The following article appeared in the September, 2003 issue of the Cub Club Newsletter . . .

Piper Cub brakes are actually pretty good brakes, as things go. They were designed over a half-century ago, and replacement parts haven't been available for decades, yet they still work fine. Most Cub users, however, have been tempted to spring for “Clevelands”, because they allow for inexpensive replacement parts and reasonably-priced tires and tubes. For my part, in forty-plus years of Cub ownership, I have never actually gone out and tried to buy a Goodyear/Hayes brake part; there always seemed to be enough used parts dropped in my hangar to keep going. And I am in love with those cartoon-like tires. They simply look like they belong on a Cub. After a disastrous experience or two in the mid-sixties, I settled on using a 1/8” spacer ring on the axle to keep rivets and brakes apart, and on automotive brake fluid to keep the expander tubes from expanding when I wasn't looking. Lately, I have graduated to “DOT 5” fluid – nasty stuff in that it gets all over everything, but great stuff in that it doesn't eat paint, and is non-hygroscopic. So I am actually pretty happy!

But Len Buckel and Jim Laudeman, both San Diego Cub nuts, mentioned to me that I ought to meet Robbie Grove, who had made prototype disc brakes for the 8:00x4 Cub wheels. I have always envied those folks who have disc brakes, but not enough to go to 6:00 wheels and lose my antique status. So I found Robbie, and introduced myself. He simply handed me a set of disc brakes and said “here – try them out.” I was standing there with checkbook in hand, planning to spring for at least $500, since these things were beautiful, and obviously embodied a lot of work and engineering, but Robbie said “here.” Not only that, but he did the riveting (steel, and probably not as easy as aircraft rivets) for me. I probably should have tried the riveting, but he was happy to do it .

Next, how to test these things? My first thought was to get a one-time field approval, and then do the testing. However, rumor has it that the FAA doesn't do field approvals on wheels and brakes. And going experimental might be an answer, but I just wanted to do a few landings and taxi tests, so like a good guy, I simply went to a foreign country (there are several close by) and borrowed a J-3 for my tests. I suppose I could have borrowed an experimental “Cuby” here in the states (my friend Skip Beers has one in Phoenix) but they all have Clevelands, so the comparison would be difficult.

I really shouldn't have had to do that. After all, the absolute worst that could happen would be a total wheel lockup, and in a J-3, that's almost a non-event. I changed the brakes from drum to disc on my '66 Mustang convertible, and no paperwork whatsoever was required. A brake failure on an automobile could easily cause a fatal accident, but the same failure on a Cub most likely would never be noticed by anyone but the pilot. Who among us has not had a “single brake” experience? One simply taxis a bit more carefully. In fairness, the “feds” did ease up a bit on paperwork for most of us. Did you know that a Cub could legally be equipped with shoulder harnesses with no testing, and only a logbook entry? And that you can use military or SAE harnesses? It's true, and I salute the reasonableness of whoever is responsible for that!

Anyway, these discs are not yet approved, and you and I cannot put them on certificated Cubs until the FAA approves them. As I understand it, the FAA is looking for a test flight by an FAA designated engineering test pilot. If any of you know of such a person who would enjoy a taildragger checkout for free in exchange for a certification, send him or her my way! Or tell me where they are, and I'll go there, at my expense, if I can get a temporary NX number.

It took two hours to put the first brake on, and most of that was because I forgot to take the tube bender to the airport. The next day, I pulled it off and re-timed the installation. I had to do that anyway, because I was not happy with the tube extending below the disc, and needed to check the angle of the caliper mount. It took just over an hour, with absolutely no modification to the airframe or existing brake tubing. I had to get an additional flare fitting – a female union – to correct the route of the connector tube. I am sure Robbie will include such a fitting in all kits that go out in the future; his kit was so complete when I got it that I found myself amazed at his foresight. He even includes a special drill bit for those courageous enough to drive their own steel rivets!

Installation is a breeze, assuming one has the discs riveted to the wheels. All I recommend is that you ensure that the torque plate is mounted so as to place the caliper assembly as far aft as it will go without interference with the rear tube of the gear leg, with the big part pointing inboard. A trial fit of everything before torqueing things down will make all of that obvious! While you are at it, install the connector tube to the caliper and to the existing brake line prior to installing the wheel. It just makes fitting it together easier. Bleeding is less troublesome than Robby's manual would have you believe: simply open the master (under the front seat), then crack the bleeder valve. Air will come out, followed by fluid. Close the bleeder, and attach the hose from your brake fluid squirter. You do have one, if you own a Cub. Mine is a simple trigger-type oilcan with a length of model airplane fuel line attached. With the squirter attached, squirt fluid into the bleeder valve (open it, of course, after the squirter hose is attached) until it comes out of the master cylinder. Then cap the master, and squirt two more shots in prior to closing the bleeder valve. That's it , folks. No air in the system, and a hard pedal with a half- inch travel. Do make sure the wheel rotates when the pedal is released; if it doesn't, then crack the bleeder until enough fluid comes out to permit rotation.

If you are like me, and don't do copper tube flares very often, use some care. I polish the ends of the tube prior to flaring, and then examine the results with the 10x magnifying glass that I use on the Decathlon's crankshaft flange. If it is clean with no visible cracks, it should be leak-proof with moderate snugging. Mine always leak at first, probably due to that DOT 5 stuff – it just wants to go everywhere!

I only put the right side on for the first tests. I figure that is the only way I can get a good comparison of performance. The original Hayes brakes will stop a Cub on a dime with minimum effort, if the pilot has any feeling in his/her heel. Drum brakes have an inherent “servo” effect, reducing pedal effort during application. In the case of Hayes, that means those little pucks rotate a bit due to friction, and bite into the drum. Disc brake pucks cannot so rotate, so heel pressure is all you have to get the brake to engage. All things being equal, then, one might expect disc brakes to require more pressure for a given stop rate. Things are not equal, though; disc brakes are more efficient. Robbie designed these things to have roughly equivalent stopping power, and with disc on the right, Hayes on the left, I can assure you he succeeded. I am doing rough 200 foot stops every day, and the only difference is that it is easier to lock up the Hayes brake. The disc allows for a more even application of pressure. That's really a major difference between a drum brake and a disc brake, and has a lot to do with the aforementioned servo effect.

With a closed system, one might expect that the pucks would retract a bit when the brake pedal is released. Normally, the disc just kicks the pucks back, and that's how a disc brake releases. But Cub brakes are closed – no reservoir, and no shuttle valves, just that little spring inside the Scott master cylinder for managing fluid. So, with no air in the system, there should be a positive release of the brake when heel pressure is removed. I may still have a tiny bit of air in mine; so far, on lift-off, I get about two revolutions of the wheel before residual brake friction stops it. The Hayes side spins until I hit 400 ft. AGL, but then, the pedal on the Hayes side has twice the travel of the disc side. It probably takes twice the fluid transfer to get the Hayes brake to engage.

Break-in is standard, as far as disc brakes go. However, it is really hard to generate a lot of heat when panic-stopping a 1000 lb. aircraft from a 35 mph touchdown, so I wound up dragging the brake on taxi-in for about a quarter-mile. That did it; the disc was too hot to touch, and the pucks got the requisite glaze.

I have made fifty landings to a full-stop with the hybrid setup. The test aircraft now has discs on both sides, and I am documenting each landing until I hit 150. At that point I will disassemble and check wear. I am more than satisfied with the performance of the disc, and quite happy with the ease of installation and the fact that I can change back to original brakes with no hassle, and no changes to lines or fluid. If Robbie can get this setup certified, it will be a real plus for Cub owners – decent brakes with excellent replacement parts service, and no-hassle bleed/ pump-up procedures. For those who want power brakes, the STCd brake augmentation systems that bolt on to the Scott masters will make pedal pressures less, but for those of us with long experience with the original Hayes brakes, the feel and stopping power is darn near identical, except for the reduced tendency for wheel lock-up. Wheel lock-up has good and bad features; the good feature is that you can really bump the Cub around in a tight swivel; the bad feature is that you can sacrifice a perfectly good valve stem if tire pressure is a bit low.

Engineering- wise, I intend to suggest only one thing beyond recommending that Robby include a pair of flare unions (Weatherhead part # 302X4). My suggestion will be to re-drill the torque plates to rotate the caliper assembly until it almost touches the rear gear leg, thus getting it away from ground contact in the event of a flat tire. This is not a big deal on a Cub, since a flat tire is rarely a big deal. You can't taxi in any case, but the slowing down phase would be a bit less abrupt if only the tire and disc were flopping around on the runway. Scraping the bottom of the caliper on the pavement would be slightly more unneeded friction, not to mention the extra cost if it were damaged.

It turns out that Robbie drilled the torque plates for the Super Cub gear leg, and the J-3 has a slightly different hole pattern. I suspect that the solution is to drill the torque plate on assembly for each aircraft, since I find variations in J-3 hole patterns. Using the plates as supplied will give an almost perfect mount for the left brake on the J-3, but the right side assembly will hang down below the disc, possibly causing the above-mentioned ground contact in the event of a flat tire. I have found that the caliper must clear the rear tube of the landing gear “vee” by only a few thousandths of an inch (say, .020). Marking and drilling the torque plates is a trivial job if the marking is done with the caliper on the pins, and with a centerline scribed on layout dye on the torque plate. A drill press is almost a necessity, but now good drill presses are available for under $75, so that's not a problem for any of us.

I have had absolutely no problems of any kind in over 65 actual landings, most of which were panic stops of between 150 and 250 feet from the threshold (yes, we have it all marked off). I can see no real difference in handling, although my guests so far have all raved about the improvement. I suspect it is the hard pedal and limited pedal travel that has them so impressed; stock J-3 brakes take some getting used to. My feet have forty years of Cub practice, so pedal softness and travel are a variable I use only to tell when to add fluid. My disc surfaces are both incredibly smooth, although too shiny for a Cub. One cannot even tell the discs are there unless attention is drawn to them, and even then the only give-away is the shiny disc itself. The caliper and tubing, once dusted with flat black paint, are darn-near invisible.

Robbie has saved us from those miserable-looking 6:00x6s. All we have to do now is get this fine system approved, and get the 8:00x4 tire and tube prices down a bit. Oh, yeah, and for those of us approaching our senior years, a good key-start system for our small Continentals. Then, these fine aircraft ought to make it another half-century.

Update

It is now January 2004, and I have, after 290 landings on the right and 240 on the left (125 of which were full-stops, and most of those panic stops!) practically nothing else to report. Wear is almost negligible, braking action has remained consistent, and pedal travel is now slightly more than ¾ inch, still less than a normally adjusted Hayes brake. Others who have tried these brakes rave about them, and say they never want to try the Hayes brake ever again! I can't say I am anxious to re-convert.

I did a complete heat and stress analysis on the setup, with all 14 of those conditions for continuing airworthiness all pretty and typed up. I'll allow the Cub Club to give you a copy, with the proviso that I remain anonomouse, since I am not yet convinced that I want to go head-to-head with the FAA on this stuff. Everybody says that a 337 would be rejected regardless of how well I do the computations and testing. Just the new policy. Period. After 42 years of aviating, with no adverse contact with the feds, I am just not ready to stick my neck out. But by golly, these brakes are a major step forward for the venerable J-3 Cub. I promise!

One final update: It is now February, and rumor has it that Robbie is close to PMA and maybe STC status. Also, a friendly Fed told me that field approvals are not yet impossible, and that FAA engineering will indeed consider one-time approvals on non-PMA parts. I will wait, so as not to get in the way of anything that would allow all of you to legally use these brakes under STC. If that happens, I strongly recommend a set of these. Save a set of Hayes-equipped 8:00x4's for the occasional air show, so you can be 100% original, and operate with these, for real safety. Conversion back and forth is indeed trivial, except for bleeding the Hayes brakes, and you will save wear and tear on the Hayes stuff. It doesn't seem to go bad on the shelf (they don't make rubber like they used to!) and these discs just don't wear at all in service!

A FINAL FOLLOW UP

The brakes are really a good thing - I now have over 320 landings on one of them, with absolutely no problems of any kind. If Robbie has any real trouble getting the STC, my plan is to send you my rather complete structural and thermal analysis, so that you can share it with CC members. Somebody surely knows a friendly Fed - mine say that one time field approvals are still possible, but I'd have to take the brakes off to go through the process, and I just cannot bear to do that just yet. Maybe at rebuild time I'll start the process.