Some (many? most?) of the traditional rubber-powered flying scale model kits available in the UK have quite a poor reputation when it comes to flying ability, partly because of the inexperience of the people who built them as their first model, partly because the structure was often what I shall politely call “reasonably robust”, and often because of the extraordinarily heavy wood sometimes supplied in the kits.

                                       

These days, many of the plans are available on Outerzone, and the Vintage Model Company are selling updated laser-cut versions of the original Keil Kraft Flying Scale and Veron Tru-Flite kits – this allows those of us of a certain age to re-live our youth (if only!) with the huge advantage of knowing what we’re doing this time around.

Some outdoor Kit Scale competitions are being run under BMFA rules, but these precision events where everyone tries to fly for a set time, usually about 30 seconds. This has the advantage that no-one is disadvantaged because that’s an easily achievable time with most well-trimmed and lightly built Kit Scale models. However, we think that these models are capable of so much more – hence this Kit Scale duration competition which is designed to see just how long some of these models can be made to fly for.

There are two competition classes.

The Kit Class is open to any rubber powered scale aircraft kit model ever manufactured (Keil Kraft, Veron, Comet, Dumas, VMC, Aerographics, West Wings, etc.).

Open Class is open to any rubber-powered scale model that is not eligible for the Kit Class (e.g. Aeromodeller designs, Flying Aces Club plans, Czech scale design from Mike Woodhouse, own designs, etc.) .

There will be no static judging (just a go/no go eligibility judgement by the CD). All sorts of modifications are allowed, including correcting the outline if you want and even enlarging the design so that the span is bigger.

There will be three flights to a maximum time set by the CD on the day. The time for each flight will be rounded down to the nearest second.

The total score is the total of the three flights + any points awarded according to the bonus points chart:

Construction Type	Bonus points (cumulative)
Design is classic Dime Scale or Pseudo Dime Scale, or is bigger but has Dime Scale type construction (e.g. 1/16” square leading edges, trailing edges, tailplane, fuselage members and generally light and sparse structure).	-40
Design was originally sold as a kit, has box fuselage with formers and more robust construction than dime scale. Only applies if model has not been enlarged.	25
Design was originally sold as a kit, has keel-and-former fuselage construction with stringers at least 1/16” square. Only applies if model has not been enlarged.	40
Wingspan
Wingspan >= 14” and <17”	40
Wingspan >=19” and < 21”	30
Wingspan >=21” and < 23”	20
Wingspan >=23” and < 28”	10
Colour & Markings
Colour and markings generally agree with optional supplied documentation (e.g. profile, colour picture, etc.)	20
Aircraft Configuration
Subject has a very low-aspect-ratio high-wing (~<4) with a box fuselage (or nearly so) (e.g. Lacey M-10, Fike, etc.)	-100

The full rules can be downloaded here

The Oxford MFC Rubber Scale Duration CDs Notes can be found here

 

Hints and Tips Department

The following hints and tips are intended for people who haven’t built one of the models before, or who haven’t built one for more years than they care to recall. In no particular order:

• Build it big. Bigger models are easier to trim, easier to build, and will generally fly for longer. Some of the Flyline kits (plans available on Outerzone) are really pretty good, but anything 24” span or over is worth a try.
• Keep it light. Use really light wood for the formers, ribs and keel pieces. You can probably get away with medium-grade balsa for stringers or medium-hard for the longerons of a box fuselage. Use built-up tail surfaces. If it’s an old design, consider moving the rear peg forwards.
• Use the lightest tissue that will do the job. Be careful how you attach it, try steam-shrinking rather than water shrinking. Thin the dope to about 25-30%, use only a couple of coats on the flying surfaces and if the tissue looks tight enough before doping, use non-shrinking dope.
• Use a big propeller and a long rubber motor. A 6 ½” or 7” propeller on a 20” span model is perfectly reasonable, and a motor that is about 2.8x the hook-to-peg length is usually perfectly useable.
• Some kits (Keil Kraft in particular) have less dihedral than the full-size (!). I would counsel using about 9 degrees of dihedral on a low-wing airframe, and at least 2 or 3 degrees on a high-winger.
• On a low-wing model with retracting undercarriage, leave off the retracting parts of the undercarriage because they will cost drag and (more important) weight.
• When it comes to competition flights, bear in mind that the rubber will get tired quite quickly if it’s used hard – the usual giveaway is that the model doesn’t climb as high as it used to at the start of the day. Carry some new, pre-run-in rubber motors and change motors regularly!

Additional Notes for Competitors

The essence of the rules is that there is no static marking and flight scores are a total of three flights plus some bonus points; the bonus system is designed to give smaller models a reasonable chance of getting on the podium. A few (20) bonus points are available if your (optional) documentation more-or-less matches the model.

Choice of Model

At first sight, it might appear that the best model to use is a big one, but that might not always be the case. Granted, if thermals are difficult to find on the day (e.g. wet grass, no direct sunlight, etc.) then you’re probably better off flying a larger model (say around 30”) that can score maximum flight points (180 points for three flights) without thermal assistance.

However, if lift is relatively easy to find (and in summer, it usually is, even for me) then you’ll probably do better with a model of around 18-20” simply because there will be bonus points available that can easily take the final score over 200 points if you can find some lift on every flight.

Preparation

You don’t want to be fixing niggling little problems with the model when you’re out flying, because it gets in the way of having a good time, so try and check everything several days before you want to fly the model.

Rubber motors will tend to pick up small nicks and scratches as they’re used which can easily turn into a broken motor. I’m sure nobody wants to spend a morning fishing out a tightly-wound motor from a fragile fuselage when they could be flying.

So if you do nothing else, I recommend that you make up and pre-stretch at least one new rubber motor – rubber is funny (as in odd), pernickety stuff, the motor you have in the model might survive the day’s exertions but if you put a foot wrong with it (put on too many turns, not leave it long enough between flights, etc.) it’ll “get tired” and will refuse to work properly, and will have to be changed. Keen duration class (P30, Coupe, etc.) competitors will of course have made up a batch of new motors for use during the day, and each one will be used on just one official flight…

On the Day

I usually try and get in a test flight with the model of choice at reduced turns before the event, just to make sure that the trim is still OK. If this isn’t possible then the original motor is left in, and the first flight is a trimming flight. Then the motor is changed for a new one and the turns used as follows:

Flight 1: 80% turns, rest the motor for 12-15 mins.

Flight 2: 90% turns, change the motor for a new one.

Flight 3: New motor with 80% turns. 

Dethermalizers

With larger models it’s very sensible to fit a modern battery-powered DT, it’ll cost you nearly 5 grams but if it’s a large model that won’t be a problem. A Viscous Button timer might be useable for smaller models and will cost about a gram, although they tend to run at different speeds as conditions change and it can be difficult to get a reliable run.

However, a simpler way of getting out of a thermal which – so far – has always worked for me is to make sure that the glide is a) straight, or nearly so, and b) quite a bit steeper than the normal “floaty” glide that we usually aim for; the model will happily circle within the thermal as long as it’s under power but when the power runs down the glide trim takes over and it executes a fast (=inefficient) glide (almost a shallow dive) out of the thermal.