ABS

I believe the Dunlop Maxaret system of HS Trident fame was adopted for the 1966 Jensen Interceptor FF, the first British car with ABS.
What a car that was. The 4WD and ABS system were British, the design Italian and the 6.3 litre V8 engine and Torqueflite automatic transmission American.

Things have moved on now for cars – for the past couple of years I’ve worked on Brake Assist Systems (BAS) which takes over from the driver if panic braking is detected to apply maximum effective brake pressure faster than the human operator.

Either detects pedal speed or line pressure increase over time and hopefully saves a few meters of stopping distance. Now a requirement for new models of car.

Thread drift…pah thats nothing Paul …if you want to see real thread drift and have an hour or so to spare – have a look at this one…lovely thread drift picture on post 34 :)…it is a real hoot 😀

http://www.google.co.uk/url?sa=t&rct=j&q=did%20mitchell%20copy%20heinkel&source=web&cd=4&cad=rja&sqi=2&ved=0CEAQFjAD&url=http%3A%2F%2Fforum.keypublishing.co.uk%2Fshowthread.php%3Ft%3D86503%26highlight%3Dspitfire%2Bcopied%2Bheinkel&ei=RYyyUIqvDeaY1AWem4GgCg&usg=AFQjCNGA7P9j_Es83fy-LyxUF0ojZf25Qw

Brazen thread hijack.
Who made the first successful all aluminium aircraft? This has just come into my mind as I am painting the wheels of a Hurricane model as we speak. Anyone know as I don’t?

Yes ABS is like any other anti skid system…it only operates when a skid condition is sensed,the major difference between car + a/c systems is that on an a/c the anti skid is disabled below approx 10mph whereas on a car it remains active at all times…as alluded to in my earlier post – on my usual x country route there is one T junct with the stop line on a very steep downslope and even at half an mph it is very difficult to avoid abs operation in certain conditions…..mind you the nearest village is called ‘Steep’ 😉

rgds baz

Agree with PeeDee as in essence the ABS remains dormant until required.

There are a few misconceptions regarding ABS brakes whereby some believe it increases the brake efficiency, allows a driver to stop shorter than normal and even lets some drivers drive beyond their normal limits. All are erroneous beliefs and I would suspect such belief being a cause of some/many accidents.
Richard

In the last two years I’ve owned two cars. A Sierra and a Mondeo. Both of which don’t have ABS. So I’ve learnt to brake optimally. On the odd occasion I have used a car with ABS (Audi A3) the ABS has not kicked in. I guess I’ve learnt to drive without it?

It won’t kick in until is senses a skid. Hall sensors reading a reluctor ring detect a locked wheel and then it kicks in with it’s on/off action.
So, you should be thankful that it didn’t kick in, it means you were in no emergency or “Brown trouser” situations.

Hi Richard…unfortunately all a/c are a compromise between performance/weight/space and cost…none of them are perfect 🙂

rgds baz

…………but weight tends to win.

Hi Richard…unfortunately all a/c are a compromise between performance/weight/space and cost…none of them are perfect 🙂

rgds baz

Hi Baz, I would not have thought much space would be required as the flutes could be formed in the wheel periphery, or, even the tyre for that matter.
I would also think that once the wheels were on the runway with the a/c weight on them then the flutes would have no energy left. All conjecture on my part of course.
Interesting though that as expensive a/c tyres are, their limited life and the punishment they take on initial landing, there seems to be no call for wheel spin prior to touchdown.
Richard

Richard…the main reason on many a/c would be lack of space,the a/c I work on simply have do not have any spare space.
On larger a/c with multi bogies then you would need 2+ units for each bogie depending on whether they have ‘live’ axles or not.
They might also ‘fight’ any braking action during heavy braking at high speed !

rgds baz

Many (and some) years ago I worked in workshops linked to a research physics lab. They had designed a very small conical shaped spinner made of metal, very much like the old Apollo space capsules. This had tiny flutes cut into the slanting face; this face then resting on a conical bed which had tiny holes in it from which compressed air exited. They managed at that time (1964) to reach speeds of up to 7,000 revs per second and were aiming for 15,000 rps.
Could not the same flutes be designed into aircraft wheels so that they rotate when lowered into the airstream? Doesn’t really matter how fast they go as any speed will reduce the sudden wear currently experienced. I do though think that brains better than mine may have thought of this already and for some reason decided against the idea. Still, I would like to know why.
Richard

IIRC some manufacturer (Poss. Boeing) experimented with the MLG Wheels being rotated just before landing to prevent the flat spotting of the impact. We’ve all seen the smoke.

It obviously failed as it isn’t around. (Presume weight of driving mechanism contributed to failure?)

The story I heard was that the idea was abandoned because they had trouble getting the wheels to spin at the right speed.

Voisin in the late ’20s was the first…. (although the Americans try to claim it was the B47 in the late 1940s…..

Maxarets were pretty standard from the 1950’s up to the early 70’s when the electrical types came into use.

Maxarets use centrifugal force (or lack of…) to open the brake lines

The first mainstream electrical type is a sensor and what can be best described as a castellated mainwheel – essentially the sensor counts the rotations of the wheel and compares it to a wheel on the other side of the aircraft. If the count drops significantly, a signal is sent to the braking system which releases the brake pressure.

The second common type is a generator with a vane on the end. The vane rotates with the wheel, while the generator is held in the axle. Again, the wheels are compared to each other and brake pressure is reduced if one wheel decelerates quicker than the others.

Apparently the Cessna Citation does have a nosewheel spin-up facility as an option…. (prevention of FOD from the nosewheel tearing itself apart on initial contact).

Spinning the wheels is complex, heavy and apparently only saves 10% wear. (Most tyre wear is doe to taxiing anyway)

No my ABS does not normally kick in either,there is one T junct where it tends to operate…very steep downslope at stop sign…even at half an mph it still tends to go Brrrr 😀

But to return to a/c anti skid,in the early 70’s I was on the Canberra OCU….one day (on late shift) our Chief Ground Instructor definitely ”did not Land with the brakes on ” 😉 but he landed with both wheels locked solid – the wheels were filed almost down to the axles :rolleyes:
That cost the taxpayer a new brake control valve,brake units and wheels …but more importantly cost me a date with a mini dress wearing young lady LOL !

rgds baz

In the last two years I’ve owned two cars. A Sierra and a Mondeo. Both of which don’t have ABS. So I’ve learnt to brake optimally. On the odd occasion I have used a car with ABS (Audi A3) the ABS has not kicked in. I guess I’ve learnt to drive without it?

Thanks for response/answers ,most interesting .

…a very slight diversion if ya don’t mind….
IIRC some manufacturer (Poss. Boeing) experimented with the MLG Wheels being rotated just before landing to prevent the flat spotting of the impact. We’ve all seen the smoke.
It obviously failed as it isn’t around. (Presume weight of driving mechanism contributed to failure?)

Yes the first anti skid system I worked on was the Dunlop Maxaret (max arrete :)),this was a basic hydraulic/mechanical type unit that released the brake pressure when the wheel stopped rotating during a skid.
The a/c I work on now have a slightly later (late 60’s/early 80’s) type electrical sensing system where it has a wheel speed sensor to tell the anti skid control box what either mainwheel is doing,most of our a/c have been updated to have touchdown protection so that the tyre(s) will not blow if the a/c is landed with the brake(s) inadvertantly ‘on’.
A great system to prevent aquaplaning and flatspotting of tyres (or wheel covers for the pedantic :D),and slightly more subtle in operation than car ABS systems which seem more frenetic in operation than perhaps they need to be LOL…BRRRRRRRRR 🙂

rgds baz