SonexBuilders.net

Greetings,

I can already hear a chorus of groans from people reading that subject line :-)

I have a Onex, and it has the Azusa mechanical drum brakes. I think I've read everything that's been written about making these works, but no luck so far. I'm going to spend one more session working on them, and if there isn't a marked improvement, I'm giving up. Note that this thread is NOT asking for tips on making these work unless you have a secret that's never been published.

I started a Onex project years ago, but life got in the way and I sold it. On that install, I had the Aeroconversion brake upgrade, which I thought was clever, and certainly compact. I've read plenty of comments both good and bad. Other hydraulic brakes exist (O'Keefe, Matco, etc) but they're not nearly as compact, though I expect they'd have more braking force.

My question is whether the Aeroconversion brakes will hold enough to do a high power run-up? I don't need max braking force, but I DO need to be able to do a run-up, which I can't do now. I would likely start with a single handgrip master, but eventually would go with differential of some sort.

For anyone who didn't like them and took them off, I might be interested in buying them.

Thanks,
Rusty

I've had the Aeroconversion brakes on my Sonex for years, and they work great. I usually run up to around 2400 or 2500 RPM with no issues.

Thanks for the comments. I have a 912UL which is supposed to be run up to 4000, but I can't make 3000. It's quite possible the geared engine will be more of a challenge for run-ups than the direct drive engine.

Rusty

Hi,

I had the Aeroconversion hydraulic brakes in my 120HP Jab Sonex A. The total package with calipers and lever operated master was provided by Sonex. They provided holding power barely adequate for a modest static runup. Braking power on my fairly short grass strip was an experience for those especially interested in hair raising situations.

The plane has since been re-engined with the R912ULS. To nobody’s particular surprise brake efficiency has gone from hair raising to useless. Ground runup is barely 3000 rpm, which should be 4000. Roll-out braking is now even worse, as the plane put on some weight during the engine swap.

I can’t decide what to do. I like the Sonex system and its parking brake setup. Differential braking is not a neccessity. However, it has been explained by knowledgable parties to me that more pressure is needed. The culprit in the setup is the master, which is too big (3/4’’). This is the smallest that the manufacturer can supply. And a smaller master would mean longer lever travel- there goes the parking brake!

I know of one R912 Sonex which kept the original Aeroconversion calipers and went with two hand lever operated masters (1/2’’) from Matco (??) mounted centrally on a bracket (so no parking brake). It transformed the roll-out braking.

What to do??

What to do indeed... Great info, though you aren't making my decision easier :-)

A smaller diameter master would be the key, and it's good to know that the Aeroconversion brakes will work if you get them enough pressure. In theory, there really shouldn't be much travel in the master cylinder. If there is, it would mean there's air in the lines, or the lines are expanding under pressure. There may be better tubing options to minimize expansion.

I removed the original brake handle, because I don't have enough hands to do a run-up with a separate brake handle. I went to a stick mounted lever, which I like. Toe brakes are an option as well, and as a last resort maybe heel brakes.

Rusty

Rusty,

I think you’ve got a point: a hand lever operated master mounted on the stick might be an option. Both Matco and Hegar can supply, I think. However, I am uncertain what dimension to select (1/2’’ or 5/8’’).

And, you’re right. The travel on the lever down on the master is really not anything to worry about: its the huge brake lever poke Sonex suggests that really restricts practical parking brake operation: once finished it is not so easy to rebuild without starting from scratch.

Another issue: the dot 5.0 brake fluid Sonex (and the brake components manufacturer) suggests, is silicone based. Use anything based on glycol (common for cars), and whoops there goes anything made of rubber. However, the red automatic transmission fluid (formerly ATF A), now Dextron something, is also based on silicone. My brother in law uses it with great success on his aircraft with hydraulic Beringer disc brakes. It stops the thing like there is no tomorrow. I am wondering why Sonex has not suggested this option- liability?

Hi all,

Have you been asked what is the best modification you have made to your Sonex? My answer would be using the Sonex hydraulic brakes and the O'Keefe hand lever master cylinder. http://www.okeefeaero.com/-hydraulic-brakes.html

I fly a OneX, AeroVee & Sensenich prop. I can run the engine up to 2600 RPM without any wheel slip or creep. That's high enough to hear that the engine is running well and that the numbers are where they should be. My WOT for take off is ~ 3200 so 2600 is good enough for the run up.

The biggest advantage of the hand brake is that I can do short field take offs properly. Left hand on the throttle and right hand holding the brake. It also gives me a good parking brake. This is hard to describe in words; really deserves a picture but I don't have one. When I squeeze the brake handle a gap opens up at the bottom of the handle. I stick a narrow piece of metal into that gap. I can then release my hand, but the handle doesn't move. Simple & effective.

Outstanding information! That sounds like my best plan for right now- Aeroconversion brakes and Hegar 1/2" bore hand lever. At some point I'll want to figure out how to make that differential, but I don't need it for now, or maybe ever. I'm still committed to trying to fix the mechanical brakes one more time, probably tomorrow.

Rusty

I’m with Rusty here!

But still- O’Keefe and Hegar: are those the same? A little confusing in the two last postings.

Thx

Kai wrote:But still- O’Keefe and Hegar: are those the same? A little confusing in the two last postings.

I'm assuming O'Keefe is just selling the Hegar master cylinders without mentioning it, or giving any other useful info like bore size or the stick clamping size. The lack of info seems to make it cheaper though :-) I have an email into O'Keefe, but will call them today if they don't reply this morning.

As tempting as it is to give the mechanical brakes one more try, I had to ship my Dynon back for service, so the plane will be down for 3-4 weeks. Since I have that much time, I think I'll just go straight to the hydraulic brakes, and get the wheel pants installed. I can still run the engine and taxi, but there's a big hole in the panel where my EFIS/EMS should be.

Rusty (looking for a spare D180)