Avia BH-25J (oz14419)

About this Plan

Avia BH-25J. Free flight scale model for rubber power.

Direct submission to Outerzone.

Update 19/9/2024: Added article, thanks to ilgk48. This is an extract from his full magazine scan as posted on HPA at https://www.hippocketaeronautics.com/hpa_plans/details.php?image_id=13298

Quote: "Peanut scale airliner from Czechoslovakia is ready to rattle the rafters. Avia BH-25J, by Antonin Alfery.

IN 1925 the Czech Ministry of Public Works (Ministerstvo Verejnych Praci, or MVP) invited tenders for a new airliner to be powered by the Lorraine Dietrich 12CC engine. The Avia company responded with the BH-25 project, and construction of this five-passenger craft began at the end of 1925. First flight of the machine, registered L-BABA, was on 17th July 1926.

Acceptance by the then-new Czechoslova-kian airline Ceskoslovenska Letecka Spolec-nost (CLS) was swift and the BH-25 entered service on the Berlin-Dresden-Prague-Vienna route in March 1927. Avia built five aircraft, designated BH-25J, for the Walter Jupiter engine, a lighter powerplant which enabled an extra passenger to be carried. Registra-tions were L-BABB to BABF. Wings and tail were silver, the fuselage was light blue; registrations were black overall. Undercar-riage struts were brown. In later years a dark blue fuselage with white 'outline' registration letters was the adapted scheme.

L-BABD crashed near Kassel on 9th May, 1929 but the others remained in CLS service until 1931, by which time the fleet had accumulated 5575 hours of flying time, covering a total distance of 771,587km. Six more BH-25Js were sold in Romania. All were powered by Gnome-Rhone Jupiter engines.

Now to the model: The original was built for a Peanut Airliners contest in 1987; it won the event with a best flight of eight seconds. Subse-quent trimming boosted duration by a further ten seconds. The only deviation from scale is the small amount of dihedral.

Traditional balsa construction is shown on the plan although the original fuselage was built from lmm. polystyrene foam sheet. Difference in weight is negligible. Assuming you choose to follow the plan, build two identical sides from 1/16 sq balsa; join one over the other on the protected drawing, with 1/16 sq spacers and 1/32 sheet top formers. Fuselage decking is from 1/64 balsa. Nose contours are formed from 1/32, 1/16 and 3/16 sheet where noted. The longitudinal strips along the fuselage sides are added after covering.

Windows are best represented by circles of darker tissue; if you go for foam construction they may be cut out and glazed! Thinned Humbrol enamel was used on the original fuselage; coloured tissue is the alternative.

Wings: Ribs are cut to pattern with the aid of the template. Lower strips are glued in place between leading and trailing edges, then front and rear spars are added, followed by the tops of the ribs. After the wings are covered, paper strips are doped on at every rib station to represent the full complement. See plan. Differential washout is employed; 1/16 at the port wing tips, 3/16 starboard. This is far more satisfactory than using positive on the left tip; models so equipped often fail to recover after hitting the ceiling or other obstructions. Tail surfaces are entirely straightforward. Again, paper strips repres-ent all the ribs after covering.

Prop and power Balsa prop blades are carved to shape and covered with tissue. The system detailed allows pitch adjustment; thirty degrees at the tip seems optimum. Of course, you may substitute a commercial plastic equivalent of six inches diameter. George Wallbridge of SAMS, who can be contacted on 0763 88384, is an ideal source (their free catalogue, available for a 9 x 7in, envelope and 28p stamp, is compulsory reading for all F/F aeromodeilers). Nose block assembly is straightforward. A single loop of 1/16 rubber, up to three times the length from hook to rear peg, is a good starting point.

Rubber thickness will influence power output; loop length affects duration. Exper-iment to suit your own flying site. Flight trim is a left turn under power and during the glide. Enjoy this early Eastern European airliner!"

Supplementary file notes

Article.

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