Model Ditching Investigation of a Jet Transport Airplane With Various Engine Installations Page: 3 of 28
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NACA RM L56G10
APPARATUS AND PROCEDURE
Description of Model
The 0.043-scale model of a jet transport airplane with various
engine arrangements shown in figure 2 was used in the investigation.
The model was constructed of balsa wood and spruce, and was covered with
silk to provide a durable water-resistant finish. Internal ballast was
used to obtain scale weight and moments of inertia. The model had a
wing span of 5.59 feet and an overall length of 5.50 feet.
The landing flaps were installed so that they could be held in the
down position at approximately scale strength. In order to accomplish
this, a calibrated string was fastened between each flap fitting and a
corresponding wing fitting so that water loads within 10 percent of
the ultimate design load (5,000-pound full-scale normal load applied
near the trailing edge of a flap) would cause the string to break. When
the scale-strength connections failed, the flaps rotated to the retracted
position.
The strut-pod engine nacelles were installed at approximately scale
strength, in a manner similar to that described for the landing flaps.
Each nacelle strut had a parting line near the nacelle; the strut and
the nacelle were connected with a calibrated string which failed within
10 percent of the ultimate drag load (40,000 pounds, full scale).
When the scale-strength connections failed, the nacelles became detached
from the model. The other three engine installations were made with the
engines rigidly attached to the model.
The model was constructed so that a portion of the fuselage bottom
could be replaced with an approximately scale-strength section. The
assumed full-scale ultimate strength of the fuselage bottom surface was
approximately 10 pounds per square inch. The scale-strength bottoms
were constructed of cardboard bulkheads and balsa-wood stringers and
were covered with aluminum foil. A bottom is shown installed on the
model in figure 3. Scale-strength bottoms were used to indicate the
location and extent of damage that might occur in a ditching. The scale-
strength fuselage bottoms were applied only with the strut-pod engine
installation, but all engine installations were tested with the model
having a simulated damage bottom as shown in figure 4. The simulated
damage bottom was used to expedite the test program because the use of
the scale-strength bottoms indicated the portion of the fuselage bottom
that would be damaged and the behavior resulting with the simulated
damage bottom was not appreciably different from that with the scale-
strength bottom.2
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Thomson, William C. Model Ditching Investigation of a Jet Transport Airplane With Various Engine Installations, report, August 20, 1956; (https://digital.library.unt.edu/ark:/67531/metadc62557/m1/3/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.