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Rudder use

Pro Member First Officer
eyton402 First Officer

I know rudder is used on turns but I thought they might also be useful on final approach when attempting to line up with the runway. This appears not to be the case. Each time I have used the rudder to line up the aircraft moves significanly left or right preventing a landing. Under what circumstances are rudders used the most.?
Im sorry for the rudimentary nature of this question.

Pro Member Chief Captain
Jonathan (99jolegg) Chief Captain

No need to apologise.

The rudder operates the aircraft around the yaw axis, think of it as a vertical axis through the centre of the fuselage. This is a slightly different axis of flight since it isn't solely used to achieve a climb / descent or roll (strictly speaking) by itself like the elevators (lateral axis) or the ailerons (longitudinal axis).

The rudder (therefore, yaw) can be seen to used as a secondary function to the elevators / ailerons.

When banking the aircraft, to fly in balance i.e. not side slipping the aircraft into the relative air flow you will need to add rudder. This makes your turn coordinated. When flying straight and level, you may need rudder to fly coordinated. When making power changes, you will need rudder due to the slipstream (single engine props only) affecting yaw.

So in short, to start a turn, you will use ailerons. To keep that turn in balance and to keep that aircraft in the turn and not skidding out or slipping in, you use rudder.

To try and bank the aircraft using rudder alone is wrong.

To complicate things a bit further, both the ailerons and rudder have secondary effects. Ailerons induce roll and then yaw and rudder induces yaw and then roll. Balancing them both is the key.

Does that make sense - I'm not sure I explained it very well.

Pro Member First Officer
oldsamer First Officer

99jolegg covered it well.

eyton402 asked,

Under what circumstances are rudders used the most.?

UNFORTUNITY it's during landing. The only exception being the US B-52 bomber with steerable bicycle landing gear.

Remember that as approach speed falls off, so does control surface authority (effect). That's why pilots are taught to pick a relatively high approach speed and fly that constant speed till solid touch down on all wheels. Otherwise you are constantly adding rudder and ailerons and elevator!

Pro Member Chief Captain
Jonathan (99jolegg) Chief Captain

oldsamer wrote:

That's why pilots are taught to pick a relatively high approach speed and fly that constant speed till solid touch down on all wheels. Otherwise you are constantly adding rudder and ailerons and elevator!

Are you sure that's correct?

Vapp is around 1.5 x VS0 (to about 5 DME) and Vref is around 1.3 x VS0, isn't it?

I would have said that approach speed couldn't get much lower (for traffic flow issues amongst other things) than 1.3 x VS0 - the margin is reduced significantly otherwise to the point that a bit of wind shear would have you stalling.

Pro Member First Officer
eyton402 First Officer

Thnks 99jolegg. That was very informative answer.

Pro Member First Officer
oldsamer First Officer

99jolegg Chief Captain wrote:

Are you sure that's correct?
Vapp is around 1.5 x VS0 (to about 5 DME) and Vref is around 1.3 x VS0, isn't it?

Sorry, I am not correct for the majority of operating environments. For almost everybody, approach velocity(V) of 1 1/2 of stall speed is frightingly slow and sluggish. However, my comment that rudder input adjusting can be minimized by a constant approach V is valid I believe. After all, the throttles are a control input also and must be balanced with ailerons, elevator and rudder.

I suppose we are conditioned by our flight environment. There is (or was) a subspecies of operators where 1.5 x VSO is too high on final. In the US, the postal system still subcontracts rural air mail pilots! What this amounts to is weekly delivery into remote ranches and camps. Sadly, that postal service will be discontinued at year end. There you want Vstall and touch down right at the back fence.

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