Originally Posted by safetypee
To add to the deficulties of simulating crosswind landings, consider ground effect. At best (still wind), good quality in-flight data is difficult to obtain; it would be interesting to know what data (or assumptions) is used in simulating ground effect with the effects of drift or turbulence.
A further thought, in real conditions most pilots’ experience of crosswinds is gained by extending their previous limit, this differs from most other operations where conditions are often repeated and, perhaps excepting turbulence, are similar. For crosswinds, some conditions can be a significant extension of previous landing experience (#1), thus with additional demands in turbulence, perhaps there is some apprehension (the unknown) driving the need for quality simulation.
Hi safetypee
Obviously, I am unaware of how familiar you might be with the simulation requirements of your, or any other, regulatory authority, so ... here, for your reading pleasure (or for treatment of your insomnia) is the US FAA requirements – initially contained within Advisory Curculars – until their legal officers let them know that they could not withhold the issuance of a qualification or interfere with the issuance of an approval to use a simulator simply because it didn’t match a “recommendation,” which is all that an Advisory Circular really is. That is the reason the FAA developed and published these requirements as a full-fledged regulation, 14CFR Part 60.
For information, here are just a few of the relevant requirements (at least now they're requirements) regarding “ground effect” and “crosswinds” as found in the above-referenced rule. Suffice it to say that the amount of data and the method of collection has been through several trials, errors, corrections, trials again, modifications, etc., etc. The bottom line is that what is produced today, and essentially for the last decade or two, while it may have some inevitable shortcomings, is actually pretty darn good data.
From the FAA Part 60 Regulation:
OBJECTIVE TESTING FOR CROSSWIND TAKEOFF.
TOLERANCE: ±3 kts airspeed, ±1.5° pitch angle, ±1.5° angle of attack, ±20 ft (6 m) height, ±2° bank angle, ±2° sideslip angle; ±3° heading angle. Correct trend at groundspeeds below 40 kts. for rudder/pedal and heading. Additionally, for those simulators of airplanes with reversible flight control systems: ±10% or ±5 lb (2.2 daN) stick/column force, ±10% or ±3 lb (1.3 daN) wheel force, ±10% or ±5 lb (2.2 daN) rudder pedal force
FLIGHT CONDITIONS: Takeoff
TEST DETAILS: Record takeoff profile from brake release to at least 200 ft (61 m) AGL. Requires test data, including information on wind profile for a crosswind (expressed as direct head-wind and direct cross-wind components) of at least 60% of the maximum wind measured at 33 ft (10 m) above the runway.
INFORMATION: In those situations where a maximum crosswind or a maximum demonstrated crosswind is not known, contact the NSPM.
OBJECTIVE TESTING FOR CROSSWIND LANDINGS.
TOLERANCE: ±3 kt airspeed, ±1.5° pitch angle, ±1.5° angle of attack, ±10% or ±10 ft (3 m) height ±2° bank angle, ±2° sideslip angle ±3° heading angle. Additionally, for those simulators of airplanes with reversible flight control systems: ±10% or ±3 lb (1.3 daN) wheel force ±10% or ±5 lb (2.2 daN) rudder pedal force
FLIGHT CONDITIONS: Landing
TEST DETAILS: Record results from a minimum of 200 ft (61 m) AGL, through nosewheel touch-down, to 50% decrease in main landing gear touchdown speed. Test data must include information on wind profile, for a crosswind (expressed as direct head-wind and direct cross-wind components) of 60% of the maximum wind measured at 33 ft (10 m) above the runway.
INFORMATION: In those situations where a maximum crosswind or a maximum demonstrated crosswind is not known, contact the NSPM.
OBJECTIVE TESTING FOR GROUND EFFECT.
TOLERANCE: ±1° elevator ±0.5° stabilizer angle, ±5% net thrust or equivalent, ±1° angle of attack, ±10% height or ±5 ft (1.5 m), ±3 kt airspeed, ±1° pitch angle.
FLIGHT CONDITIONS: Landing.
TEST DETAILS: The Ground Effect model must be validated by the test selected and a rationale must be provided for selecting the particular test.
REQUIREMENTS FOR OBTAINING GROUND EFFECT DATA:
a. For an FFS to be used for take-off and landing (not applicable to Level A simulators in that the landing maneuver may not be credited in a Level A simulator) it should reproduce the aerodynamic changes that occur in ground effect. The parameters chosen for FFS validation should indicate these changes.
(1) A dedicated test should be provided that will validate the aerodynamic ground effect characteristics.
(2) The organization performing the flight tests may select appropriate test methods and procedures to validate ground effect. However, the flight tests should be performed with enough duration near the ground to sufficiently validate the ground-effect model.
b. The NSPM will consider the merits of testing methods based on reliability and consistency. Acceptable methods of validating ground effect are described below. If other methods are proposed, rationale should be provided to conclude that the tests performed validate the ground-effect model. A sponsor using the methods described below to comply with the QPS requirements should perform the tests as follows:
(1) Level fly-bys. The level fly-bys should be conducted at a minimum of three altitudes within the ground effect, including one at no more than 10% of the wingspan above the ground, one each at approximately 30% and 50% of the wingspan where height refers to main gear tire above the ground. In addition, one level-flight trim condition should be conducted out of ground effect (e.g., at 150% of wingspan).
(2) Shallow approach landing. The shallow approach landing should be performed at a glide slope of approximately one degree with negligible pilot activity until flare.
c. The lateral-directional characteristics are also altered by ground effect. For example, because of changes in lift, roll damping is affected. The change in roll damping will affect other dynamic modes usually evaluated for FFS validation. In fact, Dutch roll dynamics, spiral stability, and roll-rate for a given lateral control input are altered by ground effect. Steady heading sideslips will also be affected. These effects should be accounted for in the FFS modeling. Several tests such as crosswind landing, one engine inoperative landing, and engine failure on take-off serve to validate lateral-directional ground effect since portions of these tests are accomplished as the aircraft is descending through heights above the runway at which ground effect is an important factor.
Additionally, should you want to check a bit more, here is a link …
eCFR ? Code of Federal Regulations