> -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of > David Luff > Sent: 19 April 2004 09:52 > To: FlightGear developers discussions > Subject: RE: [Flightgear-devel] Spitfire & Hurricane manuals > > > > > 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.
This seems to be correct. This is from a contemporary test of a Spitfire MkIIa: http://www.fourthfightergroup.com/eagles/p7280speed.gif > > 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." I think it was also known as the Boost Control Cut-out. These documents explain that your latter interpretation is correct: http://www.fourthfightergroup.com/eagles/spit1-12lbs.jpg http://www.fourthfightergroup.com/eagles/ap1590b.jpg http://www.fourthfightergroup.com/eagles/dowding1.jpg http://www.fourthfightergroup.com/eagles/dowding2.jpg > > Can anyone confirm either one or other of the possible > functions of this? > > Cheers - Dave > Regards Vivian _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
