This blog is for entertainment purposes only, and is not meant to teach you how to build anything. The author is not responsible for any accident, injury, or loss that occurs as a result of reading this blog. Read this blog at your own risk.

Friday, October 17, 2014

Brake/Rudder pedals - part 7

Pedal base modification (1.8 hrs)

Work has had my full attention recently, and progress on the plane has slowed to a crawl as I prepped for my yearly simulator check-ride. 

B-787... I'm still trying to decide whether I want to go there, or not.

A-320... nice plane, but I'd have to give up Europe.

I think I'll stick to the good old B-757 and B-767 for the time being.

Back in the "EZ shop" after the 3 day long training event, I’ve had to address one more of my friend Walter’s concerns, this time having to do with my choice of fasteners, and their mounting arrangement.

Original setup using McMaster-Carr's T-nut in the plywood

Same thing with the brake bracket bolted on

His concern was a valid one as usual, and I appreciated him keeping an eye on me, though I so hate doing things over. 

Walter thought that by using the 10/32 tee nuts acting in shear to hold the assembly to the cockpit floor, I would be counting on common hardware store quality lock-washers to keep the bolts from loosening. This may or may not work as the soft wood may gradually yield a bit under braking stresses over the years, letting the lock-washers loosen their grip, and allowing the brake pedal assembly to move back and forth. Obviously not something I’d like to see happening.

To improve the quality of the fasteners, I decided to try the  aviation grade K1000-3 anchor nuts, to see how they’d fit in the original plywood holes.

Luckily, the fit was nearly identical.

Never mind the burnt spots, this piece is scrap anyway.

More importantly, the K1000-3 does not stick above the plywood surface.

If left alone, these fasteners would tend to rock even more so than the previous T-nuts. So, to address the second issue, I decided to weld them to a 0.050” (0.127 mm) 4130 steel plate.

Size and shape of the plate would not be critical, but the hole pattern would have to be spot on in order to match any hole combination in the aluminum brackets. So I used the CNC mill (high precision) to drill three holes exactly 3.000” (76.200 mm) apart from each other...

Getting ready to center-drill 6 holes

6 precision holes enlarged to fit the bolts

...and the band saw and belt sander (low precision) to rough out an acceptable contour. 

Separating the tabs on the bandsaw

Roughing out a contour with the belt sander

In order to minimize distortion during welding, I mounted the plates to the first bracket I made (now scrap) using bolts, then added the nut plates and welded away.

Because of the accuracy of the holes, the bolts slipped right in.

TIG welding was done with the tab firmly bolted to the bracket

I ended up countersinking the steel plates into the plywood, to make the fit better, and use less flox at installation time.

Outline of the plate traced on the wood before countersinking

Rough countersinking following the traced contour

Countersunk plate tying all nut-plates together.

As of last time Walter inspected my work, he felt I had successfully addressed all of his concerns, and gave me his “Quality Control” stamp of approval.

If you are building your airplane in semi-isolation, as we almost all are, I highly encourage you to get a second set of eyes on your project, especially when you are modifying some of the structure as I have, in order to give proper consideration to issues you might not have thought about. It would be even better if this second set of eyes had already built and flown their own Long EZ, and belonged to an engineer.

“Thanks for watching over my project Walter!”

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