Crosswind Landings / "Impossible Landing" TE / Crosswind landing advice
-
Some info, just gee whiz
CROSSWIND LANDING
The recommended technique for landing in a crosswind is
to use a wing level crab through touchdown. At touch-down,
the ARI switches out. Undesirable yaw transients
may occur if roll control is being applied at this time.
After touchdown, perform two-point aerodynamic braking
using the rudder to maintain aircraft track down the run-way and
flaperon to prevent wing rise. In crosswinds, the
aircraft may drift downwind due to side loads imposed by
the crosswinds or travel upwind due to insufficient di-rectional
control inputs/availability. As the airspeed de-creases, increasing
amounts of rudder are required to
maintain track. Maintain two-point aerodynamic braking
until approximately 100 knots or until roll or directional
control becomes a problem. As the pitch attitude de-creases,
the nose tends to align itself with the ground
track.Aft stick and fully opened speedbrakes reduce stopping
distance. Apply brakes after nosewheel is on the runway;
however, if stopping distance is a factor, refer to SHORT
FIELD LANDING, this section. With all LG on the run-way, maintain
directional control with rudder, differential
braking, and NWS if required.
During landing rollout, the main concerns are wing rise
(roll control), weathervaning (directional control), and
downwind drift. Wing rise is controlled by flaperon into
the crosswind. Excessive flaperon deflection degrades di-rectional
control. Use rudder and differential braking to
control ground track, especially on wet or icy runways.
Engage NWS if required to maintain directional control
and to prevent departure from the runway. Excessive dif-ferential
braking may result in a hot brake condition. High
rudder pedal force may result in a yaw transient when
NWS is engaged. NLG strut compression is required to
engage NWS but sustained forward stick may result in full
horizontal tail deflection which decreases weight on the
MLG and thus reduces wheel braking effectiveness.Rudder Subsystem Theory of Operation. ISA
movement positions the rudder in response to commands from
the DFLCC. Yaw command signals from the yaw rate gyro
and the rudder pedals assembly are input to the DFLCC
. Additional inputs from the normal/lateral ac-celerometer, gun firing command, and YAW TRIM control
are also used to generate rudder position commands.
Aircraft yaw is controlled by inputs from the yaw
rate gyro assembly. This assembly is mounted to allow the
internal gyro spin motors to sense the rate of movement about
their axes. These motors generate four redundant yaw rate
signals to the DFLCC through their respective pickoff trans-formers. The Aileron-Rudder Interconnect (ARI) feature
counters the yawing moments produced by the roll control
surfaces. There is a wide variation in lateral control induced
yaw with flight condition and AOA. As a result, the ARI gain
is varied as a function of AOA and mach number. Sideslip
during roll maneuvers is minimized by combining the roll rate
signal and yaw rate feedback signal. The roll rate signal is
gain-adjusted by the angle of attack.
Normal/lateral accelerometer transducers sense lat-eral movement of the aircraft and generate input signals to the
DFLCC. These signals are combined with the yaw rate input
signals in the DFLCC. The resultant command is transmitted
to the rudder ISA to position the rudder control surface
accordingly.
A compensation signal is provided for the yawing
moment caused by firing the off-centerline mounted gun. The
gun firing compensation signal produces a static and dynamic
pressure adjusted rudder deflection command. This command
is also fed to the roll control system to compensate for the
rolling moment due to rudder deflection. An accelerometer
mount assembly is installed between the accelerometer and
the airframe. This mount isolates and inhibits
inadvertent lateral accelerometer input signals during gun fir-ing.
Yaw trim commands may be input through the
rotation of the YAW TRIM control. Deflection of the left or
right rudder pedals provides a nose left or nose right move-ment. Rotating the YAW TRIM control counterclockwise
moves the nose left and clockwise moves the nose right.
Markings adjacent to the control provide visual trim indi-cation. Yaw commands are summed electronically in the
DFLCC. These commands are applied to the coils of servo
valves SV1, SV2, and SV3 in the ISA. Under normal con-ditions, servo valves SV1 and SV2 are active and SV3 is in
standby. Active servos will port hydraulic fluid to position the
main control valve. This control valve then ports hydraulic
power to drive the ram in the desired direction. A mechanical
feedback nulls the main control valve and servo valves when
the ram has reached the commanded position. Each servo
valve coil contains two separate windings (SD 27-26-_ _).
Normal operation of the servos is possible with either the
primary or secondary winding. Outputs from the DFLCC
servoamplifiers are monitored by other DFLCC circuitry. A
malfunction will switch operation to the standby amplifier and
the secondary winding for that servo valve.
A hydromechanical monitoring and voting system
within the ISA monitors the outputs of the three servo valves.
A detected system failure in SV1 or SV2 will vote out the
malfunctioning servo and transfer control to SV3. A failure
will illuminate the MASTER CAUTION light and FLCS
caution light. A fault message will also appear on the Pilots
Fault List Display (PFLD). Failure detection/correction is
latched in after a malfunction. Reset is possible by placing
FLCS RESET switch to RESET and releasing. Reset cannot
be accomplished if the malfunction still exists. The flight
control panel is available in the forward cockpit only.
If a servo malfunction is indicated (rudder PFL),
positioning the FLCS reset switch to RESET will attempt to
reset the appropriate ISA. A recurring fail (same pressure
switch) will redisplay PFL (provided previous reset attempt
was successful). If an additional malfunction occurs, the
FLCS FAULT light will blink (if previous fail has not been
reset) to indicate additional FLCS fault(s) has occurred. The
ISA will continue to operate with one hydraulic system failed.
If pressure for both hydraulic systems drops below 720 psi,
the spring will command the ISA to neutral -
I thought that is what most aircraft do on approach due to ground effect.
Ground effect only occurs when your height above ground is equal to or less than your aircraft’s wingspan. So in an F-16 you would have to be around 30ft off the ground to experience ground effect.
-
After touchdown, perform two-point aerodynamic braking
using the rudder to maintain aircraft track down the run-way and
flaperon to prevent wing rise. In crosswinds, the
aircraft may drift downwind due to side loads imposed by
the crosswinds or travel upwind due to insufficient di-rectional
control inputs/availability.…
With all LG on the run-way, maintain
directional control with rudder, differential
braking, and NWS if required.
During landing rollout, the main concerns are wing rise
(roll control), weathervaning (directional control), and
downwind drift. Wing rise is controlled by flaperon into
the crosswind. Excessive flaperon deflection degrades di-rectional
control. Use rudder and differential braking to
control ground track, especially on wet or icy runways.
Engage NWS if required to maintain directional control
and to prevent departure from the runway.Sounds like every other flight manual I’ve read. The only thing I can find are (supposed) pilots saying the aircraft waddles down the runway when landed in a crab, and it doesn’t waddle/bounce as much if you kick out of the crab before touchdown.
http://www.f-16.net/f-16_forum_viewtopic-t-9288-start-0.html
Are there any data available on the dynamics of crosswind f16 landings? I’d like to see some.
-
There is an series of articles I always refer to from codeone magazine called “Semper Viper” where is a very good article about landing cross wind. If you can find it online it will say the same thing Dee-Jay and all the guys have been saying.
-
-
This seems to be unique to the f16. Are there any other aircraft that right themselves while landing in crosswind? In BMS just now, landing in a 15 knot crosswind from left to right, the aircraft yawed itself to the right, while the rudder went hard left to try to arrest the yaw.
I’m just wondering what in the design makes it different.
-
This seems to be unique to the f16. Are there any other aircraft that right themselves while landing in crosswind? In BMS just now, landing in a 15 knot crosswind from left to right, the aircraft yawed itself to the right, while the rudder went hard left to try to arrest the yaw.
I’m just wondering what in the design makes it different.
Juts my opinion, the landing gear. The way they landing gear compress, etc. Part of it. Aerodynamics and other things come into play.
-
Wish I knew about this when looking for a project in my stability and control class. heh.
-
This seems to be unique to the f16. Are there any other aircraft that right themselves while landing in crosswind? In BMS just now, landing in a 15 knot crosswind from left to right, the aircraft yawed itself to the right, while the rudder went hard left to try to arrest the yaw.
I’m just wondering what in the design makes it different.
not really unique… you get a similar reaction from an evektor sportstar LSA. of course, you will also likely pull tyres off too, and it wont be as violent…
the main gear are aft of the CoG. they also have a fair amount of friction - loads more if they are not aligned with the direction of travel.
the momentum is forwards, and that will want to drag the gear as the point of contact behind the CoG relative to the direction of movement…
the rudder part is due to the FLCS, but the rapid yaw right is more than I would expect to see if both gear touch down simultaneously.
I dunno. I started out thinking it wasnt a massive difference, but now that I reflect, it is a fairly violent maneuver (in BMS).
-
This seems to be unique to the f16.
Absolutely not. Same on Mirage2000, Rafael, certainty on F22, Typhoon etc … And (IIRC) on
(not 100% sure)EDIT:
For A380:
-
Absolutely not. Same on Mirage2000, Rafael, certainty on F22, Typhoon etc … And (IIRC) on
(not 100% sure)EDIT:
For A380:
And the space shuttle it’s pretty much standard landing for every FlyByWire aircraft…
-
For Duck Hawk:
-
Can someone tell me what the chime is @ 20 sec?
-
-
This seems to be unique to the f16. Are there any other aircraft that right themselves while landing in crosswind? In BMS just now, landing in a 15 knot crosswind from left to right, the aircraft yawed itself to the right, while the rudder went hard left to try to arrest the yaw.
I’m just wondering what in the design makes it different.
I already answered to that argument.
Flcs has nothing to do with this. This is just basic physics, the friction on gear and the fact wheel can only rotate around 1axis forces the AC to align on its velocity vector. The torque generated is a function of tire friction which is dependant on tire rubber / runway/ weight on wheel, tire pressure.
All AC in the world have this, of course a A380 is less sensitive because yaw inertia is too much important.
I can’t say if the BMS behavior is too much or not as so many parameters enter in the game here. I would need to land a f16 myself to judge
However it has nothing to do with FLCS, the rudder effect is just a consequence of the physical effect not the cause
-
yay I was right
-
the main gear are aft of the CoG. they also have a fair amount of friction - loads more if they are not aligned with the direction of travel.
That makes sense, but there is more than just tire friction acting on an aircraft during a crosswind landing. The moment that the main gear provides is countered by the weathervane effect of the aircraft. You still need some rudder to keep the plane from turning into the wind.
I dunno. I started out thinking it wasnt a massive difference, but now that I reflect, it is a fairly violent maneuver (in BMS).
It might be exaggerated a bit. Maybe its not, since the plane is pretty small, heavy, and has a fairly high landing speed. Its not like I could say tho, the planes I’ve flown have a hard time cruising at its touchdown speed. The f16 video posted above does show a strong correction at touchdown, which looks similar to what we see in BMS.
Quote Originally Posted by starbird View Post
This seems to be unique to the f16.
Absolutely not. Same on Mirage2000, Rafael, certainty on F22, Typhoon etc … And (IIRC) on A380 (not 100% sure)The difference between what I see in BMS and that 380 landing is that the 380 needs a lot of rudder to decrab, where the BMS f16 needs no rudder at all (not just input, no rudder movement). But I do agree that the effect is correct.
-
hmm. with you on the difference between their VSO and our VNE!!!
I havent thought of it as need rudder for this, I think of it as keep it on the centerline. but yeah, they weathercock. hmm. I still dont think my friction Idea is that far off though. in BMS, you have a heavy plane, so it is less affected by weathercocking.
-
I expect the same answer but I got different answer from the pilot, he flies 1350 hours F-16A/B and said decrab was needed just before touchdown and the secondary effect of rudder (roll) was still small.
But maybe it’s because he flies the block 15. I don’t know about block 50. Just fyi…
-
@Duck:
But maybe it’s because he flies the block 15. I don’t know about block 50. Just fyi…
IMO, no big differences (or even no differences at all) between blk15 and 52 … but ?