Page 18 - Volume 12 Number 4

Ask the Expert
Applying Takeoff Power ... and
Never Being Surprised Again
by Tom Clements
Iaddressed this in an article many moons ago, but I still observe lots of King Air pilots who have never been taught the trick that makes setting takeoff power easier and better than the technique they are currently using. The trick? Do not look at the Torque or ITT gauges until you have monitored the propeller speed gauges and veri ed that they stabilize at the proper takeoff RPM.
For the great majority of you who have the engine instruments arranged in a vertical stack, always make your scan from bottom to top, not top to bottom, when the checklist issues an “Engine Instruments” challenge. We cannot really operate the airplane normally and successfully without looking at the top three instruments often: ITT, Torque, and Propeller Speed (Np). Yet the bottom three – Gas Generator Speed (N1), Fuel Flow (Wf), and Oil Temperature/Oil Pressure – get the short end of our attention stick. Seek them out rst before going up to the ones that are your old friends. Doing so increases the chances that you will spot any abnormality in these “out of sight, out of mind” gauges.
Following in this habit pattern, as you start adding takeoff power, scan the gauges from bottom to top. A quick check of the Oil Temp and Oil Pressure veri es that a missing or loose oil dipstick has not yet wreaked any havoc. Fuel Flow and N1? Not much to see there now. But now the important Np display draws our needed attention.
Perhaps a lot of King Air pilots have unrealistic expectations when it comes to engine control rigging. Yes, in an ideal world, we could advance the power levers side-by-side and both engines would accelerate in perfect synchronization. But in the real world, it very, very rarely works that way! This is why it works so well to watch those Np gauges like a hawk as you s-l-o-w-l-y begin to advance the power. When one side’s propeller speed starts getting ahead of the other side, then stop advancing that side’s lever, slide the other side’s lever forward a bit, and get those prop speeds matched again.
the FCU (Fuel Control Unit), but then fall as the engine accelerates and brings in more cooling air. This rise and fall is the ITT “spike.”
Once N1 speed reaches the High Idle setting of about 70 percent, the engine is able to accelerate more rapidly with hardly any ITT spike at all since the air and the fuel ow increases are better matched.
In every PT6-powered King Air, by the time Np reaches 1,500 RPM on the ground, N1 will be great enough that the ITT spiking is not a factor. Also, the mis-match of engine acceleration rates is much less troublesome. Hence, after the prop speed gets to 1,500, move the power levers as rapidly as you wish while still splitting the levers as required to keep the prop speed closely matched, left and right.
As Np gets within 10 or 20 RPM of takeoff redline, slow or even stop power lever movement momentarily to allow the Primary Propeller Governor to begin its function smoothly and without surging. Not only is this smoother overall, but it 100 percent guarantees that you will observe that the primary governor is truly working correctly. Until pilots have learned to watch the props before torques and temps, it is depressing how many continue a takeoff in the simulator even though one side’s prop speed is stabilized on the Overspeed Governor’s setting. This error will never happen when the propeller gauges are monitored rst during the takeoff power application.
Once it is con rmed that propeller speed has become properly governed, now is the time to move the power
Why did I emphasize doing this s-l-o-w-l-y? To avoid unnecessarily large ITT spikes. When the engine is at Low Idle – and this is especially true for the three-blade King Airs with their Idle N set closer to 50 percent
1
instead of 60 percent – there is not a lot of excess air
for cooling. If the power levers are advanced rapidly, the ITT will rise dramatically as fuel is introduced by
16 • KING AIR MAGAZINE
APRIL 2018