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Author Topic: Leadout Bend Angle  (Read 7399 times)

Offline Howard Rush

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Leadout Bend Angle
« on: January 03, 2015, 02:04:42 AM »
I got to wondering what angle the leadout wires make at the wing tip where they get pinched by guides that aren't usually as far apart as the spacing at the bellcrank.  We use rather fat cable.  I was wondering about the springiness they add (as handle cables do) as well as friction.  I made a little add-on to the control geometry program so I could see the effects of different stuff.  Here's a sample plot.  

In this sample:
Bellcrank is on the CG
Forward leadout is 2.1" aft of CG
Aft leadout is 2.35" aft of CG
Distance from leadout guides to bellcrank pivot is about 29.4"
Bellcrank and leadouts are on the X-Y plane (X is on the chord, Y is parallel to the span)
Bellcrank diameter is 4"
Bellcrank is skewed so it is approximately perpendicular to the average leadout angle at neutral.

What do you think?
The Jive Combat Team
Making combat and stunt great again

Offline Russell Shaffer

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Re: Leadout Bend Angle
« Reply #1 on: January 04, 2015, 10:59:04 AM »
If friction is significant, it wouldn't be very difficult to build roller guides.  Maybe print the rollers on your vortex machine?  Maybe put the rollers near but not at the wingtip and use standard leadout guide construction?

Russell Shaffer
Klamath Falls, Oregon
Just North of the California border

Offline Dennis Toth

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Re: Leadout Bend Angle
« Reply #2 on: January 10, 2015, 02:30:36 PM »
Howard,
I agree with Russell, the friction is a major problem. I went through a problem with solid leadouts were I had 3/4" tubing in the guide and it was a very close fit to the wire. The problem was around neutral the ship would hedge-hop. I changed to cable leadouts (this was on my bipe with exposed leadouts) and that solved the problem.

It seems that to get the leads perfectly in-line is likely impossible for all flight conditions. Using the shortest length of leadout guide helps. Russell's roller idea should reduce the friction problem but it seems like a lot of work. I have been using short nylon eyelets or the short brass ones from Sig seems to work well with the cable. Solid leads are another story and need lots of slop to prevent pinching.

Best,       DennisT

Online Brett Buck

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Re: Leadout Bend Angle
« Reply #3 on: January 11, 2015, 12:04:30 AM »
BTW, this (and other friction sources) is VASTLY more critical on electrics. With an IC engine, the vibration tends to break free any stuck control parts. With electrics, the controls stick very easily.

   We had previously speculated that the electric tendency to hunt was a function of some aerodynamic effect where the boundary layer transitions or some other undefined mystery phenomenon was at work. Recently I flew an electric that hunted *severely*. I don't know why I hadn't noticed before, but it was perfectly clear that I was moving the handle and the lines were sagging differently but the airplane kept doing what it was doing - until I put in enough control to break it loose, at which point it went too far, in a classic sticky control system hunt. I was stunned at how well the pilot managed to fly it, but all he did was get some oil on the controls and it went away completely.

   I am again convinced that aerodynamics essentially never cause hunting - it's almost always some control system drag.

    Brett

Offline Howard Rush

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Re: Leadout Bend Angle
« Reply #4 on: January 11, 2015, 02:14:19 AM »
What to do about it?  I'm dithering.
The Jive Combat Team
Making combat and stunt great again

Offline Russell Shaffer

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Re: Leadout Bend Angle
« Reply #5 on: January 11, 2015, 09:26:56 AM »
If all that's needed is some vibration it should be easy to get just the right amount. 
Russell Shaffer
Klamath Falls, Oregon
Just North of the California border

Online Brett Buck

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Re: Leadout Bend Angle
« Reply #6 on: January 11, 2015, 12:35:12 PM »
If all that's needed is some vibration it should be easy to get just the right amount. 

   Right, but now you are back to having build the airplane up to handle the vibration. Many/most of them I have seen are very lightly constructed to  take advantage of the lack of vibration to offset the weight of the system.

    After grasped the issue, I stopped work on the current airplane and am contemplating cutting the wing back apart to alter the bellcrank bearings, and am redesigning the fuselage.

     Brett

Offline Paul Smith

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Re: Leadout Bend Angle
« Reply #7 on: January 11, 2015, 07:15:35 PM »
BTW, this (and other friction sources) is VASTLY more critical on electrics. With an IC engine, the vibration tends to break free any stuck control parts. With electrics, the controls stick very easily.

   We had previously speculated that the electric tendency to hunt was a function of some aerodynamic effect where the boundary layer transitions or some other undefined mystery phenomenon was at work. Recently I flew an electric that hunted *severely*. I don't know why I hadn't noticed before, but it was perfectly clear that I was moving the handle and the lines were sagging differently but the airplane kept doing what it was doing - until I put in enough control to break it loose, at which point it went too far, in a classic sticky control system hunt. I was stunned at how well the pilot managed to fly it, but all he did was get some oil on the controls and it went away completely.

   I am again convinced that aerodynamics essentially never cause hunting - it's almost always some control system drag.

    Brett

Perhaps the necessary vibration could be synthesized by clipping a playing card into the prop arc with a clothes pin, or just using a regular engine.
Paul Smith

Offline Tim Wescott

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Re: Leadout Bend Angle
« Reply #8 on: January 11, 2015, 07:46:50 PM »
    After grasped the issue, I stopped work on the current airplane and am contemplating cutting the wing back apart to alter the bellcrank bearings, and am redesigning the fuselage.

You're not going electric, are you?  If not, why the work?
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Howard Rush

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Re: Leadout Bend Angle
« Reply #9 on: January 12, 2015, 12:48:24 AM »
Perhaps the necessary vibration could be synthesized by clipping a playing card into the prop arc with a clothes pin, or just using a regular engine.

Good idea, Paul. I didn't think of that, but I had one with me at the field all along: my dad told me to always keep a jack in the car. This would have been a good application for it.
The Jive Combat Team
Making combat and stunt great again

Online Brett Buck

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Re: Leadout Bend Angle
« Reply #10 on: January 12, 2015, 01:55:31 PM »
You're not going electric, are you?  If not, why the work?

  I have tried every new powerplant there has been since about 1979, so yes.  I am going to see how it goes, and see how it compares to what I already have.

   I haven't tended to be an early adopter, but in this case, we have been trying to make engines run like electric motors since about 1995 anyway, and managed to get pretty darn close, so I don't think I am at much, if any, disadvantage.

  My competitive weakness are not in the equipment realm, more like in the motivation realm. I was doing pretty good all week at the NATs, until Saturday morning, and I just wasn't "on" that particular day. I used to overdo it and have to try to calm myself down, now, I have trouble keeping my concentration for a whole week, even in the flyoff.

   Brett

Online Jim Kraft

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Re: Leadout Bend Angle
« Reply #11 on: January 17, 2015, 07:34:39 AM »
There is no sticky lines when running an Anderson Spitfire unless you have real problems. Howard, I would recommend using the club instead of the jack. You will still have an ace in the hole.
« Last Edit: January 17, 2015, 08:23:42 AM by Jim Kraft »
Jim Kraft


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