Saturday, September 1, 2007
de Havilland Beaver
Sixty years in the sky de Havilland Beaver
The Beaver is slab sided and sensitive to wind on the surface, but an experienced pilot can handle the airplane easily. For takeoff, the throttle pushes manifold pressure to 36.5 inches at 2,300 rpm. An idling R-985 rumbles a pleasant note, but at takeoff power, it emits a deafening roar. Attention to manifold pressure is important—it's easy to overboost. Our maintenance chief told me that if I saw trees in the top half of the windshield during a takeoff, I should shove the throttle to the stop. If I missed the trees, call him and we'd talk. On at least one such occasion, I cleared the trees with the MP gauge reading well over 40 inches, and I was thankful for a strong engine.
On takeoff, the Beaver struts its stuff. This is what the airplane was bred for: STOL operations. Even heavy, the airplane outperforms most four- to six-seat airplanes. With modifications, the Mk.I Beaver can seat seven, the Mk.III up to 11. Ask any experienced pilot who's flown the Beaver and other bush airplanes which one he or she would choose to depart a small lake with a load, and the answer will be predictable.
Takeoff requires flaps. The designers refused to follow popular recommendations and dropped the ailerons when flaps deploy. These "flaperons" significantly improve the airplane's STOL capability. For takeoff, I lowered flaps to match aileron deflection with the yoke cranked over fully in one direction.
Once airborne, the Beaver's control harmony is actually quite nice and light. Adverse yaw is prominent, so proper application of rudder is required. With a 48-foot wingspan, a "leisurely" roll rate and lots of adverse yaw are inevitable.
The heavily loaded Mk.I Beaver doesn't exhibit spectacular climb capability, but with patience and bumps of the throttle to maintain power during climb, it'll get you there. The airplane climbs best with partial flaps. Engine temperatures may limit climb performance on hot days.
Cruise speed of a loaded float-equipped Beaver is around 110 knots. When I first flew the airplane, it seemed difficult to find a proper cruise pitch attitude, because of the rounded cowling. I learned to level the bottom of the left wing with the horizon, and I flew with a bit of flaps deployed when heavy. Flaps are hydraulically activated, permitting an infinite range of deflection. Fuel burn in cruise ranges from 22 to 28 gph.
On approach, the Beaver exhibits a characteristic typical of DHC aircraft: A very nose low pitch attitude is required to maintain airspeed. These airplanes illustrate the concept of flight "behind the power curve" graphically. These are draggy airplanes, and raising the nose increases drag. As a Beaver slows, you must keep the nose down. Get low on final, raise the nose and the airplane will sink like a stone. The airplane won't climb, even with a lot of power until you push the nose down. Push and the airplane will climb nicely, assuming it's not too far into the pit before the pilot awakens. My mentor flew an Otter into the ground with a big load in this configuration, so my initial checkout in the Beaver included extensive exposure to this behavior. Everyone's should.
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