Forward Slip Vs Side Slip – When To Use And What’s The Difference
Forward slips and side slips are the same in terms of aerodynamics. They are both un-coordinated flight manoeuvres involving the use of crossed controls – that is stick and rudder applied in opposing directions.
However, a key difference between the two is in their application. Forward slips are a safe way to lose height quickly without gaining excessive airspeed, whilst side slips can be used for crosswind landings. Another key difference concerns the position of the aeroplane’s longitudinal axis, in relation to the flight path. In a forward slip, there is an angle between the longitudinal axis and the flight path. In a side slip there isn’t.
Here is a video which I think does a good job of explaining the subtle differences between these two manoevres. I apologise in advance for the intro music – it does stop eventually!
A Forward Slip To Lose Height Quickly
So why would you want to lose height quickly? Well maybe you have misjudged an approach and realise you are too high to make the runway threshold safely. Or during an engine failure you spot an ideal field in which to land, but you need to lose some height. Being able to forward slip an aircraft is a very useful skill for a pilot to have as you are able to lose height without increasing airspeed much above approach speed.
In order to forward slip to landing:
- Bring power back to idle
- Use pitch to decrease to approach speed
- Pick a fixed point in front
- Bank into wind
- When you see fixed point moving, apply opposite rudder to get back to it
And that’s about it; a safe way to lose height on approach, without having to pitch down and gain excessive airspeed. Remember that the steeper the bank angle, the greater the rate of descent.
Forward slipping isn’t currently part of the UK NPPL(m) training syllabus and it is difficult to understand why not, as it is a very useful manoeuvre to have up your sleeve.
A Side Slip To Counteract A Crosswind
There are two techniques for handling a crosswind landing; the crab method and the side slip. I will discuss the crab method in another post.
When using the side slip method for crosswinds, apply into wind aileron with opposite rudder to stop the aircraft turning. Continue to adjust until the longitudinal axis of the aeroplane is aligned with the runway centreline. The stronger the crosswind, the more aileron and rudder you will need.
The side slip is held all through the approach, flare and landing meaning the into wind wheel will touch down first.
So there you have it, the forward slip and side slip. Each has the same aerodynamic principles but each is used in very different situations.
Go slip those surly bonds!