Page 40 - Twin & Turbine May 2017

On the Baron Takeoff Distance chart I plotted ground roll distance (zero obstacle height) for a 20-degree C day at a 2,000-foot elevation airport. The airplane is at maximum gross weight (5,500 pounds). Note that this calculation assumes the pilot adheres to the Associated Conditions technique at the upper left of the chart, and uses the liftoff and 50-foot speeds tabulated for the airplane’s weight.
In this example, a zero-wind takeoff would require approximately 2,800 feet from the beginning of the takeoff roll
to clear a 50-foot obstacle. Factor in a 10-knot headwind component and the computed takeoff roll distance is 2400 feet, a roughly 14 percent improvement. Make that 10-knot breeze a tailwind, however, and the computed 50-foot obstacle distance is 32 percent longer than the zero-wind takeoff – the tailwind’s detrimental impact is more than twice the amount per knot as the positive effect of a takeoff headwind.
From either the simple Cessna’s tailwind warnings or the Beech twin’s performance charts, we can confirm the
wisdom of taking off into the wind in all but the most unusual cases.
Coming Down
Let’s look at the performance change on landing when comparing a headwind component to a tailwind. Cessna’s 172S POH has already told us a knot of tailwind is worth nearly 5 knots of headwind. The Beechcraft Baron 58 POH gives us a sample calculation below.
On a 20-degree day at 2,000 feet and assuming a maximum gross weight
38 • TWIN & TURBINE
May 2017