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Author Topic: How to “easily” reduce pushrod travel on a built airplane?  (Read 1481 times)

Offline frank mccune

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      Hello All:

      What is the easiest to limit the pushrod travel on profile that is finished?  As it is now, the flaps and elevator have about 45 degrees in each direction!

        Methods that come to mind are:

         Block the travel of push rod by placing stops on the side of the fuselage or use a handle with close spacing.

         Longer horns.

          I would like to employ the lest invasive method as these planes (6) are ready to fly and are real beauties!

Online Tim Wescott

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Re: How to “easily” reduce pushrod travel on a built airplane?
« Reply #1 on: July 11, 2019, 08:34:42 AM »
You do use one handle and set of lines per airplane, yes?

If the spacing at the handle isn't drastically smaller than your other planes, just adjust it so that it flies nicely and have at it.  It's generally not a good idea to put hard stops in the aircraft except as a last-ditch effort to keep things from binding -- it doesn't do anything for control in the air, and it adds weight.

Post a picture of the flap horn -- if it's a typical setup, with the flap actuated by the bellcrank and the elevator actuated by the flap, then you may be able to move the bellcrank-to-flap link outward on the horn.
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Online Ken Culbertson

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Re: How to “easily” reduce pushrod travel on a built airplane?
« Reply #2 on: July 11, 2019, 09:29:03 AM »
      Hello All:

      What is the easiest to limit the pushrod travel on profile that is finished?  As it is now, the flaps and elevator have about 45 degrees in each direction!

        Methods that come to mind are:

         Block the travel of push rod by placing stops on the side of the fuselage or use a handle with close spacing.

         Longer horns.

          I would like to employ the lest invasive method as these planes (6) are ready to fly and are real beauties!
There really are only three ways to limit control.
Hole Location on the bellcrank, flap horn and elevator,
Line spacing at the handle, and
Stops.
The only way I would use stops is to prevent the bellcrank from over centering.

So that leaves me with the why question.  45 degrees is not too much control if you learn not to use it.  Restricting it only takes away an emergency tool.
So, why do you want to restrict the control?

No point in repeating Tim's suggestions because really, those are your only choices.

A recommendation for the future - make up a "jig" that lets you lay our your controls outside of the plane and get them doing exactly what you want before mounting them.  Tom Morris has a picture of one (don't think it is for sale) on the Stunt Hangar Hobby page.

Send us a picture and we will quit guessing and maybe actually have a solution!

Ken
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Online Brett Buck

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Re: How to “easily” reduce pushrod travel on a built airplane?
« Reply #3 on: July 11, 2019, 10:50:53 AM »
use a handle with close spacing.

         Longer horns.

    The fact that it moves a long way is not intrinsically a problem. The problem is if it moves a long way over a short movement of the leadouts; that is, the rate of movement is what matters, not how far it moves. This is resolved by reducing the rate by making the horns longer (preferably) or the handle spacing smaller (if you can't slow it down enough with longer horns, or it's impractical to change them).

    Brett

Online Tim Wescott

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Re: How to “easily” reduce pushrod travel on a built airplane?
« Reply #4 on: July 11, 2019, 11:14:14 AM »
    The fact that it moves a long way is not intrinsically a problem. The problem is if it moves a long way over a short movement of the leadouts; that is, the rate of movement is what matters, not how far it moves. This is resolved by reducing the rate by making the horns longer (preferably) or the handle spacing smaller (if you can't slow it down enough with longer horns, or it's impractical to change them).

I'm going to have to measure some planes when I get home, but on a full-sized stunter, if my surfaces are moving +/- 30 degrees and my leadouts are moving +/- 3" with respect to one another, then I'm a very happy camper.  The same amount of control deflection with +/- 2" at the leadouts is probably marginal, and that amount with +/- 1" is bad -- I'd work hard to correct it.  If you're getting 45 degrees with barely any leadout motion, then things are bad indeed.  If you're moving the leadouts 4" with respect to one another and getting 45 degrees, you're probably OK.
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Online Peter in Fairfax, VA

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Re: How to “easily” reduce pushrod travel on a built airplane?
« Reply #5 on: July 11, 2019, 12:03:56 PM »
Interesting thread.  Tim and Brett have made very good points here.

Seems the easiest thing to do is use a handle with close spacing.  I can't think of any downside to that, though I'd be interested to hear any thought as to why close spacing at the handle could, in itself, introduce a problem.  "Pulling less line" with close handle spacing would be expected to amplify any linkage slop relative to handle movement, but I doubt that's an issue.

If the setup is typical, and there is a bellcrank to flap horn linkage, I'm wondering how to extend the horn, in practice.  If it's a wire horn, removing it could be tough.  An idea for lengthening the horn would be to "sister" on an extension, probably by bolting the extension to the existing horn.  That would introduce a point of failure, and change the location of the pushrod, as well, which might make it not clear the wing.  A different lengthening idea is a new horn, a platform type typical in R/C or for sheet elevators in U/C.

Tim's idea to measure how much line pull gets 30 degrees was interesting, and I measured my two planes.  The one that tracks well in level flight measures 2-1/4".  The one that hunts a bit is 3".  The opposite of what I expected. But the rule of thumb is appreciated.

Peter

Online Brett Buck

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Re: How to “easily” reduce pushrod travel on a built airplane?
« Reply #6 on: July 11, 2019, 12:16:13 PM »
Interesting thread.  Tim and Brett have made very good points here.

Seems the easiest thing to do is use a handle with close spacing.  I can't think of any downside to that, though I'd be interested to hear any thought as to why close spacing at the handle could, in itself, introduce a problem.  "Pulling less line" with close handle spacing would be expected to amplify any linkage slop relative to handle movement, but I doubt that's an issue.

  That, and any compliance in the rest of the system (lines, handle) is exacerbated. You want the system in the airplane to be as slow as you can tolerate, and wider spacing, over a fast system and a narrow spacing. But, if it's already built and you can't access the system, you don't have any options. Build it different next time...

    Brett

Online Tim Wescott

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Re: How to “easily” reduce pushrod travel on a built airplane?
« Reply #7 on: July 11, 2019, 01:04:13 PM »
The one that tracks well in level flight measures 2-1/4".  The one that hunts a bit is 3".  The opposite of what I expected. But the rule of thumb is appreciated.

There's a lot of reasons that a model may hunt, and hunting is not closely related to too-fast controls.  If you have one that's too fast, and has narrow handle spacing to compensate, then it may be wonderful in level flight (because none of the other sources of hunting are present) but still be terribly soft when you ask it to do a square maneuver.

OTOH, if it hunts and it's too fast with narrow handle spacing, then the overall softness in the control system will make the hunting worse.
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Offline Perry Rose

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Re: How to “easily” reduce pushrod travel on a built airplane?
« Reply #8 on: July 11, 2019, 02:06:18 PM »
At the hardwre store get a piece of 1.5" x 1.5" thin wall aluminum angle. Then make a new flap horn with the bellcrank push rod higher up and the elevator pushrod lower down. The Pathfinder plans shows a very good optional flap horn that can be made longer to suit.
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Online Ken Culbertson

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Re: How to “easily” reduce pushrod travel on a built airplane?
« Reply #9 on: July 11, 2019, 03:12:25 PM »
I think we are overlooking a simple solution.  It is a profile and it does have a horn so by cutting off the existing horn at the base and adding a flap mounted horn you can create any new bellcrank to flap ratio you want.  Personally I hate the things but in your situation I would make an exception.  That may be exactly what Perry is suggesting except I would be more inclined to get one made for the task.  The RC guys have some really big horns (on their planes).

Ken
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Offline frank mccune

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Re: How to “easily” reduce pushrod travel on a built airplane?
« Reply #10 on: July 11, 2019, 03:35:46 PM »
     Thanks for all of the replies!

      Perhaps the real problem is that I also bought five other stunt profiles at the same sale that may also have the same problem.
     Since I have not flown any of these planes, I guess that I should first fly the plane in question and determine how well it would fit with my flying style.  How often does one use full handle deflection when flying the pattern?

     I do have handles that have closer line spacing that may be the answer.

     Again, thanks for the  help.

                                                                        Frank  McCune
     

Online Tim Wescott

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Re: How to “easily” reduce pushrod travel on a built airplane?
« Reply #11 on: July 11, 2019, 03:39:39 PM »
     Thanks for all of the replies!

      Perhaps the real problem is that I also bought five other stunt profiles at the same sale that may also have the same problem.

Do we even know if there's a problem?  How much do you have to move the leadouts to get that 45 degrees motion?
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Online Peter in Fairfax, VA

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Re: How to “easily” reduce pushrod travel on a built airplane?
« Reply #12 on: July 11, 2019, 04:00:20 PM »
There's an echo in here.  Also, when using a platform horn, I like to add 1/32" plywood at the base, glued to the flap / elevator.

>> A different lengthening idea is a new horn, a platform type typical in R/C or for sheet elevators in U/C.

> By cutting off the existing horn at the base and adding a flap mounted horn you can create any new bellcrank to flap ratio you want.  The RC guys have some really big horns.

Online Ken Culbertson

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Re: How to “easily” reduce pushrod travel on a built airplane?
« Reply #13 on: July 11, 2019, 04:05:27 PM »
       How often does one use full handle deflection when flying the pattern?   
Never!  Let me retract that.  I give it full up and down before taking off and I do use full down to stop the landing roll.

ken
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Offline Trostle

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Re: How to “easily” reduce pushrod travel on a built airplane?
« Reply #14 on: July 11, 2019, 04:14:10 PM »
Never!  Let me retract that.  I give it full up and down before taking off and I do use full down to stop the landing roll.

ken

That is interesting.  When do you give it full down on the take off?  Is this with a conventional gear?  I look forward to see you fly sometime.

Keith

Online Ken Culbertson

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Re: How to “easily” reduce pushrod travel on a built airplane?
« Reply #15 on: July 11, 2019, 04:50:41 PM »
That is interesting.  When do you give it full down on the take off?  Is this with a conventional gear?  I look forward to see you fly sometime.

Keith
I once had to rebuild a ship because I didn't test the full range of my controls before taking off.  Turned out that the bellcrank had over centered and I didn't know it.  Worst part is that I have been flying for 60 years and I did that last year. 

Sorry you took that to mean I actually gave it that much control on take off, no it is just before the release.  I use the full down to break on landing so that the guy up next doesn't have to walk half way around the circle mumbling things he thinks I can't hear.   I let it roll out in competition.

ken
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Offline Gary Dowler

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Re: How to “easily” reduce pushrod travel on a built airplane?
« Reply #16 on: July 11, 2019, 07:11:00 PM »
Pardon the butting in by the amature, but Tim mentioned the plane in question hunting. Any chance this is simply an issue with CG too far aft?  I know there are many reasons s it will hunt, and many have been brought up in this discussion , but I've yet to see a mention of CG, unless I overlooked it.

Gary
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Online Tim Wescott

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Re: How to “easily” reduce pushrod travel on a built airplane?
« Reply #17 on: July 11, 2019, 09:55:45 PM »
Pardon the butting in by the amature, but Tim mentioned the plane in question hunting. Any chance this is simply an issue with CG too far aft?  I know there are many reasons s it will hunt, and many have been brought up in this discussion , but I've yet to see a mention of CG, unless I overlooked it.

That was in a side discussion -- it's not really pertinent to Frank's original question.
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Online Peter in Fairfax, VA

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Re: How to “easily” reduce pushrod travel on a built airplane?
« Reply #18 on: July 12, 2019, 02:18:47 AM »
Can someone please explain this idea:

> At the hardwre store get a piece of 1.5" x 1.5" thin wall aluminum angle. Then make a new flap horn with the bellcrank push rod higher up and the elevator pushrod lower down. The Pathfinder plans shows a very good optional flap horn that can be made longer to suit.

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Re: How to “easily” reduce pushrod travel on a built airplane?
« Reply #19 on: July 12, 2019, 05:52:54 AM »
Ha, push rod on wrong hole in bellcrank, seen it many times before. Just get that sharp new #11 blade and slice right into the planking. No one will ever see it in a wing over.


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Offline Perry Rose

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Re: How to “easily” reduce pushrod travel on a built airplane?
« Reply #20 on: July 12, 2019, 01:26:46 PM »
Can someone please explain this idea:

> At the hardwre store get a piece of 1.5" x 1.5" thin wall aluminum angle. Then make a new flap horn with the bellcrank push rod higher up and the elevator pushrod lower down. The Pathfinder plans shows a very good optional flap horn that can be made longer to suit.
[/What do you need explained???quote]
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Online Peter in Fairfax, VA

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Re: How to “easily” reduce pushrod travel on a built airplane?
« Reply #21 on: July 12, 2019, 02:25:39 PM »
Perry,

Thanks for writing about the 1.5" x 1.5" aluminum angle idea.  Is the idea to disassemble the flaps off the airplane, remove the wing from the fuselage, remove the old horn, construct a new horn, and then assemble the airplane again?  Or, is it to use some portion of the aluminum angle and add it to the already installed flaps in some way? I'm going to assume this is similar to the Pathfinder plans you reference, though I do not have access to those.

Further explanation is appreciated, as it sounds like you are aware of a solution.

thanks again,

Peter

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Re: How to “easily” reduce pushrod travel on a built airplane?
« Reply #22 on: July 12, 2019, 09:59:36 PM »
You cut a 1/2" piece of the aluminum angle to make a longer flap horn that gets bolted to the flap surface. Since the controls are on the outside of a profile fuselage it's easy to get to.


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Online Peter in Fairfax, VA

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Re: How to “easily” reduce pushrod travel on a built airplane?
« Reply #23 on: July 13, 2019, 01:13:41 AM »
> cut a 1/2" piece of the aluminum angle to make a longer flap horn that gets bolted to the flap surface.
> Motorman

Got it, thanks.  Similar solution to bolting on a long R/C platform horn.

Offline Perry Rose

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Re: How to “easily” reduce pushrod travel on a built airplane?
« Reply #24 on: July 13, 2019, 05:07:58 AM »
Exactly.
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Online Ken Culbertson

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Re: How to “easily” reduce pushrod travel on a built airplane?
« Reply #25 on: July 13, 2019, 07:55:45 AM »
One thing I forgot to mention in suggesting the RC horn (I am an Aggie so using the words "Long" and "Horn" in the same sentence is not acceptable).  If the existing horn has a small diameter wire it may be a problem to mount a horn on one side.  Hold the inboard flap and see if you can move the outboard easily.  If you can then this will happen in flight and you are going to get a rolling motion.  It may not be much but it will be there.  I always mount my profile controls on the inboard side so that if I get roll from a weak horn it will be rolling out, not in.  You can fuss with the flap area to balance.  An 1/8" horn probably will not have a problem. 3/32 might be ok if good wire.  Most horns are designed to be driven from the center so that they flex about the same on both sides.

So, if your controls are on the outboard side and you have a weak horn then don't use my suggetion.

Ken
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Online Peter in Fairfax, VA

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Re: How to “easily” reduce pushrod travel on a built airplane?
« Reply #26 on: July 13, 2019, 03:40:02 PM »
Some thoughts on control throw based on today's flying experiences.

As others point out, a plane being "twitchy" and less stable in level flight is not necessarily linked to throw rates or limits. The basics of both turning tight and maintaining smooth level flight involve weight and balance.

Today, adding a Harry Higley Heavy Hub to a plane that hunted made it handle very differently.  Though it was only about two ounces of nose weight, the plane now tracks well.  Maintaining consistent level flight helps present a good stunt pattern.

Of course the plane does not turn as tight with a forward CG.  An even more precise adjustment is in this Brodak Profile Cardinal's future.

There are likely more advanced aspects to trimming for good level flight, including stab incidence angle, stab height, engine thrust angle, etc.  However, my experience is that getting the CG where you want it is an important primary step.

thanks,

Peter 

Online Ken Culbertson

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Re: How to “easily” reduce pushrod travel on a built airplane?
« Reply #27 on: November 04, 2019, 12:46:06 PM »
I'm going to have to measure some planes when I get home, but on a full-sized stunter, if my surfaces are moving +/- 30 degrees and my leadouts are moving +/- 3" with respect to one another, then I'm a very happy camper.  The same amount of control deflection with +/- 2" at the leadouts is probably marginal, and that amount with +/- 1" is bad -- I'd work hard to correct it.  If you're getting 45 degrees with barely any leadout motion, then things are bad indeed.  If you're moving the leadouts 4" with respect to one another and getting 45 degrees, you're probably OK.
Tim - This is an old thread but you have come closest to answering a question that came up yesterday.  I got a wing from a reputable source that already had the controls installed.  Contrary to my own advice I just left them alone but never really measured the movement.  BIG mistake.  I test flew the plane yesterday (electric so I fly them as soon as the airframe is sealed).  It was still super sensitive around neutral with the line spacing down to 2 1/2" at the handle.  1 1/2" line differential gives me 45 degrees flap.  We won't discuss how this went unnoticed until I was wrapping the leadouts.  So my question, since I am going to have to do major surgery is what is the preferred differential.  I can get to about 3" by moving the connection to the bellcrank in about 1/4".  Even 3/4" seems to be a lot.  I also can't find any "standard" on how many degrees the bellcrank should rotate.  I would think somewhere around 60 should be a maximum.

4" is not a good idea on a 4" bellcrank.  I got 3" on a 3" bellcrank my classic and it over-centered.  The flap pushrod is currently 1" from the bellcrank pivot which is excessive and probably costing me leverage.

I am willing to bet, given our extensive archives that these questions have been answered multiple times, I just can't find them.

Ken
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Offline Larry Renger

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Re: How to “easily” reduce pushrod travel on a built airplane?
« Reply #28 on: November 04, 2019, 01:21:15 PM »
A totally different solution is to use a Bob Palmer style control system.

Make a long horn for the elevator and run the pushrod back from the bellcrank back to the elevator horn. This gets rid of non linear angle problems. Then run a second pushrod forward from the elevator to the flap horn.

This allows great adjustment capabilities and has another beneficial feature. If you figure out the torques required to drive the system, the flap torque and elevator torques fight each other instead of reinforcing the bellcrank force required! Bye bye Netzband wall!

I did not think this up,  Bob taught me about it. (Sadly, yes, I am that old)
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Re: How to “easily” reduce pushrod travel on a built airplane?
« Reply #29 on: November 04, 2019, 01:42:58 PM »
If you figure out the torques required to drive the system, the flap torque and elevator torques fight each other instead of reinforcing the bellcrank force required!

Yes, the two hinges are torquing in opposite directions but the control horns are opposite top and bottom so they cancel each other out. The force on flaps and elevator still adds up against the bellcrank.

The non linear angle problem is solved by tilting the top connection of the flap horn forward 1/4".

You can adjust your elevator flap ratio without effecting the sensitivity from the bellcrank to the elevator but is it worth 2 full length pushrods.

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Online Brett Buck

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Re: How to “easily” reduce pushrod travel on a built airplane?
« Reply #30 on: November 04, 2019, 01:50:22 PM »
A totally different solution is to use a Bob Palmer style control system.

Make a long horn for the elevator and run the pushrod back from the bellcrank back to the elevator horn. This gets rid of non linear angle problems. Then run a second pushrod forward from the elevator to the flap horn.

This allows great adjustment capabilities and has another beneficial feature. If you figure out the torques required to drive the system, the flap torque and elevator torques fight each other instead of reinforcing the bellcrank force required! Bye bye Netzband wall!

   That doesn't work, and they don't cancel out, they still add. It reduces the load on the pushrod from the bellcrank to the flap. but that isn't an issue.

    Brett

   

Online Ken Culbertson

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Re: How to “easily” reduce pushrod travel on a built airplane?
« Reply #31 on: November 04, 2019, 02:18:08 PM »
A totally different solution is to use a Bob Palmer style control system.

Make a long horn for the elevator and run the pushrod back from the bellcrank back to the elevator horn. This gets rid of non linear angle problems. Then run a second pushrod forward from the elevator to the flap horn.

This allows great adjustment capabilities and has another beneficial feature. If you figure out the torques required to drive the system, the flap torque and elevator torques fight each other instead of reinforcing the bellcrank force required! Bye bye Netzband wall!

I did not think this up,  Bob taught me about it. (Sadly, yes, I am that old)
I have seen that done as well as separate pushrods and an "X" style bellcrank with one wire on each side.
(Sadly, yes, I am that old too!) They all worked but I see no real advantage over the classical setup unless you just needed some tail weight.  Unfortunately I have to restrict myself to things that can be fixed inside a 2" hole in top of the wing and a 1" in the bottom.  I am seriously considering a permanent removable hatch from the BC to the flap horn on the top.  Someone talk me off of the ledge! ~^

Just read the next three posts.  We are headed back into the weeds again which is cool, I like the weeds but I really need opinions on my earlier post before I cut big ugly holes in the top off of a perfectly good ship tonight.  If I am going to fix it I might as well do it right rather than another version of wrong.


ken
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Online Tim Wescott

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Re: How to “easily” reduce pushrod travel on a built airplane?
« Reply #32 on: November 04, 2019, 04:20:28 PM »
... before I cut big ugly holes in the top off of a perfectly good ship tonight.  If I am going to fix it I might as well do it right rather than another version of wrong.

The lesson that was handed to me by Paul Walker himself (actually, he gestured and said "take the plane!") is that you should just go ahead and whack holes in the thing, and you should make them as big as necessary.

I have a plane that he gave away, that shows obvious signs of cuts around the control system.  BIG cuts, top & bottom.  I'm pretty sure from the stories that I heard that he was trying to solve a hunting issue (he ended up cutting out the stabilizer and replacing it, as related in a build article for Flying Models).

So -- get out the knife, and cry as many tears as necessary while you do it, but get the job done (just don't cry on the bare wood -- that would warp it up).

And hey -- not only will you never make that mistake again, but there will be less to refinish this way.
AMA 64232

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

Online Tim Wescott

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Re: How to “easily” reduce pushrod travel on a built airplane?
« Reply #33 on: November 04, 2019, 04:22:33 PM »
I aim for around plus/minus 45 degrees on the bellcrank equaling about +/- 20 degrees on the flaps, and I try for +/- 60 degrees overall.  Just from memory that's what's going on inside the Atlantis.
AMA 64232

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

Offline Cody bishop

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Re: How to “easily” reduce pushrod travel on a built airplane?
« Reply #34 on: November 04, 2019, 06:03:59 PM »
A brodak push rod guide (flat head 4-40 screw with washer soldered in slot)  with a wheel collar on each side.

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