Was Jupiter an experimental aircraft ?
An experimental aircraft :-
- is of novel design,
- does not get delivered to an operating organisation
- is used for experiments
- is usually modified during its flight test period
Out of these four, Jupiter scores about half a point, thereby contrasting strongly with most HPAs.
Very few innovations. Similar to its immediate predecessors in many respects.
During its design stage and all of the construction stage which required assembly jigs, Jupiter was under the control of an engineer. During its flying stage it was under the control of, and at the base of, an operating organisation, the Royal Air Force. The relevance of this "delivery" lies in differing learnt attitudes of the two people. As an engineer, I was used to thinking of an aircraft as something that one designed and built. John Potter, an RAF pilot, who had also flown with the Cambridge University Air Squadron was accustomed to climbing into aeroplanes and flying them.
John Potter achieved a very hign usage of the plane, unusual in the sixties and seventies. he also fine-tuned the "engine", doing much cycle-training, Although he found himself at the helm of an overweight aeroplane of mediocre design, he concentrated on achieveing longer flights and was thus able to claim the World Distance Record. Those responsible for other HPA. such as Puffin 2, made many changes to the lateral control system and concentrated on trying to make the plane turn. With Jupiter it was not so much "let`s change this and see if it makes it fly better", as, "let`s pedal harder this time".
Jupiter flew without needing any alterations, straight from the drawing board. The only modifications made after the first flight were the addition of a chain tensioner and of instrumentation.
Thus it can be claimed that Jupiter was the first non-experimental HPA. What was certainly true was the benefit to be gained by having a person of one background leading during the construction stage, and a person of a different background leading during flying.
THE AUTHOR'S SUBJECTIVE ACCOUNT of JUPITER
MY EARLIER YEARS :-
" One of the first things I was taught at school was that I had spelt my surname wrong. To prove teacher wrong took twenty-four hours. I took my birth-certificate to school the next day to show that I had spelt it right. "Another thing I was taught at school was that in order to fly by your own power you would need arm muscles six feet (two metres) thick. To prove teacher wrong in this instance took twenty-seven years and the help of a lot of other people.
I have always been interested in off-beat vehicles. In 1947, when I was 10 years old, I made what was effectively a skateboard. Unfortunately this was hampered by a fifth wheel in front for steering, and was much too long.
Later, when cycling down and up the valleys of Berkshire in my early teens, it often occurred to me, when about to descend a hill, how good it would be to be able to cut across in a straight line through the air to the top of the next hill.
I was an aircraft engineering apprentice from 1953 to 1958, and a design draughtsman until 1961, thereby gaining experience in many departments of aircraft-manufacturing firms, both in the technical offices concerned with design of airframes (not engines) and in workshops. With the possibility of sometime building an HPA in mind even then, I wanted to get experience in one of the offices concerned with production (analogous to the builder, rather than the architect, of a house. Quantity production is not necessarily implied; the `production' departments are busy on prototypes as well). However it was generally considered necessary for an apprentice to be versed either in design or in production, but not both, so I never worked in a production office. My main hobby was building canoes and then paddling them. These were all made with a spruce framework onto which was stretched a canvas skin. ("Fibreglass" was being used by others for some sailing dinghies). In one of these canoes I travelled down the Thames from home, and then around the coast and across to France, camping overnight on the way
The 1950s in Britain were a time of expansion. The Festival of Britain in 1951 showed that the nation had got its breath back after the war. For the first time ever there was a `youth culture' exemplified by rock-and-roll, and there was the money to buy gramophone records, teddy-boy clothes and motor-bikes. The power of youth was increasing and in 1958, as conscription for two years of `National Service' ( the draft ) ended, many males suddenly discovered that they had two years of unexpected freedom.
In 1959 I was feeling that I would like to attempt something more original than another canoe and was wondering whether to build a human-powered submarine or a human-powered aircraft, and had started calculations and sketches for the former. Nobody offered a prize for a human-powered submarine in 1959, but I can remember being at home in my parents' suburban house where I lived, one lunchtime that November, and turned on the wireless to hear, as the valves warmed up, `...businessman has offered a prize of five thousand pounds for the first man powered flight. Our next broadcast .... '. I wasn't interested in their next broadcast, and suddenly I wasn't interested in submarines either. I reached for my slide-rule and started to calculate how much wing area would be needed. At this time I was more ignorant about what an HPA would look like than anyone reading this, although within a few months I began to get to hear of Mufli and Pedaliante through the RAeSMPAG. The details of the first Kremer Prize were not published for two months. I made a mistake that was consistently made by many people for several years, namely to suppose that anything that could fly would be able to get round the figure-eight course. I was a 22-year-old with no tools but those I built canoes with, and those I shaved with. I did have a Higher National Certificate in Aeronautics, and I was full of optimism. I even convinced myself that my ignorance on the subject of engines was almost an advantage on a plane that would not have one! Muscle-powered-flight had never been accomplished and maybe it would never be, but if anyone was going to, it might as well be me.
There was another big event in my life in 1959. I met Susan Jones, later to become Susan Roper. This was three weeks after the Kremer announcement. Before long I had to tell her `Look, I am building an aeroplane', `I will help' she replied. I was 22, she was 19; we thought it would take two years. As it transpired she devoted eight years of her life to me and to the project. We married in 1963.
It never occurred to me that any type of aircraft other than a monoplane would be the appropriate layout. A cycling attitude for the pilot was chosen because it would require no experimentation. Bicycles work. You can take a dynamo drive off the wheel ( for the lights). I would take the propeller drive off in a similar way. However, there was no point in the weight of two big bike wheels and centre-of-gravity calculations of my first sketches showed the ( single) wheel position to be interfering with where the pilot's feet should be.
To make the pedals and wheel concentric as in the "penny-farthing" bicycles seemed to solve this, and my 1960 design had this feature. This dictates a minimum wheel size for the feet to clear the fairing (see fairing in Glossary) and the fairing to clear the ground. During various re-thinks, this layout for the front end remained
. My brother Geoffrey and I conducted some tests bicycling up and down a hill to determine power-output and air-resistance of the unfaired cyclist. The strengths of a few wood/glue/wood joints were tested. My job at this time was design draughtsman for metal aeroplanes. I needed to fill out the gaps in what I would need to know. At about this time,(early 1960), I visited The Cycle Show, an annual event in London, to see if there was anything which might be relevant. On one of the trade stalls were displayed a number of samples of chain. `Do you have a chain that twists ?', I asked. `Our chains do not twist' was the emphatic reply of the salesman. I then took hold of one end of the yard long sample of 8mm pitch chain with my right hand and of the other end with my left hand - and twisted - easily. I looked at the salesman. `Our chains do not twist' he repeated in exactly the same tone of voice. The drive chain for Jupiter was therefore acquired through a stockist, rather than direct from the manufacturer. This chain is about a third the weight of bicycle chain. For test, I made, by hand, an 8mm chain-wheel and sprocket to suit my bicycle and road-tested it for a year, before it showed signs of wear.
There are various methods of arriving at the best size of wing and of making the other quantitative design decisions. Since that time it has become common to set up a computer program, but this will often be preceded by one of the more primitive techniques. I saw that the most important thing was to so arrange matters ( "arranging matter" includes the quantitative decisions) so that the pilot would not have to pedal harder than necessary. The job was to find the combination of span, area and other parameters which would produce the lowest value of required power. Thus the power-required would be the parameter which would be optimised,(ie minimised). All these things that are being varied are numerically definable, and at this stage exist only hypothetically. But the final sizes chosen will be translated into concrete reality. I would list a set of values, sufficient to define the size and the general shape of the aeroplane, seeing always that each value was within practical constraints, and then calculate the result, namely the required power with that set of dimensions. Then one of them would be varied and the process repeated. In order to do this one needs a set of assumptions, for instance as to the manner in which increasing the size of the wing will increase the weight. I made the best estimate that I could, which at that time was based mostly on guesswork. No-one knew for sure how much a 60 ft (18.3 m) HPA wing would weigh, or even how much less it would weigh than an 80 ft (24.4 m) HPA wing. Although I had studied aerodynamics, there was a certain amount of guesswork here as well, because although the principles of flight were to be the same as for any conventional aircraft, the expected profile drag could not be accurately predicted, since flight would be outside the range of Reynolds numbers which had previously been of interest.
The aerofoil section chosen for the wing was NACA 653618 which seemed to be the most appropriate. I boldly extrapolated the published drag figures down to the relevant Reynolds number. The second 6 denotes camber, and of the sections of various camber for which ordinates had been calculated and test results published, this was the most cambered section. It did occur to me perhaps to try to squeeze a little more lift out of the wing by adding another 2% camber (2% of the chord, over the length of the chord). This would have meant extrapolating beyond the published data. I decided against this, because I preferred to stay with what had been proven and because down-ailerons would be adding yet more camber still. Meanwhile the Southampton group had done just this, but they knew that they could tunnel-test their own section.
FIRST WING TEST SPECIMEN
One of my colleagues at work suggested making a test-section of wing: a few feet of span, at full scale. Making this would serve many purposes, provide an estimate of the likely weight of an entire wing, demonstrate and provide practice on a form of construction with a good enough surface profile shape and give an indication of feasibility in general. I discovered that thin wooden panels warp, and this is particularly the case when it is covered and doped. The shape of this test-piece was awful. This was clearly an aspect of the project that would need further attention if a laminar-flow aerofoil was going to be used, and for a while I considered basing the design on a non laminar wing section, which would not need such accurate construction.
Either I had to find a way of making the thin panels which formed the outside shape retain their correct shape accurately without warping. or else resign myself to the fact that they would warp, in which case I would switch to a different shape which can be built lighter.
It is an either/or decision laminar or turbulent flow section. Turbulent flow creates more drag but the wing can be built lighter because it does not need to be so accurately made.
Initially, these various items of work such as tests, calculations and finding what chain and other necessities were available were not well co-ordinated. When RAeS grants towards HPF projects were announced in mid 1960, I started to prepare an application for one of these. The grant application forms of that time requested information on many relevant aspects of the project, some of which I had considered insufficiently, if at all. Thus I was encouraged to consider the project as a whole, rather than just parts of it.
TAIL-BOOM DESIGN & APPLY FOR GRANT
My 1961 design, the `Hodgess Roper', showed a span of sixty feet (18.3 m), an area of 200 sq.ft (18.6 m2), and the pilot without a fairing, although I wrote that this could always be added later. On the drawing, the propeller was just aft of the wing, and from behind the propeller hub extended an aluminium tube, at the aft end of which the tail surfaces and a skid were fixed. As far as I know, this was the first drawing of a propeller concentric with a tail-boom; although the design published by Beverley Shenstone in 1957 showed the propeller in a similar position but around a more normal fuselage. The time-estimates which I quoted in the grant application were little more than guesswork. The grant was not awarded, but the experience of having made the application was useful. I continued to refine the design, and to make tests. Also I attended all of the RAeS lectures on the subject of HPF which were more frequent than annually then.
PROPELLER and TAILPLANE
I decided to make the propeller first. I felt that being the smallest component it committed me the least. Also I felt that if I could make this complex shape then I could certainly produce the simpler shaped components. It was very satisfying to see the blades swing. In the front room of Susan's flat a jig of 2 inch by 4 inch (50 mm by 100 mm) timber was erected for the construction of the tailplane. This jig was subsequently used for the other tail components. Susan was helping with the construction, working to a high level of accuracy.
1962 TUBE ORDERED
The aluminium tube that I needed for the tail-boom, 2.5 inch (64 mm) diameter and 0.022 inch (1 mm) wall thickness, was not a standard size, but British Aluminium Co Ltd quoted me 19 pounds 6 shillings and eight pence for 4 lengths of 17 feet (5.2 m). This was ordered in November 1961 and arrived in January 1962. It was the most expensive item up till then.
TAIL to BOOM
The tail components were completed and assembled to one of these lengths in my father's garden, taking up half the lawn. One of my sisters boldly declared that any aeroplane which you needed to pedal would not be so good as one that you did not have to pedal. To a greater or lesser extent my other four siblings gave occasional help, and tolerated the monopoly of the lawn. The work was being done mostly by me with assistance from Susan. Despite the domestic surroundings, I was working as I would on any aeroplane. A record was kept of the weight of each part, and testpieces had indicated that each part would be strong enough to withstand the loads which I estimated would be applied in flight. Looking back, I can see that I was excessively aping standard aircraft practice, for instance ball-race-pulleys were used for the control surface hinges. Another mistake was an over-elaborate detail design. The tailplane tips were built up like half a model-aircraft fuselage with their own frames and stringers.
SIR STUART MALLINSON CBE DSO MC JP DL
It began to occur to my father that there was not going to be room for the wings in his garden, and he contacted Sir Stuart Mallinson who was one of the more colourful characters of an otherwise dormitory suburb. His grandfather had started the Mallinson plywood factory, which had flourished, and Sir Stuart had a large estate bordering Epping Forest. He was a prolific benefactor and interested in sport and in enterprise. A part of his estate was open for Scouts to camp in, and he was allowing Christine Truman (then Wimbledon centre-court frequenter) the free-run of his tennis-court. Sir Stuart was invited to view the tail on the lawn. He was impressed. He would provide spruce for the wing-spars and advice on how to use it, and he offered the use of a double garage for construction. In August 1962, Susan and I carried the components there.
The new surroundings elicited a new approach from me, and I began to re-appraise the design. I was now free to think wing. I took advantage of accounts of SUMPAC and Puffin, and I now had the experience of the tail fitted to the boom.
The first job at Sir Stuart's was to make another wing-test-specimen. This was of 3 ft (0.9 m) span with the same 5 ft (1.5 m) chord and the same taper as at the centre of the proposed wing. After many amendments this proved satifactory in all respects. We developed the technique used on Puffin of using sponge under the Melinex. The weight was less than estimated. Crude timber girder extensions to the spar at each end made a thirty foot bridge, the wing-specimen being the centre-section of the bridge. Thus the specimen could be tested structurally. On first tests the joint fittings to the extensions, which were to the design of the transport-joint fittings of the actual wing, tore away from the spar. Mallinson's (Sir Stuart's firm) made up some special sheets of birch ply bonded to light alloy. The fittings were cut from these sheets and then glued to the spruce booms using wood glue. These held. However there was one thing that those working in Sir Stuart's garage could do, and those in his plywood factory couldn't. That was to make Balsa-plywood. We heard from members of their technical department that the Puffin group had approached them with just that request, and Mallinson's said it couldn't be done. Puffin I wing was skinned with a single thickness of Balsa. This involved the complication of a two-cell torsion-box, the grain of the wood being different in each, so that torsion in either sense would be resisted. We had already been using our home-made Balsa ply on the tail-components of the 1961 design. The details of how to make such panels and other techniques used are described more fully in `Aero Modeller' (Roper 1973). I used the data from the weight of the test-specimen, and each part of it, to re-optimise the wing, and to finally establish Jupiter's wing dimensions. The actual weight of the wing was in excess of the value estimated from this test-specimen. To a considerable extent this was because we could not control the weight of glue on a large assembly so readily as on the test-piece; for on a large assembly there is an urgency to get the whole area wetted in a certain time. John Potter quite rightly blames the Woodford people for this (Potter 1973).
The ordinates for each of the 55 rib stations along the wing were calculated by a colleague of my brother John Roper who, on the staff of Manchester University at the time, had access to one of the few computers in the country. My brother offered other computer-help, but I didn't know what other questions it could answer. Writing programs and even the range of programs that could be written were mysteries known, at that time, only to a few. Optimisation was done by calculating a series of values by slide-rule, and plotting graphs. The prop design was particularly tedious and took 3 weeks use of logarithm tables.
Spruce and Balsa were ordered and we launched into the construction of the wing. This had a main spar at 40% chord, with spruce booms and Balsa-ply web. Skinning with Balsa-ply between there and a front spar at 7% chord completed the torsion box. The nose forward of this was skinned with spanwise grain Balsa. Ribs forward of the spar were of 1/16 inch Balsa-sheet and were stacked in a pack 20 inches high and sanded to profile together. Aft ribs were Balsa girder construction. The only jig used for the wing was an 18 ft long bench. The spars, skin panels and the five sections of the wing were all made on this bench.