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BreninTW
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How are pushback tugs driven?

Tue Mar 14, 2017 2:41 am

One of my hobbies is building model trucks, and one of the subjects I've long wanted to build is a pushback tug. Looking at a picture of one a friend just posted, I thought that it's too short to have a traditional drive train: Engine, gearbox, transfer box, drive shaft, front and rear differentials (talking about the widebody tugs that are 4WD here).

Then I thought to myself that the huge torque required to move an aircraft from standing would be hell on gearboxes and drive shafts. Which got me wondering -- how are they driven? I know mining trucks often use diesel-electric propulsion, with the engine basically working as a generator to drive massive electric motors in the wheels. Not sure tugs have enough space for a diesel-electric drive train ... are are they hydraulic?

EDIT: I'm thinking mostly of the traditional push-bar tugs, but I imagine that it would be similar for the big "scoop-and-lift" tugs.
 
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Starlionblue
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Re: How are pushback tugs driven?

Tue Mar 14, 2017 4:11 am

You can find the specs for some of these online. http://www.tugtech.com/brochures/GT110.pdf. It's basically a diesel tractor with with a torque converter transmission and four wheel drive.

Doesn't seem any shorter than the tractor part in a cab-over tractor trailer.

Looking at the linked model, the torque is a bit under 800lb/ft. A nice number but not really a monumental one. AFAIK The problem with tugs tends to be traction, not torque. Which is why they are heavy and have large wheels.

More tug specs here http://www.tugtech.com/tugproducts/tug-pushbacks/
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Horstroad
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Re: How are pushback tugs driven?

Tue Mar 14, 2017 8:23 am

Some are driven hydrostatically (especially towbarless tugs). A diesel engine produces hydraulic pressure which powers hydraulic motors in the wheel hubs. This beast has two engines with a combined power of 1000kW (1360PS). It has 6 wheel drive, 6 wheel steering and lifting power of 600kN (135,000lbf):


Image
 
Bostrom
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Re: How are pushback tugs driven?

Tue Mar 14, 2017 9:05 am

There are also diesel-electric hybrid ones. http://www.kalmarmotor.com/products/tbl ... 6b8c7a16a0
 
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VapourTrails
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Re: How are pushback tugs driven?

Thu Mar 16, 2017 1:23 am

BreninTW wrote:
EDIT: I'm thinking mostly of the traditional push-bar tugs, but I imagine that it would be similar for the big "scoop-and-lift" tugs.


Forgive me I don't know much about this topic, but I saw one at SYD where the whole front of the aircraft was up, on the pushback tug. I didn't see how they attached it, but when they disonnected it, they drove out from underneath it and it moved, or slid back down to ground level. The aircraft was a Q400, had not seen that before. This might be the latter one you mention above?
Time now to spread your wings, to take to flight, the life endeavour - Savage Garden
 
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Starlionblue
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Re: How are pushback tugs driven?

Thu Mar 16, 2017 1:36 am

VapourTrails wrote:
BreninTW wrote:
EDIT: I'm thinking mostly of the traditional push-bar tugs, but I imagine that it would be similar for the big "scoop-and-lift" tugs.


Forgive me I don't know much about this topic, but I saw one at SYD where the whole front of the aircraft was up, on the pushback tug. I didn't see how they attached it, but when they disonnected it, they drove out from underneath it and it moved, or slid back down to ground level. The aircraft was a Q400, had not seen that before. This might be the latter one you mention above?


What you saw is indeed a towbarless tug, like the one that says "Lufthansa" in the post above. It sorta clamps the front wheels and lifts up. The advantages are that it uses the plane's own weight for traction and there's no need for a towbar.

If you're at the pointy end, you can feel the front of the plane lift when it clamps on.

Image

Image
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
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BreninTW
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Re: How are pushback tugs driven?

Thu Mar 16, 2017 3:27 am

VapourTrails wrote:
BreninTW wrote:
EDIT: I'm thinking mostly of the traditional push-bar tugs, but I imagine that it would be similar for the big "scoop-and-lift" tugs.


Forgive me I don't know much about this topic, but I saw one at SYD where the whole front of the aircraft was up, on the pushback tug. I didn't see how they attached it, but when they disonnected it, they drove out from underneath it and it moved, or slid back down to ground level. The aircraft was a Q400, had not seen that before. This might be the latter one you mention above?


There are some videos on YouTube showing how they work. Quite fascinating pieces of engineering.
 
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VapourTrails
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Re: How are pushback tugs driven?

Thu Mar 16, 2017 3:54 am

Starlionblue wrote:
What you saw is indeed a towbarless tug, like the one that says "Lufthansa" in the post above. It sorta clamps the front wheels and lifts up. The advantages are that it uses the plane's own weight for traction and there's no need for a towbar.If you're at the pointy end, you can feel the front of the plane lift when it clamps on.


Thanks. :thumbsup:

BreninTW wrote:
There are some videos on YouTube showing how they work. Quite fascinating pieces of engineering.


Indeed it is. Thanks for that. So then what are the (other) advantages and disadvantages of each, it sounds as if the towbarless are more modern and replace the towbar ones eventually? Increased risks of malfunctions on the towbarless ones though?

Slightly off-topic I know.
Time now to spread your wings, to take to flight, the life endeavour - Savage Garden
 
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BreninTW
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Re: How are pushback tugs driven?

Thu Mar 16, 2017 4:29 am

VapourTrails wrote:

BreninTW wrote:
There are some videos on YouTube showing how they work. Quite fascinating pieces of engineering.


Indeed it is. Thanks for that. So then what are the (other) advantages and disadvantages of each, it sounds as if the towbarless are more modern and replace the towbar ones eventually? Increased risks of malfunctions on the towbarless ones though?


The towbarless (TBL) tugs offer better control and lower risk of damage. There's only one pivot point between the aircraft and the tug, which simplifies driving and gives better control. There are two pivot points on a traditional tug. There's also no risk of the towbar coming loose or a shearpin giving way.

I think the risk of over-turning the wheels on the aircraft is greater with the TBL, but I'm not sure about that.

Because the TBL uses the aircraft weight to give it traction, it is lighter when running empty, so uses less fuel and is less damaging to airport infrastructure.

In general, hydraulics is a very mature technology, so the risk of malfunctions is probably fairly low -- the main risk will be associated with control failure and pipes blowing out.
 
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Starlionblue
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Re: How are pushback tugs driven?

Thu Mar 16, 2017 5:28 am

One apparent disadvantage of a TBL is that you need different sizes for different weight ranges. As you can in this manufacter comparison chart, the -400 and -600 can't take anything smaller than a 767, while the -180 can't take anything bigger than a 767. So if you have an airport with low volume but high aircraft variation...

Having said that, I don't know if towbar tugs are limited in this way as well.

Image
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BreninTW
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Re: How are pushback tugs driven?

Thu Mar 16, 2017 6:52 am

Starlionblue wrote:
Having said that, I don't know if towbar tugs are limited in this way as well.


Towbar tugs are indeed limited, but probably not to the same extent that TBL are. Mostly they have an upper aircraft weight limit -- but there could also be problems when trying to use a 744-capable tug on a 737 ... it simply won't fit!
 
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Horstroad
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Re: How are pushback tugs driven?

Thu Mar 16, 2017 10:31 am

BreninTW wrote:
VapourTrails wrote:

One advantage of the towbarless tug is that you don't need personnel in the cockpit that brakes the aircraft in case of a broken tow bar. So only one employee can tow an aircraft between parking positions without assistance.

One disadvantage is that there is no tow bar that can break in the event something goes wrong. I've seen what a nose landing gear looks like after a tobarless tug made a 360 around it on slippery surface. Lots of bent metal, burst hydraulic lines and torn wires.
Once I've seen a broken down tug with a B747 still attached. For whatever reason they could not disconnect the tug from the aircraft. They jacked the tug up together with the aircraft to replace a wheel or something.

Here are some capability range tables. They overlap a lot. With just two different models you can tow anything from an ERJ135 to an A380.

Image

Image
 
StereoTechque
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Re: How are pushback tugs driven?

Thu Mar 16, 2017 12:24 pm

Starlionblue wrote:
Having said that, I don't know if towbar tugs are limited in this way as well.



They are limited but not as much as a TBL Tug. Also you need different towbars of rated load for different Aircrafts. A single tow bar is not certified to do the job.
The main concern of a Tug is not the displacement power of it, its the Traction as someone has mentioned above(both when starting and stopping).
I have seen a rated Towbar Tug coupled with Aircraft shuddering when stopping. This happens when the Tug is no more as efficient/Brakes of Tug worn out.

Tugs look after the tractive effort/momentum.
Towbars take care of the safety margin of the shear loads.
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COSPN
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Re: How are pushback tugs driven?

Fri Mar 17, 2017 12:22 am

It just a normal diesel tractor .. but uses planetary gears on each drive wheel...
 
CXfirst
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Re: How are pushback tugs driven?

Fri Mar 17, 2017 7:59 pm

At the ground handler I used to work at, we generally used towbar pushback tugs for most pushes, while the towbarless one was used for all long distance towing. It was generally a lot easier to drive at higher speeds, no real worrying about towbar pin shearing.

However, that pushback was larger, more expensive (so we had less of them), and somewhat restricted in aircraft types. Our traditional pushbacks generally had a max size limit, but we had pushback tugs that were used for aircraft as small as the F100 and all the way up to 77W.

I always found it funny that on some of our pushbacks, the pushback tug was heavier than the aircraft!
 
Apprentice
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Re: How are pushback tugs driven?

Fri Mar 17, 2017 10:04 pm

Hi:
As a curiosity, Russian tug , that was used in 1980-1990, was build over a T-34 Tank's chassis
Rgds
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