...Not much input since the previous Posting, gang. To fatten up this one, after I post the SMALLsters' messages, I'll add some stuff of my own, condensed from replies to readers of my Engine Shop column in Model Aviation magazine. [JW]

...Sure! I well remember the Miss Tiny. Modelcraft kitted that model. It was designed by Barney Snyder. Plans are still available from various places. That was a cute little craft !

I never built a Miss Tiny myself, but I recall the kit fairly well. It featured a spun aluminum cowl if I remember right.

The Miss Tiny would make a neat radio control project for .049 glow or diesel power -- or for one of the many small electric-power combinations. [JW]

...Phil, SOMEWHERE around here I have an intact set of plans for the Flyline Jungmeister. If you can't obtain a set from one of the other SMALLsters, let me know. I'll perform the necessary archeology, and have the plan copied for you.

As for the trip to Little Rock, OF COURSE it's worth a 10-12-hour drive each way -- high gas prices and all ! Heck sakes to Betsy, my wife and I (and young daughter) used to drive all the way from Pennsylvania every year for that meet.

Pat Tritle comes to Little Rock from Albuquerque; Alan Porter and Steve Adams drive from California; Eric Clutton makes the trip from eastern Tennessee...

There must be a reason we do all that road travel ! Come this year and find out what that reason is... [JW]

... In one of my Model Aviation columns I reported on a wild experiment of mine. Briefly, I added 20% water to some 15% nitro glow fuel, just to see how badly it would affect the performance of one of my old faithful control-line engines.

What happened was (1) the needle needed to be opened about a quarter-turn or so; (2) I had to leave the glow plug connected for about 30 seconds to let the engine warm up enough to keep running on its own; and (3) the engine gained about 100 rpm over its performance with unwatered fuel.

I thought I'd get a storm of protest from readers who have taken great care for decades to INSTANTLY re-seal their glow fuel jugs after use, to prevent the methanol from sucking up moisture from the air.

But I only got two letters. One was from Bob Angel, who writes a column for one of the West Coast Free Flight club newsletters. Bob said that he did about the same thing, adding water to 1/2A glow fuel a few years ago.

Unlike me, who dumped in 20% water all at one go (I used to have a friend who, when some kind of adjustment was needed -- to anything -- would quote : "Artillery makes bold corrections !") -- anyway, Bob added water in small increments, testing each time.

Bob said that he noticed no performance change until he got to 15% water. But he was working with .049-size engines, whereas the C-L motor I used for my "water tolerance test" was a Johnson .29. And the smaller the engine, the more cooling area it has in proportion to its combustion chamber volume...

So far, so good. But then came a passionate letter from a guy in Colorado who chewed me out for recommending such a horrid thing to do with glow fuel. He provided a couple of anecdotes to prove to me how damaging even a trace of water could be to glow fuel.

One tale was about this friend who accidentally left the top off his fuel jug for an hour or so. After that, his engine refused to idle properly. Gosh !!!

I've been an aero engineer for too long to be satisfied with "anecdotal evidence" -- especially after seeing one of my engines run exceedingly steadily on fuel that had 50% more water in it than nitro...!

So I looked up the relevant data; did some calculating; then replied to this skeptical Coloradoan as follows: (condensed version) -->

"...From Van Nostrand's Scientific Encyclopedia: At 90 degrees F. & 100% relative humidity, air contains .03 lb. of water per pound of air. .03 lb = about 0.5 fluid ounce. (100% relative humidity means that the air contains all the water vapor it can hold at that temperature.)

"From Pratt & Whitney's "Vest-Pocket Aeronautical Handbook" (p.11): Specific weight of air in lbs/cu. ft. = 1.325 X barometric pressure (inches of mercury) / temperature in degrees Rankine -- i.e. degrees Fahrenheit + 460.

"Therefore at 90 degrees F (550 R.) and 30 inches of mercury barometric pressure, the density of air is 1.325 X 30 / 550 .072 lbs per cubic foot.

"A standard gallon can's interior dimensions are 4" X 6 1/2", which has a surface area of 26 square inches. The volume of a layer of air 1/4" thick inside that can is 6 1/2 cubic inches, or approximately .004 cubic feet. And at 90 degrees F and 100% relative humidity, that air can contain -- at the most ! -- .004 X .072 X .5 fluid ounces of water.

"Multiplying it out, that's .000144 fluid ounces of water (in the form of vapor) in the immediate vicinity of the fuel surface inside a gallon can. To me, that's absolutely and utterly insignificant.

"As for the notion that leaving a fuel container open permits the alcohol to continuously suck moisture out of the air, that implies constant air circulation over the fuel surface.

"But that doesn't happen. One reason it doesn't is the little-understood fact that moist air is LIGHTER -- i.e. less dense -- than dry air. For that reason, when a layer of high-humidity air lies atop the surface of an alcohol-type fuel, and its water content (however small an amount that is) gets drawn into the alcohol -- the air layer in contact then becomes denser, and acts as a "shield" between the fluid surface and the moist, lighter air above.

"Inside a fuel container, the air ordinarily isn't turbulent; therefore no significant mixing will occur between the "dry" lower layer in contact with the fuel and the more humid air above that.

"Look again at the numbers above. Then check them for accuracy (in reference books at your library) to make sure I'm not lying to you. Then that data should explain why, though I DON'T recommend adding water to model fuel, and never did -- I'm no longer concerned about leaving the top off my fuel jug for a few minutes..."

...And speaking of fuel jugs -- I for one am rather tired of foozling with the "childproof" tops on those. I've come up with a better solution -- a better container, in fact, than the ubiquitous polyethylene bottles and jugs that glow fuel usually comes in.

Instead, I've been using empty half-gallon grapefruit juice jugs. The grapefruit juice available at my local supermarket comes in a neat, chemically impervious plastic jug with an easy-to-remove top, and a handy -- well: handle. The opening is just the right size to admit a fueling syringe, such as the all-glass units that Larry Davidson sells.

...Another reader asked me recently about some technical points of airfoil performance. Here's part of my reply:

"...responding to your query about undercambered airfoils for 'slow, floater sort of flight'. Opinions are divided on this point (although all modelers everywhere agree on every other aspect of aerodynamics).

"I've had excellent results from Goldberg's 'G-8' (used on his Sailplane), and the RAF 32 (Buzzard Bombshell airfoil).

"However, for smaller, lighter models, Bill Winter highly recommended the NACA '6400' series. In particular he liked the NACA 6409 and 6412. So did Frank Zaic.

"My own experience has been that flat-bottomed airfoils work just as well. Case in point (the one that opened my eyes): I LOVED the looks and gliding performance of the Thermic 72 and 100 pod-and-boom gliders. I built several. But the last '100' I built (circa 1947) suffered a preflight accident.

"One of my friends visited me while I was working on the final assembly stages of the big Thermic's wing prior to covering it. He was talking about some aviation movie he'd just seen, and waved his hands wildly to emphasize the fantastic aerobatics in this movie. (I think it was 'Blaze of Noon'.)

"Anyway, my friend's swiftly-darting hand encountered my almost-9-foot-span glider wing. That was constructed of 'contest grade' balsa -- Jasco kits were noted for their excellent, light wood -- and EVERY DAGNAB RIB got fragmented.

"To simplify the plotting of the Thermic 100 wing's tapered ribs, so I could cut a replacement set, I eliminated the undercamber. And the resulting '100' had the best floating glide of ANY of my towliners. It even outdid the much-more-lightly-loaded 'Floater'. (That design of Frank's used a flat-bottom wing.)

"As a possibly-interesting sidelight on this: For many years modelers depended on slow-speed airfoil performance data that had been derived at Darmstadt, Germany in the 1920's.

A truly monumental series of wind tunnel tests on airfoils were made there, and the results were widely published. These had been in common use by aircraft designers (both model and full-scale) for a couple of generations.

"Then a German college student (Werner Theiss) decided to write a thesis on the Darmstadt tests. He obtained the original Darmstadt 'raw data' as part of his research. In looking through this, he suddenly noticed an 'anomaly'.

"As I understand it, Theiss found to his surprise that the 'tunnel wall correction factor' had been erroneously applied in an entire series of test results. (I forget whether that was for the 'flat- bottom' or 'undercambered' series.) But the result of correcting that mistake was that the relative efficiency of the two types was now reversed.

"In other words, the earlier belief that undercambered airfoils had a higher lift-to-drag ratio than flat-bottomed types was wrong.

"On the other hand, I've found distinct benefits IN SMALL MODELS for undercambered, 'single-surface' airfoils. They make the wing act as if it were much larger in area: more lift; more drag. But I haven't flight tested 'single-surfaced' wings of more than 7-inch chord.

"I did try ONE, but abandoned that without even flying it, because I just COULDN'T stop it from warping." [JW]