 skin-friction measur incompress flow skin-friction measur incompress flow experi conduct measur incompress flow local surfac-shear stress averag skin-friction coeffici turbul boundari-layer smooth flat plate pressur gradient local surfac-shear stress measur float-element skin-friction balanc calibr total head tube locat surfac test wall averag skin-friction coeffici boundari-layer veloc profil boundari-layer profil determin locat virtual origin turbul boundari layer data obtainec rang reynold number 1 45 attend chang mach number 0 11 0 32 measur local skin-friction coeffici float-element balanc agre well schultz-grunow kempf reynold number 45 measur averag skin-friction coeffici agre schoenherr curv rang reynold number 1 3 30 45 rang reynold number 3 30 measur valu predict schoenherr curv univer skin-friction constant propos cole appraoch asymptot constant reynold number exceed mention constant limit reynold number rang investig doubt valid turbul skin-friction law written basi friction law propos friction resist flat plate calcul momentum method integr measur local surfac shear reynold number 14 45 method result lower valu reynold number momentum method base veloc profil uncorrect effect turbul friction resist 4 percent higher integr shear measur local surfac shear calibr preston tube appear accur inexpens calibr preston modifi slighlti yield float-element skin-friction balanc 