Flap pushrods

These pushrods always looked to me to be too small for the task, they're OK.

A few weeks ago the tower had me go-around because a Cessna was taking
too long to clear the runway. By the time I started getting the flaps up
I noticed I was at 110 Kts. Once back in the hangar and also because it was close
to annual inspection time I disassembled all the flap components for a close
look and found no issues.

I went ahead and ordered the new type hex rods from Van's and finished the annual.
I was curious how strong the old pushrods are and because I have access to a load frame
I was able to find out:
1) How much force they could take.
2) How it would fail.

At 680 lbF the pushrod was still hanging in there. Approaching 700 lbF. it started
to bend and it was all over. Once the the bend started it took only about 300Lb. to
bend it furthur and I stopped the test.

This is an AWESOME post. We need more like this. Kudos and huge thank you. Love seeing raw data like this. Makes you ponder if a load cell could be placed on items and measured in flight perhaps. I'm sure everyone always wonders about the value of upgrades, that is if you really need to spend the money on upgrades on things like this.
Great post.

I agree, thanks for posting this! Seeing real numbers on what our parts can withstand is awesome! I wonder what load Van's designs these for...

I have made numerous posts in the past indicating that the standard kit push rods have been tested at Van's in the past.
The results were the same.
They will take way more load than is anticipated to be produced by the flap.

what is the load on the flap rod at 110 kts, full down position?

OK, good info. Now here is a different scenario. I had a 200 lb "visitor" who wanted to try my RV-6A on for size. I wasn't watching as he got out of the cockpit and he stepped on the DO NOT STEP decal I had on the flaps in the full up position. $@&!!

I pulled the flap...no damage or twist. But I did replace the push rod link because I could not be sure the threads weren't damaged. I also replaced one of the rod bearings because it felt a little "bindie".

Steve Melton said:

what is the load on the flap rod at 110 kts, full down position?

Click to expand...

This could probably be calculated or more accurately measured using strain gauges.
I wonder if anyone has gone fast enough to actually cause damage. I'm thinking the flap itself would start to warp.

40 deg flap deflection, momentum change of the airflow, kinematics of the rod, 110 kts. someone should calculate it.

Or a rough estimate using the equation for fluid dynamic drag, some wags at flap area exposed to the free stream, drag coefficient, air density etc and some vector math based on the flap and pushrod geometry. Which I would take a stab at if my RV-7 wasn’t several thousand miles away. Though I have confidence in Van’s calculations.

Edit: just saw Steve’s reply before mine. What he said. I’ll take a stab if no one else does, though it will be a week or two.