SLIDE 1
ME EN 415 Andrew Ning aning@byu.edu
Structures: V-n Diagrams
Lecture 18
SLIDE 2 Safety Factor
https://youtu.be/Ai2HmvAXcU0 B777 Wing Bending
§25.303 Factor of safety. Unless otherwise specified, a factor of safety of 1.5 must be applied to the prescribed limit load which are considered external loads on the structure.
SLIDE 3
Air Speed
True airspeed (TAS): speed of aircraft relative to air Equivalent airspeed (EAS): airspeed at sea level with equivalent dynamic pressure 1 2ρTAS2 = 1 2ρSLEAS2 EAS = TAS r ρ ρSL
SLIDE 4
Design airspeeds (all in EAS)
VA : VB : Vs : VC : VD :
SLIDE 5
V-n Diagram
V (EAS) n VD VC nmmax stall stall
SLIDE 6
V-n Diagram
V (EAS) n VD VC nmmax stall stall
SLIDE 7 V-n Diagram
V (EAS) n VD VC nmmax stall
except that n may not be less than 2.5 and need not be greater than 3.8
stall
SLIDE 8
V-n Diagram
V (EAS) n VD VC nmmax stall stall
SLIDE 9 V-n Diagram
V (EAS) n VD VC nmmax stall
From an initial condition of stabilized flight at VC/MC, the airplane is upset, flown for 20 seconds along a flight path 7.5° below the initial path, and then pulled up at a load factor of 1.5g (0.5g acceleration increment). The speed increase occurring in this maneuver may be calculated if reliable or conservative aerodynamic data is used.
stall
SLIDE 10
V-n Diagram
V (EAS) n VD VC nmmax stall stall
SLIDE 11
V-n Diagram
V (EAS) n VD VC nmmax stall stall
SLIDE 12
V-n Diagram
V (EAS) n VD VC VB gusts
SLIDE 13
Reference Gust Velocities
15,000 ft 60,000 ft altitude 60 ft/s 30 ft/s 56 ft/s 44 ft/s 20.86 ft/s VB — VC 28 ft/s 22 ft/s 10.43 ft/s VD
SLIDE 14
Gust Equations
Kg = 0.88µ 5.3 + µ (using standard metric units) ng = 1 ± KgUref(EAS)CL,α 1.63(W/S) µ = 2W/S ρ¯ cCL,αg reduced mass gust factor
SLIDE 15
V-n Diagram
V (EAS) n VD VC VB gusts 1 intersection
SLIDE 16
SLIDE 17
V-n Diagram Critical Points
V (EAS) n positive low angle of attack positive high angle of attack negative low angle of attack negative high angle of attack
SLIDE 18
positive high angle of attack compression tension compression tension positive low angle of attack
SLIDE 19
negative high angle of attack compression tension compression tension negative low angle of attack
