Length of Lines

I was out flying my Prowler yesterday and getting slack lines on some overhead's. I running 5.2 sec laps on 62' lines. I feel I should shorten up to mid 50' or even low 50' length. Am I correct here or mistaken?

LAST EDITED ON Jun-13-06 AT 07:32 AM (CST)
 
Hi Steve:

If it were me, I'de be looking at leaving the lines same and flying the plane faster. My own experience has been that things improve faster with faster plane speed vs. shorter lines. In fact, I fly my .36 size 480 sq inch profile on 64' lines--and pretty much in any kind of flyable weather up to 25kts.

I fly at 5.2 - 5.0 laps so the plane is flying at a good speed.

All of the control response gets firmer and more positive with increased flight speed and the plane is better able to deal with wake turbulence, wind gusts, etc.

Shorter lines will do what you wish, but more speed, and even longer lines to maintain the lap times, will, in my opinion, be a better alternative. At least worth trying.

THe plane will need to be fine tweaked for trim of course--with any line length/speed change. Make sure it doesnt have any trim issues.

FWIW

Curt

PS: Noticed on picture that you have a substantial amount of rudder offset. Depending on leadout position, these could combine to give tension problems overhead. Anytime the plane loses energy (velocity) in maneuvers, the tension will drop (Ha!) since overhead is the lightest tension position anyway, it is easy to feel this result. Be certain you aren't flying too abrupt or too tight up top--these bleed energy pretty fast and can lead to issues.

I flew my Brokak 40 powered Oriental on 65' loop to loop lines all last year and didn't have any tension issues. Also no engine offset and no rudder offset. I was running at about 5.2/lap. It did get a bit light at the one windy comp I flew at but stayed out for the whole class 2 pattern. This year I am flying my Mo-Best on 65' lines and it too seems reasonably happy. Last sunday I did have some tension issues as I was having a problem getting the ST51 to run consistantly for the whole pattern I started off in the first round at 6.0/lap - quite scary for the reverse wingover and it held that most of the way through speeding up to 5.8/5.7 at the end. Managed OK as the wind was almost non-existant. after the first round the wind got up a bit, still light but a test flight showed that I was now too slow to risk the reverse wingover so I tweaked the needle to get me up to 5.6/5.7 at the start but after the outside loops it was up to around 5.2 and by the end it was tearing round at 4.9.5.0 with the inevitable affect on the accuracy of the pattern. Some advice that I was given was to find the speed that the model was happy at and then adjust the line length to give the lap times that the pilot is happy with.

Regards

Mike

LAST EDITED ON Jun-13-06 AT 09:19 AM (CST)
 
Hi Steve,

Nice looking Prowler!

Can you tell us your set up? Engine, prop, fuel, overall weight?

Could be a lot of things, but if it's good everywhere but the overheads, it could be LO position, tip weight, too much rudder offset, or lack of power. Plus some others!

>I was out flying my Prowler yesterday and getting slack
>lines on some overhead's. I running 5.2 sec laps on 62'
>lines. I feel I should shorten up to mid 50' or even low 50'
>length. Am I correct here or mistaken?

There are other causes besides line length and lap times, but I would start here. You are not looking for lap times as such, but air speed. The plane will need a certan air speed no matter what line length you fly it on. And that means the shorter the lines are, the shorter will be your lap times.

But you don't need to go as short as you were suggesting, nor may you even need to shorten the lines. Shortening the lines without adjusting the plane speed won't help (much). Get your plane speed first, then adjust lines as you feel best. But 62 foot lines for that plane may not be bad.

You can generally fly 5.2 to 5.3 second lap times with 66 to 68 foot lines. If you had 58 foot lines, then you would want to fly around 4.7 second lap times. At 62 feet, 5 second lap times might be closer to what is needed. (And since each plane is different and conditions will vary, you may need to adjust this).

One consideration is the plane and flying weight. Another big consideration is the engine pulling it and how it is set up. If you have a weak power plant with low potential thrust output, you are gong to need to fly faster. If you have a strong power plant with large thrust potential (when you turn the corner it doesn't bog down) you can fly somewhat slower laps. (Read that as "somewhat".)

Also, the final set up is up to you. Some people like to fly light on the lines and they know how to finesse the plane through the maneuvers and keep it at the end of the lines in each maneuver. Others (like myself) like the positive feel of the plane at the end of the lines. So your needs may be different from others.

Looking at the picture, I would think your leadouts are too far back and you have rudder offset, both of which will cause your problem. It also looks like you forgot to install an engine. A given airplane has an airspeed at which it flies best. The engine and prop need to work best at that speed. Then the line length can be adjusted to give a comfortable lap time and line tension at that flying speed. This is presuming the airplane is trimmed to fly well in the first place.

>I was out flying my Prowler yesterday and getting slack
>lines on some overhead's. I running 5.2 sec laps on 62'
>lines. I feel I should shorten up to mid 50' or even low 50'
>length. Am I correct here or mistaken?

Those are extremely short lines for that airplane. 5.2 seconds a lap on 62 foot line seems quite reasonable for this airplane and shouldn't result in a lot of problems. It could be a little faster but 50 feet at the same airspeed is 4.2 seconds/lap is crazy fast, and if anything, you should use 60-62 foot lines and crank up the engine or prop pitch if it isn't fast enough. That way you get more airspeed, instead of just dropping the lap time.

As others have mentioned, you have a huge amount of rudder offset and it looks like a fair bit of line rake. Both of these things are well-known to kill overhead line tension. Let me predict what you are feeling - tons and tons of line tension in low maneuvers, and dying off overheads. Very scary entries into the 4-leaf. And, when you look at the airplane, you are able so sight right along the leading edge, and teh outboard wheel is well behind the inboard wheel.

Straighten out the rudder (assuming it's glued on straight (and check it with rulers...)) to no more than about 1/8" offset, and put the leadouts about 3/4" behind the CG. You will have much less tension in level flight but more overhead. Be a little careful on the first flight, since your extreme offset might be covering for lack of tip weight or some other problem (like a tweak).

Hi Steve

How is the CG? you may need to add some nose weight. Just bolt a little on and try it again. I find the CG, leadout position and wingtip weight all work together to find that happy place.

Steve --

Great question, and a lot of great answers. I built a spreadsheet, and it says that the experts agree on a rather narrow range of actual airspeeds. Below 53 MPH and much over 55 MPH is pushing the envelope (If I did the math wrong, someone will call me on it). I did the math assuming an arm length of 24" and defined line length as center of airplane to center of handle. I don't know, and when one doesn't know, believe the experts do know -- especially when they all agree!

Larry Fulwider
"God thinks e and pi are round numbers"