Stuka Stunt Main Forum · 15 of 15 known posts recovered
I'd like some feedback on the line length
recomendations for a "Nobler" around 40oz
in flying weight?
Sorry I can't be more specific.
Jim Thomerson
What Jim said.
Randy Powell
Jim Pollock
Now that is low (overhead). You should be able to trade off some "down below" tension for additional overhead. I remember Matt "borrowing" a ride from a fellow competitior a time back just to see how his plane flew and Matt was afraid to take it over 45 degrees the tension was so light. We are used to having tension all around, and that includes overhead. If your plane is 40 to 48 ounces in weight, then I can realistically see 7.5 to 9 pounds in level flight. But I would also expect at least half of that overhead.
But, back to the original question, it very definitely depends on the size of the plane, power plant, and how you have it set up. We were flying the 35 FP on essentially the same line length and lap speeds at the piped 61. In fact, I had a modified Magician I would fly on 70 foot lines at around 5.3 second lap times.
Just remember, there is a certain air speed that the plane must attain in order to fly correctly and this will vary with design, etc. A flapless plane will probably need to fly faster, and a weaker powered plane will need to fly on shorter lines, even if the lap speeds then turn out to be quicker.
For a ball park figure, Fox 35 type powered planes may be more comfortable around 60 foot lines. Bigger ship, with more power, maybe 65 to 70 foot. There are no absolutes. Even with the same plane and power plant, one person may prefer a different set up from another.
Leonard Neumann
Depends mostly on the engine. When I was flying a Nobler with a Fox, I was using 58' eyelet-to-eyelet, and based on what I know now, I would even look at shorter, particularly for a really light airplane like yours. But do that with a 25FP, and you'll screw yourself into the ground it'll be going so fast.
If you have a Fox, Stalker, Double Star, etc, I would start out at 57-58 and be ready to cut them down. With a Rustler/Merco, AeroTiger, Magnum 32/36, 25FP, think more like 62-65.
Brett+
Never stunt on an overlean engine!!
I guess what I'm actually asking is whether you guys keep lines of various lengths to try or custom cut a set for each plane?
George
Yes
(pause)
OK, the answer is that you will have a good "estimate" with the type of plane you are flying. If it is new, I will try with a set I have on hand of the approximate size I "think" will work. Once length has been determined, then it is time for a new set of lines if this is a plane I will be flying for a while, set a handle for it appropriately, and they become a matched set.
Leonard Neumann
I have a variety of line lengths on hand. Sometimes I borrow a set from another airplane to try if I don't have an extra set in approximately the right length. (I have a handle & line set for each airplane I'm flying regularly.) When I find the right length I make up a new set for the new airplane.
/\/\/
This one has me befuddled. 60 foot lines (probably 62 or so to the center of the plane) and 6 second lap times???? What engine/prop are you using? It seems to me that you need either a little more rpm out of the engine or more pitch in the prop. That plane is flying way too slow. Shorter lines will not increase the flying speed of the plane. You need to increase the plane speed. Your line size may be just fine.
Leonard Neumann
While there is no "magic formula" which will tell you what line length to use, consideration of the physics for uniform circular motion yields some useful simple formulas, which can help guide and inform your quest for the optimal line length for a given model.
The formulas are very easy to derive, and can be found in any high school or first year undergraduate physics text book. The only bother is in converting from "physics units" (meters, kilograms, seconds, newtons of force, meters/second for speeds) to "standard control line units" (feet for line length, ounces for model weight, pounds of line tension, seconds for lap times, MPH for speeds). This I have done, so that the "experimenter's units" used by control line flyers can be plugged into the formulas directly, and the results obtained are in familiar units as well:
Brackets {} contain the units in which each quantity is expressed.
T{pounds}=Total tension for *both* lines. Each line carries a load of T/2
W{ounces}=Model weight
R{feet}=line length, from center of circle to center line of model
V{MPH}=Flight speed of model.
t{seconds}=Lap time of model
I've carried all the decimal places on my calculator. The constants can be rounded as desired. I use "*" for multiplication and "/" for division.
Here are three useful relationships:
(I) V{MPH}=(4.283989982)*(R{feet}/t{seconds})
(II) T{pounds}=(0.004181496)*(V{MPH}*V{MPH})*(W{ounces})/R{feet}
(III) T{pounds}=(0.076741207)*W{ounces}*R{feet}/(t{sec}*t{sec})
These relationships are for level flight. An elementary application of Newton's second law yields a simple relationship for the reduction in line tension during overhead flight:
(IV) T(overhead)=T(level flight)- Weight of Model
T(overhead){pounds}=T(level flight){pounds}-W{ounces}/16
That is, the tension for the model directly overhead is the reduced from that in level flight by the model's weight. This is because directly overhead, the model's weight is now providing part of the force needed to keep the model accelerating in a circular path, and the line tension is reduced accordingly so that the *sum* of the weight and tension produce the same acceleration toward the circle center as in level flight.
Now let's look at our generic example: a 40 ounce airplane on 60' lines turning 5 second laps:
Formula (I) yields V=51.408 MPH
Formula (II) yields T=7.367 pounds
Formula (III) also yields T=7.367 pounds, as it must.
Formula (IV) indicates that the tension directly overhead will be reduced by the model's weight of 40 ounces (2.5 pounds) and therefore will fall to 4.867 pounds.
Probably the most important lesson is to note that the tension in the lines increases as the *square* of the speed, or equivalently, as the *inverse square* of the lap time. So the most effective method for improving line tension is to fly faster, at a given line length. Line tension will also increase inversely with line length, and in proportion to model weight, provided that the flying speed remains approximately constant.
The general rule of thumb is that small changes in line length will not change the flying speed much, that is, we neglect the additional drag due to longer lines, or the drag reduction due to shorter lines, both of which will change the flying speed. You can always *measure* the actual flying speed by measuring the lap time and using (I). It is also important to note that these formulas ignore lift generated by the fuselage which will produce additional tension in the lines. That's why the amount and distribution of side area can make such a pronounced difference in line tension, particularly in the overheads. And has been pointed out many times, you cannot dictate the flying speed to the airplane. Heavier airplanes must fly faster to fly at all. Once you determine at what speed the airplane is flying reasonably, (II)-(IV) can provide some guidance in tuning the line length to get reasonable lap times.
Finally, it should be easy to pop (I)-(IV) into a spread sheet to generate tables of flying speeds and line tensions given lap times and line lengths.
Have Fun!
Andrew Tomasch
AAAHHHH Don't you have to convert pounds the "Stones" to get correct mass vs pull of airplane???
Scott(not steven hawkin)Riese
Scott Riese
Well, slugs actually. Except that you can be sneaky and convert forces in Newtons into kilogram equivalent by throwing in the acceleration of gravity in the right spot
(9.8 meters/(second*second), don't you know).
Aren't you glad you asked? 
Hope it proves useful...
Andy Tomasch