NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS

CONFIDENTIAL MEMORANDUM REPORT
for
Army Air Corps
MEASUREMENT OF THE FLYING QUALITIES OF THE BOEING XB-15 AIRPLANE (A. C. No. 35-277)
By R. R. Gilruth and M. N. Gough

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July 31, 1939

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Conclusion

As a result of the tests, considerably more information was obtained regarding desirable and undesirable flying characteristics in terms of measurable quantities. The test methods have been further proven and simplified.

With regard to the flying qualities of the XB-15 airplane, the following undesirable features are believed to exist.

1. The static longitudinal stability with power-on is undesirably small both as. regards stick travel and stick force. The elevator-control friction masks stick-force variation with air speed.

2. The ailerons are far too heavy and they are virtually ineffective at high speeds because of the high hinge moments and excessive cable stretch.

3. Aileron-control feel is destroyed by the predominating control friction and irreversible action.

4. The strong yawing moments accompanying small angles of bank in sideslips are objectionable, particularly in view of the poor aileron action in raising a low wing.

5. The rudder force was observed to lighten in sideslips made with flap up at large rudder deflections.

6. The airplane, when left to itself, enters a spiral turn with increasing angular velocity.

7. The stall with partial flap and partial power (usual landing-approach condition) is sudden and violent and has very little warning.

Langley Memorial Aeronautical Laboratory,
National Advisory Committee for Aeronautics,
Langley Field, Va., July 31, 1939

Approved:
Elton W. Miller
Principal Mechanical Engineer

/s/ Robert R. Gilruth,
Assistant Aeronautical Engineer

/s/
Melvin N. Gough
Senior airplane test pilot.