Designing and Building for (BMFA) Scale Comps

I'm working on a paper on the above subject that I'll present at the BMFA Free Flight Forum in November, but as there are several Forum members thinking of designing/building models for scale competition, I felt it worth presenting the bare bones here. So lets start with....

Step 1: Read the Rules and Judges Guide:

bmfa.org/DesktopModules/Bring2mind/DMX/D...PortalId=0&TabId=219

www.scalebmfa.co.uk/Forms/JUDGES%20GUIDES%20ISSUE%204.pdf

You should now have a good idea of what's required and what the judges are looking for. Points to take on board include that adequate scale documentation for the proposed model is vitally important in getting static marks. It's also important that, depending on the competition, the model should realistically produce most, or all of, the following: take-off, climb, cruise, transition, approach and landing. It will also need to fly for a minimum time between 10 and 30 seconds depending on the event chosen.

When choosing documentation, bear in mind that there is no such thing as an accurate three-view, and more importantly, the model will be judged to the photographs in preference to the three-view drawing. So use the photographs to build the model, not the drawing!

Step 2 - Chose a prototype that you can document and make fly.

Step 3 - review your documentation and the Rules to make sure they are compatible.

Step 4 - Draw up plans for the model

Step 5 - Start cutting wood...

Depending on how this thread progresses, I'll fill in more details later, but the above should be enough to be getting on with.

Great idea for a thread and very informative.

I'm still pretty much at the collecting documentation stage at the moment for my future project so your timing is excellent. I have a published 3 view of the full-size from AM and am currently pondering exactly which full-size example to go for.

I think I can make it fly but then that's part of the fun I guess. There are a few challenges it has to be said . I'm puzzling over size too. I fancy 1/12 scale which is a bit small perhaps. It's a size which worked well with the DH60 Moth and this would be a similar size which is what attracts me. Redfins while good seem to need a bit of a technique to get the to start quickly and consistency and good access to the comp screw to do it so I'm considering going a bit bigger for Mills .75. Or maybe a Banks .5cc or similar Mills would be better behaved.. or maybe the new Ukrainian Redfins are better handling.. so as you can see its very much early days

Fascinated to hear more

Always interested to read your jottings, Andy, always time well spent. I look forward to this one too.

Will you incorporate a few comments/thoughts on strategy? Assuming the reader is interested in designing and building for winning scale comps - maybe implicit but not always the case for everyone. Would you agree your recent win demonstrated there is a diminishing return on scale detail compared to good flight scores, for example?

What happens to the papers once delivered to the (other) forum?
N

I'll add more to this one when I have a bit more time, but post no 1, and a good read of the Rules and Judges Guide should be enough to be going on with....

In answer to your last question Nigel, it's not a Forum in the way that this is a Forum. The Free Flight Technical Committee sponsor a day of presentations in aid of their International travel fund after the BMFA Dinner at Coventry. They call it the Free Flight Forum. The papers are then published in a pamphlet at the following FF Nats at the princely sum of £12 ea inc post. You can find the details here:

freeflight.bmfa.org/free-flight-forum

It's time for an update.

The way the marking system works is that the judges give a mark out of 10 to the model under each heading. The marks given are multiplied by the K factor for the relevant section and the result summed. The K factors for static and flight each add up to 100. So each judge effectively gives marks out of 1000 each for static and flight. Thus, when both judges marks have been summed for static and flying, a maximum mark would be 4000 points.

A look at the recent Scale Indoor and Outdoor FF Nationals, show winning marks of around 3000

www.scalebmfa.co.uk/Results/Scale%20FF%2...onals%2028-05-17.pdf

www.scalebmfa.co.uk/Results/Scale%20Indo...0Nats%2023-04-17.pdf

In most cases, the static marks are roughly similar to the flight marks, which should imply that a high scoring model is a compromise between static and flight points. The exception could be my Lacey at the outdoor champs that scored 1290 for static and 1790 for flight. Bottom line here is that a good flight score will always take precedence over a mediocre static score. Ergo, whatever detail you put on the model and however accurate it is, it must still fly!

To score well in flight, the model must be stable, have good flight qualities and look realistic. Taking each in turn:

Stability - good lateral stability needs one or more of dihedral, sweepback and/or a high wing. Whatever natural stability you might have in the model will be helped by making the extremities light - the model will then have less inertia to overcome following an upset. Longitudinal stability required a forward C of G. This also helps a straight take off with conventional undercarriages (taildraggers). A forward C of G will also compensate for a small tailplane. Forget lifting tails, they are for duration models with large tailplanes and rearward C of Gs. If you must make the tailplane lift, make it lift downwards! The forward C of G may need excessive longitudinal dihedral (or decalage, the angle between the mean chord line of the wing and tailplane). Therefore make the elevators work and bend them up to a pre-determined position before flight.

Good flight qualities - lighter models fly better. This is why I nearly always choose silver for the finish on my models. It's the lightest pigment and has the best covering power. As an aside here, I tend to choose simple colour schemes too, they are much easier to repair than complex ones. Weight can also be reduced by making the models bend rather than break. Therefore, thinner wood, knock-off structures and lighter materials are de-rigeur!

Looking realistic - We need the model to have the right 'sit' in the air, so it's vitally important that the rigging angle of the wing and tailplane are appropriate. This can only be achieved by practice in flight.

Looking realistic is also a requirement in static judging. Accordingly, the surface finish must mirror that of the full-size. When we reduce the size of an aircraft, the depth and reflectivity of the surface finish changes. Shiny surfaces do not look right, they should be dulled. Colour should also be changed subtly to give the appearance of the full-size in model terms. Think of it as looking at the full-size from a distance rather than close too.

That's all for today......

I have read through the BMFA rules on documentation and they seem to be saying that all the photo's would not need to be of the scheme chosen for the model but could be of another full size example of the same mark. At least two would have to be of the chosen scheme though and some evidence of the correct colour would be needed.

Am I reading this correctly or should all the reference photos be of exactly the same scheme that has been modelled ?

Squirrelnet wrote: I have read through the BMFA rules on documentation and they seem to be saying that all the photo's would not need to be of the scheme chosen for the model but could be of another full size example of the same mark. At least two would have to be of the chosen scheme though and some evidence of the correct colour would be needed.

Am I reading this correctly or should all the reference photos be of exactly the same scheme that has been modelled ?

Good question Chris!

The requirement is as stated in the Rules. Practically, to enable the possibility of full marks, you need to adequately document the scheme on the subject aircraft, i.e. ideally top, bottom, left, right, forward and backward shots should be presented. However, pictures of other aircraft of the same mark can be used to help document the shape and detail on the subject aircraft.

If you go the route of using other aircraft shots, beware of any differences (there were quite a lot in the build of older aircraft) and if you use such photographs, annotate the differences accordingly.

We can talk in more detail at Old Warden next week if you're interested in following up.

That would be very useful