Just replied to an email from 'BrightGarden.' He seems to think we are all blowing smoke....

I restated my post, above, in simpler terms.

Another advantage of MonoLine: Line tension is not essential to keeping control of the model! As mentioned above. The model DID get aloft and out to the end of the line, eventually...

Wa-a-ay back when, CL models published in mag articles had a few design quirks that look funny today. Rudders were offset MANY degrees to assure line tension, but the leadouts were usually straight out from the bellcrank, parallel to the "barn-door" (rectangular) wing's leading edge. Nowadays, we know about the effects of leadout rake due to line drag, and about possible problems from the leadout guides being too far apart.

Rudder offset can cause the model to fly crabbed w/respect to the direction of flight - unnecessary drag and compromise of control surface efficiency.

Line rake from the leadout guides to the CG is the important thing. Getting that wrong can cause the fuselage to fly yawed regarding the direction of flight - again unnecessary drag and compromise of control surface efficiency.

Even today, we don't often think to account for the curved path the fuselage travels. IF the model should fly "tangent" to its circular flight path, where do we put the reference point along the fuselage length? I feel the CG is the appropriate location.

(Pull force direction reaches the model at the leadout guides, along the direction of the center of the flying line wires or cables. Dynamically, if we 'aim' forces ahead or behind, above or below, the CG, the model will attempt to roll or yaw to align pull to the CG, as aimed through the leadout guides.)

So, on modern mid-size stunters, the prop is 10" to 15" forward of the CG, and the horizontal tail aero center is 20" to 30" aft of CG. (Roughly, your mileage may vary.) It is a simple geometric effort to find the 'natural' engine out-thrust angle when there is no built-in angle from the fuse centerline. With these sample numbers, we could find a 1.5° "automatic", "structural" engine offset, and about double that - 3° - fin/rudder offset even if they are aligned at 0° to the structure. I am not recommending turning the engine and tail in to yaw the model in to compensate that!

Thrust line, for example, causes very little loss of forward thrust unless the angle is extreme. (Side F= prop thrust * Sin ( (net) Offset angle) ) and remaining forward thrust is = prop thrust * Cos ( (net) Offset angle) ). THE main reason for some thrust offset is dynamic, not simply static. Prop thrust varies continuously, according to load. MAX Thrust occurs, probably, several feet into the takeoff roll, when the prop cleans up from a stalled condition. As the model accelerates from there, thrust load decreases. At steady, level flight conditions, the only applied thrust is that needed to meet the drag load of a clean model flying at a very low lift coefficient. (We use fuel, prop, and mixture settings to set this comfortable cruise condition. More lift causes more drag. Drag loads - as in turns and corners - rise, and increase engine loads.)

SO , when drag loads slow the model, thrust load increases. Its outward component also increases. If the model (never you, but always the model) does something disastrously dumb and loses a lot of forward speed, ONLY the thrust and its outward component increase. That outward component is the only life-line that might-could save the model. Its cost, in normal flight conditions, is slight, so why not - keeping the structural and added engine offset below 5° total.