- any aileron/spoiler deflection creates adverse yaw
and will
actually flip the aircraft opposite the direction of
intended turn
(the yaw causes the inside swept wing to get more
perpendicular to the
relative wind causing greater lift here than the
outside wing,
therefor rolling the airplane to the outside of the
turn.

Gene K
You don't have much 'feel' in the stick on the ground.
You can tell when the NGS is engaged by how the nose
tracks across the ground, but not much feel in the
stick. 
In the air, the F4 has a relatively complicated feel
trim system using ram air bellows, hydraulics and some
electrics. The stick force can be tremendous, my
stabilator trim once failed to the full nose up
position over the South China Sea and we had to fly
400 miles back to home plate - when the strength in my
arms and my pilots arms gave out, I flew about 200
miles with both feet planted on the stick so that we
would have some strength left in our arms to land! 
The hydraulic systems take out just about all of the
actual aerodynamic forces on the F4, but, "Artificial
feel systems provide simulated aerodynamic forces on
the control stick and the rudder pedals" to quote the
dash one manual. This artificial feel system does give
you pressure on the stick when the jet is out of trim,
so you feel back pressure to hold the jet in level
flight if you have nose down trim input. 
That is how you tell if you are out of trim. To tell
if the ailerons are trimmed up the back seater looks
in his mirrors and trims both ailerons level with the
wing fuel dump vent masts and if the jet then starts
to roll 'hands off' or you feel side pressure on the
stick then the jet is either out of rig or the
external or internal wing tank(s) did not feed. To
tell if the rudder is trimmed, the pilot asks the back
seater when 'the ball' (on the turn and slip
indicator, which is larger and more accurate in the
back seat) is centered (the WSO tells the AC something
like 'the ball is half a ball left' and the AC trims
out the rudder until the ball is centered)(the rudder
trim switch is in the front cockpit on the inboard
engine control panel). There is really no way to tell
if the rudder is out of rig inflight unless you can
see a huge deflection in the mirror or your wingman
can see. You trim the rudder amidships with the help
of the crew chief on the ground during the flight
control checks after engine start.
 There is an interconnect between the aileron and the
rudder that automatically causes rudder displacement
proportionate to aileron displacement to provide
coordinated turns at low airspeeds. The rudder will
displace 15 degrees when the automatic flight control
system is in the stability augmentation or autopilot
modes, and 10 degrees when the yaw stab aug switch is
disengaged. 
Also, artificial feel is supplied to the rudder pedals
by an artificial feel trim system. An airspeed
pressure switch is set to convert from a low to a high
gradient of pedal pressure at airspeeds between 228
and 252 knots while accelerating; during deceleration
the gradient changes between 232 and 218 knots. The
purpose of this is to provide the pilot increased
awareness/sensitivity to rudder inputs at lower
speeds. You can actually feel the gradient change if
you have any rudder input when the shift occurs (it
can be quite a surprise!). Rear cockpit rudder pedal
forces are about 1 and a half times those of the front
cockpit rudder pedals. There is also a stall warning
vibrator on the front cockpit left rudder pedal that
is electrically connected to the AOA indicator. The
'pedal shaker' activates at 22.3 units AOA with the
gear down. 
A significant change in handling qualities occurs at
.92 to .95 Mach. When you go supersonic you can feel
the change in static longitudinal stability and
stabilator effectiveness by a slight nose drop or nose
heaviness (this phenomena is not unique to the F4 and
is called "Mack tuck"). The reverse happens when you
go from super to subsonic flight and the effect
increases with g and decreasing altitude. More than
one Phantom jock has over-g'd the jet when transonic
dig-in occurs in the middle of a dogfight! 
When you put the speed brake out, the jet tends to
buffet, especially at higher airspeeds. And the jet
can buffet quite a bit at higher g loads.
David  Beatty 
 

===========
Hi,  I've got a couple of questions I would like to
ask John P. Miguez =
and Ben Jones.=20
On F4s and other fighters of that time, do the control
forces increase =
with air speed? Also what degree of feedback do you
get on the stick =
from buffeting etc.
Thanks,    Brian West.


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