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#1
Old 04-30-2012, 07:18 AM
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What happened to half-tracked vehicles?

Up until the 1950s, half-tracked vehicles cars or trucks (with two front wheels at the front and caterpillar tracks at the rear) were quite popular as military vehicles. The Allies alone built something like 50,000 M3 Half-Tracks during WWII and the Germans had their own half-tracked vehicles as well.

But after that, everyone seemed to have collectively lost interest in them. I realise with around 50,000 units produced there probably wasn't a need to make any more of them, but even so.

So, what happened to half-tracks as a vehicle design?
#2
Old 04-30-2012, 08:55 AM
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I have to wonder why they where used in the first place. What's the benifit.
#3
Old 04-30-2012, 09:10 AM
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Quote:
Originally Posted by enipla View Post
I have to wonder why they where used in the first place. What's the benifit.
A nice summary from Wikipedia:

Quote:
A half-track is a civilian or military vehicle with regular wheels at the front for steering and caterpillar tracks at the back to propel the vehicle and carry most of the load. The purpose of this combination is to produce a vehicle with the cross-country capabilities of a tank and the handling of a wheeled vehicle.

It is not difficult for someone who can drive a car to drive a half-track, which is a great advantage over fully tracked vehicles which require specialized training. Half-tracks thus facilitate moving personnel and equipment successfully across varying terrain.

The main advantage of half-tracks over wheeled vehicles is that the tracks reduce the vehicle's overall ground pressure and give it greater mobility over soft terrain like mud and snow, while they do not require the complex steering mechanisms of fully tracked vehicles, relying instead on their front wheels to direct the vehicle, augmented in some cases by track braking controlled by the steering wheel.
The Wikipedia article mentions some half-tracks were used recently with good results, but does explain why they fell out of favor:

Quote:
Half-tracks were in use by the Israeli Army until recently, where they were deemed to outperform fully tracked and fully wheeled vehicles for non-combat payload tasks such as carrying telecommunications equipment.

As of March 2008, 600 half-tracks were still officially listed as on active duty.
#4
Old 04-30-2012, 09:11 AM
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they give more traction on a loose surface, like sand and snow.
#5
Old 04-30-2012, 09:31 AM
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They were replaced either by fully tracked APCs like the M75, M59 and eventually the ubiquitous M113; they had the advantages of having overhead coverage for the passengers, being amphibious capable for river crossing, and well, being fully tracked or by fully wheeled APCs such as the most of the Soviet BTR series and the French VAB which also had overhead cover and were usually amphibious.

ETA: It's not really that hard to learn to learn to drive a tracked vehicle where steering is accomplished by differential track speed. It also gives the added advantage of not having a turning radius; tracked vehicles can pivot to infinity by putting one track in forward drive and the other in reverse at the same speed.

Last edited by Dissonance; 04-30-2012 at 09:33 AM.
#6
Old 04-30-2012, 09:57 AM
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Seems to me (with no knowledge in the field, please be kind) that tracks provide two advantages: added traction and ability to cross chasms, ditches, etc. in proportion to the length of the caterpillar tract. A vehicle with wheels in front basically loses the latter advantage because the wheels can still get stuck.

And I can imagine that tracked vehicles don't provide much of a traction advantage on paved roads, are probably slower than normal trucks, and will probably cause damage to the road itself.

So, in the mid-20th century, as nations developed paved highway networks that could be used to move vehicles around, it became less attractive to use tracked trucks that would need to be loaded onto normal trucks for ferrying.

(The preceding has been a huge WAG.)
#7
Old 04-30-2012, 10:33 AM
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Quote:
Originally Posted by Heracles View Post
And I can imagine that tracked vehicles don't provide much of a traction advantage on paved roads, are probably slower than normal trucks, and will probably cause damage to the road itself.
Tracked vehicles also damage themselves, in a sense -- tracks wear out pretty fast compared to standard tires. "Throwing a track" is a pretty common problem for tankers.
#8
Old 04-30-2012, 11:32 AM
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Quote:
Originally Posted by Heracles View Post
And I can imagine that tracked vehicles don't provide much of a traction advantage on paved roads, are probably slower than normal trucks, and will probably cause damage to the road itself.
Consider a truck wheel might have a footprint of, oh 16 square inches x 4 wheels = 64 square inches. Now consider a crawler track having a footprint of maybe 20 square feet. They do quite well on paved & unpaved surfaces. And despite weighing a lot, they distribute that weight over the entire track surface which yields a significantly lower weight per square inch than a weeled vehicle. That means, when you get your hummer stuck to the floorboards in muck, any old tracked vehicle can waddle on out into the bog, chain you up and haul you out no problem.

Tracks kick all kinds of ass.
#9
Old 04-30-2012, 12:41 PM
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One of the toys on my short list is a Kettenrad.

Perhaps next year I'll get one.
#10
Old 04-30-2012, 01:09 PM
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They make farm tractors with a half-track design. Supposedly they pack down soil less than the giant wheeled models, but that's a point of debate.

And, no, they aren't really designed to travel on paved roads.
#11
Old 04-30-2012, 02:30 PM
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Quote:
Originally Posted by kunilou View Post
They make farm tractors with a half-track design. Supposedly they pack down soil less than the giant wheeled models, but that's a point of debate.

And, no, they aren't really designed to travel on paved roads.
I've never seen half-track versions. They're either conventional full track designs, or articulated 4-track designs.
#12
Old 04-30-2012, 04:20 PM
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Quote:
Originally Posted by Gorsnak View Post
I've never seen half-track versions. They're either conventional full track designs, or articulated 4-track designs.
Come to think of it, I believe you're correct.
#13
Old 04-30-2012, 06:13 PM
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Originally Posted by ducati View Post
One of the toys on my short list is a Kettenrad.

Perhaps next year I'll get one.
Go cruising down Main Street, the Highway Department will just love you.
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#14
Old 04-30-2012, 07:09 PM
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Quote:
Originally Posted by Gorsnak View Post
I've never seen half-track versions. They're either conventional full track designs, or articulated 4-track designs.
You see this kind of thing from time to time:
http://farmshow.com/view_articles.php?a_id=1284
#15
Old 04-30-2012, 07:29 PM
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Quote:
Originally Posted by jnglmassiv View Post
You see this kind of thing from time to time:
http://farmshow.com/view_articles.php?a_id=1284
I stand corrected. That looks like an aftermarket thing to replace drive wheels with tracks.
#16
Old 04-30-2012, 08:18 PM
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WAG:

Hasn't tire technology improved significantly over the years? It seems that that may have influenced the half-tracks becoming less favorable.
#17
Old 04-30-2012, 09:49 PM
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Wouldn't a snowmobile count as a half track? Sure, the front part is skids instead of wheels but isn't the principle the same?
#18
Old 04-30-2012, 10:13 PM
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Quote:
Originally Posted by tanstaafl View Post
Wouldn't a snowmobile count as a half track? Sure, the front part is skids instead of wheels but isn't the principle the same?
Not quite. A snowmobile requires a large traction footprint, given it rides on snow. A half-track would be quite happily at home on any road driven by a wheeled vehicle.
#19
Old 05-01-2012, 12:12 AM
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Quote:
Originally Posted by jnglmassiv View Post
You see this kind of thing from time to time:
http://farmshow.com/view_articles.php?a_id=1284
This company has them for trucks, ATVs and even trailers too. Pretty much anything with wheels and enough space in the wheel wells for them I guess. These aren't half tracks though, they are just neat, although there's probably nothing preventing a person from only installing two of them and making a half track.
#20
Old 05-01-2012, 06:59 AM
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Here is a good article about the merits of wheeled and tracked military vehicles.(pdf)
It concludes that both have uses. Tracked vehicles are better for tactical off road uses. Wheeled vehicles are more reliable, and faster for use in logistical operations.

A half track has the advantages and disadvantages of both, making them a vehicle without a special use.
#21
Old 05-01-2012, 09:00 AM
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Sailboat, thanks. I wouldn't have thought training would be an issue.
#22
Old 05-01-2012, 01:14 PM
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Quote:
Originally Posted by kunilou View Post
They make farm tractors with a half-track design. Supposedly they pack down soil less than the giant wheeled models, but that's a point of debate.

And, no, they aren't really designed to travel on paved roads.
The Challenger tractors (shown in link) and others actually do move quite well on roads. They don't travel quite as fast as wheeled tractors, which can travel in excess of 20 mph in road gear, but the track machines move right along....probably 15 mph or so. Unlike older track-laying machines which rode on a belt of linked metal plates, the new ones run on an endless belt of cleated rubber and don't damage road surfaces.
SS
#23
Old 05-01-2012, 04:05 PM
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Quote:
Originally Posted by Dissonance View Post
ETA: It's not really that hard to learn to learn to drive a tracked vehicle where steering is accomplished by differential track speed. It also gives the added advantage of not having a turning radius; tracked vehicles can pivot to infinity by putting one track in forward drive and the other in reverse at the same speed.
In theory. In practice performing a neutral steer can cause problems. You are OK if the surface is hard concrete. If you neutral steer on asphalt, the asphalt becomes gravel which may piss off whoever owns that asphalt. If you neutral steer on loose surface, its a good way to throw a track.
#24
Old 05-01-2012, 06:27 PM
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Quote:
Originally Posted by Sailboat View Post
Tracked vehicles also damage themselves, in a sense -- tracks wear out pretty fast compared to standard tires. "Throwing a track" is a pretty common problem for tankers.
I wouldn't characterioze it as a common problem, but it was a common concern, and track maintenance was no joking matter. A TC who threw a track had better have a good explanation ready to go because pointed questions will be asked by higher.

We threw track on an FTX at Hood, just driving at a moderate pace across open ground, and the BMO stopped by to chew us out. I, my TC, and our company XO respectfully disagreed with the BMO's assessment of our maintenance deficiencies.

We (correctly, IMO, and the battalion XO later agreed) pointed out expected track life, current track life, the readily visible condition of my tank's track, and the stack of 2404s going back many months with the red circle-X's and the annotation "Deferred" endorsed by the BMO.

We didn't so much as "throw track," as it just sort of fell apart on us.

Quote:
Originally Posted by Loach
In theory. In practice performing a neutral steer can cause problems. You are OK if the surface is hard concrete. If you neutral steer on asphalt, the asphalt becomes gravel which may piss off whoever owns that asphalt. If you neutral steer on loose surface, its a good way to throw a track.
+1 QFT! The vast majority of thrown track that I saw was from neutral steers or pivot steers.
#25
Old 05-01-2012, 06:32 PM
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Quote:
Originally Posted by ExTank View Post
I wouldn't characterioze it as a common problem, but it was a common concern, and track maintenance was no joking matter. A TC who threw a track had better have a good explanation ready to go because pointed questions will be asked by higher.

We threw track on an FTX at Hood, just driving at a moderate pace across open ground, and the BMO stopped by to chew us out. I, my TC, and our company XO respectfully disagreed with the BMO's assessment of our maintenance deficiencies.

We (correctly, IMO, and the battalion XO later agreed) pointed out expected track life, current track life, the readily visible condition of my tank's track, and the stack of 2404s going back many months with the red circle-X's and the annotation "Deferred" endorsed by the BMO.

We didn't so much as "throw track," as it just sort of fell apart on us.



+1 QFT! The vast majority of thrown track that I saw was from neutral steers or pivot steers.

Is it possible to fix the track without lifting the tank? How is it done? How long does it take to fix or replace a track?
#26
Old 05-01-2012, 08:37 PM
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Quote:
Originally Posted by MichaelEmouse View Post
Is it possible to fix the track without lifting the tank? How is it done? How long does it take to fix or replace a track?
I can only speak to Abrams, of course.

If the track isn't all the way off the road wheels (the center guides had come out of their groove between the road wheels, but the track is otherwise pretty much where it's supposed to be), then sometimes it's possible to "walk the track" back into place. This typically required firm ground.

If the track has come out of its usual position on the drive sprocket, you pretty much have to break track.

Breaking track! :cracks knuckles:

First, you hope that you've thrown track on relatively flat, firm, dry ground.

Heh. Heheh.

Yeeaah.

Second, pick a section of track between the idler wheel and the #1 road wheel to break track.

3) Next, you install a device called the track support chain. It is a cantilever-style chain-and-binder rig that you attach to the side of the hull (not the armored skirts, the bit behind them) between the Idler Wheel and the Sprocket (essentially, the length of the hull) and snug it down tight. As in, "That's-going-to-kill-someone-if-it-snaps" tight. It's purpose is to physically support the track once the track tension is released and the track is broken.

4) Then, you back off the jam nut on the Compensating Idler Arm, and pop the relief valve. Grease will now spew out like Linda Blair puking pea soup, and the adjuster arm will contract, pulling the idler wheel with it, and tension will be released on the track.

5) Now, you take out your track jacks (linear "pincer"-style screw jack) and your end connector puller, a hydraulic jack similar in concept to a gear puller, but configured to pull end connectors (item 3) off of the track ends (the metal rods sticking out of the track pad).

6) Next, ensuring that your center guide (parts 6, 7, 8, & 9) is still firmly attached, remove the wedge bolts and wedges (4 & 5) from both the inside and outside end connectors. This will be problematic since the exposed threads sticking out end of the wedge will be destroyed. Imagine a horribly cross-threaded bolt and nut. Use 3/4" drive tools, a cheater pipe, and a strong, young, back. Sometimes it's easier to just tighten the bolt until it breaks, and beat the wedge out with a sledge hammer.

7a) With the wedges and bolts removed, put the end connector puller (a ~30 pound hydraulic jack that you must hold in place until someone pumps the handle a couple of times to put some pressure on the end connector) on the outside end connector, and extract the end connector just far enough to get a track jack on. Install the track jack and make sure it has enough tension on it to hold the track together (being "pincer"-style, the jaws go over the track rods that the end connectors sit on and hold the track sections together). See this video. Wimps.

Have the lowest-ranking member of the crew repeat the process for the inside end connector. It's what God made Privates for.

7b) Remove the center guide nut (9), tap the bolt (8) with a ball-peen hammer to knock it out, and the two center guide halves (6 & 7) should just fall out. Percussive persuasion may will be required. Cussing doesn't help, but it may make you feel better, and entertain your crewmates.

7c) Now the track jacks are holding the two track sections together. Using 3/4 drive ratchet and socket, slowly open the inner and outer jacks evenly until they are far enough apart that they essentially just fall off. Your track is now "broken," and you're ready for the next step.

7d) Warning: The U.S. Army has determined that the following is fucking insane, and only a lazy, dumb-assed tanker or congenital retard would ever attempt this.

7a-c take too damned long, and are a pain in the nuts.

Remove the center guide nut. Use your tanker bar (a 60" aligning bar) and a sledge hammer to knock your end connectors off. Stand a bit back and use same to smack the center guide very hard. Do NOT look at the center guide when you do this, as a face full of flying steel hurts. Helmets recommended.

7e) Your track is now apart. Have your driver back slowly until it falls off of the drive sprocket and is laid out flat on the ground. It is ready to be put back on; remove any bad section(s), install new/good section(s).

8) Putting the track back on is pretty much the above in reverse, with the exception that to get the track back up onto the drive sprocket, you use a rope; tie one end to the first track link, and wrap the other end around the sprocket. Have the driver sloooooowly neutral steer away from whatever side you're working on and the sprocket will winch the track back up onto it.

9) Once the track section is firmly on the sprocket, remove the rope, and have the driver slowly drive forward. Be ready with the tanker bar to help it along over the Return Rollers and such, and it will go over the top of the Idler Wheel.

10a) Ideally, the two track sections will be long enough/close enough to slip the track jacks (now fully extended) over the track rods, and then begin tightening them up to bring the two track sections together close enough to get end connectors on (what the [email protected]$#%& guys are doing in the youtube video, above)

10b) If not, stick the small end of the tanker bar in between two track sections about where it curves over the Idler Wheel, and have the biggest, heaviest guy hang off of it like Cheetah off of a tree branch. If that's not enough, also have the driver sloooowly neutral steer to give you those few extra inches of track.

10c) Laugh your ass off when the tanker bar slips out and the big fat dude hanging on it falls flat on his ass, and smacks himself in the face with a 60" long, 15 pound chunk of hardened steel.

11) If all else fails, back the track back off, take another hitch on your track support chain (see step 3), and try again.

12) Break out the grease gun and tension the track by pumping grease into the Compensating Idler Arm. Don't forget to do this, or you'll drive about a quarter mile and throw track. Again.

That's about what I remember of how to do it "The Army Way." We came up with some shortcuts, circumstances permitting. See 7d.

New track comes palletized in 8-block sections. To put new track on, you have to back the old track off using the steps above, take it apart in 8-block sections, and pull it all out of the way. Pull new sections off of the pallets (an 8-block section weighs about 400 pounds; bring friends), line them up in front of the tank (and yes, you have to be pretty darned close in your alignment), connect them, and drive it on in the manner I described above.

Fixing one bad track block/section is a three-man job and on flat, firm, dry ground takes about 2-3 hours for a crew of average experience and motivation. Completely changing both sides of track on an Abrams (first one, then the other) is an all-day evolution for about 4-6 guys which is typically 2 crews, usually sans TCs. They have to stand back and fart, scratch, holler, look bored, and frequently check their watch in a meaningful manner, while saying things like, "In my day, we could change both side at once, in the snow, at night...." and so on in this manner.
#27
Old 05-01-2012, 09:26 PM
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ExTank, I read the dope because of people like you. Your first hand knowledge and willingness to share in a fun way is something unique in the age of wikipedia. Thanks for that!
#28
Old 05-02-2012, 05:07 AM
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I too can only congratulate ExTank on a most informative post. When I started the thread I had no idea I might actually gain an insight into what's involved in changing the tracks on an M1 Abrams Tank, but it's exactly the sort of thing I enjoy learning here.
#29
Old 05-02-2012, 04:20 PM
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Always happy to provide some perspective

Just remember that there are also "fun quotient modifiers", aka "Fuck You" modifiers, which enhance the track-changing experience.

Some FQMs include, but are not limited to:

1) Mud. Deep mud. Soupy mud. Cold mud. That thick, clay-like mud that has its own gravitational effect on everything around it.

2) Cold. For some reason, smacking your fingers with a hammer hurts twice as much when they're practically frozen numb than when they are not.

3) Heat. Add humidity for that final FQM Additional Misery Identifier. Sweat dripping off of you so much that you just about can't see what you're doing, or hold onto a tool even with leather gloves on.

4) Insects. There's nothing like a scorpion, tarantula, or centipede crawling down your shirt while you're on the ground wrestling tools and/or track sections about.

5) Tools. Lack thereof. As in, "Private Snuffy, where in the [email protected]#$%& is the track support chain?! What do you mean, you took it off the tank and put it in the CONEX?!"

6) Superiors. Standing over you and asking (not more than 5 minutes after the last time they asked) when the 2-hour job you're doing will be done. They won't do anything usefull like hand you tools, provide refreshing beverages, fetch food, or go AWAY!

7) Weather. Separate from 1, 2, & 3, as few things enhance the track-changing experience like freezing rain, a dust storm, or a violent thunderstorm spewing hail and funnel clouds.
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