How do Finger Brakes work?

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Jon Matcho

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While at SnF I noticed a few planes had "differential finger brakes". I am curious as to whether anyone has knowledge of these, particularly how they work. How exactly is finger force transferred to the brakes with sufficient force? How do these work?

You can find a picture of them here.
 

StRaNgEdAyS

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Have you ever ridden a motorcycle?
The force would be transmitted in a similar way to that of a motorcycle front wheel brake. The finger brakes would operate hydraulic pistons which would transmit the force to the brake calipers via hydraulic fluid.
A rather interesting Idea, but for my money, I'd much rather have both my hands free to operate the controls, than have one hand alternating between the throttle and brake. However, if one could attach the finger brake levers to the throttle lever then I'd be interested. That way I could leave my hand on the throttle to quickly apply power in the event of an unforseen go around (having to lift off again to avoid something running out onto the runway, something not unheard of out here in country OZ... a Kangaroo can make an awful mess of a plane :eek: ) and still have your fingers on the brake levers ready to apply braking on landing.
 

orion

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I was wondering if there wasn't some form of a boost system involved along with the hydraulics. First, the levers that the pictures show don't seem to be oriented in such a way that you could get as much power into the lever as you can on a motorcycle hand brake.

Second, the motorcycle is lighter than the airplane and the braking disk on its brakes is substantially larger in diameter than what you see on airplanes. As a result, it takes much less force on a bike brake to get effective stopping forces.

To get even a light airplane to stop and steer effectively will require a substantial amount of force input into the hydraulics (remember, normally we brake with our feet), well beyond what normal hand brakes could deliver.

All this makes me think that the finger brakes are really just remote controls for the physical system.
 

StRaNgEdAyS

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Yes that point did occur to me some time after I'd posted the reply, while I was considering adapting a motorcycle braking system for use on my design.
Typically the front discs of the motorcyle are pretty large in diameter, and the positionig of the levers DO allow for quite a bit of force to be transmitted, unlike in the pic there, which appears to be operated by dragging the controls back with one's fingers. The rear disc however is considerably smaller by comparison, and probably small enough to be of use in a aviation situation and, coincidentally, is operated using the foot. (with a couple of specially modified exceptions, one being a thumb operated rear brake system used by Mick Doohan on his 500cc GP bike) But the braking force here is not very large, and the weight is, as Orion said, considerably less.
 

wsimpso1

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Well, I make my living engineering friction systems and isolating vibration, so I am qualified to answer this one. Since I know of more than one paraplegic pilot with unboosted handcontrols, and I am loathe to shoot off my mouth until I KNOW where the numbers are, I decided to "run some numbers" to see if we really are out of reach without boosting...

Assumptions (Engineering estimates based upon personal memory, not perfect but a reasonable starting point):

Max effort braking is 0.25 g in an airplane (1 g plus in motorcycles);
Pilot can come up with 50 pounds per finger or 150 pounds on the front brake lever of a motorcycle;
Airplane at 1800 pounds (about right for the Liberty):
Leverage gain of 4:1 between the finger piece and master hydraulic cylinder;
Tire radius of 6.5 inches;
Brake radius of 1.75 inches;
Brake caliper piston diameter of 2 inches.

Hydraulic gain would only have to be 35:1, and the pistons would only have to be 0.34 inches in diameter. That dimension is not only doable, but within the range of what is out there right now. You might be able to build such a system off of the shelf, but I will leave determination of the truth on that to someone else.

So, in my engineering judgement based upon actual analysis, no, finger brakes would not inherently require boosting - they could be entirely manual, and might be possible with existing hardware.

Billski
 

Jon Matcho

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Thank you

Everyone, thank you for the feedback. I just might consider changing the per-plans braking setup on the Cozy IV to use finger brakes of my own manufacture.

The Cozy specs are a bit more demanding than the Liberty, but perhaps manageable:

Gross weight = 2,050lbs
Landing speed = ~80-90mph

Does this remain within the comfort zone for such a design?
 

Dust

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In the cozy the brake travel is at the end of each rudder pedal. first comes full deflection of a rudder, then comes braking, NO toe brakes.

Full Rudder travel is only 3/4 inch and then braking.

Are you getting rid of the rudder pedals too?

enjoy the build

dust
 

Jon Matcho

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Pedals on a Cozy

No, still need the pedals for rudder. So everyone understands, the pedals on a Cozy are dual-purpose. It is an elegant and simple system. The majority of pedal travel is assigned to the rudders, with the remaining travel engaging the brakes.

The problem is ONLY on landing; at times when heavy rudder is required. In this situation you can actually land with brakes ON, which slams the nose down a bit and you bounce down the runway (just doesn't feel or look good/comfortable). This can be worked around, but some consensus exists that this is an issue to contend with, by default after everything is built and you're flying.

I am not even close to this point of my build, and am only considering separating the brakes from the rudder pedals. Given the choice of toe brakes vs. the current system, I would keep the current system.
 

wsimpso1

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Matcho,

The Cozy is not enough heavier to make it undoable. In fact, a heavier airplane will just require smaller pistons on the master cylinder (and a little more travel too. One hint here - use metal lines to keep the strokes short enough...

Landing speed doesn't matter to this stuff, it matters to the size of the pads and the mass of the discs. The more energy the brakes have to suck up, the bigger these parts have to be to keep the temps in bounds. You should not be changing any of that...

I will check Pazmany's book, and see who else covers this topic so that I can recommend some reading, but I will bet that you can find something to help with hydraulic design when the time comes...

Billski
 

StRaNgEdAyS

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Sounds great!
I must admit I like the idea of them, but I'd still want to have the levers hooked up in such a way as I didn't need to take my hand off the throttle to operate them. Perhaps a pair of motorcross style mini levers or decompression levers that are small enough to for one or two fingers attached either side of the handle. it might take a little bit of fiddling to work out the attachments, but it would, in my opinion, be a little safer than having to take your hand off the throttle to use the brakes.
Dust,
you say the cozy brakes operate at the end of the rudder travel? How do you operate both brakes then to pull up in a straight line??
 

John Slade

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Rudders (and brakes) in the Cozy are independant of each other.
That is you can operate one rudder and not the other, or both in varying amounts at the same time. There's no crosslink.

Having flown maybe 6 hrs in a Cozy (just over 1 in my own) I really like the way the system works. When you brake, you auromatically have both rudders extended for max aerodynamic braking.

Flying onto the runway with one or both rudders out wouldn't be good... so you don't do it. You release the rudders just before touchdown. It's not an issue.

I'd recommend that anyone building a Cozy install the plans system first and fly with it a while before even considering changing it.

I am not even close to this point of my build, and am only considering separating the brakes from the rudder pedals.
Jon - I'd strongly recommend that get you're pilot certificate and accumulate some time before making changes like that. You don't [yet] have the background to know what will work well and what won't.
 

Jon Matcho

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Originally posted by John Slade
You release the rudders just before touchdown.
Interesting, but I cannot help my knee-jerk reaction that if this is the required technique, there is a weakness in the design.

Jon - I'd strongly recommend that get you're pilot certificate and accumulate some time before making changes like that. You don't [yet] have the background to know what will work well and what won't.
<taken aback> I had to make an effort not to feel insulted by that.

I wouldn't even be asking such a question if it wasn't put in my head by a Cozy builder local to me who I walked around with at Sun-n-Fun. He pointed out 3+ planes with finger-style brakes, and noted them as "an interesting possibility for the Cozy". He's a 737 pilot for Continental.

It's not an issue.
Prior to considering changing the design, and making this post, I did ask a Cozy pilot w/high time, "How do you know if you're landing with the brakes ON?" The answer was, "Well, that IS an issue."
 
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pylon500

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I have recently been involved with a paraplegic who built himself a Slepcev Storch and fitted independant finger brakes to the stick.
Basically it seems to be a question of leverage and movement available, but also the factor of dissability compensation.
As this guy has to lift himself and propel himself by hand, his hands are actually quite strong so he has no trouble.
I can manage the brakes OK myself, and it's a good thing the Storch operates so slowly!
We have another popular aircraft here in OZ that uses finger brakes, the Jabiru!, it also has a little cam shaped lever that drops in front of the brake levers to act as a park brake.
A point to consider with finger brakes is how the application is opposed, (you know, action and reaction) on the stick install above the reaction is against your palm or thumb, depending on how you're holding the stick.
On the Jabiru and the Europa (Liberty) it appears to be pull with your fingers and react against your shoulder in the harness, or in the long version, pulling with your hand and pushing (reacting) with your feet on the pedals! (lots of muscles, and probably a bit tiring?)
As for the Cozy situation;

You release the rudders just before touchdown.
I think it's more a question of adjustment, maybe you should allow at least half rudder travel before the brake starts to engage, that way you can hold some rudder right down to the ground, without touching down with brake.
Any more rudder requirement than that, and you probably want to land with brake on anyway!!
Arthur.
 

Jon Matcho

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Originally posted by pylon500
As for the Cozy situation; I think it's more a question of adjustment, maybe you should allow at least half rudder travel before the brake starts to engage, that way you can hold some rudder right down to the ground, without touching down with brake.
That is exactly the intended technique the designer puts forth for landing the Cozy. I have asked a couple Cozy flyers "How do you know if you have any brake on when you are landing?" and the general answers seem to be "I'm not exactly sure. / It doesn't matter. / It's an issue to reckon with."

Hearing these answers, and with the new finger brakes receiving favorable reviews and results for other planes of similar mass, I do expect to further analyze the options, and carefully consider whether such a change is safe.
 

John Slade

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I think it's more a question of adjustment, maybe you should allow at least half rudder travel before the brake starts to engage
Perhaps theres some misunderstanding here. On the Cozy the brakes begin to engage only AFTER the rudder hits the stop.

<taken aback> I had to make an effort not to feel insulted by that.
Wasn't intended as an insult, just what I think is good advise. As a 1000hr pilot I've found that a few of the changes I made were a waste of time and effort when it came to actually flying the plane. A builder with no flying experience could easily get lost in complex changes that aren't helpful, or are even detrimental. It's a lot easier in most cases to just follow the design and build it. Once you're flying you'll know better what works and what doesnt. Nat is always complaining about people trying to fix non-existant problems. In many cases he's right.
 

Jon Matcho

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Originally posted by John Slade
Perhaps theres some misunderstanding here. On the Cozy the brakes begin to engage only AFTER the rudder hits the stop.
Yes, but I understand it's hard to feel the exact point at which this happens. If the concern is NOT to have brakes on at touchdown, you may not be fully flaring a rudder when you really want to.

John, how have your landings been? Does your nose hit, bounce, and finally dampen as you progress down the runway? Apparently this is the trademark landing style of the Cozy, with gentle nose touchdowns being the exception. I noticed this on my first Cozy ride ever, with the designer, Nat Puffer. I know the front elevator is also in the equation, but so are the brakes if on at touchdown.

A builder with no flying experience could easily get lost in complex changes that aren't helpful, or are even detrimental. It's a lot easier in most cases to just follow the design and build it. Once you're flying you'll know better what works and what doesnt. Nat is always complaining about people trying to fix non-existant problems. In many cases he's right.
I agree and appreciate the feedback, in any form it comes.

Thank you everyone!
 

John Slade

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John, how have your landings been? Does your nose hit, bounce, and finally dampen as you progress down the runway? Apparently this is the trademark landing style of the Cozy, with gentle nose touchdowns being the exception.
So far I have about 5 landings in Dan Cruger's Cozy and 4 in my own. All were the same. Gentle touchdown of the mains followed by a fairly abrupt nosedown pitch to the nose gear touch. No bounce. Although I've never experienced one, I'd say the "carrier landing" analogy is probably fairly close, if a bit exaggerated. I'm sure you can hold the the nose off by pulling back on the stick. I haven't tried that yet. There's a remote possibility of pulling back WAY too far and tipping over backwards, although I've never heard of anyone doing this. The other reason to avoid a "flared" landing and holding off the nose is that it will always take up more runway than a "plant". The Cozy lands pretty fast, and I only have 3400ft to play with. There isn't a lot of time for finesse. Having said this, I have been getting off the runway well before the end in more recent landings.

At least for me, it's a fairly natural and automatic thing to come off the rudders in the last couple of seconds before touchdown. You always want the engagement with terra firma to be in a straight line. The trick (in any airplane) is to get the plane where you want it using whatever technique works best, until you're a foot above the runway, then you usually want to straighten the controls before touching down.
 

Jon Matcho

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Originally posted by John Slade
The trick (in any airplane) is to get the plane where you want it using whatever technique works best, until you're a foot above the runway, then you usually want to straighten the controls before touching down.
I do have enough virtual experience (with PC simulators) to know this, and when not done properly, you do crash -- but without being subjected to any bodily injury or premature death.
 

Dust

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Strange, do you have it now?

left ruddder ONLY deploys left
right rudder ONLY deploys Right

at the end of right rudder travel the rudder hits a stop and you begin to depress brake for the right wheel. The same applies for the left rudder pedal and wheel.

So in the EZ case it is a rudder and then brake pedal. The plumbing is wicked simple.

enjoy the riveting

dust
 
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