Between the Foot and the Rudder

When man took to the skies, he was certain about one thing: The efforts you put into flying, determine how well you fly. The relentless Wright brothers got it right, and then everyone followed suite.

Looking at it from a different angle, more from an operational perspective, for aircraft such as the Beechcraft King Air C90, the logic still applies. With metallic cables linking the controls with the control surfaces, the effort the poor pilot applies totally determines how the metallic bird flies.

Now, the C90 is a twin engine turboprop aircraft, member of the Beechcraft King Air family of popular and widely sold turboprop aircraft from Beechcraft (now part of Raytheon). “The Beech King Air is the world's most popular turboprop aircraft” [1]

But least popular with the girls, when an engine fails.

PA who flies the C90 talked of her experience with these marvelous C90s; And when one engine fails, humor breaks loose.

For an aircraft with two engines at a distance from each other, the failure of one creates an unbalanced torque that tends to yaw the aircraft. To compensate for this, the pilot must use the rudder pedals to create a countering torque: His or her foot on the pedal forcing the rudder to deflect towards the side of the engine which is still alive. And now is when you must remember, “The efforts you put into flying, determine how well you fly”.

The description of the scene was hilarious: PA was given a “single engine” scenario on the C90, by her instructor. The aircraft started to yaw, and she did as she was instructed: to kick on the correct rudder pedal. She kicked, but it didn’t move enough. And desperate times call for desperate measures: PA had to use her whole body weight on one single rudder pedal! “The rudder was very hard, and so I had to literally stand on the rudder pedal”. The thought of a pilot standing and flying is, well, hilariously imaginable.

But with technology, things these days get very “sunny”. Imagine, if for a small aircraft weighing 4500kgs, a pilot has to throw his/her whole body weight to achieve straight flight, what would anyone do for an Airbus A380 weighing 560,000 kg, in case of an engine failure?

The A380 is a 4 engine aircraft, and “basically even if both engines fail on one side u still DO NOT have to kick the rudder”, says Capt SK who flies the A380 for Singapore Airlines. No, he is not re-writing the books of physics.

“The TAC (which he thankfully expanded for me: Thrust Asymmetry Compensator) is part of the rudder which automatically compensates for an Engine Out (EO) or any form of thrust symmetry”. Computers on board the Airbus calculate the compensation required for a level flight, and feed it via 5000psi hydraulic lines to the upper portion of the rudder, a.k.a, TAC.

Some engineers out there may raise their eyebrows. “5000psi of pressure?”

Adds Capt SK, “Almost ALL electro-hydraulics tried out on this bird are completely new in the world of aviation......too many firsts. Firstly we have all hydraulic systems working on 5000 psi instead of the usual 3000 psi”.

All Airbus aircraft except for the A300 and A310 (both are no longer in production) use fly-by-wire technology (FBW). In an FBW aircraft, a pilot’s controls send electrical signals to computers which determine how much pressure needs to be pumped to the control surfaces. Aircraft manufacturers may decide to induce some artificial feedback to the control column (such as what Boeing does on its 777 FBW), or may have no feedback at all (such as on the sticks of Airbus FBW aircraft).

With technology, “The efforts you put into flying (or the lack of it), determine how well you fly”.

Gone are the days of the (w)right fliers!

TFE

[1] http://www.pilotfriend.com/aircraft%20performance/Beech/King%20Air.htm

Images:

Beechcraft King Air C90 : Copyright Dean Cully, from Airliners.net

A380 Image : Copyright Wim Callaert, from Airliners.net