Chronicling my Long EZ construction (and a few other things).
Disclaimer
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.
Although it’s been looking like a “brake pedals only” website lately (past 4 months), I have finally reached the end of the R&D and fabrication phases, and moving on to installing them once and for all.
Note to self: I need to drastically reduce the number custom made parts if I want to finish this plane in one lifetime.
With the pedals looking as good as they were going to get, the next "most important thing" became where to put them, so I spent even more time in the saddle playing with them, as since I kept coming up with the same position over and over (same as in the last post), I decided that that was it, and to just go for it.
Remember, once the bases are attached to the structure, it would be easier to start building a new plane rather than getting them out! Ok, maybe not, but you get the idea.
The |____| marks the spot
I started getting ready by cutting fiberglass plies, arranging them between plastic sheets, and wetting them with epoxy (aka pre-preg). I used 3 plies of BID each, and gave a generous 2.5” (6.4 cm) overlap on the existing floor and sidewalls.
Two 3 plies pre-preg cut, and stacked between plastic sheets.
Pre-preg ready for use after trimming the extra plastic
Using my Saran wrap trick, I plugged all the threaded holes, to prevent flox from rendering them unusable, and buttered the bottom of the plywood bases with it (after wetting them with epoxy).
Stuffing the holes with plastic wrap
One base bottom epoxied, the other epoxied and floxed.
Carefully, I laid the bases on the fuselage floor, pressing down on them to squeeze the excess flox out of all four sides. I then shaped this same flox to aid in transitioning the fiberglass onto the adjacent surfaces.
This part is aways fun
So many shapes in such a small part
Other base getting the same treatment
Talking about laying fiberglass, this time around I was plagued by lots of air bubbles, undoubtedly due to my lack of recent experience with it, and spent quite some time trying to get them all. Using an additional light source helped revealing them, however I still missed a quarter-sized one sitting over the back end of the right plywood base.
Left base with all the kinks worked out (pun intended)
Right base. Can you see the big air bubble? Neither could I!
Thinking I had gotten them all, I peel-plied over the glass, and went to bed.
Left base resting overnight
Right base peel-plied
The next morning I anxiously ripped the peel-ply, and was quite shocked by the size of air bubble I had missed.
Holy crap! How did I miss that air bubble?
Here is the offending air pocket, highlighted with a silver marker.
To fix something like that, you have to inject epoxy under the skin with a syringe (I added a very small amount of flocked cotton to my epoxy). But first, you have to drill an “entry hole” for the epoxy, and as many “exit holes” as necessary, depending on where you want the epoxy to go (epoxy needs to be able to displace air, or it won’t go there).
With my triangular shaped air pocket, I needed at least three holes, one per vertex, two of which would be exits.
Surgery in progress
"Relax, this won't hurt a bit!"
How to remove an air bubble
Getting the Saran wrap out of the threaded hardware proved to be a bit of a pain, but it was nevertheless straight forward… drill a small hole, enlarge it carefully, and try to get the recalcitrant wrap out with whatever tool you can stick in the hole. The smaller the threaded hardware, and the tighter packed the wrap, the harder will be to get it out.
I overpacked as usual!
Aiming for the center of the Saran wrap
Fun time digging plastic wrap out of threaded hardware
Finally, reaching the climax of this whole subproject, I bolted the pedals to the fuselage.
Left pedal of awesomeness!
I know... it brings tears to the eye (Aluminum tape will be removed later)
You are going to have to picture this in your mind a bit.
As my foot presses forward on the brake pedal, the force is going to be transmitted to the bracket, and its plywood base. This force is an order of magnitude greater in the forward direction than in any other, and would peak during maximum breaking.
With only two things attaching the plywood base to the floor, namely 3 plies of fiberglass laid over the top (primary), and some flox underneath (secondary), does it really make any sense having the front edge of the plywood as sharp as a knife?
I didn’t think so, since repeated brake applications might force the plywood base to act like a blade trying to slice the fiberglass bond. Not good.
The sharp ramp I cut into all sides of the plywood was designed to ease the laying of fiberglass, so I decided to blunt its leading edge, and make the forward ramp out of flox instead (flox fillet).
This will eliminate the slicing tendency of the once sharp plywood base, and create a hardened abutment to contain it, as well as the gentle transition for the fiberglass I was looking for. A win win win situation.
Plywood base leading edge proposed change
Squaring the front edge of the plywood base
The bond between flox and wood is very good, but the one between flox and metal is very weak. So, in order to reduce the chances that the flox might loose its grip on the base during shear load applications (aka "using the brakes"), I decided to drill the steel base from below. This will allow flox to penetrate the base from below, and act the way a motocross tire would in the dirt, grabbing hold of the base with upward fingerlike protrusions, in addition to flox’s already excellent adhesive qualities (with the wood at least).
The holes were drilled to a depth of ⅛” (3.2 mm) through the steel plate, and into the hardened flox. The steel plate will thus be completely embedded in flox, gripping it from both sides.
I hope I will never need to remove this!
New set of holes drilled into steel and flox (bottom of part shown)
That means I’d better find the perfect position for the pedal assembly, because there will be no turning back.
Spending most of the day trying out multiple pedal locations, the one position I kept going back to was the one right against the sidewalls, sometimes a little more forward, sometimes a little more backward, depending on what shoes I was wearing.
This created a "small" problem for me, because the rudder cable attaching point rubbed against the sidewall, and if left this way it would eventually wear through the structure. Definitely not good.
The issue is pretty obvious
"This ain't gonna work!"
I obviously jinxed myself two posts ago when I said: "It seems that I always end up building at least 3 versions of everything I design...".
That statement is fast becoming like "the EZ shop's general law of relativity", and since I had only modded the pedals twice... guess what?
"Yes Virginia, there is only one cure for this… shorten the stick-out of the rudder cable attaching point!"
Version #3 would involve more cutting, grinding, machining, and welding. I wouldn't expect any less at this point.
Separation is always painful
The middle piece is headed for the recycling bin
Machining a chromoly sleeve (later divided into two shorter ones)
Sleeve inserted, and all surfaces prepped for TIG welding.
Dry fitting parts (gap is intentional)
TIG welding in progress
Pedal version #3 is 0.420" (10.7 mm) narrower than version #2
Old and new side by side
Much improved clearance
Here's the math behind the re-engineering
With all said and done, this mod went pretty fast (a couple of hours per side), and will improve positioning flexibility by eliminating any chance of contact with the sidewalls.
With the pedal brackets 1” (2.5 cm) longer, the plywood base with its steel insert no longer fit, and had to be made all over again (of course).
After welding the K1000-3 nuts to the steel flanges, I drilled a few of holes in them in order to remove some metal, and give the flox something to grab on to.
I reused my old Saran wrap trick to keep the flox out of the threads.
New flange with nuts welded to it
Saran wrap twisted into the nuts' threads to keep the flox out
I mixed some quick drying West System flox, and filled the plywood cavity, then I pressed the steel flanges into them, and removed the excess flox.
Flox filling the bottom of the plywood base
Flange being pushed in place
To save time, I "baked" them for maybe 20 minutes at 140℉ in my home made oven, then removed the Saran wrap, and sanded the bottoms flat.
Excess flox removed while wet, and bases drying up in my cardboard oven.
Saran wrap being removed
The whole bottom of the base got a good sanding
So, here are the once again completed pedals…
Reengineered pedals attached to reengineered bases
Hoping I can now live with these two
The next step will be finding a proper position for the pedal assemblies in the nose of the plane, and the testing has already started.
In the past I mentioned that the main purpose of this blog is to have as many eyes looking out for my mistakes as possible, and once again the concept has proven its worth.
Yes, I have made another mistake, but luckily this one is only going to cost me a few more days of work.
Someone brought to my attention that the correct mechanical advantage for the Matco master cylinder should be 2.5 to 1, and my pedals did not look right. After investigating the issue I discovered (or better... rediscovered) that to be correct, and my geometry to be off.
Crap!
I remember considering this very fact at the beginning, but months later, as I started shortening the bracket, I had completely forgotten about it.
With the current set up, the best I could achieve using the lowest flange hole was just a 2.0 to 1 ratio. While this would have provided less hydraulic pressure to the brake pads, it might have still worked ok given my choice of oversized brakes, however I was not willing to paint myself in a corner from the get go.
In order to fix this, the flanges would have to be moved, and the brackets redesigned and machined once again, this time 1” (2.5 cm) longer.
Here we go again…
I found the short welds on the flanges to be amazingly strong, I had a very hard time getting the tabs off, and had to grind through most of the welds before the flanges gave up.
Grinding the flange off the pedal
These welds turned out to be incredibly strong
Eventually the Dremel won
Since the pedals are 7” (17.8 cm) long, the new hinge position for the piston needs to be at 2.8” (7 / 2.5 = 2.8).
In order to reliably reproduce this measurement, and to help hold the flange while I tacked it with the TIG welder, I drilled two holes 2.8” (7.1 cm) apart in a piece of plywood (first thing within reach) and ran some bolts through them, using washers as spacers to align the flange with the center of the pedals.
Improvised wooden jig
Jig made it possible to line up the components with precision
As before, I had to preheat the flange in order to facilitate the welding to the thinner tube.
I knew the wood would not last under the heat of the welding, but I only needed it to endure two such treatments. After removing the wooden jig, I continued on with the welding.
Same flange, new position. We'll call this version #2.
Here you can see the lowered flange compared to the original. This increases the mechanical advantage.
The last step on this process was machining the longer brackets.
Braket ⅓ machined used to verify the desired pedal angle
Finished brake assembly (pedal version #2, bracket version #3)
Can you see why the bracket needed to be lengthened? After lowering the flange the pedal laid far too flat.
It seems that I always end up building at least 3 versions of everything I design, and the brake brackets turned out to be no different.
