Question

[turboplanner]

I have no idea what you mean. Nev

 

 

 

Having done the pre-flight check in the second video, where you are checking for hydraulic leaks, disk pad thickness, looseness or fouling, and done a rolling brake check at the very start of the taxy roll (so very low speed, clear in front), the downwind check is the reverse of this brake set, with a little pull to ensure operating hydraulics (the lever will come up in your hand if there's been an exhaustion of oil during the flight).

 

The Cherokee has exceptionally good toe brakes, and the nose wheel is hard linked to the rudder pedals, so you get very precise taxying,  and can fling it round 180 degrees using momentum and a toe brake if you have to. The toe brakes will squeal the tyres if you need an emergency stop, so maximum braking effort for the disk diameter.

 

The park brake is good enough that it will hold you on the ground prior to takeoff if you forget to release it, and if you somehow are fiddling during the flight, of a kid next to you happens to lock the park brake on, and you don't do your downwind check, you'll leave a trail of blue smoke all the way along the very short skid., so immensely better performance than most RA aircraft.

 

Park Brake Lever (Setting) (PA-28-181)

 

 

 

 

[Geoff_H]

Years ago landed a Mooney with one brake locked on.  When the speed dropped to around normal braking speed the locked wheel took over and the craft ground looped.  It stopped very quickly indeed.  Wheels going sideways can do that.  Assuming that one brake is working, quite possibly so, then maybe just applying both brakes will result in a ground loop stop.

 

 

[facthunter]

Turbs... The pull the lever had me foxed. Ta Nev

 

 

[kgwilson]

I installed differential  Matco disc brakes & didn't bother with a park brake so I don't have to remember to make sure it is released. I can get the brakes to lock up with enough pressure but to do this would be just silly. On downwind if you have pressure that shows the brakes are working but not that they are free.

 

 

[K5054]

Need more details.

 

landing on grass?

 

carrying too much speed on touchdown?

 

where was touchdown?

 

did they fade or fail?

 

how long is runway?

 

what is pilot skill level?

 

is there grass on side of flightstip?

 

Landing weight?

 

headwind/tailwind.

 

braked and non braked performance?

 

etc etc

 

with all the variables you have to make the call at the time.

 

 

[Yenn]

You did check your brakes before you took off, didn't you when you did a run up perhaps. So you know they are working.

 

If they have no pressure when you check, pre landing, they have just failed, because they worked last time. That means it is possible for them to work OK when testing, but fail next time around, so I really cannot see what good a brake check is as part of pre landing. It can pass and still not work when you need them.

 

 

[old man emu]

Need more details.

 

landing on grass?

 

Landing on grass, or dirt will reduce the distance to stop because the coefficient of rolling friction is higher on those surfaces than on a sealed runway

 

carrying too much speed on touchdown?

 

Extends the roll distance as because the initial velocity value used in the calculation is higher

 

where was touchdown?

 

An undefined variable, but the distance (overall runway length - point of touch down is a critical variable)

 

did they fade or fail?

 

For the sake of the argument it is assumed that the brakes failed

 

how long is runway?

 

Another undefined variable - see "where was touchdown"

 

what is pilot skill level?

 

A unquantifiable variable.  Let's assume that the pilot has practised brakeless landings and knows what is going to happen.

 

is there grass on side of flightstip?

 

See "landing on grass"

 

Landing weight?

 

The Rolling Resistance of a tyre is affected by the weight of the aircraft and load. For consistency we could calculate the rolling resistance at MTOW, and include that in the calculation. Then we would know that this was the worse case scenario for the particular aircraft.

 

headwind/tailwind.

 

Headwind will reduce ground speed and tailwind will increase it. That is why the calculations were done on the assumption of nil wind.

 

braked and non braked performance?

 

The shortest stopping distance will be achieved if the brakes can be applied with a pressure sufficient to bring the wheel to just before lock-up (the beginning of a skid). This is almost impossible for a pilot to do without masses of experience (that's why we have ABS systems). We are taught to make sure brakes are unlocked before landing and to use them sparingly on the ground.

 

Don't forget that we only have braking on two contact points out of three, so the nose or tailwheel don't aid braking. One could take advantage of those wheel's steering properties to make the aircraft follow a weaving path on the ground. That would increase the available distance for stopping.

 

etc etc

 

with all the variables you have to make the call at the time.

 

 

 

[turboplanner]

I installed differential  Matco disc brakes & didn't bother with a park brake so I don't have to remember to make sure it is released. I can get the brakes to lock up with enough pressure but to do this would be just silly. On downwind if you have pressure that shows the brakes are working but not that they are free.

 

With no park brake control, what would make them lock up in the air, since they had to be free to take off?

 

 

[kgwilson]

With no park brake control, what would make them lock up in the air, since they had to be free to take off?

 

When you apply the brake on downwind to check hydraulic pressure it is possible (though not likely) that it may not release.

 

 

[turboplanner]

When you apply the brake on downwind to check hydraulic pressure it is possible (though not likely) that it may not release.

 

Well I have had one stick through my carelessness - the vehicle had been sitting in a shed for several months and the guide shafts had gummed up enough to overcome the release spring, so yes, it could happen after a brake application if the slides gum up.

 

But wouldn't it be much more likely for the hydraulics to leak or the line to take a hit from debris in the runway?

 

 

[pmccarthy]

Well I was taught the downwind check is "brakes free" which means not locked on. I don't think I will be otherwise fiddling with them in the air.

 

 

[Yenn]

If there is something blocking the vent to the brake fluid reservoir, it is possible for the brakes to stick on when you try them in the air. The blockage can act as a one way valve, allowing air in when the pedal goas down, but restricting its venting out. Don't ask me how I know this.

 

 

[spenaroo]

I'm currently learning,

and were taught, "brakes full and free"

 

my understanding of this is that pull the lever to make sure there is pressure, and also ensure the brake lever isn't locked on.

 

I land on a grass strip, so my thoughts would be to touch early, and get that stall warning buzzing. cant drop any further when already on the ground.

The exception was if Id done a late touchdown. then Id go around

 

 

[skippydiesel]

These days all my landings are intended to be short field - have had one brake failure in 10 years (this aircraft) and obviously didn't make the first taxi  turn off but let the speed and available runway length reduce and made the last turn easily, to taxi back for investigation/repair. Got to confess this is more necessity than good management, as home paddock (short & one way) frequently requires strong braking and lucky for me, above incident happened at a good long grass strip.

 

 

[facthunter]

In most U/L brake systems  failure  will be from light application for a longish period as when taxying.  One will slowly sink to the floor because the cups or O rings seal OK when stomped on when the fluid pushes them out better, but gradually leak on continuous light application.

 

        The test in the air is to see they are not parked, but other things might be able to be checked depending on the type of plane /system. You can usually feel pressure.. The first thing most pilots do after adjusting the seat is to park the brakes, which is often depress both  pedals firmly and pull park knob. This can become pretty automatic. by association. In the air one depresses the pedals firmly and...??? don't do it automatically.... or you have just parked the brakes. If a wheel jambs you have a little time to apply the other firmly or you are going somewhere off the strip rapidly. If one brake fails and you are trying to steer and still stop it's a fine balance of one against the other. Depends on what you want most of. Nev

 

 

[old man emu]

Isn't this discussion a bit useless, considering the short landing distances of recreational aircraft?

 

Although I enjoyed applying the physics of the situation.

 

 

[turboplanner]

Isn't this discussion a bit useless, considering the short landing distances of recreational aircraft?

 

Although I enjoyed applying the physics of the situation.

 

There are people with 300 metre strips who land long.

 

 

[facthunter]

IF you are used to using "barely long enough" strips,  when you train, the habit stays with you for a lifetime and it's not a bad one. You will be asked to accept downwinds at some controlled aerodromes, sometimes. Only juvenile birds do it as they learn by crashing early in the piece. So you can learn from the birds or do some practice with an instructor doing down wind landings as you will certainly need more runway length and tailwheel planes are particularly difficult at times, like the last part of the landing roll. IF you are not happy at the prospect, land into wind and delay the prang you don't need to have .Nev

 

 

[turboplanner]

IF you are used to using "barely long enough" strips,  when you train, the habit stays with you for a lifetime and it's not a bad one. You will be asked to accept downwinds at some controlled aerodromes, sometimes. Only juvenile birds do it as they learn by crashing early in the piece. So you can learn from the birds or do some practice with an instructor doing down wind landings as you will certainly need more runway length and tailwheel planes are particularly difficult at times, like the last part of the landing roll. IF you are not happy at the prospect, land into wind and delay the prang you don't need to have .Nev

 

You're talking about reasonable distances and ALAs; people are carving out strips where there is no EFATO landing space ANYWHERE in the circuit or overrun except into trees.

 

 

[facthunter]

 Not too many alternative places to land in the circuit at many places where aerodromes are these days, except the bush . Bendigo has been somewhat challenging in that respect for years, and houses are being built right up to the edges of the drome. People who do all their flying at places where the runways are far more than adequate can get lazy or NEVER did use a short strip technique. For Airlines the touchdown zone is just that. Outside of it is a "fail" on a check if the checkkie  wants to be strict . Your stopping and go around performances charts are predicated on the correct approach, sink rate, speed and touchdown point. so those markings have  a lot of significance.. They don't have to for a U/L or light GA type, but if you are real low at the threshold or float  excessively you aren't doing much of a job and will be found wanting when your strip is minimalised if you are not careful. Nev

 

 

[Yenn]

For those landing downwind the biggest difference in the approach is going to be the much flatter angle of descent. I know most off us do not use a 3 deg. approach, but usually a certain sink rate. the difference between a 5 kt headwind and a 5 kt tailwind is quite dramatic. Add in a bit of drizzly rain and you can be easily deceived.

 

 

[skippydiesel]

Hi Yenn - I routinely do tail wind & short field landing combined (one way paddock) On approach I always check my ground speed against air speed and if the difference is over 10 knots, I go around - it can be a little too exciting at times.

 

 

[facthunter]

 The  feeling of going fast(er) is based on the FACT that you are going faster (actual groundspeed) but if you slow the plane in response it will  not have the safe airspeed you need, It is not an illusion but rather an effect. Also the normal dropping off of a headwind (component) near the ground tends to decrease the airspeed and if you are in a tailwind situation the near ground windshear does the opposite and you might just float for a while and use up even more runway to wash off your excess airspeed. Nev