Motley Crew displays the finished Bergfalke IV.

Downsizing the Bergfalke IV

Part I: What do you mean you don’t remember the cabriolet version with winglets?

For those of you reading this on your phone (which apparently is well over half of you!) note that you can tap on any photo for a larger, more detailed version. — Ed.

The Bergfalke IV is the culmination of the Scheibe’s series of the type, making its debut around 1969, being of steel tube structure in the fuselage and traditional wooden flying surfaces. It has long been a favourite of mine, and three Bergfalke I’s and three Bergfalke IV’s bring us to the current version. As an OAP, I have found my designs becoming smaller over time, which is why this one is scaled to a very convenient 1:4.7-scale.

Left: Basic fuselage construction starts on the ‘Bridson’ jig. | Right: Top decking of the nose comprises off planks of 1.5mm ply.

Left: View of the basic fuselage underside. | Right: Making up the cabriolet hatch.

The hatch, ready for sheeting.

So, full disclosure: I can find plenty of full-size cabriolet conversions for the Bergfalke III, but none for the IV. I have found one IV with winglets. Not to be daunted I carried on with the project, deciding halfway through that this would be an ideal model for electric assist (e-assist) as it would, hopefully, be small enough to easily hand launch on the flat and extremely useful on light days on the slope. As it turns out, these predictions were fully borne out.

Left: View of the rear end and tail feathers. | Right: First stage of the wing construction.

Left: Basic airbrake assembly. | Right: Airbrake installed in the wing.

Given the structure of the full-size version, the fuselage would have to be built on a jig, not a problem as I have the use of my purpose-built ‘Bridson’ jig, although a simpler method with a wooden base is the more traditional way. The flying surfaces are of spruce, ply & balsa in the normal fashion. The cabriolet hatch is retained with magnets, and full top & bottom airbrakes were designed in.

Left: View of one of the removable winglets. | Centre: Configured for e-assist mode with the prop on. | Right: Pure glider mode with blanking plate fitted.

The nose is made up my usual way, with multiple applications of car body filler. This is then drilled out ready for one of my pal Smallpiece’s aluminium housings into which a bearing is placed. The motor shaft is removed and replaced with a longer version coming out the other way: this allows the motor to be screwed to the rear of the front former, thus obviating the need for spinners or cowlings. The final advantage of this system is that the prop can be removed and a blanking plate fitted to restore the model to pure glider status.

The Bergfalke IV airframe, ready for covering.

Curious to know how it all turned out when the Bergfalke IV is placed “into the tender hands of gravity”? Tune in next month for Part II. Until then, thanks very much for reading.

©2023 Chris Williams

Resources

• Plans and Construction Photos — Working drawings of the Bergfalke IV in PDF format along with over 150 construction photos.
• The Williams Anthology — The collected works of Chris Williams as found in the pages of the New RC Soaring Digest.
• Turnigy G32 Brushless Outrunner 600kv from HobbyKing. — “Designed to be a direct swap out for your 32 size glow engine. This brushless outrunner will provide more power and with its high efficiency, long run times…”

Where it all started for me — the 1/4-scale version of the Bergfalke IV.

All images by the author. Read the next article in this issue, return to the previous article in this issue or go to the table of contents. A PDF version of this article, or the entire issue, is available upon request.