Differential Brake Pedals Bent

[racaldwell]

I did my first taxi test which I tested the differential brakes for the first time. I had the FAA visit the other day for my AWC inspection. They wanted to see the brakes stop the plane and for me to taxi it. The AeroConv. brakes didn't hold very well at all but I did get it to stop and tried a 180 but couldn't hold one wheel still to break free the tailwheel. I ended up getting out and moving the tail over by hand. But I passed the FAA test. I was going to try another taxi test today but noticed the brake pedals were bent. I bought these pedals as part of a group buy here so I know more of these are out there. Take notice:

The 1/8 x 1 flat bar on the side does not take much force to bent it. I removed mine to repair today and bending it back straight on the vise I could do with one hand with a 1 foot long tube slid over the pedal. It obviously is no match for my chicken legs.

I had a piece of 1" square x 0.065" 4130 tube in the scrap box so I cut that in half to make a reinforcing channel to weld on the side. I haven't welded in years so a good opportunity to get some practice. Here is the repair so far.

Rick Caldwell
Xenos 0057 is now an airplane

Brake Pedals Bent Sm.jpg (217.06 KiB) Viewed 3586 times

Brake Pedals Reinforced Sm.jpg (189.63 KiB) Viewed 3586 times

[Scott Todd]

When I decided to add differential hydraulic brakes to my Onex, I talked it over with some of the airport mechanical guru's and homebuilders. It was a common consensus that they take a lot of abuse and that a person can easily generate several hundred pounds of force with their legs. One person commented it was like hanging an engine off one side if your foot wasn't completely centered. Everyone said they should be WAY overbuilt. Here is what we came up with. They were done by our local welding expert. I realize the Sonex is basically upside down from this but you can see how we wanted to distribute the load to both sides. The hinged upper part can't be taken apart. He added some tiny oil holes. He said if they ever give me trouble, he'll just take them apart and fix them :)

[sonex892.]

I havent heard of anyone bending those pedals before.

Here is my slight variation of that design. I used 1/8" chromoly cut from sheet, not flat bar, and shaped so it has a bit of a gusset to help resist the twist. I offset the pedals to bring them forward a bit more . The pivot shaft doesn't float, I made that slightly longer than the rudder pedal lower tube. It has a threaded hole in the end for a bolt and small fender washer to hold it in place. I now have 250hrs and probably 500 landings since installing them.

[racaldwell]

Scott got good advice. They need to be strong. Looks like you have a good set up.

I am surprised at myself for thinking an 1/8 x 1" sheet or bar would take that force of a foot out on the foot pedal tube. I just didn't think about it since I thought this was a proven design. I told my hangar neighbor after my first taxi and brake application that my cylinders may bleeding because I had a soft pedal. The soft pedal was me bending the brake pedals. Good idea to offset the foot pedal forward. It was awkward trying to press so far with extended toes. I'll try adding a rubber sleeve before I do more surgery on the pedals.

I noticed I had cracked the rosette weld of the foot tube in the 1/8" side sheet so I fillet welded that on the inside and rosette welded it to my channel reinforcement I added. I also have a nice fillet weld on the flat sheet on the cylinder mount that I hope keeps it in position.

I have been wanting to get welding practice and bought full oxy & acetyl. cylinders in prepping for that. But I have been so busy trying to get the Xenos finished that the practice has been on hold. I am glad I discovered this right in front of the hangar on the taxiway and also glad I am now getting the practice I wanted to do at the same time of getting the Xenos ready for flight. So this worked our alright. I primed them today.

Rick Caldwell
Xenos 0057

[Scott Todd]

I've done lots of run ups and REALLY layed on them. They are comfortable and seem to be holding up just fine. FWIW, I used this article from Matco for the geometry.

https://www.google.com/url?sa=t&rct=j&q ... XkB5EXrlkU

[sonex892.]

FWIW, I used this article from Matco for the geometry.

https://www.google.com/url?sa=t&rct=j&q ... XkB5EXrlkU

I too found and used that Matco info for geometry when I built my brakes. It's great advice and saves a lot of trial and error.

Good idea to offset the foot pedal forward. It was awkward trying to press so far with extended toes. I'll try adding a rubber sleeve before I do more surgery on the pedals.
Rick Caldwell
Xenos 0057

Rick. Just a thought. The way one pedal on the Sonex is angled forward and the other rearward you might be able to get away with just offsetting the pedal that angles rearward. As for stress testing the pedals I too have really pressed hard on them and not bent anything yet. The brakes after nearly 500hrs of work, stopped functioning properly last year, I was really having to push hard to get it to slow. New pads and disc's has now fixed that, they're now back like new again. I have great plains brakes.

[DCASonex]

Made my own before this design came out, much stronger design. It was posted on the foundation website, sending you the drawings separately.

David A.

[Carlos Trigo]

Made my own before this design came out, much stronger design. It was posted on the foundation website, sending you the drawings separately.

David A.

Hi David

Would you please also send me those drawings. (trigo @ netcabo . pt)

Thanks
Carlos

[XenosN42]

Made my own before this design came out, much stronger design. It was posted on the foundation website, sending you the drawings separately.

David A.

Note from Sonex Builders & Pilots admin:

The site is back up and is being rapidly repopulated with the contents from the old site. If you know of any articles that were on the old site but not on the new site email me with a copy of that content and I'll post it right away. mailto://admin@SonexFoundation.com

I have uploaded one article that I just found related to toe brakes. You can access it from the 'Safety & Education' page. https://sonexfoundation.com/safety-%26-education

Thanks!

[DCASonex]

Michael, The photo in the link is not of my design but does look to be much stronger than the design Wes had, with a tube running up to the pedal rather than the torsion-ally weak flat bar. Mine would have been posted on the old website back around 2012. I have a file with every modification I posted back then if of any interest, Some would apply only to the old A series and some like my 6" tail wheel design have been supplanted by Sonex offering their own.

David A.