Issue 67 – Published and distributed in April of 2018. Click on image below to read the table of contents.
The Editorial tells a very short history of the National Advisory Committee for Aeronautics, NACA. We quote so often their marvellous research on airfoils, propellers, stability, etc., that a glimpse at the organization that produced such admirable work is totally necessary. Later in the same issue is a longer essay on some of its best work.
Jim Baguley continues his analysis of the A2 gliders of the 1950’s and 1960’s. This time he casts a stringent look at his own designs, as they progressed in their ultimate flight performance, but also their reliability and ease of construction was seriously discussed. There is no denying that some of the later examples, about 1960 have a restrained elegance that is most appealing, simple construction of low cost, whilst coming close to the “magic” sinking speed of 1 ft/s. Included in the showcase of Baguley models are several “giants” of 10 ft span. The large models did seem to have construction problems if a reasonable weight was desired; scaling up successful A2 models was not a practical proposition.
Volodymyr Sychov is a very successful F1C flyer from Ukraine. Some readers may remember his unique attempt at creating a new type of folding arrangement for the wings that Sychov developed about 16-17 years ago. This was an F1C model where the straight-dihedralled wings folded back, parallel to the fuselage, creating what looked like a plank. Interested readers can look in You Tube the flight of Sychov’s “plank”. In this arrangement he echoed the catapult versions of the Jim Walker gliders of the 1940’s. The outlandish-looking plank was actually quite stable in the climb and achieved good heights. However, Sychov found that it was unreliable in the pull-out and glide transition and returned to a more conventional design. In this article Allard van Wallene chronicles the history of Sychov as designer in Ukraine, later with Graupner in Germany, and the sophisticated methods of design and production of the Flapper/Folder described in the article, design that led to him winning the World Cup in 2014.
The essay by Adrian Duncan on the Sharma Diesel engines produced in India and but little known in the West continues with a second part that covers the various Diesel and Glow plug engines manufactured by this concern. What started as engines outwardly similar to the PAW 15, ie conventional plain bearing, radially ported, front rotary valve engines is shown by Duncan to have developed into superbly-built motors of excellent performance. Using the same basic design, engines of 0.09 and 0.19 cu.in. were also manufactured, but the 0.15 cu.in. did prove the most popular in its Free Flight and Combat versions. Under test, the power of the engines was so good (equaling that of a tuned Oliver Tiger) that an incredulous author repeated the tests, which are documented more fully in the last part of the article, to appear in the July issue of FFQ.
Our prolific airfoil designer, Slobodan Midic presents here two new airfoils, the MID 405 W2 and MID 406 W2. These airfoils are suitable for large gliders with high wing loadings, and are a development of the Drela DAE-11 airfoil . The main difference is a much thicker trailing edge that improves the torsional resistance of the wing. These are thick airfoils of maximum thickness of the order of 13 to 15% and cambers of around 6%. Their maximum CL is correspondingly very high.
Obsession is a Mulvihill/Dawn Unlimited design by Bob Lipori, which is described by the author in this article. It was developed from a highly successful 100gr Coupe design, the “Paper Doll”. According to Lipori, the main change from the original Coupe was the use of the Bogart BO-560-26 airfoil of 6% thickness and 6.2% camber. The propeller in both models is a Carrol Allen design, with maximum width close to the hub. It is also detailed in the article. The record of successes of this design in Eastern USA Dawn Unlimited contests is quite remarkable, with a stretch of 12 consecutive victories in the 1980’s and 1990’s.
Paul G. Seren is a designer and flyer from Germany. He gave an interesting presentation of F1Q model design in a workshop/meeting at Baden-Württemberg. The material he presented there was set (with the author’s cooperation) into an article for this issue of Free Flight Quarterly by Chris Stoddart. It covers the basics of electric power and control, as well as the fitting of timer and RDT devices. Design tools, such as Ecalc and Prop Calc are used for a design example. There is a short discussion on design trends and several successful models of long engine run and 2 m span are presented, along with with detailed 3-views. These are models from Israel, Ukraine and Germany.
Fitting of an RDT system to older models is today easier than ever, thanks to the miniaturization and availability of the necessary components. Ronald Borg shows how to use common components from the RC world to retro-fit RDT devices in F1A glider (the Tropik) and also in the well known Tilka by Bror Eimar. These developments are increasingly important if flying from smaller fields and even city spaces is to be contemplated.
Many of the construction materials that we use in our model planes can be cut with great precision by inexpensive Computer-Controlled Craft Cutters, no bigger than a common computer printer. Paul Bradley shows how to cut balsa wood for ribs, thin plywood and plastic parts, even complex tissue shapes used to cover a spinner. And of course lettering for wings and decorative effects can also be cut, to great effect. The procedure to hold the material to be cut in the Craft Cutter to obtain accurate results is carefully reviewed by Bradley. Many examples of his work are shown in the article.
Building propeller blades for rubber models by using cylinders or conical surfaces as moulding forms is a widely used method due to its simplicity and in many cases by the good results obtained, particularly in the smaller classes. The method goes back some 75 years, as by 1943 articles were published showing how to design a constant pitch propeller using a cylindrical mould. The problem with this approach is that the centerline of the propeller is highly curved, which seems to be an aesthetic obstacle for most modellers, who prefer straight centre lines of more realistic appearance. Sergio Montes reviews the more modern approaches initiated by Baguley in 1960, later by Chernoff in 1964 to approximate constant pitch propeller blades by moulding them over a cylinder. The deviations from constant pitch when using a cylinder as a mould are important and it was found that a conical mould works better in this regard. The author describes here the important work of Halsas and Jolma. These Finnish writers produced a nomogram in 1996 for the easy application of a 30 degree conical mould that allows almost exact constant pitch along the blade. As a check, alternative methods of propeller design on a conical mould suggested by Fred Rash are found to agree closely with the Halsas and Jolma nomogram results.
One of the most important developments in general aviation during the 1920’s and 1930’s was the invention of the NACA cowling. This cowling, that fitted closely around radial, air-cooled engines, decreased the drag of the engine without reducing the cooling flow. Initially the cowlings were designed on a mainly empirical basis by a team headed by Fred Weick at the NACA Langley Labs, near Washington. The early results, dating from 1928, were spectacularly good, the best of the NACA cowlings reduced the drag of the Wright J-5 uncowled engine by 60% or more. Later in the 1930’s a more theoretical approach consolidated these early achievements by providing a better understanding of the flow inside the cowling. The invention was immediately picked up by the American aviation industry and only a little later by manufacturers in Europe and Japan. Sergio Montes tells the story of this remarkable invention that made the large radial engine really practical, including some different early cowling alternatives, such as the Townend ring of about 1930. Many illustrations of the NACA cowling applications are provided in the article.
E-lectron 2.1 is the name of a high-performance E-36 model developed by Duncan McBride from an original design by Harry Grogan. The present design is slightly reminiscent of the LSARA designs from Great Britain, rapid climbers from that design organization that flowered in the early 1950’s, but much sturdier and practical as a contest model. The E-lectron 2.1 model is still under development, but has already shown scintillating performance, according to the altimeter readouts provided in the article. Components, weights, a detailed 3-view and building tips are included.