Climbing On the Prop
True or false: Apart from tilt-rotor or “powered lift” category aircraft, it is physically impossible for a propeller airplane (whether piston or turboprop) to either maintain altitude (or as the expression goes, “hang on its prop”) or to climb straight up, by virtue of sheer thrust alone.
Answer: False. Obviously, we have all heard of aircraft such as the Bell XV-15, the V-22 Osprey, or the Bell 609. These don’t count. And some jet fighters such as the F-16, with a thrust-to-weight ratio greater than one, can accelerate going straight up. And of course one might think of the Harrier Jump Jet. But those don’t count, either. Oh, and zooming upward, trading kinetic energy for the potential energy of altitude–well, that’s obviously cheating. We’re talking raw, blistering, prop fury here.
It can be done, and it has been. First, a little background. For a helicopter or anything else going straight up without the assistance of a rocket, the force of lift is proportional to the mass of the air directed downward, as well as its speed. You can accelerate a lot of air at a modest velocity, or a small amount at a tremendous velocity, or anything in between. It takes power to do that however, and how much depends on the kinetic energy imparted, according to that old equation:
KE = 1/2 mv2
This tells us that the least expensive way to shove the air down is to push on gobs of it, as slowly as we can get away with. Well, propellers aren’t too great at that job. But curious minds want to know, and gosh darn it, we built two different models. (This was in the early 1950’s, of course.) Intended as experimental VTOL fighter aircraft, there was the Lockheed XFV-1, and there was Convair’s (Consolidated Vultee Aircraft Corporation) XFY-1. Both had maximum horizontal speeds around 500 mph and both had monstrous turboprop engines driving coaxial contra-rotating propellers. They sat on cruciform tails having small castoring wheels (without brakes) at their tips, and their respective pilots each sat on gymbaled seats. They were known as the “tail-sitters” or in the case of Convair, the “pogo”. Lockheed’s entry never made takeoffs and landings from the vertical, but the XFY-1 did. For the precise reason that their very flight regime epitomized the word “precarious”, these birds got the axe after only a few months.
There are incidentally a very few present day equivalents to these airplanes which, thanks to modern technology, can also hover vertically (although they dare not take off from the ground in a vertical position). The 10-10-220 Challenger flown by Sean Tucker is one such airplane that can hang on its prop. It is very light weight, with the right prop, and gobs of power.
At left: the XFV-1, and at right, the XFY-1
Too Good To Be True
Before 1900, there was a “law” of aerodynamics, derived experimentally by the renowned Samuel Pierpont Langley, which said that the total power required for flight decreases, as speed increases. While his data were not in error, his methods were still flawed. Why?
- He failed to account for parasite drag.
- He used mathematical modeling techniques to apply data taken from smaller-scale models, but he did so incorrectly.
- He used a limited range of velocities, none of which exceeded the minima on the curve of power vs. airspeed..
- He used airspeeds which were too high.
Answer: C. His inductive reasoning was flawed because he never ventured beyond speeds above those which exist on what we now know as the “back side” of the power curve! (In addition, there were some scale effects for which he did not correctly account.) This speed is one which we know today as either the speed for maximum endurance or, without power, the speed for a minimum sink glide.
Samuel Pierpont Langley was actually a professor of physics and astronomy at the University of Pittsburgh. In 1886, the year before he was named to be the assistant secretary of the Smithsonian Institution (originally the National Museum), he went to Buffalo, New York for a meeting of the American Association for the Advancement of Science. His interest was captivated, or so the history books say, by the lectures that he attended on the subject of flight. (The Secretary of the museum died several months after Langley’s appointment, and Langley then succeeded him as Secretary.)
Then, as now, getting research funded was always an issue, and when he did secure funds, he began to measure how much power was required to lift a weight with a moving wing, using a technique described 50 years earlier by Sir George Cayley. Using a “whirling table” with a wing attached to a 30-foot arm that rotated at up to 70 miles per hour, he measured lift and drag forces. In his 1891 paper, “Experiments in Aerodynamics,” he concluded that the higher the speed, the lower the drag. This incorrect conclusion was accepted at the time and named “Langley’s Law”.
Hey, Didn’t the Wright Brothers Ever Smile?
The Wright Flyer was not displayed at the Smithsonian until:
Answer: D. The Wright Flyer was not displayed at the Smithsonian until 1948. Heck, it wasn’t even in the United States for about 40 years! Up until 1948, the Smithsonian actually displayed Langley’s Aerodrome as the first airplane “capable of flight”. (The whereabouts of the Flyer are a bit more complicated.) This may have had something to do with the fact that Samuel Pierpont Langley had been the Secretary of the Smithsonian at the time of the Wright Brothers’ historic flight, that he had been in feverish competition with them to achieve the first manned, sustained, and powered heavier-than-air flight, and that he had been soundly beaten by them (despite all of the financial resources at his disposal). The story is also a bit complicated, but as to the reason for Langley’s failure, the biggest reason was probably that his models simply didn’t account for the much greater influence of all things affecting a full scale machine (such as for example, drag), or other aerodynamic factors. Langley was Secretary of the Smithsonian (or as it was known until 1911, the United States National Museum) from 1887 to 1906, the year of his death. There was pretty much a fued–and that’s the right word for it–going on between Orville Wright and the Smithsonian, from about 1914 to 1943. Although the Flyer was not offered to the Smithsonian until 1910, officials at the museum were still determined to “redeem” the reputation of its former director. Langley’s Aerodrome was left with the Smithsonian, which in 1914 asked Glenn Curtiss (whom the Wrights had sued for patent infringement) to rebuild it, and to conduct further tests. With many improvements, he succeeded in getting the Aerodrome airborne for short straight-line flights at Hammondsport, New York, after which it was returned to the Smithsonian (restored to its original unsuccessful configuration), and put on display in 1918 (with the above-mentioned claim that was at best, inaccurate). This indignity was probably what most angered Orville, and which was what precipitated his lending the Flyer to the London Science Museum in 1928.
So where was the Flyer during the years before it was ceremoniously unveiled in the Arts and Industries Building of the Smithsonian, on December 17, 1948? Well, in London, mostly, but from the end of 1903 through 1913, the airplane slept in crates inside a shed behind the Wright Cycle Company in Dayton, Ohio. The Miami River flooded in March of 1913, and the Flyer lay covered under mud and water for eleven days. In 1916, Orville and a Wright Company mechanic uncrated the Flyer and restored it for a brief exhibit at MIT, and it was also exhibited at the New York Aero Show in 1917. In 1921, it was again reassembled to provide evidence for a lawsuit against Orville Wright that was filed by the survivors of a California glider builder. The Flyer was also exhibited at the 1924 National Air Races held in Dayton. During this time, many interested American museums approached Orville about acquiring the Flyer. He had considered transfering it to the Science Museum in London as early as 1924, and the construction of its new building in 1928 was a likely reason for his decision to do so. Between 1928 and 1943, Orville negotiated with Smithsonian officials, and went so far as to seek the assistance of Supreme Court Justice (and former president) Taft. But it wasn’t until President Roosevelt intervened in 1943 that Orville was persuaded to return the Flyer home. At FDR’s request, Orville wrote to the director of the London Science Museum in December 1943, requesting its return.
The Aerodrome continued to be displayed in the Smithsonian’s Arts and Industries building (with a revised label) until 1971. It was then removed from public exhibition. And the Wright Flyer? The estate of Orville Wright made sure that the airplane would always be displayed with the following label:
THE ORIGINAL WRIGHT BROTHERS AEROPLANE THE WORLD’S FIRST POWER-DRIVEN, HEAVIER-THAN-AIR MACHINE IN WHICH MAN MADE FREE, CONTROLLED AND SUSTAINED FLIGHT INVENTED AND BUILT BY WILBUR AND ORVILLE WRIGHT FLOWN BY THEM AT KITTY HAWK, NORTH CAROLINA DECEMBER 17, 1903 BY ORIGINAL SCIENTIFIC RESEARCH THE WRIGHT BROTHERS DISCOVERED THE PRINCIPLES OF HUMAN FLIGHT AS INVENTORS, BUILDERS AND FLYERS THEY FURTHER DEVELOPED THE AEROPLANE TAUGHT MAN TO FLY, AND OPENED THE ERA OF AVIATION
By the way, you can now see a reproduction of the 1903 Wright Flyer and the original Langley Aerodrome, on display together for the first time ever, at the Virginia Air and Space Center, in Hampton, VA.