Originally Posted by
sycamore
Cracker,as a point of interest ,how do you control your Gnomes;do you use the `computer Mk1/1A/2,or do you run in `manual...?
Do you have `electrically operated HP cocks`; flight-idle stops, HPT overspeed-trip`and how do you do the `surge-margin checks`...?
Have you had a `surge` on a Gnome...as unless you have an `instant HP COCK` you`ll have a very pretty decorated jet-pipe....?
sycamore, we don't use the computers at all, we have manual throttles, with idle stops which operate a small servo motor at the fuel valve. We have larger servo, also manual, on the HP cock. We have our own build electronic monitoring system for GG & PT speed and turbine temp. Any over speed (or PT under speed, indicating a broken PT tacho drive quill shaft) or over temp condition triggers the opening of a high pressure solenoid valve in the HP fuel line to the combustor, this dumps HP fuel pressure from the rail very rapidly causing an instant flame out and run down (hopefully!). This acts well well as an instant HP cock and is, I believe, the system they used to have on the SRN6 hovercraft. At the same time as the fuel dump, the HP cock servo automatically closes although this takes half a second or so.
Yes we have had (many
) surges but only ever lost a compressor once, which if IIRC was cause rather than effect, and fortunately we haven't lost any turbines in 20+ years of operation <touch wood emoji>.