The SIDESLIP can be an uncomfortable maneuver if performed incorrectly, but if you know how to do it right, it is a valuable tool in your arsenal of flying skills.
WHY?
Because you can lose one heck of a lot of height in a very short distance.
This is oh so useful when you are high on a normal approach, or high on a glide. I use it a lot because we often have a frighteningly enthusiastic downdraft on short finals 16 at Pietermaritzburg Airport which affects light aircraft with the malicious joy of a three year old pulling a cat's tail. The topography is such that where the runway ends, the ground drops away suddenly. A little wind or a hot day results in what I fondly refer to as the welcome to Pmb bumps on short finals. This is usually accompanied by an impressive sink rate. Ergo, my cautious high approach in glides.
I have been caught by sudden sink in other places too, in our General Flying Area 1000ft rate of descent on the VSI on downwind in the Sling 2, which normally descends at 500 to 600 ft/min flaps up. This was during a forced landing exercise. At the Agricultural Strip, Baynesfield, that the EAA now look after, (they have improved that runway so much! Thanks guys!), also a forced landing exercise, I also got caught in a downdraft. This was embarrassing for two reasons:
It was a Flight Test
The DFE warned me of the sink, and I did not listen
So now, I stay high on purpose. One can always make a plan to get down, but you simply cannot stretch your glide. You cannot and will not fly with airspeed you do not have.
Make sure you know if your aircraft may sideslip with flaps, or if the sideslip is a flaps up only maneuver. Cessna's (specifically the C150 and C172, but I apply this to all small Cessna's), may NOT sideslip with flaps. Why? Because the pressures cause the linkages in the flap to bend. Over time, this makes your flaps stutter when you deploy or retract them, and can cause a breakage. It is very hard to fly an aircraft with one flap down and one up, or one flapping, and one not. It kind of spoils your day. So rather avoid damaging the aircraft. The only time I would sideslip a Cessna with flap is if I was in a real forced landing and needed to. The linkages might bend, but who cares if it is a real emergency. The aircraft can be fixed if necessary afterwards.
Low wing aircraft are usually sideslip friendly with any flap setting. I have not flown one yet that may not sideslip with flap. That said ALWAYS read your POH cover to cover (more than once!)
So without further ado, here's the trick to Sideslipping Smoothly:
Entering the Sideslip Smoothly
Pick a point ahead outside your cockpit. You will be aiming straight for it.
If you have separate fuel tanks, note which fuel tank you are using. You want this tank to be on the up-going wing because you want to make sure the fuel inlet to the engine remains covered with fuel. This is especially important when you are low on fuel.
Close your power.
Keep your speed to the high side inside the white arc (you will be lowering your aircraft nose slightly as you enter the maneuver).
SLOWLY and smoothly feed in the rudder on the same side as your selected fuel tank. Eg. right fuel tank, right rudder, (right wing up in step 6). As you feed in your rudder you will notice the aircraft nose wants to yaw in the same direction as your rudder input. Prevent this from happening by:
Opposite aileron input. Also slowly. But at just the right speed so the aircraft nose stays nailed to the spot you picked in point 1. In our example, left control / joystick input.
Keep your speed just inside the white arc on your ASI, usually about 80kts.
If you check your VSI, you will notice you have a 1000ft or more ROD (Rate of Descent). Flaps full makes this ROD larger.
Recovering from the Sideslip
Remember the effect of INERTIA when you come out of the sideslip. Take 10% of your ROD, and add this to the altitude you want to level out at. Exit smoothly and firmly from this slightly higher altitude to compensate for your inertia.
Keep your eye on your aiming point.
Reduce your RUDDER input slowly, bringing it back to neutral, and at the same time
Bring your ailerons back to neutral at a rate that allows your aircraft nose to stay fixed in your chosen direction.
As you bring everything back to neutral, add power smoothly to your chosen cruise power for the speed you want to achieve, and adjust your attitude.
POWER + ATTUTUDE = PERFORMANCE
Tips
Entering and exiting the sideslip should take about 5 seconds EACH.
Aim for FULL rudder deflection. You will reach the stop on the rudder and still have plenty of aileron left.
Be smooth
If your aircraft nose wobbles at any point, you need more practice.
Practice at height.
Sideslip to land
The Sideslip is not only useful to lose height quickly. Executed with power on to reduce the vertical rate of descent, and not necessarily with full rudder deflection, (the extent of your rudder input would be dependent on the strength of the crosswind), it is a crosswind landing technique.
The other crosswind landing technique is the CRAB METHOD.
But that's a story for another blog post.