Viewing page 75 of 84

This transcription has been completed. Contact us with corrections.

[[image - drawing of a slide rule]]
TECHNICALLY SPEAKING

WING WEIGHT AND STRENGTH

The air line pilots for some time now have been flying multiple wing tank type aircraft. No doubt, most pilots are familiar with the effect on structural strength of airplanes which permits a faster cruising speed at full gross weight with full wing fuel tanks than is permissible with the airplane loaded with a small amount of fuel in the wings. However, a review of the cause of this principle should prove interesting and informative. This principle can be summarized as follows. With full wing fuel tanks maximum cruising speeds may be safely attained in smooth air. As fuel is used from the wing tanks, cruising speeds must be reduced in accordance with the operations manual of the airplane being flown. Of course, in any airplane at any time in rough air SLOW DOWN.

An Explanation-The above principles have been stated rather bluntly without explanation. In order to give the reasoning behind the above remarks, let us assume we have a 70,000 pound airplane with all the weight concentrated in the fuselage. That would mean that each wing would have to support 35,000 pounds in order to keep the airplane in the air. This would mean that as the wing joints the vertical load would be 35,000 pounds on each side. Of course, we have assumed in this first example that the wings have no weight. This is false and the true example would be as follows:

Total airplane gross load ----- 70,000 lbs.
Fuselage weight* -------------- 61,000 lbs.
Two wings @ 1,500 lbs ---------  3,000 lbs.
Four engines @ 1,500 lbs ------  6,000 lbs.
Wing joint load --------------- 30,500 lbs.

*Assuming all gasoline was in the fuselage. This shows that the wing joint load has been reduced to 30,500 pounds on each side. As you can see, we have still neglected to consider the effect of fuel. We have assumed that the fuel was somewhere in the fuselage. In the next example, we will consider the distribution of fuel as follows:

Total airplane gross weight ------------------ 70,000 lbs.
Fuselage weight ------------------------------ 45,000 lbs.
Two wings @ 1,500 lbs ------------------------  3,000 lbs.
Four engines and nacelle @ 1,500 lbs. --------  6,000 lbs.
Gasoline in wings ---------------------------- 16,000 lbs.
Wing joint load ------------------------------ 22,500 lbs.

An Example of Reduction-This example shows how the wing joint load has been reduced to 22,500 pounds. The differences in the wing joint load are proportionate to the amount of total load which is in the fuselage as compared to the distributed load in the wings. It can easily be seen that if there were no concentrated load at the fuselage and we had a flying wing airplane, for all practical purposes the lift distribution would be the same as the weight distribution on the wing except for minor differences due to concentration of loads at engine nacelle points. This for all practical purposes would make the wing joint loads at or near the center line at the fuselage approximately zero. This does not mean, of course, that there would be no stresses at the center line of the fuselage but it would mean that the stresses would be to an irreducible minimum because the distribution of the loads were at the most advantageous points for support. A practical example of this principle can be shown as follows: If two men use a board suspended between them to carry four 50-pound blocks, and if the 50-pound blocks are all grouped at the 


THE ART OF "SKIP BOMBING"

[[image - photograph, INS Photo]]
[[image - photograph, INS Photo]
[[image - photograph, INS Photo]

This unusual series of high speed photos made at the U. S. Air Forces First Annual Gunnery Meet demonstrates the fine art of "skip bombing." Top: a Republic F-84 has just released a 100-pound bomb at target at left. Center: a dust cloud (at right of photo) is kicked up where bomb hit and skipped through target. Bottom: The F-84 makes its pull-up after scoring bull's eye.


[[image - photograph]]
The United States has unveiled its newest jet fighter, the Republic XF-91 (shown above), following completion of its first test flights at Muroc Dry Lake, Calif. Powered by a General Electric J-47 jet engine, the plane will also have rocket motors, which have not yet been installed. The rockets will be used for accelerated take-off and climbs and for operation at high altitude. The XF-91 is 45 feet long and has a wing span of about 30 feet.

PAGE 10                       THE AIR LINE PILOT