Aircraft brake systems

[Dafydd Llewellyn]

Well , I was not talking about ABS, tho the thread drifted off onto it. I'm talking about a simple pressure-relieving anti-locking valve of the simplest type, that drops the brake mechanical advantage by (say) 50% when the tail wheel comes off the ground.

 

 

[SDQDI]

How about a NORC (Nose Over Recovery Charge) if your plane goes too far past horizontal while the mains are spinning (need to be able to nose down at altitude without the charge going off) a small charge shoots out of the top of the tail pushing the tail back down.

 

It could be a sustained charge (10 or 15 seconds) so as to stop porpoising.

 

It's past my bedtime obviously but I am well known for good ideas that are silly:scratching head:

 

But it is an idea as it shouldn't ever get used unless you were well over horizontal and it could be a totally standalone setup.

 

The thought of it accidentally discharging in flight is not a pretty picture though......... Maybe a ground sensing radar cutoff could be incorporated.

 

Ok too much goodnight:happy:

 

 

[Dafydd Llewellyn]

Try a couple of aspirin . . .

 

 

[aro]

There are a couple of rather obvious problems with ground handling with an ABS type braking system on a tail wheel aircraft:1. When you want differential braking, for example when you want to ground loop the aircraft by stomping on say the left brake to turn the aircraft, the right wheel will travel faster and the ABS will attempt to release the left wheel brake to counter your intentions. That could also be a real problem taxiing in strong crosswinds as well as landing in real strong crosswinds where at the last moment on a full stall touch down you might want to ground loop the aircraft to maintain control.

2. It will not stop the roll over as we saw in that Cessna 180 unless the brakes locked and from what I saw he over braked and let the control yoke move forward ( might have had the seat move forward under heavy braking). ABS can't stop that kind of **** up unless it has a G positioning sensor that releases the brakes when the CofG moves too far forward as a result of the tail rising.

1) is all down to the programming - it can do whatever you like. As I understand it, primitive ABS just senses the rate of change in the rotation of the wheel. If it exceeds what is possible from normal braking (i.e. a locked wheel goes from rotating to stopped almost instantly), it releases the brake. However systems now could be much smarter, and take more parameters into account. However, the anti-groundloop stability suggestion obviously would be a problem if you felt the need to deliberately groundloop.

 

2) If you tied it into a system like a Dynon (or any similar system) you could have a pressure sensor to detect when the brakes were applied, and release them if the tail lifts (say) 10 degrees from the attitude where the brakes were first applied. This would stop a nose over even when tail up braking after landing. The more I think about it, the more I think a mechanical switch in the tail is the hard way to do it... we have the technology to make it a much smarter (and simpler and more easily tunable) system.

 

 

[Dafydd Llewellyn]

1) is all down to the programming - it can do whatever you like. As I understand it, primitive ABS just senses the rate of change in the rotation of the wheel. If it exceeds what is possible from normal braking (i.e. a locked wheel goes from rotating to stopped almost instantly), it releases the brake. However systems now could be much smarter, and take more parameters into account. However, the anti-groundloop stability suggestion obviously would be a problem if you felt the need to deliberately groundloop.2) If you tied it into a system like a Dynon (or any similar system) you could have a pressure sensor to detect when the brakes were applied, and release them if the tail lifts (say) 10 degrees from the attitude where the brakes were first applied. This would stop a nose over even when tail up braking after landing. The more I think about it, the more I think a mechanical switch in the tail is the hard way to do it... we have the technology to make it a much smarter (and simpler and more easily tunable) system.

Not if you want to get a Type Certificate. Take a look at what is involved in certificating software. In a certification exercise, the KISS principle applies.

 

 

[aro]

I thought you get maximum braking in a tail dragger in 3 point - proper braking puts more load on the mains increasing traction resulting in better retardation. If the tail comes up from 3 point you are overdoing it.

The earlier you start braking, the bigger difference it makes in your stopping distance. The problem in a taildragger is that you have a high AOA in a 3 point attitude, so by the time you get the tail down, let alone get enough weight on the wheels for significant braking you are too late to make a big difference to your stopping distance.

 

I have seen suggestions to touch down almost at approach speed and brake immediately with the tail up for the shortest landings, eliminating the time spent in the flare, because at flying speed the tail is powerful enough to stop the nose over and the early braking has most effect on the total distance. This is obviously a potentially risky technique requiring a large amount of skill to reduce braking as the tail loses effectiveness. I suspect it was more appropriate to larger, faster taildraggers requiring long runways. I wouldn't try it myself. In the tailwheel aircraft we fly, we are better to accept that the brakes make minimal difference to landing distance.

 

(Incidentally, I have noticed that wheel vs. 3 point landings give a good demonstration of how much drag the wing can produce. The aircraft slows noticeably faster without braking in a 3 point attitude than tail up.)

 

 

[Downunder]

Well , I was not talking about ABS, tho the thread drifted off onto it. I'm talking about a simple pressure-relieving anti-locking valve of the simplest type, that drops the brake mechanical advantage by (say) 50% when the tail wheel comes off the ground.

Would probably like to see something more "proportional", say from tail wheel on the deck to horizontal rather than an on/off situation.

 

 

[Dafydd Llewellyn]

The earlier you start braking, the bigger difference it makes in your stopping distance. The problem in a taildragger is that you have a high AOA in a 3 point attitude, so by the time you get the tail down, let alone get enough weight on the wheels for significant braking you are too late to make a big difference to your stopping distance.I have seen suggestions to touch down almost at approach speed and brake immediately with the tail up for the shortest landings, eliminating the time spent in the flare, because at flying speed the tail is powerful enough to stop the nose over and the early braking has most effect on the total distance. This is obviously a potentially risky technique requiring a large amount of skill to reduce braking as the tail loses effectiveness. I suspect it was more appropriate to larger, faster taildraggers requiring long runways. I wouldn't try it myself. In the tailwheel aircraft we fly, we are better to accept that the brakes make minimal difference to landing distance.

 

(Incidentally, I have noticed that wheel vs. 3 point landings give a good demonstration of how much drag the wing can produce. The aircraft slows noticeably faster without braking in a 3 point attitude than tail up.)

I've always found that the most effective short-field technique with a taildragger is to dump the flaps at (or an instant before) touchdown, in a full 3-point attitude. That puts it firmly on the ground, and you can then use the brakes quite heavily if you need to. The same technique also works in tricycle undercarriage aircraft, provided you can hold the nosewheel off and put it down gently. For that reason, I dislike electric flaps, in a tailwheel aircraft; the inability to dump the flaps cripples their utility. However, this technique does require that you be able to judge your hold-off height accurately, and that you know when it is going to stop flying; so it's not taught to ab-initio students - or not taught at all. Also, you need to be very careful doing this in an aircraft with retractable undercarriage; it's far too easy to dump the undercarriage instead of the flaps.

QUOTE: Would probably like to see something more "proportional", say from tail wheel on the deck to horizontal rather than an on/off situation.

 

The idea sounds nice, but it's very difficult to achieve with any sort of stone-axe simple system. Also, I don't think it would work if the effect it delayed until the aircraft is horizontal; by that stage, it's almost on the point of falling over, and it will have considerable overturning momentum. What is needed, I suggest, is something that acts much faster than any pilot can react. A small effect at the right time, rather than a large effect, almost too late.

 

 

[bushcaddy105]

Are we missing the obvious as stated earlier in the thread? A properly engineered brake system will not allow a nose-over on run-up. Even with greater than normal pedal pressure a good system will allow the aircraft to creep forward once, for example, 75% power is achieved. With the stick fully back (as it should be!) a nose -over is pretty well impossible. Why look for technology to solve what could have been fixed by better engineering in the first place?

 

 

[facthunter]

Having a "decent" set of brakes with FEEL might be something worth aiming for. Brakes on small aircraft are almost an afterthought. With tiny wheels "hubs" (as the tyre may be flat sometimes) limits the size, but a multiplate disc might be appropriate. Large aircraft are a different kettle of fish. Heat dissipation critical and ,MUST have antiskid or you will blow tyres in a flash. Holding at an active runway with the engine running with some of the brakes we have is a hazard to the aircraft which may be taking off. A slow seal or hose leak and you roll forward. A lot of work to be done, in this area., but then many fly with no brakes working. You get away with it on grass as long as it isn't downhill. Nev

 

 

[Dafydd Llewellyn]

Are we missing the obvious as stated earlier in the thread? A properly engineered brake system will not allow a nose-over on run-up. Even with greater than normal pedal pressure a good system will allow the aircraft to creep forward once, for example, 75% power is achieved. With the stick fully back (as it should be!) a nose -over is pretty well impossible. Why look for technology to solve what could have been fixed by better engineering in the first place?

Wrong:

§ 23.735 Brakes.

 

(a) Brakes must be provided. The landing brake kinetic energy capacity rating of each main wheel brake assembly must not be less than the kinetic energy absorption requirements determined under either of the following methods:

 

(1) The brake kinetic energy absorption requirements must be based on a conservative rational analysis of the sequence of events expected during landing at the design landing weight.

 

(2) Instead of a rational analysis, the kinetic energy absorption requirements for each main wheel brake assembly may be derived from the following formula:

 

KE=0.0443 WV 2 /N

 

where—

 

KE=Kinetic energy per wheel (ft.-lb.);

 

W=Design landing weight (lb.);

 

V=Airplane speed in knots. V must be not less than VS√, the poweroff stalling speed of the airplane at sea level, at the design landing weight, and in the landing configuration; and

 

N=Number of main wheels with brakes.

 

(b) Brakes must be able to prevent the wheels from rolling on a paved runway with takeoff power on the critical engine, but need not prevent movement of the airplane with wheels locked.

 

 

[bexrbetter]

Millions of light trucks and tray back utes use a brake load proportioning valve, go down to your local wreckers, stick your head under the rear and you'll see a lever arm running from the rear axle to a box of types bolted to the chassis rail usually with brake lines in and out. As the load gets heavier, the arm raises and strengthens the proportioning spring weight so you get more brakes to the rear and vice versa as the load decreases.

 

Any good race or rally car shop sells hand adjustable brake proportioning valves.

 

http://www.bing.com/images/search?q=brake proportioning valve &FORM=HDRSC2

 

Pad knock-off is mitigated by floating discs; I suspect very few U/L aircraft brakes feature that.

No common cars have floating discs.

 

Pad knock-off in modern cars is mitigated by non-flexing alloy wheels, decent size wheel bearings and the tension of the sealing/piston rings on the brake pistons. In the 60's Renault R8s, with steel wheels, were the first common man's car to have 4 wheel disc brakes when disc brakes were still in their infancy and they used a small valve in the line to hold a minute amount of pressure to stop pad knock-off. Other manufacturers over the years have and still use for racing and rallying an inline valve or light spring behind the caliper piston.

 

For decent brake calipers I would be looking at 80cc or 125cc Motocross bike brakes, small, ultralight, strong, efficient and cheap

 

 

[turboplanner]

I'm a bit overwhelmed with what I'm reading here, and wondering if our vehicle manufacturers spend all those millions when solutions can be plucked out of the air. For example, when PBR were supplying US cars they had a Corvette permanently running at the Anglesea Proving Ground with an engineering team for YEARS.

 

Sure we have EBS today, but have you checked the cost per vehicle? Remember in the pre-emission days when we paid $5,000.00 for an upmarket Falcon.

 

It's the simple solutions that are needed.

 

 

[Dafydd Llewellyn]

Millions of light trucks and tray back utes use a brake load proportioning valve, go down to your local wreckers, stick your head under the rear and you'll see a lever arm running from the rear axle to a box of types bolted to the chassis rail usually with brake lines in and out. As the load gets heavier, the arm raises and strengthens the proportioning spring weight so you get more brakes to the rear and vice versa as the load decreases.Any good race or rally car shop sells hand adjustable brake proportioning valves.

 

http://www.bing.com/images/search?q=brake proportioning valve &FORM=HDRSC2

 

No common cars have floating discs.

 

Pad knock-off in modern cars is mitigated by non-flexing alloy wheels, decent size wheel bearings and the tension of the sealing/piston rings on the brake pistons. In the 60's Renault R8s, with steel wheels, were the first common man's car to have 4 wheel disc brakes when disc brakes were still in their infancy and they used a small valve in the line to hold a minute amount of pressure to stop pad knock-off. Other manufacturers over the years have and still use for racing and rallying an inline valve or light spring behind the caliper piston.

 

For decent brake calipers I would be looking at 80cc or 125cc Motocross bike brakes, small, ultralight, strong, efficient and cheap

Thanks, BR; now to find one compatible with mineral hydraulic fluid . . .

 

 

[turboplanner]

I notice many people seem to be having problems with taildraggers; it would cost us nothing going forward to dump the 1920's style taildraggers and stick to proper tricycle undercarriage for all the safe reasons it was introduced, then you can set your braking by the ability to lock up the mains on bitumen like you can with a Cherokee.

 

 

[SDQDI]

I notice many people seem to be having problems with taildraggers; it would cost us nothing going forward to dump the 1920's style taildraggers and stick to proper tricycle undercarriage for all the safe reasons it was introduced, then you can set your braking by the ability to lock up the mains on bitumen like you can with a Cherokee.

It would cost us nothing?? I wouldn't be able to fly a tricycle undercarriage out of the paddocks at Hillston.

If tricycle gear was so foolproof why do nose wheels keep snapping off?

 

Tail wheels have their issues but I don't think too many of us are complaining about them, looking for better brakes seems like a good idea and if we combine that with some decent training or education it should help considerably. Insurance rates are a whole different picture but for myself I don't mind paying higher rates as it enables me to fly where I want to fly:thumb up:

 

 

[facthunter]

Nosewheels snap off U/L's for two main reasons. Bad airmanship and they are not strong considering the loads they may be subject to if things go wrong. A utility aircraft IF small, should be tailwheel . Much more assurance in rough strips and outlandings. Nev

 

 

[turboplanner]

Oops, didn't see your avatar, I was after Foxhunter.

 

The nosewheels don't seem to be snapping off GA aircraft, so the difference could be:

 

(a) In the RA aircraft less sophisticated materials and less developed design is more forgiving.

 

(b) Some people are actually trained to land by pointing the nose down for altitude and throttle for speed, so the arrival is much more likely to be on the nosewheel.

 

© Training - see the dozens of incidents in Pilot Notes over the years where aircraft have swerved after landing and hit ditches, flipped over the wingtip etc.

 

 

[bexrbetter]

If tricycle gear was so foolproof why do nose wheels keep snapping off?

:

Wheels too small for the holes/edges they have to contend with and half of the suspensions I've seen require the wheel to travel forwards in compression increasing the stress.

 

 

[Dafydd Llewellyn]

Tailwheel aircraft generally have better performance than their equivalent nosewheel bretheren; and vastly better propeller clearance when taxiing; and - believe it or not - better crosswind capability. They definitely have their place. As a CAR 35, I've seen lots of damaged fuselages due to nosewheel loads. The history of the early Jabiru nosewheel is informative; it started out meeting FAR 23 drop-test criteria - and people kept breaking it. It was beefed-up in several increments, and ended up twice as strong as FAR 23 requires; Rod Stiff commented that every increment in strength seemed to bring out another level of pilot ham-fistedness. It's now at a strength such than the fuselage breaks instead. I've also been asked for opinions in regard to prop strike (See CASA AD/ENG/6 Amdt 1) for scores of nosewheel aircraft - but almost never for tailwheel aircraft. Yes, they require a little higher level of pilot skill - so not the "flying Chevrolet" epitome. However, I definitely prefer them - and so do most "bush" pilots.

 

 

[SDQDI]

It's getting close to my bedtime again so ill be careful and think through what I am going to post.

 

Arguing between nose and tail wheelers seems to be silly and driven sometimes by our pride instead of common sense. (Who would have thought that possible?) it is the same as arguing about high or low wing at the end of the day it depends on how and where you are going to be flying and also importantly taxiing, there are horses for courses and what suits one persons needs will not always suit his mates.

 

I think we could discuss breaks though as even in a nose wheel plane that never operates on anything but tar brakes are important, as was mentioned earlier when your "never missed a beat before" engine knocks of for a break while you are happily cruising and you have to land in a confined space brake effectiveness could be the difference between a tragic and not so bad outcome. I think any brainstorming that comes up with new ideas (maybe some of them not worth the data they take up:nerd:) is worthwhile and could lead to positive changes not just for tail wheelers but all forms of ultralights.

 

Wow I held all my good ideas in tonight:whistling:

 

 

[David Isaac]

I notice many people seem to be having problems with taildraggers; it would cost us nothing going forward to dump the 1920's style taildraggers and stick to proper tricycle undercarriage for all the safe reasons it was introduced, then you can set your braking by the ability to lock up the mains on bitumen like you can with a Cherokee.

Shitstirrer ......