This section focuses largely on the IO540 powered Bearhawk, but with some reference to the IO360 powered aircraft.
Landing Distance
A realistic landing distance expectation when learning to fly the Bearhawk would be 150 - 200m (600 ft) landing roll at 2200lbs (1000 kgs). On my aircraft this equates to 2 POB, overnight gear and 3 hours fuel.
With practice it can be consistently landed with a landing roll of 80-120m (450ft) at light weights and sea level altitude. It is important to understand that most airstrips are still around 300m (600ft) length, leaving a safe margin for error. It's also important to realize that most pilots don't carry a full payload into backcountry airstrips because the increased weight also increases both the stall IAS - and therefore the landing roll - disproportionately. Many backcountry airstrips are several thousand feet above sea level. Landing at a higher density altitude can significantly increase the landing (and takeoff) roll.
As a general rule of thumb when operating into short airstrips, keep the aircraft light. I usually stay below 2200lbs - 2 POB, some gear, and 120 liters fuel (30 gallons).
Takeoff Distance
Takeoff distances are very similar to landing distances. With an IO540 powered Bearhawk they tend to be slightly shorter, with an impressive rate of climb once airborne. The same effects of weight and density altitude apply.
Take-off and Landing distances - effect of engine size
IO360 For the same payload and a lighter aircraft, the landing distance is shorter because the landing weight and therefore the stall speed are both less. The takeoff distance is very similar to an IO540 powered Bearhawk when at light weights.
IO540 The IO540 powered Bearhawk has an advantage in the rate of climb and particularly when hauling heavier weights. This is more noticeable at altitude.
Cruise Speed - IO540 with 29" ABW's
Lean of Peak - 110 KIAS
Rich of Peak - 125 KIAS
A real world expectation is to cruise at approximately 110 KTAS at low altitudes, and 125 KTAS at higher altitudes, while consuming 38-40 LPH LOP. The cruise speed can be increased by 10 KTAS easily, but at a fuel burn of around 55 LPH.
Smaller tire sizes will increase the cruise speed by up to 10 KTAS, so a cruise speed of 120 - 125 KTAS at lower altitudes is realistic.
Rate of Climb
The IO540 shines in rate of climb. Under normal ISA conditions with at medium weights it would climb at 1500 FT/MIN at lower altitudes, reducing to 1000 FT/MIN at higher altitudes for an IAS of around 80-90 KTS.
Stall Speed
My aircraft is fitted with Vortex Generators, tested to establish position error, and has a stall speed of:
- Flaps up, power off, 2700 lbs, 48 KTAS.
- Flaps 4, power on, 2200 lbs , 38 KTAS.
These stall speeds appear to be very typical.
Stall speeds vary with weight (among other things). When discussing stall speeds, the unit of measurement is very relevant. Airspeed indicators usually read in Knots Indicated Air Speed (IAS). The actual speed of the aircraft is measured in True Air Speed (TAS) which is more closely correlated to ground-speed in still air conditions.
Due to variation in installation of the pitot and static system is a corresponding variation between aircraft in the IAS stall speed. Therefore it is important to establish position error (between IAS and TAS) before comparing stall speeds or approach speeds between aircraft.
For example, two aircraft might approach parallel runways side by side, at the same groundspeed, and the same TAS. However one might indicate 50 KIAS and the other might indicate 38 KIAS due to variation in the location of the pitot tube and static ports. This is to be expected. For this reason it is imperative to use a conservative approach speed until position error testing (HERE) has been done.
