Mechanical disc brakes?

[13brv3]

Greetings,

OK, so this will likely be a new spin on brake questions. Has anyone seen a mechanical disc brake setup on a sonex, or similar sized plane? I had an Airbike last summer, and had to get rid of the terrible Azusa brakes that wouldn't come close to holding enough to do a run up. I had seen some talk of using mountain bike disc brakes, which are really light. I was able to make the parts for the conversion, and they worked very well. I even had a dual hand lever on the stick for differential brakes. Of course the first thing to note is that the Airbike is half the weight, and lower speed than the Onex I'm finishing.

For the Onex, I planned to leave the stock Azusa (machined hubs) and single lever on the left until I determined how well they actually worked. I've done enough taxiing now to know that they're horrible, and worse yet, they require one more hand than I'm equipped with to attempt a run up. I removed the stock handle, and cables, and installed a hand lever on the stick. I need to make a couple simple changes, but it already has as much braking force as the original handle gave me, and now I have enough hands. I believe this will be good enough for initial flying at my home airport, but I'll want to upgrade the brakes before too long.

There are several hydraulic options, namely Aeroconversion, and O-Keefe. If I did that, I'd go with the hand lever master cylinder, and probably the O-Keefe brakes. It would be nice to have differential brakes, but I haven't seen a dual hand lever that will do that. I'd imagine it would be pretty bulky if it existed.

I prefer the simplicity of mechanical brakes, and the braking force needed just isn't that high, so I'm thinking about trying the bike disc brakes again. I'd love to find a bit heavier mechanical discs as an option though.

Rusty

[GordonTurner]

Hi Rusty

I’m sure what you’re looking for is out there somewhere. What are the big heavy electric cargo bikes using?

Keep us posted. Gordon

[13brv3]

I had never heard of a cargo bike, but after a very brief search, it seems they're split between hydraulic and mechanical disc. One brand that's frequently listed is Tektro, with 180 mm rotors. Tektro has a main site that's not easy to sort through, but does have mechanical disc units. It appears they're OE equipment for someone. The Tektro USA site has no mechanical discs that I can see.

What I used before was 180 mm rotors, and Avid BB7 calipers.

Thanks,
Rusty

[peter anson]

A builder in the UK, I think it was Mick Greenway who follows this forum, has fitted mechanical calipers that I think are intended for mini bikes. They look really good and apparently work well. As with all those things, I don't think the supply chain is necessarily reliable. If you search for mini bike brakes on eBay, plenty should show up.

However, it is possible to get the standard Azusa drum brakes working well. A couple of years ago I had the standard Azusa brake shoes relined by a local brake specialist as the original linings were separating from the shoes and the improvement was very noticeable. My Sonex is fitted with the standard pressed steel drums. No problems with fade and they are adequate for run-ups.

Peter

[13brv3]

Thanks Peter. I'll add mini-bike to my searches. At first glance, most look pretty much like the mountain bike brakes I've been seeing, though there's a smaller diameter version that seems more robust. Those seem to generally be attached to a rotating shaft though.

FWIW, this is the dual cable lever I'm using for now- https://www.amazon.com/dp/B0186OPM8Q It's actually pretty nice, but on the Onex stick, there isn't much clearance below the adjusters, and the cables are too close together to clear the 7/8" tube. I've found that it's awkward to hold the brakes when the stick is full back anyway, and it will be more natural to rotate the handle about 45 degrees CCW. That will give me more clearance for the adjusters, so I'll do that next time my work schedule and non-life-threatening temps align.

I also haven't given up on the Azusa brakes yet. Once I get the brake lever settled, and get a bit more time on the brakes, I'll pull the wheels and investigate to see what can be done. Did you have them install linings with a different material for more grip?

Rusty

[Onex107]

I built the Onex to print with all the left hand levers and knobs and didn't like the brakes either during a runup. I added a foot pedal in the middle, in front of the rudder pedals, that is simply attached to the bottom of the brake lever. I can hold the brakes with my foot during the runup without a problem and both hands are free to handle the throttle and mixture. Granted, the Azuza brakes are not the best but it's a simple fix for a bad situation.

[13brv3]

Sounds like a pretty unique solution.
Rusty

[peter anson]

Hi Rusty, I can't give you any information on the lining material because it was whatever was available, but it does seem to have better grip. In the days before disc brakes became common, racing motorcycles often used so called "green linings". These were linings with a higher coefficient of friction and presumably shorter wear life. Choice is more limited now.

Peter

[13brv3]

Thanks Peter. The project I bought was originally purchased 10 years ago, so the brakes could be that old. I can't find definitive evidence that linings get hard with age, but for the cost of a set of shoes, I figured it was worth ordering a new pair. Sonex actually has the best price on them also. Since I'll eventually be pulling the wheels to investigate, I might as well clean up the drums and change the shoes at the same time. If that doesn't help, I supposed I could try to get someone to reline the old shoes if they believe they can do better than the original linings. I don't think any of this will stop me from flying.
Rusty

[scotttro]

They do make dual lever setups. https://bikerumor.com/hope-tech-3-duo-lever-pulls-2-hydraulic-brakes-with-1-hand-tech-3-x2-uno-does-too/: