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jumbojim747
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Gear Retration Why So Fast

Wed Aug 23, 2006 6:37 am

Why do pilots insist on packing up the gears so fast after positive climb.?
Surely it would be better if they kept them in the air for a minute or so so
1- the wheels and tyres cool down a little.
2- All the brake dust from the previous landing is blown away.
I'm not sure on this but wouldn't it be unhealthy to have a wheel well bay or cargo hold that is full of dust from brakes.
Sure it would cost a few dollars more to have the wheels hanging in the air for that little longer but wouldn't it be better off in the long run.?
Cheers
On a wing and a prayer
 
flight152
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RE: Gear Retration Why So Fast

Wed Aug 23, 2006 7:06 am

Quoting JumboJim747 (Thread starter):
the wheels and tyres cool down a little.

They have the whole flight to cool down.

Quoting JumboJim747 (Thread starter):
All the brake dust from the previous landing is blown away.

Most of it already is blown away before retraction anyway, not really a case for keeping it in the down position longer.

The performance gain of loss of drag greatly overcomes these items.
 
boeingfixer
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RE: Gear Retration Why So Fast

Wed Aug 23, 2006 7:09 am

Short answer is drag! The gear being down is a significant performance hit and hurts your second segment climb performance. Another benefit of retracting your gear early is that the wheels are stopped rotating as they are retracted. This eliminates any gyroscopic effects the spinning wheels tend to have on the aircraft.

There is only one reason to leave the gear down longer and that's due to brake cooling. If the brakes don't need cooling, get that gear up.

Brake dust isn't a problem as most airliners are taking off at 130+ knots and all the loose brake dust, which isn't much, is gone by then. BTW, the wheel wells are totally separate from the cargo pits. The cargo pits are in the pressurized portion of the fuselage and the gear is in its own wells. You've got a big problem if you're getting brake dust into the cargo pits  Wink

Cheers,

John
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aerobalance
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RE: Gear Retration Why So Fast

Wed Aug 23, 2006 7:10 am

Quoting JumboJim747 (Thread starter):
1- the wheels and tyres cool down a little.

From what?

Quoting JumboJim747 (Thread starter):
2- All the brake dust from the previous landing is blown away.

I believe that this would happen from the t/o run to liftoff - plenty of time to have the 'dust' blown off...
"Sing a song, play guitar, make it snappy..."
 
NicolasRubio
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RE: Gear Retration Why So Fast

Wed Aug 23, 2006 8:00 am

Airbuses in general keep the gear down some more seconds than Boeings... I don't know why... At least it was what I saw in some IB A346's taking off from EZE...

Well, maybe what happened is that the crew was conformed by Javier Guerrero on the left seat and Ander Aguirre on the right one, and they where so busy shooting 30 seconds exposures that they forgot about the landing gear Big grin
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bio15
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RE: Gear Retration Why So Fast

Wed Aug 23, 2006 8:42 am

Pilots don't really insist in retracting the gear ASAP. It is a recommended practice by aircraft manufacturers to have increased second climb segment performance, as was mentioned.

Quoting JumboJim747 (Thread starter):
1- the wheels and tyres cool down a little.

The brake discs are the ones that may need to be cooled down. Sometimes when airplanes are on short legs with quick stopovers, a hard braking during the landing heats the brake discs enough to remain hot at the next leg takeoff.

Sometimes the brakes are cooled down with fans while on the ramp.


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fspilot747
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RE: Gear Retration Why So Fast

Wed Aug 23, 2006 9:42 am

When you lose an engine on take-off and there's nowhere to go (like more runway), you're going to want that gear up. I don't know if jets are powerful enough for this not to apply, but this is how I always understood it. A major source of drag.
 
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HAWK21M
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RE: Gear Retration Why So Fast

Wed Aug 23, 2006 1:24 pm

Quoting JumboJim747 (Thread starter):
the wheels and tyres cool down a little.

If they are overheated.The crew would know.[WW Fire Lt] [EICAS Indications] [Brake Temp induication].If not why add to the Drag.The faster the Aircraft is cleaned up the better in case of any IFSD.

Quoting JumboJim747 (Thread starter):
All the brake dust from the previous landing is blown away.



Quoting JumboJim747 (Thread starter):
I'm not sure on this but wouldn't it be unhealthy to have a wheel well bay or cargo hold that is full of dust from brakes

Most would have already blown away.The rest would blow out on Extention during landing.The Gear is Autoretract braked,so no question of damage by that dust to the MWW Components.

regds
MEL

[Edited 2006-08-23 06:25:23]
I may not win often, but I damn well never lose!!! ;)
 
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jumbojim747
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RE: Gear Retration Why So Fast

Wed Aug 23, 2006 6:08 pm

Hey Guys you sure know your stuff.
I thank everyone here for making things clear for me and for the fast responses .
Cheers all
On a wing and a prayer
 
DH106
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RE: Gear Retration Why So Fast

Wed Aug 23, 2006 6:33 pm

Quoting Aerobalance (Reply 3):
Quoting JumboJim747 (Thread starter):
1- the wheels and tyres cool down a little.

From what?

There's been at least one instance (a 727 if I recall) where an overheated brake exploded inside the well sometime after retraction. The explosion was severe enough to rupture fuel lines from the wing causing further a castrophic explosion and loss of the aircraft.
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HAWK21M
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RE: Gear Retration Why So Fast

Wed Aug 23, 2006 8:43 pm

Quoting DH106 (Reply 9):
The explosion was severe enough to rupture fuel lines from the wing causing further a castrophic explosion and loss of the aircraft.

The older B737s had Tire Burst Screens,The late ones have Frangible Fittings.Purpose was to protect the Components in the MWW.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
boeingfixer
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RE: Gear Retration Why So Fast

Thu Aug 24, 2006 12:24 am

Quoting DH106 (Reply 9):
There's been at least one instance (a 727 if I recall) where an overheated brake exploded inside the well sometime after retraction. The explosion was severe enough to rupture fuel lines from the wing causing further a castrophic explosion and loss of the aircraft.

That was a Mexicana Airlines 727-200 that had a faulty tire explode in the wheel well taking out the hydraulics/controls and causing the crash.

There was also a Nationair DC-8 that crashed after taking off from Jeddah, Saudi Arabia. The investigation revealed that several tires were under-inflated and also required replacement. Two tires blew on takeoff and were on fire when the gear was retracted. The rest is history.

Both of these accidents were not caused by overheated brakes.

Cheers,

John
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bohica
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RE: Gear Retration Why So Fast

Thu Aug 24, 2006 3:18 am

Quoting Bio15 (Reply 5):
Sometimes the brakes are cooled down with fans while on the ramp.

Some (if not all) Airbus A/C have the option of cooling fans installed in the main gear wheels to cool the brakes and blow out the brake dust. Problem solved.  Smile
 
CRJonBeez
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RE: Gear Retration Why So Fast

Thu Aug 24, 2006 4:37 am

speaking of brake fans, what is the purpose of the hot vents on the ERJ? i would imagine it keeps components warm during cold temperature operations, but they run on 90 degree days as well. just bleeding excess heat?
 
n685fe
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RE: Gear Retration Why So Fast

Thu Aug 24, 2006 5:55 am

Many a/c have ram air cooling with ducts directed toward the wheel assembly for cooling. I will try to look for some pics.
psp. lead by example
 
n685fe
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RE: Gear Retration Why So Fast

Thu Aug 24, 2006 6:15 am

Here are some pics, on the first one look towards the far right side of the pic. Just aft of were the body to wing fairing begins is an inlet.

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Enlarge these photos and you will also see it.

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HAWK21M
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RE: Gear Retration Why So Fast

Thu Aug 24, 2006 8:01 pm

Quoting N685FE (Reply 14):
Many a/c have ram air cooling with ducts directed toward the wheel assembly for cooling. I will try to look for some pics.

What rate of cooling would be accomplished by this.
On the B737 On the Ground the Ram Exhaust heated air tends to strike the Inboard wheels depending on which pack is running,indirectly heating them.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
ImperialEagle
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RE: Gear Retration Why So Fast

Fri Aug 25, 2006 5:24 am

Any graybeards out there remember how fast a Martin could get 'em up!

They were fast!

 old 
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n685fe
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RE: Gear Retration Why So Fast

Fri Aug 25, 2006 10:01 am

Quoting HAWK21M (Reply 16):
What rate of cooling would be accomplished by this.

What are you asking, do you truly not know? It's just like your car, pass ambient air over the brakes, transfers heat, which cools them off. The pack exhaust that you mentioned is also cooling the brakes. Brake temp can exceed several hundred degrees, so even 100+ pack exhaust is cooling the brakes.
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HAWK21M
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RE: Gear Retration Why So Fast

Fri Aug 25, 2006 10:42 am

Quoting N685FE (Reply 18):
The pack exhaust that you mentioned is also cooling the brakes

On the Contarary.Its heating the Wheels [not brakes] due to impact especially #2 & 3.
Im sure you are aware that Ram Air Exhaust Air is Hot & not cool.Unless you state a comparative cooling of "Hot" brakes.ie if the Brakes were at a higher Temp that the Ram air exhaust in the first place. Smile
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
n685fe
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RE: Gear Retration Why So Fast

Tue Sep 05, 2006 2:57 am

Let's start over.

Quoting HAWK21M (Reply 16):
On the B737 On the Ground the Ram Exhaust heated air tends to strike the Inboard wheels depending on which pack is running,indirectly heating them.

Are you talking about while parked at the gate, pack exhaust is heating the wheels?

Quoting HAWK21M (Reply 19):
heating the Wheels [not brakes] due to impact especially #2 & 3.

What impact are you referring to, retraction?

Here are some descriptions from M/M's.

"DC10 Main Brake Cooling System
A. A main brake cooling system is provided in each main gear wheel well to supply a ram air flow to the brakes when the gear is retracted. The cooling system consists of a flush type inlet located in the fuselage skin forward of the wheel well, and a metal duct which directs the flow of ram air to the forward and aft pair of brakes."


"MD80 Main Gear Ram Air Brake Cooling System
A. The ram air brake cooling system is provided to prevent a cumulative hear buildup in the brakes from a series of landings in a short time span, that could result in premature brake replacements.
B. The system consists of a ram air inlet located on the lower fuselage forward of main gear well left and right side, ducting, and an air outlet assembly to direct ram air to brakes for cooling when landing gear is in retracted position."
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troubleshooter
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RE: Gear Retration Why So Fast

Wed Sep 06, 2006 3:47 pm

Quoting CRJonBeez (Reply 13):
speaking of brake fans, what is the purpose of the hot vents on the ERJ? i would imagine it keeps components warm during cold temperature operations, but they run on 90 degree days as well. just bleeding excess heat?

What "hot vents" are you asking about? Do you have any pictures to add more details to your question?
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CosmicCruiser
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RE: Gear Retration Why So Fast

Wed Sep 06, 2006 9:28 pm

Quoting BoeingFixer (Reply 11):
That was a Mexicana Airlines 727-200 that had a faulty tire explode in the wheel well taking out the hydraulics/controls and causing the crash

I haven't researched this and haven't thought about it for yrs. but I remember hearing that the tires had been serviced with O2 by mistake. Has anyone researched this?
 
David L
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RE: Gear Retration Why So Fast

Wed Sep 06, 2006 9:55 pm

Quoting CosmicCruiser (Reply 22):
Quoting BoeingFixer (Reply 11):
That was a Mexicana Airlines 727-200 that had a faulty tire explode in the wheel well taking out the hydraulics/controls and causing the crash

I haven't researched this and haven't thought about it for yrs. but I remember hearing that the tires had been serviced with O2 by mistake. Has anyone researched this?

Not research exactly but an amateur shortcut finds this:

http://www.aviation-safety.net/database/record.php?id=19860331-1

Seems to tie in with your recollection:

"It was found that the tire had been serviced with air rather than nitrogen. The air, under high temperature and pressure, resulted in a chemical reaction with the tire itself. This led to a chemical explosion of the tire."
 
OPNLguy
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RE: Gear Retration Why So Fast

Wed Sep 06, 2006 10:43 pm

Quoting DH106 (Reply 9):
There's been at least one instance (a 727 if I recall) where an overheated brake exploded inside the well sometime after retraction. The explosion was severe enough to rupture fuel lines from the wing causing further a castrophic explosion and loss of the aircraft.

In addition to having serviced the Mexicana 727 tires with something other than the approprioate nitrogen (IIRC they used compressed air, not pure oxygen), they had a dragging brake (partially applied) which is what caused the friction/heat and was another link in the accident chain...

The left main gear brake was overheated during the take-off run
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HAWK21M
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RE: Gear Retration Why So Fast

Wed Sep 06, 2006 10:46 pm

Quoting N685FE (Reply 20):
Are you talking about while parked at the gate, pack exhaust is heating the wheels

Depending on the Pack operated & direction of wind.The Inboard wheel faces the Ram Air Exhaust generated by the Turbofan on Ground.

Quoting N685FE (Reply 20):
What impact are you referring to, retraction?

Im referring to the Impact from the Pack Turbofan exhaust flow through the Exhaust louvers.

regds
MEL
I may not win often, but I damn well never lose!!! ;)

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