747400sp
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Why So Many Wheels For HS-121 And TU-154?

Thu Jan 15, 2009 3:14 am

I see that HS-121 had 10 wheels and the TU-154 has 14 wheels, both these a/c seems to have more wheels then their weight needs, so why do, or in the HS-121 case, did these jets need so many wheels?
 
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Starlionblue
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RE: Why So Many Wheels For HS-121 And TU-154?

Thu Jan 15, 2009 3:29 am

It could be that there is a space constraint on the wheel wells, and thus small wheels in a long array work better than large wheels that would take more space in another direction.

Also, more wheels are good for landing on less than perfect runways, for example gravel.
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tdscanuck
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RE: Why So Many Wheels For HS-121 And TU-154?

Thu Jan 15, 2009 5:45 am



Quoting 747400sp (Thread starter):
I see that HS-121 had 10 wheels and the TU-154 has 14 wheels, both these a/c seems to have more wheels then their weight needs, so why do, or in the HS-121 case, did these jets need so many wheels?

In the case of the TU-154, Russia has some funky runways. Many Western-built airliners pick up landing gear limitations operating in some Russian airports. So they may have been lowering the wheel loading to accomodate the lower load capability of the runways. I'm not sure what the original airport spec for the HS-121 was, but that may also be at work on that aircraft.

Tom.
 
Tristarsteve
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RE: Why So Many Wheels For HS-121 And TU-154?

Thu Jan 15, 2009 5:12 pm



Quoting 747400sp (Thread starter):
HS-121 had 10 wheels

Well not really. The Trident had a two wheel nose gear, that retracted sideways, and 8 mainwheel tyres, but these tyres were mounted on 4 mainwheel hubs. Each hub had two tyres mounted on it, and they came off as one piece. I believe the reason was space. The main gears actually rotated as they retracted. The strut retracted normally, but inside it was another strut that rotated about a big bolt as it extended. Difficult to explain really, you have to see it, but it got the wheels into the bay sideways.
And the mainwheels were a pig to change. Took a lot of kicking to get them off, and then after you had fitted the new one, the Maxaret (mechanical antiskid) needed adjusting so it sat tight against the rim.
 
legoguy
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RE: Why So Many Wheels For HS-121 And TU-154?

Thu Jan 15, 2009 5:20 pm

Is it just me or was there ever a twin bogey A320 or 737 built for use on less than perfect runways. For some reason I seem to recall a picture of one of these aircraft with 4 wheels on each main undercarriage strut. Is it just me maing things up?  Confused
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northstardc4m
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RE: Why So Many Wheels For HS-121 And TU-154?

Thu Jan 15, 2009 5:36 pm



Quoting Legoguy (Reply 4):
Is it just me or was there ever a twin bogey A320 or 737 built for use on less than perfect runways. For some reason I seem to recall a picture of one of these aircraft with 4 wheels on each main undercarriage strut. Is it just me maing things up?

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Buyantukhaa
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RE: Why So Many Wheels For HS-121 And TU-154?

Thu Jan 15, 2009 6:29 pm



Quoting TristarSteve (Reply 3):
Difficult to explain really, you have to see it, but it got the wheels into the bay sideways.

While not a video, maybe this helps:

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Viscount724
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RE: Why So Many Wheels For HS-121 And TU-154?

Thu Jan 15, 2009 8:15 pm



Quoting Starlionblue (Reply 1):
It could be that there is a space constraint on the wheel wells, and thus small wheels in a long array work better than large wheels that would take more space in another direction.

That probably explains why the 727's two-wheel main gear uses some of the largest wheels/tires of any commercial aircraft, narrow or widebody, larger than any other Boeing narrowbody.

I believe the only significant US-built commercial types that use slightly larger main gear tires than the 727 are the 747-400, DC-10-30/40 and MD-11. I think the 49x17 main gear tires on many 727s is the same size as on the 747-100/200/300/SP. Some heavier 727 models use 50x20 tires. Both sizes are much larger than the Trident's tires. I can't find the tire size for the Tu-154 (Goodyear and Michelin have detailed tire specifications for most aircraft models on their websites.)
 
legoguy
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RE: Why So Many Wheels For HS-121 And TU-154?

Fri Jan 16, 2009 3:27 am



Quoting NorthStarDC4M (Reply 5):
A320 for Indian Airlines

Never on the 737 but proposed for the MD90-30T Trunkliner for China that never got built.

Ahhh bingo, thanks for the info and picture. I knew I couldn't have been imagining things! Looks mighty different than the usual single bogey A320's.
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wingscrubber
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RE: Why So Many Wheels For HS-121 And TU-154?

Fri Jan 16, 2009 4:00 am

Braking/tyre wear are the trade offs with rubber footprint size... If you add more tyres or use a larger tyre you're more likely to skid with a given weight, but your tyre wear will be reduced (assuming you don't lock wheels on every rollout) a bit like big rig trucks - often many will raise a set of wheels clear of the road when not laden due to the reduced load on the wheel and increased skidding risk, but on the other hand more surface area means more available braking surface...
Alternatively less rubber on the road for a given weight usually means more load on the tyre affording better braking but causing higher wear, reducing tyre life.
In addition, tyre pressure and rotational weight comes into play too, a bigger heavier wheel takes more energy to spin-up on touchdown and will scrub more rubber off.
In short, landing gear design is a balancing act between available stowage when retracted, braking force required, tyre longevity required and the intended landing surfaces.
Personally I love the odd look of a bush plane wearing tundra tyres  Smile
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Max Q
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RE: Why So Many Wheels For HS-121 And TU-154?

Fri Jan 16, 2009 6:01 am

The 727 landing gear arrangement resulted in it having a higher pavement loading per wheel than the 747.
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Starlionblue
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RE: Why So Many Wheels For HS-121 And TU-154?

Fri Jan 16, 2009 9:53 am



Quoting Max Q (Reply 10):
The 727 landing gear arrangement resulted in it having a higher pavement loading per wheel than the 747.

Doesn't the 727 have the highest pavement loading of any airliner, followed by the 777-300?
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Alessandro
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RE: Why So Many Wheels For HS-121 And TU-154?

Fri Jan 16, 2009 7:43 pm



Quoting Legoguy (Reply 4):
Is it just me or was there ever a twin bogey A320 or 737 built for use on less than perfect runways. For some reason I seem to recall a picture of one of these aircraft with 4 wheels on each main undercarriage strut. Is it just me maing things up?

Since the early B737 had gravelkits availble I think their undercarriage was pretty good.
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Mender
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RE: Why So Many Wheels For HS-121 And TU-154?

Mon Jan 19, 2009 8:37 pm

Anyone know it the Trident has retract braking on the nose gear?

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