Tim Hooper fits a top spec motor to his R/C assist Keil Kraft rubber model.
Skipping back a couple of episodes to the ongoing saga of my Keil Kraft Gipsy (as recently re-kitted by Ripmax), we’d reached the giddy heights of winding several hundred turns onto the five metres of rubber that lay within the fuselage. We’d also reached the conclusion that winding all that rubber by using a finger pressed against a prop blade was a definite no-no.
What we need is a ‘stooge’. A stooge is simply a stable platform to hold the rear of the model, at a convenient height from the ground, to stop it from trying to rotate as we pile on the torque. There’re loads of ways of making a stooge; I used an old studio lighting stand and some aluminium scraps, but they all share the same feature in that instead of holding the fragile balsa airframe itself they go straight to the heart of the matter and utilise that hollow rear dowel as their attachment to the model, in most cases by inserting a sturdy metal peg through the rear dowel and into the stooge.
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STRETCH WINDING
Just to make life even more complicated, there’s another factor to contend with when winding a heavy-duty rubber motor and that’s the knotty problem of knots in the motor. If you were just to wind up the prop, as it sits within the fuselage, then the motor wouldn’t wind up equally throughout its length. Nope, it would form unequal knots and clumps as it bunched up. Not only would this diminish its efficiency as it unwinds, but the unpredictable weights and position of the knots could play havoc with our carefully calculated CG position of the model itself. Not good.
The way to avoid this is by stretch winding the motor. With the rear end of the model nicely secured in the stooge the winder is attached to a loop in the front end and the human in charge takes several paces backwards to pull the motor taut, and then he (or she) can start to wind it up. As the tension increases, he’ll walk forwards towards the model, until his arrival at the nose block should more or less coincide with the optimum number of turns being achieved.
Needless to say, all this stretching malarkey is very like to pull the stooge over – together with the model – resulting in catastrophic damage to the aeroplane and to the owner’s fragile ego. For this reason, stooges are usually secured by pegs and guy ropes that run aft of the model.
GEARED WINDER
Just when you thought it was all over, we get to the problem of the winder itself! The obvious method of making a geared winder is simply to bung a hook into the chuck of an old hand drill, right? Well, sort of…
As I delved deeper into the issues caused by the management of a fully loaded rubber motor, I read quite a few horror stories centred around tales of a modeller piling on the turns, at which point the hook gets pulled out of the drill’s chuck and pulled by the stretched motor, becomes a rapidly accelerating missile, guided unerringly down the gullet of the model’s fuselage, thrashing the whole thing into tiny pieces in a split second.
There’s also a second unhappy scenario when the entire hand drill is pulled from the owner’s sweaty mitt and into the model. If you think about the design of the average hand drill it’s designed to operate under compression, with the user pushing the handle to encourage it to drill into a solid piece of work, whereas we’re asking it to operate under compression’s exact opposite force – tension.
Ideally, we need to minimise the risk of our winder falling apart under the strain of winding a hefty rubber motor.
There’s a couple of approaches that are in use, and the first tackles the issue of the winder hook being unexpectedly pulled free of the chuck. In my own case, I started by making a hook from a length of heavy duty 3mm push rod, using the threaded end to accept a nut and washer. With the drill’s chuck completely disassembled I was able to able to insert the push rod from the rear of the chuck, so the nut and washer were physically behind the chuck’s jaws, and, unless the threaded portion failed, the rod could not be pulled out.
Obviously, this is entirely reversible, in that the rod can be easily removed and the drill once again used for drilling holes, as it was designed to do.
LEYTOOL DRILL
The other snag with using a conventional hand drill lies in the orientation of the handle. It’s usually in-line with the rest of the tool, meaning that the operator has to hold that handle very firmly indeed to stop it rotating and/or pulling free out of his hand at moments of maximum stress.
My online guru friends suggested that a better placed handle was available on the ‘Leytool’ series of drills, so that the grip was at 90° to the direction of tension. A quick delve into eBay saw a choice of these vintage items up for grabs, so I picked one that featured a long crank handle, giving the operator greater leverage when winding up the rubber band. A longer crank would ease the amount of strain on the arm of the rapidly aging operator, should he decide to further pursue this particular form of aeromodelling madness in the future…
If you think that winding up a rubber band can’t be all that hard, then consider that a hand drill is geared around 3.5:1 against you, so that the rubber motor’s torque is amplified by that factor, with only your winding arm to restrain it. I was really surprised how hard it was to pile on the turns; above, say, four or five hundred and it becomes something of a struggle!
RECAP
To recap, this simple stick and tissue, rubber powered model aeroplane has become something of a monster, requiring more support equipment than the average F1 racing car. We have carved propellers, freewheels, stooges and winders so far. The thing is, all of this peripheral gubbins only needs to be sorted once, I hope. After this point, I’m hoping that any other rubber models can utilise all these aids. A bit like having all of your R/C models programmed into a single posh transmitter, I guess.
It was suggested that I rig up the stooge in the back garden and then wind up the rubber motor all by itself. leaving the model safely ensconced in the hangar. This proved to be a good idea, allowing me to sort out the pegging out and winding procedure without posing any risk at all to the absent model. Five hundred turns seemed to be the comfortable maximum for the supplied rubber, which disappointed me slightly. I’d been hoping to get at least eight hundred rotations loaded into the fuselage.
EXPERT HELP
By now, I’d also worked out that the rubber strip supplied in the kit wasn’t really up to the task of turning that new 17″ balsa prop in any meaningful fashion, so I contacted free flight guru, Mike Woodhouse, who was happy to advise me and supply a useful hank of 3/16″ rubber, for me to make up my own motor. Mike’s website can be found at www.freeflightsupplies.co.uk and is well worth a visit and a browse, even if you’re not considering embarking on the road to free flight utopia just yet!
Josh Finn is another online free flight notary, and I followed his YouTube channel as a guide when formulating my own rubber motor. The basic idea is to measure the distance between the rear peg and the nose block, multiply that by 120% and then multiply that by the number of strands of rubber you’re wanting to use. The peg-to-hook distance on the Gipsy is around 550mm, so I allowed for 650mm, multiplied by 16 strands to give a total length of 10.4 metres. That’s around 34 feet in old currency.
There’s a tried and tested procedure to forming a pre-wound and braided rubber motor, which meant that I had to halve the big, initial loop of rubber (some 17 feet long) a further two times, to yield an eight-strand motor over 1200mm long. One end of this hank is placed over a convenient hook (a door handle in my case) and then it’s pre-tensioned and wound by around 40 turns. Only then can the final halving be carried out, with the result that the motor will then twist itself into a substantial rope, which is just the right size to fit into the model. Too tight and it would be a real chore to fit the nose block. Too loose and the nose block won’t be retained on the front of the fuselage when the motor is relaxed.
Mike Woodhouse also supplied a small jar of pukka lubricant for the motor, an absolutely revolting concoction of liquid glycerine gunk! The motor had a bobbin added at each end and was placed into a small plastic bag, followed by a dollop of lubricant, which was then thoroughly kneaded in to saturate the rubber motor.
LET’S FLY!
By now it was time to head to the field for some actual model flying! Test glides seemed to indicate that the model was balanced and trimmed reasonably well, so I started to add a few winds on the prop, using my finger to spin the prop around.
50 turns did exactly as I’d hoped and just lengthened the glide a tad. 100 turns saw the Gipsy actually climb away when launched, to a giddy ten feet of altitude, I’d say. Things were looking promising, but when the evening breeze abruptly changed into a gusting wind, I called it a day.
The next session saw the Gipsy up to 250 turns, which meant that after launch I actually had time to pick up the transmitter and wiggle the rudder stick, which kept the model within the confines of our strip. I’d added a few degrees of down thrust at the nose block by this time, to cope with the sudden unleashing of power as the rubber motor flexes its muscles immediately after launch.
By now I was getting confident and cocky, so the Gipsy went into the stooge for winding using the Leytool drill. This worked a treat; I could stretch the motor out of the fuselage’s nose by several feet and then start winding, moving in towards the model as the turns piled on.
The flights now were getting quite impressive, both for rate of climb and duration. 350 turns meant a circuit of the strip, followed by a landing back near the pilots’ box. Needless to say, the other club members present were either quite impressed or totally bemused at all this fuss to get an elastic band powered model in the air. It would have been cheaper and quicker just to buy an electric ARTF to fly!
BATTLE DAMAGE
Now we come to a sad chapter of the story, I’m afraid. Having wound on 400 turns, I launched the model and as it climbed away that rear motor peg slipped out of one of its mountings in the fuselage, releasing the rear end of the tensioned and torqued motor. The escaped motor instantly thrashed its way forwards, towards the nose, causing considerable damage in the process, especially in the area forward of the windscreen.
Somewhat disheartened, I took the battle-damaged Gipsy home to consider my next move. The wings and tail were still pristine, as was the rear end of the fuselage. A post-mortem conformed that the hollow peg had probably vibrated out of the fuselage, so I needed to address this issue, to prevent any reoccurrence in the model’s possible future.
Despite looking pretty awful, the fuselage was a straightforward repair – if you can call juggling a fistful of glue-covered matchsticks ‘straightforward’ at all. Given that the model had been carrying 10 grammes of redundant lead in the nose anyway, I wasn’t too bothered about adding a little bit of reinforcement in the form of doubling up the front end of the four longerons and enlarging all the relevant gussets around the undercarriage mount.
The rebuilt nose was covered in tissue, which really highlighted just how much the original covering had already faded, despite only being a few weeks old. Never mind, it’ll soon blend in.
Back at the field, I reloaded the rubber motor into the Gipsy and took the precaution of wrapping a tiny elastic band around each of the rear peg’s protruding ends, to stop it from travelling sideways and causing a repeat of the incident.
That’s the story so far. Although I’ve not been able to grab any in-flight photos as yet, the Gipsy has proved to be a reliable flier, even in a breeze. That little rudder tab won’t allow for tight turns but is exactly what’s needed to keep the model in the bounds of my vision, followed by a gliding arrival back on the strip.
EYE OPENER
As an aside, our club has had a recent intake of middle-aged members who are trying the hobby for the first time. Sensibly they’ve all opted to fly foamie trainers, which is great. A couple of them had never heard of or seen a stick and tissue model before and were intrigued by its apparent frailty, especially when they saw me bracing myself against the pull and torque of the rubber motor as I wound 600 turns on! They’d never heard of a rubber-powered model (except for those little stick models you can buy for the kids at the seaside), so they certainly weren’t expecting to see the Gipsy munching its way skywards at a 60° angle, before settling into a smooth, gently descending glide pattern lasting several minutes!
Sadly, since then a sordid combination of winter weather and statutory lock downs means that the Gipsy will have to wait for quite a while until it sees the skies again. Will the Gipsy remain my only rubber powered model? I very much doubt it, so watch this space!
BUYER BEWARE
Here’s a bit of a salutary tale for you…
It’s no secret that in the last few years I’ve had the privilege of becoming a sort of club repository for old and disabled diesel engines. Most have come my way as goodwill gestures and I’m using them in models as and when it’s convenient.
However, there’s a thriving market in vintage diesels on eBay and I’ll often go on there to browse and to marvel at the phenomenal prices that these bits of old, man jewellery change hands for.
Recently though, I stumbled upon a real bargain – a brand new Redfin .061 (1cc) diesel with a ‘Buy it Now’ price at a third of its retail cost. I hesitated for a nano-second and hit the ‘Buy’ button.
Intrigued, I searched the seller’s other items to see if he had anything else of interest. There were over 200 listings, mostly clothes and toys, but nothing else aeromodelling related. He’s obviously an established trader, dealing in auctions, house clearances, bankrupt stock, etc. His history and feedback were spotless.
The shiny little Redfin engine duly arrived a couple of days later and was as good as promised. The only thing missing was any form of documentation or instructions. However, inside the lid of the box was an easily missed sticker, stating that the engine had been built for a particular customer. We’ll call him Mr. Bould, shall we? Entering Mr. Bould’s name into Google immediately flagged up a traditional aeromodeller of that name living in New Zealand. This was the point when a faint alarm bell started to ring.
Anyway, the engine was equipped with a simple venturi intake for free flight use and I wanted a variable R/C carb instead, so I thought I’d email Alex Phin (the proprietor of Redfin engines) and see if he could supply me with the R/C carb that I wanted. I quoted the serial number of the engine, as it was stamped onto the crankcase.
Alex’s response was, yes, he had a carb in stock, but there was a problem. The problem was that my engine was supposed to be in (you guessed it) New Zealand with Mr. Bould! Actually, there was a consignment of three engines that had been dispatched a couple of months earlier to Mr. B in NZ that never made it to their destination.
So, here was my quandary. I had bought an engine that didn’t belong to the seller in the first place. He may well have come by it in all good faith, it’s true, but somewhere in its past journeys that little diesel had either gone astray or been deliberately stolen, together with its two similar brothers.
Alex and I swopped several emails over the next couple of days to resolve the situation. From costly experience, it seems to Alex that delivery losses are becoming more frequent, especially on items destined for international destinations, where the contents of the package are required to be cited on the parcel itself for Customs and Revenue purposes. Good security, that.
Since then, Alex has been in touch with the eBay seller, who openly stated that he bought lost and displaced items from carriers as a matter of course and sold them on to various dealers for disposal.
It’s no longer a case of dealing with a single carrier in a transaction these days. The whole operation is subcontracted to various companies and packages can change hands several times in a single journey. Tracing a missing item is nigh-on impossible. Yes, there’s a degree of insurance payable in some cases but this is only for a limited amount of money.
The upshot of this particular tale is that Alex has his engine back, as is only proper, and I’ve been given very favourable terms for a Redfin .061 RC of my very own, which is properly mine, with my name on the Certificate of Provenance and everything. Hopefully Mr. Bould will also gain satisfaction to some degree.
In wider terms, the old adage that ‘if something seems too good to be true, then it probably is’ is something we need to be mindful of when dealing online.
So, if anybody else has come across a bargain Redfin diesel recently, then Alex would appreciate an email from you.
