Push rods
 

Hi to everybody.

I am finishing my first pattern plane (Kaos) and need advice on push rods to rudder and elevator.
On smaller planes I used with success wooden push rods, steel wire and flexible push rods.

For this proyect I would prefer wooden rods. Did anybody used it? Did you support them at the end and in the middle in order to prevent vibrations?

Another question is how did you make "Y split" for elevator.
Any photo would help.

Regards,
Marian

RE: Push rods
 

I have used wooden push rods with great success. I usually add as little metal rod as possible at the end to keep it stiff.

For the split elevator push rods I drill a hole in the wooden rod. I then make "L" bends in the rods and stick them in with a touch of glue and wrap string tightly around the whole thing followed by a piece of heat shrink tubing. Then I go up about half an inch and wind some thin wire around the two rods. I then heat the wire and rod and wick some solder in.

PS: The Kaos was a GREAT choice! Have fun!

http://members.cox.net/scaleaviator/Pushrod.jpg

RE: Push rods
 

Thank you Nathan.

What kind of wood did you use and which section?
What was diameter of the wire?

RE: Push rods
 

For the Kaos 1/4 square hard balsa pushrods with 2-56 steel ends works just fine, so long as you keep the wire as straight and short as possible. This way, there is no trim change with temperature change, which is a bit of a pain with the normal flexi rods.
Evan.

RE: Push rods
 

Evan,

Did you install any support of the rod? My concern is excesive vibration.
Marian

RE: Push rods
 

Arrow shafts work good too. ;)

RE: Push rods
 

Tim, I've been wanting to use some arrow shafts, not only for push rods, but to make a simple wing jig (based on the RCM/Great Planes type). The problem is that even at discount places like Dick's Sporting Goods they are very expensive. So, I have used the Dave Brown fiberglass ones instead.

David

RE: Push rods
 

Tim,
If I may...
I assembled a Focus II over the Winter.
It calls for a single arrow shaft (Dave Brown) type elevator pushrod Y'd at the tail.
They recommend a brace for the arrow shaft mid length.
This can be a simple pair of balsa cross pieces above and below or a foam bearing the shaft runs thru.
Post #22 in this thread shows a picture of how one guy did it.
http://www.rcuniverse.com/forum/m_52..._2/key_/tm.htm
I ended up installing two elevator servos in the tail so I didn't have to use the brace.
They do caution you that elevator flutter can be induced by the vibration of the pushrod.
Hope this helps!
JLK

RE: Push rods
 

Could you explain me what "arrow shafts" are?

RE: Push rods
 

I like the Dave Brown shafts also...I'm a bit un-easy using 2/56dia rod...I try my best to use 4/40 stuff for all my control linkages...I may use 2/56 on 40 size aircraft..But that's about it for *Me*...Anything bigger gets 4/40...I'm just kinda particular like that?? Oh Well..

Here is a link to the Dave Brown pushrods..
http://www2.towerhobbies.com/cgi-bin...?&I=LXB901&P=7
http://www.dbproducts.com/store/prds.htm

I have some Carbon Fiber pushrod also:
http://www.centralhobbies.com/contro...e/pushrod.html

They are actually referring to the shaft of an Arrow...Guys will use Arrow Shafts for pushrods...

Have Fun...

Chuck

RE: Push rods
 

2-56------------------NEVER had a failure up through---yes THROUGH --- 5.1cu.in.and 100" span on a scratch 260.

For some (not all) fly ins 4-40 is specified-------never had a failure there either. Competitions?? well adhere to the rules or don't fly----it's that simple.

2-56 is simply vastly under rated-----BUT that's what the rules say sooo-------OK.
As far as air-load/vibration failure my rather extended experience indicates zip, nada,nyet etc.

My flying group has never had one either and most of us have been at it for more than a short time----I believe the least experienced flier we have in the group has been flying for 25 years.

I expect a lot of nay-sayers and flames---------won't do any good because those are the facts!

Edit-------then again, we've got that ever present group who break anvils with a rubber hammer---let's face it, nothing is fool proof! ---------perhaps knitting; crocheting????

RE: Push rods
 

Dave, You mean a wing jig like this one designed by my Dad? We use 1/4" steel rods from Home Depot and guess fiberglass would be good too. PM me your email address if you want a detailed plan and bill of materials to make one of these jigs.;) Tim

RE: Push rods
 

Marian,
No, no supports, if you have so much vibration that the pushrods need supporting, then there is something else that really needs looking into. Just make sure that the rods are not touching each other at the extremes of movement.
Evan.

RE: Push rods
 

Tim, PM on the way. Thanks!

David

RE: Push rods
 

While I have used forked pushrods as pictured with success, I also lost a prized Extra to one. The bends allow a little sponginess and can allow flutter. I flew the Extra for several seasons before elevator flutter in level flight took the whole elevator, 1/2 the stab and the rudder off the plane. This plane was set up with carbon arrow shaft pushrods but the "pickle fork" at the back end made the control system too soft for me.

A better solution for forked pushrods is to fork them at the other end. Essentially giving you 2 separate pushrods that are tied together at the servo end. This allows you to keep the pushrods straighter, giving you less play in the control system and less tendency to flutter. When forking a pushrod this way, I just use 4/40 wire pushrods for the full length. I wire wrap and silver solder them together at the servo end. The pushrods are set up for straight runs from the fork to the control horn and are supported at several points along their run.

This is the way I set up my Dirty Birdy 60. It gives solid controls with no push rod flexing that is much less prone to flutter than a system with the fork in the rear.

The same could be done with wood or arrow shaft pushrods if you've a mind to and have room in the fuselage.

Dave

RE: Push rods
 

I am coming to this topic a little late but I stopped using push rods years ago and now only use pull-pull setup on the elevator and rudder. This give the best possible setup, simple, light, tight with zero slop. I experimented on the ailerons but found it not worth the trouble there.