Way back in the sixties and seventies in Malaysia we were having problems with our single Gnome Whirlwinds stopping which was a bit embarrassing over the jungle. A team from Westlands and Rolls Royce came out to see what the problem was. After the first, for Singapore, light shower of rain it was established by them that it was rain ingestion. We protested that it had happened when it hadn't rained for weeks so to prove their point they set up a trial.
We put a Whirlwind on the tie-down base and Roy Moxham, the Deputy Chief Test Pilot for Westland, and I carried out this trial. Roy did the business, I held the instant cutout so that I could kill the engine before it cooked itself. Rain was simulated by a fire tender in front of the aircraft with two fireman holding a fire hose in front of the open intake door. Their job was to direct the water directly into the intake of the engine.
We started it up and then increased the collective to normal cruise power, 400 lbs/hr. At the signal they turned on the high pressure hose using a mains supply as the base. This meant that the pump would run at its maximum rated quantity straight into the intake.
The engine shugged it off as if nothing had happened.
The collective was slowly reduced and at about flat pitch with the same water flow the engine started hunting about 1,000 rpm or so. After being at flat pitch for about twenty seconds the amplitude increased to such an extent that it was considered logical to shut it down as it was required for training that afternoon.
That was a high pressure fire hose directly into the intake. The Orions were washed when they returned from a sortie. They would taxi to the entrance to their dispersal where two fire engines would give the aircraft a thorough soaking from the front and side. Then they would continue to their parking spot.
Use foam or water to stop a runaway jet engine? Forget it.
The only use I have known where a fire hose is useful in a helicopter emergency was with the Bristol Sycamore. Should a droop stop fail on a Sycamore's rotor head it's blade would strike the boom on shutdown. There was a massive pad on the boom at the critical point that would encourage the blades to bounce over the boom but this was not 100% so an alternative system was used.
A fire engine would be positioned so that its hand held hose would point over the boom just before the pylon joint on the starboard side. The water would be turned on and then the pilot would closed down the engine. As the rotor decayed the errant blade would ride the water jet over the boom until the rotor was stationary.
The blades would then have to be removed as they were made of wood, dried out and then sent down to the tracking tower at Yeovil where they would be retracked as a set.