Merlin negative G cutout too quick?

[41Sqn_Banks]

Originally Posted by JtD

The Mk.Va came with a float type carburettor. The Tilly orifice would only have an effect when flying at 12lb boost and 3000 rpm, if you did not do that, it was pretty much meaningless. If you did, however, the engine would continue to work under negative g just fine.

To me it sounds as if combustions stops during the inverted flight and the engine spools back up thereafter, which indicates the behaviour to be typical for a Merlin with a standard float type carburettor.

On the other hand the engine spools up quite nicely (though on a very rich mixture) immediately after returning to positive g's, so maybe a fuel flow restrictor (i.e. Tilly orifice) was in place. The Merlin handbook states up to 10 seconds of recovery after a neg g situation, which clearly isn't there.

Which Merlin handbook are you referring to? Don't you mean Pilot's Notes General? Standard procedure for inverted flying was close the throttle to allow a smooth recovery.

[JtD]

Not a plane handbook / pilot notes, but a Merlin document, which I can't seem to find at the moment. Sorry.

Good point about closing the throttle, slipped my mind and it would indeed limit the problem, but the fuel pump would still flood the engine to some extend.

[41Sqn_Banks]

The throttle also had to be closed when negativ g cut out occured. IIRC Reason is that when the throttle remains opened and the fuel flow is restored the engine might overrev as power is regain so quickly that the CSP can't react quick enough.

[ZaltysZ]

Originally Posted by 41Sqn_Banks

The throttle also had to be closed when negativ g cut out occured. IIRC Reason is that when the throttle remains opened and the fuel flow is restored the engine might overrev as power is regain so quickly that the CSP can't react quick enough.

Engine starves briefly at first and then gets flooded with fuel, because things get reversed: the more fuel you have in float chamber, the more fuel you get into it. Tilly orifice simply restricted fuel flow to amount engine needs at max power setting, so even when things are reversed, float chamber gets no more fuel than engine can burn (at max power setting). Lower the fuel usage (cut the throttle or lower the RPM), and Tilly orifice won't prevent the flooding anymore. Without orifice things are the same, except engine gets flooded even at max power setting.

Running engine at max RPM and open throttle softens the flooding by some extent, but recovering with same settings can indeed result in overrev. It is probably better to cut the throttle just before recovery and not the moment cut out occurs - this seems more optimal.

[Crumpp]

Did you watch the video? I was referring to the video.

Rolling upside down is not a negative G maneuver, it is positive G. I do it sometimes the time in my plane.

[JtD]

Originally Posted by Crumpp

Rolling upside down is not a negative G maneuver, it is positive G. I do it sometimes the time in my plane.

Watch the video.

[Osprey]

Originally Posted by Crumpp

Rolling upside down is not a negative G maneuver, it is positive G. I do it sometimes the time in my plane.

You didn't watch the video. It's not a roll, it's an inverted flypast. I don't see the prop windmill but regardless if I did this move in game it would most certainly cut out completely.

[Crumpp]

It's not a roll, it's an inverted flypast.

It is definately NOT a float carburetor then.

[klem]

Originally Posted by Osprey

You didn't watch the video. It's not a roll, it's an inverted flypast. I don't see the prop windmill but regardless if I did this move in game it would most certainly cut out completely.

Its more a case of listening to the engine. It cuts to occasional firing.

[JtD]

Originally Posted by ZaltysZ

Engine starves briefly at first and then gets flooded with fuel, because things get reversed: the more fuel you have in float chamber, the more fuel you get into it. Tilly orifice simply restricted fuel flow to amount engine needs at max power setting, so even when things are reversed, float chamber gets no more fuel than engine can burn (at max power setting). Lower the fuel usage (cut the throttle or lower the RPM), and Tilly orifice won't prevent the flooding anymore. Without orifice things are the same, except engine gets flooded even at max power setting.

Running engine at max RPM and open throttle softens the flooding by some extent, but recovering with same settings can indeed result in overrev. It is probably better to cut the throttle just before recovery and not the moment cut out occurs - this seems more optimal.

Yes but...

if you cut throttle there's less air flow to suck the fuel out of the jet nozzle, so the engine does not get flooded as much. It's true what he said, it was recommended to cut throttle during neg g manoeuvres, in order to get the engine "get going earlier".

Throttle also had to be reduced and was not to be applied quickly due to low oil pressure in (longer) neg g manoeuvres.