Question

What are the factors in determining your takeoff critical field length for a certain runway? If after doing initial calculations you find the runway is too short, what might you be able to do as the pilot in command to be legal for takeoff?

Compare and contrast the longitudinal stability of a conventional aircraft in two conditions: forward CG and aft CG? Discuss control forces and aircraft responses from trimmed condition if you pulled back on the stick and let it go.

Compare and contrast a supercritical wing with a laminar flow wing? Discuss modern aircraft that have utilized these wings. What are the enhancements and drawbacks?

Answer 1

The factors that affect takeoff critical field length for a certain runwayare: the localelevation, temperature, wind, and air density. The aircraft takeoff mass and balance, flaps setting,runway conditions, and airframe contamination also play a factor in takeoff roll.I would first refer to my Pilot’s Operating Handbook for Short field takeoffs and thenfollow all the steps. In a short field situation, be particularly attentive to maintaining the correctairspeed. Only the recommended obstacle clearance speed, or Vx, will give you the best angle ofclimb. Anything faster or slower will not work as well.

The position of the aircraft’s Center of Gravity in relation to its neutral point affectslongitudinal stability. An aircraft can be considered stable when its center of gravity is aft of itsneutral point. This configuration of an aircraft will be stable in flight. When pulling back on thestick and letting go, nose would pitch back down to level flight. An aircraft that has its center ofgravity forward of its neutral point would be not as stable. Pulling back on the stick and thenletting go, the aircraft nose would pitch down and continue to require more trim force to levelout.

Supercritical wings are flatter on the top, rounded on the bottom, and the upper trailingedge is accented with a downward curve to restore lift lost by flattening the upper surface.SCW’s reduce a supersonic shockwave strength allowing an aircraft to fly faster with less effort.(NASA, 2004) Laminar Flow has the maximum camber in the middle. Drag is considerablyreduced since the laminar airfoil takes less energy to slide through the air. The super critical wing was designed with one thing in mind. To delay the onset of wave drag in the transonic speed range. They have a flatter upper surface and the aft section has a high camber. Thereason for this design is that it is more efficient for high-speed flight and develops the shockwaves further aft which helps to reduce drag as well. Laminar flow wings were designed for smooth laminar or uninterrupted flow over the wings to aid in no interruptions in the boundary layer. The advantage of these wings is that the smooth flow of the laminar air is that drag is significantly reduced.