nikes
Posts: 38
Joined: Mon Aug 27, 2001 9:26 am

777 CBT

Fri May 31, 2002 3:45 am

When I was doing my 777 CBT homework it mentioned that when the gear is extended using the alternate gear extension, the gear does not incline upwards.

My question is why is it tilted in the first place and why doesn't it incline upward during the emergency alternate extension?

Oh one other thing-
Also I noticed on the 777 test flights that there was a string and a ball on the top of the rudder? Again can anybody help?

Thanks
Nikes
 
LMP737
Posts: 4800
Joined: Wed May 08, 2002 4:06 pm

RE: 777 CBT

Fri May 31, 2002 5:09 am

That ball on a string you speak of senses static pressure for flight test data.
Never take financial advice from co-workers.
 
Beefmoney
Posts: 1065
Joined: Tue Oct 10, 2000 2:16 am

RE: 777 CBT

Fri May 31, 2002 5:43 am

Most people say that it is tilted, so that the gear will fit into the gear bays easier, also I believe that they are free tilted like that and not rigid, is that when the aircraft flares, the rear part of the gear assemblies will touch down first, and the forward part will come down slower depending on how fast the sirplane comes down, but if the assembly was rigid, the back end would touch down and the gear would snap off because the forward part would not be able to come down on its own. Take two toothpicks, and glue them together to creat a "T" shape. now press it down on the table with one end of the horizontal part of the "T" on the table (like how it would look if a 777 was landing with non-tilting landing gear.) Part of the "T" would snap off.Now, that was very confusing, im not even sure what I wrote now, but im pretty sure thats why.
 
Guest

RE: 777 CBT

Fri May 31, 2002 7:06 am

I'm no expert on the 777 but I'm perplexed at what the CBT is telling you. Is there a human there you can ask for details? I'd be interested in the answer. Right now, I'm having problems believing that there is any difference between the two methods. The only mechanical difference that I know of is that, with the normal method, the gear doors are closed. With the alternate extension, where a electrically driven pump is used, assuming normal hydraulic failures, the hydraulically powered gear doors remain open.

To answer your second question, the device on the tail is commonly referred to as the trailing cone. It senses static pressure far away from the aircraft pressure field thus free from errors. The data are used to calibrate the aircraft altimeter and airspeed (determine Position Error correction).

Regards,
Nut
 
FredT
Posts: 2166
Joined: Thu Feb 07, 2002 9:51 pm

RE: 777 CBT

Fri May 31, 2002 7:20 am

Now, this is a "d'oh-slap-forehead" kind of question.  Smile

The bogey tilts upward in order to add additional suspension travel. As the rear wheels touch down, the bogey straightens out but not without resistance. Thus, the descent has been gently slowed down a bit even before the front wheels touch down and the main gear strut begins to compress. Simply makes it easier to grease'em.

No idea why it won't tilt up during alternate extension, but an educated guess would be that it is untilted in stowed position and tilted on extension using hydraulic power. Don't want to waste any precious hydraulic volume during an alternate extension..

Cheers,
Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
FredT
Posts: 2166
Joined: Thu Feb 07, 2002 9:51 pm

RE: 777 CBT

Fri May 31, 2002 7:21 am

Oi, Nikes, drop me a line at ft@sparta.lu.se?

Cheers,
Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
cdfmxtech
Posts: 1319
Joined: Wed Jul 05, 2000 11:37 am

RE: 777 CBT

Fri May 31, 2002 12:01 pm

B777s use Center Hydraulics for landing gear extension & retraction. The tilt also utilizes center hydraulics.
If center hydraulics are loss, the main gear can't tilt. The CBT was probably referring to a no ctr hydraulics condition. I believe if u use Alternate extension for extending the gear with ctr hydraulics available, the gear will tilt. It is only when there is no ctr hydraulics.
---------------
As for the tilting and wheelwell relation - the gear is NOT tilted going into the wheelwell. This tilt is not to be confused with those on the B757/767. Those gear tilt upon liftoff and stay in that tilt during retraction. The B777 "straightens" out prior to entering the wheelwell
 
Tuffty
Posts: 91
Joined: Tue Mar 13, 2001 8:03 pm

Beefmoney

Sun Jun 02, 2002 5:31 am

if your second point were correct why is it that the 767 has its gear tilted so the forward wheels are hitting first. i dont mean to sound rude or offensive toward you im just making a point, that it primarily is to fit the gear into the bays. i guess that it proberbly does reduce the stresses that the gear is under when it hits if the bogies tilt aft.

Regds tuffty Smile
 
bio15
Posts: 1048
Joined: Fri Mar 23, 2001 8:10 am

RE: 777 CBT

Sun Jun 02, 2002 8:44 am

I heard that as well, the 767 main gear is tilted with the front wheels low for matters of appropeiate fitting in the well.

-bio
 
cdfmxtech
Posts: 1319
Joined: Wed Jul 05, 2000 11:37 am

RE: 777 CBT

Sun Jun 02, 2002 5:59 pm

With weight of of the wheels, the B757 & B767 gear tilt actuators will position the gears tilted (from wheels up and forward respectively).

With the weight off of the wheels on the B777, the gear tilt actuators will position the gears tilted to something like 12-13 degrees. When gear up is selected, the wheels untilt to 5 degrees (barely even noticeable) forward wheels down.

I never said that the tilt on the B757 & B767s weren't for wheelwell stowage. I just said that the tilts on the B777 and those aircraft is different.

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