Why can a helicopter become twitchy, fidgety or downright skittish when hovering out of wind? Jonny explains weathercocking, tail-rotor control and unanticipated yaw in simple, practical terms — without the aerodynamic textbook.

Hovering Out of Wind – Twitchy, Fidgety or Skittish? (According to Jonny)

There are many scholarly articles out there talking about the tail rotor in the hover, this is NOT one of them….

Feel free to go and read about “LTE – Loss of Tail Rotor Effectiveness”, “unanticipated yaw”, Fenestron aerodynamics, tail-rotor vortex ring and a multitude of other things that you'll find in the books.

They’ll be no yawing translating inflow distortion thrust saturation in this article that you can find in the books.

Let’s try and KISS (Keep It Simple Stupid) for the average pilot… like me!

The main reason is – when you are flying you just need to know the absolute basics, the rest you can look up on YouTube later, which is what many students think is the holy grail of helicopter aerodynamics (it’s not!).

This article is based on the anticlockwise main rotor system (R44, R66, B206 etc.), if your main rotor blades go the “other way”, just simply turn left to right and vice versa,

Helicopters are designed to fly into wind, hence the pointy bit at the front and not so pointy bit at the back.  The vertical and horizontal stabilisers and aircraft's aerodynamic surfaces are designed with forward flight in mind.  So…. where possible let’s keep the helicopter into wind shall we.

However, it is important to know how the helicopter acts when not into wind.  Also – the stronger the wind the harder the situation can become.

Weathercocking

Firstly, for those “non-native” English speakers, a history lesson on the aviation term “weathercocking”.

A weathercock is an old-fashioned weathervane, traditionally made in the shape of a cockerel, which sits on top of buildings and turns with the wind.  The word weathercock dates back to around the 13th century. Cockerels became a traditional shape for weathervanes, including those found on church steeples.  When the wind blows, the “weathercock” naturally turns into wind.

So, when we say a helicopter is weathercocking, it simply means that the helicopter is trying to turn its nose into the wind — just like the weathercock on top of the village church.

Wind from your left (Left Crosswind):

Basically, the wind is interfering with the airflow through the tail rotor, reducing its efficiency.  This means that you will need more pedal to overcome the crosswind.  The side of the helicopter and vertical stabiliser are also trying to weathercock you into wind so you will also feel the helicopter trying to yaw left and right as you have these 2 interactions.    You might also have the helicopter main rotor downwash moving into the tail rotor airflow just to add to your excitement!

Very unpleasant, you will find the helicopter yawing, rolling and requiring constant pedal corrections to maintain heading with all sorts of power and RPM fluctuations.

Left crosswind can be a particularly unpleasant position in an anticlockwise main rotor system.

Jonny's technical aerodynamic term we can use is “Skittish”

Wind from behind (Downwind):

The helicopter is not “aerodynamically efficient” as the wind is blowing the wrong way around the helicopter.   The vertical and horizontal stabiliser are not facing their right way to the wind so their aerodynamic effects can change, and you can have changes in both pitch and yaw.

You will need to move your pedals more to keep stable, meaning that the tail rotor will need to work harder, which means more power will be required

If the wind catches the vertical stabiliser, then the aircraft may immediately try to weathercock around as well (left or right).

Jonny's technical aerodynamic term we can use for this is “Twitchy”

Wind from the right (Right Crosswind):

Slightly less unpleasant than the equivalent left crosswind but you will still encounter the vertical stabiliser weathercocking effect so some yawing may develop.  There could also be some main rotor downwash interaction as well.

Jonny's technical aerodynamic term we can use for this is “Fidgety”

Loss of Tail Rotor Effectiveness / Unanticipated Yaw

This is where the helicopter yaws right and you cannot stop it, the yaw rate increases, often leading to a loss of control.

Just to understand what happened:

The Tail Rotor NEVER Lost its Effectiveness – it was always working as designed

The helicopter did NOT let you down; YOU let the helicopter down.

The aircraft started to yaw, you did not correct it fast enough and as the rotation increased you either did not increase pedal sufficiently to stop the yaw, or in the startle effect you lost control of the helicopter.

The aircraft yawed without you realising what was about to happen – basically the yaw was “unanticipated” … hence the name.

How can I stop this from happening to me?

Step 1 – awareness

Be aware where the wind is from, if there is a strong crosswind consider your options.  If coming into land or taking off try to keep it into wind, if you cannot then beware of the potential yaw issues.

Step 2 – pilot in command

You are the Pilot in COMMAND – so COMMAND the helicopter.  We teach you to hover, gently, nicely, small pedal movements, positive control.  This is the one time you need to kick the helicopter.  You are in charge of the helicopter, not the helicopter in charge of you so you must tell it what you command it to do.

Step 3 – Hovering into wind if near maximum pedal or power limits

Sounds counter intuitive, but if you are near the pedal or power limits, spot turn left – yes, you will need more pedal and more power, however – if you reach the maximum of either limit or if you subsequently lose directional control, the helicopter will yaw right - back towards the headwind - rather than continuing into a downwind condition.

When should I watch out?

Whenever you're operating slowly, at high power, especially close to the ground

Awareness is the biggest saving grace.  Hopefully someone reading this will be coming into land, or taking off, notice the wind is off to the side and think “I remember reading some idiots article about this”.

If you are making an approach, nice and slowly, and you start to reach the limits of pedal travel – this is your early warning sign – go around, and plan B

How’s it made worse?

The nearer to the helicopters pedal or power limits the less margin you have available to overcome any out of wind tendencies so the famous 4 H’s apply:

HOT / HIGH / HUMID – Density Altitude increasing power required AND reducing power available

HEAVY – weight increasing power required

What if it starts spinning and I can't stop the yaw?

Surprisingly - apply maximum left pedal to stop the yaw. 

In many cases the pilot thought they had applied absolute full pedal but were nowhere near the limits! 

Little tip – During your pre-start control checks, make sure you have full pedal travel available in both directions and that the pedals are set in the correct position you use.

Jonny’s Top Tip – do not wait for the helicopter to demonstrate “LTE” to you, be the pilot in command and command the helicopter at all times.

And finally…

Jonny Greenall is the founder and Head of Training at Balearic Helicopters, with 25+ years of helicopter flying and training experience and more hours in helicopters than he probably cares to admit. Despite all that, he’s still learning to fly!

The point of this article is not to replace proper training or a helicopter flight manual. It’s simply to make a few important concepts easier to understand and, hopefully, make you think a little more about what the helicopter is telling you.

If you want to learn how to hover, control and fly a helicopter properly, have a look at our Helicopter Training courses at Balearic Helicopters.