Tommy Cookers wrote:McV bought the plane to win the race, it was a very rare and far from usual Mos
this engine spec was shown to destroy exhaust stubs in hours, causing real hazard to the airframe
it finished 3rd flying about 800 miles single-engined (this famous event is readily checkable ?)
his written account of what I call screwdriver tuning (by reducing the prop pitch) is the only one I have ever found
IMO vindication, if Merlin nn gives 1600 hp at 3000 rpm it will give maybe 1700 hp at eg 3150 even with auto boost control
I suspect that many fighter COs would make sure their engineer found them an extra 50 rpm eg 50 hp this way
also the auto boost is not invincible ?, it's only a pressure capsule moving a butterfly throttle against a big air load ?
maybe auto boost actually yielded slight overboost from selecting High Blower when the book said Low Blower ?
also McVs mention of 'manually' overboosted operation (and its legitimacy) in 'bush' flying, it's all in his last book
there was an official report on RAF Allison Mustangs in the TAF in 1942 run overboosted to eg 75" to survive over France
of course this 'manual' overboosting potential only exists at low altitude ie below FTH
just read of B-24 pilots crashing, scared to go WOT because they were on 91 Octane not their accustomed 100 Octane
the accident report said they should have overboosted as necessary even with the 91 Octane
Cook Cleland said he ran his '3000 hp 5min on ADI' engine at 4500 hp for 70 min with continuous ADI (80 gallons)
the most overboostable engine ever was the '450 hp' P&W Wasp Junior, ridiculously low-rated rpm and boostwise (80 Octane)
airshow people like the Coles bought them new (surplus) for $50 and got maybe 700 hp just by using WOT and 100 Octane
thanks Trini about the Robby transmission ('elastic bands') - and no need for a torque-limiting slipper clutch for rotor run-up
I assume that no (N/A) piston engined fixed-wing aircraft are throttled as per the Robby
not yet looking at the sleeve valve info linked by JAW
AFAIK ......
the SV was a British fetish via Ricardo's finding in the 20s that the SV was the answer to detonation limiting mep and/or CR
this was with the (then) low Octane fuel and no internal valve cooling
then ......
Heron took his 'sodium cooled' valve to the US and it was made to work well
a NACA paper reported that piston crown temp was the driver for detonation (presumably they had cooled valves)
fuel Octane was improveable, and was steadily improved for 20 years, enabling increased CR, power and efficiency
so .....
by the time the SV was made to work it was unnecessary or pointless
in the US the military liked the idea, but that's their job
the engine makers didn't like it, nor did the airlines
like all cylinder-wall valving/porting, the SV becomes less competitive at larger bore: stroke ratios
(as a conventional 2 stroke would be badly matched to frozen N/A F1's huge and unprecedented B:S ratio of 2.7)
unlike cylinder-head valving/porting (ie poppet or rotary valves), which becomes more competitive at larger B:S ratios
the 100000 ? Bristol SV engines had quite a low B:S ratio, poppet valved engines gradually went to higher B:S with rises in fuel Octane
C F Taylor said that the SV was deficient in port area (ie the 4 stroke SV, not necessarily the 2 stroke Crecy etc open-top SV)
yes, this deficiency could be relieved with eg 24 smaller cylinders as the Sabre, but why bother ??
btw @ JAW
according to Eric Brown the 8th AAF was losing P-47 and P-38 pilots who dived into the ground (in pursuit) due to compressibility
Doolittle was all over Farnborough about this, and F's mod of the 47 became standard in production (Brits also needed 47s)
the 38 was worse, but Lockheed went their own way
the Mustang airframe was better compressibilitywise than either
the Merlinisation of the Mustang standardised internal tankage that took the cg aft of safe limits at full fuel
because of this thousands of missions would have been abandoned if there had been early enemy intrusion
btw the Mosquito suffered from potentially poor dive pullout due to 'leading edge bubble' (a premature and partial stall)
due to the wing section, chosen for speed, unrelated to compressibility but maybe a cause for a speed restriction
btw British load factors (strength requirements) were lower than the US's, and later the Mosquito was found to fall short anyway
and the whole 'lightweight Mustang' project was a designing-down to the British level, and the US didn't want it
they wanted and got a lengthened Mustang so there was no cg issue with fuel
No problem. You have it muddled up a little bit though. In the Robinson R22 helicopters case the "elastic bands" are actually belts, similar as to what you would find in your car to power the ICE ancillaries such as a fan, alternator and such. Big difference being the strength of each belt. They have a little stretch in them but not to much.
There is a clutch unit of sorts, the belt tensioner and the belts themselves are he clutch. When you initially start the engine the belts are fairly slack and so will slip on the output drive from the engine and input drive to the rotor system. This allows the engine to start without having the starter trying to turn the rotor system as well. After start the belt tensioner then starts to place tension on the belts pulling them tight against in input and output 'gears' the tension on the belts is what actually keeps the, locked and keeps the input and output drives spinning at the same RPM. There are main rotor rpm and engine rpm sensors that control the action of the belt tensioner automatically if slip starts to happen (although if you see the clutch light come on for more than 7 seconds, as per the pilot operates handbook, then you want to pull the clutch circuit breaker to freeze the tensioners action. The light coming on means the tensioner is either getting tighter or looser).
The transmission also consists of a free wheeling unit that works by only locking drive in one direction (like pedalling and then coasting on bicycles). This is so that of the engine quits it doesn't not stop the rotor system from spinning.
Last but not least there is the transmission unit itself which consists of step down gears going to the main rotor. The tail rotor is driven directly by a shaft coming off of the freewheeling input.
Of which of them is the limiting factor I can't remember as it was a few years ago that I went but I would suspect that it is the drive belts themselves. Those are the most commonly replaced items.
As per your next question there are other N/A piston engines aircraft throttled this way (by limiting allowable manifold pressure) but many times the limitations are there more to extend in service engine life than specifically altitude performance.
