Engine technology free-for-all

[wuzak]

@ both
pilot training films show that P-47 turbo rpm had to be limited by pilot action in response to a graduated flashing light
this at high&rising altitude, compressor load was falling but exhaust pressure:atmospheric pressure differential increasing

No, after critical altitude the turbo can't produce sea level pressure to the engine any more so the exhaust energy is falling. And It falls away more rapidly than a mechanically supercharged engine, though its critical altitude can be higher.

Most P-47s were fitted with CH superchargers - H meaning high altitude. Their critical altitude was >30,000ft.

the pilot mentioned is now deceased from natural causes, anyway the war was a sensitive topic
he survived flying a Spit 14 with reversed aileron cables (then fittings were made foolproof)
Spit 14s were limited to 3 lb boost takeoff as torque overloaded 1 wheel and tyres burst (so he tried a 0 boost takeoff - 'once !')

I doubt they used anything like 3lb boost except at WOT - ie at very high altitudes.'

Take-off
7. During take-off the aircraft tends to swing to the right and to drag the right wing; full power should therefore not be used immediatelllly on opening the throttle, but only when the aircraft is almost airborne, ie +6 lbs boost is quite sufficient. The nose must not be allowed to fall lower than the horizon as the propeller clearance is very slight.

http://www.spitfireperformance.com/spit14afdu.html

Sq Ldr Martindale had in 1943 a prop rpm runaway at around Mach .92, this maybe was the cause of the placarding of RAF P-47s

Speed dive limits were a matter of structural limits, due to the loads seen in pullout or due to vibration, or the onset of compressibility at high mach numbers, which would lead to the loss of control of the aircraft. P-47s had a limit in USAAF service as well.

The Spitfire's normal max mach was ~0.85. The P-47's was ~0.75, the P-51's 0.80 and the P-38's ~0.62.

Martindale was investigating high mach numbers for the RAE. He dived from a very high altitude and achieved speeds >600mph TAS. The failure was not in the constant speed unit, but the engine's reduction gear housing had failed, and had broken away.

[J.A.W.]

Ultimate limiting Mach values are one thing.. ..& certainly some such as the P-38,P-47, & F8F needed & got 'dive flaps'..
..to enable recovery from other-wise terminal compressibility control issues..

However, tactical combat dive characteristics were different, & Bf 109/FW 190 types would use their dive ability..
..to evade, or catch - evading Spitfires, P-38s & P-47s..

The Mustang & Hawker Typhoon/Tempest could both tactically & critical Mach outdive 109/190 sans 'dive flaps' ..
retaining combat useful control characteristics to the higher speed zones..

'Pilots Notes' list 'limitations' on ASI ( & pitot correction factors), now known as Vne..
Max allowable ASI speeds below 10,000ft were listed for..
Tempest V: 540mph; Typhoon I: 520mph; Mustang III: 505mph; Thunderbolt I: 500mph; Spitfire XIV:470mph; P-38:430mph.
Bf109/FW 190 were increased from ~470mph to 520mph following late war refinements, as was the 20 series Spit..

Interestingly, the 1st British turbo-jets were Mach limited to around 0.74 too..

& for piston engines, allowable dive rpm was also a limiting factor, the Centaurus radial powered Tempest was
dive limited to lower speeds than the Sabre powered machines, which were cleared for 4,000+rpm..

[gruntguru]

No, after critical altitude the turbo can't produce sea level pressure to the engine any more so the exhaust energy is falling. And It falls away more rapidly than a mechanically supercharged engine, though its critical altitude can be higher.

All correct except the "falling away". A turbocharged engine (with no controls) loses boost more gradually with altitude than its mechanically supercharged counterpart. The turbo tends to spin faster as altitude increases due to reduced BP on the turbine and thinner air entering the compressor.

[J.A.W.]

http://www.avialogs.com has the 'Pilots Notes' & USAAF equivalent available for perusal, if any want the official sophistications - technicalities-wise of P-47 turbo handling ins & outs..

[Tommy Cookers]

@ both
pilot training films show that P-47 turbo rpm had to be limited by pilot action in response to a graduated flashing light
this at high&rising altitude, compressor load was falling but exhaust pressure:atmospheric pressure differential increasing

No, after critical altitude the turbo can't produce sea level pressure to the engine any more so the exhaust energy is falling. And It falls away more rapidly than a mechanically supercharged engine, though its critical altitude can be higher.

Most P-47s were fitted with CH superchargers - H meaning high altitude. Their critical altitude was >30,000ft.

the pilot mentioned is now deceased from natural causes, anyway the war was a sensitive topic
he survived flying a Spit 14 with reversed aileron cables (then fittings were made foolproof)
Spit 14s were limited to 3 lb boost takeoff as torque overloaded 1 wheel and tyres burst (so he tried a 0 boost takeoff - 'once !')

I doubt they used anything like 3lb boost except at WOT - ie at very high altitudes.'

the turbo wants to overspeed primarily because atmospheric pressure decreases with altitude
the turbo has more driving it relative to the load on it (at these high altitudes)
it's in the training film

Spit 14 - my man said that they were ordered not to use more than 3 lb on takeoff

btw postwar a Spit 19 reached mach .96 due to compressibility issues when descending from a true 56000'
on a weather recce flight in the Far East (equipped with recording barometer and radar-tracked)
people should know that the so-called standard atmosphere obtains around 45 deg latitudes
nearer the tropics the atmosphere is quite different

[wuzak]

No, after critical altitude the turbo can't produce sea level pressure to the engine any more so the exhaust energy is falling. And It falls away more rapidly than a mechanically supercharged engine, though its critical altitude can be higher.

All correct except the "falling away". A turbocharged engine (with no controls) loses boost more gradually with altitude than its mechanically supercharged counterpart. The turbo tends to spin faster as altitude increases due to reduced BP on the turbine and thinner air entering the compressor.

Turbine rpm was a critical factor.

[wuzak]

btw postwar a Spit 19 reached mach .96 due to compressibility issues when descending from a true 56000'
on a weather recce flight in the Far East (equipped with recording barometer and radar-tracked)
people should know that the so-called standard atmosphere obtains around 45 deg latitudes
nearer the tropics the atmosphere is quite different

The Stratosphere is higher, so the high altitude temperatures are lower, than over Europe.

Flight Lieutenant Ted Powles went to 50,000ft true altitude (48,500ft inidicated) in 5,000ft increments to record barometric pressures. He then decided, as the aircraft was performing so well he decided to try for 50,000ft inidcated, a true 51,550ft. At that altitude he was flying at 108kts IAS (124mph IAS/275mph TAS) and barely above stall. His cockpit prssurisation system failed and he needed to drop several thousand feet quickly.

He bunted over and soon found his aircraft vibrating badly. His instruments now read 280kts IAS. He could see the shock waves on the wings. He tried to pull up, but steepened the dive instead, until he was nearly vertical.

He dropped from 50,000ft to 44,000ft in 9s and took a further 47s to dive to 2,000ft where he made is recovery.

It is estimated that his speed was over Mach 0.94/690mph TAS at 15,000ft.

[wuzak]

Ultimate limiting Mach values are one thing.. ..& certainly some such as the P-38,P-47, & F8F needed & got 'dive flaps'..
..to enable recovery from other-wise terminal compressibility control issues..

However, tactical combat dive characteristics were different, & Bf 109/FW 190 types would use their dive ability..
..to evade, or catch - evading Spitfires, P-38s & P-47s..

In the tactical situation it was all about the accleration in the dive. The aim was to gain separation, and if you have to wait until the other aircraft gets to its lower Vne then you are probably lost.

Early Spitfires had carburettors which would cut out under negatibve G conditions. So while the Bf 109/Fw 190 could bunt over into a dive a Spitfire could not, or at least its engine would cut out if it did so.

Later Spitfires, like the XIV, had injection carburettors, which could withstang negative G.

Note that Ted Powels flew his XIX back to base, intact. And that Martindale flew several high speed dive missions, one of which he flew back to base sans proepllor, another where his blower exploded in te dive before tried to fly back to base before he hit some high tension wires.

He'd also done dives to Mach 0.85 and some to Mach 0.89, the same speed at which the engine's reduction gear broke.

The XIV was still oupaced by a P-51 in a dive, but not by a lot. The extra weight of the Griffon helped here.

[gruntguru]

No, after critical altitude the turbo can't produce sea level pressure to the engine any more so the exhaust energy is falling. And It falls away more rapidly than a mechanically supercharged engine, though its critical altitude can be higher.

All correct except the "falling away". A turbocharged engine (with no controls) loses boost more gradually with altitude than its mechanically supercharged counterpart. The turbo tends to spin faster as altitude increases due to reduced BP on the turbine and thinner air entering the compressor.

Turbine rpm was a critical factor.

OK - thanks.

[wuzak]

& cylinder radiall based on VW parts

http://www.macsmotorcitygarage.com/2014 ... ee-it-run/

[wuzak]

Turbine rpm was a critical factor.

OK - thanks.

They had a tendancy to fly apart when they overspeeded.

GE had to revise the control system for the turbo because the system failed at high altitudes and caused the turbo to explode.

[strad]

Just learned today that the term "Balls to the Wall" is and aeronautical term .
The old plane throttles had balls ,like a shifter , on top, and when shoved forward for full acceleration they very nearly touched the bulkhead.. thus balls to the wall.

[J.A.W.]

I heard that "balls to the wall" was an expression derived from the steam era..
.. & relates to when the machine was pumpin' so hard that the balls spinning in the governor - would fly loose..

[J.A.W.]

British test pilot Eric Brown flew a number of aircraft in high Mach/compressibility tests in WW2,
Not a bad effort for a wee fella, with having to muscle those big powerful planes & using non-powered controls..

He recorded 0.87 Mach in a Tempest, & just pulled it up..

http://hawkertempest.se/index.php/contr ... 10-stories

[J.A.W.]

In the tactical situation it was all about the accleration in the dive. The aim was to gain separation, and if you have to wait until the other aircraft gets to its lower Vne then you are probably lost.

Early Spitfires had carburettors which would cut out under negatibve G conditions. So while the Bf 109/Fw 190 could bunt over into a dive a Spitfire could not, or at least its engine would cut out if it did so.

Later Spitfires, like the XIV, had injection carburettors, which could withstang negative G.


The XIV was still oupaced by a P-51 in a dive, but not by a lot. The extra weight of the Griffon helped here.

There was a bit more to it than that.. ..acceleration in the dive, to catch or evade an opponent..
& the ability to manoeuvre accordingly.. to keep latched on to an enemy/get out of his sights..

The fighter test & tactics establishments ran trials to determine best use of tactical attributes,
& the Spitfire was found to be wanting in comparative dives.. ..for practicable A2A vs 109/190..
..seeming to 'hang' or 'float' in the dive - a disadvantage against the German types..

The Mustang came as a shock to German pilots who were used to being able to utilize their diving
superiority, & the Tempest was noted to be even better, inc' its zoom climb altitude recovery..
..likewise for high speed rolling.. .. the Spit needed a stiffer wing design for the 20 series..

& it was more a matter of slick aero, & power on.. rather than weight, as the Tempest showed over the Typhoon..