• Version
• 136 Downloads
• 941.57 KB File Size
• 1 File Count
• November 25, 2016 Create Date
• November 25, 2016 Last Updated

National Advisory Committee for Aeronautics, Technical Notes - Notes on the Calculation on the Minimum Horizontal Tail Surface for Airplanes Equipped With Wing Flaps

In connection with a flight investigation of different
types of wing flaps it was observed that where flaps had
been installed on an airplane not designed for them, longi-
tudinal instability in the form of a reversal of ilevator "'
control forces at low angles of attack usually occurred
when the flaps were lowered. An increase in the horizdntal
tail area was generally required to make the airplane efa~'
ble. A preliminary study to determine the amount that the
horizontal tail surfaces should be increased to insure sta—
bility with the flapped wings indicated that existing
methods of tail design, which had been formulated prior to
the time wing flaps had come into general use, were not
adequate for the purpose. A further study was therefore
made to evolve a method of tail design applicable to air—
planes with wing flapS. As a result of this study the
method for the calculation of the minimum horizontal tail
area discussed in this paper was developed. _It combines
and extends the two methods given by Diehl in referenCe l
to obtain the tail area necessary for a statically stable
airplane. In addition to the area required for stability,
that required for longitudinal trim is considered. The
method is applicable to any type of wing or high lift de—
vice.

The complete equations of the.momente acting on an
airplane in flight are too involved for design use. Also,
the information on some 0f the factors is so inadequate
that the use of the complete equations is not justified at
the present time. The use of the simplifying assumptions
made in reference 1 has, therefore, been continued. So
little-is known of the effects of propeller thrust and
slipstream that the discussion has been confined to the
condition of power—off, or gliding, flight.

The moment M about the center of gravity of an air—
plane equals the sum of the wing moment MW, the tail mo«
ment Mg, and the residual moment Mr attributable to
the fuselage, the landing gear, and the exposed structural
members. The residual moment is generally small relative
to wing and tail moments and may be neglected.