Aeroconversion brake performance?

[Kai]

All,

Further to our recent discussion, the concensus seems to be that a differential system with toe brake pedals linked up to 2 pcs ø1/2’’ master cylinders is the preferred way to go. Next comes the single hand lever brake with 1 pcs ø1/2’’ master on the stick.

No mention has been made of differential heel brakes. I seem to recall that in my far away younger days I accumulated some hours in a plane so equipped. As far as I can remember, they worked as advertised. Yet- nothing! Is there any paricular reason for this?

What about 2 separate ø1/2’’ master cylinder heel brakes, one for each caliper? Hegar seems to have something particularily well suited for this. I am thinking it might be possible to manufacture some sort of solid base plate with appropriate brackets for the masters. The base plate could then be bolted to the cockpit floor for the shoe heels to comfortably control the ‘buttons’.

Comments?
Thx
Kai

[GraemeSmith]

I seem to recall that in my far away younger days I accumulated some hours in a plane so equipped. As far as I can remember, they worked as advertised. Yet- nothing! Is there any paricular reason for this?

I believe heel brakes have fallen out of favor because they cause even more ground loops and outright nose overs than toe brakes. They are prone to accidental activation by lazy feet. Or people like me with big feet that can keep their heels on the floor and work the rudders with their toes.

I flew a Champ that had them and after an hour of pattern work my calves were aching because I was having to hold my feet up so unnaturally high in order to keep my heels away from them!

[Bryan Cotton]

I learned to fly with heel brakes. They are not as convenient as toe brakes. The advantage of learning to fly in an antique is that you learn to never be dependent on brakes for normal ops. But I personally think they are fine.

[DCASonex]

Kai,

A single 1/2" bore master cylinder has slightly less area than a 3/4" bore ( 0.196 Sq. in vs 0.442 Sq. in. ) and thus would result in more hydraulic pressure for a GIVEN FORCE on the master cylinder. However, there are other considerations. A 1/2" bore cylinder will have to move a bit more than twice the distance to move the brake pad cylinders a given distance than would the 3/4" bore. That makes maintaining complete fill in the cylinders more important, and less able to compensate for any air that might find its way into the system. I am not sure what size the Hegar cylinders are that I purchased from O'Keeffe (was Great Plains back then) with my toe brake setup, These cylinders do not have built in hydraulic fluid reservoirs like those of some much more expensive and bulky cylinders and over time I find a bit of air in the lines, but this only means slightly more travel of the pedals. I do bleed and top them up about twice a year before air affects operation. Another consideration is the geometry of how the master cylinders are to be operated. A long lever can greatly multiply the force applied to the cylinder while requiring longer hand travel. Foot pedals and hand grips have about same amount of travel, but two feet can usually apply a lot more force than one hand.
David A.

[Scott Todd]

I've flown a few different Sonex's with the hand brake. For operating out of long or grass runways, they were adequate. I get John's goal was simple and inexpensive, which he attained. However, for operating on tight ramps, short runways, strong crosswinds, nothing beats differential toe brakes. Every certified GA airplane built over the last 70 years can't be wrong. My brakes are discussed a bit on the Onex forum. The probably cost $1000 after the custom hoses, master cylinders, reservoir, AeroConversion brakes, etc but were well worth it. They will hold a full power run-up with a bit of work but a Mag check is no problem. And when I want to stand on them to make a short field or turnoff, they really work!

Here is a nice document from Matco talking about brake geometry.

https://www.google.com/url?sa=t&rct=j&q ... XkB5EXrlkU

[13brv3]

Good to see some actual numbers, even if it only relates to the Matco brakes. I can certainly verify that direct pressure on heel brakes is terrible, though good exercise :-) I'm not a fan of heel brakes, and toe brakes never seem to fit my big feet. It's always too easy to be on the brake when you don't mean to be.

[Scott Todd]

Its an Experiment(al) homebuilt airplane. Make those rudder pedals and brakes any way you want to fit your feet. If you can't, someone in your local EAA chapter can weld them or modify what you already have :)

[13brv3]

Can they also move the fuel tank out of the way so I can make the toe brake lever taller :-) I might end up making a small lever that's only on the inside or outside edge of the pedal, so I can more easily avoid it. A dual hand grip style on the stick would be fine as well, but it would be overly bulky with hydraulic brakes. I made a dual handle for another plane with mechanical cables, and really liked that.

Rusty

[GraemeSmith]

Just for fits and giggles - my handbrake is hand brakeS. I cut the wire and attached it to two levers and "T topped the handles so I can twist the top for differential braking.

It should be noted that Sonex don't recommend differential brakes with the non-castoring tailwheel. I can see why - it adds side load to the setup that was perhaps never intended. And for sure you can "skid" the tailwheel if you try - not very hard.

I do like the ability to differential brake on one main to help control any potential ground loop. But I avoid using it to spin the plane around. The fasteners in the 6" machined wheel fork are not set up to take it.

[mike.smith]

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.

That doesn't seen to make sense. The ENGINE spins that fast, but with the gear reduction (2.43), the max RPM of the PROP is 2,386 rpm. That's according to Rotax's info on that engine. That engine is 100 hp, vs the 120 hp of something like the Jab 3300. If the brakes hold for a Jab why not a Rotax?