ngr
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Question About Jet Throttles

Tue Apr 29, 2008 12:15 am

Hello all,

I have two questions about jet throttles, and wasn't able to find what I was looking for via search.

When a pilot pulls up the reverse thrust levers on landing, at what point to the reversers actually begin to engage. Do they deploy as soon as there is movement, or do they have to rotate through "30 degrees" etc. Along the same lines, is there a detent for idle reverse, or is it simply done "by feel".

My second question is, how stiff are airliner throttles? I know the tension can be adjusted, but on average how heavy do they feel?

Thanks!
 
DashTrash
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RE: Question About Jet Throttles

Tue Apr 29, 2008 12:41 am

They should be easy to move with the friction control adjusted as such, and then very difficult to move with it set to its maximum.

The reverser handles on the airplanes I've flown that had them needed to be lifted to a detent to open the buckets. After they're open, the piggyback levers function as the throttle so you can modulate the reverse thrust.
 
fr8mech
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RE: Question About Jet Throttles

Tue Apr 29, 2008 12:44 am



Quoting Ngr (Thread starter):
at what point to the reversers actually begin to engage.

It really depends on the aircraft. Some will begin the deployment sequence as soon as the lever is moved, others after some movement. Most reverse thrust levers (most familiar with Boeings, but I'll guess the Airbii are the same) will reach the idle reverse detent and stop until the reverser is fully deployed. After that, power application is possible.

Quoting Ngr (Thread starter):
how stiff are airliner throttles

Not stiff at all. I don't remember the actual force required, but as I recall, on a B747 classic (for example) each individual power lever was allowed to go to 5 lbs (maybe 7...) with all levers (moved as a unit) not allowed to go over 15 (I think). Like I said, I don't remember the exact numbers, but they are definately on the low end.

And I haven't seen a friction lock on anything since I worked on B727-100.
When seconds count...the police are minutes away.
 
ngr
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RE: Question About Jet Throttles

Tue Apr 29, 2008 1:27 am

Thanks for the responses so far!

How would you say stiffness of airliner throttles compares with most commercially-available flight simulator throttles.

Additionally, on Boeing jets, what happens when the pilot manually adjusts the throttles while the autopilot is controlling thrust? Does it automatically disengage, or will the autopilot "fight" to keep control until the switch is flipped?
 
tdscanuck
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RE: Question About Jet Throttles

Tue Apr 29, 2008 2:11 am



Quoting Ngr (Thread starter):
When a pilot pulls up the reverse thrust levers on landing, at what point to the reversers actually begin to engage. Do they deploy as soon as there is movement, or do they have to rotate through "30 degrees" etc. Along the same lines, is there a detent for idle reverse, or is it simply done "by feel".

The details are pretty aircraft dependant. In general, the reverse levers have to move by some amount to start the deploy cycle and an interlock will prevent the engines from spooling up until the deploy cycle is nearly complete (not necessarily totally complete). At least on Boeings, the interlock is also the reverse idle position.

Quoting Ngr (Thread starter):

My second question is, how stiff are airliner throttles? I know the tension can be adjusted, but on average how heavy do they feel?

Heavier than they look! At least for a 777, in my experience.

Quoting Ngr (Reply 3):
Additionally, on Boeing jets, what happens when the pilot manually adjusts the throttles while the autopilot is controlling thrust? Does it automatically disengage, or will the autopilot "fight" to keep control until the switch is flipped?

There's a slipper clutch in there. I believe the autopilot will fight a small motion but will disengage as soon as the clutch lets go.

Tom.
 
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HAWK21M
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RE: Question About Jet Throttles

Tue Apr 29, 2008 8:17 am

The T/R levers move partially & are mechanically locked from going further aft until the T/Rs have moved to their deploy position,before reverse thrust can be provided.This is achieved by a feedback cable/pushrod.

The Thrust levers are quite smooth,Friction is provided by drum & brake assys to ensure that they don't move with vibration.

The Thrust control drum has a few other units attached too,like the Spoiler Actuator,Resolvers etc.

regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
planenutok
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RE: Question About Jet Throttles

Tue Apr 29, 2008 12:02 pm

Dont forget that alot of newer airliners have throttle by wire, On the ERJs and CRJs that i work on there is no physical cable connecting the throttle levers to the engines. The throttles simply send electrical signals to the fadecs and they govern and control the engines. In most cases the engines change power without actually moving the levers themselves.

The TRs work on the same principle, an electronic box controls the TR actuators and don't allow the power to come up until certain parameters are met, ie. both reverser's fully deployed.
 
wilco737
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RE: Question About Jet Throttles

Tue Apr 29, 2008 2:45 pm



Quoting Ngr (Reply 3):
Additionally, on Boeing jets, what happens when the pilot manually adjusts the throttles while the autopilot is controlling thrust? Does it automatically disengage, or will the autopilot "fight" to keep control until the switch is flipped?

I remember on the 737! the A/T was engaged but I advanced the throttles! I felt the A/T trying to reduce the thrust again, because we were accelerating and the commanded speed was slower! But - of course - I was stronger than the A/T and we accelerated! Then I removed my hand and the throttles were moved back from the A/T to get back to the commanded speed!
During LVL CHG (level change) descent, the A/T retards the throttles to idle and adjusts the pitch to maintain the current selected speed. IF I put my hand on the throttles and HOLD them at let's say 60% N1, then the A/T tried to retard them to idle, but I am still stronger, so after a few seconds the A/T gave up and then the A/T was only ARMED but not OFF! Means, the throttles aren't being moved by the A/T anymore, but the next change in the pitch mode (altitude acquire) then the A/T returned to the speed mode and maintained the selected speed...

WILCO737 (MD11F)
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fr8mech
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RE: Question About Jet Throttles

Tue Apr 29, 2008 2:54 pm



Quoting WILCO737 (Reply 7):

That's how I remember it. I've flown jumpseat plenty of times and recall seeing the flightcrew move/hold the power levers when they wanted to control the power level. The autothrottle did not disconnect, it just "sat" there, waiting.
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wilco737
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RE: Question About Jet Throttles

Tue Apr 29, 2008 5:11 pm



Quoting Fr8mech (Reply 8):
That's how I remember it. I've flown jumpseat plenty of times and recall seeing the flightcrew move/hold the power levers when they wanted to control the power level. The autothrottle did not disconnect, it just "sat" there, waiting.

 thumbsup  Yes, basically is it in the standby mode (called armed here)... It's more comfortable for the passenger then because the A/T doesn't move the throttles back and forth all the time, it's a constant powersetting (like during climb out as well if you use LVL CHG).
Now at Cargo the things are a little different Big grin We don't have a switch for the A/T! On the ground you engage the A/T hitting the AUTOFLIGHT button (there is only one) and during flight you hit the PROF button... But you never switch it off (unless you fly manually during approach or so) On the MD11 everything is a little different Big grin

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MQTmxguy
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RE: Question About Jet Throttles

Tue Apr 29, 2008 5:41 pm



Quoting Planenutok (Reply 6):
Dont forget that alot of newer airliners have throttle by wire, On the ERJs and CRJs that i work on there is no physical cable connecting the throttle levers to the engines. The throttles simply send electrical signals to the fadecs and they govern and control the engines. In most cases the engines change power without actually moving the levers themselves.

The TRs work on the same principle, an electronic box controls the TR actuators and don't allow the power to come up until certain parameters are met, ie. both reverser's fully deployed.

Correct, on the ERJ (never worked on a CRJ) there is no TR lever like on Boeings and Airbii. There is a detent at TLA0 (forward idle thrust position), to open the TRs use 2 fingers to pull up on the 2 switches below the thrust lever handle, then move the throttles aft past the idle detent. This engages microswithces that send signals to the FADEC and hydraulics and open the TRs (assuming all required parameters for TR deployment are met). TR deployment can be confirmed by an indication on the EICAS (one for each engine). To increase reverse thrust beyond idle, continue move the trust levers aft past the idle reverse position.

In my experience on the ERJ, the throttle levers are firm and solid but pretty easy to move. I don't remember if there is a friction adjustment, but I'll look tonight at work.
Well at least we can all take comfort in the fact that NW will never retire their DC-9s
 
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Jetlagged
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RE: Question About Jet Throttles

Tue Apr 29, 2008 5:59 pm



Quoting Tdscanuck (Reply 4):
There's a slipper clutch in there. I believe the autopilot will fight a small motion but will disengage as soon as the clutch lets go.

The A/T will not usually disconnect simply because the crew overrides the thrust levers. The clutch simply slips, and when the crew stops moving the throttles the A/T drives them back to follow the programmed command.

Quoting MQTmxguy (Reply 10):
Correct, on the ERJ (never worked on a CRJ) there is no TR lever like on Boeings and Airbii. There is a detent at TLA0 (forward idle thrust position), to open the TRs use 2 fingers to pull up on the 2 switches below the thrust lever handle, then move the throttles aft past the idle detent.

Actually the A320/319/321 has a very similar system of reverser control to that you describe for the ERJ. However the A330/A340 has piggy back levers like a Boeing.
The glass isn't half empty, or half full, it's twice as big as it needs to be.
 
MQTmxguy
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RE: Question About Jet Throttles

Tue Apr 29, 2008 7:13 pm



Quoting Jetlagged (Reply 11):
Actually the A320/319/321 has a very similar system of reverser control to that you describe for the ERJ. However the A330/A340 has piggy back levers like a Boeing

How bout that, learn somethin new everyday
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DeltaGuy
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RE: Question About Jet Throttles

Tue Apr 29, 2008 7:18 pm

On the Gulfstream IV/V, the throttles can only be moved into reverse at the idle stops, with contact switches engaged (provides ground spoilers). The reverser handles are moved up 2--3", and held momentarily to allow the reversers to unlock and open fully. After that you can move the levers almost vertical to put some EPR on the buckets. You must be out of reverse thrust before 70kias, and have the buckets stowed after that.

DeltaGuy
"The cockpit, what is it?" "It's the little room in the front of the plane where the pilot sits, but that's not importan
 
MQTmxguy
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RE: Question About Jet Throttles

Tue Apr 29, 2008 7:41 pm



Quoting DeltaGuy (Reply 13):
You must be out of reverse thrust before 70kias, and have the buckets stowed after that.

Wow that seems fast. The ERJ will give you TRs down to 25 Kts. After that you just pull a few breakers and...

On the G IV/V is the high minimum deployment speed due to FOD ingestion or comp stall?
Well at least we can all take comfort in the fact that NW will never retire their DC-9s
 
MQTmxguy
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RE: Question About Jet Throttles

Wed Apr 30, 2008 12:10 pm



Quoting MQTmxguy (Reply 10):
I don't remember if there is a friction adjustment, but I'll look tonight at work

Yep it's got one, right behind the throttles.
Well at least we can all take comfort in the fact that NW will never retire their DC-9s

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