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737NG Tail

Sun Apr 30, 2000 6:33 am

Can anyone explain why the new 737's (-600,-700,-800) have taller tails? And while on the subject can you explain why the 747SP has a taller tail too?
Thanks
 
BigGiraffe
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RE: 737NG Tail

Sun Apr 30, 2000 9:50 am

The 747SP had a taller fin and longer horizontal stabilizers to maintain stability after the fuselage was shortened. The shorter "moment arm" caused by moving the empennage closer to the center of gravity (vertical and horizontal stabilizers came forward along with the back end of the fuselage) had to be compensated by increasing the size of the tail surfaces.

I don't know about the new 737's -- do they have increased engine thrust which would require a larger tail in the event of engine out?
 
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RE: 737NG Tail

Sun Apr 30, 2000 12:19 pm

The 737-300 -400 -500 used the CFM 56-3C engine, Next Generation 737's use the CFM 56-7 series, which can have an output as high as 10% greater. because of the greater thrust, fin and horizontal stab was enlarged to compensate for the increase in torque from the engines. Also NG's fly @ 41000 feet , 4000 higher than older 737's, where directional stability is less because of thinner air. check http://www.boeing.com/commercial/737family/background.html
 
OPNLguy
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RE: 737NG Tail

Wed May 03, 2000 12:08 am

Mr. Giraffe and HP hit it....

By the same token, ever notice how *snall* the tail on the DC-9/MD-80 is?
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Guest

RE: 737NG Tail

Wed May 03, 2000 1:27 am

Thanks, guys, for responding. Speaking of shorter fuselage, there are several aircraft with different versions but with the same size of fin, or at least it seems like that. The A320/321/319 series comes to mind. Assuming these three planes have a same size fin, does this have anything to do with the fact that these are FBW planes and that the rudder is controled by the autopilot, unlike the 737's?
 
sabenapilot
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RE: 737NG Tail

Wed May 03, 2000 2:07 am

I am not 100% sure the A321 doesn't have a slightly differently sized tail, but the A319/A320 indeed has the same tail. This doesn't matter too much, because the difference is not that dramatic.
After all, not every B737NG has a different vertical fin although they all have a different dimention.
For the A318 (a shorter version of the A319) the tail is made somewhat bigger by increesing the hight.
 
pilotbryan
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RE: 737NG Tail

Sat May 06, 2000 8:07 am

Has anyone noticed that same 737NG's have one hole in the tail for APU exhaust? and others have two. If I remember correctly the -600 has one hole and the -700 two holes. I might have them backwards but what gives?
 
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Spacepope
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RE: 737NG Tail

Sat May 06, 2000 5:04 pm

The A318 incorporatres a dorsal fin into the tail design, much as the 737 300/400/500 did over the 737 100/200, look for this before the leading edhe of the vertical tail.
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HAWK21M
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RE: 737NG Tail

Fri Apr 14, 2006 2:51 am

Quoting Pilotbryan (Reply 6):
Has anyone noticed that same 737NG's have one hole in the tail for APU exhaust? and others have two. If I remember correctly the -600 has one hole and the -700 two holes. I might have them backwards but what gives?

Isn't one the Exhaust outlet & the other the Cooling Air Inlet.
regds
MEL
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avioniker
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RE: 737NG Tail

Fri Apr 14, 2006 5:57 am

Quoting HAWK21M (Reply 8):
Isn't one the Exhaust outlet & the other the Cooling Air Inlet.

And once again the Hawk wins the prize.
I haven't heard of any NG's with a single hole tail cone...

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Starlionblue
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RE: 737NG Tail

Fri Apr 14, 2006 6:12 am

Quoting Tripl7 (Reply 4):
Thanks, guys, for responding. Speaking of shorter fuselage, there are several aircraft with different versions but with the same size of fin, or at least it seems like that. The A320/321/319 series comes to mind. Assuming these three planes have a same size fin, does this have anything to do with the fact that these are FBW planes and that the rudder is controled by the autopilot, unlike the 737's?

As has been pointed out, while theoretically you could change the size for each length of plane, doing so is just too much money (certification, design, manufacturing). You want to have as many common components as possible.

And btw the 737 rudder is controlled by the autopilot just as much as the 32x one. FBW has little to do with this problem. You could have a somewhat smaller horizontal stab with computerized control, and thus decrease drag, but that's another matter entirely.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
troubleshooter
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RE: 737NG Tail

Fri Apr 14, 2006 1:58 pm

Quoting Avioniker (Reply 9):
I haven't heard of any NG's with a single hole tail cone...

Correct. All NG´s have this new designed tail section. The upper hole is the eductor inlet which sucks in cooling air. The lower one is the APU exhaust.
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HAWK21M
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RE: 737NG Tail

Fri Apr 14, 2006 5:56 pm


Classics.

Next Generation.

12 decibel quiter than the classics.

regds
MEL
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Pihero
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RE: 737NG Tail

Fri Apr 14, 2006 6:35 pm

Quoting HP-873 (Reply 2):
The 737-300 -400 -500 used the CFM 56-3C engine, Next Generation 737's use the CFM 56-7 series, which can have an output as high as 10% greater. because of the greater thrust, fin and horizontal stab was enlarged to compensate for the increase in torque from the engines. Also NG's fly @ 41000 feet , 4000 higher than older 737's, where directional stability is less because of thinner air.

Sorry,guys, you are way off in a tangent, here.
The reason for a biggerr tail is for one engine-out controllability and nothing else. With an engine failure, the increased thrust dissymetry has to be countered by a bigger directional surface, given a similar fuselage length.
If you shorten the fuselage, i.e. the moment arm, you'll need a bigger tail (that's for th 747SP or the A 318). Or, if you keep the plan geometry, but increase the engines thrust, the result is the same.

As for thinner air, rememberflying at 240 kts IAS at 10,000 ft is broadly the same as flying at 240 kts IAS at 41,000 ft, albeit the Mach will be .80 at that altitude.

Fan jet engines do not generate torque.
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wing
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RE: 737NG Tail

Fri Apr 14, 2006 7:39 pm

Quoting Starlionblue (Reply 10):
And btw the 737 rudder is controlled by the autopilot just as much as the 32x one.

Its been a while that I havent reading the 737 books but as I remember 737 AP doesn't control the rudder.Thats why there are procedure differences on a single engine departure on A320 and the the B737.
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Grbld
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RE: 737NG Tail

Fri Apr 14, 2006 9:21 pm

Quoting Starlionblue (Reply 10):
And btw the 737 rudder is controlled by the autopilot just as much as the 32x one.

Not so on our 737NGs, and definitely not so on older models. I know there are a few new ones out there with the Collins APFD and a CAT IIIb autoland capability, but most don't have it (some of ours have the Collins APFD, but no CAT IIIb autoland).
 
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Starlionblue
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RE: 737NG Tail

Fri Apr 14, 2006 10:58 pm

Ok good info. But doesn't the yaw damper control the rudder, and isn't the yaw damper technically a form of autopilot? Ok semantics...  Wink

Quoting Pihero (Reply 13):
Fan jet engines do not generate torque.

Not torque in the way you mean, but torque just means "rotational force". If you have an engine out situation, you will most definitely have a torque force on the aircraft in the yaw axis.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
Pihero
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RE: 737NG Tail

Sat Apr 15, 2006 3:12 am

Quoting Starlionblue (Reply 16):
Not torque in the way you mean, but torque just means "rotational force". If you have an engine out situation, you will most definitely have a torque force on the aircraft in the yaw axis

Semantics again, Starlion ?
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Pihero
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RE: 737NG Tail

Sat Apr 15, 2006 3:14 am

Quoting Starlionblue (Reply 16):
isn't the yaw damper technically a form of autopilot?

More a flight augmentation system i.m.o.
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AirWillie6475
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RE: 737NG Tail

Sat Apr 15, 2006 10:02 am

Actually another question would be why they kept the same fuselage for the 700 as the 300 series? Like pressurization. The 700 goes up to 41k but the 300 only goes to 37. If they both have the same fuselage, how did they deal with that? Also the 700 is much louder from the inside than the 300, I think that's contributed from using the 300 fuselage.
 
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Starlionblue
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RE: 737NG Tail

Sat Apr 15, 2006 9:29 pm

Quoting Pihero (Reply 17):
Quoting Starlionblue (Reply 16):
Not torque in the way you mean, but torque just means "rotational force". If you have an engine out situation, you will most definitely have a torque force on the aircraft in the yaw axis

Semantics again, Starlion ?

Always.  Wink

Quoting AirWillie6475 (Reply 19):
Actually another question would be why they kept the same fuselage for the 700 as the 300 series? Like pressurization. The 700 goes up to 41k but the 300 only goes to 37. If they both have the same fuselage, how did they deal with that? Also the 700 is much louder from the inside than the 300, I think that's contributed from using the 300 fuselage.

Cost seems obvious. Changing the manufacturing rigs costs a lot of $$$. Also, the service ceiling is not only dependent on pressurization. I would hazard that the 300 fuse could handle 41k pressure wise (after all, the difference from 37k is minimal) but the smaller wing and engines don't let it get up there.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
Pihero
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RE: 737NG Tail

Sat Apr 15, 2006 10:38 pm

Quoting Starlionblue (Reply 20):
I would hazard that the 300 fuse could handle 41k pressure wise (after all, the difference from 37k is minimal) but the smaller wing and engines don't let it get up there.

And some airplanes cannot achieve a descent from their max ceiling to 10,000 ft in the certification allocated time, therefore limiting them to a lower certified flight level.
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troubleshooter
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RE: 737NG Tail

Sun Apr 16, 2006 12:56 am

Quoting AirWillie6475 (Reply 19):
The 700 goes up to 41k but the 300 only goes to 37. If they both have the same fuselage, how did they deal with that?

The reason is the bleed system. I would think that the -3 engines on the classics can not supply the bleed demand to keep the cabin pressurized at altitudes above 37k.
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troubleshooter
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RE: 737NG Tail

Sun Apr 16, 2006 1:09 am

Quoting Starlionblue (Reply 10):
And btw the 737 rudder is controlled by the autopilot just as much as the 32x one.

No A/P actuators installed in the 737 rudder control system. Not on the Classics ond not on the NG´s. Only the ailerons and elevators can be controlled by the autopilot.

Quoting Starlionblue (Reply 16):
But doesn't the yaw damper control the rudder, and isn't the yaw damper technically a form of autopilot?

The yaw damper system can operate without the autopilot engaged. Yaw damping is controlled by the SMYD´s (Stall Management Yaw Damper Computers) on the NG´s and is completely independant of the autoflight system.
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Buyantukhaa
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RE: 737NG Tail

Sun Apr 16, 2006 2:27 am

Quoting Spacepope (Reply 7):
Reply 7, posted Sat May 6 2000



Quoting HAWK21M (Reply 8):
Reply 8, posted Thu Apr 13 2006

Hawk, I think you beat the record for putting the oldest thread back to life... Do you often read threads from 2000?  Smile
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777236ER
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RE: 737NG Tail

Sun Apr 16, 2006 2:49 am

Quoting Troubleshooter (Reply 23):
No A/P actuators installed in the 737 rudder control system. Not on the Classics ond not on the NG�s. Only the ailerons and elevators can be controlled by the autopilot.

If a Cat IIIb EDFCS is installed, it has a rudder servo to perform ROLLOUT and engine-out landings.
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Spacepope
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RE: 737NG Tail

Sun Apr 16, 2006 5:10 am

He had to pull a post with a typo in it from 6 years ago. Amazing!
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David L
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RE: 737NG Tail

Sun Apr 16, 2006 5:32 am

Quoting Spacepope (Reply 26):
He had to pull a post with a typo in it from 6 years ago.

Thanks for pointing that out. I was trying to pluck up the courage to ask what an "edhe" is and how you become a leading one.
 
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Spacepope
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RE: 737NG Tail

Sun Apr 16, 2006 6:17 am

Quoting David L (Reply 27):
Thanks for pointing that out. I was trying to pluck up the courage to ask what an "edhe" is and how you become a leading one.

I think I meant "edge". Keys seem to be right next to each other.


As for becoming a leading "edhe", I'm pretty sure if I knew that, I'd be much richer!
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David L
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RE: 737NG Tail

Sun Apr 16, 2006 7:19 am

Quoting Spacepope (Reply 28):
As for becoming a leading "edhe", I'm pretty sure if I knew that, I'd be much richer!

Or in jail.  Smile
 
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Starlionblue
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RE: 737NG Tail

Sun Apr 16, 2006 11:18 pm

Quoting Troubleshooter (Reply 23):

Quoting Starlionblue (Reply 16):
But doesn't the yaw damper control the rudder, and isn't the yaw damper technically a form of autopilot?

The yaw damper system can operate without the autopilot engaged. Yaw damping is controlled by the SMYD�s (Stall Management Yaw Damper Computers) on the NG�s and is completely independant of the autoflight system.

Thx to all for yaw damper info.

I know we're in semantics here, but you can still say that both the 737NG and 32x control their rudders with silicon instead of carbon  Wink
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