AE 2350 Lecture Notes #10 May 14, 1999

TOPICS TO BE STUDIED Take-off and Landing Performance Introduction to Aircraft Stability and Control

Take-Off Performance FAA has a number of regulations called FAR that the aircraft should meet. –e.g. Total Takeoff Distance including a clearance of 35 foot structure at the end of the runway. –One engine out condition. Figure and figure in the text give curves for the total takeoff distance, for all engine operation, and one engine out condition, respectively. Compute these for your fighter and ensure they are below 6,000 ft. Use C l,max = 1.7, Here  is the wing sweep computed as sweep of the line joining the midchord at the root and the midchord at the tip. The above equation (13.4) empirically corrects for sweep and aspect ratio.

Takeoff Performance Theory Ground Roll 80% of total takeoff distance, from experience. Transition and climb 20% of total takeoff distance, from experience We attempt to compute the ground roll as accurately as possible. Add an extra 20% distance to account for transition and climb.

Ground Roll Let v be the aircraft speed. dv/dt = a where a= acceleration of the vehicle a= (All horizontal forces acting on the aircraft) / (Mass of aircraft) Integrate: v = at Velocity at lift-off v LO = a t LO Integrate again: d = 1/2 a t 2 d LO = 1/2 a t 2 LO = v 2 LO /(2a)

Ground Roll (Continued) From the previous slide, the total roll distance is d LO = 1/2 a t 2 LO = v 2 LO /(2a) a = Acceleration of the aircraft due to horizontal forces on it. These forces are: Thrust, Drag, Ground Friction Thrust far exceeds the other two factors during takeoff. Thus, a = T/(Aircraft Mass) = T g/ (GW) Then, total roll distance is d LO = v 2 LO /(2a) = v 2 LO. GW/(2Tg)

Ground Roll (Continued) Total roll distance d LO = v 2 LO. GW/(2Tg) The pilot usually lifts off at 1.2 times stall velocity. Stall velocity V Stall is defined from: 1/2  V 2 Stall C Lmax S= GW V 2 Stall = GW/(1/2  C Lmax S) v 2 LO =(1.2 V Stall ) 2 = 1.44 GW/(1/2  C Lmax S) Then, d LO = v 2 LO. GW/(2Tg)= 1.44 (GW) 2 / (Tg  S C Lmax ) Multiply this by 1.25 to include transition and climb The result, after additional factors of safety, is figure in text.

Landing Performance Use figure 15.35, which was derived using arguments similar to take-off performance. There is considerable scatter in landing distances due to use of spoiler, brakes, reverse thrust, human factors ground conditions : wet runway, dry runway Use the dotted line in figure in the text.