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Table 2.17 Energy Absorption E ff i c i ency of Tires and

Shock Absorbers

Element: Energy Abso rpt ion Eff ic iency;

Tires: = 0.47

Shock absorbers:

ai r springs ti =0 .6 0 to 0.65

smetal springs

w i t h o i l damping = 0.70

l i q u i d spr ing s = 0.75 to 0.85

oleo-pne umatic = 0. 80

canti lever spring = 0.50

Table 2.18 Suggested Landin g Gear Load Fact ors

C e r t i f i c a t i o n Base: Landin g Gear Load Fac to r, N

FAR 23 N = 3.0g

FAR 25 Ng =1 .5 to 2.0

Fighters and Trainers N = 3.0 - 8.0: See Fig.2.26for more details

M i l i t a r y t ransports = 1.5 - 2 .0

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load per l eg to th e maximum st at i c load per l eg .

^ is the t i r e energy absorption e f f i c i enc y.

is the energy absorption e f f i c i e n c y of theshock absorber.

s is th e maximum al lo wab le t i r e d ef l ect ion as determined f r o m Eqn.(2.4) .

s_ is the stroke of the shock absorber,s

Eqn.( 2.9) may be used to compute the r equ ire d shockabsorber length:

S g = [ { 0 . 5 W j ^ / g ) (w^)^/(ngP^Ng)} - n ^ s ^ l i g (? i U

I t i s suggested to add one inch to this length:

s s •'• ^ (2.12)design

Table 2.18 shows the values f or land ing gear loadfac to r s which may be used i n pr el im in ar y des ign . Howthese landing gear load factors are related to designtouchdown rat e and to shock absorber str oke is shown i nFigure 2.26 for some example air pla nes .

The diameter of the shock absorber (s tr ut ) may beestimated f r o m :

d = 0.041 + 0.0025(P ) ^ ^ (2.13)s m

Note that Eqn.(2.9) t a c i t l y assumes that the maingear react ion load is t ransferred d i r e c t l y i n to the shockabsorber. This condi t ion i s no t s a t i s f i ed fo r gearswhere the reac tio n load is not i n l i n e w i t h the shockabsorber. A land ing gear where the re ac tio n load is a-ligned w i t h the shock absorber i s given i n F i g . (2 .7 ) .Examples of landing gears where this alignment is absent,are given in Pig .( 2. 24 ). For the la tt er type gears, therequire d value f or shock absorber str oke (and thus s tr utlength) must be determined for the particular landinggear geometry at hand. No gene ral r ul es can be gi ve n.

For main gears where the design ca ll s f or a siirplecanti lever ( leaf or tube) spr ing , Ref .8 contai ns anexample siz in g cal cu la ti on . Figure 2.27 shows an exampleapplicat ion, seen mostly in l i g h t a i rplanes.

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