Many years ago, a work colleague at Boscombe Down was making snide remarks about the Spitfire, saying it was inferior to the Bf 109 because it couldn’t fly inverted. This due to the fact that it had a carburettor, and not fuel injection like the 109.
I was told later by a boffin that a modification programme was initiated to make said carburettor suitable for inverted flight.
Has anyone got any factual data on this?
Bri:confused: 😡
By: MerlinPete - 30th October 2007 at 22:10
I don’t believe ‘Miss Shilling’s orifice’ aided inverted flight.
Didn’t it just temporarily maintain flow in the bunt, nose forward, negative G manoeuvre, which had previously starved the earlier carburettor variants of the Merlin. A manoeuvre picked up by the Luftwaffe to advantage.
Mark
That`s right, as far as I am aware, none of these aircraft of any nationality were designed to fly inverted as such. Neither the oil pressure or scavenge systems will work effectively when inverted.
Merlin SU carbs after the Battle of Britain era had a modified float needle valve to restrict maximum flow, Miss Shilling`s orifice being an interim field mod.
Some single-speed Merlins with SU carbs also had a diaphragm-fed float chamber for this reason.
According to the relevant manuals, the diaphragm-feed allowed both inverted flight and negative G manouevres, but I still say the lubrication system would be pretty lacking!
Pete
By: pogno - 30th October 2007 at 21:27
The engine cutting under negative ‘G’ was caused by over rich mixture. A partial fix was the RAE fuel restrictor. Later a negative ‘G’ SU carb was developed, which helped but did not solve the effect.
Merlin 66 and 70 series used a Bendix design injection carb which cured the problem.
Later the Merlin 100 series used single point injection the fuel being injected into the centre of the supercharger.
By: 109ster - 30th October 2007 at 17:32
I seem to recall a kind of “Anti_G” version of the SU carburettor from my training? I think this gave up to 15 seconds of inverted flight. Maybe someone can elaborate on this.
Thanks
Chris
…also didn’t they try injecting directly into the supercharger for temporary inverted flight?
By: Moggy C - 30th October 2007 at 14:10
Indeed – the ability to maintain inverted flight for any length of time was no particular asset to a WW2 dogfighter.
But the temporary fuel starvation caused as negative ‘g’ is generated by pushing the stick forward was an embarrassment, enabling the 109 to get a better start when running away (No implication of cowardice – it’s a valid furball tactic)
Moggy
By: Mark12 - 30th October 2007 at 13:50
I don’t believe ‘Miss Shilling’s orifice’ aided inverted flight.
Didn’t it just temporarily maintain flow in the bunt, nose forward, negative G manoeuvre, which had previously starved the earlier carburettor variants of the Merlin. A manoeuvre picked up by the Luftwaffe to advantage.
Mark
By: SqL Scramble. - 30th October 2007 at 13:36
Hi,
a certain device commonly known as ‘Miss Shillings Orifice’ springs to mind.
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October 30, 2007 at 1:27 pm