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larshgf

Questions to startup procedure

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A few questions in relation to the startup procedure.....1. Why is it that we want the SPAR VALVE and the ENG VALVE closed by setting the startlevers to cuttof?2. When I open the L PACK and R PACK blue signs are lit saying "RAM doors full open". I guess RAM doors must be some kind of valve opening when you turn on the PACK's - but what does RAM stand for (the acronym I mean)?RegardsLars

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Lars,To answer your questions.1) When starting a Turbine engine, its not a good idea to have the fuel selected ON when you initially start the engine as it causes quite a bit of excess heat in the turbine section of the engine usually resulting in small molten metal balls from what used to be engine parts. Some engine manufacturers recomend you reach "max motoring"(maximum N2% the starter will reach without the fuel on) speed before putting the fuel on while others bring it in as early as 10-15% General rule of thumb on the NG, fuel on when the N2 reaches the cue on the indicator.2) The "RAM" doors are the Ram air inlet doors on the bottom of the aircraft that provide cooling air for the pack heat exchangers. Normally full open on the grd and in some other situations. Ian!!!!RegardsPaul Gollnick :-cool Technical Operations/Customer Operational SupportPrecision Manuals Development Groupwww.precisionmanuals.comhttp://www.precisionmanuals.com/images/forum/devteam.jpg


Paul Gollnick

Manager Customer/Technical Support

Precision Manuals Development Group

www.precisionmanuals.com

PMDG_NGX_Dev_Team.jpg

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Guest boxjockey99

LarsPaul is indeed correct, the fuel MUST be off prior to starting the engine primarily because during the start process it is the flow of air that provides the cooling ncessary to stop the hot end of the engine from melting. The CFM56 family are recommended to be no less than 20% N2 and ideally 25% N2 prior to putting in the fuel. Once you reach this figure and you have checked tht you have both N1 Rotation and oil pressure you should introduce the fuel. The airflow caused by the spinning engine (being spun by the starter) keeps the inards cool when the fuel lights up and the engine begins to spool up. As the engine hits 46% the starter cuts out and the engine continues to accellerate to its stable speed of approx 55-60%n2 / 21% N1. As the engine starts you see the EGT rising but this is normally in direct proportion to the speed of the N2 speed. The NG is also fully FADEC controlled and so fairly idiot proof but the -300 I drive is not and so starting is still a well monitored phase of the flight. The ram doors have nothing to do with the fuel system and as Paul rightly points out they are there to provide cooling external air to the air cycle machines and air con packs. The overhead panel is designed sensibly so you can see which systems are inter-related and as you can see the fuel system is on the left while the RAM door lights are just above the aircon panel on the far right. Hope that helpsKris

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Thank's for your answer Paul,Regarding the N2%: After switching the ignition to GRD, I'm not sure I can get that much higher than 20% in the PMDG-737NG. I guess it's OK and not a peculiarity in my add-on or in my way to start up the engines??Do you - by chance know what RAM stands for (I mean as an acronyme)?A last question if I may, now I have a technician "in the house": the electrical system has BUS'es. In the computer I guess that the BUS is a "highway" that conducts data to the RAM and back. What is it if we are talking about the elec trical system in an aircraft??Thank you in advanceLars PS: I have an ambition to give an explanation of every single step in the checklist for the 737NG. I have neeeded that for a long time (if I get a better understanding of what's going on, the flightsim experience will be much greater for me!). Do you think it's possible to find such explanations somewhere or to start a thread on this forum where we all give a contribution to this work. Afterwards I can upload it to AVSIM file library. Crazy idea??

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Guest boxjockey99

LarsThe 20% N2 is a problem with MSFS not the PMDG add-on, it will go higher than 20% but in my experience the sound of the starter recycles at 20% so it sounds funny but it does all work! RAM is not an acronym it simply means ram air as in it is being rammed into the aircraft, you can see the inlets just below the forward wing root, the forward motion of the aircraft through the air forces (Rams) air into the ducts and cools the packs. The RAM air doors are nothing to do with anything remotely computer based! The busses are a shortened term for the electrical bus bars. There are several on the B737 and without getting too complesx think of them as the ring main electrical system in your house. A long run of wire with sockets from which systems plug in and draw power. There are 2 main electrical busses, one for each engine generator and from this other busses feed all the essential and non essential electrical services. It's all a bit complex to describe in words and alas I don't have an electronic copy of the schematic to post. Again though the busses are not controlled by computers so much as big heavy duty relays that close and open according to switch positions (this is of course over simplifying the whole affair). SO just to clarify, the bus simply supplies electricity, there is no 'data' being transferred, all it is doing is providing power! The data transfers etc are handled by little black boxes in the electronics bay which have little goblins in them which only avionics engineers understand! I think I have an expanded checklist somewhere that I might be able to share but I will have to remove all of my company identities from it as it is classed as company confidential as it forms part of the ops manualSpeak soonKris

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Guest boxjockey99

Thanks Thomas, thats the one, the ram door can be seen just inside the inlet in the fully open position, once in flight the Air con system controls the door position as it needs toKris

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Thank's for your answer Kris!I know it's not necessary to know the technical issues in every detail, but somehow it's more fun for me to know just a little about the reason why you do "so and so" in your checklist. It gives me a better experience with the flight simulator and I usually remember things better when I have some knowledge of the subjects. On this forum I know I'm not the only one who has loooked for a sort of "why do we do it that way"-kind of checklist. I think it could be a good thing to many beginner's to have such a thing. If I'm able to collect the necessary knowledge about most of the points in the checklist for the different 737NG-procedures I could upload it to the AVSIM file-library ti the pleasure of many people. If you have an expanded checklist that might contain some explanations too I would be very glad indeed. Best RegardsLars :)

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"1. Why is it that we want the SPAR VALVE and the ENG VALVE closed by setting the startlevers to cuttof?"This would be like leaving your tap/faucet running when you are not having a bath :( (Or, much worse, the gas tap on your gas cooking stove open... then coming back a few hours later and lighting it). The valves stop fuel getting from your tanks to your engine burner when the engine is not running."2. When I open the L PACK and R PACK blue signs are lit saying "RAM doors full open". I guess RAM doors must be some kind of valve opening when you turn on the PACK's - but what does RAM stand for (the acronym I mean)?"The aircon packs are supplied with very hot bleed air from the engines or the APU. This hot air needs to be cooled down before it reaches the cabin. In the case of most aircraft, outside air is used to cool down air going into the pack (and at other points). However, the outside air and the hot bleed air are not directly mixed together. A heat exchanger is used (something like a car radiator or the device on the back of an (older) home refrigerator).To force colder outside air to flow over the heat exchanger, there is an air (Naca) scoop at the front of the heat exchanger and an exit door at the back of the heat exchanger. The scoop is known as a "Ram Air Inlet".To help control the temperature of the air going through the heat exchanger at different aircraft airspeeds and different temperatures, a motorized blocker door is put inside the air scoop ducting. This is the Ram Air Door.The Ram Air Door door is controlled by a number of different methods. Air/Ground Relays and Flap Relays are used on the ground and in the air when the flaps are extended. In flight (flaps up), the doors are controlled by a Pack Temp Controller (computer) and temperature sensors.Normally the blocker door is almost shut in cruise (the outside air is very cold and it is moving very quickly). However, if you see the DOOR FULL OPEN light illuminated in cruise, it usually means there is a fault with the system.Hope this helps.Cheers.Ian

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Thanks everyone who contributed in this very interesting and informative thread!Lars...hope you'll manage to collect the info needed for the kind of extensive checklist you mention, such a checklist would really be great!!All the best,


Richard Åsberg
Beta tester for FS2Crew and HiFi Simulation Technologies

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