Quotes from
chornedsnorkack:
(1)
I should assume that the effects of weathercocking would be rather different depending on which wheels contact ground (e. g. front wheels on ground, tailwheel off ground, vs. main wheels supported, nosewheel off ground...).
(2)
Drift and sideslip should work in a more similar manner.
[Unquote]
(1) Yes. This is a bit off-topic,
, but may help to build the picture of crosswind effects on V
MCG (see sooty615, john_tullamarine, BelArgUSA and fireflybob posts).
Tricycle L/G: If noseheel firmly on ground and steering is HELD central (using the pilot's tiller), weathercocking can be stopped, but this can only be used at taxiing speeds. [If the pilot takes his/her hand off the tiller, or relaxes feet on the rudder pedals, the nosewheel will be free to castor - and the aeroplane is free to weathercock.] Rudder-fine-steering, if you have it, helps at speeds up to 60 - 80 kts. Above that speed the directional control of the nosewheel(s) cannot be relied upon, and trying to use tiller-steering can be lethal.
So on take-off the prime directional control is by aerodynamic rudder, mainly opposite to the crosswind. On landing you also have the option of differential brakes, which can likewise be used in taxiing.
Tailwheel L/G: Tail-draggers are much more susceptible to weathercocking, because the wings are in a flying attitude which catches the wind at low speed. Also, for a given size of aeroplane, the tail surfaces are further behind the pivot point (the main-wheels) than on a trike, giving a bigger moment. Few tailwheels are steerable. On taxiing you steer and control weathercocking with differential brakes, aerodynamic rudder, or differential power (difficult). Once the tail starts swinging, quick action is needed to avoid embarassment! However, additionally for take-off and landing, the tailwheel can often be LOCKED fore-and-aft. On take-off, weathercocking can also be anticipated by differential engine power (difficult), and on landing is invariably combatted with differential brakes.
On a crosswind take-off on the DC-3, for example, the pilot pulls the "stick" (control column) fully back initially, the propellers' slipstream forcing the locked tailwheel firmly on the ground to keep the aeroplane straight. Once the rudder becomes effective (about 40 kts IAS), the tail can be lifted quickly.
Once the nose is level, the weathercocking tendency reduces, and is controlled with opposite rudder, backed up by into-wind aileron.
[For crosswind
landing on the DC-3, the standard technique is to "wheel it on" well above stalling speed with the tail quite high. You then have to use more and more forward stick as you slow down. The trick is to pick the right moment to allow the tail to descend rapidly on to the ground, after which you pull the stick back to hold it down firmly. The locked tailwheel then provides directional stability, which the pilot backs up with liberal amounts of brake on the downwind side...]
(2) Not sure what you mean.
Sideslip must not be confused with
drift.
Let me explain
SIDESLIP (already done drift to death)
. It is when the aircraft is travelling slightly sideways
through the air (forget the ground).
For example, if you slowly put 10 degrees of right bank on, you will normally turn to the right. But IF you simultaneously feed in opposite rudder, you can stop the aeroplane turning. [I believe it works for a helicopter too.] The "ball" goes off to the right side, indicating that you are now in a sideslip. The aircraft creeps sideways in relation to the air, in the direction of the bank. DRAG is greatly increased, which can be used to get surplus height off on an approach (NOT on an airliner, please).
The only connection between sideslip and drift is that, on a crosswind approach, the former is sometimes used to counteract the latter, so that the nose of the aircraft can be pointing straight along the runway. [A right-banked sideslip can counteract a crosswind from the right. This technique is normally frowned upon in airliners, partly because all the loose glasses slide off the galley work-tops...]
On landing, the upwind wheel(s) touch down first. As the downwind wheel(s) come down, you already have downwind rudder to help counteract the tendency of the aeroplane to weathercock. [Rudder is backed up by aileron into wind.]