Contents
POH Takeoff Factors
Many airports of the U.S. are long enough and wide enough for all G.A. aircraft. Oddly, most are not. When the runway has variations of length, obstacle clearance, surface texture, slope, and density altitude the pilot is called upon to do some combination of artistic and technical figuring. He must figure the foregoing variables into the POH as they apply along with the aircraft weight and balance. He must factor in his pilot skills and knowledge of technique which is, perhaps, the most unknown variable. An airplane can land in considerably less distance than it needs for takeoff. Pilots tend to over-estimate their skills. The POH is required reading.
Every takeoff is as unique as every landing. Every takeoff occurs in unique conditions. After landings, takeoffs are the most frequent source of accidents. The minimum safe runway takeoff length should be one and a half times that indicated by the POH. The extra 50% is required to cover pilot optimism. The first warm day of spring gives a completely different takeoff than those you have made all winter. Also, this takeoff will be different from the first 100-degree takeoff of summer. The hotter it is, the less pitch attitude recommended during acceleration.
For standard temperatures you should increase takeoff distances by 25% for each 1000 feet of elevation. Increase POH distances by 10% for every 25 degrees Fahrenheit above standard for any altitude. Every 2500' of increased elevation causes 10 degree standard reduction in temperature. If an airport at 2500' elevation is warmer than 70 degrees you have a density altitude situation.
Factors that make a difference have some rules of thumb that a pilot should know and perhaps reference on his lap board. For every 15 degrees F above standard temperature raises density altitude by 1000'. Every 2 knots of tailwind increases takeoff distance by 10%. A firm turf takeoff requires 7% more distance, short grass requires 10% more distance, and soft surface/tall grass requires 25% more distance than recommended by a POH for a macadam runway.
Most common takeoff mistake is using apparent ground speed to initiate an early rotation. Making a proper rotation using indicated airspeed may cause a pilot to pitch for a sea level climb. It is not unusual to find the aircraft a mile or two off the runway end after having mushed through the air that far without climbing.
Attempting to climb out of ground effect with insufficient airspeed is the problem. You must be patient and prepared to stay in ground effect to gain airspeed. Any go-around decision must be made early in the approach will carefully controlled changes in configuration and airspeed.
By listening on the radio you can get insight into the ATC mind and prepare for such things as "taxi closer and hold, prepare for an immediate", "taxi into position and hold", etc. You must become aware as to what is occurring with other aircraft in the air and on other runways. The mental process required to execute a safe takeoff extend far beyond just moving the aircraft.
Consider:
1. Pre-takeoff checklist/position Emergency list
2. Clearing the approach area both base and final
3. Configuration and yoke set for wind direction
4. What-if considerations such as power, aborting, emergency, etc.
5. Vso speed for rotation and attitude for Vy climb
Takeoff Notes
Check weight and balance
Density altitude 'begins' to make a difference at 2000' and 80 degrees F.
Keep the nose straight with rudder
Crosswinds require crosswind controls
Rotate sooner rather than later
Don't hesitate to abort a takeoff
--Except for x-winds, get the nose wheel off the ground and let the airplane fly itself off the runway. Don’t force a takeoff. Note the nose attitude that gets you airborne at 60 knots will just touch the end of the runway. Pre-plan heading to be used for any x-wind runway alignment and options selected for engine failure on takeoff.
--Look back at runway above 300’ to confirm that you are aligned and not drifting over adjacent runway.
--Make ten-degree cut away from adjacent runways at the departure end of the runway.
--Trim for hands-off climb, not within the range of speeds given in the POH, but on an exact Va speed.
--Practice holding that speed while moving the trim through its full range of movement. Lock your elbow against the door panel to do this. If you ever fly with some out-of-trim yoke pressure a distraction will create a problem.
--Use climb-out as practice time for Dutch rolls. It helps you clear the flight path and gives x-wind skills you will need for landing.
--Always make your first airwork turn to the left. Any following traffic should be passing to your right. Fly at altitudes other than even thousands or five-hundreds when within 3000’ of the ground. Select your area to be clear of common air routes and airways.
--Practice left/right climbing turns only at 30 degree bank. Take feet off rudder during entry and while in left climbing turns. Note that ball stays centered. P-factor.
--Practice using the right rudder to come out of a left turn with very little aileron. Practice making right climbing turns using right rudder for your entry. Note that at 30 degrees of right bank your yoke is held as though in a left turn. To level wings from a right climbing turn relax on the right rudder and use the aileron.
The POH (Pilot Operations Handbook) has compiled the manufacturer's experience with wind velocity and direction, flap configuration, density altitude, runway surface, and slope to determine the performance capability of the aircraft for a given weight to lift off and overfly the FAA 50' obstacle. The POH has determined the flap requirements, the rotation speed, tire inflation, and the climb speed. If the surface is firm an over-inflated tire is preferred, under inflation can increase required distances by 15%.
Many POH charts fail to provide for variables of runway surface, for this we must use 'rules of thumb' that provide safety margins. For grass runways increase lift-off distance by 20%. If the grass is long or damp add 50%. Slope of the runway and wind direction can be compounded by the slope and turn clearance area of the departure path. For specifics you must consult with the locals. Distances can be reduced by 5% for every 100 pounds below gross or POH weights. A 3000' runway becomes very short when temperatures exceed 80 degrees at 3000' elevation
In the aircraft POH there is reference data that show how the aircraft will perform under a variety of conditions. One of these conditions is going to be an appropriate fit for most any takeoff you will make. You should make a practice of referencing some of your takeoffs with the information contained in the POH. The more often you do this the least likely will you be a pilot who if found by the NTSB (National Transportation Safety Board) as not understanding takeoff data and responsible for improper decision-caking. The POH will have charts that cover the takeoff influence of weight, power, runway surface, wind and density altitude. Any one of these factors can alone or in combination cause a takeoff accident. The worst thing that can happen to a pilot is to get-away-with-it one time.
An overweight aircraft may be pitched too high during the takeoff roll. This pitch limits the ability of the aircraft to accelerate. The perception of attitude improving takeoff from previous flights or even a flight simulator may get you off the ground only to cease flying out of ground effect and stall to the surface. The pitch attitude puts the aircraft behind the power curve. The aircraft may fly off the runway but it will crash because once behind the power curve, you must lower the nose and lose altitude before gaining flying speed.
P-Factor
P-factor results when there is a differential in thrust between two propeller blades. This asymmetric disc loading of the blades moves the line of thrust from the axis of rotation. The result is adverse yaw which must be countered by rudder application. When the propeller blades differ in thrust there is a proportional decrease in total propeller performance.
Every time an aircraft rotates for takeoff or for landing flare the propeller has asymmetric loading of the propeller blades and the resulting adverse yaw. The higher the pitch angle or the power the greater need exists for rudder application to keep the nose straight. Some lack of climb performance is due to the inefficiency of the descending propeller blade.
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