Lon Enloe
Nov 07, 2008, 11:19 PM
...but a bit of science and aviation history, with a little bit of a modeling connection.
I was able to access an interesting document recently: a copy of Jimmy Doolitte's doctoral thesis from MIT, 1925. I didn't even know that this document existed until I read about his having earned the degree in James Bradley's excellent book "Flyboys," and it was indeed an earned doctorate: it turns out that one of America's heroes and top airmen could handle a partial differential equation as well as he could handle a racing plane or a B-25.
The title of the thesis is "The Effect of the Wind Velocity Gradient on Aircraft Performance" and it addresses the issue of whether one's aircraft's performance--rate of climb, etc.--varies with orientation to the wind. This would seem to be a no-brainer (once you're in a moving fluid you're just in a different frame of reference) and in fact he obtained a null result experimentally, although he cast the problem specifically in terms of flying very low to the ground where there would be an appreciable vertical gradient in wind speed which, he shows, in theory would affect the circulation around the wing, leading to a variation in angle of attack with orientation to the wind, although not to rate of climb per se.
It is interesting, though, just what a controversial topic this was in the day. He starts off his thesis by interviewing some of the top pilots around, asking the question, "Can a plane be climbed faster into the wind than it can when going with the wind?" and the responses were split right about 50-50 between the group. There's a brief anecdote from one of the Douglas World Cruiser pilots: "Lt. Nelson took his heavily loaded World Cruiser off the water at Hong Kong, China, into a 30 mile an hour wind. He turned to go with the wind and was unable to prevent the plane from settling until he came to the lee of an island where, in the comparatively quiet air, he was able to turn and as soon as the plane was nosed into the wind was able to climb again."
(As a complete aside, I think it's way cool that I've got hanging in my living room a patch of fabric from the plane that was flown by one of the other World Cruiser pilots Doolittle interviewed, purchased when the Smithsonian was restoring the plane a couple of decades back.)
To do his experiments, Doolittle flew a number of carefully instrumented aircraft low over the water and took detailed readings of their behavior. In the thesis, he concludes that performance effects atributed to orientation with the wind really have to do with a pilot's perception. He gives the example of confusing ground and air speed, getting the plane into an undesirable angle of attack and actually losing rate of climb trying to point the nose in the direction you want to go--up. He says that this would, of course, be most noticable if a plane is "heavily loaded and already flying near its most efficient climbing angle."
Hmm...worrying about the performance of a heavily loaded aircraft flying close to the deck...I think it's worth noting that it wasn't just bravery and superb airmanship that got those B-25's off the Hornet and into the history books, but bravery and superb airmanship backed by a keen intellect.
Besides, now when I'm flying one of my models in the wind and misjudging its performance because I can't keep myself from using the ground as a reference, I know who's looking over my shoulder saying, "Stop that!"
I just thought the Modeling Science community might be interested--I hope my brief synopsis did justice to the author.
I was able to access an interesting document recently: a copy of Jimmy Doolitte's doctoral thesis from MIT, 1925. I didn't even know that this document existed until I read about his having earned the degree in James Bradley's excellent book "Flyboys," and it was indeed an earned doctorate: it turns out that one of America's heroes and top airmen could handle a partial differential equation as well as he could handle a racing plane or a B-25.
The title of the thesis is "The Effect of the Wind Velocity Gradient on Aircraft Performance" and it addresses the issue of whether one's aircraft's performance--rate of climb, etc.--varies with orientation to the wind. This would seem to be a no-brainer (once you're in a moving fluid you're just in a different frame of reference) and in fact he obtained a null result experimentally, although he cast the problem specifically in terms of flying very low to the ground where there would be an appreciable vertical gradient in wind speed which, he shows, in theory would affect the circulation around the wing, leading to a variation in angle of attack with orientation to the wind, although not to rate of climb per se.
It is interesting, though, just what a controversial topic this was in the day. He starts off his thesis by interviewing some of the top pilots around, asking the question, "Can a plane be climbed faster into the wind than it can when going with the wind?" and the responses were split right about 50-50 between the group. There's a brief anecdote from one of the Douglas World Cruiser pilots: "Lt. Nelson took his heavily loaded World Cruiser off the water at Hong Kong, China, into a 30 mile an hour wind. He turned to go with the wind and was unable to prevent the plane from settling until he came to the lee of an island where, in the comparatively quiet air, he was able to turn and as soon as the plane was nosed into the wind was able to climb again."
(As a complete aside, I think it's way cool that I've got hanging in my living room a patch of fabric from the plane that was flown by one of the other World Cruiser pilots Doolittle interviewed, purchased when the Smithsonian was restoring the plane a couple of decades back.)
To do his experiments, Doolittle flew a number of carefully instrumented aircraft low over the water and took detailed readings of their behavior. In the thesis, he concludes that performance effects atributed to orientation with the wind really have to do with a pilot's perception. He gives the example of confusing ground and air speed, getting the plane into an undesirable angle of attack and actually losing rate of climb trying to point the nose in the direction you want to go--up. He says that this would, of course, be most noticable if a plane is "heavily loaded and already flying near its most efficient climbing angle."
Hmm...worrying about the performance of a heavily loaded aircraft flying close to the deck...I think it's worth noting that it wasn't just bravery and superb airmanship that got those B-25's off the Hornet and into the history books, but bravery and superb airmanship backed by a keen intellect.
Besides, now when I'm flying one of my models in the wind and misjudging its performance because I can't keep myself from using the ground as a reference, I know who's looking over my shoulder saying, "Stop that!"
I just thought the Modeling Science community might be interested--I hope my brief synopsis did justice to the author.