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b767
Topic Author
Posts: 86
Joined: Mon Feb 18, 2008 9:23 pm

Md80 Main Gear

Sat Nov 29, 2008 7:23 pm

I have been told that MD80,s should be cross controlled the last 50 feets in hard crosswinds.But on the other hand I have seen so many maddogs land with huuge crab angles at touchdown.On airpics.com there is a very interresting picture of a Finnar MD80 landing in a heavy crosswind.There was also a video circulating on the net a few years ago of a AA MD80 which very drifting off in the flare in SFO.Instead of lovering the wing into wind,the pilot kicked rudder into wind and tuched down in a huge crab.I have heard some maddog pilots are afraid of lovering the wing because they are afraid of tip scrapes.But I have also heard that you don,t have to bank so much to prevent drift.So my question is :Is the MD80 landing gear designed for taking repetedly beatings like this.Is it castoring with shimmy dampers like the 737 main gear.Correct me if I am wrong but I belive every passanger jet have to withstand crab landings at max crosswind limit under the certification ,but for most aircrafts it should be avoided in the long run. So if there are any with MD80 knowledge please comment.
 
AAR90
Posts: 3140
Joined: Fri Jan 21, 2000 11:51 am

RE: Md80 Main Gear

Sun Nov 30, 2008 7:53 pm



Quoting B767 (Thread starter):
So my question is :Is the MD80 landing gear designed for taking repetedly beatings like this.

Yes.

Quote:
Is it castoring with shimmy dampers like the 737 main gear.

No.

Quote:
Correct me if I am wrong but I belive every passanger jet have to withstand crab landings at max crosswind limit under the certification

Consider yourself "corrected." Big grin There is a "max demonstrated" crosswind, but there is no certification requirement that specifies either technique or wind limit.... that's for the manufacturer to determine.

Quote:
...but for most aircrafts it should be avoided in the long run.

Yes, because the less stress to the airframe the better... IF the conditions permit.
*NO CARRIER* -- A Naval Aviator's worst nightmare!
 
PGNCS
Posts: 2261
Joined: Sun Apr 15, 2007 5:07 am

RE: Md80 Main Gear

Sun Nov 30, 2008 9:07 pm

The MD-80 is very easy to land wing low; I don't know anybody that intentionally lands in a crab, and wing low is the official company policy for crosswind landings. It is occasionally difficult to visually determine if all the crab is completely nulled out, but certainly I am not afraid of dragging a wingtip at 30 knots of crosswind, which is our maximum.
 
dl757md
Posts: 1483
Joined: Mon May 24, 2004 9:32 am

RE: Md80 Main Gear

Tue Dec 02, 2008 6:37 am



Quoting AAR90 (Reply 1):
Quote:
Is it castoring with shimmy dampers like the 737 main gear.

No.

Actually it is quite like the 737 main gear. Both have upper and lower torque links that have a shimmy damper at the connection between the two. Seperate the torque links and the main gear would castor (rotate around the strut) 360 degrees. The shimmy damper allows very small amounts of castor (nothing even close to say that of the gear on a B-52) while preventing the main wheels from behaving like those on the front of a shopping cart at high speed.

DL757Md
757 Most beautiful airliner in the sky!
 
AAR90
Posts: 3140
Joined: Fri Jan 21, 2000 11:51 am

RE: Md80 Main Gear

Tue Dec 02, 2008 8:11 am



Quoting Dl757md (Reply 3):
Actually it is quite like the 737 main gear

They may be designed similarly, but they operate differently. The MD80 does NOT caster its main mounts (at least not noticable) and the plane taxies straight. The 737 does caster its main mounts and it does NOT taxi straight --at least not unless you taxi in an absolute straight line for about a mile. It truly is rare to get behind a 737 on a taxiway and see it aligned with that taxiway. Hardest thing to adapt to.... taxiing "sideways."
*NO CARRIER* -- A Naval Aviator's worst nightmare!
 
dl757md
Posts: 1483
Joined: Mon May 24, 2004 9:32 am

RE: Md80 Main Gear

Tue Dec 02, 2008 9:30 am



Quoting AAR90 (Reply 4):
The MD80 does NOT caster its main mounts (at least not noticable) and the plane taxies straight. The 737 does caster its main mounts and it does NOT taxi straight

The amount of caster designed into the main gear on these two aircraft is similar and the gear DO operate in the same manner. The airframe differences between the two airplanes account for the observations you have made about their differing taxi behaviors.

The wheel base on the MD-88 is 72' 5" while that of the 737-800 is 51' 2" and the 737-700 comes in at a go-kart like 41'4". A shorter wheelbase lends to a greater tendancy to yaw or crab during slow speed ground ops. The center of thrust of an MD-88 is 8'8" from the center of the fuselage while the 737NG is 15'10". Again the 737 with it's center of thrust further away from the center of the fuselage will tend to yaw more during single engine ground ops. SOP at most airlines call for single engine taxi. Combine that with the above airframe differences and that will easily explain what you have stated about the taxi characteristics of the above planes. The MD-80 main gear DOES caster it's just not as noticeable during taxi as it is on a 737 because the MD-80 airframe is inherently more stable in yaw during ground ops.

DL757Md
757 Most beautiful airliner in the sky!
 
AAR90
Posts: 3140
Joined: Fri Jan 21, 2000 11:51 am

RE: Md80 Main Gear

Tue Dec 02, 2008 4:11 pm



Quoting Dl757md (Reply 5):
The MD-80 main gear DOES caster it's just not as noticeable during taxi as it is on a 737 because the MD-80 airframe is inherently more stable in yaw during ground ops.

This appears to be something Boeing is completely unaware of. Perhaps you should notify Boeing of this so they can change their operating manuals.

Here is how one highly regarded 737 website --b737.org.uk -- lightheartedly describes the unique 737 taxi characteristics:

One of the peculiarities of the 737 is that it invariably appears to crab when taxying. Theories for this include: A slightly castoring main gear to increase the crosswind capability; Play in the scissor link pins; Weather-cocking into any crosswind impinging on the fin; Torque reaction from the anti-collision light !!! Engineers will tell you that is due to the main gear having a couple of degrees of play due to the shimmy dampers.
*NO CARRIER* -- A Naval Aviator's worst nightmare!
 
b767
Topic Author
Posts: 86
Joined: Mon Feb 18, 2008 9:23 pm

RE: Md80 Main Gear

Wed Dec 10, 2008 7:33 pm

Well to take the disqussion a little further.The 737,md80 and a320 can be crab landed,but wing low is recomandated to save wear and tear on the airframe.So far so good.But there are several crosswind videos on the net where they drive it all the way to the runway in crab,and not touching rudder until after touchdown.And this in very stiff winds on dry runways.There are also several photos of the events.I am living next to a very windy airport in Norway,and when the Braathens and SAS pilots were landing,they always used the wing low method in crosswinds.Could it be that many just lands in crab because it is much more easy than a perfectly coordinated sideslip,and that it is not their problem if the landing gear has to be overhauled much sooner?Talked to a old 737 driver who said pilots handling skills were better before,but I am not in the position to comment on that as there are plenty of proffesional on this forum.
 
User avatar
Poadrim
Posts: 140
Joined: Sat Oct 04, 2008 11:22 pm

RE: Md80 Main Gear

Thu Jan 01, 2009 5:27 pm

I came to think of a thing this with x-wind landings.

The main gear of a 777 could turn during taxi right? So why not use the taxi-turn knob to align the main gear with the runway and then "force" the plane straight in the rwy after the align gear is on the ground? If this is any logic at all?

//Poadrim
Good judgment comes from experience.
Good experience comes from someone else's bad judgment.
 
jetstar
Posts: 1414
Joined: Mon May 19, 2003 2:16 am

RE: Md80 Main Gear

Fri Jan 02, 2009 1:31 am



Quoting Poadrim (Reply 8):
The main gear of a 777 could turn during taxi right? So why not use the taxi-turn knob to align the main gear with the runway and then "force" the plane straight in the rwy after the align gear is on the ground? If this is any logic at all?

I believe only the rear 2 wheels on the 6 wheel main landing gear turn to prevent the tires from scuffing in tight turns, so this would not work in a crosswind landing

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