A Model is Born.

Over the past couple of years I have designed several ‘hack’ models – “The Freddies” , nothing spectacular just basic everyday models.

All of these, when I have tired of them, have been snapped up by a flying buddy, the worlds first and only “Freddie Fan”. Recently Freddie Fan has been murmuring; time for a new Freddie, time for the lineage to have a successor, time for a Low Wing Freddie.

So, just for fun, here we have the development and build of Freddie IV – “The Crimes Against Aviation Continue”. You must bear in mind that this is no retrospective, no how I did it, but this is a forward moving, making it up and posting as I go along document. It is no forum narcissm, no platform for the exhibitionist engineer par excellance. It may all end in tears, or more likely, a bin bag, but let’s enjoy the journey anyway. And so it begins. Freddie IV.

March 2011. First Decisions.

How big says I?

40” span says Freddie Fan.

OK. We want lots of wing area – Freddie Fan likes to fly slowly – so lets have a 9” chord. This gives a wing area of about 2.5 square foot. Maximum all up weight should be 2lbs (32oz), which would give a wing loading of 12.8 oz / sq ft. Good.

Wing section. Based upon my encyclopaedic knowledge we will go with Clarke Y, because the other one is symmetrical ! Flat bottomed is fine for our purposes, and easier to build. We will have a couple of spars, some inter-spar webbing, full length ailerons, and Freddie Fan wants some leading edge sheeting on top. I guess that is the wing design done – time to bash some balsa.

Of Wings and Wood.

The wing so far. The most interesting thing here is the clamps holding everything down. These clamps were used to assemble the Pyrometers for the RB199 Turbine, used in the Tornado. And now they are stopping my wing from being warped. Nice.

Freddie’s wings are almost complete now. The leading edge sheeting is in place, and some shaping of the leading edge has been done. The leading edge has been left a little blunt as this gives more gentle stall characteristics: Freddie Fan likes to fly slowly and a gentle, predictable entry into the stall will help him greatly.

This Freddie also boasts a spar which chordwise is very deep. The earlier Freds, being lightly built, suffered from a tendency of the wings to warp, and consequently Warren Truss style diagonals had to be fitted to resist twisting. So the theory here then is that the deeper spar will resist twisting forces, as will the leading edge sheeting. There is no advantage to doing it this way over the diagonals; the beauty of designing your own is that you are free to experiment with different methods for no other reason than personal inclination.

The wood for the sheeting and spars, and in fact all of the wood that will go into Freddie is carefully selected to ensure that the strength and weight are properly distributed. For our purposes we can consider that there are 2 cuts or grains of balsa, generally referred to as A and C.

A, or tangent cut balsa is, as it’s name suggests, cut at a tangent to the rings of the tree. It has a long visible grain and a smooth almost creamy appearance. It is quite flexible but lacks stiffness and is therefore best used in tension or where curving of the wood is necessary. Ideal then for curved fuselage sides, or for D boxing Freddie’s leading edge or even for spars, where a little flex is often desirable.

C or quarter grain, has a beautiful mottled or choppy appearance and is somewhat darker than A grain. It is produced by cutting perpendicular to the growth rings of the tree; it is very stiff and consequently can be brittle. It works best in compression and resists warping well.  C grain will feature in Freddie’s all sheet flying surfaces, flat fuselage sides, wing ribs, formers and trailing edge.

Why no B grain? Well of course there is, and it is a random cut anywhere between A and C and as such is more difficult to clearly define.  It has properties of both, depending on which cut it is nearest to. B cut grain will not feature heavily in Freddie’s future.

Calculations and Crayons.

Fred’s wing, being a simple constant chord affair didn’t really need to be designed per se. Once dimensions and a general layout were decided, building could commence in quite short order. The fuselage however requires a little more care. The proportions, whilst not critical, should be within certain parameters to make for a smooth flying and easy to balance plane. The various angles and relative distances between wing and tailplane can have a dramatic effect upon Fred’s performance, or lack of.

So, it is time to break out the Crayons, and do some scribbles and sums.

We already have our starting point. The wing: 40 inches by 9 inches of grade A and C balsa; so all Fred’s remaining dimensions will be derived from this. Depending on who you read and believe there are slightly different figures available for the relative proportions of your everyday sport model, but they are all of similar value, and aerodynamics isn’t an exact science – not when I do it anyway !!

General guidelines suggest that the total fuselage length needs to be about 75% of the span, of which about 40% should be between the wing trailing edge, and the tailplane leading edge. Talking of tailplanes, the area should be about 20 to 25% of the wing area. Typically about 20% of the fuselage should be in front of the wing leading edge, but providing there is enough room for the internals, and the Centre of Gravity can be attained this isn’t critical.

By drawing Freddie out on paper and following these simple guidelines, I can set relative positions of wing, tailplane and nose, which will all but guarantee a successful first flight, and also create what will hopefully be not too obtuse a shape for Freddie. I can also use this basic drawing to develop shapes for internal formers around which the fuselage build will progress.

So, half an hours scribbling and we have to nearest thing to a design that Freddie will ever have.

From Paper to Planks.

And so the design is transferred from paper to wood, and the fuselage construction begins.

Construction of the fuselage is neither revolutionary or particularly interesting. The word ‘Fuselage’ you will not be surprised to hear, is French in origin, as are many aeronautical terms, reflecting much of France’s early endeavour in the field. It derives from the word fuselé, meaning ‘shaped like a spindle’ or simply ‘spindle’, as many early fuselages would have been. Apparently the word entered English usage around 1909.

From the pictures you will see once again the RB199 pyrometer clamps, holding everything in place and square. The pyrometer measures the temperature of the turbine blades on the Turbo Union RB199 Turbine, used in the Panavia Tornado. Turbo Union was an amalgamation of  Rolls Royce, MTU (Germany) and FiatAvio, and their only product was the RB199.  Early flight testing of the engine was performed using the Avro Vulcan, the engine being strapped underneath in a specially made nacelle, and in a nice continuation of heritage, the early prototypes of Eurofighter Typhoon were in turn powered by the RB199 before their Eurojet EJ200 turbines were available.

Sticking Sticks so they Stay Stuck.

Freddie now sports an upper deck, for no other reason than aesthetics; to make him more ‘Mick Reeves Gangster’ or ‘Galaxy Wizard’ than ‘Ugly Stik’.

The next job will be to make and attach the front former, to which the motor will be bolted. This former will be epoxied in place, which brings me neatly onto the subject of glues.

Three types of glue will feature in Freddie’s formation, Cyano, PVA and Epoxy.

Most of the build is done using PVA; Polyvinyl acetate, also known as wood glue, or white glue. It is water based and non toxic, which makes it easy to work with. Unlike the similar yellow Aliphatic Resin it has little or no ‘grab’, making clamping or pinning of parts essential, but giving plenty of time for positioning of components. PVA’s rely on evaporation to set so depending in the exact brand it usually takes an hour or two for initial hardening, and 24 hours to fully set.

Cyano, or Cyanoacrylate is the instant Super Glue favoured by many of todays modellers. Whilst it’s speed makes for a very quick build, this can, where careful positioning is needed, not always be desireable. Also, due to it’s thin nature it requires that parts be mated very accurately for best strength, and with very small models, where the contact patch is minimal, it may be impossible to attain sufficient strength. Cyano is a resin, and like all resins relies on the combination of two components to create the ‘setting’ reaction. In this case the second component is water, which it usually absorbs from the atmosphere.

Interestingly, to me anyway as a photographer, Cyano was discovered by mistake in the early 1940’s by Kodak Laboratories whilst trying to create transparent plastic. The glue was later marketed as “Eastman 910”.

Epoxy, sometimes called Structural Adhesive, is of course a two part resin, which in the case of Freddie is used where maximum strength is more important than weight. There are many classes and types of expoxy but all share a common trait – strength. In an interesting link, the RB199 clamps which have so far been essential to Fred’s construction, serve to hold a Silicon Detector to a Fibre Optic light guide whilst the Epoxy holding the two together sets. If it’s good enough for Tornado, it’s good enough for Fred.

Half Term Report.

Much of Freddie’s airframe is now built, and he is definitely starting to look aeroplane shaped. Before I go much further it is a good time to take stock. The first thing is to see how the weight is progressing.

One of the few parameters set for Fred was his wing span, and from this, wing loading, based upon a predicted AUW (all up weight) of 2 lbs. So, throwing all that we have so far on the scale (servos, motor, battery, Rx Etc) we can see that at this point Fred is around 1 lb. The remaining woodwork, and Solite covering which is destined to clothe Fred are unlikely to add another whole pound, so weight wise we are on track. Also this confirms that the 200W motor earmarked for Fred will be giving the magical 100W per lb figure to endow him with the sports performance required.

So, to sum up Fred’s half term report: a good start and showing good progress, but is prone to flirting with Miss Piper Cub, and I have had to make them sit at separate tables. Whilst not an outstanding student he has a good workmanlike approach and should have a bright future. B+

Mundane Models – a Defence.

I recently read a piece which, frankly poured scorn and vitriol upon Freddie and his kind. Why design a model just the same as 1000 before it? Can you claim to really have designed a model which eschews innovation? If you can’t be innovative and profoundly creative don’t bother.

Well, allow me to defend myself and Freddie.

Flying radio controlled models, as much as we may like to gather in clubs, is essentially a solitary and hedonistic activity. Building is largely a solitary task, and no matter how many others are present, when flying the sole  focus of concentration is on self and model. It is done in pursuit of personal pleasure, for the personal satisfaction of the build and the flight, and often, by design.

This being the case then, irrespective of what others have done, we can derive personal satisfaction from the self achievement of design, build and flight irrespective of complexity or innovation. To imply that the only designs worth creating must be innovative is akin to saying it is only worth flying if you are going to create some new manoeuvre. Flying Circuits? Why? It’s been done a million times before. I’ve eaten Ice Cream before, but it makes it no less satisfying on a warm summer’s day.

I will derive a great deal of satisfaction from the creation of Freddie, and Freddie Fan will derive a great deal of satisfaction from flying him. It’s a bit of fun between consenting adults; I am sure no one objects to that!

Incidentally I note that many of the people who deride the likes of Freddie favour the “innovative” unorthodox design, such as the canard, delta or even ornithopter.  The first successful powered aircraft – the Wright Flyer was of course a canard design, making it’s first flight in 1903, and the style remained popular with early aviators, notably being used in Santos Dumont’s 14 bis with it’s distinctive box appearance.

The first flight of a Delta winged aircraft (that is to say a Tail less Delta) took place in 1931, and is now common place, being especially favoured for interceptor style aircraft where the compromises to low speed handling are not an issue.

Flying model ornithopters have been commercially available in France since 1879, and radio controlled craft since the late fifties.  Interestingly in 1942 Adalbert Schmidt even built, and sucessfully flew, a man powered ornithopter.

“If only the bird with the sweetest song were to sing, the garden would be a quieter and less beautiful place”

Some Snaps in the Raw.

Most of Freddie’s airframe is complete now, and ready for fitting out with servo trays, pushrods and wing fixings. But I don’t intend to do any of this until I have spent some quality time with Fred and his new best friend, Mr Sanding Block. But before then, here are some pictures to get an indea of how he is looking.

Here we see the rough laminated nose block. The motor will sit inside here, front face open to the elements for cooling.

The Tail group, or Empennage if you prefer. The tailplane was originally to be sheet, the same as the vertical stabiliser, but in the interests of saving weight I changed my mind at the eleventh hour. Note the diagonals to resist warping.

So the next time Freddie will appear he will have been thoroughly rubbed up the wrong way and ready for that first, all important “pin everything together to see what it looks like” photo shoot.

Nothing to See Here. 

Like all children young Fred is now past his initial growth spurt, and is now starting to mature, with little visible change. That is not to say that nothing is happening; there are myriad details being taken care of. Servo trays made and fitted, dowels for wing retention carefully marked and fitted, wing tips added, ailerons cut, and extensive sanding.

Also at this stage Freddie is checked for accuracy. He is positioned perfectly level in both axis using a spirit level on his long nose, which I know is my 0 degree datum. By measuring relative to the flat bench I can check that both the tailplane and wing bottom are at 0 degrees fore and aft, and horizontal laterally. This is best done now when problems can be rectified with a little sanding, rather than later when adjustments may be disturbing new covering.

Fred also now sports a canopy. I had intended to carve a plug and make one from scratch, but I found an “almost fits” in the bits box. This was modified into a “fits near enough” by pulling the canopy firmly onto Fred whilst judiciously applying localised heat from a heat gun. This causes the Perspex to shrink onto, and take the shape of, the turtle and top decks.

Odds, Sods, and Skin.

So what has Fred been up to this week? Getting sanded mainly, and one or two other little odds and sods, none of which spring immediately to mind. But what is happening now is covering.

A skin of Dark Green upper, and Cream lower Solite is being first tacked at strategic points, then sealed around the edges, trimmed and then shrunk, all with the use of my trusty travel iron – lighter and less unwieldy than a domestic iron, cheaper, and I find easier to use than the long handled specialist irons. I can’t claim credit for this discovery: like most men I am married to a genius, if only we would recognise it.

Speaking of genius brings me onto two things. Firstly Harry Wesley Coover, one of the inventors of Cyano, mentioned earlier in thie blog, died this week aged 94. Secondly, Fred’s wings are now fully covered. The plan was to cover the bottom, fit the servos, feed the wires through the specially prepared little holes in the ribs, and then cover the top. You know what’s coming now. Guess who forgot to fit the servos? So, how do I get the little wire throug the little holes? Answers on a postcard please, whilst I stand in the corner repeating “Leave the wine alone when building, leave the wine alone when building . . . “

The Devil’s in the Details.

Like a caterpillar engorged with the nourishment of a thousand lettuces Freddie grew quickly through the stages above. But now we enter the chrysalis stage; nothing appears to be happening, progress has halted. But no, like the chrysalis a myriad changes are taking place.

The servos are fitted. Plopped into place, the holes drilled and secured. Golden rods are put into place, ensuring adequate support, straight runs, and roughing up at the glue points.

The control horns are fitted. Placed square to the hinge line, drilled and fitted. Did I mention the hinges? Carefully cut slots on the centre of the surface and wicking hinges are the method here.

The point I am surrupticiously trying to labour here is that the little jobs, if done properly, take time. And it is the doing of these little details properly that will give Freddie the best chance of success, and also the best chance of longevity even when subjected to the harsh operating conditions frequented by Freddie Fan.

Parting shot – wing location is by front pegs and rear bolts, great care must be taken to ensure that the wing is located both securely and accurately. Note the epoxy coating on the face of the former where the wing will locate.

RTG – Ready to Go.

Fred is finished. Well, one or two decals wouldn’t go amiss, but lets make sure he flies first.

Those all important vital statistics go something like this; all up weight, with 3S 1300mah li-po is 1 1/4 lbs, and with said li-po and an 8×4 prop he gives 150W of power, so we have cracked the mythical 100 watts per pound figure, and the motor is good upto an 8×6 prop, so we have some headroom to play.

The CG, with the battery at the rear of it’s compartment is around 25% of the chord; this is safely forward – “Models with a forward CG fly poorly, with a rearward one fly once” – but unfortunately moving the CG back will entail tail weight.

So, the only task left is to pack the bin bag, and pray to whichever diety is controlling the weather this week, and wait for some good maiden weather, or some good maidens.

Fin.

They, whoever they are, say a picture is worth a thousand words so:

A half a dozen flights in and Fred has pretty much proven to fulfil the original spec; enough power to loop from level, nice slow flight characteristics, and pretty forgiving of ham fisted fumbling.

So there we have it, not spectacular, not revolutionary, not profoundly original, but an enormous sense of pleasure and satisfaction for both myself and Freddie Fan, and after all, that is what our hobby is about.

December 2011 – Of Hedge Funds.

Hedge funds. In this case not some dubious banking practice, but the cash that Freddie fan needs to pay me to restore Freddie to his former glory after attempting to pass Fred through a hedge.

The fudelage is largely unscathed, the wing however, as you can see, has been comprehensively “stoved in” as we say round our way. It was a 50:50 call whether to build a new wing or attempt a repair. It was decided enough of the wing was intact to repair, I also decided that I am too lazy to build a new wing from scratch.

Getting it Straight.

Of course when building a wing, or anything else for that matter, it is important that it be straight and true, and this is doubly so when performing repairs with broken or mashed pieces of wood.

Here the port wing (picture right) has been raised up to the correct dihedral, and the steel rule used to ensure leading edge straightness. The wing on the board has been weighted and pinned down. So with everything fixed into place as it should be repairs can commence in the knowledge that all will be as it should be.

After a couple of hours the wing is starting to take shape. Why so long? Each piece has to be made to fit exactly to replace the shattered pieces. It is a case of measuring, cutting, trial fitting and adjusting. There have also been extra pieces fitted; extra webbing and gussets to try and put some strength back into the wing.

The picture above shows the port wing repair. An area of leading edge and sheeting was pushed in by the unwanted attention of the hedge branches. The damaged area has been cut out ant a new piece of leading edge inserted. The significanct thing here is that the new piece has been cut at approximately 45 degrees at the ends. This serves two purposes; firstly it increases the contact area over which glue can be applied, and secondly it provides more strength to small leading edge impacts.

Most of the structural woodwork is now complete, but the leading edge sheeting is still to be replaced. the above picture shows a sub rib; several of these will be made and attached to ribs at each end of the area to be sheeted. These will provide support for the 1/16 sheeting at the point where they are butt joined to the existing wood.

Here I have replaced the sheeting, sitting atop the supports. It will be noted that I have not shaped the leading edge first – this way all the elements will be shaped and sanded such that they all conform together; you will also notice the copious amounts of pins, to hold the shetting accurately in place whilst the PVA dries; it is all too easy with repairs to allow errors and inacurracies to creep in leading to the “it never quite flew the same again” syndrome. More eagle eyed people may also notice the scarf joint in the sheeting. There is a profound reason for this – I didn’t have a sheet of 1/16″ big enough in my bits box, and I am too tight (translation for the non-Yorkshire: tight = unwillingness to spend money) to buy a fresh sheet !

And so we reach the final stages, and that inevitable step which can be the make or break of all woodwork; sanding. Needless to say all the new sheeting and woodword was sanded to blend with the existing structure, continually running the fingers over the joints to check for smooth transitions.

 

Here we can see the completed repair, sanded and ready to cover. And below is the other wing.

 

The repair is more visible on this side, this is due to the differing tone of the wood, and the remains of the outline felt tip marks, once covered the repair will not be detected. It was decided at this stage to completely re-cover the wing, rather than to patch up the repaired areas.

I wont’ go into detail of the covering; it is the same process as when Fred was built. Needless to say the whole was given a final ‘eyeball’ to ensure no misalignment had crept in, and then Fred fully reassembled.

Coming soon – the final Pic, and did he fly again. . . . .

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