Hydraulic disc brakes

[bob turner]

I am more of a Cub guy, and got introduced to Robbie Grove back when he was looking in to discs for the J-3. My aircraft has the set that was used during STC evaluations. I have field-approved master cylinders as well. They work great.

The mechanical brake Aeroncas have some problems - one of them is that the wheels are cracking (old age?) and new wheels are prohibitively expensive when they become available.

So I got a field approval to use essentially what the factory is now using - Grove from master cylinder right on through the calipers, and including a brand new wheel. I was going to have the owner struggle with assembly under my supervision, bu.t he and his mechanic both got the flu, and have been out of commission. So, Monday I ducked into his hangar and began assembly. Hardest part is getting the old cable and housing out. The new stuff just drops in. There is a clamp that goes on a transverse tube - it is spread to go over the tube, then cinched up with an AN-bolt. Takes five minutes, because you are on your back.

I used a Tee for the master cylinder output - I should have saved the Edelman part number, butit is still a standard tee, with one male 1/8" NPT and two female. The top received a standard bleeder screw - I personally find a bleeder screw on the master cylinder to be essential, but I haven't convinced Robbie yet. The female outlet gets a Weatherhead elbow - 352x4. That mates with a copper tube, flared, with a 105x4 tube nut. We used just over four feet of soft 1/4" copper tube to go from there to the caliper, coming through the same hole in the fabric that the cables came through.

The caliper installs easily, and gets the same inverted flare Weatherhead connection. I was going to use a flexible rubber hose somewhere, but any flex will be distributed over about 18" of tube, well within its elastic limit. Wheel and tire are more or less standard, except you need a special sleeve and new axle nut - all supplied with the new wheel.

Master cylinder reservoirs go in easily, and require a 1 1/2" pipe nipple - again 1/8" NPT. Holes in the floorboard above the reservoir enable easy filling once every six months.

I expect a test flight next week. I get to fly it - hopefully one of the owners will be well enough to enjoy the back seat. They all had flu last week.

My PMI has promised a field approval on a 7EC that already has hydraulic drum brakes and Cub master cylinders. Sort of a different setup. I don't know if the owner will spring for the parts - it seems to be flying ok with fairly regular diaphragm replacement. They tell me the brakes are barely adequate.

[MikeB]

Does the 7EC have cable or hydraulic brakes? It seems to me that if the wheels are no longer available for the Van Sickle brake systems it should almost be a 'no brainer' to go to another (in this case) hydraulic brake system which would in most cases mimic experimental airframes that are on the market using the Grove wheels, etc. My biggest concern would be that they (hydraulic) would be too good and cause the A/C to 'nose over' if they were applied to hard on a roll out. Realizing these would have a field approval. Here again, we're not talking brain surgery installing a different working brake system but............
Mike

[bob turner]

Same brake that is used on new Citabrias. Same brake that I have used on J-3s for a decade. The difference is that a disc brake is modulable - less pressure means less braking action. Older drum brakes are often either on or off.

For instance - we had a Waco UPF-7 with original brakes - a true handful in a crosswind. It had been on its back four times. We installed Cessna 310 brakes, and converted it to a Piper Cub!

If you jump on the poorest brakes at slow taxi speeds, you will break a prop. Brakes are a control system, and not something you abuse.

[MikeB]

Bob,
Agree. Both my Champ and L16 had (Champ) have (L16) Goodyear heel disk brakes. Not much surface area for the pucks so they are kind of ho-hum on a full power run up. On the other hand, they work great for a tap here and there on a landing roll out and turning. My 11CC Chief project has Van Sickle toe brakes so that will be a new experience (along with getting used to using a wheel again instead of a stick). Be interesting as to how your conversion works out. Keep us informed.

Mike

[bob turner]

Successful taxi and test flight today, logs all signed off, etc. I have very little experience with mechanical brakes, so I cannot tell you first hand that it is better, but it feels as good as my Decathlon.

After the test flight, the owner came by and was apparently quite pleased. He said "no more stabbing at the brake - they work much, much better".

I have only one thing to further research - we used a single copper line, which absorbs the flex of the axle tube over about 18", and I believe we are well within the elastic limit of the line. I have a test setup, and can do exact measurements, but need to know exactly how far that oleo can move, so I can compute the angle of swivel at the center bolt. If any of you know that dimension, I would appreciate it. It is, of course, trivial to insert a flexible hose - but if it is not necessary, why haul the extra weight?

[MikeB]

Bob,
Is it possible to get a copy of the approved 337 for future use?
Mike Berg

[bob turner]

Sure.

The FAA inspector who was willing to sign these things retired in January - our great loss. It is my impression that possessing a previously approved 337 does not automatically or even often result in a subsequent approval.

Checked with the owner today, and he was gushing: "Absolutely no comparison. These brakes are dramatically different!"

I am surprised that there is not more interest here - I suppose that all the other mechanical brake Aeroncas are doing quite well?

[kyleb]

Sure.

The FAA inspector who was willing to sign these things retired in January - our great loss. It is my impression that possessing a previously approved 337 does not automatically or even often result in a subsequent approval.

Checked with the owner today, and he was gushing: "Absolutely no comparison. These brakes are dramatically different!"

I am surprised that there is not more interest here - I suppose that all the other mechanical brake Aeroncas are doing quite well?

I'm sure people look at the cost and think "As long as the existing brakes work and I can find support for them, I'm not turning loose $3k. But when the day comes, Grove has a viable option." The talk of having to do it via 337 is also a disincentive.

[bob turner]

I don't know what the complete kit will cost, but I will guess that, paying a mechanic to do the installation, three grand will be about right. How much is a replacement wheel?

This aircraft has had three cracked wheels and one cracked brake shoe. It is not used for student training, and rarely landed off- pavement. They found one used wheel for $700, but it did not have the brake drum, and we did not have the necessary machinery to transfer the drum we had. The cracked brake shoe was discovered after we had one side already converted.

In short, it looks like a lot of 7AC and EC owners will be faced with a choice of the Wag kit or the hassle of a field approval. When you see the difference in price, I bet you will vote Grove.

The STC Cleveland kit will give you the same performance, but unless you go Wag toe brakes, I have no idea what you use for approved master cylinders.

[hammmike]

I talked to Rob last week about the champ brake conversion for the Champs. he said the hydraulic conversion will run around $2600 or $2700 for the complete kit. He said at the present time he will not pursue a STC for the conversion kit. He has one installed with a 337 and will send a copy of it to anyone wanting to install a set. He said the cost of getting a STC approval is so cost and time expensive that he will have to charge a significantly higher amount. The kit can be installed without any welding or uncovering fabric.

[bob turner]

With that inspector who was willing to sign these things retired, I have no idea how we proceed.

However, here is what I suggest: Point out to your inspector that all components are just about identical to those used on new ACA products, with the exception of that clamp. Point out that the existing approved installations are wildly successful - I flew ours yesterday, after two weeks of the owners flying it almost daily, and am pleased.

As soon as one of the owners writes a glowing report and gives me permission, I will post it. Use that as a lever, to convince your PMI that this conversion is a dramatic increase in safety for this aircraft. The safety aspect cannot be stressed enough.

[bob turner]

I wrote the 337 to include automotive type flex lines. Tomorrow we will incorporate two flex lines on one side. I am not convinced they are needed, but the one at the caliper will make pad renewal easier, and the one at the master cylinder will absorb any flex present as the gear goes up and down on the oleos. I will have part numbers and comments tomorrow.

[bob turner]

We have been operating for a month with copper lines - two of them, terminating at the master cylinders and calipers. I did some testing, and determined that the gear leg flex, spread over 18" of curved line, did not exceed the elastic limit of the copper.

The owners had the option of flex lines, and so we are about to install them - one at each caliper, and one where the lines come out of the belly behind the inner gear leg bolts.

The choice, of course, is between Aeroquip and automotive, and I put automotive in the 337. I am inclined toward auto, since it is tested to much higher pressures, seems to be lighter, and is a bit less than half as expensive.

From about 1930 through 1980, automotive standards involved pipe threads and what are called "inverted flare" connections. Now, of course, every auto is different, and you simply cannot buy standardized anything, let alone brake hoses. But, surprise! The Piper Cub brake hose is pretty much the 1967 Mustang brake hose, with a female #4 inverted flare on one end and a male 3/8-24 on the other, set up either to bottom out in a threaded hole or to mate with a #3 inverted flare fitting.

So at the caliper we use a 90 degree fitting - 1/8" NPT to #3 inv flare, Weatherhead part #403-3. The other end of the hose fits the copper line with a tube nut 105x4. Of course this is all 1/4" soft copper line. Aluminum is also ok. Use care when flaring - examine the flare with 10x magnification, in sunlight.

Then, at the top of the inner gear leg, the copper tube goes in to another flex line using the same tube nut/flare. The flex line then goes into the belly, up, and forward to the master cylinder. Matching the male end of the flex tube to the copper line from the master cylinder requires a #3 inv flare fitting - Weatherhead #202x3 - and a fitting up to the #4 flare -Weatherhead #252-4. These must match, with a male pipe on one, female on the other.

At that point, it is a straight shot with another short copper line with two tube nuts, into a Weatherhead #352x4, going into the master cylinder port.

The hose itself is NAPA 36549. You need two or four, depending on whether you mind copper going to the caliper (most J-3s are set up that way by STC).

I can give you a complete shopping list, including the Edelman cross-references if you need them. If you try this, you will be delighted with the brakes, I promise.

[bob turner]

So, a summary: Assume you will use two flex hoses each side, and one will be centered on the hole in the fabric:

90 degree fitting for caliper - 403x3, or Edelman 122320. You need two.

Tube nut - 105x4, or Edelman 121004. You need eight.

Hose - NAPA 36549 or Car Quest 4312. You need four (still under fifty bucks for all of them).

Adapter 202x3 - Edelman 124320 to adapt male end of hose, and 252x4 to boost that up to the right size (Edelman 126420). Two pairs.

And finally, at the master cylinder - two 45 degree elbows 352x4, Edelman 125420.

And that 1/4" Copper tube - six feet, to be safe. And a good tubing tool kit.

The owners are using giant Adel clamps to hold the copper line on the aft side of the inner gear leg. I cannot fault that, but if it were mine, I would simply wire it up to the left over brackets the cable ran through.

Also, I used bleeder screws on this installation at the master cylinder. We do not need them! If you do a J-3 style installation, the high point is not at the reservoir, but at the outlet end, and I find them necessary there. If you want bleeder screws, you need a "tee" with 1/8" NPT threads, at the output of the master cylinder.

[Hiperchamp]

Hi Bob;
I'm new here (posting wise; I've been visiting the forum for 6-7 months) and am in the process of doing the same conversion to a 7AC project I acquired here in Louisiana. As the Baton Rouge FSDO is spring-loaded to "hell no" I am doing the 337 with the help of a DER in Texas. My wheels, brakes and master cylinders should be here Friday and the ACA/Wag Aero stuff arrived on Monday. AN/MS hardware is on the hangar wall. I'm doing the straight weld-in of the lower brake brackets in my bird as it still un-covered and will be easier to explain to the feds...

If I have any questions I hope you don't mind me picking your brain via this forum...

Chris in Shreveport
Champ N28558
Hiperbipe N777HT