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DH106 wrote:I wouldn't have thought 4 throttles would be a problem, their curved indentation shape natually fitting to 4 fingers of a hand, but I've often wondered about 6 engined (An225?) or even 8 engined (B52?) aircraft. Are their throttles easy to manipulate togther?
Boeing757100 wrote:For aircraft like the 747/A380/A340 there obviously has to be 4 throttle levers. However, when you're lined up ready to take off and set TOGA or any detent, are the levers too wide to all move with one hand? Even for 3 engined planes like the MD-11/DC-10, the 2nd engine throttle lever is slightly higher than the other 2, so is it awkward to move when pushing it to a certain detent? Sorry if it is a weird question but I've wondered this for a long time. I'd imagine it would be hugely inefficient to use both hands when moving throttles. I also heard that at some airlines it is common place for both pilots to push the throttles forward on takeoff, but it's not at all airlines...
VMCA787 wrote:No flight engineers on the B-52! But, the thrust levers are configured so you can grab all 8 with one hand and then fine tune the setting with each individual thrust lever.
DH106 wrote:I wouldn't have thought 4 throttles would be a problem, their curved indentation shape natually fitting to 4 fingers of a hand, but I've often wondered about 6 engined (An225?) or even 8 engined (B52?) aircraft. Are their throttles easy to manipulate togther?
77west wrote:VMCA787 wrote:No flight engineers on the B-52! But, the thrust levers are configured so you can grab all 8 with one hand and then fine tune the setting with each individual thrust lever.
Interesting, I kind of assumed with the age and complexity of them and military nature there would be. You often see on the classic 747s the PF will advance the levers to roughly takeoff power and the FE will reach over and fine tune them a bit. Normally ends up with all 4 levers slightly offset. I assume this would be similar on the 52 if it has cable control. On the FBW quads (A340/380) I have never seen them moved individually outside of non-normal ops.
Starlionblue wrote:77west wrote:VMCA787 wrote:No flight engineers on the B-52! But, the thrust levers are configured so you can grab all 8 with one hand and then fine tune the setting with each individual thrust lever.
Interesting, I kind of assumed with the age and complexity of them and military nature there would be. You often see on the classic 747s the PF will advance the levers to roughly takeoff power and the FE will reach over and fine tune them a bit. Normally ends up with all 4 levers slightly offset. I assume this would be similar on the 52 if it has cable control. On the FBW quads (A340/380) I have never seen them moved individually outside of non-normal ops.
The one normal operation situation where you sometimes use thrust levers asymmetrically is tight turns during taxi.
Given FADEC engine thrust on a modern jet would give equal thrust for equal thrust lever angle. Pre-FADEC, this was not the case, and there would be variations.
Starlionblue wrote:Boeing757100 wrote:For aircraft like the 747/A380/A340 there obviously has to be 4 throttle levers. However, when you're lined up ready to take off and set TOGA or any detent, are the levers too wide to all move with one hand? Even for 3 engined planes like the MD-11/DC-10, the 2nd engine throttle lever is slightly higher than the other 2, so is it awkward to move when pushing it to a certain detent? Sorry if it is a weird question but I've wondered this for a long time. I'd imagine it would be hugely inefficient to use both hands when moving throttles. I also heard that at some airlines it is common place for both pilots to push the throttles forward on takeoff, but it's not at all airlines...
"Thrust levers", not throttle levers, in jet aircraft.
For some reason, they're called "throttles" in military pointy jets. Not sure about military transport jets.
77west wrote:You often see on the classic 747s the PF will advance the levers to roughly takeoff power and the FE will reach over and fine tune them a bit.
Starlionblue wrote:Boeing757100 wrote:For aircraft like the 747/A380/A340 there obviously has to be 4 throttle levers. However, when you're lined up ready to take off and set TOGA or any detent, are the levers too wide to all move with one hand? Even for 3 engined planes like the MD-11/DC-10, the 2nd engine throttle lever is slightly higher than the other 2, so is it awkward to move when pushing it to a certain detent? Sorry if it is a weird question but I've wondered this for a long time. I'd imagine it would be hugely inefficient to use both hands when moving throttles. I also heard that at some airlines it is common place for both pilots to push the throttles forward on takeoff, but it's not at all airlines...
"Thrust levers", not throttle levers, in jet aircraft.
For some reason, they're called "throttles" in military pointy jets. Not sure about military transport jets.
N1120A wrote:Then technically it is thrust in a diesel car.
rjsampson wrote:N1120A wrote:Then technically it is thrust in a diesel car.
Well, no. Cars do not produce thrust.
rjsampson wrote:
Anyway back to my original question: Why "thrust lever" and not throttle?
Avatar2go wrote:rjsampson wrote:
Anyway back to my original question: Why "thrust lever" and not throttle?
I believe the distinction came about with computerized engine controls such as FADEC. Prior to that the throttle levers regulated the flow of fuel to the engine. With computerized controls, they regulated the percent thrust of the engine. While similar in function, the curve of position vs engine thrust may be different. The thrust levers would be nearly linear, the throttle levers would depend on the engine's fuel flow & throttle mapping.
Today they tend to be used interchangeably, because all modern commercial engines have FADEC.
Avatar2go wrote:rjsampson wrote:
Anyway back to my original question: Why "thrust lever" and not throttle?
I believe the distinction came about with computerized engine controls such as FADEC. Prior to that the throttle levers regulated the flow of fuel to the engine. With computerized controls, they regulated the percent thrust of the engine. While similar in function, the curve of position vs engine thrust may be different. The thrust levers would be nearly linear, the throttle levers would depend on the engine's fuel flow & throttle mapping.
Today they tend to be used interchangeably, because all modern commercial engines have FADEC.
LH707330 wrote:
How many of today's engines actually regulate thrust linearly though? I know several engines use N1 as their primary parameter, and thrust scales as roughly N1^2. Do those systems linearly set N1 (so x amount of deflection gives you y amount of delta-N1)?
I'd think that an old-school system with a linear increase in fuel flow would then also have a slightly better-than-linear thrust output, because the higher CR would increase the efficiency, so you'd get more thrust for a given amount of fuel. Now I'm curious how those old HMUs were rigged up and whether the modern FADEC engines were programmed to mimic them. Given fleets with mixed engine controls (e.g. CF6-80C2 on the A300/767/747) it would make sense to try and make them feel the same, but who knows.
N1120A wrote:It is still silly and rather pedantic to do the old throttle/power/thrust lever differentiation.
Avatar2go wrote:LH707330 wrote:
How many of today's engines actually regulate thrust linearly though? I know several engines use N1 as their primary parameter, and thrust scales as roughly N1^2. Do those systems linearly set N1 (so x amount of deflection gives you y amount of delta-N1)?
I'd think that an old-school system with a linear increase in fuel flow would then also have a slightly better-than-linear thrust output, because the higher CR would increase the efficiency, so you'd get more thrust for a given amount of fuel. Now I'm curious how those old HMUs were rigged up and whether the modern FADEC engines were programmed to mimic them. Given fleets with mixed engine controls (e.g. CF6-80C2 on the A300/767/747) it would make sense to try and make them feel the same, but who knows.
A modern FADEC has two options for thrust control. First is N1 as you mentioned, which is the most similar to a throttle control. Second is EPR which is an estimate of engine thrust, and compensates for changes in altitude, temperature, and other operational conditions. Thus is more similar to a thrust control.
Engine manufacturers have different preferences.
Here are some good articles on how these two parameters function, advantages and disadvantages. Second article gives example thrust tables for N1.
https://www.dj-airways.com/epr-vs-n1/
https://theflyingengineer.com/flightdec ... ndication/
LH707330 wrote:Thanks for those articles. Makes one wonder if it makes sense to have a density-compensated output of those parameters to control the actual amount of thrust delivered (e.g. "set takeoff thrust to x kN).
RetiredWeasel wrote:As an FO on 747-200s for many years, when it was my leg, I'd set the power for T/O to the precomputed T/O EPR setting. Then the FE (SO) would fine tune them with the lever extension on the back of the thrust levers. Then I'd take my hand off the levers and the CPT would place his right hand just aft of the levers on the console as it was his sole decision to initiate a rejected T/O if needed.
chimborazo wrote:RetiredWeasel wrote:As an FO on 747-200s for many years, when it was my leg, I'd set the power for T/O to the precomputed T/O EPR setting. Then the FE (SO) would fine tune them with the lever extension on the back of the thrust levers. Then I'd take my hand off the levers and the CPT would place his right hand just aft of the levers on the console as it was his sole decision to initiate a rejected T/O if needed.
Interesting. Was this meant to be just forward of the levers? Curious as to why it would be behind: if the captain wanted to reject, would have thought the hand would either be on or in front of the levers. Of they rejected, was it with the “FE levers” or the pilot ones?