1. Sometimes, not always?, a rudder and an engine offset is applied – I presume this is to keep the lines tight when influenced by wind and compensate for the yaw caused by the dragging control wires?
This is primarily to keep line tight at all time and all conditions.2. A weight (1/2 ounce) is placed on the outboard wingtip – I presume this is to compensate for the weight of the control lines? – why only ½ ounce?
Yes. However most modern stunt models have a weight box. as part of the trim process we adjust the weight to get the wings level in flight upright and inverted. Wings not level could be a warp and is fixed with a trim tab.3. The outboard wing is often slightly shorter than the inboard wing - as found elsewhere on this forum – this is because there is more lift on the outer wing as the wing is further out – presumably this would vary with the model wingspan and the length of the control lines?.
No. A longer inboard wing has more lift to help support the weight of the lines.4. The bell-crank can be placed anywhere in the wing are long as it’s on a structurally sound point and pushrods are kept relatively short?.
Yes.5. Bell-crank size: This varies between 2” and 4” – not sure why. Surely all that matters is the pushrod arm movement and this arm could be made as long as necessary? Is there a reason to use 4” instead of 2”? (Will make my own from printed circuit board fiberglass as I read somewhere that is strong enough).
Bell-crank size is part of the combination of line spacing on the handle. If it radically too big or too small it makes it hard to adjust handle line spacing to get a required control response feel. 6. Elevator control horns are sometimes on the top surface and sometimes on the bottom surface. This seems weird to me as you will have to fit your control handle with “up” to the rear for a control horn on the bottom surface and “up” to the front for a top mounted horn. (Seems dangerous, as you would have to check each time what is “up”, if you have several models)
No. All that matters is that you know which of the lead out is up and which is down. I mark mine red for up and black for down. ALWAYS check up-down at the handle every time you hook up a set of lines.7. Control line leadout: This is stressed as being important, but seems to vary greatly.
If 10 people make a suggestion, there are usually 10 opinions.
True. The important thing is to size them a little bigger than to size of the flying lines. As flying lines age you can replace them. Lead outs need to be robust enough to last the life of the model. I have seen the suggestion that you hang the model vertically and set the wire angle when the model is balanced, but this makes no sense. If your bellcrank is located at the cg point then the wires would be at right angles to the fuselage.
Owing to air resistance, the control lines will be always be slightly dragging behind the model, so it would make sense to takes these out at an angle to the rear, but sometimes (in the plans), the rear wire is perpendicular to the fuselage and the forward wire brought back close to the rear wire??, sometimes the rear wire is brought slightly forward and the front wire is brought back to about 0.5” between them.
Are the wires brought together because the lines will be close anyway when coming into the wingtip?
Why not bring both control wires out to the rear and split them to the top and bottom of the wingtip in that case?
? The location of the bell-crank doesn't matter. What matters is the exit point of the lines out the wing tip. Most modern stunt ship have adjustable lead outs. The lead outs are adjusted to get good line tension during level flight and overhead flight.8. What should the elevator travel be – some plans indicate 45 deg and some do not define this.
Go with what is suggested on the plans. In truth it takes less travel to control an airplane than to think.9. Is there any reason why an RC glow engine can’t be used in control line? – it would seem to be simple enough to arrange a clamped rod to control the engine revs.
Yes. I have done this. However a control line ventury weighs less than than an RC carb. I am not an engine expert but I am told that the internal timing of an RC engine is different then the inturnal timing of a control-line engine. I fly all electric.I do not need to build a model for competition (still no clubs around) but would like to build a first model that is as stable as possible.
PS where are you located?
Topic: Control line model design parameters (Read 4477 times)
