You ARE the weakest link...  
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All Forums >> RC Airplanes >> Questions and Answers >> You ARE the weakest link...
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You ARE the weakest link... - 12/3/2002 10:50:22 AM   
rc_for_me



Posts: 97
Joined: 11/15/2002
From: Goodyear, AZ,
Status: offline 		I have been flying for about a year now with great success and even more enjoyment.

I have no "building" experience other than the several ARF's I have assembled. I always followed the assembly manual and took for granted that everything would be as it should.

My experience both flying and assembling brought me to the point of the Kyosho Majestic. It was going to be the first time where I was really going to get into the assembly of the aircraft. In the past, I was in more of a hurry to fly than to build.

I wanted the control linkages to be as strong and tight as possible. I did'nt have the experience to change out the standard wood dowel/threaded rod pushrods, but assembled them with care. I did replace the nylon/plastic clevises with Sullivan Gold-n-Clevises

I wanted it to be perfect. I bought and used a laser incidence meter to line everything up. Set up both high and low rates with my deflection meter. To my thinking it was setup perfect.

On it's maiden flight, it took off the ground just perfectly and straight as an arrow. I only had to add two clicks of up elev to trim it out. I've always heard the expression of "it flies like it is on rails". Well, I learned first hand what that meant.

On it's third flight of the day, I was testing it's rudder only turn capability. Suddenly, it rolled fully on to its side and dove for the ground. Being only about a half-a-crash high in elevation, it augured itself quit a hole in the alfalfa field.

I hope no one ever has to feel the disenheartment of crashing a brand new aircraft.

Upon inspecting the wreckage, I found that the rudder clevis and threaded rod had separated. Of course it difficult to tell if this was the cause or effect of the crash. But separation was possible in the direction of the turn, and the crash should have driven the pushrod through the clevis.

Mulling it over in my mind, I recalled that during assembly, the Sullivan clevis I installed vs the stock one did not seem very tight on it's threads. But I just figured that it was "good enough" for the rudder.

Learning that #2-56 clevises do not fit well on metric pushrods was a hard lesson to swallow.

This lengthy story brings me to my questions...

What are the best connector to use on the control horns. Clevises seem to slop just a bit where the clevis pin is fitted to through the control horn hole. Would a ball joint be preferable as it is screwed through the control horn?

As I work my way forward to the servo, the next joint is where either the clevis connects to the pushrod. Is the threaded connection good enough (provided I match the size properly). Perhaps I should solder the connection once adjusted. I don't think I need to worry about the threads turning, but slipping. Maybe using nylon vs metal clevises is the answer but then I've read how the nylon pin can break. Again I fall back to the ball joint as they are nylon with no pin to break and the control rod threads should be tight.

Then there is the pushrod itself. My only experience is with wood dowels and metal rods. But we have a wealth of choices available. Carbon Fiber, Wood, and Fiberglass rods. Metal rods inside plastic/nylon tubes, carbon fiber rods inside plastic/nylon tubes, plastic/nylon rods inside plastic/nylon tubes, etc. (Note: I started another thread Carbon Fiber Pushrods for Split Elevator and received great response and answers. Thanks)

How about at the servo end? I have seen lots of discussions here on the Universe on Z-bends vs Screw Lock connectors. But again I am intrigued by the ball link solution.

Maybe the answer is staring me in the face...there all good, just assemble them correctly in the first place.

I (like everybody I would imagine) am looking for the most secure with the least amount of play pushrod solution.

I am about to assemble a .40 Kyosho Flip3D Pattern/Aerobatic and a .60 Graupner Extra 300 Aerobatic. I would like to avoid pulling another "Majestic"

What are your favorite pushrod assemblies from the servo to the control horn?

Thank you all in advance for your time and considerationn

_____________________________

Jeff Nelson (RC_For_Me), Vice President,
Instructor Pilot, Arizona Model Cropdusters
       Post #: 1

You ARE the weakest link... - 12/3/2002 4:55:30 PM   
vinnie



Posts: 651
Joined: 1/7/2002
From: hollywood, MD, USA
Status: offline 		Jeff, I never use the metric pushrods, especially Kyosho's, since discovering they're smaller than 2-56 and brittle as well. Twice while making an L-bend the wire broke. I substitute 2-56 or 4-40 rods which I purchased in bulk from Great Planes with the approprite clevis.

_____________________________

Regards,
vinnie
AMA 680367

(in reply to rc_for_me)
       Post #: 2

You ARE the weakest link... - 3/10/2003 11:49:53 AM   
David Cutler



Posts: 2163
Joined: 9/13/2002
From: Los Angeles, CA, USA
Status: offline 		It's rather too easy to accidentally mix metric with 2-56 threaded rods; I've done it loads of times. The metric thread just binds and finally pulls out of the 2-56 clevis.

However, if you are really sure the clevis and the rod are both 2-56 that seems to be a good solution to the never-ending decision about what push rods to use.

my 2c worth!
David C.

(in reply to rc_for_me)
       Post #: 3

You ARE the weakest link... - 3/10/2003 4:25:11 PM   
RCaeroguy



Posts: 929
Joined: 5/7/2002
From: Arcade, NY, USA
Status: offline 		I use the Sullivan Gold-n-clevis all the time. Yes they do fit a little loose but I just use lock-tite on the threads. I don't use the clevis to adjust the pushrod but rather e-z connectors on the servo horns. I've NEVER had a problem (knocking on wood).

_____________________________

Where are all the good men dead: in the heart or in the head?

(in reply to rc_for_me)
       Post #: 4

You ARE the weakest link... - 3/10/2003 9:44:35 PM   
FLYBOY



Posts: 8691
Joined: 1/7/2002
From: Missoula, MT, USA
Status: offline 		I throw the metric stuff away and use 2-56 clevises and rods. I put a 2-56 nut on and when the clevis is set, tighten the nut to it and it won't slip around. You don't need to solder them. Kind of defeats the purpose of using a threaded coupler. Don't use ball links. they too can come off. I like the sullivan clevises that have the lock key on them. If i use the black dubro clevises, I tend to put fuel tubing over them to keep them on.

Sorry for your crash, its a hard lesson to learn. Just like anything else flying, take the time to do it right and it will work. If you do it quick just to get in the air and it is not right, chances are it will take the plane from you.

_____________________________

Fly it till the wings come off.

(in reply to rc_for_me)
       Post #: 5

You ARE the weakest link... - 3/11/2003 10:32:15 PM   
CafeenMan



Posts: 3906
Joined: 1/19/2003
From: Spring Hill, FL, USA
Status: offline 		I've built a couple ARF's for people and the hardware has been junk without exception. That black pushrod material is brittle and like you say, it doesn't fit American hardware. I just trash all the hardware that comes with ARF's and replace it with what I know works and is available. Sorry to hear about your plane. As much as it would be nice not to crash a brand new plane, it happens to everyone eventually. Fix it or build another and carry on.

_____________________________

Work is what I do for the love of it. A job is how I pay for it. :)
Please visit AirfieldModels.com

(in reply to rc_for_me)
       Post #: 6

You ARE the weakest link... - 3/12/2003 6:30:22 AM   
JohnBuckner



Posts: 3916
Joined: 12/23/2001
From: Kingman, AZ, USA
Status: online 		Sometime ARF hardware can be pretty poor but some of the Kyosho stuff I have attempted to use and given up on, is the bottom of the barrel.

John

_____________________________

"Keep your controllines tight"

(in reply to rc_for_me)
       Post #: 7

You ARE the weakest link... - 3/12/2003 6:38:50 AM   
YNOT



Posts: 2063
Joined: 11/29/2001
From: Lake Jackson, TX, USA
Status: offline 		It is staring you in the face. You have mentioned it several times. Ball links.

With the amount of stress on the aerobatic planes and the extreme forces you will put on that Flip, you want strong, slop free linkage.

Best stuff going is the carbon fiber pushrods with titanium ends, using Nelson ball links. Not the cheapest way to go, however the absolute best way to go. The Hanger 9 Titanium rods are great also, however you run into a length issue, they are too short for some applications, including your Flip.

Also, take in to consideration the control horns and servo arms you use. The standard nylon servo arms and control horns are OK, however they will flex. MK makes some great aluminum control horns and several people make great aluminum servo horns.

On two of my planes, I have over $100.00 in linkage, control horns and servo arms. In R/C, you get what you pay for. It is slop free and strong!

Central Hobbies has all this stuff. And if you really want to go crazy, do the ball bearing clevis with the ball links.

_____________________________

YNOT, Snap, Flip & Hover,
Tony D

(in reply to rc_for_me)
       Post #: 8

You ARE the weakest link... - 3/13/2003 8:07:53 PM   
rsallen13



Posts: 538
Joined: 5/20/2002
From: Montgomery, IL, USA
Status: offline 		You can use K&S 3060 thick walled tube that you cut to lenght also. These tubes can be tapped to accept 4-40. You insert a 2 inch 4-40 threaded rod about 1 inch into the tube. Lock the rod down witha nylon insert nut and the had a ball link. I tried to draw it in paint brush to show what it would look like as I don't have a digital camera.

Attachments
Click to see the file in new window.Attachment.bmp

(in reply to rc_for_me)
       Post #: 9

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