Piper Flyer Association - Technical Know-how, Serious Fun read more

Modern Stopping Power for Classic Aircraft

Modern Stopping Power for Classic Aircraft

Print
(1 Vote)

by Dennis Johnson

 

Upgrade your Cub with a disc brake conversion kit

I’d been thinking about that old aviation adage, “you don’t have to go up, but you do have to come down.” I thought it might be equally true that, “you don’t have to start, but you do have to stop… somehow or the other.” And it’s also probably best if that stop doesn’t come suddenly off the end of a runway, or involve tree branches. 

With these cheery thoughts in mind, it wasn’t a difficult decision to update the drum brakes on my 1952 Super Cub to modern disc brakes when it underwent a complete restoration in 2014.

A Super Cub Special restoration, with improvements

Bob Hunt, the ragwing aircraft restoration expert I chose to transform a pile of dusty and rusty parts into a shiny new airplane, showed me the original drum brake parts at his shop. As he pulled them from a tattered cardboard box I remarked, “These are off a go-kart, right?”

“Nope,” he said. “So I guess there’s no need for me to explain to you why I recommend this disc brake conversion kit?” 

For this historic aircraft restoration Bob wanted to keep everything as authentic to the time period as possible. Our project was not a typical civilian airplane, but a minor warbird, and we were determined to return it to its original appearance. 

Although the aircraft never saw any fighting, it did help train the military pilots who did. These 1952-1953 PA-18-105 Super Cub “Specials” were specially built for the Air Force during the Korean War and are fairly rare. Only 242 were built, and mine—N105T—was the fifth one off the line, rolling out on Nov. 12, 1952. 

In Roger Peperell’s book, “Piper Aircraft – The development and history of Piper designs,” the author describes what set these planes apart from other Super Cubs:

“1952 saw the start of a special version for the Civil Air Patrol (CAP), the PA-18-105 Special. This was used for training purposes by the CAP, U.S. Army and Air Force flying clubs as well as for some actual military pilot training, and was referred to as the PA-18T. It had the Lycoming O-235-C1 of 108 hp and provision for seat parachutes; no flaps, but it had horn balanced elevators.”

Because the N-number of all these Specials end with a “T,” they are often known as “Tango Cubs.”

While keeping historic accuracy in mind, Hunt also wanted to update my Tango Cub with modern safety improvements.

Hunt recommended the new disc brakes, an updated fuel system, a GPS ELT, strobe lights, a Mode S transponder and new radios to improve the safety of flying a 64-year-old plane. (See “Dump the Tanks” in the March 2016 issue of this magazine for details on how the fuel system was simplified. —Ed.)

 

Modern brakes offer multiple benefits

Of all the modifications, the disc brakes are the only items that alter my Tango Cub’s original appearance. (But still, you have to look closely to notice these 21st century brakes on the 1950s plane.) Hunt selected an FAA-STC approved disc brake conversion kit made by Grove Aircraft Landing Gear Systems for the project. 

The new disc brakes offer multiple benefits. Along with the obvious one—that they will actually brake the plane when needed—with improved braking comes easier ground handling. 

For tailwheel airplanes, a good application of the brakes on one side will allow a taxi turn in almost the length of the plane. That’s very handy for parking at a jaunty angle on the grass at your favorite airport restaurant. It’s also handy after back-taxiing on a narrow grass strip to face into the wind for takeoff. 

Besides working better, the disc system is more reliable and needs far less maintenance. Also, many parts for older brake systems are becoming increasingly hard to find, so installing this new upgrade means parts can be readily ordered from Grove. That’s especially helpful if you have a problem while away from your home base and need a part quickly.

 Caliper 2

 Caliper 2

Cub Kit

Cub Kit

Cub Kit

The conversion process

Anyone with a bit of mechanical experience and know-how can perform this simple conversion. However, the FAA requires that work on certificated aircraft is done under the supervision of an FAA licensed mechanic, and he or she will need to sign off on the project. 

All of the parts and a few special tools are included in the kit from Grove Aircraft. Installation only requires standard hand tools and a rivet gun—and there’s no need to change any wheels, tires or other brake system parts (such as the master cylinder and brake lines), so that keeps the cost fairly reasonable. 

No modifications are needed to any part of the landing gear strut or any other part of the aircraft, except for the wheel assembly. 

This is not a step-by-step guide; you’ll follow the instructions that come with the kit. But essentially, the process goes like this:

  1. Jack up and support the landing gear. Remove the hubcap to expose the wheel hub. Pull the cotter pins, nuts and washers to remove the wheel.
  2. Disconnect the brake lines and drain the fluid.
  3. Remove the existing brake frame and inspect the gear leg and axle for damage; repair if needed. Bolt on the new torque plate.
  4. Take the wheel to your workbench. Deflate the tire and remove it from the wheel.
  5. This next part requires some care. The brake drum, which is riveted to the wheel, needs to be removed. If you have a good drill press, the rivets can be drilled out, but do this only if you’re sure you won’t enlarge the holes in the aluminum wheel. Grove Aircraft recommends grinding off the back of the rivet and then punching it out.
  6. Clean and inspect (and repair, if needed) the wheel. Then, new holes must be carefully drilled in the wheel and the new disc brake rotor riveted on. 
  7. Reinstall the tire on the wheel and inflate it.
  8. Reinstall the wheel onto the axle, with fresh grease. The nut should be tightened until the wheel won’t turn 
  9. and then eased off until the wheel just turns freely. 
  10. Insert the cotter pin. Install the hubcap.
  11. Install the brake caliper according to the instructions—which you are following, right? It bolts into the existing holes.
  12. This next step may require some advice from a mechanic, as the brake lines on many planes have been changed over the years and may not use the same connectors. You are only instructed to hook up the brake lines using the appropriate connectors. You may have to make your own flexible line with hose material and fittings.
  13. Refill the brake system with aviation-grade brake fluid, and make sure the brakes are purged of air. The detailed instructions included with the kit tell you how to do this. If you have a soft brake pedal, this is an indication of air in the system or that adjustments need to be made. The instructions will guide you through troubleshooting.
  14. Complete the paperwork. (Yes, this is a real step listed in the installation manual!)
  15. Clean all the greasy fingerprints off your beautiful plane, take a selfie with your new brakes, and try them out on the ramp.

Now, go out and fly, remembering to always land in a manner such that you never have to put these highly effective brakes to the test.

Dennis K. Johnson is a writer and a New York City-based travel photographer, shooting primarily for Getty Images and select clients. He spends months each year traveling, flies sailplanes whenever possible and is the owner of N105T, a restored Piper Super Cub Special. Send questions or comments to .

RESOURCES 

Further reading

Piper Aircraft: The development and history of Piper designs,” by Roger Peperell. Air-Britain, 1996.

 

December 2016

Save

Save

Please login to continue enjoying members-only content

 

.

This section of the article is only available for our members. Please click here to join to view this part of the article. If you are already a member, please log in.


Login to post comments