Cathay Pod Nod's
Thread Starter
Joined: Oct 2003
Posts: 85
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From: New Zealand
Cathay Pod Nod's
Hi there
Can someone please point me in the right direction to where I can find information on the 'pod nod'.
I understand it is to improve the engines efficiency at long range cruise?
Cheers
TTD
Can someone please point me in the right direction to where I can find information on the 'pod nod'.
I understand it is to improve the engines efficiency at long range cruise?
Cheers
TTD
Thread Starter
Joined: Oct 2003
Posts: 85
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From: New Zealand
Hi Jizz, yup, that's pretty well as I understand it. I'm really after verification (preferably email link from fome officaial sit) to get my answer straight for 1st interview.
Also, am I to understand that this is only a CX mod?
Cheers
TTD
Also, am I to understand that this is only a CX mod?
Cheers
TTD
Joined: May 2002
Posts: 1,124
Likes: 16
From: GC Paradise
If memory serves me right, we did this at CX on some of the Classics in the late 80's. I think the mod dropped the nose of the pod about 1.5 degrees to more closely align the thrust vector with the flight path in the cruise at LRC. We had a rather colourful Director Eng at the time who claimed full credit for the idea. He was such a character that I wondered at the time whether he bothered to clear the idea with Boeing (or CAD).
I don't know how successful the idea turned out to be in terms of fuel burn or undesirable side-effects. But nothing more was mentioned after a few months...
I don't know how successful the idea turned out to be in terms of fuel burn or undesirable side-effects. But nothing more was mentioned after a few months...
Joined: Jan 1999
Posts: 187
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From: hongkong
TTD,
'Pod Nod' that you refer to was an L1011 phenomenon I believe. It occured when at moderate thrust (as I recall...memory's a bit slack these days!) and started during light turbulence when a harmonic motion of the wing got the engine pod oscillating up and down. Looked quite dramaric from the cabin but apparently there were no ill effects. Was stopped by adjusting the power a little.
'Pod Nod' that you refer to was an L1011 phenomenon I believe. It occured when at moderate thrust (as I recall...memory's a bit slack these days!) and started during light turbulence when a harmonic motion of the wing got the engine pod oscillating up and down. Looked quite dramaric from the cabin but apparently there were no ill effects. Was stopped by adjusting the power a little.
Joined: May 2002
Posts: 476
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From: Chilterns/Blighty
I seem to recollect back in Golden Budgie Tristar days in BAH that a wag of an F/E put in the tech log: 'Pod Nod on Number 2'.
After an exhaustive look into the snag someone pointed out to the techies the date on the tech log:
April 1...............
After an exhaustive look into the snag someone pointed out to the techies the date on the tech log:
April 1...............
Joined: May 2003
Posts: 137
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From: In a box
Pod nod was indeed a L1011 and not a Boeing problem, as described above. As for the 747 the angle of incidence of the engine nacelles was changed from about the second -300 on, nothing to do with SJ, but a refinement by the manufacturer (probably when the -400 RR design was verified) Supposed to make a small difference on fuel burn, but not enough for retrofitting costs. If you look at HVY and compare the engine 'angle' on the wing to the -400 you will see the difference.
Joined: May 2002
Posts: 1,124
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From: GC Paradise
Schrody,
I flew the L10 and I agree with that pod nod originally referred to an areoelastic phenoma on that a/c.
But SJ also applied the term pod nod to the modified thrust angle of the RRs on CX 747s. If memory serves me right. the Company Pravda (CX News) also reported the mod as a CX SJ engineered idea.
I flew the L10 and I agree with that pod nod originally referred to an areoelastic phenoma on that a/c.
But SJ also applied the term pod nod to the modified thrust angle of the RRs on CX 747s. If memory serves me right. the Company Pravda (CX News) also reported the mod as a CX SJ engineered idea.
Joined: Nov 2002
Posts: 73
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From: Australia
Hi TTD,
I believe the Pod Nod was done on a few of the classics as part of the Ultra Long Haul programme, when CX stretched the range of selected 747-200's ( and one -300) with extra tankage and upgraded engines to do HGK-LGW/YVR
Also the 747 was designed when the price of fuel was significantly lower. As the price of oil went through the roof in the 1970's, the fuel costs dictated a lower cruise speed for economy.
Lower cruise speed means higher angle of attack and body angle , which leads to the design engine thrust line being a little out. Hence the mod.
Fly safe.
I believe the Pod Nod was done on a few of the classics as part of the Ultra Long Haul programme, when CX stretched the range of selected 747-200's ( and one -300) with extra tankage and upgraded engines to do HGK-LGW/YVR
Also the 747 was designed when the price of fuel was significantly lower. As the price of oil went through the roof in the 1970's, the fuel costs dictated a lower cruise speed for economy.
Lower cruise speed means higher angle of attack and body angle , which leads to the design engine thrust line being a little out. Hence the mod.
Fly safe.
Joined: Oct 2003
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From: Gweriniaeth Cymru
Hi Gent's
tecchie response coming up! One of the most common causes of Pod-Nod on the RB211-22B(L1011) and the early RB211-524's C2/D4 is an oscillation of fuel flow. Causing the engine speed to 'pulse'. The change in the engine rotor speed as a result of this harmonic pulsing was for the engine to swing from side to side, I've seen them move by 6-10' in the test cell, probably more on wing. Exactly the same way the engine in your car rocks as you blip the throttle open and closed.
The most recent cause of this phenomena was a weeping fuel seal in the pump and governor (PAG) fuel pump. As it was weeping the change in fuel pressure caused the demanded fuel flow to increase and decrease, thus causing the pulsing/oscillation. Needless to say this unit is made by LUCAS, say no more!
Hope this helps you guy's.
Brgd's
A Tecchie
tecchie response coming up! One of the most common causes of Pod-Nod on the RB211-22B(L1011) and the early RB211-524's C2/D4 is an oscillation of fuel flow. Causing the engine speed to 'pulse'. The change in the engine rotor speed as a result of this harmonic pulsing was for the engine to swing from side to side, I've seen them move by 6-10' in the test cell, probably more on wing. Exactly the same way the engine in your car rocks as you blip the throttle open and closed.
The most recent cause of this phenomena was a weeping fuel seal in the pump and governor (PAG) fuel pump. As it was weeping the change in fuel pressure caused the demanded fuel flow to increase and decrease, thus causing the pulsing/oscillation. Needless to say this unit is made by LUCAS, say no more!
Hope this helps you guy's.
Brgd's
A Tecchie
