Chapter 9 - Section 5

Axles, Brakes and Brake Lines


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Based on all the discussion in the Cozy forum regarding the braking capacities, I decided to use the Matco brakes instead of the Cleveland brakes per plan. Matco's web site also has a section that helps you to determine braking power needed and recommends their brake model for your aircraft. It allows you to enter in the aircraft weights, landing speeds, etc. Then it cranks through their equations and provides you the results. I ran through that exercise and came up with the same model as most of the Cozy builders are using.        


I ordered the Matco brake model W51LT( triple puck) from them directly. The brakes arrived within a week. I even got a call from their tech support, advising me that I had ordered a couple extra parts that are included in their kits already. Saved me some money... My experience with Matco was very good!


Axle Mounting Template

Installation of the brakes and axles requires an precise positioning of the axles, the orientation of the calipers and trimming of the strut ends. Initially, I got a copy of the template (AutoCad format) from Jim Springer, who installed the Matco brakes and was gracious to share his template with anyone who needed it. I downloaded an AutoCad viewer and with some manipulation, was able to print it out to almost the exact size as my axle flange.


I went ahead and made the template out of a 1/4" thick board and trial fit it to my Matco brakes. To my surprise, the top curvature didn't quite fit. I didn't want to burden Jim any more than I have to, so I transferred some of his dimensions and customized my own template with Corel (I do not have AutoCad). I made a new template and trial fit to my brakes.


As shown, my template consists of the hole locations for the axle, the orientation of axle flange relative to the sides of the gear leg, relative position of the caliper and the cut line for the landing gear strut. I did follow the plan direction regarding the parallelism of the axle flange to the side of the gear leg. Once that's set, the orientation of the caliper is pretty much set as well. I also made a mirror image for the inside and outside of the strut. 


This template is available to all Cozy builders. Just send me an e-mail and I'll send it to you. I think I can convert it to any graphical format (such as .jpg, bmp etc.). So, if you have any graphical viewing software, you should be able to modify, view and print as desired.


Determining Axle Position

The position of the axle was set as FS110.0 per plan. FS110.0 was easy to find, I just dropped a plumb line from the cross beam (picture below) and placed a vertical mark on the strut. However, I was a bit surprised that the vertical position of the axle was not obvious (other than .5" below the edge of the strut in Fig. 37). I eventually got my answer from Rick Maddy's search engine and found it at the back page of the plan. It is supposed to be at WL-19. The question is how do I know dropping the flange .5" from edge of the strut equates to WL-19? Especially since I am not using the Cleveland brakes and that the Matco brake flange has different dimensions. 


Since we know the top edge of the longeron is WL23 and the center of the axle is supposed to be at WL-19, the total distance should be 42" (23"+19"). I clamped a digital level against the edge of the longeron and leveled it to 0o. Then I dropped a measuring tape from the top as shown. The center of the axle, therefore should be 42" up from the top of my digital level. I placed a cross-hair at FS110 & WL-19 - that's where the center of my axle should go. 


Based on the measurement above, the center of my axles are 2" below the edge of my strut - making them around WL-19 to WL-19.125.









Once the axle centers were established (marked), I clamped a straight edge between the two centers and confirmed that they were level. Then I used my template and traced out the strut trim line hole locations and axle flange orientation. 









3 Layer BID

I made a 3 layered 7"x8" BID tape and cut it up to two 3.5" x 8" pieces. I glassed the end of the struts with the 3 BID per plan. I peel plied the entire BID layer (front and bottom) such that I will have a nice transition to the rest of the strut. I allowed it to cure overnight.


Notice the markings on the strut are different - its because my axle position was off a bit when I re-confirmed its WL, therefore I re-drew the trim lines. Only the trim lines and axle flange orientation and position were included this time. 





Drilling the Axle Holes 

I clamped the axle down at the precise location (1 at center and 3 corners), while I positioned my 12" drill bit and put in my first hole. Once drilled, I put a bolt and nut through it. Then I removed the second corner clamp and drilled the second hole. I repeated the process until all 4 holes were drilled. I did the same for the other axle.         







Toe-In Targets

One of the most difficult to achieve requirements (for this step) is setting the toe-in alignment - it must be set to 1/4 degree. Since I am installing the Matco (instead of Cleveland) brakes, the plan direction does not quite apply, though I followed the general concept and approach. First, I used a laser and projected a cross-hair on a white board 213.25" from FS110.0 - not the back of the fuselage. Then I transferred the distance between the center of the fuselage and the outside edge of the strut, onto the white board per plan. The next step is to calculate and mark the toe-in position on the same horizontal line.  


I tried the 1/4" tube sighting method as suggested in the plan. I have to admit, I can't eye-ball a cross hair 20 feet away through a 3" tube with any precision or consistency! I gave up after several tries and decided to try a laser beam instead.


I know leaning the laser against the strut was not going to work because of its curved surface. For any stability, I must have a flat surface to mount the laser body. I removed the caliper assembly from the wheel housing and slipped the wheel housing through the axle (as shown). I set the laser unit on two of the three screw tabs and then clamped it against the side of the wheel. I rotated the wheel such that the laser is leveled to 0o (its important). Now I have a definitive cross hair planted on a surface that can be marked and measured.







Laser Position Offset

Again, I followed the plans method to establish the outside edge of the strut from the center of the fuselage (d1), then I measured the distance between the outside edge of the strut to the center of the laser beam (d2). If the laser is targeting at a point (on the white board) that is (d1+d2) from the center of the fuselage, the beam should be parallel to the fuselage... right? Not quite, there is one more consideration...


Laser Beam Offset

In almost all cases, the laser beam does not exit square and parallel to its housing. I would be very surprised that my 'Costco special' is an exception. This offset is not minor in this application and needs to be determined and added into our toe-in calculations. To support my point, for the 1/4 degree toe-in, it equates to ~1" distance at 20' away. Let's assume your laser beam exits by 1/4 degree off (from its housing), which is very likely, it would essentially be off by 1", giving you a 100% error!


To determine the laser beam offset, I place my laser on a flat table, 213.25" inches from the wall (same distance between the axle and my alignment surface). I marked the cross hair position on the wall. Then I turn the laser body upside down and mark the laser cross hair position again. The horizontal distance between the two marks is 2x the laser beam offset. Therefore, take that distance, divide it by 2, then add or subtract (as appropriate) to the overall alignment measurement.








Toe-In Calculation Summary

With all the above measurements and calculations, I can establish my final laser toe-in target on the far wall (white board) for alignment. For my case, the measurements for the left wheel was as follows:

- center of fuselage to outer edge of strut 33 15/16"

- add laser position offset of 31/32" because it is further away from the center of fuselage

- add laser beam offset 9/16" because my laser is exiting to the left of the housing

- subtract toe-in calculation (based on my forward distance of 213.25") 15/16" 


Therefore, my laser target position with 1/4" toe-in for the left wheel was calculated to be 34 17/32" left of the center of the fuselage. I did the same for the right strut, except I subtract the laser beam offset from the overall calculation. 








Trial Run

Once the toe-in position was accurately measured and marked on the far wall (white board), I did a trial run with the bolts and nuts that were holding the axle in place. The bolts provided such a fine adjustment (and you need it), I can place the laser right on target with ease. If you look close, you can probably see the laser cross-hair right on the toe-in mark. 













Preparing for Floxing

I put packing tape on the back and sides of the axle flange and slit a small cross-hair at the center of each of the bolt holes. I did not want to flox the axle in place because many builders had to remove their axle for one reason or another down the road. On the other hand, I plan to flox the back plate in place, therefore, no packing tape was applied. I also coated the bolts and nuts with Turtle wax (per Wayne Hicks recommendation), because I definitely do not want to flox the bolts in place. 







I didn't like the look of the square back plate as suggested in the plan. By the time I remove its top corners to fit the strut cutouts, it will look odd. I liked Jim Springer's circular plate and decided to do the same. So I cut up 2 circular plates, alodined them and used them for the back plate. Note that I was using the plumb line as a counterweight to keep the wheel from turning as well as keeping the laser stable and parallel.













Floxing in the Axle and Back Plates

I spread flox on the face of the axle flange and the circular back plate. Then I painted pure epoxy on the joining surface of the strut. I held the axle and plate in place and pushed the bolts through the axle, strut and back plate. I tightened the nuts by hand so that I would not squeeze the flox too aggressively and at the same time to get the laser beam to the right toe-in proximity. Then I used a small wrench to bring the laser to precise target (slowly). I repeated the process on both sides and left for cure. I returned every 2 hours and double-checked their target positions to make sure they stayed put - they did.


After the flox was cured overnight, I removed the bolts & nuts and cleaned them off. The Turtle wax paid off (Thanks, Wayne). I also cleaned the wax out of the holes. The axle popped off cleanly, leaving a flat and smooth platform. I removed the packing tape and cleaned off the surfaces. 


I used the Fein tool, palm sander and circular sanding stick to remove the strut cutout. Then I re-mounted the caliper and wheel (as shown).





Mounting the Wheels

Initially, I got a set of Cheng Shin tires 11.00 x 4 x 5 tires to be used temporarily during the building process. The Cheng Shin tires were cheap (~$25 a set for tire & tube) and was recommended by someone in the Cozy Forum. It turned out that the valve stems were too short and the wheels were too narrow. After further investigation, I found the Cheng Shin tires were more for the Long Easy & not the Cozy Mk IV. I took them back and traded them for a set of Michelin Condor tires as recommended by Matco.


The Condor tires seemed big, ~13.5" in diameter! With the main gear axle position at WL-19, ground surface should be at WL-25.75" (-19 - 13.5/2). I compared that against the nose gear (axle at WL-20 and wheel diameter of 10"), the ground surface at nose gear should be at WL-25 (i.e. -20-10/2). That means the plane should be nose down by .75". A bit confused, I posted the question on the Cozy Forum. The answer (per Marc Zeitlen) was that there will be compression at the main gear (due to weight etc.) in excess of 3/4" minimum. However, there will be no compression at the nose gear. With that projection, my plane should be close to level or even a bit nose high. Marc stated that his plane is ~1 degree nose high measured at the longerons. I think I am on the right track as far as main gear axle positions are concerned.


I went to an auto tire store and got a bit of slip-tac (fancy name for tire soap) and brush a bit along the contact surfaces between the tire and metal rim. Following the Matco instructions, I installed the tires and tubes without pinching the inner tubes. I also cleaned and packed (greased) the axle bearings as instructed. The wheel installation is now complete!


Heat Shields

There has been quite a bit of discussion on the Cozy Forum that the disc brakes generate lots of heat on the rotor which radiates onto the struts. Supposedly, someone's strut caught fire and the entire plane burned to the ground.  Since then, many builders have made a set of heat shields and mounted them between the strut and the rotors. Most of the heat shields I have seen (from various Cozy sites) consist of a rectangular sheet metal with 4 holes (~1/16" thick) and are sandwiched between the axle flange and the strut. It's simple and supposedly, works fine.


Though not in the plans, I figured I better get it done while I am at it. However, I didn't like the way it was mounted because of the following reasons:

-    Heat from the heat shield will conduct right down to the strut as it is in direct contact with the strut;

-    The heat shield potentially messes up my 1/4 degree toe-in position;

-    It adds thickness to the axle flange, which in turn, moves the wheels further out.


All the above reasons may be minor in the scheme of things but just didn't feel right to me. I decided to made some minor changes to the 'popular' design. I used the axle template in the earlier section and designed a heat shield that I can sandwich between the axle and the brake plate instead.


I made a template out of thick paper and trial fit it first before I made the actual part out of 1/16" aluminum sheet. Since there is an offset to accommodate the calipers, I have to make a left and a right shield. Its the same template, except its a mirror image. A friend of mine has a buffer and we decided to buff it up just for fun - see how nice and shiny they are! As always, the template (electronic format) is available for any builder per request.




Here is a trial fit of the new heat shield... It is sandwiched between the axle and the brake plate. Note the offset is to accommodate the caliper and at the same time provide maximum protection to the strut.             










This is how it looks after it is mounted onto wheel assembly.
















Here's a shot showing the bend on the heat shield and the clearance between the rotor and the strut. I can still adjust that bend angle a bit so that the shield is closer to the strut, but for now, its somewhere in the middle.


How well will this work? I dunno... I will find out when I do the taxi test light years in the future! But for now, it looks pretty .     


[Hindsight] There had been some discussion on the Cozy forum regarding the mounting location of the heat shields. You should be able to find them in the archives. The key concerns were 1) adequate clearance between the heat shield and the rotor and 2) how does the heat (from the rotor) transferred to the landing gear. After reading and weighing all the comments, I still prefer my design rationale. First, the joggle provides clearance from the rotor and, second, the attachment point - creates a heat gradient mid way between the gear leg and the heat source - thus minimizes conductive heat from reaching the gear legs. But, bare in mind, I am not flying yet, others are...


[Hindsight] During separate visits by a couple very well respected Cozy builders and fliers, I have them take a close look at my heat shields and solicited their opinion on the design and placement. I was pleased to receive their nod of approval...       



Landing Gear Box

I have to turn the fuselage up-right to make the landing gear box. Since the next section (the landing brake) requires the fuselage up side down again, I decided to work on the landing brake first before I turn it over. Besides, I have to do the landing gear cover as well.


Landing brake completed and fuselage turned over...


I made the landing gear box pretty much to plan. Dimensions for the two center holes are not well defined. I made them 5" in diameter for top to bottom access. In the event I do not need it, I think I can easily seal it off with a cover.


I glassed both sides of the foam and then cut the circles out with a router and touch up sanding. I also BID taped all edges top and bottom.  







Things on Hold :


Brake Lines

I decided not to install the brake lines until the structure at the front of the plane is in place. Then I know for sure where the brake paddles and reservoirs are. In addition, I still have to move the strut and brakes on and off, having the brake line in place now will be more of a hinder. Therefore, to be continued...         


Fiberfrax & Aluminum Tapes

The plan suggests to wrap the strut and brake line opposite the disc with 1/8" fiberfrax and then aluminum foil tape. Since the strut is not painted at this point and the brakes lines are not in place, this task will just have to wait until then as well.  



On to the landing brake...



  LG Bulkhead Reinforcement   Preparing Strut   Attach Tab 


  Landing Gear Cover   Axles, Brakes & Brake Lines   Landing Brake