Letters to the Editor
All letters will be carefully considered; those of general interest will be used. Send to Model Aviation, 815 15th St., N.W., Washington, D.C. 20005
Thanks to Ed Whitten
We should like to express a special thanks to Ed Whitten for his concern and assistance in helping a few beginners in indoor modeling. Ed has been gracious enough to practice what he has been preaching in his "Junior Flight" page for some time. He gave a series of evening workshops for teachers and supervisors from the New York City Public Schools.
His interest was to promote modeling to at least 100 students for each teacher, and perhaps initiate a city-wide model flying contest among the schools. Giving of his time and expertise has been, we feel, an act of love and compulsion on his part. Even his son, Richard, assisted at critical times and where it counted.
Our commendation to Ed and Richard for a real job needed doing and well done.
- Samuel Garry, Supervisor, Bureau of Industrial Arts
- Joel McDonald & Howard Smith, Industrial Arts Teachers
- Ellen Goldstein, Science Teacher
Ed and Richard set a good example for all of us interested in solving the junior "problem" to follow—that of digging in on a personal basis and not waiting "for George to do it."
Agosta's Jungmeisters
After reading your December issue, I learned how Gottfried Leibniz must have felt when he announced his formulation of the calculus and then found out that Sir Isaac Newton had beaten him to it.
What, you may well ask, has that got to do with modeling? Bear with me. I'll tell you the sad story.
Two years ago, having seen a picture of Art Yadven's Jungmeister in James Gilbert's The Great Planes, I felt compelled to build a model with as careful attention to detail as my limited modeling skills might permit. So I bought a Pica kit and went to work with Gilbert's pictures as a guide, modifying the kit accordingly.
None of the details were too difficult until I got to the exhaust stack. I finally worked that out, got it in place, and completed the model in early November. I was about to invite my neighbors in to view my masterpiece when the December issue arrived. No show! I pictured my friends whispering to each other, "Big deal! All he had to do was follow the instructions."
I've enclosed a few pictures of my model. The sad-looking gent in one of the pictures is me wondering whether or not to fly the plane off the very high roof to a certain crash and take up knitting as a hobby.
Arthur Post Stamford, CT
More on Props
The November Letters column (p. 65) presented some comments by Mark Julicher on how props work. Based on his Figure 2, showing a section of a cambered airfoil, he concluded that "it becomes even more clear that the prop can't travel farther than the geometric pitch dictates."
This is in direct contradiction to my earlier article on the subject, and those who read both the article and Mark's comments must wonder which is correct. Perhaps the following comment will help them decide.
Airfoils have a geometric chord which is either the bottom surface line (Clark Y) or a line between the center of the leading edge radius and the trailing edge (0012, 2412, 4412, etc.). They also have a zero-lift chord which is displaced from the geometric chord proportional to the camber in the airfoil. This is generally slightly under one degree per percent of camber. The geometric angle of attack is the angular difference between the relative wind and the geometric chord line. The effective angle of attack is the angular difference between the relative wind and the zero-lift chord line.
The Clark Y airfoil has 5.8% camber and a zero-lift chord that is -5 degrees from the geometric chord. It is clear, then, that when the relative wind approaches parallel to the geometric chord, the effective angle of attack is actually +5 degrees. This gives a Cl value of about 0.37 for AR = 6 and generates quite a bit of thrust. When the relative wind is approaching about one degree negative to the geometric chord, a Cl of about 0.30 is developed. Lots of commercial props with design lift coefficient of 0.3 have been built and successfully used.
Just remember, then, that before deciding whether a wing or propeller will develop positive or negative lift or thrust, make sure you are comparing the relative wind line to the zero-lift chord. Also, if you ever try to use the equations for incidence and trim, you must use the zero-lift chord or you will not get the correct answer.
John Brownlee Decatur, AL
Our Fabulous Hank
Hank Clark did a nice article on Hank Clark. But I have known the guy for many years—and if he were to relate all the things he did and does, the article would have been ten times longer!
Yes, he rode his bike to all the airports around New York to take pictures, just as a bunch of us also did at the time. We took trains, buses, walked, hitchhiked—but ol' Hank rode the bike. He was in darn good physical shape.
Yes, he rode his bike to the airports, but I caught him one time at Roosevelt Field—photo enclosed. In the event that anyone doubts that he rode a bike to the airports—well, pictures don't lie!
Hank Clark is quite a guy—wouldn't you know he'd be riding the bike backwards in that old picture? But he hasn't changed. The other picture, this one from 1982, shows Hank pushing Kevin, his grandson—on skates yet. Let us quote Hank: "We're all grown-up kids. I think it's great to be grown-up and a kid too." What a talent you have, Hank, in more ways than one.
Anyone who wishes to know more about Hank, please look at the article which appeared in the June 1982 issue.
Warren D. Shipp San Diego, CA
Transcribed from original scans by AI. Minor OCR errors may remain.
