737NG Ground Spoiler control system
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737NG Ground Spoiler control system
I read in my old notes that the spoiler mixer opens the ground spoiler control valve as the speedbrake lever is pulled past 29 or 31 degrees. I seem to have used two different numbers, albeit close, for some reason?? If someone could put me straight I'd appreciate.
More surprised I was to read the flight detent is at 40 degrees speedbrake lever angle. If I pull the speedbrake lever to Flight Detent in flight does it actually open the ground spoiler control valve? I know the ground spoilers won't deploy unless gear strut compression opens the interlock valve, but what if there's a failure of the interlock valve? First, are my numbers correct? Second, if they are what's the point of having the ground spoiler control valve open before the Flight detent?
Thanks in advance,
More surprised I was to read the flight detent is at 40 degrees speedbrake lever angle. If I pull the speedbrake lever to Flight Detent in flight does it actually open the ground spoiler control valve? I know the ground spoilers won't deploy unless gear strut compression opens the interlock valve, but what if there's a failure of the interlock valve? First, are my numbers correct? Second, if they are what's the point of having the ground spoiler control valve open before the Flight detent?
Thanks in advance,
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I couldn't find anything in my books on reasons for the angles. Perhaps the 30 degree opening is necessary for faster deployment on the ground? (especially if the autospeedbrake isn't working). Or perhaps the 30 degree deployment is best for loading up the wing progressively?
I wouldn't worry about minor angle differences. The books are full of these minor angle differences. The mechanical/hydraulic setup probably has a degree (or two) of hysteresis. Temperature variations will also affect angles. I don't think the system is set up by Engineering using angles, but, I suspect, by fitting rig pins to get the correct positions for adjustment.
The interlock valve failure scenario is interesting, but there are probably a few safeguards. e.g. the valve is spring loaded to the flight position. i.e. if the cable from the gear breaks, the valve will be held in the closed position. The valve has a proximity sensor and a hydraulic pressure switch which may offer warnings in a timely manner. Signals are sent to the PSEU and the SPEEDBRAKES EXTENDED light.
Cheers
NSEU
I wouldn't worry about minor angle differences. The books are full of these minor angle differences. The mechanical/hydraulic setup probably has a degree (or two) of hysteresis. Temperature variations will also affect angles. I don't think the system is set up by Engineering using angles, but, I suspect, by fitting rig pins to get the correct positions for adjustment.
The interlock valve failure scenario is interesting, but there are probably a few safeguards. e.g. the valve is spring loaded to the flight position. i.e. if the cable from the gear breaks, the valve will be held in the closed position. The valve has a proximity sensor and a hydraulic pressure switch which may offer warnings in a timely manner. Signals are sent to the PSEU and the SPEEDBRAKES EXTENDED light.
Cheers
NSEU
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Yes, the interlock valve is spring loaded closed. Thank you for sharing your view on the matter. There is a checklist "Landing Gear lever will not move up after take-off" that cautions against using speed brakes in flight. Wonder if it's got something to do with it?
Cheers,
Cheers,
