Flying F4B models
(These tips apply equally to Sport Scale and 3 Line Bellcranks)
If you already have or are thinking of taking up the F4B challenge then you are perhaps wondering as to the best method of making the electronic/electrical connection from the lines to model. I have seen numerous methods but I have again Vladimir Kusy to thank for this method and to my mind it is the best solution I have yet seen.
Cut a short length of copper tube about 1 inch long (10 or 12 gauge) .
Strip about 4 inches of the insulation from the end of the lines.
Pass the stripped wire through the copper tube.
Fold the wire back on itself and push it into the copper tube.
Once in position crimp the brass tube to hold the wire securely.
Clean the surface of the copper tube and solder the wire from the electrical connector to it.
Cover the whole connection with the appropriately sized Heat Shrink plastic sleeving.
This method has the advantage over others, in that, in the event of a break occurring in the electrical wire it may be replaced once the shrink sleeving has been removed. If the tubing used had been aluminium and the electrical wire crimped within the tube along with the flying wire then replacement would be impossible.
Note: this method may be used for making up conventional line connections, use smaller diameter aluminium tubing.
3 Line System, Bellcrank and Handle
A previous article in Aeromodeller which showed my method of positioning of the bellcrank on a scale Control-Line model [half an inch inboard and half an inch rearward of the CG] has raised the question once again as to whether the position of the bellcrank is critical ? The theorists will tell you that it isnt and they are correct. But what is critical is the fact that scale fliers require very stable models. As the models we fly are relatively heavy and not over-powered we want our models to fly in the most realistic and efficient manner possible.
Indeed, it is not the position of the bellcrank that I am trying to establish, it is the leadout guide position !
The position for the bellcrank/leadout guide I recommend is tried and proven and will enable your model to recover from some very nasty flying situations eg; buffeting in high winds / poor take-offs.
Draw a line at 90 degrees (relative to the model centre line) at the bellcrank rear most lead-out hole. Follow this line out to the wing tip and position the leadout guide on this line.
It is the leadout guide position that is critical and it is this position that will be the saviour of your model. Routing all of your lines through this one leadout guide is part and parcel of my method.
The origins of Control line flying were Tethered models flown on a single line attached to the wing tip!
You may position the bellcrank anywhere you like, but firstly it will look silly two inches back of the wing and second, a position that does not create (as near as possible) a direct line to the fliers control handle will result in extra friction at the leadout position and cause kinking in the lines. Ideally the bellcrank position best suited for balance would be directly on the centre of gravity, allowing for a well balanced model. But we have a need to maintain line tension and also to reduce over sensitivity.
Other considerations for scale models have to be made regarding the position of the scale cockpit and scale pilots legs relative to the bellcrank. I try and position my bellcrank so that it lines up with a side view centre line drawn through the propeller on my low wing subjects. Moving the bellcrank mount to a lower position has not been a problem in my experience. Positioning the bellcrank as suggested will find the leadout guide position for your model, attach the leadout guide to the models wing tip. I use a loop of 20g piano wire epoxied into the block tip [again, assumes low wing type] see fig 4. You may of course opt to use two or three guides, but as you move them forwards line tension will reduce.
Always ensure that the bellcrank and pushrods are completely free running with NO sticky or tight flap / elevator hinges. Try this test - Hold your handle up in the air with the lines hanging slack (not touching the ground) and try to operate your elevator if it will not move without line tension then recovery from a flying situation where the lines have become slack will be impossible !!
Further aids to safe flights.
Rudder off-set should be kept to a minimum. I recommend using between 5 and 10 degrees of off-set as any more will cause the model to adopt a crabbing attitude in the air - remember we are still looking for realism.
For smaller or lighter models I have used about 1 ounce of lead embedded into the outboard tip. As my models have become larger and have required thicker lines I have now increased the amount of weight to 2 ounces. The insulated lines that Im about to use are much thicker still, but as there are only two of them as opposed to three uninsulated lines I have not increased the tip weight.
Some deflection may be used. In my experience only the slightest amount could be used [inboard down / outboard up]. Keep any deflection equal as the static judges will notice any difference. Using large amounts of aileron deflection could have catastrophic results if you plan to fly Wingovers or Loops, so bear this in mind.
Before you leave for the flying feild check for any wing warps (be honest with yourself), if there are any, try and remove them, if you are unable to remedy the situation then you may use aileron deflection to counter the problem.
Check undercarriage tracking.
Undercarriages / take offs / taxiing are perennial problems for the control line flier as there are conflicting needs for the model to fly whilst pulling away from the pilot and for the model to taxi in the opposite direction. The choice of scale subject you choose will have the greatest influence on your ground handling experiences. If the full size subject was a so and so on the ground then there is little chance that its 1/7 th scale version will behave any better ! especially as we are going to ask it to scuff around anti-clockwise on the end of a set of lines !
Before initial flights are undertaken check that the wheels are free running and tracking in a straight line. Take your new model to a tarmac or concrete site and test by pushing the model along the ground. I prefer to have the model run in a straight line and not to the right or left, the model may be encouraged to keep its nose pointing out of the flying circle by careful leading with the control handle and lines. It is always preferable to lead the model on take-off by holding the handle higher than normal (to avoid snagging the lines on the tarmac) and also forward of your body (a la whipping style). Return to a normal flying style once a good flying speed has been attained.
Making the undercarriage construction material as stiff as possible is probably all else you can do to aid your cause, as the length and thickness of the scale undercarriage is already determined.
Do not rely on an off-set tail wheel to keep the nose pointing out of the circle.
Using the aforementioned modifications will do away with the need for any engine off-set, thus keeping the scale lines clean .
Test, test and test again is my motto, if your engine is fully cowled (it should be) then the need for good cooling is paramount, if the engine wont hold maximum RPM on the ground then you can be sure that it will overheat whilst flying .