Help All:
I was recently told that I have been doing it all wrong for all of my C/L flying days!
I have been using 52' lines for .15-.25 powered planes and 60' lines for .29-.40 powered planes.
I have been told that I should be using 52'-58' lines for my .29-.40 powered planes. This information came from some very experienced stunt flyers. They cited better line tension with the shorter lines.
I have never noticed the lack of line tension when using 60" lines IF the engines were running well. I think that line length is determined by how much power the engine can provide. I have Noblers powered by an OS .40 S. and one powered by a HP .40. on 60' foot lines. When the engines and props are working correctly, I have plenty of line tension. I also use an OS .35S in a Midwest Me 109 and it too has tons of line tension on 60' lines.
Am I missing something? If I am happy with my lap speed, line tension and engine run, 4-2-4, what else could I need? How much line tension do you guys have when flying stunt?
It's more or less impossible to make blanket statements based on engine size. If what you have is working pretty well, I would suggest making a set a foot shorter, a foot longer, and see what effects it has. Note that you might have to re-trim it to optimize it at each point before you can make any good conclusions as to whether it is is better or not.
It's not really about line tension. If you hold the same lap time, you get more tension with *longer* lines, not shorter, because the airplane will have to go faster to maintain the same lap times, since it is further around. If you hold the same airspeed, then you will get more line tension with shorter lines, but the lap time will be shorter. That's all sort of beside the point, because the trim effects of even a foot or so of line will completely swamp these sort of static line tension effects.
Most people run shorter lines than would have been used in the olden days (of 25 years ago...) because you tend to get more control precision, and, we have much better control over the engine, so you can afford to let the maneuvers get physically smaller. Recall that the maneuver sizes are specified as angular dimensions, not absolute size, so the shorter the lines, the smaller the physical size of the maneuvers. Part of the possible advantage to running longer line is to give the airplane more room in which to maneuver - so shorter gives you less space.
With better engines we can corner harder and control the speed and acceleration, so you can use generally shorter lines and still maintain reasonable maneuver sizes.
Part of the trim changes you may have to deal with:
Shorter lines - less tip weight, more flap differential, leadouts forward, more handle spacing, less flap, less nose weight, less pitch, less wash-in, less venturi
Longer lines - more tip weight, less flap differential, leadouts aft, less handle spacing, more flap, more nose weight, more pitch, more wash-in, more venturi
The tip weight effect is obvious, I think. The fore-aft CG effect is less obvious. What tends to happen with longer lines is that you have less control force in the rounds, since they are larger, and the tracking tends to go away. You can get that back by moving the CG forward. The converse is that with smaller round loops, you have to apply more force to hold the radius, and moving the CG aft reduces that. The rest of the effects are for similar reasons and some of them ("wash-in? wash-in of what??*") are pretty obscure.
All that having been said, I suggest if you try one foot changes, just do it, and change *nothing*. If you are not already in optimal trim for your current system, you might be closer to optimal when you change. And it's really fast to change lines. I do suggest that you do something to make sure your line lengths are consistent enough that you can switch them without having to spend 5 flights setting the neutral.
Bottom line - start wherever you are, and experiment from there. Line length, even a foot, can make a remarkable difference, and you can't just say, a priori, what length to use. Old baffle-piston engines, like the Fox, I would run them as short as I thought I could get away with (because that's what Bob Gieseke said to do). But with anything llke a regular stunt plane, choose something about the same as what other people are using, and then experiment around there.
Brett
*wash-in in the prop pitch, i.e. how much, if any, the pitch increases at the tips.