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Building Tips and technical articles. => Building techniques => Topic started by: Rob Killick on June 05, 2007, 09:07:12 PM

Title: What size of CF pushrods ?
Post by: Rob Killick on June 05, 2007, 09:07:12 PM

Hi there ,

Sorry to continue on about push rods , but I would like to know how to "size" the carbon fiber rods to the aircraft size ?
I have a smaller plane ( 42" span , with flaps and .25 Brodak engine ) and was wondering what size of CF tubing to use ( inside / outside dimensions ) ?

Thanks :)

Title: Re: What size of CF pushrods ?
Post by: Leester on June 06, 2007, 01:42:47 AM

Hi Rob: I use the 3/16th" OD carbon rods with 1/8" ID.

Title: Re: What size of CF pushrods ?
Post by: Bill Gruby on June 06, 2007, 03:51:00 AM

Hi Rob;

   If you are looking for a formula to figure out diameter, I can't help you. I don't know if there is one? I do know this though, we had "Jim Snelson" of C/L Central make up a set of "Drop In Controls" for the "Ringmaster 1000" and that is what he used, 3/16 Dia. Remember now this ia a 68" Span beauty powered by a Fox .78. If 3/16 is big enough for that I believe it is big enough for most anything.

          "Billy G"  H^^

Title: Re: What size of CF push rods ?
Post by: Dick Fowler on June 06, 2007, 05:30:38 AM

My concern would be how long is the unsupported length of the push rod. The rod (actually a tube) is strong enough in tension and compression to handle mucho load but if it's very long and not well supported, then it will deflect and the controls will get spongy. I would jump up to 1/4" O.D. CF tube if the push rod is much over 18" and not supported some place along its length.

Title: Re: What size of CF pushrods ?
Post by: Bill Gruby on June 06, 2007, 08:19:35 AM

   I have to agree with Ty on this one absolutely. My pushrod is 25" long and DOES NOT BEND (flex) under mucho stress. 3/16 is just fine. 1/4 inch would add to your security, but I do not think it is necessary.  FWIW

         "Billy G"   HH%%

Title: Re: What size of CF pushrods ?
Post by: Bill Little on June 06, 2007, 08:29:58 AM

AFAIK,  Tom Morris (and Jim Snelson) use the Central Hobbies CF tubes.  At least Tom probably gets them from the same source.  All they have is the 3/16th tubes.  Their threaded rod ends fit this size for ball link usage.  If the rod is slightly too small ID, then run a jewelers rat tail file in them until the end fits.  Don't force the file, in fact the best way I have found is to put the file in a cordless drill and run them backwards very slowly.  This also prepares the end for gluing.  JB Weld (not "quick set") is recommended for gluing, and wrapping the exterior end of the rod with CF tow, veil strips, or some other reinforcement is also recommended to prevent splitting.  Also, do not lubricate the ball links if you use them.  This system I have used for all size planes up to 60 powered piped ships with no problems.