[ilangop]

Dear Experts,
I had a few doubts on the operation of a passenger carrier like the A320 or 727. Though the title reads about engine issues, I see this as the right place to post the questions as this place is flooded with experts in this field.
1. Why are aeroplanes moved a tractor for reverse motion? Is it technically impossible to have a reverse moving mode for an aeroplane? This is my observation at Chennai and Pune airports. Pardon my ignorance if a reverse driving mode exists.
2. While taxiing are the wheels driven by hydraulic pressure applied to any hydraulic motors in the wheels or else the plane moves by the virtue of thrust alone?
3. Where is the brake for the wheels located? Is there a friction based hydro - mechanical braking system like in cars?

Thanks in advance.

Regards,
Ilango

[the_skyliner]

Originally Posted by ilangop

1. Why are aeroplanes moved a tractor for reverse motion? Is it technically impossible to have a reverse moving mode for an aeroplane? This is my observation at Chennai and Pune airports. Pardon my ignorance if a reverse driving mode exists.

Technically yes, but practically it is an expensive affair.

Originally Posted by ilangop

2. While taxiing are the wheels driven by hydraulic pressure applied to any hydraulic motors in the wheels or else the plane moves by the virtue of thrust alone?

Thrust alone.

[silversteed]

Originally Posted by ilangop

1. Why are aeroplanes moved a tractor for reverse motion? Is it technically impossible to have a reverse moving mode for an aeroplane? This is my observation at Chennai and Pune airports. Pardon my ignorance if a reverse driving mode exists.
2. While taxiing are the wheels driven by hydraulic pressure applied to any hydraulic motors in the wheels or else the plane moves by the virtue of thrust alone?
3. Where is the brake for the wheels located? Is there a friction based hydro - mechanical braking system like in cars?

I am no expert, and I rely on forums and information from people in the aviation industry to gather information. AFAIK, anything and everything that goes inside an aircraft should be safe to use. So, if something can be avoided, there is one less item that has a chance to break mid flight and cause trouble. And any problem would mean a lot of money. I assume that itself has given enough hints to you.

I'll try to answer your 3 questions in simple words, leaving the explaining and correction part to the experts in the forum:
1. Technically feasible. Some jets can do it using thrust reversers, but most of them do not. Propeller aircrafts with variable pitch are also capable of doing it. However, the fuel burn for taxiing in reverse is more expensive than using a tug for push back. There could also be the challenges with visibility from the cockpit versus the clear view at ground level from the tug and ground staff.

2. Taxiing usually is done with the engines and not by additional motors on the wheels. Motors et al will add dead weight which means reduced payload and increased fuel burn. In addition, that's one additional system to be checked and maintained, adding to the cost of operation.

3. Brakes are located in the wheel hub, and they work on friction between the rotor and brake pads.

[A350XWB]

Originally Posted by ilangop

1. Why are aeroplanes moved a tractor for reverse motion? Is it technically impossible to have a reverse moving mode for an aeroplane? This is my observation at Chennai and Pune airports. Pardon my ignorance if a reverse driving mode exists.

Like the_skyliner mentioned, technically it is possible to do a push back using reverse thrust. But it is a fuel intensive affair and usually, the engine spool-up is not done, when the aircraft is at the gate. This is also due to safety considerations. Here is a video of a DC9 moving back on its on power. But I don't think this is followed any more, especially at busy airports.

https://www.youtube.com/watch?v=mO-FdDKxuNU

Originally Posted by ilangop

2. While taxiing are the wheels driven by hydraulic pressure applied to any hydraulic motors in the wheels or else the plane moves by the virtue of thrust alone?

Taxiing is done using engine thrust.

Originally Posted by ilangop

3. Where is the brake for the wheels located? Is there a friction based hydro - mechanical braking system like in cars?

Video of A320 brake assembly and working is shown in the below video. Hydraulic pressure is applied on the pistons, which moves compresses the brake discs/array of discs. Even ABS (Anti-Lock Braking System) was originally invented for airplanes in 1929.

https://www.youtube.com/watch?v=kVZ6mbeP1fU

Also, a video of the A320 Main Landing Gear wheel removal/installation.

https://www.youtube.com/watch?v=RSrTX1Oi2hc

[bejoy]

Originally Posted by ilangop

1. Why are aeroplanes moved a tractor for reverse motion? Is it technically impossible to have a reverse moving mode for an aeroplane? This is my observation at Chennai and Pune airports. Pardon my ignorance if a reverse driving mode exists.

As others have rightly pointed out, the two significant factors that govern the aviation sector are safety and cost. When the fuel prices were very high a few years back there was a major push for electric-taxing and Safran/Honeywell developed the technology and many airlines backed at that time. However when the fuel prices eased down, the airlines shelved their plans for adopting it.

https://www.flightglobal.com/news/ar...ic-tax-427400/

At the Paris air show in 2013, Honeywell and Safran demonstrated an initial version of their main landing gear-mounted Electric Green Taxiing System on an Airbus A320 as part of the daily flying display. However, a source familiar with the programme tells FlightGlobal that the narrowbody has since been decommissioned.

Honeywell confirms that it has terminated its joint venture with Safran. "After thorough market analysis", the US supplier says, the two partners "agreed to stop work on the Electric Green Taxiing System due to dramatically lower oil prices and the current aviation industry's economic environment".

Though Safran/Airbus still offer the system:
https://www.safran-landing-systems.c...amily-20170621

Airbus and Safran to market an electric taxiing system for A320 Family
The electric taxiing solution, which is the result of an extensive R&T phase led by Safran and Airbus has received ‘Authorisation To Market’ approval by Airbus and Safran for an application on the A320 Family.

Depending on the airline feedback, the actual program could subsequently be launched in the near future. The system's electric motors in the main landing gear, powered by electricity from the APU (auxiliary power unit), will allow an aircraft fitted with it to pushback and taxi without using its jet engines or requiring airport tractors or tugs. This system will provide airlines with a sustainable solution which combines savings on operating costs (including a reduction of around four percent in fuel costs, equal to several hundred thousand dollars per aircraft annually), independent movement on the ground, improvement of on-time departures, as well as environmental advantages such as reduced carbon and NOx emissions, and less noise during taxiing.

[itwasntme]

Originally Posted by ilangop

1. Why are aeroplanes moved a tractor for reverse motion? Is it technically impossible to have a reverse moving mode for an aeroplane? This is my observation at Chennai and Pune airports. Pardon my ignorance if a reverse driving mode exists.

See this MD80 behaving like a M800 at Dallas-Fort Worth. Not only a smooth reversing move with just the right amount of TR, but even a very tight pirouette to taxi away. Must have been insanely noisy for passengers in the terminal building too.

https://www.youtube.com/watch?v=-Zkxh903s_w

I also remember childhood flights in the ancient Alliance Air 727s. Insanely noisy buzzy engines, decrepit cabins where the luggage racks or folding trays would fall open in the near-crash landings and finally, the bucket-style thrust reversers which would alarmingly open up like on this MD80 :-)

[Jeroen]

Just to add a few more thought/comments.

Reversing out of the gate parking as pointed out by others is feasible for many planes. The biggest concern these days is safety as on many airports the planes are very close to the terminal building. So in most airports I believe it is strictly forbidden and you would need special permission. I remember a few cases at European airports where ground personel went on strike and the airlines got special permission to use reverse thrust to get their planes away from the gate and the respective airport ultemately.

It does happen now and then. Here is a video I shot only a year ago> I must admit it is the very first time I have seen a plane reversing onder its own power ever. And I have platinum status with three major carriers as I fly all over the world for my job.

https://www.youtube.com/watch?v=8pyWMv2pWiM

The two earlier video's show so called bucket reversers. These days with high by pass ratio engine the so called reverse thrust is actually not that much reversed as more or less thown out at a very slight forward angle. So it blows out everywhere and is/can be very destructive.

The braking action of the so called reverse thrust is actually not so much on air being thrown the opposite direction as additional drag due to the fact that no rearwards thrust is present during reverse operation.

Some carriers are switching from diesel push back tugs to electric vehicles. KLM is one of those carriers that is changing out all of its diesel ground vehicles to electric. The most tricky ones are the tugs used for the big heavy jets as you can imagine.

https://klmtakescare.com/en/content/...trical-loaders

Jeroen

[Sutripta]

Originally Posted by itwasntme

I also remember childhood flights in the ancient Alliance Air 727s. Insanely noisy buzzy engines, decrepit cabins where the luggage racks or folding trays would fall open in the near-crash landings and finally, the bucket-style thrust reversers which would alarmingly open up like on this MD80 :-)

727 or 737?

Regards
Sutripta

[itwasntme]

Originally Posted by Sutripta

727 or 737?

Regards
Sutripta

Haha, you are right - I think they were the vintage B737-200s which I recall. Do correct me if I am wrong!

I used to fly them on Kolkata - Bagdogra and some other NE airports I cannot recall now. Maybe Silchar too.

[ilangop]

Originally Posted by Jeroen

https://klmtakescare.com/en/content/...trical-loaders

Originally Posted by bejoy

Though Safran/Airbus still offer the system:
https://www.safran-landing-systems.c...amily-20170621

Originally Posted by A350XWB

Like the_skyliner mentioned, technically it is possible to do a push back using reverse thrust.

Originally Posted by silversteed

I am no expert, and I rely on forums and information from people in the aviation industry to gather information.

Originally Posted by the_skyliner

Technically yes, but practically it is an expensive affair.

Thrust alone.

Thank you all for patiently replying my question. I am clear now.
Had been working with buses for a few years. Buses with pneumatic brakes have a spring loaded brake chamber that applies brake till compressed air reaches the operating pressure needed for the brake system. I believe such safety systems do exist with the disc brakes to ensure releasing the brakes only if hydraulic pressure is built sufficiently in the system.

[phamilyman]

Blog from a friend who survived such an engine shutdown talks about his near-death experience:
http://silentorchestrator.blogspot.i...really-so.html

Here's what he had been through:

[Jeroen]

Originally Posted by phamilyman

Blog from a friend who survived such an engine shutdown talks about his near-death experience]

Although it is very likely he felt it was a near death experience, in all reality it most likely wasn't.

So the engine had some problems and made loud noises, fire smoke etc which must all be very unsettling. But they had just taken off and returned and made what appears to be a normal landing albeit on one engine. Fire tenders at the ready for the obvious reasons, again very unsettling when you see them chasing the plane if you are inside

Jeroen

[vishy76]

Originally Posted by ilangop

Dear Experts,
I had a few doubts on the operation of a passenger carrier like the A320 or 727. Though the title reads about engine issues, I see this as the right place to post the questions as this place is flooded with experts in this field.
1. Why are aeroplanes moved a tractor for reverse motion? Is it technically impossible to have a reverse moving mode for an aeroplane? This is my observation at Chennai and Pune airports. Pardon my ignorance if a reverse driving mode exists.
2. While taxiing are the wheels driven by hydraulic pressure applied to any hydraulic motors in the wheels or else the plane moves by the virtue of thrust alone?
3. Where is the brake for the wheels located? Is there a friction based hydro - mechanical braking system like in cars?

Thanks in advance.

Regards,
Ilango

1. There is little practicality and more of logic to this. The Jet blast from the engine is reversed when the thrust reversers are activated. This might blow out terminal windows, especially in case of aircrafts where engines are mounted on the wings.

2. The Aircraft moves by virtue of thrust only. None of the wheels have motors (electric or hydraulic) for that matter.

3. The Aircrafts also have disc brakes. Albeit, they are a lot stronger and can also withstand huge amounts of heat without any signs of brake fade. There is also a pedal to operate the brakes manually in the cockpit, but they are electronically assisted. Usually, there is an "Autobrake" knob, which has different levels of braking. After touchdown, the computers decide the pressure to be relayed to the brakes. In the Airbus A380, you can even specify the taxiway at which you want the aircraft to exit, and the auto brake will brake accordingly, so that you stop exactly where you need to.

Here's an image of the A380's setup:


Sorry for the long post. Used to be an aviation enthusiast before I came across Team BHP.

[Jeroen]

Originally Posted by vishy76

After touchdown, the computers decide the pressure to be relayed to the brakes. In the Airbus A380, you can even specify the taxiway at which you want the aircraft to exit, and the auto brake will brake accordingly, so that you stop exactly where you need to.

It is not the pilot who decides where to exit the runway. The tower will tell you. You can ask for your preference though. Planes typically don't come to a full stop on the runway either.
Jeroen

[audioholic]

Originally Posted by Jeroen

It is not the pilot who decides where to exit the runway. The tower will tell you. You can ask for your preference though. Planes typically don't come to a full stop on the runway either.
Jeroen

He is mentioning about the BTV(Brake to Vacate) system on the A380. The pilot can choose a preferred runway exit. Whether or not the tower agrees is a different thing altogether.