Issue 69 – Will be published and distributed in October of 2018. Click on image below to read the table of contents
The Editorial by Sergio Montes offers a short remembrance of that great English writer on aeromodelling matters, Ron Warring. This is prompted by the publication in this issue of a joint article by Bob Copland and Ron Warring on the design and construction of Lightweight Duration models. It appeared in 1944 and refers especially to rubber models of up to 36 in. span. Warring was an incredible prolific writer with more than 100 book titles to his name on vast diversity of subjects. Aeromodelling was an important subject important, but by no means the only one. He was also a top contest flyer about 1950.
We have in this issue an interesting article from the Czech Free Flight publication Volny Let. It is the F1G design that its author, Mihal Kohutic proudly holds in the cover of the present issue. The name Geo is due to the geodetic structure of the wing, stab and fin. The model is trimmed according to the PGI rules of Jean Wantzenriether, needs no VIT, no auto-rudder.
Sergey Vorvihvost from Ukraine is well known for his beautiful F1Q models; this one follows the nice lines of previous designs but adds a special motor/propeller combination. It uses a large F1B size propeller and a geared motor. According to the author this combination is the best performing set-up in the F1Q category. The propeller, using blades with a balsa core with carbon cloth covering has 580 mm diameter and pitch, but can be adjusted for pitch and diameter. Details of the best trim are included, balancing side thrust with right wing wash-in.
The Sunrise competitions in Bavaria in the early 1960’s for A/2 gliders produced some great performers. This ritual comprised a single flight early in the morning, no thermals. Gerhard Woebbeking tells the story of the record set in 1963 by Franz Weyrauther with an orthodox balsa and tissue model of 2.08 m span and 25 grams overweight, it used the Sokolov wing airfoil. His winning flight of 205 seconds from a 50 m. towline, represents a sinking speed of 25 cm/sec, which would be an excellent standard even today. There was no zoom-launching at the time, of course.
The comprehensive article by Bob Copland and RonWarring on small rubber duration models deals with design and construction details of models of up to 36in. span, wing area of 144 to 200 sq. in. and all-up weight between 3 to 6 oz. (84 to 168 gr) . The authors found that ultra-lightweight models were not consistent in their performance. They recommended that for wing areas below 144 sq. in. the models could have a slab-sided fuselage, while models with larger wing areas benefited from circular-section fuselages. Propeller size of up to 18″ were favoured, with up to 10 strands of 1/4″ rubber. A graceful design by Copland is included in the article, with straight dihedral , 144 sq. in. wing and free-wheeling propeller.
The fifth part of Jim Baguley’s analysis of contest gliders covers details on A/2 glider performance. Baguley analyzed 48 glider airfoils used in the UK, and in other European countries, as well as in USA. It includes several original airfoils too. His preferences were for not very thin airfoils with medium cambers. Many aspects of glider performance were discussed by Baguley, including the effect of wing Aspect Ratio, Turbulators, the CG position , the effect of Induced Drag and Wing Tip Shape, the Parasitic Drag of of non-lifting portions of the model.
The famous French engineer Gustave Eiffel is best known for his great bridges, railway stations and of course for the Eiffel Tower. Due to causes commented in the article by Sergio Montes, he decided about 1900 to abandon his engineering projects and concentrate in aeronautical and meteorological research. Using first the Eiffel tower as his aeronautical lab, sliding objects along a vertical cable and measuring the time to fall he could determine coefficients of drag. He found that better results could be obtained in a wind tunnel, and his design for an open wind tunnel proved very satisfactory. Two tunnels were built, one near the Tower and a larger one later in 1912 in the Paris suburb of Auteuil, which still exists today. The work performed in the tunnels is analyzed in the article. Eiffel’s work was published in several superb books, which were quickly appreciated and translated into English about 1920. The Eiffel airfoils, well known in older models were the fruit of his research in the tunnel, testing models of actual aircraft. A selection of them is presented in this article.
Dave Hipperson analyzes the state of Free Flight models and competitions. He stresses that to a great extent the future of FF competitions depends on simple rules, intelligently applied. There are many problems in FAI competitions, especially in selection of flying fields and the organization of the contests, we need to make the contests more enjoyable. He also takes a look at the specifications of the FAI categories and the Builder of the Model rule , which “continues to haunt” the competitions. A powerful article.
After folding propellers for rubber models were developed about 1938 in USA, the next improvement was to to fold the blades flat against the fuselage and also keep them aligned with it, both conditions are needed to minimize the drag. These two effects can be achieved by a proper alignment of the folding hinge, which must be twisted (skewed) in two planes. The skewing angles depend essentially in the Pitch to Diameter ratio of the propeller. In this article Sergio Montes discusses the historical development of the skewing angle calculation, noting that the first correct analysis was published in 1943, but in very sketchy form. Using the techniques of Descriptive Geometry, Tony Benson published 15 years later (1958) a general method for determining the skewing angles for perfect folding. This method is extended in the present article by a simple algebraic method that allows the calculation of accurate skewing angles for cases different form that analyzed by Benson. Graphs are presented that give the skewing angles for usual types of rubber propellers.
Slobodan Midic presents here a new and quite different airfoil, designed for F1B, F1G models or other that fly in the range of Reynolds numbers from 30,000 to 40,000. This airfoil is distinguished by a very slender rear section that is sharply curved, in the manner of a Gurney flap. Although this airfoil has yet to prove itself in the flying field, the calculated performance is quite good. The comparison using Xfoil calculation with the And-Viv airfoil (a compound of Andriukov AA30 and the Vivchar’s F1B airfoils) reveals a clear performance advantage to the new Midic airfoil. The author stresses that these advantages must be verified later in the flying field.
Chris Stoddart continues with his presentation of electric motor control in this part 9 of his series.