By: Norm Goyer
The number of new biplanes manufactured each year can be counted on your fingers. In years past, a trip to any airport would reveal a number of stately biplanes . One of the acknowledged most beautiful aircraft of all time is the Beechcraft D-17 Staggerwing. I personally would add the 1946 WACO cabin bipe to this list. That’s the one with the Pratt & Whitney 450-hp radial engine up front, a truly beautiful airplane. There are reasons why biplanes were so popular for so many years and there are reasons why they are not now.
Early aircraft including, most of World War I aircraft, such as this SE-5A used struts, cables and flying wires to add necessary strength to the wings.
I can think of only one certified biplane that is still popular and that is the Pitts S2C two-place aerobatic trainer built by Aviat that has been around for 60 years, starting with Betty Skelton’s “Lil Stinker” homebuilt. You can still custom order a newly manufactured WACO open cockpit biplane, if you have a lot of time and money, or you can build a biplane Experimental, if you love multi-wings and the wind in your face. At one time, the mighty bipe dominated the competition aerobatic scene. Then the influx of European and American low to mid-wing monoplanes demonstrated that excess drag of two wings greatly diminished vertical climb performance. The Pitts and Eagles (almost identical aircraft, Pitts is certified and the Eagle is Experimental) were clearly outclassed for competition, but were in high demand for air shows. Some of the most popular air show performers still prefer to fly the Pitts such as Sean Tucker. There is also a much larger version of the Pitts with a Russian radial engine that makes an ideal air show vehicle; The Monster Pitts/ Pitts 12 is a homebuilt however. Stearman PT-17s, which have been fitted with a Pratt & Whitney 450-hp radial engines, twice as powerful as the standard Continental engine, are the choice of many air show performers and air show teams such as the now disbanded Red Baron Team.
This Grumman F3F retractable-gear biplane was the last biplane fighter to be ordered by the US Navy and Marines. Note the thin airfoil and multitude of struts and wire bracing.
The 1903 Wright was a biplane, but it was not the first biplane to fly; glide is more accurate. Early aviators often experimented with biplane gliders. This is how the Wrights tested the concept of their powered aircraft; they started with a glider. The original reason for biplanes was their ability to eliminate most of the stress of flying loads. The two wings, with their many struts, cables, turnbuckles formed a box structure which is incredible strong, if installed properly. Not only are there struts and double cables, between each section of wing, which is then connected to the fuselage with more cables and struts. Another factor leading to the need for the bracing of two wings, was early airfoils which were very thin and under cambered. In many cases the wing was only a few inches thick. Many World War I aircraft used these under cambered airfoils. This allowed only small spars to be used and they lacked strength. A wing is only as strong as its spar. A wing has to be capable of being strong enough to handle both flight and landing loads. These loads occur when the plane rotates into the air, these are lift loads. Upon landing the wing has to be able not to flex downwards, landing loads. However, It is normal for a cantilever wing to flex under loads, the longer the wing the more the flex. The wing of the B-52 rises about 15 feet when flying.
Colonel Roscoe Turner was very successful racing his cantilever, mid-wing monoplane in the mid 1930s. The Turner Special was faster and better designed than contemporary military aircraft.
The big switch from biplanes began in the early 1930s, when Thompson and Schneider Cup racing aircraft proved that a monoplane could be just as safe as a biplane. The first monoplanes did use struts and/or cables to handle the loads but as metallurgy improved, along with the engineering design of the interior wing structure, it was shown that a cantilever wing was the low-drag way to go. The strength of a cantilever wing is due to the depth of the airfoil allowing large strong spars and internal bracing which were once on the outside of the wing in the form of struts and cables. One of the first military monoplanes was the Boeing P-26 Peashooter which used cable bracing. One of the first aircraft to use a cantilever wing was the Turner Racer. The infamous Gee Bee used cable bracing. The last hurrah for military biplanes was with the training elements of World War II. The Beech Staggerwing was available in 1946 as was the WACO but then it was basically over for the realm of the mighty bipe.
Early military monoplane fighters used flying wires and struts in their designs
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