• Version
• 197 Downloads
• 804.80 KB File Size
• 1 File Count
• September 1, 2016 Create Date
• September 1, 2016 Last Updated

National Advisory Committee for Aeronautics, Report - Effects of Wing Flexibility and Variable Air Lift Upon Wing Bending Moments During Landing Impacts of a Small Seaplane

The smooth-unter-landing inrestigation was conducted with a
small seaplane to obtain erperimental wing-bending—moment
time histories together with time histories of the carious pa-
rameters necessary for the prediction of wing bending moments
during hydrodynamic impact. The experimental results were
compared with calculated results which include inertia-load
ejects and the (fleets of air-load variation during impact. The
responses of the fundamental mode were calculated with the use
of the measured hydrodynamic forcing junctions. From these
responses, the wing bending moments due to the hydrodynamic
load were calculated according to the procedure giren in R. di- Elf.
No. 2221. This comparison of the time histories of the experi-
mental and calculated wing bending moments showed good
agreement both in phase relationship of the oscillations and in
numerical values.

The ejects of structural flexibility on. the wing bending
moment were large, the dynamic component of the total moment
being as much as 97’ percent of the static component. Changes
in the wing bending moment due to the rariation in air load dur-
ing impact were of about the same magnitude as the static
water-load component.

Recent trends in the design of aircraft have led to an
important increase of the stresses produced in wings by land-
ing impacts. Two significant factors contributing to those
increased stresses during landing are an increased proportion
of the airplane weight in the Wings and an increased struc-
tural flexibility, since, in most cases, these factors have caused
the ratios of the times to peak of the applied landing loads
to the period of the fundamental mode to approach a critical
value.

Several simplified methods have been developed for deter-
mining the inertia loads in wing structures during landing
impacts, and studies have been made of the landing-impact
inertia loads in simplified structures with the use of the
principles of those methods. Although experimental investi-
gations have been made to determine the magnitudes of
inertia loads in actual airplane structures, little correlation
of theory and experiment has been made concerning the
nature and magnitude of inertia loads in airplane wings
during actual landing impacts.