lincoln
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Can Someone Explain Tow Bars To Me, Please?

Fri Dec 26, 2008 9:27 pm

So I've always been curious about what the purpose of a tow bar is, and why it seems that the bars are aircraft-type specific...

In a recent thread it was mentioned in passing that (if I understood correctly) there are actually two different and incompatible towbar types for a certain aircraft type (737NG?) so if that type appears at an airport you may or may not have the correct tow bar unless you have both types.

So I know what the "broad" purpose of a tow bar is (e.g. to tow/push an aircraft) but beyond that would someone be so kind to explain all of the details, such as (but by no means limited to):

- Why there's not just a "universal" tow bar / why the tug isn't directly connected to the aircraft in some way?

- Why a single aircraft type would have more than one tow bar option?

- Etc., Etc.?

Thanks,

Lincoln
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EMBQA
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RE: Can Someone Explain Tow Bars To Me, Please?

Fri Dec 26, 2008 10:30 pm



Quoting Lincoln (Thread starter):
- Why there's not just a "universal" tow bar / why the tug isn't directly connected to the aircraft in some way?

Because aircraft have different nose gear to handle the different design requirments

Quoting Lincoln (Thread starter):
- Why a single aircraft type would have more than one tow bar option?

Because different models have different nose gear to handle the design changes...
"It's not the size of the dog in the fight, but the size of the fight in the dog"
 
tdscanuck
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RE: Can Someone Explain Tow Bars To Me, Please?

Fri Dec 26, 2008 11:08 pm



Quoting Lincoln (Thread starter):
- Why there's not just a "universal" tow bar / why the tug isn't directly connected to the aircraft in some way?

To elaborate a little on EMBQA's post, it's about handling overloads. If you overload the gear you do *not* want the nosegear (or the nosegear support structure) to be the thing that fails. That's the most expensive and difficult to repair option. So you want the towbar to fail to protect the airplane (a mechanical fuse). Since every model has a different nosegear with different design loads, each towbar has to have different capabilities for both push/pull and for fusing.

Quoting Lincoln (Thread starter):
- Why a single aircraft type would have more than one tow bar option?

Provided the two towbars met the load requirements (and were the right heights and attachments), there's no reason. But, at that point, you're talking about the same towbar design, just a different vendor.

Tom.
 
boeing767mech
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RE: Can Someone Explain Tow Bars To Me, Please?

Fri Dec 26, 2008 11:24 pm

There are some towbars that can be used on differnet airplanes. The towbar for the 767 can be used on a DC10/MD11,767,and 777. The towbar for the 757 can be used on the 757 and A-300. It depends on the operator but the little airline I work for have 4 types of towbars for 6 types of airplanes. But we also have a tug that will tow any type of airplane we operate by lifting the nose gear in a cradle. So we can do anything from a MD-80 to a 777 with on tug.

David
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113312
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RE: Can Someone Explain Tow Bars To Me, Please?

Fri Dec 26, 2008 11:45 pm

This is why the SuperTug is so great. It doesn't use a towbar at all. Instead, it grabs the nosewheels and lifts the whole front of the airplane up.
 
pilotpip
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RE: Can Someone Explain Tow Bars To Me, Please?

Sat Dec 27, 2008 12:06 am



Quoting 113312 (Reply 4):
This is why the SuperTug is so great. It doesn't use a towbar at all. Instead, it grabs the nosewheels and lifts the whole front of the airplane up.

And there are even different sizes of those  Smile I doubt the giant goldhoffers would move my ERJ-170 very well.
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HAWK21M
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RE: Can Someone Explain Tow Bars To Me, Please?

Sat Dec 27, 2008 12:22 am

A Towbar also has shear bolts that shear off to prevent serious damage to the Towbar or NLG in case of excess & abnormal loads.
regds
MEL
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acNDTTech
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RE: Can Someone Explain Tow Bars To Me, Please?

Sat Dec 27, 2008 3:36 am



Quoting HAWK21M (Reply 6):
A Towbar also has shear bolts that shear off to prevent serious damage to the Towbar or NLG in case of excess & abnormal loads.

And I know all about those shear bolts/pins.....I've broken a couple in my day. The strange thing is.....I had been towing about 10 years before I broke my first one. Ahhhhh, better the bolt, than the NLG.
 
boeing767mech
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RE: Can Someone Explain Tow Bars To Me, Please?

Sat Dec 27, 2008 3:51 am



Quoting AcNDTTech (Reply 7):
nd I know all about those shear bolts/pins.....I've broken a couple in my day. The strange thing is.....I had been towing about 10 years before I broke my first one. Ahhhhh, better the bolt, than the NLG

Funny thing we had the ramp push an airplane. The pins shears and the center pin for the towbar head. The towbar and tug drove away from the airplane, while the towbar head was still hooked to the Nose Gear.

David
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DiamondFlyer
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RE: Can Someone Explain Tow Bars To Me, Please?

Sat Dec 27, 2008 4:00 am



Quoting HAWK21M (Reply 6):
A Towbar also has shear bolts that shear off to prevent serious damage to the Towbar or NLG in case of excess & abnormal loads.

Boy do I wish GA planes were like that. It was real nice working at an FBO, learning about each different aircraft's towing characteristics. All of them were different. For instance, on some planes, there was no overturn protection. On Beechcraft Bonaza's, the shear point was not in the towbar, but in the landing gear. Broke a couple, not fun to take the walk of shame in to find a replacement. But all the jets had their own towbar head, that fit on the same actual bar.


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tdscanuck
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RE: Can Someone Explain Tow Bars To Me, Please?

Sat Dec 27, 2008 4:21 am



Quoting 113312 (Reply 4):
This is why the SuperTug is so great. It doesn't use a towbar at all. Instead, it grabs the nosewheels and lifts the whole front of the airplane up.

SuperTug's are great for the tug operators, but they can cause fits for the landing gear manufactures because they can transmit more load to the nose gear than the gear is designed to take and there's no obvious way to mechanically fuse them. Some airplanes actually have caps on the percentage of towing that can be done with towbarless tugs.

Tom.
 
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HAWK21M
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RE: Can Someone Explain Tow Bars To Me, Please?

Sat Dec 27, 2008 8:10 am



Quoting Boeing767mech (Reply 8):
Funny thing we had the ramp push an airplane. The pins shears and the center pin for the towbar head. The towbar and tug drove away from the airplane, while the towbar head was still hooked to the Nose Gear.

What type?

Quoting Tdscanuck (Reply 10):
Some airplanes actually have caps on the percentage of towing that can be done with towbarless tugs.

During Pushback/Towing with TBL tugs its important to avoid using the Aircraft brakes.As damage can be worse than a Towbar type.
regds
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Tristarsteve
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RE: Can Someone Explain Tow Bars To Me, Please?

Sat Dec 27, 2008 10:03 am



Quoting Boeing767mech (Reply 3):
The towbar for the 767 can be used on a DC10/MD11,767,and 777

And the Tristar!!!!.
But seriosly, if you use a B767 towbar to push a B777, be very gentle. The B777 weighs an awful lot more than a B767 and it is very easy to break the shear pins that are dimensioned for a B767.

Quoting Tdscanuck (Reply 10):
Some airplanes actually have caps on the percentage of towing that can be done with towbarless tugs.

First I have heard that. Here we use TBLs nearly all the time. There is no TBL here for a full B744 so they push back with a towbar, but all towing and pushbacks apart from this are TBL.
For this I am grateful. The amount of time that towbars used to take. Finding them, maintaining them, keeping spare pins in stock, finding a brakesman when you have to tow, and the worst of all was towing the Fokker100. I must have sheared the pins on that at least once a month. There was a dip in our taxiway and as the aircraft went over it, the nose leg extended, self centered, and sheared the pins. We only had one F100 towbar, so I had to sit in the aircraft while the driver went off to "borrow" the Swissair one.
 
ThirtyEcho
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RE: Can Someone Explain Tow Bars To Me, Please?

Sat Dec 27, 2008 10:31 am

Why are there different jacks for different cars? Can't there be a universal jack for all cars? Why are there different jacks for the same type of car?

My car has four wheels and your car has four wheels but my jack won't work on your car.
 
boeing767mech
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RE: Can Someone Explain Tow Bars To Me, Please?

Sat Dec 27, 2008 11:47 am

Quoting TristarSteve (Reply 12):
But seriosly, if you use a B767 towbar to push a B777, be very gentle. The B777 weighs an awful lot more than a B767 and it is very easy to break the shear pins that are dimensioned for a B767.

They telling that to a ramprat. They push 777's all the time without shearing the pins with a 767 towbar. I didn't know that about the Tristar. We never flew them, they had ordered them but bought DC-10's

David

[Edited 2008-12-27 03:48:22]
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tdscanuck
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RE: Can Someone Explain Tow Bars To Me, Please?

Sat Dec 27, 2008 10:49 pm



Quoting TristarSteve (Reply 12):
Quoting Tdscanuck (Reply 10):
Some airplanes actually have caps on the percentage of towing that can be done with towbarless tugs.

First I have heard that.

Check out Boeing Service Letter xxx-SL-09-001 (all MD models plus 777 & 787) or xxx-SL-09-002 (727-767).

I wrote the initial quote badly though...it's not a cap on the percent of towbarless towing, but a cap on the safe life of the nose landing gear. For certain combinations of tractor and airplane, you start eating the safe life of the NLG.

Tom.
 
QFA380
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RE: Can Someone Explain Tow Bars To Me, Please?

Mon Dec 29, 2008 2:18 am

Slightly off topic, but how do the tugs that tow from one of the main landing gear work? I've seen this used on DJ 737s and JQ A320s. It doesn't look like they lift the gear up and the ramper doesn't connect any bar. He just drives the thing up with the little remote control, tows it back and drives it away.
 
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Starlionblue
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RE: Can Someone Explain Tow Bars To Me, Please?

Mon Dec 29, 2008 3:32 am



Quoting ThirtyEcho (Reply 13):
Why are there different jacks for different cars? Can't there be a universal jack for all cars? Why are there different jacks for the same type of car?

My car has four wheels and your car has four wheels but my jack won't work on your car.

If we're still talking towbars, weight is a factor I guess. A 747 weighs many times a CRJ.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
pjflysfast
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RE: Can Someone Explain Tow Bars To Me, Please?

Tue Dec 30, 2008 12:35 am

Some business jets carry a tow bar on board in case they need it and the place they are at does not have one. For instance the Global 5000 and the challenger 600,601,604 and so on.
 
2H4
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RE: Can Someone Explain Tow Bars To Me, Please?

Tue Dec 30, 2008 12:58 am

You also want to avoid this:


image courtesy of Dauntless Software


2H4
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KELPkid
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RE: Can Someone Explain Tow Bars To Me, Please?

Tue Dec 30, 2008 1:01 am



Quoting Lincoln (Thread starter):
- Why there's not just a "universal" tow bar / why the tug isn't directly connected to the aircraft in some way?

Well, speaking from a former (GA) lineboy's experience: (the other end of the towbar was a push handle-we didn't get to move them with the tug per the FBO's owner )

There were generally three types of towbars you had to be concerned with:

Cessna
Piper
Beechcraft

General Aviation's "big three" each had their quirks in nose gear design, which made it difficult to have a universal towbar. However, there were some "universal" towbars out there, which were more akin to the "Jack-of-all-trades, master of none" variety (i.e. it would go on the nosegear, but never very well), and there were all sorts of hokey thumb screws and such you had to twiddle to get it to fit the plane you were trying to move. The best policy was just to grab a manufacturer-specific model.

Throw in an "off-brand" plane that you had to move, (something like, say, a Grumman Cheetah or a Socata Tobago), and you'd better hope that the owner left the baggage compartment unlocked so you could get to their towbar  Wink
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jetmech
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RE: Can Someone Explain Tow Bars To Me, Please?

Tue Dec 30, 2008 2:48 am



Quoting QFA380 (Reply 16):
Slightly off topic, but how do the tugs that tow from one of the main landing gear work? I've seen this used on DJ 737s and JQ A320s. It doesn't look like they lift the gear up and the ramper doesn't connect any bar. He just drives the thing up with the little remote control, tows it back and drives it away.

Those tugs work by using a set of rollers. The rollers make contact with the back and front of the main landing gear wheels, and are covered in a non slip coating to increase friction. One of the set of rollers is powered.

The rollers transmit torque to the main landing gear wheels, which is what actually moves the plane. IIRC, the operator of the tug communicates with the pilots, who steer the plane via the nosewheel.

Regards, JetMech
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57AZ
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RE: Can Someone Explain Tow Bars To Me, Please?

Tue Dec 30, 2008 6:51 am

On smaller nose wheel tugs (built for GA), the nose wheel is connected via winch to the tug. When connecting to the plane, the operator connects the straps to the nose or tail wheel and winches it up the ramp.
"When a man runs on railroads over half of his lifetime he is fit for nothing else-and at times he don't know that."
 
JoePatroni
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RE: Can Someone Explain Tow Bars To Me, Please?

Fri Jan 02, 2009 6:45 pm

Also some tow bars have interchangeable heads. One I can think of off hand is the tow bar for the CRJ. The -100/200 has a smaller head than the -700/900. So, instead of using 2 different tow bars, the ground crew can just change the heads.

JP.
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Tristarsteve
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RE: Can Someone Explain Tow Bars To Me, Please?

Fri Jan 02, 2009 7:33 pm



Quoting JoePatroni (Reply 23):
Also some tow bars have interchangeable heads

Not quite the same, but Concorde carried a towbar adapter on board when it did charter flights. It connected to a standard B747 towbar. There were only a few of them so they were carried on board.
I once did a pushback on Concorde at ARN. When the pushback was complete, I detached the adaptor and the engineer opened the R1 door and dropped down a rope so I could tie it on and he could haul it back in. And there must have been 2000 people watching us scratching their heads.
 
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HAWK21M
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RE: Can Someone Explain Tow Bars To Me, Please?

Sat Jan 03, 2009 2:45 pm

On Towbars....The AN124 has a two piece bar that if carried on board has to be offloaded/assembled/aircraft pushed/disassembled/reloaded.... Smile
regds
MEL
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57AZ
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RE: Can Someone Explain Tow Bars To Me, Please?

Sun Jan 04, 2009 8:45 am

Some tail wheel aircraft have a two piece tow bar that is used when towing the aircraft from the front. The Thunder Mustang (3/4 scale P-51D) has a hinged two piece tow bar-each leg of the tow bar connects to a main gear using a locking pin. The aircraft also has a removable hook that can be installed behind the tail wheel. If we're towing the aircraft using a truck or tug from the front, we use the tow bar. If we're towing it from the rear, we use a properly rated towing strap with hook.
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DC8FriendShip
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RE: Can Someone Explain Tow Bars To Me, Please?

Mon Jan 05, 2009 7:50 pm



Quoting Lincoln (Thread starter):
Why a single aircraft type would have more than one tow bar option?

Some airlines requested this option to make their towbars less fleet specific, so that a line station would not have to keep as many towbars. for instance, AA had the standard 707/727 towbar that fit bothe fleet types, but UA had it's 727's fitted so that they were commoon with their 737s.
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HAWK21M
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RE: Can Someone Explain Tow Bars To Me, Please?

Wed Jan 07, 2009 7:34 am



Quoting DC8FriendShip (Reply 27):
but UA had it's 727's fitted so that they were commoon with their 737s.

what was the method used to ensure commonality?
regds
MEL.
I may not win often, but I damn well never lose!!! ;)
 
DC8FriendShip
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RE: Can Someone Explain Tow Bars To Me, Please?

Wed Jan 07, 2009 10:24 pm



Quoting HAWK21M (Reply 28):

what was the method used to ensure commonality?

The 727 and 737 towbars for united have a U shaped clamp, which fastens to a fitting on the fromt of the NLG. normal 727 's had two fittings protruding from the gear, by which the the towbar connected by spreading two pins into the fittings. UA 727 NLG had a rod across these, that the 737 towbar attaches to.
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HAWK21M
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RE: Can Someone Explain Tow Bars To Me, Please?

Thu Jan 08, 2009 8:12 am



Quoting DC8FriendShip (Reply 29):
UA 727 NLG had a rod across these, that the 737 towbar attaches to.

Thats what we use for our B737s.One day we hired a towbar from IC/CD & it had the clamp type.

regds
MEL
I may not win often, but I damn well never lose!!! ;)

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