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Guest glide

747 Hydrolics and flaps

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Guest glide

Can sombody confirm that it is not possible to move the flaps without at least one engine running? I dont understand why they dont move as all indications show full HYD pressure from ground power to the electric demand pumps? or is duct press related?thanksFynn

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Hi,a real world pilot told me that the leading edge slats are pneumatically driven, i cannot comment on the rest.BestHolger


Holger Kneib

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Guest Totalbeginner

>Can sombody confirm that it is not possible to move the>flaps without at least one engine running? I dont understand>why they dont move as all indications show full HYD pressure>from ground power to the electric demand pumps? or is duct>press related?>>thanks>FynnI've never understood this either. With the DEM pumps on there IS hydraulic pressure and the flight controls will operate, so why don't the flaps?

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Guest glide

I also noticed that the leading edge flaps still opperate when using reversers even when there is no air supplied from the ground ,or APU these and the engine cowling will still move even with a totally dead aircraft, but perhaps this has been covered beforeFynn

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Guest glide

after further testing i realise this is not the case as suggested in my last reply and the front flaps and reversers do not work in a dead aircraft it was just some pressure left in the system that caused them to work after the air was disconected so appologies for thatFynn

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>Can sombody confirm that it is not possible to move the>flaps without at least one engine running? I dont understand>why they dont move as all indications show full HYD pressure>from ground power to the electric demand pumps? or is duct>press related?>>thanks>FynnHi Fynn,On the real 744 you can operate the flaps with the engines shut down as long as you have bleed air. The TE flaps are powered via the 1 and 4 hydraulic systems which require bleed air to run the Demand pumps if the EDP's(Engine Driven Pumps) are not providing pressure.As for flap operation in the sim, they appear to be coded into the engines instead of the hydraulics. Just checked and the flaps can be operated with #1 and #4 engines running but with 1 and 4 hydraulic systems depressurized(EDP's and Demand Pumps OFF). In this configuration, the TE flaps will not move on the real 744.There are a few other flap anomalies such as the LE flaps retraction on reverse thrust. They retract fine but extend immediately once out of reverse thrust. IRL, they have a 5 second delay to allow the translating cowls to close before extending.Cheers,JohnBoeing 727/737 & Lockheed C-130/L-100 Mechanichttp://www.sstsim.com/images/team/JR.jpgwww.SSTSIM.com

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Guest glide

John, thanks for the answerFynn

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Guest glide

>flaps can be operated with #1 and #4 engines running but with>1 and 4 hydraulic systems depressurized(EDP's and Demand Pumps>OFF). In this configuration, the TE flaps will not move on the>real 744.and i had not even realised that the TE flaps would extend with all hydraulics off in the simFynn

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"Just checked and the flaps can be operated with #1 and #4 engines running but with 1 and 4 hydraulic systems depressurized(EDP's and Demand Pumps OFF). In this configuration, the TE flaps will not move on the real 744."Actually, they will... In Primary Electric mode. They will also run in Alternate (Electric) mode. Both modes extend the flaps very slowly however. Electrics are backup to hydraulics (T/E flaps) and pneumatics (L/E flaps).(Edit) Primary Electric and Alternate flap extension does not use bleed air OR hydraulic pressure. Note that flap L/E-T/E flap sequencing may be affected. E.g. In Alternate Mode, the TE flaps need to be fully retracted before the L/E flaps start retracting.Cheers.Q>

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Guest glide

strange findings here, i have been messing around with the flaps in the different electric modes and much to my suprise they started moveng ext and ret in seccondary mode and also in primary mode yet previously i know they have not moved at all without engines as i have tried many times. then after a couple of retractions and extentions they stopped moving in both electrical modes and refused to move again, and i cant find any logical explanation for this inconsistancy? is this down to accurate moddelling or just quirks? Fynn

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"is this down to accurate moddelling or just quirks?"I have seen a few quirks in the flap system (in PMDG as well as the real aircraft) :-lol The aircraft sometimes gets confused when you switch from one mode to another during flap transit....and sometimes it's the flap operator who has the quirks ;)Cheers.Q>

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With the emphasis on Hydraulics eh 'Q' ;-)


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Am I correct in assuming the alt flap and gear systems are not modeled in PMDG. When you fail 1 and or 4 hydraulics gear and flap operate normally. This is not how it operates on the real a/c.

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