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General control line discussion => Open Forum => Topic started by: Doug Moon on June 18, 2023, 10:02:24 PM
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I am setting up controls on a new plane. I usually use bushed horns with UHP clevises all the way through. The flap horn 1.25" to the top hole and 1" to the lower hole. Then the elevator horn is 1" so I have a 1:1 setup elevator to flap. I have used that for many years. Well this time I wanted to try ball links. I have Morris threaded horns I got many years ago at the nats. The flap horn has a tapped hole at 1.25" 1" and .75". The elevator horn is bushed at 1". When I use a lock nut or standard 4/40 nut with split washer on the back side of the horn it interferes with the ball link below and wont work. If I used a stand off the ball link is clear. See pic. NOTE: I will cut off the extra bolt length so that it is even with the lock nut. My question is will the bolts be strong enough when using a stand off in this configuration. My gut tells me this will not be sufficient and may bend and break over the long haul. What to you think?
Thank you
Doug
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Can you make something like this work? (single bolt of minimal total length, loaded both sides minimizes any twist load on horn) Especially good if you want option of faster elevator and still use a tall elevator horn...
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The pic looks like the flap horn is split? Are you trying to use a Paul Walker flap tweaker?
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You might look at Paul Walker's ball link elimination method.
http://flyinglines.org/pw.ballinks.html
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Recon you need them adjacent ,
OR
Braze hard brass tube across , so it completely alters the load path , as the bolts will be supported along a half inch or so , if the tubes the same length each side . :P
Like the man says , one ball joints enough for any man . ! S?P LL~
Looks also as if it could fall off outward , whereas it cant fall off inward . But people put a bit of wood , outboard , so it hits that instead if it trys too . ;D :(
Some might say STEEL TUBE across . rather'n brass . >:(
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No this is not a split horn. There is one ball link on either side.
The arm on horn in Threaded steel. So Brazing in bushings wont work on this one unless I drill it out and its already installed on the wing so that would be more difficult.
Dennis, they way you have will change the speed of the controls moving the BC to Flap horn link down closer to the horn...
hmmmm
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No this is not a split horn. There is one ball link on either side.
The arm on horn in Threaded steel. So Brazing in bushings wont work on this one unless I drill it out and its already installed on the wing so that would be more difficult.
Dennis, they way you have will change the speed of the controls moving the BC to Flap horn link down closer to the horn...
hmmmm
Yup, UNLESS you also have a tall horn on the elevator - which I try to do...
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I like Dennis’s idea, but with one ball link on each side of the horn instead of both on the same side. That would give the same torque on each pushrod as the original set up.
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Hi Doug
I feel your pain, been there. You don't want the aluminum standoffs that you show. Right side - left side will work ok ... you just have to get the ball links right up to the horn. Minimize the offset arm.
But, the stuff won't fit,.... I know .....
I was going to mail you some tiny 4-40 lock nuts that I ran across ...... but like so much stuff ... I put it up so I wouldn't loose it .... can't find it anywhere I'll keep looking, but we may try Grainger on someone like that. They are regular nylon lock nuts that are real tiny. They will give you the clearance. you need.
A second thought is 4-40 Heli-Coil inserts ..... just barely bigger than the bold itself .... You would have to CA them on though ... either that or "booger up" the threads on the bolt so they wouldn't come loose.
Frank
p.s. check the RC car section of the LHS
https://www.jhpfasteners.com/4-40-miniature-self-locking-self-clinching-nuts
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I've used several of these horns. I'd be concerned with rust in the screw holes. Run an oily tap through there, clean then re-oil. Great Planes made some plated 4-40 bolts, might be nice if you can find them. Not sure they were grade 8 though.
As to the other problem. Drill and tap the elevator horn at 11/16ths then use the 3/4" hole on the flap horn. Or, you could drill it 1:1 but, when I use adjustable elev horns they alway end up shorter than the mount point on the flap horn so, ymmv.
MM
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Doug,
Why would you want to use a ball link for stab pushrod at all? You could just solder a bronze tube directly through flap horn and use a simple L-shaped piano wire pushrod end. L
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I am setting up controls on a new plane. I usually use bushed horns with UHP clevises all the way through. The flap horn 1.25" to the top hole and 1" to the lower hole. Then the elevator horn is 1" so I have a 1:1 setup elevator to flap. I have used that for many years. Well this time I wanted to try ball links. I have Morris threaded horns I got many years ago at the nats. The flap horn has a tapped hole at 1.25" 1" and .75". The elevator horn is bushed at 1". When I use a lock nut or standard 4/40 nut with split washer on the back side of the horn it interferes with the ball link below and wont work. If I used a stand off the ball link is clear. See pic. NOTE: I will cut off the extra bolt length so that it is even with the lock nut. My question is will the bolts be strong enough when using a stand off in this configuration. My gut tells me this will not be sufficient and may bend and break over the long haul. What to you think?
Thank you
Doug
Hi Doug.....
I have been using the exact same method as you show in your picture for at least 5 years on 4 different airplanes.
Two of them are Rojett 67 powered.
As you mentioned, the bolts on mine are ground off flush with the face of the stop nut.
There is no interference because the plastic link won't rotate far enough to hit the nut.
The only real difference I can see is that I used the standard 4-40 ball link standoff. (heavy duty 4-40 links)
There has been no problems with any of them.
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I am setting up controls on a new plane. I usually use bushed horns with UHP clevises all the way through. The flap horn 1.25" to the top hole and 1" to the lower hole. Then the elevator horn is 1" so I have a 1:1 setup elevator to flap. I have used that for many years. Well this time I wanted to try ball links. I have Morris threaded horns I got many years ago at the nats. The flap horn has a tapped hole at 1.25" 1" and .75". The elevator horn is bushed at 1". When I use a lock nut or standard 4/40 nut with split washer on the back side of the horn it interferes with the ball link below and wont work. If I used a stand off the ball link is clear. See pic. NOTE: I will cut off the extra bolt length so that it is even with the lock nut. My question is will the bolts be strong enough when using a stand off in this configuration. My gut tells me this will not be sufficient and may bend and break over the long haul. What to you think?
Thank you
Doug
https://www.mcmaster.com/products/threaded-standoffs/thread-size~4-40/
Attached is a link to some 4/40 standoffs from Mcmaster Carr.
The threaded horn is not ideal because the length of the thread is not sufficient. It should be at least 1X the diameter or better yet 1 1/2X the thread diameter. Your UHP clevis probably more length for the thread if it is a threaded clevis).
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Doug;
Frank Williams mentioned low-profile lock nuts. I suspect he is thinking about 'jam nuts'. McMaster has then in 4-40 that measure 1/8" (one a bit less) in height. Might allow you to reduce the thickness of the spacer significantly...
https://www.mcmaster.com/products/nylon-jam-nuts/thread-size~4-40/
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You might look at Paul Walker's ball link elimination method.
http://flyinglines.org/pw.ballinks.html
This is a well engineered system. Looks like the ball joint clevis was drilled out for a pressed n bushing and the pivot is a shoulder screw (also available from Mcmaster Carr).
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This is a well engineered system. Looks like the ball joint clevis was drilled out for a pressed n bushing and the pivot is a shoulder screw (also available from Mcmaster Carr).
I HAVE SOME ROCKET CITY LINKS THAT COME WITH A SLEEVE RATHER THAN A BALL..WORKS PERFECT ON THE ELEVATOR END
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Doug, I am assuming you have a tall adjustable elevator horn. I had the exact same issue with Endgame I. I used a Dremel drill and a lot of profanity to made another hole 1/8" below the second hole and tapped it to 4-40. My horn was already mounted too so I did it carefully. The loss of leverage is minimal, and you can use the adjustable elevator horn to realign the ratio's.
Another thought, I am switching my game to metric since just about everything we use now is metric and I just ordered a zillion #M3 .5 metric Allen head bolts which are very close to UNC 4-40. They came with a zillion very small and thin nuts. The horns are easily tapped to M3 and since there is no pulling force on the threads it will not weaken anything.
You can always put them on opposite sides of the same hole (use the second) and get your ratio from the elevator horn.
Ken
Final thought, why are the holes on the "Morris" horns so close together? It is not like Ball Links are new.
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Doug, I am assuming you have a tall adjustable elevator horn. I had the exact same issue with Endgame I. I used a Dremel drill and a lot of profanity to made another hole 1/8" below the second hole and tapped it to 4-40. My horn was already mounted too so I did it carefully. The loss of leverage is minimal, and you can use the adjustable elevator horn to realign the ratio's.
Another thought, I am switching my game to metric since just about everything we use now is metric and I just ordered a zillion #M3 .5 metric Allen head bolts which are very close to UNC 4-40. They came with a zillion very small and thin nuts. The horns are easily tapped to M3 and since there is no pulling force on the threads it will not weaken anything.
You can always put them on opposite sides of the same hole (use the second) and get your ratio from the elevator horn.
Ken
YES, I ALSO USE A BALL LINK ON THE OTHER SO THERES NO BINDING....THE SLEEVE IS NOT MOVABLE SO THE PLASTIC LINK PIVOTS AROUND THE SLEEVE
Final thought, why are the holes on the "Morris" horns so close together? It is not like Ball Links are new.
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Hi Doug
I feel your pain, been there. You don't want the aluminum standoffs that you show. Right side - left side will work ok ... you just have to get the ball links right up to the horn. Minimize the offset arm.
But, the stuff won't fit,.... I know .....
I was going to mail you some tiny 4-40 lock nuts that I ran across ...... but like so much stuff ... I put it up so I wouldn't loose it .... can't find it anywhere I'll keep looking, but we may try Grainger on someone like that. They are regular nylon lock nuts that are real tiny. They will give you the clearance. you need.
A second thought is 4-40 Heli-Coil inserts ..... just barely bigger than the bold itself .... You would have to CA them on though ... either that or "booger up" the threads on the bolt so they wouldn't come loose.
Frank
p.s. check the RC car section of the LHS
https://www.jhpfasteners.com/4-40-miniature-self-locking-self-clinching-nuts
Haha! Frank I did the same thing. I used to have a small package of tine brass 4/40 locking nuts. Cant find them anywhere! I will keep searching for an option.
Helicoil insert is not a bad idea. I could use red loctite as well.
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Doug,
Why would you want to use a ball link for stab pushrod at all? You could just solder a bronze tube directly through flap horn and use a simple L-shaped piano wire pushrod end. L
My pushrodhas a threaded end on either side.
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https://www.mcmaster.com/products/threaded-standoffs/thread-size~4-40/
Attached is a link to some 4/40 standoffs from Mcmaster Carr.
The threaded horn is not ideal because the length of the thread is not sufficient. It should be at least 1X the diameter or better yet 1 1/2X the thread diameter. Your UHP clevis probably more length for the thread if it is a threaded clevis).
This is good to hear!
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https://www.mcmaster.com/products/threaded-standoffs/thread-size~4-40/
Attached is a link to some 4/40 standoffs from Mcmaster Carr.
The threaded horn is not ideal because the length of the thread is not sufficient. It should be at least 1X the diameter or better yet 1 1/2X the thread diameter. Your UHP clevis probably more length for the thread if it is a threaded clevis).
The standoffs I am using are simply spacers to keep the ball link out off of the but below. Bolt passes all the way through.
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I guess the main question I have is will the 4/40 bolt bend under load of a full sized rig with a 75 in it?
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I guess the main question I have is will the 4/40 bolt bend under load of a full sized rig with a 75 in it?
I do not think it will bend. I know we are all a bit gunshy after what happened to Matt. I have quite a large standoff on my new ship with the Rube Goldberg flap horn. Not enough flights to say for sure but there has been no distortion so far. I do have a hatch on my equally Rube Goldberg fuselage for inspecting the flap horn and I do it after each session.
Ken
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Doug,
If you want to keep going with your current approach, you might consider another option, using your "problem" to good advantage. In the sketch, I show two steel doublers that will sandwich the arm on the existing horn. One hole is clearance for your bolt size (around .112 for the 4-40) and one is threaded for 4-40. (If your horn is threaded then you would have to clearance the hole.) Be sure to put a shallow radius on the bottom to minimize the stress concentration from bending. The horn arm will suffer from lateral fatigue due to the weight of the pushrod and concentrating the stress with a sharp edge on the doubler is not good.
The parts are easy to make. Use some decent steel (4130 would be ideal) and thick enough to get 5 full threads if you can manage it. That's .125 thickness.
I wouldn't worry about bending of the bolts. That's not really the issue. You need sufficient preload in the bolts to prevent the joint from opening. Having the joint clamped solid prevents the bolt from bending up to a tensile failure. But the alternating stress in the bolt will cause fatigue. This isn't about control motion cycles, it is about engine vibration characteristics and the resonant frequency of the suspended pushrod(s) as a system. It is a lateral spring-mass system where the pushrods are the masses, and the horns are the cantilever springs. If the airframe vibration, as excited by the engine/prop combination shakes the frame, the pushrods will lag in phase and displacement. As you approach resonance, the system is getting pumped by the vibration energy coming from the unbalanced engine. At resonance, and without sufficient damping, it is only a matter of time before something breaks....
Another key advantage is that the joint is now clamped with two screws, not one. This makes it more failure resistant. The screws should definitely be high quality carbon steel capable of 160ksi, which we most often see in cap screws with the black oxide finish. Avoid the 300-series CRES screws since their yield strength is nowhere near as good. Also be skeptical of pan head or low profile screws unless you are sure of the grade.
The caveat here is (a) I have not done this before and make no claim as to adequacy; (b) sounds like you are running a honkin' engine which I have not done; (c) I didn't run any calculations for your design case, including the weight of your pushrods, the geometry of the control horn arm, etc.
I wish you success with your controls installation,
Dave
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I guess the main question I have is will the 4/40 bolt bend under load of a full sized rig with a 75 in it?
The offsets are a problem. You want to get the force of the output shaft as close to centered on the horn as possible. That is why the clevis is ideal (the UHP type). Keep in mind that if the bolt doesn't fail you will be stressing the other components in the system. Industrial actuators are all set up to be in line using clevises or self aligning couplers. Your system would not pass a mechanical design review (depending on the clown doing the reviewing). You might be able to remove a little material from one or both of the UHP clevises so that they clear one another on the flap horn, if this is possible.
That being said your system might last forever.
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Losi 4-40 miniature lock nuts #LOSA6306. Note that these are ALUMINUM.
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Would we be better to have a set of twin horns with the ball links captured between them? That should eliminate any asymmetrical loads on the ball links and prevent them from jumping off the ball.
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Would we be better to have a set of twin horns with the ball links captured between them? That should eliminate any asymmetrical loads on the ball links and prevent them from jumping off the ball.
The ball links are too large. The distance between hole 1 and hole 2 is 1/4". Nothing but a bushed L-bend rod or some super thin clevis connectors will work if you want to avoid using offsets. I have gone to over/under horns. No fighting over space and it lets the pushrod exit the bottom of the wing where a convenient hatch allows adjusting things, inspecting things, replacing things.
Ken
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Losi 4-40 miniature lock nuts #LOSA6306 ....... yes that the one
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I like Dennis’s idea, but with one ball link on each side of the horn instead of both on the same side. That would give the same torque on each pushrod as the original set up.
Hi Bruce:
Note that the rod from the bellcrank is in the middle, and the (resisting) connection from the flap is on one side and the elevator is on the other side. Thus, the stack up as shown is the only way to (roughly) balance the load either side of the rod from the bellcrank, any other stack puts BOTH the flap and the elevator on the same side of the ball link from the bellcrank pushrod.
BTW the flap horn is tapped for 4-40, it is not a deep or especially strong thread, but it does not have to be. It just makes it convenient to hold things together until the locking nut is torqued down. The stack is all metal to metal and can be clamped down securely.
Of course, to achieve 1:1 ratio requires that the elevator horn be as tall as the flap horn.
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If it’s not too late... whole lot lighter too.
Dave
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Dave, what material is that, how is it connected to the torque rod?
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Dave, what material is that, how is it connected to the torque rod?
That is 3/16" Delrin. MANY times stronger than nylon and itself a bearing material. It will never wear out. The 1/8" music wire has a small steel strap with holes that is brazed onto the wire (NOT soldered) Then the delrin is riveted to the steel strap.
Dave
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Hi Doug
Put the ball links on opposite sides of the horn directly touching the horn. Us the stand-off's (which are smaller than the nuts) on the OTHER side to provide clearance for the ball link then tighten the nuts on top of the stand-offs.
Does that provide adequate clearance? If not you might be able to file the diameter of the stand-offs down a little and still retain enough wall thickness for adequate crush strength...
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This is some really good stuff! Thank you all for the thoughtful responses. I do like Dave Hull's suggestion with the stacked steel spacer that is also attached at both bolt hole locations. This keeps the ball link in direct contact with the horn but spaces it off enough to clear.
I also like the simplicity of the Losi 4-40 miniature lock nuts #LOSA6306 These are the ones I had many years ago. I have lost them or used them all up. I will check local shop tomorrow. They have lots of car stuff. If they work then the standoffs will not be needed and the system will work as designed by Tom Morris many years ago.
Dennis Idea is simple as hell. I will try that and get back.
Another option I am thinking about is the split horn that Paul uses that allows for flap adjustment. That is also a possibility. I have a few more days to figure this out while I wait on covering. Once it gets here then it's decision time and move on and get this pup in the air and ready for Fall TT!
If you have more ideas keep it coming..
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Just to start moaning . ;D S?P
The ORIGINAL PICTURE , with a PA 75 , in a hurricane , or similar . !
Theres TORSION / Twisting . If you look Straight Down on it ( the Upright Arm ) theres Twisting Involved , with the offset - under ( severe ) load . like youd expect to get on occasion .
say a 20 kt. gust at a bottom of a square or wingover , Hr Glass etc . to be a bit pessimistic . Getting realistic you set up a sacrificial test piece , estimate load test input from handle loads ?
( holding on both hands leaning back , sweating grinning and bearing it . Or Estimate Load of flap twist . FOR a PA 75 Id think youd need a fairly durable horn . 16 g High Tensile ./ moly
or whatever . Id use 3/32 mild steel ? from 70's chrysler seat mount brackets ! and have . IF that in the picture were Mild steel , Id say youre doomed .
If it were fancy steel , will it exceed its elastic limit under load . If EVERYONE there uses them , on those , no worries ; That may well apply there .
Al, i was seeing was it may TWIST the vertical arm . Whereas a 1/8 steel pushrod in a 3/8 long bush , holds itself in alighnment . IF youre gouing to fly in foul weather ? .
https://www.youtube.com/watch?v=uz25O5W09pI
IF ALL your worried about is THE BOLTS , get some fancy AIRCRAFT QUALITY bolts of the appropriate grade to the purpose , as in a bit of sheer and cantalever . So NOT Brittle . Or CHEAP .
Taitanium'd do nicely . :)
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Last I looked for SHMS, they were almost always made in PRC, and neither cheap nor good. I'm not sure if I ever found any hecho en EUA. R%%%% Steve
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Well I tried some really small tight bolts and standoffs but couldn't get clearance. I went to the hardware store and got some steel and made my own horn with more spacing. Its way overkill too..hahaha! The lengths are the same but there is more spacing front and back to get the needed clearance.