tsl thrust to weight ratio and aspect ratio
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THRUST TO WEIGHT RATIOAND ASPECT RATIO
Nguyễn Anh TuấnNaval Architecture and
Marine Engineering [email protected]
(+84) (0) 944 113 787
TSL_Oct2010
T/W Ratio
T/W ratio estimates:• Part of the takeoff distance• Rate of climb• Maximum velocity
http://www.centennialofflight.gov/essay/Theories_of_Flight/Performance_Class2/TH25G1.htm
Takeoff distance = sg + sa = 2500 ftAccording eq. [6.95] (see [1]), Ground Roll sg
For FlapPlain Flap deflection 20o for takeoff (see table 5.3 [1])Section maximum lift coeffient (cl)max of 45o flap deflection is 0.9 (see Fig.5.28, [1])(cl)max = 0.9 (20/45) ~ 0.5 (For linear changes)
For the whole of wing, average (cl)max = 1.7 + 0.5 = 2.2
3D- effect of the finite aspect ratio
Raymer, Ref [25] of [1]
The liftoff velocity
Flight path radius
Velocity of airplane
Flight path angle == 50 ft : obstacle height
Airborn distance
Takeoff distance = sg + sa = 2500 ft
Requirement powerPA =
Note: 550ft.lb/s = 1hp
Power of the takeoff constraint ≥ 119 hp
Shaft brake power
Gross takeoff weight = 5,158lb
(cl)max
T/W W/S(Cl)max
sg
Vstall
R
sa
𝜃𝑂𝐵
T/W
VLO
V
PR = PA
P
Wo
T/W ratio and Aspect ratio
Effects
Maximum Rate of climb (R/C)max = 1000ft/min = 16.67 ft/s at sea levelSingle-engine general aviation airplanesThe ratio of wetted area to the wing referenece area Swet/Sref = 4 (See fig. 2.54, [1])The skin –friction coefficent (for early jet fighters) Cfe = 0.0043 corressponds to Reynolds number Re = 107 (See fig 2.55, [1])
The zero-lift drag coefficient (the zero-lift parasite drag coefficient)
The drag polar for airplane
The drag due to lift (downwash and so on)
The span efficiency factor to account for a nonelliptical lift distribution
along the span of the wing e
The coefficient
Based on data from famous existing airplanes, estimating a reasonable first approximation for maximum of Lift to Drag ratio for 4-6 peoples aircraft (See p.403 [1])
= = 0.075
A reasonable estimate The Oswald efficiency eo for a low-wing general aircrafts is 0.6 (See p.415 [1]) =7.07
Maximum rate of climb for a propeller-driven airplane
Shaft Brake Power for the constraint of rate of climb
W/SK Wo
Aspect Ratio
Themaximum velocity V = Vmax = 250 mi/h = 366.7 ft/h at midcruise weight and level flight 20,000ftIn level flight T=D
The weight at maximum velocity is less than the weight at takeoff stage
The midcruise weight WMC
Estimating the weight fraction
Gross takeoff weight = 5,158lb
For a propeller-driven aircraft, we use power to weight ratioFor a jet aircraft, we use thrust to weight ratioT/W and P/W are same mean
Thank you!
References
[1] John D. Anderson, Jr. 1999. Aircraft Performance and Design. McGraw-Hill[2] E. L. Houghton and N. B. Carruthers. 1986. Aerodynamics for Engineering Students. 3rd edition. Thomson Press