On 4/19/04 at 9:24 AM Vivian Meazza wrote: > >Finally, I've had some difficulty understanding the concept of using >absolute pressure for the Boost Control Valve (BCV). In the real world a >BCV >comprises, in principle, a plate exposed to manifold pressure on one side >and to the local atmospheric pressure on the other and held closed by a >spring which opens at the designed boost pressure (in this case 9 psi >adjustable by the pilot to allow 12.5 psi for up to 5 mins), and is thus >corrected for altitude. I've been scratching through the code, and can't >confirm that YASim models this behaviour. Perhaps I don't need to bother?
My understanding of it is that at rated throttle position, the boost control attempts to maintain sea-level-ambient-pressure + 9psi boost, approximately 42inHg manifold absolute pressure (MAP), regardless of altitude. This is well within the supercharger rating at sea-level, since its designed for altitude, and the BCV is controlling the pressure. As the plane climbs, the BCV maintains the 42 inHg MAP (if the rated-boost throttle position is maintained) until an altitude is reached at which the full supercharger output is being used to maintain 42in, and from then on MAP falls as height is gained. Thus the BCV is attempting to maintain an absolute pressure, not local-pressure + boost. I don't know how it works though - I had assumed it would have a sealed sea-level-ambient-pressure chamber at one side and MAP at the other, but that's just a guess. Can anyone clarify the function of the "Boost cut-out EMERGENCY control" mentioned in the manual. The name implies that it cuts the boost completely in an engine emergency. However, the text implies that it overrides the BCV for extra emergency boost: "If it is desired in an emergency to override the automatic boost control, this control can be cut-out by pushing forward the small red-painted lever (14) at the forward end of the throttle quadrant. The lever is sealed as a check against inadvertant operation." Can anyone confirm either one or other of the possible functions of this? Cheers - Dave This message has been scanned but we cannot guarantee that it and any attachments are free from viruses or other damaging content: you are advised to perform your own checks. Email communications with the University of Nottingham may be monitored as permitted by UK legislation. _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
