Four Square (1937)

[Music] on time the Clipper across the Pacific Ocean from the Orient the ships that are making new history in man's conquest of the air and setting new records for dependability these airliners are now in regular scheduled flights between Manila in the Philippine islands and San Francisco carrying passengers mail and Freight with stops at Honolulu Midway wake and Guam they travel a third of the way around the world in 60 hours flying time this 25 1/2 ton oceangoing liner of the air and its sister ships with their luxurious passenger accommodations are the largest practical flying boats in the world such huge ships have to meet the severest kind of strains from wind and weather and heavy caros the planning of this airplane called for new developments of Structural Engineering for example look at that Wing spread 130 ft from tip to tip and those wings have to carry the entire load every bit of that 130 ft of metal had to contribute its share of strength and dependability to get the necessary rigidity Engineers selected two long beams to be used as the framework for each Wing these two beams or spars as they're called run straight from wing tip to Hole together they form the two sides of a box the top and bottom of the Box are formed by two Metal Sheets covering the top and bottom of the wing this four-sided box construction has proved to be the strongest possible structure to carry the 25 1/2 ton load these box beam wings are capable of supporting a load equal to the weight of almost 2,000 average human beings let's perform an experiment or two and find out the principle of this box beam design first we get a metal sheet and place it flat in a clamp like this notice that it has very little stiffness it sags under its own weight however if we bend a sheet just just like the first one into an angle we find that it will support considerable weight that's progress but when we load the angle Beam with three lead weights it starts to bend right there where the side bulges out of line to get more strength let's try a sheet of metal of the same size and thickness shaped to form a three-sided beam that's nearly three times as strong but eight Le weights put too much strain on it the three-sided beam is bending two by turning the three-sided Beam on its Edge we find that it has more resistance it holds 17 lead weights before the sides bulge out and it gives way three sides aren't enough now if we complete the Box by bending up the fourth side then welding the edges together to make it one piece it will Support 32 lead weights almost twice as much weight as the open box with plenty of strength to spare each side helps to keep the other sides firm and rigid even though the four-sided box is smaller because we have used up some of the material in making the extra side it is almost twice as strong an 81 ft box beam is the backbone of the modern pulman car with a its Splendid record for safety in modern building construction the world over box girs are frequently used where great strength and resistance to bending are needed great steel girders on overhead cranes in factories and steel mills carry loads of hundreds of tons in perfect safety the Statue of Liberty Rises 305 ft above New York Harbor held safe and secure on foursided box beam girders box girder towers of massive strength carry the strain of huge cables in many modern suspension bridges strength and dependability are important in a train bridge or airplane and just as important in an automobile if you ask an automobile engineer what takes the punishment from Road shocks and bumps he'll tell you it's the frame and on Sharp curves on a downhill grade it's the frame that is tortured and r the automobile frame has developed step by step and even recently only a three-sided Channel construction was used the old style frames had an unfortunate tendency they would shift out of shape on bumps and curves to prevent this diagonal cross pieces were added between the side girders but even with cross braces the frame would still warp out of shape under heavy loads and twisting Road shocks the three-sided beam was not rigid enough Engineers weren't satisfied so after research and testing a design was developed to use the extra strength and rigidity of the four-sided box now with four-sided box girds the frame has been made four square construction has been made far more rigid by this new advance in motorc car development This Modern frame has greater resistance to bending and twisting even the sturdy cross members are of box beam design and the simplified bracing gives the strength to withstand the shock of bumps and twisting strains on the road these box girder type frames will support almost unbelievable loads strains far greater than will ever be met in ordinary service on the highway these two box type automobile frames are placed side by side to make a single Bridge wide enough for a roadway with planks laid crosswise to make a level floor now here comes the [Music] test that's what the four square frame has done for strength strength and rigidity in the modern automobile [Music]