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Classic designs. How good are they now?


Jon H
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Classic kits/designs. We all know them and many are held in high regard even 40 or 50 years (or more!!) after they were designed. 

 

My question is, are they actually any good today?

 

I ask this from a point of personal experience with the Precedent (now slec) 1/4 Stampe as elements of the design are woeful and, frankly, present a safety risk in the present day.  This is a bit of a brain storm session so i dont want to get swarmed with recommendations on fixing specific problems as i know what to do there, im just thinking out loud and using this as an example. 

 

The root cause of the problem is the design of the wing centre section (both top and bottom but top is pictured as it is the worst) and this is going to get a bit complicated so bear with me and check out the drawing.

 

sv4.thumb.jpg.90baee02fe1483615788f63c245464c1.jpg 

 

The wing cs is built on a flat 1/8 lite ply plate with half ribs (also 1/8 lite ply) top and bottom to give the shape. There is also a 1/8 lite ply half brace top and bottom running spanwise (Red in the drawing). The red arrow points to the less than desirable joint between the wing top spar and this spanwise brace. This join and 1/8 ply brace accept all negative G load forces the model will see during inverted flight or aerobatics and shock loads from landing. Not ideal! 

 

If that wasnt bad enough, there is an even bigger issue. The bottom wing spar terminates in a 1/8 lite ply half rib UC8 (blue in the drawing) and this is a major problem as this rib is outboard of the cabane strut anchor point which is arrowed purple. As a result, there is no way the forces carried by the lower spar can be transmitted to the cabane strut and down to the fuselage meaning you are relying almost completely on the top spar. This results in very bendy wings and people have managed to pull them off in flight. On my own model, the wings bend so much i am always breaking my dummy rigging. I cant use load bearing rigging without rebuilding the wing with stronger anchor points. As a result, i am very gentle when doing loops.  

 

There are a bunch of other problems with it, but this is by far the most serious. 

 

So why has the model been so successful for so long and why is this a problem now? Why was it designed this way if it was rubbish? 

 

The simple answer i can see is weight and available power. When the model was designed a 60 or perhaps a 90 was the best you could hope for where as i use and recommend a 180 in this model. A 1/4 scale biplane will not fly well on a 60 2 stroke so they were built light, perhaps half the weight of the same model today. Modern radio gear is also far superior and we are able to do more aerobatics with better control, powerful servos, greater engine power etc. 

 

So, We have access to far more power than these models were originally designed for and so we are less concerned by the weight. The product of more power is also more speed as well. So with greater weight, power, speed, and aerobatic performance, overall airframe loading is increased by a massive figure. This brings me back to my original question. Are old designs built today actually any good or do they need substantial modification to keep them relevant and safe? Things like hardwood mounting rails and bellcranks are out of date now, structural integrity may be called into question in some cases, so how close are we to outgrowing these classic designs or at the very least having to completely refresh them? 

 

In the case of the stampe, its not a bin job but certainly, but there are a long list of modifications i recommend to improve the model and keep its wings on.

 

So anyway that is my little thought for the day. Has anyone else experience of something similar? It would be interesting to hear

 

 

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Not every designer had much engineering nous, I guess. Don't get me wrong I'm not suggesting going overboard with the due diligence, but there really isn't much excuse for making poor joints on main load bearing members of the structure. These spars need to be continuous top and bottom or scarfed into a straight centre section in a structure like this.

 

Stress risers seem to be a favourite grolley, as well. Cockpit openings, wing saddle, those kind of areas. Tailplanes just stuck to a thin sheet side with no reinforcement. Fins that are just stuck to the top of a fuselage without reinforcement.

 

I'm also a big fan of having a bit of a think about where my clumsy mitts will be grasping the end result. A few carefully placed extra riblets or some solid wood near the nose can work wonders to resist handling accidents.

 

Bellcranks, torque rods, might be out of date but they still work, I would not be worried by that sort of stuff in a design. You can almost always easily replace that kind of thing with a servo near the control surface, if that's your inclination.

 

 

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You are right about the bellcranks etc still being functional. The point i was making was that we have upgraded some aspects of these models to improve their performance but we rarely look at the underlying structure. I also agree with the points you make about tail's and so on. 

 

I just wonder if models were designed that way as it did the job well enough back then with the expected performance. That said, and as you rightly point out, its a pretty duff design even with that in mind. 

 

Another case in point for me is undercarriages in foam wings. Ideally you want spars supporting the mount plate and these spars need to tie to a wing root rib, which in turn transmits the load into the wing mounting dowels and the wing bolts. This would send undercarriage loads directly into the fuselage and i would expect that to be much stronger than sending those loads into the foam wing. 

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I suppose there are a number of ways of looking at old (classic) designs. Quite a number are still flying having been built many years ago or indeed recently from an old kit but without modification to the basic structure. How many of these do you see falling from the sky as a confetti of pieces? Not many. Of course if you build a classic design and use a power train several times more powerful than the original design used without modification, expect problems.

However if you are building a classic model then power it appropriately and fly it appropriately. Don't expect your Kwik fli 3 to execute 3D type manoeuvres As far as control linkages are concerned, all forms have their place. I recently built an Ugly stick using the original plan from Outerzone. Built to the plan and as strong and straight as an Ox. My only mod is using two aileron servos because I didn't have any bell cranks but I had two suitable servos! It's powered by a contemporary K&B  45. I don't expect it to fall apart in the air or to do harriers.?

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You are right of course Martin, but what im saying is we often dont build/power these older models as they were intended. My guess is the stampe was intended to mostly float around looking lovely as was not expected to do even scale aerobatics. I imagine many other designs are similarly out of their design envelope, hence the original question. 

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As previous commentators have mentioned, many ways of looking at the 'Classic/Great' designs of previous years and what influenced their renowned status.

Depending on the era you choose:

  • Materials available Earlier e.g. Silk & Nylon Doped coverings, mostly balsa, ply & maybe spruce V Contemporary supplies e.g. carbon, kevlar, glass fibre, plastic film coverings.
  • Spare time to design, build and construct assuming finances/'pocket monies' allowed. Today, greater demands on spare time plus other interests, hence the ARTF.
  • Design itself e.g. Airfoils often derived from the shape of a drawn 'shoe outline' & poor structural ideas as knowledge base was less widely available with no internet to spread the words of wisdom, sometimes heavy over engineered too v Today's Computer drawn, CAD, Wind tunnel tested airfoil, designs, stress tested etc.
  • Power systems available - Early less powerful engines, material supplies restricted post 1945, short(er) motor runs, home brew fuel V Current Powerful, light engines & electric motor systems, quality fuels, longer, smoother operation &  duration(s). Reliable Radio Control equipment.
  • Types of model flier: Earlier times more free-flight, rubber, control-line including by youngsters v Today many niche types flown and specialities but overall fewer participants, probably an ageing demographic too viewing their yoof-full halcyon flying days and models through 'rose-tinted' specs etc!
  • Classics (I know everyone will have one or more I miss), Here are just a few which still seem popular as ever and can be seen on flying fields up & down the country 'WOT4', 'MR Gangster', 'Junior 60', 'Some of Boddingtons Designs', 'Cambria/Cambrian' Range', Other classics are there but in lesser numbers e.g. 'Curare/Prettner designs', 'Dave Smith Models', 'Bowman', Galaxy/Pegasus Models', 'MFA Yamamoto', 'Precedent Hi & Lo Boy', 'Chris Foss Gliders e.g. 'Middle Phase' etc.
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2 hours ago, Martin Dance 1 said:

I recently built an Ugly stick using the original plan from Outerzone. Built to the plan and as strong and straight as an Ox.

 

Which raises another good point, the typical covering du jour at the time of the design...

 

Did you cover the open structure wing with doped nylon, or with film?

 

If film, then I doubt it as strong as an ox, as film has absolutely squat diddly tensile strength on a hot day.

 

Covering with film puts more stress on the wood. See the ubiquitous D box for a good answer to sport wing construction with film covering.

 

Ugly stik fuselage, balsa box, covering matters not.

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2 hours ago, Jon - Laser Engines said:

Ideally you want spars supporting the mount plate and these spars need to tie to a wing root rib, which in turn transmits the load into the wing mounting dowels and the wing bolts. This would send undercarriage loads directly into the fuselage and i would expect that to be much stronger than sending those loads into the foam wing. 

 

Yes indeed. Lashings of epoxy to securely fix a hardwood block to some crumbly foam is, well, not a great design. Have experienced that before, and its ability to hold tight when faced with rough ground.

 

Two ply riblets, to transfer load to the wing skin, is also not a bad shout as designs go. This approach then suggests reinforcing the inner wing skin area to cope (i.e. some glass).

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I think the answer is that if you want to build an old designed model then build it in the manner it was built when designed and use a similar power setup to the original.

Anybody wanting to build the same model to "current standards" should be prepared (and capable) of  making the relevant construction changes required and if not then find a more modern design of the same, or similar model. 

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Was liteply so popular when that kit came out or would they have been marine grade ply originally?  Either way, I'd have expected a hardwood wedge to join things up at the red arrow and better lower spar integration at the root, even for a 90 two stroke of the time.

Certainly these larger designs were pared down to the bone but that's just poor design.  My own gripe is with Flair Scouts in the way the wing root sheet ends abruptly and the lack of support around the trailing edge and spar at the aileron cut out (Baronette particularly) creating stress points.

As for updating power trains, yes, it needs to be done with care.

Edited by Bob Cotsford
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3 hours ago, Nigel R said:

 

Which raises another good point, the typical covering du jour at the time of the design...

 

Did you cover the open structure wing with doped nylon, or with film?

 

If film, then I doubt it as strong as an ox, as film has absolutely squat diddly tensile strength on a hot day.

 

Covering with film puts more stress on the wood. See the ubiquitous D box for a good answer to sport wing construction with film covering.

 

Ugly stik fuselage, balsa box, covering matters not.

Film covering pre-dates the Ugly Stick. Film (mainly red) covered Ugly sticks were common from their first appearance. 

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I have not been flying long, so classics are not something that I remember, but what I hear about. 

 

There are some designers where the quality or ease of construction is what is talked about, but for most classic designs it is a pleasing shape, or one that will fly well, or an accurate scale design. That is all about the external shape, wing profile and layout and incidences of the flying surfaces. If there are deficiencies under the hood they are given minor consideration. Maybe a comment to beef something up, though more often a comment to build lighter.

 

If I read build threads of classic models there are always changes made from the original. Each person takes parts of other builds and does their own thinking. For a plan-built model there is not really a mechanism for incorporating improvements back into the actual plan. Kits are different, someone is turning out copies of a plan, instructions and parts, so they could change. However I imagine the actual runs are pretty small for any one design as there are so many different models for so many different tastes. Just not possible to put in the effort and testing. For something like the Stampe, it is a big and complicated model. I agree that makes weak points more serious, but also anyone attempting to build it is likely to have a lot of experience or it will fail anyway.

 

The Vintage Model Company seem to have done redesigns on their re-released classics. They are all small and cheap and probably sell in numbers.

 

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My gut reaction is that the spars and dihedral braces (?) need to go through all the CS formers and meet up in the middle of the (thickened) UC4 and UC 9, then be gusseted to UC2 to lock it all together as one spar.  Same at the rear.

 

But looking at it again, I wonder what area UC 1 covers.  Is it the entire planform of the CS?  Difficult to tell.  If it does and everything is fixed to it, including the wing spars, then that may alter things somewhat.  Are there more wing cross-sections, or an isometric?  (Precedent were big on those!)

 

Even allowing for the likely powerplants envisaged at the time of the design, this aspect is still pretty dodgy.

 

Incidentally, I have a vague 'deja-vu-ish' recollection of the construction of this very wing being discussed on another forum a long while ago...

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Before I started my Stampe I could see straightaway that the centre sections were pants so put a little 1/8th birch ply in where possible. This was quite different to many other designs of the era which had thick ply braces everywhere, ply fuselage doublers (why?) and 3/8th ply firewalls.

I have posted before that I redesigned my TN 72" Spit with none of the eight 3/8th" sq. spruce spars, no 1/4" ply formers, no dihedral braces (three section wing this time), no doublers, and it shed 4 3/4lbs, in fact required a smaller motor.

F3A aerobatic models had to be designed so that they were under 24.5 oz/sq ft wing loading so much more thought went into those but with a limit of 10cc and all the clutter such as heavy retracts, two batteries, a tuned pipe and modernised fuel delivery system it was difficult. Foam wings were the answer.

This formula is still good today on the classic designs and little has changed.

A club mate recently built a Junior 60 as per original plan but with a modern 3.5 diesel. The wings folded.

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19 hours ago, Martin McIntosh said:

A club mate recently built a Junior 60 as per original plan but with a modern 3.5 diesel. The wings folded.

'46 or '55?  My '55 J60 (Flair kit) was built OOB and gets turned inside out with an OS40FS.  It's about 18 years old and no failures yet (touch wood ???)

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