Miss Shilling's Orifice etc

Thanks everyone that clears up the confusion. Colin

I didn’t see the post above before I posted this…..but, yes, exactly. Not for inverted flight.

I don’t know how much fuel is contained in the float-chamber of a Merlin carburettor but I don’t imagine it is as much as a gallon and, at combat power, a gallon of fuel will last about thirty seconds!

And that’s assuming that a carburettor can use every drop of fuel in the float-chamber and still allow the engine to run at optimal fuel-air mixture, which no carburettor can do; the truth is that the float-chamber is a device to supply fuel at a known pressure (or ‘head’), it is not a ‘ready use’ fuel-tank and the moment fuel stops flowing into the carburettor engine power will drop-off markedly (and the ‘wrong’ fuel-air mixture will be supplied from what fuel remains).

The carburretor mod was to help with ‘negative G’ not for inverted flying,you need a proper inverted flying fuel and oil system to do sustained inverted flying,Miss S’s orifice was to help with the momentary neg ‘G’ such as pushing over into a dive whilst following a target aircraft.

…a Hurricane cannot fly upside down other than momentarily as the engine will cut out.

As you say ‘momentarily’; what is really needed is a firmer definition of the time we are talking about. Even with the famous ‘orifice’ the regular (and required) precisely measured fuel-flow would be interrupted (very quickly)…

…and we also need to define ‘upside-down’! Surely what matters is positive or negative gravity acting on the float-chamber; upside-down with positive gravity should work fine but the right way up with negative gravity will not.

It was fitted to all combat Merlins until a more permanent solution was incorporated.

The term Miss Shilling’s Orifice was entirely colloquial, following the usual Bawdy RAF manner.

Anon.

According to Wikipedia (Yes, I know … ) it was fitted to Hurricanes.