BLEEDS ON Takeoff Weight Penalty

[Mats_J 2]

I'm here Frank.... Frank?Yes, I am still working on it. I have gathered a group of real-world dispatchers and a couple of pilots as well who will help me with the more intricate problems. Unfortunately my other commitments have been taking a heavy toll on the time I have available for the development of the VIrtual DIspatcher. But I see light in the tunnel. Don't mistrust. ;-)Thanks,

[Guest frankathl]

Much thanks for letting us know things are coming along, Mats! I'm sure many people are excited to hear that your project is alive and well."Don't mistrust. ;-)"On the contrary, Mats, I feel a special attachment to your virtual dispatcher, given that it was first revealed here on Avsim in a thread I started(now, how's that for trying to associate myself with greatness? Grin!)!"But I see light in the tunnel"...which, hopefully, isn't the 15:30 from Toronto!:-)Best wishes,Frank

[Guest Rajah]

mmm, interesting. One problem. I don't quit understand the terms-Bleed air- and -Packs- in this context. I know it has to do with the aircondotion, but I don't get to the root.Frans Dekker / TFF074

[Qavion 19]

A jet engine compresses air coming in the front of the engine with rows and rows of small compressor blades. Fuel is then added to this compressed air and the fuel-air mixture is ignited to produce thrust. However, before the fuel/fire is added, a small quantity of air is tapped off (extracted) from the engine. This air is at high pressure (and is quite hot from being compressed). This air is known as "bleed air". This air is delivered to a bleed air distribution system (a network of pipes and valves). Some of this air is used to turn airconditioning compressors/turbines which compress, cool and expand the air. These compressor/turbines are known as "Packs". In this way, the air from the engines is used in the cabin for pressurization and cooling/heating.Hope this helps.Cheers.Ian.

[Guest Hawkeyeted]

Enrico,I don't think the FMC calculates for Bleeds on either. However, this is the only airframe if've seen where you take a weight penalty, vice a runway lenght penalty, for bleed air.And, as Mark said, running the APU back-up for hydraulic systems is good measure too. As he said, the hydraulic reserviors have a head in them that are pressurized pneumatically. If you were to loose an engine (or two!) you could have the APU driving the hydraulic res, and at least have some measure of control of the aircraft.

[Qavion 19]

"If you were to loose an engine (or two!) you could have the APU driving the hydraulic res, and at least have some measure of control of the aircraft."Don't forget that the 737 has manual reversion anyway (the pilots can still move the controls if hydraulics fail).Cheers.Ian.

[marcom 139]

As I already said, the classic FMC calculates N1 for a bleed on takeoff if the bleed switches are on and for a bleeds off takeoff if the switches are turned off.Regyrding the APU: you don't really run it as a backup as a full hydraulic loss is considered too unlikely. But as a bleeds off takeoff is not a non normal situation, ie COULD happen on many takeoffs, it would damaga the hydraulic pumps if they would run without their reservoirs being pressurized.I believe some 737 operators will require their crews for running the APU during when LVP operations are in effect (low vis) as on the classic, if you lose a generator, you'll lose a lot of systems on the affected side. The APU can then power the offline systems.Regards,Mark

[Guest Rajah]

Ian,Thanks for your explanation. It's very clear now!Frans Dekker / TFF074