Ops-Normal.org

PN wrote:it looked like he stopped the roll for some reason

tango15 wrote: ↑

Fri May 01, 2020 3:48 pm

I think this was taken at Barton Air Show. The pf was a former colleague, Kevin Moorhouse, who was a test pilot at Woodford. He started there as an apprentice and worked his way up. He had flown the Mossie many times and I have always been curious as to why he would make an error like that. The second man in the cockpit was Steve Watson, who maintained the aircraft at Hawarden, where it was based.

It was apparent that there was an perception among pilots who had flown the Mosquito, that Merlin engines were likely to suffer a momentary cut under reduced or negative g conditions, with the result that such events, when experienced, were not entered in the technical log...

The Merlin's reputation for cutting under negative g conditions had endured since the beginning of the Second World War. Curiously,the fact that a successful carburettor modification had been developed(and incorporated on the subject aircraft) to remedy the problem had largely been forgotten.

TheGreenGoblin wrote: ↑

Sat May 02, 2020 7:31 am

.....Curiously,the fact that a successful carburettor modification had been developed(and incorporated on the subject aircraft) to remedy the problem had largely been forgotten.

CharlieOneSix wrote: ↑

Sat May 02, 2020 8:11 am

TheGreenGoblin wrote: ↑

Sat May 02, 2020 7:31 am

.....Curiously,the fact that a successful carburettor modification had been developed(and incorporated on the subject aircraft) to remedy the problem had largely been forgotten.

The famous Miss Shilling's orifice....
https://en.wikipedia.org/wiki/Miss_Shilling%27s_orifice

Boac wrote: ↑

Sat May 02, 2020 9:20 am

Do we know if the P Notes (Mosquito) advised against reduced or negative 'g' and did the pilot apply such during the manoeuvre? I have not seen any accident report.

Pontius Navigator wrote: ↑

Sat May 02, 2020 10:21 am

But if the modification had been incorporated was the known still relevant in this instance?

Pontius Navigator wrote: ↑

Sat May 02, 2020 11:26 am

TGG, but the earlier statement said it had been, serial 10 refers.

The investigation of the carburettors revealed that neither unit met the specified fuel flow
requirements under negative g conditions,as the adjustable stops that controlled the float height
(which in turn controlled the float valve) were not even contacting the valve links. As noted earlier,
these stops should have been set at overhaul, and not touched by the operator. As a result, it was
found that the fuel flows for the one float valve of each carburettor that was capable of being tested
were reduced to approximately 10% and 50% of the required values for the left and right
units respectively. Assuming both float valves of each carburettor were in similar states, it is
probable that with either or both flats in their fully depressed positions, the reduced fuel flow would
not sustain the left engine at moderate power settings. It is rather more difficult however, to relate
the as-found condition of the carburettors to the likely effects on the engines during the wingover
manoeuvre that preceded the accident. The display sequence was similar to countless others,
although the display line was perhaps shorter than most, with an attendant possibility of steeper
manoeuvres at either end.

With the benefit of hindsight it is appreciated that gasket thickness can have a critical effect on the
dimensional relationship between the float valve pintle and the associated valve orifice.
Accordingly it would be advisable to recheck the restricted flow rate through the carburettor
following disturbance or replacement of the gasket. No such requirement was contained within the
maintenance manuals which were examined.