Chris Williams and chums try their hand at a spot of electric powered glider tugging.
It all started a couple of years ago, when my long-time flying buddy, Barrington V. Smallpiece built a miniature scale glider – a Skylark from the West Wings kit.
Having towed up my large scale gliders for more years than I can remember, I think it was as a form of punishment that he set up a small foamie Wot 4 with a tow release attachment and arranged for me to tow him up for a change, having secretly programmed my transmitter for me to fly the tug. With the utmost alacrity, I saved the day by handing the Tx over to my pal Motley, grabbing my trusty camera and setting off across the patch to a safe distance…
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What I hadn’t anticipated was just how much fun this was going to be, and it set off a chain of circumstances, the first consequence of which was the design of the 1/7th scale Wolf, a recent plan feature in this magazine.
Electric towing is not a new phenomenon and as far back as a decade ago we started to see some very muscular electric tugs towing up some pretty large, scale gliders. This state of affairs didn’t last very long, however, due possibly to two factors. First, large LiPo batteries are very expensive, and second, it takes an inordinate amount of time to charge them, which is pretty much why electric cars haven’t really taken off yet in a big way.
Prior to my new tugging experiences, I had been experimenting with the fitting of electric ‘sustainers’ to some of my designs. The idea was that, on days when the wind was forecast to be light and unpredictable, such a scale model could be launched with no fear of a landing out at the bottom of the slope (recent changes to the White Sheet and Wessex clubs’ rules now allow this to happen).
The motors used to power these relatively large gliders were G60s from HobbyKing, currently priced at just under £53.00. These require a 6S LiPo, but it seemed a good idea to gang together two 3S LiPos, on the basis that they are relatively cheap to buy and if one goes duff you haven’t got the cost of an expensive 6S replacement. For a while this worked out splendidly, until the weather intervened, and we didn’t see suitable conditions emerge for just about the whole of 2019!
So, back to the Wolf…
Although a little heavier than the Skylark, the Wot 4 had no problem towing her up, and five or six hundred feet seemed a sensible height to which to tow with gliders of this size. One 3S LiPo turned out to be good for around six tows before a battery change would be required and, as we were fitting the micro-towing around our larger activities, two batteries were completely adequate for a day’s flying.
Filled with this new-found enthusiasm, I set to and designed a Slingsby Gull at one-seventh scale. This one, with its monocoque fuselage, was a little bit heavier again compared to the Wolf, and now the little tug struggled to get up to take off speed, although once airborne things returned to normal.
‘What’, we wondered, ‘if we were to utilise the same motors in the large E-assist gliders, and build a larger tug around them?’
Having just built the fifth scale Wolf, scaled up from the aforementioned smaller version, this added the impetus that was needed, and my pal Motley and I fell to the task of constructing the beast.
Based on the well-proven and reliable Greenley, but scaled down to a suitable size, and fitted with an extended nose, this tug was fitted with a G60 motor and had room for four 3S 2200mAh LiPos. Strictly for laughs, we finished her in an identical colour scheme to Smallpiece’s standard size version, thus claiming that the new tug was therefore a ‘scale’ model.
For the initial tests the chosen victim was the larger Wolf, which, at a comfortable 5lbs AUW, shouldn’t prove to be too much of a challenge. The power from the tug was perfectly adequate and, once again, a six-hundred-foot ceiling seemed entirely appropriate for glider release (I should point out that our club has a CAA exemption to 1500 feet).
On a roll now, I pondered ‘What next?’ and set to designing a fifth scale version of one of the most iconic of British gliders, the Slingsby Petrel, again recently a plan feature in this magazine. With its sealed ailerons and total lack of struts and windscreens the Petrel proved to be on another efficiency level altogether and now flying comparable to that of the larger stuff could be obtained. The Petrel will soar in the lightest of conditions and, despite the narrow wing tips, is perfectly safe at the stall.
Practically fizzing now, and giddy with excitement, I set to designing a fifth scale version of the little-known, one-off Brazilian Flamingo sailplane. Having built a 1:3.5 scale version some years ago, I knew this to be another elegant and efficient machine. Once again, this proved to be a delight to fly, so much so that Motley, himself overcome with excitement, just had to have one himself, and before you could say ‘overdue club fees’ there were two of ‘em.
It was at this stage that a cloud started to eclipse our otherwise pleasurable activities…
It seemed that our new tug had stall behaviour such as to soil the stoutest of trouserings. It turns out that tugging is not quite the effortless endeavour that those tricky tug pilots make it out to be:
• You might think you are steering NNE, but the tug might decide NNW is a much better option – and it doesn’t ask for permission first.
• You might be under the impression that you’re climbing at a steady rate, when the vario tells a different story.
• Turning left or right can cause the towline to sag ominously, and the resultant snatch can wrench both models into unnatural attitudes. (Not a problem for the fearful glider pilot, who will already have hit the chicken switch!)
• And climbing too steeply, not something you can easily judge from the ground, can result in both models coming into uncomfortable contact with our old friend, Mr. Stall.
It was in this last regime that trouble reared its ugly head. Once stalled, the tug could not be un-stalled without at least 150 feet of altitude in the bank. I have seen literally thousands of tows take place with a variety of Greenley tugs and never a one without the tug behaving impeccably, so some chin-scratching puzzlement took place.
The wing, boasting a symmetrical section, was as straight as a die. The CG was well forward. Yet several divots in the surrounding area testified to the results of any episodes of Dumb Thumb Syndrome.
Now, I’m as hard-of-thinking as any other armchair aerodynamicist, but I had a pretty shrewd idea what to do about the situation. Another wing was constructed, this time with the same wing section as most of my gliders – an under-cambered section that has excellent low speed handling characteristics and which has proved itself time and time again over a lifetime of model building.
By this time, we had all built up a healthy mistrust of the machine, bordering on fear, and now, when the First Flight beckoned, we shuffled about, not looking at each other. Three straws appeared, and I was relieved not to have chosen the short one. We needn’t have worried, as it turned out, as the tug was now as stall-proof as it was possible to be, and the incontinence trousers were later sent off to charity. This time around I had opted for full length ailerons and, again a glider procedure, they were programmed to come up for landing. This produces a nose-high attitude, thus increasing drag and thus far it seems to work pretty well.
Not content to keep the status quo, Smallpiece recently turned up with an ARF Hangar 9 J3 Cub, again fitted with the trusty G60 motor and two 5200mAh 3S LiPos. Also, based on his theory that any plane without a tow release is a waste of space, he had fitted same. Now we were talking – scale tows! The Lad has a lot of Cub history behind him, having campaigned a 1/4 scale Cub for many years, so this was a case of déjà vu for both of us. As I lined up the Petrel behind it, I noticed his face turn white and small tic fired off behind his right eye…
Puzzled I was, until suddenly it clicked.
Wind back to 2004; the place – a field near Caen in France. This was the Caen Club’s annual aerotow and the Cub and my 3.5 scale Petrel were two of the participants.
With the heavy Petrel lined up behind the tug (the Petrel has no wheel, only a skid) our Lad opened the taps and duo lurched slowly forward. (It must be said that this was entirely scale. Some years ago, we watched the full-size Petrel being aerotowed and it took three hefty blokes pushing on the wings to get it moving.) The pair hadn’t got very far off the ground when the Cub performed a dainty pirouette and buried itself into the rich French loam, leaving a divot that will forever be remembered as a small piece of England.
Back in the present, Smallpiece was obviously having some species of flashback, so I kicked him hard in the ankle, whereupon he shook himself and opened the throttle. The Cub proved itself to be an excellent tug, with about the same power as the Williamsley (John Greenfield, designer of the Greenley, declared that it could no longer bear his name, what with the new wing section we had fitted) and the French Fiasco came nowhere near being repeated. (It still had its occasional excitement, though!)
Now we were starting to get a little complacent and decided that twin-towing might spice things up a little. Two of the little Wolfs, mine and Smallpiece’s, were lined up behind the tug and the rollercoaster ride began. Like two elderly, but sprightly spinsters who had fallen out with each other, the Wolfs strained to stay as far apart as possible, whilst Motley, on towing duties, struggled to gain height, unaware that the flapperons were up and thus in landing mode. Not unlike a flock of pigeons, disturbed whilst feeding, there seemed to be models everywhere, all looking for safe sanctuary.
It was a bit like the old joke, wherein a snail farmer asks a tortoise to look after his field of snails whilst he pops down to the shops. When he returns, he finds the gate open and the snails all gone. ‘What happened?’, he asks the tortoise. ‘Dunno’, says the bewildered tortoise, ‘it all happened so fast!’
We all got down safely, but afterwards felt a strong desire for some lettuce. Further experimentation proved a little less exciting, but was discontinued eventually, after an outbreak of common sense.
I have always thought that scale gliding offered more than simple powered flight, purely on the grounds that it can take place either on the slope or on the flat, two completely different regimes. Chuck electric aerotowing into the mix and there’s never a dull moment -provided it ever stops raining!
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