Differential Braking

[Brian Jackson]

Greetings folks.

It's odd that in the years I've spent here I know nothing about differential braking other than in concept. For example, are there generally 2 separate hand levers or are they usually engaged with a secondary pair of pedals? I'm sure there are considerations in landing gear triangulation to prevent twisting and over-stressing the structure, much like how you don't want a super hard grip on a rotor brake twisting the mast.

I'm curious about your set-ups, how you achieved differential braking, and when & when not to use them. Not seen a lot of discussion on this topic and Search is of little use on the Forum. Thank you in advance.

 

[Vance]

The Predator uses a free castering nose wheel with differential braking for steering.

She has toe brakes and that makes it very natural; you work with the rudder first and then if it not enough to make the turn you give a little pressure with your toe that already is on that pedal.

I expected challenges and learned it quickly.

Typically my clients can learn it with very little taxi time. We just go to a big open part of the non-movement area and find lines to follow.

Anything over about 10kts of indicated air speed and it is easy to just steer with the rudder.

The Dominators I have flown use heel brakes but basically work the same way.

 

[Brian Jackson]

Hi Vance.

So your DB setup is activated by the rudder pedals? Does this mean you can only brake one side or the other but not both simultaneously?

 

[gyrojake]

Here is what I use, and recommend nothing else.
Home made primary cylinder and home made secondary cylinders.
Asusa mechanical drum brakes.
I use the hydraulic cylinders instead of cables.
I use heel brakes which gives me a lot of leverage, like power brakes.
effortless steering and stopping.
Make zero radius turns, great for parking
Good luck with your choice.

 

[Brian Jackson]

Here is what I use, and recommend nothing else.
Home made primary cylinder and home made secondary cylinders.
Asusa mechanical drum brakes.
I use the hydraulic cylinders instead of cables.
I use heel brakes which gives me a lot of leverage, like power brakes.
effortless steering and stopping.
Make zero radius turns, great for parking
Good luck with your choice.

Thank you, Jake. Going to study those photos. You always do such amazing work. So glad to see you back on the board and flying.

 

[Vance]

Hi Vance.

So your DB setup is activated by the rudder pedals? Does this mean you can only brake one side or the other but not both simultaneously?

I can step on both brakes at the same time; I recommend against it unless I am at taxi speed or less.

I also recommend only using one rudder pedal at a time; in other words more or less right pedal rather than right pedal and then left pedal.

 

[gyrojake]

I can step on both brakes at the same time; I recommend against it unless I am at taxi speed or less.

I also recommend only using one rudder pedal at a time; in other words more or less right pedal rather than right pedal and then left pedal.

You take all the fun out of it; I want to use both rudder pedals together

 

[giro5]

My AA1B had a castering nose wheel that differential braking to control steering at low speed taxing and my Citabria was a tail dragger the I also used differential braking to control taxing (and takeoff run and after slowing on touchdown).. The differential braking can be toe or heel activated and can be made as a separate controllable part of the rudder pedal or a separate control pedal very near the toe or heel area. You should be able to use the braking on either rudder pedal independently or together with each other and or the rudder function. The attached picture is the front right side of my kb2 where I copied the rudder and differential braking from a dominator. Two pedals two separate cables the top larger one for the rudder and the smaller one heel control for the right brake. I used Azusa drum brakes. Sorry about the ropes and bungee chord as they are extemporary.

 

[Brian Jackson]

I see that the Azusa drum brakes are popular here. Are these favored over, say, a bicycle disc brake because they're enclosed? Or is it simplicity due to not having calipers to align? I'm curious about the pros and cons of these systems. To my eye a drum brake looks heavier due to the enclosure, which would seem like a negative because of it being so far below the thrust line / CG.

I had planned to forego brakes altogether in favor of a simple nosewheel scrub brake but am told by Sport Copter (the maker of my nosewheel assembly) that differential braking is really the preferred method and very strongly advised.

Thank you to all whom have added to this conversation.

 

[ultracruiser41]

Scrub brakes are OK but wear out tires and won’t stop anything if it’s wet out.
Black Max brakes…. Easy and simple system.
remember….. with a castering nose wheel and differential braking ……if one side fails you probably won’t be able to steer at all. .

 

[gyrojake]

I like the drum brake because they bind better during high prop RPM while prerotating.
They are a bit heaver than a disk; I have added them after the fact and noticed no pitch difference in the hang.
Sportcopter makes a set of pedals with toe brakes and hydraulic cylinders but are dependent on your rudder cables to work.

 

[Doug Riley]

My tandem Dominator had toe brakes in the front seat and heel brakes in the back seat. the system was cable-operated and used drum brakes at the two wheelbarrow wheels. Steering was by differential braking and free castering nosewheel.

The steering worked fine. I did find the toe brakes more awkward to operate than the heel brakes. Also, as Jake says, you can really wail on heel brakes, to keep the gyro from slipping forward when prespinning. OTOH it's not possible to channel your full weight through your toes, unless you're a ballerina.

My 1-place Air Command came with hydraulic brakes. I could never get them completely bled, and the (single) pedal was therefore always soft. I could hold the gyro back during a prespin better by planting my feet right on the ground than by applying brake. I took them off, in fact, and didn't miss them in the least.

(Discussing brakes is fertile ground for confusing English words that sound the same: pedal vs. peddle, heel vs. heal, brake vs. break, etc. What a messy language we have.)

 

[Brian Jackson]

My tandem Dominator had toe brakes in the front seat and heel brakes in the back seat. the system was cable-operated and used drum brakes at the two wheelbarrow wheels. Steering was by differential braking and free castering nosewheel.

The steering worked fine. I did find the toe brakes more awkward to operate than the heel brakes. Also, as Jake says, you can really wail on heel brakes, to keep the gyro from slipping forward when prespinning. OTOH it's not possible to channel your full weight through your toes, unless you're a ballerina.

My 1-place Air Command came with hydraulic brakes. I could never get them completely bled, and the (single) pedal was therefore always soft. I could hold the gyro back during a prespin better by planting my feet right on the ground than by applying brake. I took them off, in fact, and didn't miss them in the least.

(Discussing brakes is fertile ground for confusing English words that sound the same: pedal vs. peddle, heel vs. heal, brake vs. break, etc. What a messy language we have.)

Thank you, Doug, and all who chimed in. Makes a lot more sense now, and the heel pedals w/drum brakes seem like the way to go based on others' experiences. I do like the Black Max system that Ultracruiser mentioned. However I'm not sure it could be easily (or cleanly) adapted to my ship because I am NOT bending the tube for the axle strut as is called for in the GyroBee docs. Instead I have consulted with Azusa engineers and gotten the OK to put the slight bend in the axle itself. Judging from the photos on the Black Max site it looks like any bend in their axle unit would throw off the alignment of their caliper relative to the disc.

"Wailing" in the brakes may not be necessary since the plan with this build is to employ an electric pre-rotator which is independent of engine RPM. But I can see the value of strong gripping brakes as both a safety feature and a convenience during run-ups.

For the drums I would need to take their depth (cylindrical thickness) into account. Tempted to just buy one and take survey measurements before committing to it. The journey continues...

 

[Gyeric805]

Can be problematic if you have too much weight on the front wheel or need to travel through a soft spot ,if your front wheel is small and guess the castor angle comes into play

 

[Hosko]

This is what I fit .... toe operated disc brakes.

 

[wolfy]

Personally I like a hard linked nose wheel but mainly because of predominantly operating on rough uneven ground.

wolfy

 

[Brian Jackson]

This is what I fit .... toe operated disc brakes.

What a beautiful piece of kit. Very clean. Is there any spring in your nosewheel steering linkage?

Something else I was wondering that I kit on above a little, main gear strut torsional rigidity. Has anyone noticed their strut tube pylons trying to twist themselves forward when full braking on a run-up? I keep imagining tube thru-bolts stressing the tubes on one side only and wondered if this effect has been observed. And if non-dampened "springy" legs make this effect even more pronounced. I know we don't use monster brakes on the rotor to prevent mast twist, and I'm carrying over this thought to ground braking.

 

[Hosko]

What a beautiful piece of kit. Very clean. Is there any spring in your nosewheel steering linkage?

Something else I was wondering that I kit on above a little, main gear strut torsional rigidity. Has anyone noticed their strut tube pylons trying to twist themselves forward when full braking on a run-up? I keep imagining tube thru-bolts stressing the tubes on one side only and wondered if this effect has been observed. And if non-dampened "springy" legs make this effect even more pronounced. I know we don't use monster brakes on the rotor to prevent mast twist, and I'm carrying over this thought to ground braking.

Main undercarriage is heat treated chromoly .... it will flex in any direction . Nose wheel has spring & damper , using mains to hold while pre rotating loads up this suspension without any problem .
Total collective hours for this design without failure is between 9-10k hrs on rough unprepared strip's.

 

[Resasi]

Black Max brakes…. Easy and simple system.

I’ll second that, they were great brakes and wheels on the Hornet.

So good that they almost twisted off the strut attachment on the first taxi and brake test, luckily Denis had spotted the problem contacted us and came up with a fix for that as we were at about the same stage in our builds.

 

[Georgi]

Hi, Resasi. Can you share pics/drawings of that fix? Thank you. Georgi.