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Author Topic: Control line to freeflight conversion  (Read 1035 times)
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Fourfingers
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« on: March 09, 2017, 04:17:43 AM »

Not sure where this question belongs, but ..... (no, not there, thanks)
Often seen a nice f/f or RC model and thought "that might work as a C/L" -or vice-versa as well.
I know in general that CL are smaller, heavier and maybe less inclined to glide, maybe the CG Is differently located and wing TE to tail relative distances differ, but ...
Are there any guidng principles for plan conversion one way or the other -apart from dont bother of course.
Just askin'
Thanks.
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Robmoff
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« Reply #1 on: March 09, 2017, 05:06:20 AM »

It might be easier than you think.
Many, many years ago I was watching a combat bout and one of the Warlords had both control lines cut. It flew straight and level until oos (didn't take long!), but I can't say what the glide was like.
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Hepcat
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« Reply #2 on: March 09, 2017, 06:47:13 AM »

4F
I think you would have problems but assume you are changing a C/L to FF rubber this is the best advice I can think of offhand.

1. If it is a small C/L you might want to scale it up first.
2. Divide the wing area in square inches by 2 and call that the maximum weight you can use on the rubber version.
3. Check the tail volume coefficient by the formula (tail area x moment arm)/(wing area x chord) and you need an answer around about 1.
4. You will need some dihedral.  If a straight 'V' about 10 degrees.
5. The wing section will almost certainly need changing, probably to a flat bottom, cambered top, about 10% thick.

John

« Last Edit: March 09, 2017, 06:58:39 AM by Hepcat » Logged
Fourfingers
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« Reply #3 on: March 12, 2017, 02:19:16 PM »

Thanks Gents for the comments.  Im thinking the other way round-ie free flight to control line.  But food for thought there.  I shall probably br guided by that old saw: "if it looks right, she'll be right".  Not sure of original context, mind.
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greggles47
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« Reply #4 on: March 12, 2017, 07:36:26 PM »

When you remember that the original CL planes were converted (even just tethered) FF models, it's not a big step you're planning.
A lot will depend on the planned flight envelope of your model. If you just want to fly mostly level laps the big issue will be where to place the CG and where on the wing to put the lead outs.
Have you a particular model in mind to convert?
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Hepcat
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« Reply #5 on: March 12, 2017, 10:47:53 PM »

Quote from #3 - "if it looks right it'll be right."

One of the oldest misquotes and dangerous if used in an engineering context. I believe the original was: "If it is right it looks right."

John
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ZK-AUD
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« Reply #6 on: March 13, 2017, 03:31:27 AM »

Some years ago I built a 1940s British control liner called Candy II.  This was a largish low winger with an elliptical Clark Y wing with both dihedral and incidence.   It needed down elevator all the time not surprisingly.   With a Miles-ish canopy it really looked the part.  Originally I flew it with a Forster .29 sparkie but this was a bit gutless so I re-engined it with  PAW.29 diesel which had a ton of grunt.  On reflection this was the original free flight model on lines.  With the big PAW on board I could loop and wingover nicely.  One unfortunate day I was flying it on my years-old, far-too- light,  kinked and buggered  A-class lines when they both snapped at the handle end as I pulled out of a loop.  The weight of 55 ft of lines balanced the opposite rudder nicely leaving a gentle circle to the right.  It did this for a while scribing gentle circles over about 500 metres of sky until it lost the plot and crashed not far from my feet!       
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fred
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« Reply #7 on: March 13, 2017, 06:04:32 PM »

As an 11 year old I was handed a quite nice Balsa low winger. It was V light. Thought it might Freeflight.
 So I centered the elevator and the rudder, fitted a COX baby bee to it and Tossed it.
It flew straight as an arrow.. into a seemingly 300' diameter loop.  It seemingly came straight at me on the downside of the loop.
Happily it didn't smack the ground on the loop bottom, merely got low enough to stop the prop.
 Not a scratch on it.. or me.
Removed my cox and never tried that again.
 Ever been to a Fast Combat match?
Before the engine cutoff device rules..  these often flew away. after a line cut.  Sometimes travelling a 1/2 mile or more.
Fascinating to watch the things gyrate all over the sky.. till the fuel ran out.
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