Quarter scale Bergfalke 4 fitted with E-Assist.

When slope soaring in light winds an E-Assist system can help stop an unwanted trip to the bottom of the hill, as Chris Williams explains.

There exists, amongst the more austere members of the scale soaring fraternity, a tendency towards pursed lips and muttered imprecations when a propeller is observed on the front of an otherwise scale glider.

Their condemnation is assuaged not one little bit by painting the aforementioned propeller the same colour as the fuselage. It becomes, therefore, necessary to search for Stealth Technology in order to still the criticism. But wait a minute… why would you need to commit this foul deed in the first place?

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To those of you that live in the Flatlands, miles from the nearest tug pilot, it’s probably a no-brainer. To those of us that inhabit their local slopes, well…


A slope session always begins with a weather forecast. If the wind prognostication is that it will be light and unreliable, we will probably, with some reluctance, stay at home. However, with a wind-whacker on the front, there is a paradigm shift, because now we can take a chance, knowing that there is always the get-out-of-jail-free card in our armoury.


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Spot the Prop. Super Javelot on a perfect light wind summer’s evening.

Once you have tried this, you’re done for, because flying off the hill in light air with a scale glider is one of life’s great experiences. To do so, without the prospect of stumbling down to the bottom of the hill in your shorts into the waiting nettles, only enhances the prospect even more.


Motley Crew launches the Super Javelot in E-Assist mode.

Changes to the rules of the White Sheet club in Wiltshire a few years ago made this all possible. So, how then, do we hide our activities from the Scale Police?

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Electric motors of the outrunner persuasion are designed to be bolted to the front of the foremost fuselage bulkhead, there to be hidden by a cowl. This is all well and good for a Piper Cub, but gliders have slim fuselages with pointy noses so something else will be required. Over the last few years my co-conspirators and I have come up with a solution that eventually allowed us to be able to walk past a Scale Policeman with little fear of arrest.


Changing the motor shaft.

The solution is to bolt the motor to the rear of the foremost bulkhead, facing the other way. Although the motor now appears to be facing the wrong way, the trick is to remove the shaft and replace it with an extended version, this time poking out of the rear and into the nose cone.

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With the prop removed the bearing housing aperture is revealed.

Now, engineering and I have a similar relationship to that of Alfred Hitchcock and shower curtains, so obviously I outsource this job to Smallpiece, one of the aforementioned co-conspirators. As it turns out, my practice of making solid nose cones from car body filler lends itself perfectly to this endeavour as a hole can be drilled straight through the filler to allow the shaft to exit.


The folding prop sits nearly flush to the fuselage.

Being something of a perfectionist, Smallpiece insists that the shaft should be supported within a suitable bearing (it’s something we still occasionally argue about) and this bearing is itself housed inside an aluminium cylinder, which is also let into the nose block.


Purist Mode. Here the removable plug is in place.

There are two important benefits to this arrangement:
It allows the collar of the prop bar to slip inside the ali cylinder, thus making the prop almost flush with the fuselage. And with the prop removed the recess can then be filled with a suitably sized and painted plug, which pretty much restores the glider to Purist Mode.


Super Javelot nose in Purist Mode.


I have built some half-dozen gliders now with E-Assist, culminating in this procedure. But here’s the irony… the conditions that led to this – light winds on the slope – now seem to have disappeared to such an extent that, even allowing for pandemics, it’s hard to remember the last time we flew any of them!


It shouldn’t really take a Lockdown to increase my rate of model production but I’m already on my fifth glider since it all started, about a year ago at the time of writing. The third of these was to produce a quarter scale version of the Slingsby Type 51 Dart 17r.


Quarter scale Slingsby Dart17R ready for covering and finishing.

The Dart represents the Slingsby firm’s last traditional wooden glider before glass came to rule the world, and you can see in the shape and planform how future gliders were going to look. Suffering, as I do, from that little-known medical condition, Repetitive Glider Syndrome, this is my fourth version of this sailplane and, at 1/4 scale, the smallest.


The Dart on its first outing.

As my pal Motley had also expressed an interest in building this model, I gave him the task of sourcing the retract unit. He came up with the Topmodel 1/4 scale retract, which boasts a built-in servo, placed conveniently between the two side plates, and in front of the wheel. I put my initial concerns as to what would happen if the servo failed to one side and instead looked at the advantages.

The Dart has a very minimalistic fuselage in front view, and in the past, I have had to place the rudder servo behind the pilot’s head, as there was never any room to put it anywhere else. Now, the rudder and elevator servos could be placed either side of the retract – definitely a plus on the neatness front.


Snug fit of the retract unit is on display here.

Fitting it was another matter though as Topmodel had eschewed the normal fore and aft lugs and replaced it with a flat base. Still, a determined application of Modeller’s Grit saw the job done and soon it was time for the maiden flight, which was to be scraped in just before the third lockdown.

It has often, if inaccurately, been reported that after the maiden flight of the Spitfire prototype, the test pilot, Matt Summers, said ‘don’t change a thing’, and I’m happy to report that my feelings after the Dart’s maiden flight were on similar lines.


The author gives scale to the Dart 17R.

In searching for the appropriate adjective to describe the model’s characteristics, I decided on the word ‘sweet’, and a few more launches behind Smallpiece’s tug provided further confirmation.

As with many of my designs, the drawing for the Dart is available in digital form FOC from me (or from the Scale Soaring UK forum) along with all the necessary pics etc. Although not a fully annotated plan, more of a working drawing, all the info pertaining to the build is there.

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