Introduction to Aircraft Structural Analysis (Elsevier Aerospace Engineering)

400 CHAPTER 13 Airframe Loads

Ifeachundercarriagewheelweighs2.25kNandisattachedtoanoleostrut,asshowninFig.P.13.1(b),calculate
theaxialloadandbendingmomentinthestrut;thestrutmaybeassumedtobevertical.Determinealsotheshortening
ofthestrutwhentheverticalvelocityoftheaircraftiszero.
Finally,calculatetheshearforceandbendingmomentinthewingatthesectionAAifthewing,outboardof
thissection,weighs6.6kNandhasitsCG3.05mfromAA.

Ans. 193.3kN,29.0kNm(clockwise);0.32m;19.5kN,59.6kNm(anticlockwise).

P.13.2 Determine,fortheaircraftofExample13.2,theverticalvelocityofthenosewheelwhenithitstheground.

Ans. 3.1m/s.

P.13.3 FigureP.13.3showstheflightenvelopeatsea-levelforanaircraftofwingspan27.5m,averagewingchord
3.05m,andtotalweight196000N.Theaerodynamiccenteris0.915mforwardoftheCGandthecenterofliftfor
thetailunitis16.7maftoftheCG.Thepitchingmomentcoefficientis

CM,0=−0.0638(nose-uppositive)

bothCM,0andthepositionoftheaerodynamiccenterarespecifiedforthecompleteaircraftlesstailunit.

Fig. P.13.3

For steady cruising flight at sea-level the fuselage bending moment at the CG is 600000Nm. Calculate the
maximumvalueofthisbendingmomentforthegivenflightenvelope.Forthispurpose,itmaybeassumedthatthe
aerodynamicloadingsonthefuselageitselfcanbeneglected—thatis,theonlyloadsonthefuselagestructureaft
oftheCGarethoseduetothetailliftandtheinertiaofthefuselage.

Ans. 1549500Nmatn=3.5,V=152.5m/s.

P.13.4 Anaircraftweighing238000Nhaswings88.5m^2 inareaforwhichCD=0.0075+0.045CL^2 Theextra-to-
wingdragcoefficientbasedonwingareais0.0128andthepitchingmomentcoefficientforallpartsexcludingthe
tailplaneaboutanaxisthroughtheCGisgivenbyCM·c=(0.427CL−0.061)m.TheradiusfromtheCGtothe
lineofactionofthetailliftmaybetakenasconstantat12.2m.Themomentofinertiaoftheaircraftforpitching
is204000kgm^2.
Duringapull-outfromadivewithzerothrustat215m/sEASwhentheflightpathisat40◦tothehorizontalwith
aradiusofcurvatureof1525m,theangularvelocityofpitchischeckedbyapplyingaretardationof0.25rad/s^2.