What are you guys using for pushrods on large planes?
Online search shows epoxying inserts or 4-40 rods into 3/16 carbon tube. Wondering what is a good size for 1/4 scale 25lb plane. I made up a few using 4mm carbon rods, but not sure if 5mm or 8mm should be used. 8mm I think is too large.  :o

Marc

https://en.m.wikipedia.org/wiki/Euler%27s_critical_load

https://www.basicairdata.eu/knowledge-center/design/elevator-hinge-moment/

Sorry Marc, I thought I had posted the other day, but maybe the modem, which I just had replaced, was wonkers....
5mm inside diam cf tube would be fine i think. So now the pundits can chime in and give you a better answer..according to them

Hi Mark,

Not seeing the application I can only offer this suggestion;

-Generally, many models use 4:40/3mm connection points with
larger models. I'm assuming your D1 .
-I have used 5mm carbon rods for many years on high
performance models without any issues.
-As you know, it's critical that the connection points are free from
binding and slop. (ball links are used by many modellers with
great success, I highly recommend them)
-If your pushrods are quite long you may want to consider
mounting points along their length....
-another option would be stailess or titanium pushrods (3mm)
they are easily adjusted and not expensive.

Hope this helps...
I like your model!

Thanks for the replies. Very good to know 3mm carbon rods would work.
Unfortunately, there were replies before last night so I ended up cutting the 3mm rods to make pushrods for the ailerons.  :'(
I made the rudder and elevator rods from 7mm csrbon rods. Since the 4-40 threaded rods don't fit snug, I wraped the threaded rod with fiberglass and inserted into the carbon rods. I left a tail and wrapped it around the outside to ensure the carbon rod can't split.

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Looks bullet proof to me. 8-)

Yup. That'll work.