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General control line discussion => Open Forum => Topic started by: cory colquhoun on March 26, 2018, 09:49:11 PM
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Model : Brodak p40
Engine: la 46 ,with 11 x 5 apc
Weight: 54 oz dry
Lines : 62 foot eye to eye
Lap times 4.8 secs
Watch my son flying, it flys great upright and inverted but seems to go slack at the top of loops and in the over head manoeuvres ,do I need to move lead outs back a 1/8 “
Thanks cory
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There could be a number of reasons but I’d start be making sure there is a little engine offset outward-maybe one washer under the front mounting lugs then yes you can move the lead out back in say 3/32” increments and find a better spot. At that lap time line tension should never be lacking. If he is learning it would be better to slow it down to say 5.2-3 and use the lead out and engine offset for line tension. One thing- try to bee sure it balances something close to whatever the plans show. An airplane that is too nose heavy can pull like a bear down low but go slack up high pretty easily. You didn’t mention line weight. .015 is fine and you could trim the length to 60 ft. to help some.
Davee
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What Dave said, but don't go overboard on the engine offset. I usually aim for just enough engine (and fin) offset to be sure that it's not steering the plane into the center of the circle, and leave it at that. Loose on high is usually from the leadouts being too far forward, but they can be too far back, too -- if moving them back makes things worse, try moving them forward. If you've got a leadout slider, it's a good idea to mark your starting point.
Do you have Paul Walker's trimming article? http://flyinglines.org/walkerstunt.html (http://flyinglines.org/walkerstunt.html)
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I'm not an expert flier, but have given much attention over some years to the forums. If the plane is flying pretty well with the fuselage tangent to the circle and reasonable tension in level flight, it well may be that moving the lead-out exits a little forward (1/16" - 1/8") will actually increase tension up high. I know that seems counter-intuitive. I've had a couple planes that I set up pretty well off the board or inherited needing a bit more tension up high. Both of these planes benefited from moving the leadouts slightly forward.
I looked up the P-40's span on the Brodak site and just ran your numbers through "Line II" software, based on .018 lines. While its computed airspeed didn't quite match mine from your figures and my guestimate of handle position, they were close. It recommended a leadout exit 1.0" behind your c.g. I'm guessing that the recommended spacing would probably diminish with better matched numbers. Of course, "Line II" gives only a place to start.
SK
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One thing I learned and tested at VSC, if the line tension is good level, and reasonably good at 45 degrees and light on top, add a little tip weight before moving the lead out's.
Is it lighter on insides vs outsides? Or just light at the top of the circle?
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There is one washer engine offset and slight rudder offset, it doesn’t seem to pull like other planes of this size we have , and I it’s the inside loops it’s more noticeable, it has adjustable lead outs , at the moment it is set to plan will try a bit of tip weight , also it does seem a little touchy but improved when moved spacing in a notch,will mark position and try moving lead out back a hair, forecast looks calm this weekend for a test
015 lines
Thanks cory
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I'm not an expert flier, but have given much attention over some years to the forums. If the plane is flying pretty well with the fuselage tangent to the circle and reasonable tension in level flight, it well may be that moving the lead-out exits a little forward (1/16" - 1/8") will actually increase tension up high. I know that seems counter-intuitive...
The theory is that lines too far back will slow the plane down up top, you'll have less centrifugal force* on the lines, and thus less force overall.
* Or centripetal acceleration, depending on whether you believe that the universe revolves around you (https://en.wikipedia.org/wiki/Mach%27s_principle).
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I have both the ARF and kit P-40. The kit has an OS .46 LA 11.5 x 4 APC and 62 foot .015 lines. I just checked my leadout position and it's 3/16" behind the balance point which is 2 3/4 aft of the leading edge. About one ounce of tip weight. There is plenty of tension all around. I'm at sea level. My ARF is electric. And the further back the leadouts are the more the fuselage blanks out the flap and elevator.
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Your center of plane to handle line length is at least 65 ft. and your lap times are 4.8...Holy Cow that's Combat speeds (almost anyway). Slow things down to at least 5.2 second laps. Do this by either slowing the engine down or with a 11-4 prop if you still wish to run in the RPM rang you obviously are! Add some tip weight until the outboard wing drops when you perform a pull out from a wingover or square.
Find out where the CG is by balancing the airplane on a couple of dowels with pencil erasers on the ends at the fuselage area, and check it's location relative to the recommendation on the instructions/plans etc. You did read the instructions right? If it's more than about 1/8 inch off that recommendation then add some tail or nose weight to get it where it's supposed to be than set the leadouts about 3/4 inch behind that spot and then you are ready to start trimming!
Incidentally are the wings flying level when you're up right and inverted?...be sure by having someone else check them from outside the circle!
After doing all this and only afterwards get back to us!
Randy Cuberly
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Incidentally, The best prop for this application would likely be an APC 11.5-4 with a launch RPM around 9,500-9,600 RPM. This set up will likely give you about 5.2 second laps!
Randy Cuberly