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Gasman
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Power Settings On Trijets

Fri Jul 08, 2011 8:38 am

Was it common practice for trijets to be flown with a differential power setting to the number 2 (tail mounted) engine? In other words, still symmetrical thrust with no 1 and 3 engines the same, but no. 2 either higher or lower?

It was more expensive to maintain a no. 2 engine beacause of access issues - I was thinking that this might provide an incentive to operate it at lower power settings so it would require maintenance less frequently.
 
bj87
Posts: 188
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RE: Power Settings On Trijets

Fri Jul 08, 2011 10:01 am

Quoting gasman (Thread starter):
Was it common practice for trijets to be flown with a differential power setting to the number 2 (tail mounted) engine? In other words, still symmetrical thrust with no 1 and 3 engines the same, but no. 2 either higher or lower?

I don't know for sure if this is true but if I remember correctly the DC10's original design philosophy was to shut down or at least reduce thrust on the #2 engine to conserve fuel. (might be a myth though) In the end it didn't work out and as far as I am aware the #2 engine runs at the same thrust setting as the # 1 and 3.

I am not a pilot though, so could be wrong.

Edit:

As far as the #2 engine being more expensive to maintain. This construction might actually cost a pretty penny to build but is it a lot more expensive or just moderately?


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[Edited 2011-07-08 03:06:07]
 
474218
Posts: 4510
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RE: Power Settings On Trijets

Fri Jul 08, 2011 1:26 pm

Quoting gasman (Thread starter):
Was it common practice for trijets to be flown with a differential power setting to the number 2 (tail mounted) engine? In other words, still symmetrical thrust with no 1 and 3 engines the same, but no. 2 either higher or lower?


I could go on and on but ... NO!

Quoting gasman (Thread starter):
It was more expensive to maintain a no. 2 engine beacause of access issues - I was thinking that this might provide an incentive to operate it at lower power settings so it would require maintenance less frequently.


Same answer as above!

Quoting bj87 (Reply 1):
As far as the #2 engine being more expensive to maintain. This construction might actually cost a pretty penny to build but is it a lot more expensive or just moderately?


Why would the #2 engine be more expensive to build?
 
bj87
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RE: Power Settings On Trijets

Fri Jul 08, 2011 3:40 pm

Quoting 474218 (Reply 2):
Why would the #2 engine be more expensive to build?

Lol, I did not mean the engine!

Look at the picture and the thing hanging from the ceiling. That is what I meant not the engine position/configuration  

[Edited 2011-07-08 09:08:17]
 
boeingfixer
Posts: 573
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RE: Power Settings On Trijets

Fri Jul 08, 2011 4:05 pm

Quoting gasman (Thread starter):
Was it common practice for trijets to be flown with a differential power setting to the number 2 (tail mounted) engine?

No., there is no need to do this. On the B727 we set the #2 engine idle 2% lower than #1 and #3 but this was to account for bleed services to the A/C packs by the pod engines. With the A/C packs ON the idles were matched between all 3 engines.

Quoting gasman (Thread starter):
It was more expensive to maintain a no. 2 engine beacause of access issues -

Actually on the B727 the #2 engine was easier to work on and easier to change.

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John
Cheers, John YYC
 
330guy
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RE: Power Settings On Trijets

Fri Jul 08, 2011 9:19 pm

I seen a video on you tube recently (i'll try find it and post a link) but basically its a 727 in flight and the #2 is at about half the thrust as 1 & 3, Its wasnt shut down as the skipper on occasion adjusted it...
Aircraft flown: a300/10/20/21/30/40, b727/37/47/57/67/, DC9, MD80-90, l1011, f50, atr42/72, shorts360, pc12
 
AA737-823
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RE: Power Settings On Trijets

Fri Jul 08, 2011 10:03 pm

Quoting gasman (Thread starter):
It was more expensive to maintain a no. 2 engine beacause of access issues

You state this as fact; it is not fact.

You open two doors, and you're in.
Further, marginally reducing the power setting in flight isnt' going to save you any money on maintenance anyhow- the schedules are set by flight hours. Every 4000 hours, you must complete a 4000 hour inspection, regardless of what power setting the engine has been run at during those 4000 hours.
 
Gasman
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RE: Power Settings On Trijets

Sat Jul 09, 2011 12:58 am

Quoting AA737-823 (Reply 6):
It was more expensive to maintain a no. 2 engine beacause of access issues

You state this as fact; it is not fact.

Sorry. I did read on one of these forums that the sheer height of the no. 2 on the DC-10 and L-1011 made it awkward to access - I presumed this would incur extra costs in terms of equipment, labour etc.

Quoting 474218 (Reply 2):
I could go on and on but ... NO!

Humour me, and go "on and on"  
 
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tb727
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RE: Power Settings On Trijets

Sat Jul 09, 2011 3:44 am

Quoting 330guy (Reply 5):
I seen a video on you tube recently (i'll try find it and post a link) but basically its a 727 in flight and the #2 is at about half the thrust as 1 & 3, Its wasnt shut down as the skipper on occasion adjusted it...

I haven't flown a Super -27(yet)   but I have heard that you can cruise along using #1+3 and have #2 pulled back a bit to save fuel. On the "stock" 727 I will occasionally use #2 to make finer speed adjustments, especially on an ILS.

It is also common practice to pull #2 back to idle when you begin your decent out of altitude. Normally in the 30's it will come back to idle and 1&3 come back some and by the time we are in the mid 20's they are all back to idle depending on how tight the pressurization system is.

On the DC-10, some operators have pilots avoid using thrust reverse on #2 in case of malfunction, especially at an outstation, since that isn't exactly an easy engine to work on.
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CosmicCruiser
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RE: Power Settings On Trijets

Sat Jul 09, 2011 5:38 am

We never did any of the above adjustments to the no.2 eng on the 727, dc-10 or md-10
 
Max Q
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RE: Power Settings On Trijets

Sat Jul 09, 2011 6:30 am

On the B727 we pretty much matched the power settings on all 3 engines.


Reducing power on the # 2 engine will not save fuel as you will simply have to increase power on #1 and #3 to compensate !


As someone else has mentioned, at the top of descent it was not uncommon to reduce power on the # 2 engine to idle
and then slowly reduce power on 1 and 3 leaving a little power on to make sure there was enough bleed air to stop the cabin from climbing (bleed air was not usually taken from #2)


The older 727's were notoriously 'leaky"


There was another procedure where we handled the # 2 engine differently, during take off in a strong crosswind we would run up the #1 and #3 engines to take off power and then slowly bring up the power on #2 as we accelerated.



This was to guard against compressor stall, as, in strong crosswinds the # 2 engine inlet airflow was inadequate at lower speeds.
The best contribution to safety is a competent Pilot.


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3rdGen
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RE: Power Settings On Trijets

Thu Jul 14, 2011 9:57 pm

Amazing to hear about the flying technique for a trijet, especially since you can always play around with the thrust on no. 2 without any asymmetric thrust issues.

To add my two cents, I was watching a Just Planes episode on the 727 ADV and the pilot basically said that with the upgraded PW JT8Ds on the adv you could essentially fly the plane on two engines, and the thrust setting was such that 1 and 3 were higher than 2 by quite a bit.

It raises two question though:

1) Engines are supposed to be run at high RPMs (N1, N2) at altitude, keeping them low defeats the purpose.
2) I know of many high performance car engines (Porsche, Ferrari etc.) where keeping RPMs down and not fully utilizing the engines power actually does more harm than good because they were never built to be driven at low RPMs. Is it the same with aircraft jet engines?

The obvious argument is that keeping #2 below full power might preserve the engine and its parts from the general wear and tear. I can imagine that they swap it out with #1 or #3 at some point if this is the case.
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Max Q
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RE: Power Settings On Trijets

Fri Jul 15, 2011 8:37 am

Quoting 3rdGen (Reply 11):

[quote=3rdGen,reply=11]Amazing to hear about the flying technique for a trijet, especially since you can always play around with the thrust on no. 2 without any asymmetric thrust issues.

To add my two cents, I was watching a Just Planes episode on the 727 ADV and the pilot basically said that with the upgraded PW JT8Ds on the adv you could essentially fly the plane on two engines, and the thrust setting was such that 1 and 3 were higher than 2 by quite a bit.

It raises two question though:

1) Engines are supposed to be run at high RPMs (N1, N2) at altitude, keeping them low defeats the purpose.
2) I know of many high performance car engines (Porsche, Ferrari etc.) where keeping RPMs down and not fully utilizing the engines power actually does more harm than good because they were never built to be driven at low RPMs. Is it the same with aircraft jet engines?

The obvious argument is that keeping #2 below full power might preserve the engine and its parts from the general wear and tear. I can imagine that they swap it out with #1 or #3 at some point if this is the case.




Thats a bit of an exaggeration, there still is no fuel savings to be had by reducing power on number 2 and increasing on 1 and 3.


Of course all three engines are interchangeable, although HP bleed does not come off no 2 and there is no hydraulic pump on no 3.
The best contribution to safety is a competent Pilot.


GGg
 
474218
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RE: Power Settings On Trijets

Fri Jul 15, 2011 1:44 pm

Quoting Max Q (Reply 12):
Of course all three engines are interchangeable, although HP bleed does not come off no 2 and there is no hydraulic pump on no 3.


What type of aircraft?

The L-1011 no. 2 engine supplies HP bleed air (and has two (2) hydraulic pumps) and the no. 3 engine has one (1) hydraulic pump (as does the no. 1 engine).
 
Max Q
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RE: Power Settings On Trijets

Sat Jul 16, 2011 10:07 am

Quoting 474218 (Reply 13):


What type of aircraft?

The L-1011 no. 2 engine supplies HP bleed air (and has two (2) hydraulic pumps) and the no. 3 engine has one (1) hydraulic pump (as does the no. 1 engine).

Yes, I was referring to the B727.
The best contribution to safety is a competent Pilot.


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