By Hank Canterbury
I occasionally hear pilots discussing the use of partial flaps on takeoff in their Bonanzas or Barons. Some confusion exists regarding whether this is “approved” or “authorized.” First, there is no restriction on using partial flap takeoffs in any model of Bonanza. Just because there is no pilot’s operating handbook [POH] chart for your model or year, does not mean that it cannot be done, is unapproved or is prohibited. Note: nor does it say you may takeoff on a wet or contaminated runway or at night either! So, if not specifically prohibited, you may proceed.
The older Airplane Flight Manual featured various techniques that were removed when the FAA and General Aviation Manufacturers Association [GAMA] agreed to the new POH format. The previous manual recommended lowering flaps to no more than 20 degrees for short or soft fields by turning the yoke for full aileron in one direction and then positioning the flaps to be parallel to the down aileron. That was before the “approach detent” was added. The only comment about partial flaps cautions us not to use more than 50% flaps for takeoff.
At Bonanza Pilot Training [BPT], we recommend using flaps on “soft fields” and for a “contaminated” runway, meaning rough, snow, debris or anything other than smooth runway. The technique also closely follows the Airman Certification Standards [ACS] task guidelines.
By using flaps at either 15 – 20 degrees or at the 15-degree approach flap detent – if you have it –will produce approximately a 21% decrease in takeoff roll, providing rotation occurs 6-7 knots sooner than the rotation speed shown on a flaps-up or zero POH chart. If you do not rotate sooner, you gain nothing. Considering that most of us don’t always have perfect technique, plan on about 15% shorter roll.
Here is an example from a Bonanza G36 POH. I confess I had to take the tiny print pages and enlarge them so I could get accurate readings. A wisecrack occasionally heard is, “When we get old enough to afford our great airplanes, it’s difficult to read the charts.”
The difference of 300 feet divided by 1,400 feet yields 21% shorter. But remember to achieve these numbers, you must begin the rotation at approximately 10 degrees of pitch 6–7 knots sooner than when using no flaps.
Here’s another takeoff suggestion: During takeoff roll, Bonanzas / Barons with correct strut inflation are at a slightly negative angle of attack. Without some additional “rotation” to a higher Angle of Attack, the plane will not lift off. “Takeoff trim” setting is for an airspeed of Vy with gear and flaps up. As you roll, try holding just enough back pressure on the yoke to lighten the weight on the nose wheel a bit. This will not create more drag – and it will make the rotation to climb attitude a bit smoother.
Here’s another thought: Most POH Performance Charts list either a “liftoff” or a “rotation” speed. You will also note another column that states the speed at 50 feet, which was attained by test pilots. In most cases, this turns out to be the speed for best angle of climb or Vx. The speed at liftoff and at 50 feet defines the initial post-takeoff angle. The plane is still accelerating at that point, and the subsequent climb profile will be determined by pitch attitude and available power.
Caution for Barons: Using flaps at half and with earlier rotation, Barons will lift off at lower airspeeds. In fact, well below red line [Vmca]! Regardless of your flap setting, do not begin rotation until you have reached your POH red line plus 5 kts. Although the actual Vmca airspeed is altered with configuration changes, the published red line using no flaps is on the safe side of the unknown.
In the next article, I’ll discuss the climb profile for an obstacle takeoff.
Until then: Fly Often — Train Regularly!
ATP, CFII SEL & MEI