The Kan Doo Story

Picture of Kan Doo

Can't do? - Kan doo

A few years ago, a friend in the North London club, John Evans, presented me with a box of vintage diesel engines. John was quite ill at the time and died just a few weeks later. It was clear that his intention was that the engines should go to someone who would use them and I resolved to build a model for each motor.

Included were two ED Competition Specials. Actually, there was one complete example with tank and shut-off which went into a 'Slicker 50'. The other motor had both mounting lugs broken off and lacked a tank. Included was a spare crankcase!

There has always been some controversy about the power of the Comp Spl, something which arose out of the C/L speed record established by Colonel Taplin, which many find hard to believe.

I had always wanted to build a model of the first Gold Trophy winner in 1948, Pete Cock's 'Kan Doo'. Many stories have been told about this model and the winning flight, usually by people who were beaten on the day. Let's just say that the performance of both model and motor have been cast in doubt. Incidentally, I had always thought of the model as 'Kandoo', but all of the published info and Pete's own correspondence make it 'Kan Doo'.

So, where to find information. There was a small three view (Fig.1) and some information in Ron Warrings book 'Stunt Control Line Flying' ('Special cheap edition 6/-', that's 30p), published in 1949. The only information is that it crashed several times (see later).

Fig.1 From 'Stunt Control Line Flying' by Ron Warring.

Apparently more useful was a drawing published in the 1949 'Model Planes Annual' which has an article by Pete Cock and a three view produced by the redoubtable Bill Dean (Fig.2), but no constructional information whatever (again, see later).

The text and pictures of Pete's article can be found here.

Fig.2 From 1949 'Model Planes Annual', drawn by Ron Warring
from dimensions taken by Bill Dean.

I was aware that a three view had appeared in 'Aeromodeller', some time in the 70's (actually April '76) and that this had produced a letter from Pete disputing some of the details (more anon). I tracked this down in Vic Smeed's 'Fifty Years of Aeromodeller' (Fig.3).

Fig.3 From April 1976 'Aeromodeller', drawn by Pat LLoyd.

This left me with very little to go on as far as producing an accurate model was concerned. My intention was to use the model for vintage stunt if this seemed practical, or as an entry for the 'Fireball Trophy' event (an authenticity contest) if not.

The breakthrough came when talking to John Perry at the 1997 Model Engineer Exhibition. John had a copy of the plan from the Kandoo Model Products kit and kindly sent me a copy. While there was still little evidence that this represented the actual winning model (I have since learned that the plan was produced some months before the Nats win), it was an authentic plan clearly marked with the date 1948.

From this I was able to build a 'Kan Doo' which represented a model which could have been built from a kit in 1948, which was more than adequate for the Fireball event. The only authentic item that I didn't have was a 'Bat' tank, but there was ample information available to make a replica. The plan also showed the modifications needed to the carburettor of the Comp Spl and I was delighted to find that the example that I had was already modified as required.

Carb modification
The carb modification which consists mainly of removing the integral tank.

It is interesting that the plan refers to the fuselage core which is of 1/8", 3/16", or 1/4" plywood, "as supplied". Presumably good ply was hard to find in 1948.

My model weighs 15.5 ounces which is given in the 'Model Planes Annual' article as the weight of the Gold winning model.

Now it gets difficult

One of the few real pieces of information that I had was that the prop to be used was a 9x8. I had a 9x8 'Trucut' which I was reluctant to break but did fly the model on it and soon discovered that my motor really didn't present any threat to an average rice pudding. Pete's motor was said to turn this size at 8000 rpm. My example couldn't manage 6000!

I tried various variations on the theme (once again, see later), most of which got broken fairly quickly, and was rescued by John Truscott who gave me a KeilKraft 9x7 nylon which proved to be the best compromise between performance and durability.

Most of the published accounts of the winning flight refer to the problems caused by the high wind and some accounts referred to the fact that Pete had to find some longer lines. One account from a well reputed source said that the judges couldn't recognise his manoeuvres because of the short lines. This would appear to be totally false.

So, what length lines do I fly the beast on? The above report also supplied the figure of 52 feet which seemed a little unlikely. However, I had a set of lines of that length so that was my starting point.

I immediately ran into problems with the lines locking. The model was quite happy to circulate on lines of this length but was very reluctant to climb. With a good healthy breeze blowing, just like the winning flight, the model could be 'kited' around loops and eights, but more than one bunt seemed to be beyond it. Inverted was fine.

I tried various lines from 42 feet upwards and various materials. Thread was too stretchy, single strand line locked solid after one loop, while multistrand line would eventually become very stiff and then lock. Out of 19 flights prior to the 1998 Fireball event, 14 of them ended in crashes. Yes, it's tough. The only damage was a cracked rudder and split tissue.

On the weekend of the Fireball event at Old Warden I travelled there on the Saturday in search of some new lines and drew a blank. In conversation with Barry Wade he gave me the answer to the line locking. Barry's theory was that the locking was caused by vibration of the solid leadouts. His cure was a short link of flexible material (heavy thread) between the leadouts and the lines.

That evening I cleaned up those original 52 foot lines and removed all of the rougher parts at both ends, giving me a length of 48 feet. I added a 2 inch loop of thread to each line at the model end.

On the Sunday in the event, aided by a strong wind, I had the first really successful flight of the model and even succeeded in doing two consecutive bunts. After the contest, I even persuaded it to do three bunts and was able to do continuous horizontal eights - running backwards the whole time.

My conclusion to this point was that there was little wrong with the model but Pete Cock must have had one hell of a motor.

Ah, now you tell me!

The picture which started it all.

When the first article in a series on C/L by myself was published in the October 1999 issue of 'Aviation Modeller International', the editor included a photo of myself with the model and a comment about it being more of a 'Can't-do'. This produced some interesting correspondence - the whole idea - Including one from T.F.Holland, of Southampton, who witnessed the winning flight. This ran as follows:

Regarding the article by Dave Day on control line in the 'October' issue. He states that his vintage 'Kandoo' was a 'can't do'. I beg to differ - it was a 'did-do' as it won the Gold Trophy for Pete Cock. I know, 'cos I was there!

This gave me the opportunity to reply and ask several questions regarding the flight, as follows:

"Thank you Mr Holland for putting me (or rather the editor) right in this matter. I was aware that the Kandoo (sic) won the first Gold Trophy in 1948. That was the main reason why I built the model, in the year which was the 50th anniversary. I also wanted to prove/disprove the commonly held view that the model was useless and that Comp Specials were no hazard to the skin on a rice pudding.

"As you were there, I wonder if you could answer any of the following questions for me:
"Did the model really crash 10 times on the winning flight? It certainly crashed at least once, because the photo in Aeromodeller showed it doing so.

"Did it really perform 5 loops on take-off before Pete could gain control of it? "Was that on all 10 take-offs?
"Was Pete really sent away to find some longer lines, because the manoeuvres were unrecognisable?
"What length lines did he fly on?
"Was it really blowing a gale?
"What manoeuvres were performed on the winning flight?
"Pete has written that his Comp Special would turn a 9x8 prop at 8,000rpm. Can you confirm this as, neither of mine can acheive 6,000?

"Actually, I cannot agree with the consensus that the model is useless. Mine has had 22 flights to date and has only crashed 17 times, so I am far short of Pete's record.

"If we can arrange a meeting, you are welcome to fly the model and show me how it should be done."

I received no answer from Mr Holland, but it did produce a real bonus, a letter from Pete Cock himself. Pete kindly enclosed a copy of that letter to Aeromodeller, back in 1976, which ran as follows:

Dear Sir,

My attention was recently drawn to your April 1976 issue, featuring myself and Kan Doo. Although delighted to find myself remembered in this way, I was at the same time rather saddened to see what some unknown designer had done to my ancient masterpiece. If my memory serves me correctly, I have never supplied drawings of the Kan Doo to anyone for publication, and those printed in your magazine must be someone’s guess at how the model was constructed.

By crawling about in my loft I found the original plans and remains of my last Kan Doo (which someone walked over at a demonstration). Reference to these has restored some memories.

If any of your readers build models to your published drawing, they will first of all discover that they are unable to keep the weight within the specified limits: I expect that the models will in fact be double the specified weight and will have great difficulty in flying at all with the ED 2cc motor. The general proportions and outline shapes shown in your drawing are roughly correct but some structural details are not. The most alarming discrepancy is in the fuselage, shown as 1/4in. or 3/8in. plywood; this should be 1/8in. or 3/16in. plywood which is fretted out at every convenient spot to reduce weight, and then covered with light 1/16in. balsa. The undercarriage was of 14 or 12 gauge - not 10 gauge and the tailskid was 18 gauge. The bellcrank was of duralamin and was supported on a single plywood plate which was not attached to any part of the wing structure The engine used in the contest was an ED 2cc Standard (not Comp. Special) but it was fitted with Comp. Special fins and compression screw and had a shortened piston.

I think I built 18 Kan Doo models, all basically similar but differing slightly in proportions and structural details. The model flown in the Gold Trophy contest in 1948 was the best of the bunch but was handicapped by having an overweight repaired nose section, the wrong propeller, and was made to fly on lines longer than it was capable of carrying in such windy weather. Remember - the minimum line length rule announced only about one hour before flying started was the same as applied to 10cc powered models. I had to hurriedly make up new lines and put in a practice flight, during which I lost line tension at an awkward moment and crashed. The nose was broken off the model and I had to make emergency repairs by bolting two plywood stiffeners to the engine mount. I believe that observers at the time thought that this repair was in fact the original structure and may have led to the belief that the fuselage was 3/8in. plywood.

I was rather ashamed of my performance in the contest - the model (and perhaps the pilot) having previously done much better during ‘Fly for fun’ sessions. Firstly I had to take-off from grass which was so long that I could not see the model from the centre of the circle - and broke two propellers in the attempt. Secondly, the wind speed was such that at times the model could make no headway against it and had to more or less hover waiting for a lull to get it round to the other side again. On occasions Kan Doo passed close to my nose on slack lines. I remember on one occasion going inverted by means of a half roll This was achieved as follows: just as the model is coming into wind, run towards it and let the lines go as slack as you can; the modal then turns away from you and goes back the other way with the wing-tip carrying the lines now on the outside of the circle; step back smartly to regain line tension and thus pull the outer wing-tip over to the inside. then proceed inverted. Unfortunately, the same procedure doesn’t work too well for going back to normal flight - you have to get it back some other way.

It has been a dream of mine to fly Kan Doo in the Gold Trophy contest again one day. I let the 25th anniversary go by, so perhaps I might be able to make the 50th if I can get an ED engine again. Incidentally, I have never seen the Gold Trophy and have often wondered what it looks like.

Pete's letter sent with the above was:

My attention has been drawn to the letters in your magazine, one from T.F.Holland and the reply from Dave Day, concerning my Kan-Doo design. I think that I can answer Dave’s questions.

My model was capable of doing all of the manoeuvres in the 1948 schedule, with ease, but in relatively calm weather and on 37ft. 6in. lines (flax fishing line); I believe it was of’ 12lbs. breaking strain, sold under the brand name of ‘Cuttyhunk’ on card spools of 25 yards each. The purely scientific reason for choosing that particular radius was “That was all you could get from a 25 yd. spool”.

I did not perform 5 loops before gaining control on any of the take-offs.

I was sent away to find some more lines when I presented myself for the preliminary round, elimination round that is. Someone had decided to introduce a minimum line length rule of 40ft. to make things more difficult for the ‘no-hopers’ with small engines, such as myself.

It really was blowing a gale, from a model flying point of view. Free-flighters were being blown away, many smashing into the hangars on the downwind side of the aerodrome.

During the contest, whilst doing consequent loops, I had to hover into wind, gaining height slowly before going over the top and coming round again, thus making the loops ‘D’-shaped. There were times when the model took short cuts across the circle on slack lines during both upright and inverted flight.

I did not crash ten times or have ten take-offs. In the take-off area, the grass was long, snagging the lines and hiding the model from view from the centre of the circle. Most other flyers were hand launching but I wanted the few extra points given for take-off so I chanced it, getting away only at the third attempt after breaking my two best props.

What manoeuvres were performed? I believe that I performed nearly all of the schedule but not in a continuous flow. I sometimes had an accident part of the way through a set, then re- started and did the set again properly. I don’t think I was awarded any points for the second attempts. I also probably ran over the ten-minute time limit with some of my best flying (when I had got used to the wind). I did not know that there had been a time limit until I read the magazine reports weeks later. The picture in AeroModeller which Dave mentions, showing me crashing, I think was taken when I clipped the ground during consecutive bunts.

With regard to the performance of the engine, my engine was a E.D. Mk II Standard with exhaust stubs removed, a Comp. Special cylinder head with compression screw fitted instead of’ the screw-up-and-down Mk II head, and a shortened piston skirt. My engine ran much better than a Comp. Special, due to the fact that it had cast-iron bushes for the crankshaft to run in and the later Comp. Special did not.

Dave did not ask about the propeller, although this is a very important part of the set-up. I made props of my own design, whenever I had the time, because I could get better performance than with commercial props. My props were 9 x 8in. with washed-out tips and a blade width of 1in. from the half radius point to the tip. The blades were also thin and undercambered, rather like a modern electric propeller. When I was pushed for time, or lazy, I used Technif1ow l0 x 8in. cut down to 9in. dia. (to get the extra blade width).

I wonder if Dave made his Kan-Doo from the plans published in the April 1976 AeroModeller? If he did so, then it is likely that it weighs far too much to perform properly. Those plans were published without any reference to myself and are only someone’s guess at how the model was constructed.

The model which I flew in the contest had hundreds of flights during the preceding months; I used to fly every day that weather and fuel supplies permitted, including sometimes lunch times at work, where there was only space for half a circle, standing with my back to a wall and doing continuous loops, bunts, figure eights and wing-overs. More than once I flew at night with my back to a lamp post for illumination, Those were the days!

Pete Cock with Radio Queen
A recent picture of Pete with his electric R/C Radio Queen.

It's interesting that Pete says that the model had hundreds of flights before the contest. The article in 'Model Planes Annual' says that it was new and only had one test flight. The real revelation here though, from my point of view lies in the actual length of the lines used. I have since had a long telephone conversation with Pete and he has repeated his information about flying on slack lines. All of this makes me feel rather better about my own motor which is hauling my model around on 48 feet lines.

So, I proceeded to shorten my existing lines to 38 feet 6 inches (40 feet from handle centre to model centre). The lines (0.012") are rather thicker than Pete's fishing line, but I don't know how they compare with his wire lines used in the Gold Trophy.

The first opportunity to try the reduced length was a rather breezy and cool day. The immediate problem was getting off the ground on rather long grass. Dragging the model sideways on the reduced length made the already long take-off very difficult. Once airborne there was an immediate improvement in the models response. The first loop, however, showed a marked reluntance by my particular motor to maintain its revs and it loaded up on any tight turn.

Keeping the speed, and revs, up by flying large manoeuvres helped a lot and I was now able to do continuous loops, bunts and horizontal eights. Further adjustment of the motor on the next flight led to a situation where I could even manage an overhead eight (well, more like a rounded reverse wingover). Any attempt at anything like a square loop produced a drastic reduction in motor speed and a matching lack of control power to continue.

After all of this I have to return to my original view that Pete had a very good motor. My next job is too attempt to produce a replica of his propeller. I am still using the KK 9x7 nylon, which is definitely inferior to the 9x8 Trucut which I am reluctant to risk breaking.

One overwhelming impression remains every time I fly the model. It is just so much fun to fly. Maybe this is pure nostalgia trip for me, but any model of a later vintage is so easy to fly, by comparison, that it is boring.

Once again I would like to thank John Evans, John Perry, Barry Wade, John Truscott and, not least, Pete Cock for the part they played in this chronicle.

Kan Doo

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