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747400sp
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Could An Eight Wheel Jetliner Work?

Sun Mar 21, 2010 2:51 am

I have notest that most narrow body jetliners has only six wheels. Now some of the larger narrow bodies has ten wheels, so now I wonder, could useing an eight wheel landing gear design work? Both Airbus and Boeing has said that the A32X and 737 family would be replaced by wider jetliners. So I am thinking, maybe they could design the a/c's with two nose gear like normal, but have a six wheels main gear. It would be three two wheels bogies across, so could this work?
 
BMI727
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RE: Could An Eight Wheel Jetliner Work?

Sun Mar 21, 2010 2:59 am

Quoting 747400sp (Thread starter):
It would be three two wheels bogies across, so could this work?

That would add a lot of weight and complexity since it would mean that the plane would have a third main gear.
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Starlionblue
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RE: Could An Eight Wheel Jetliner Work?

Sun Mar 21, 2010 3:01 am

You can ALWAYS add more weight and complexity.  
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FX772LRF
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RE: Could An Eight Wheel Jetliner Work?

Sun Mar 21, 2010 3:20 am

Could it work? Sure.

Would it be feasible? Most likely not. Or else someone would have probably done it already.

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vikkyvik
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RE: Could An Eight Wheel Jetliner Work?

Sun Mar 21, 2010 4:42 am

If I had to guess, I'd say it would probably be lighter and simpler to go with the SR-71's main gear config:


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Two 3-wheel bogies instead of three 2-wheel bogies.

Quoting FX772LRF (Reply 3):
Could it work? Sure.

Would it be feasible? Most likely not. Or else someone would have probably done it already.

  

Though who knows, someone may find a way to do it feasibly....
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bohica
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RE: Could An Eight Wheel Jetliner Work?

Sun Mar 21, 2010 7:12 am

Quoting vikkyvik (Reply 4):
Two 3-wheel bogies instead of three 2-wheel bogies.

I was thinking of a main gear arrangement similar to the C-17 which is a 2+1 configuration per gear.

Another idea is to have four main landing gears with two wheels each like a B-52. Ground clearance might be a problem though.
 
BMI727
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RE: Could An Eight Wheel Jetliner Work?

Sun Mar 21, 2010 7:35 am

Quoting bohica (Reply 5):
Another idea is to have four main landing gears with two wheels each like a B-52.

Again, that would add weight and complexity with the extra leg.
Why do Aerospace Engineering students have to turn things in on time?
 
vikkyvik
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RE: Could An Eight Wheel Jetliner Work?

Sun Mar 21, 2010 8:15 am

Quoting bohica (Reply 5):
Another idea is to have four main landing gears with two wheels each like a B-52. Ground clearance might be a problem though.

Being a heavy bomber, the B-52 had a whole other set of issues to deal with. You want the bombs as close to the CG as possible, so you don't have a giant weight with a huge moment-arm from the CG. But of course, on a high-wing plane like the B-52, that's typically where the main landing gear goes (a bit aft of CG). So instead, you give it two sets of main gear, and no real nose gear.

That brings in the issue of rotation on takeoff. The aft gears are too far back for the B-52 to rotate around them. I haven't seen it myself, but I've heard that the -52 actually lifts up the rear gear first, and has a nose-down initial climbout angle. You can see it here:


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Quoting bohica (Reply 5):
I was thinking of a main gear arrangement similar to the C-17 which is a 2+1 configuration per gear.

That could work, although on the C-17, I'd bet the inner gear is actually on a separate pylon. If I'm not mistaken, the inner gear on the -17 is actually higher than the outer gear, and only starts bearing weight at some certain weight. At least that's how I assumed it works. Possibly they do all touch the ground at all weights, but the outer gear just bears more load. See here:


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That's actually similar to the center gear on the A340 (I think....can't remember if it's the A340 or the MD-11) - it can be off the ground at lighter weights. Or maybe it is the MD-11, because I found this shot....the full weight of the airplane is likely not on the gear yet, but the outer gear is touching the ground, and the center gear isn't yet:


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zanl188
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RE: Could An Eight Wheel Jetliner Work?

Sun Mar 21, 2010 12:51 pm

Quoting vikkyvik (Reply 7):
The aft gears are too far back for the B-52 to rotate around them. I haven't seen it myself, but I've heard that the -52 actually lifts up the rear gear first, and has a nose-down initial climbout angle. You can see it here:

The -52 lifts off flat. This is due to the wings angle of incidence being fairly high. Nose will go down after liftoff to keep climb rate under control. Looks awkward (it taxies sidewise too) but its worked for 50 years.....
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RE: Could An Eight Wheel Jetliner Work?

Sun Mar 21, 2010 2:30 pm

Quoting 747400sp (Thread starter):
Both Airbus and Boeing has said that the A32X and 737 family would be replaced by wider jetliners.

They may be wider, but with the emphasis in keeping weight down, they may not be significantly heavier, so the extra foot print area might not be needed.
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Spacepope
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RE: Could An Eight Wheel Jetliner Work?

Sun Mar 21, 2010 2:52 pm

Quoting ZANL188 (Reply 8):
The -52 lifts off flat. This is due to the wings angle of incidence being fairly high. Nose will go down after liftoff to keep climb rate under control. Looks awkward (it taxies sidewise too) but its worked for 50 years.....

Add the fact that the B-52 is also a 10-wheel aircraft, not 8. Those outriggers are used from time to time.
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474218
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RE: Could An Eight Wheel Jetliner Work?

Sun Mar 21, 2010 3:13 pm

It already been done:


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Starlionblue
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RE: Could An Eight Wheel Jetliner Work?

Sun Mar 21, 2010 3:52 pm

My guess is that the Hustler had the same problem as the Tu-144: limited space in the gear bays.
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474218
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RE: Could An Eight Wheel Jetliner Work?

Sun Mar 21, 2010 3:56 pm

Quoting Starlionblue (Reply 12):
My guess is that the Hustler had the same problem as the Tu-144: limited space in the gear bays.

Very thin wings. By using 16 small main wheels they kept the pavement loading low and fit the wheels in the gear bay.
 
OldAeroGuy
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RE: Could An Eight Wheel Jetliner Work?

Sun Mar 21, 2010 4:01 pm

Quoting 747400sp (Thread starter):
So I am thinking, maybe they could design the a/c's with two nose gear like normal, but have a six wheels main gear. It would be three two wheels bogies across, so could this work?

If you really need more wheels, the Trident had four main gear wheels on each of the two main gear posts.

https://www.airliners.net/photo/CAAC/...d=ea5ce3ddb0207d428cf38141941cf7ac

The Trident nose gear was also unusual. It was not mounted on the airplane centerline and retracted sideways.
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Viscount724
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RE: Could An Eight Wheel Jetliner Work?

Sun Mar 21, 2010 6:51 pm

Quoting ZANL188 (Reply 8):
Quoting vikkyvik (Reply 7):
The aft gears are too far back for the B-52 to rotate around them. I haven't seen it myself, but I've heard that the -52 actually lifts up the rear gear first, and has a nose-down initial climbout angle. You can see it here:

The -52 lifts off flat. This is due to the wings angle of incidence being fairly high. Nose will go down after liftoff to keep climb rate under control. Looks awkward (it taxies sidewise too) but its worked for 50 years.....

That reminded me of the following recent (June 2009) video of a B-52 alert scramble at Minot AFB, North Dakota, with 15 B-52s taking off about 30 seconds apart.
http://www.youtube.com/watch?v=wJ7niLYSVFo
 
tdscanuck
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RE: Could An Eight Wheel Jetliner Work?

Sun Mar 21, 2010 6:58 pm

Quoting vikkyvik (Reply 7):
That could work, although on the C-17, I'd bet the inner gear is actually on a separate pylon.

Nope...it's cantilevered off the pair in a really bizarre arrangement. You can see the support beam in this photo:
http://www.google.com/imgres?imgurl=...&resnum=5&ct=image&ved=0CBEQ9QEwBA

Tom.
 
vikkyvik
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RE: Could An Eight Wheel Jetliner Work?

Sun Mar 21, 2010 10:37 pm

Quoting ZANL188 (Reply 8):
The -52 lifts off flat. This is due to the wings angle of incidence being fairly high. Nose will go down after liftoff to keep climb rate under control. Looks awkward (it taxies sidewise too) but its worked for 50 years.....

Gotcha, thanks.

Quoting tdscanuck (Reply 16):
Nope...it's cantilevered off the pair in a really bizarre arrangement. You can see the support beam in this photo:
http://www.google.com/imgres?imgurl=...QEwBA

Wow, that is bizarre! Thanks for the link.
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Jetlagged
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RE: Could An Eight Wheel Jetliner Work?

Wed Mar 24, 2010 12:31 pm

No one has yet mentioned the most widespread example of this layout, the Tu-154.


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Starlionblue
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RE: Could An Eight Wheel Jetliner Work?

Wed Mar 24, 2010 1:42 pm

IIRC, the Tu-154 gear sits entirely in pods in the wings, as opposed to most airliners where the struts are in the wings but the wheels end up in the fuselage. Thus there are severe space restrictions.
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Jetlagged
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RE: Could An Eight Wheel Jetliner Work?

Wed Mar 24, 2010 2:20 pm

Quoting Starlionblue (Reply 19):
IIRC, the Tu-154 gear sits entirely in pods in the wings, as opposed to most airliners where the struts are in the wings but the wheels end up in the fuselage. Thus there are severe space restrictions.

True, as does the Tu-134 (but with four wheel bogies). So the podded undercarriage is as much part of Tupolev's design style of the time as anything else. If six wheel bogies were necessary to spread the weight of a new airliner it probably is not beyond the wit of man to find the space for them in the fuselage centre section. Boeing managed it with the 777.
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Starlionblue
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RE: Could An Eight Wheel Jetliner Work?

Wed Mar 24, 2010 2:58 pm

It might have been beyond the wit of Soviet Man.  

Seriously though, those pods probably have an area rule function anyway. Also they allow short struts.
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Jetlagged
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RE: Could An Eight Wheel Jetliner Work?

Wed Mar 24, 2010 3:43 pm

Quoting Starlionblue (Reply 21):
Seriously though, those pods probably have an area rule function anyway. Also they allow short struts.

They certainly could have an area rule function, and the 154 had a very high maximum cruise speed (Mach 0.92 ish). It s a neat solution to stowing the bulky undercarriage in a thin wing. The wing anhedral helped the short struts too.
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RE: Could An Eight Wheel Jetliner Work?

Wed Mar 24, 2010 5:51 pm

Tupovlev used those on tons of aircraft around the same time. Not only on the 134/154, but also on the 95 (Bear), 28 (Fiddler), 16 (Badger), 104/107/110/124 series and the original Tu-22 (Blinder).

It sure seemed in style at the time.
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tdscanuck
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RE: Could An Eight Wheel Jetliner Work?

Thu Mar 25, 2010 3:29 am

Quoting Starlionblue (Reply 21):
Seriously though, those pods probably have an area rule function anyway.

It is indeed an area rule thing; this particular implementation is called a Kuchemann carrot:
http://en.wikipedia.org/wiki/Anti-shock_body

Tom.

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