Engine technology free-for-all

[wuzak]

A. Rowledge designed both the Napier Lion & R-R type-R, with master/slave big end/recip' arrangements
& Lions were used to power German aircraft.. ..again the Ju 222 does look like a mirror image Lion..

The Germans ran different ign' timings between plug sets ( & even comp' ratios per bank) on their V12s..

The R was a modified Buzzard. It initial form it, like the Buzzard, used fork and blade rods. For 1931 it was intended to also run fork and blade rods, but there were issues with either the rods and/or the big end bearing. Thus it was redesigned with the master and slave rod.

I don't think RR were using shell type bearings at the time.

Not sure on the ignition timing for German IV-12s, but the compression ratio differentiation (on DBs - not sure on Jumos) was due to oil consumption. Jumos and DBs used fork and blade rods.

[wuzak]

The Buzzard was a 6:5 scale copy of the Kestrel.

The Kestrel was built by Rolls-Royce as a response to the Curtiss D-12, and a request from the Air Ministry.

Rolls' preferred option was the Eagle XVI - an X-16 of similar capacity to the Kestrel. This used fork and blade rods for pairs of cylinders, with two sets on each crank pin. This required two banks to be set back further than the others.

The airframe manufacturers weren't keen on the X-16 layout, as they thought it would impair the forward view (banks were at 90°, and so was wider than a V-12).

[J.A.W.]

Yeah, the inverted engines brought issues with them, & none of the X-type configurations worked out well..
..though why the engine would offer a worse view over the nose than a radial.. ..does not compute..

& D-B both swapped from rolling element big-ends to plain, as well as altered firing orders for the 605.

AFAIR, the Ford V12 design intended to 'improve' the Merlin - was one of the few non-knife & fork WW2 units.
R-R seemed to skimp on conrod/big end strength & despite uprating the Merlin, current Merlin racers use Allison rods.

& Vandervell made a fortune to blow on F1 - from development/sales of Napier shell-type plain bearing designs..

[wuzak]

Rolls-Royce rods were plenty strog enough for normal duty.

Even abnormal duty in the RM.17SM at 2600hp for 15 minutes.

The problem is Reno racers are using 50% more boost than even the RM.17SM. And more rpm.

As an aside, the extra boost they run these days doesn't necessarily translate to more prop shaft power. Instead it increases the exhaust thrust.

[J.A.W.]

Well, even Lovesey admits having an issue with them during wartime..

AFAIR, Packard -9s were the highest rated mil-spec Merlins at 2200+ hp on ADI/90"Hg

& sure Merlin power has been unbeatable in recent years at Reno ( & Allison V12s haven't done much there).
Given the limits on prop efficacy, & even with the altitude being ~8,000ft, the jet thrust is significant,
& another advantage to inlines..

[wuzak]

Well, even Lovesey admits having an issue with them during wartime..

AFAIR, Packard -9s were the highest rated mil-spec Merlins at 2200+ hp on ADI/90"Hg

& sure Merlin power has been unbeatable in recent years at Reno ( & Allison V12s haven't done much there).
Given the limits on prop efficacy, & even with the altitude being ~8,000ft, the jet thrust is significant,
& another advantage to inlines..

The V-1650-9 was rated RM.14SM.

The RM.17SM was a 100-series development that didn't go into service. It was rated at 2200hp in MS gear and 2100hp in FS gear - without ADI. It was tested in 1944 at 2640hp (corrected to 2620hp), +30psi boost, with ADI @ 3150rpm in a 15 minute sprint run. It also was accidentally run for 30 minutes at 2380hp @ 3300rpm.

[Tommy Cookers]

Well, even Lovesey admits having an issue with them during wartime..
AFAIR, Packard -9s were the highest rated mil-spec Merlins at 2200+ hp on ADI/90"Hg

The V-1650-9 was rated RM.14SM.
The RM.17SM was a 100-series development that didn't go into service. It was rated at 2200hp in MS gear and 2100hp in FS gear - without ADI. It was tested in 1944 at 2640hp (corrected to 2620hp), +30psi boost, with ADI @ 3150rpm in a 15 minute sprint run. It also was accidentally run for 30 minutes at 2380hp @ 3300rpm.

US Merlin Mustangs were overboostable by holding down the spring-loaded switch intended for preflight checks of High Blower operation
someone wrote that in saving his life this way he saw 97" for 5 min
(for J.A.W - 450 ias in a B-25 with High Blower engaged at low altitude - bombardier wrote that the asi redline was 370 but he never saw it below 450 when exiting target area)

RAF Mustangs had this switch omitted
generally the USAAF/AAC didn't have automatic boost control, by WW2 British-built aircraft always did
but eg the T-6/Harvard gives about 800 hp if the throttle is fully opened on takeof because the boost will exceed 50"
the rulebook requires the throttle to be opened only as far as gives around 36" and about 600 hp
the 36" is because the engine was designed for 80/87 fuel, but normal fuel is 100/130 and 50" is ok
just watch the CHT gauge

(a few N/A planes had intentionally excess CR for efficiency and power at altitude, ie Fokker D7 and De H Comet
so were not allowed full throttle at low altitude)
(similarly the Robinson helicopter(22 not 44 says Trini), it's throttled to 25" or so ie full throttle only at suitable altitude
this gives flat rating of power wrt altitude and allows greater engine life)

with supercharging there is a further effect due to engine rpm, more rpm gives more delivery from the supercharger
this will occur with a fixed pitch prop
overboosted, over-rev takeoffs were quite acceptable and legitimate
early WW2 US combat flying was by throttling as required (limited only by detonation)
detonation is conspicuous when sitting 6' behind a 20 or 30 litre engine

IIRC Don ? McVicar got 504 ias at ground level from his (private) 3 speed Mosquito by fining the pitch to raise rpm and blower delivery
..... 'screwdriver tuning' or what !
certainly the RAF had certified rev-counters and procedures to prevent this

the RM.17SM passed the Type Tests but was rejected ? after engine no 90369 twice failed in trials in Mustang FX 858
similarly the high power R 2800/P-47Ns were pulled from service ?
but these engines were good according to due processes

btw Merlin 113 Corliss throttle had less pressure drop and lighter operation (relevant to Mosquitos)

btw Wright found that big-end fretting could be prevented by silver plating the mating faces of the rods
as required they told all US manufacturers
maybe this would have saved the Vulture ?

btw the fault in the BRM H-16 concept that the basic engine was deficient in combustion speed and consistency
as were most others eg Coventry Climax and Cosworth SCA
BRM found a cure by accident, in the reduced rod ratio resulting from the stroking of the V8 towards 2 litres
so making a viable V12

[J.A.W.]

Pretty sure that 500mph+ IAS is well above the limiting speed for the Mosquito, even in a dive ( ~440 AFAIR),
& 450mph IAS for a B-25 is surely fanciful..

Vulture conrod problems were more substantial than a bearing material issue, likely an X-configuration harmonic thing,
- & no X mills were successful in any useful military/commercial way..

Later Mustangs adopted the Euro-style engine management systems ( but radial fighter pilots & Allison users struggled).
There is a fairly glowing NACA report on the German Kommandogeraet device too.

Plenty of teething issues for the C-type R-2800s rushed into service in the ETO with the P-47M, but they
were pumping 70"Hg into them, ( with 150 grade fuel & ADI) quite a bit for an air-cooled radial.

Steady increases in allowable boost for Sabre powered Tempests raised the tested sea-level Vmax speed from..
..376mph on +7lbs to 418mph on +17.25lbs..

[wuzak]

Pretty sure that 500mph+ IAS is well above the limiting speed for the Mosquito, even in a dive ( ~440 AFAIR),
& 450mph IAS for a B-25 is surely fanciful..

Correct and correct.

450mph IAS in a B-25 is surely an error of the gauge.

Vulture conrod problems were more substantial than a bearing material issue, likely an X-configuration harmonic thing,

The "fretting"was one issue - and it wasn't the bearing, but the joint between the master rod and cap which moved causing failure of the bolts and/or bearing.

In the case of the Vulture a further issue was that the rod bolts were smaller than normal Rolls-Royce practice, and they were unable to apply the necessary clamping force.

Also, the initial design used one of the slave rod pins as a pivot for the rod cap, with only a pair of rod bolts.

Later Mustangs adopted the Euro-style engine management systems ( but radial fighter pilots & Allison users struggled).

Quite sure that all Merlins - either UK or US built - had automatic boost control.

[wuzak]

IIRC Don ? McVicar got 504 ias at ground level from his (private) 3 speed Mosquito by fining the pitch to raise rpm and blower delivery
..... 'screwdriver tuning' or what !
certainly the RAF had certified rev-counters and procedures to prevent this

As JAW said, I doubt that 504mph IAS was possible in a Mosquito.

Also, no such thing as a 3 speed Mosquito.

Either two speed single stage or two speed two stage.

the RM.17SM passed the Type Tests but was rejected after failures in service trials ?

No, it wasn't rejected after service test trials. It simply wasn't required.

[wuzak]

btw Wright found that big-end fretting could be prevented by silver plating the mating faces of the rods as required they told all US manufacturers maybe this would have saved the Vulture ?

The Vulture would have been saved if:
a) it was the only option for Hawker's F.18/37 fighter - the Tornado (Vulture) and Typhoon (Sabre).
b) more production models required it - the only production model to use the Vulture was the Manchester
c) if someone hadn't figured out that the Griffon could fit the Spitfire. The Griffon was originally designed for the FAA, but was modified so it could be used in the Spitfire. My thought is that the FAA's needs were usually trumped by the RAF's, so if the Griffon wasn't going to be useful for the RAF they may have wanted to keep the Vulture.

The con-rod issues were the biggest outstanding problem with the Vulture. The problem was its development would take time and resources away from the Griffon and, more importantly, the Merlin.

[wuzak]

Later Mustangs adopted the Euro-style engine management systems ( but radial fighter pilots & Allison users struggled).

Quite sure that all Merlins - either UK or US built - had automatic boost control.

I'll rephrase that.

Once teh Automatic Boost Control was developed, it was on all Merlins. Certainly was by the time Packard started building them.

[Tommy Cookers]

yes, my main point was to proclaim the easy ways whereby people often obtained more power than the numbers in the books

the McVicar Mosquito was the rare model with the most powerful engines (from his last book)
well known for finishing 3rd ? in the long-distance US air race (Bendix or Thomson race ?) flown much of the race on 1 engine
doing say 420 at lowish level, how would it not reach about 500 after a modest dive ?
no doubt there would be a placarded speed limit, at altitude, related to compressibility effects on trim and control

and I have found my RR Heritage Trust No 21 (Crecy) book - brilliant !

[trinidefender]

Tommy Cookers many general aviation piston engines are de-rated this way. Operators manual gives you maximum throttle settings based on 'in.Hg' and also with local temperature and pressure settings factored in which is cross referenced with a chart. I think in your example you are thinking of the Robinson R22 Beta II though. It's max manifold pressure is 24.9 in.Hg, they could make full power somewhere north of 3000 ft above MSL (mean sea level) at ISA conditions. The actual reason that Robinson gave me when I did their factory flight course is that they de-limited it because the gearbox cannot handle the torque produced at higher manifold pressures. De-rating the engine also allowed Robinson and Lycoming to extend the TBO (time between overhaul) and service intervals meaning less maintenance is needed on the engine.

The R44 (most versions) on the other hand aren't limited nearly as much with manifold pressure limits.

[J.A.W.]

yes, my main point was to proclaim the easy ways whereby people often obtained more power than the numbers in the books

the McVicar Mosquito was the rare model with the most powerful engines (from his last book)
well known for finishing 3rd ? in the long-distance US air race (Bendix or Thomson race ?) flown much of the race on 1 engine
doing say 420 at lowish level, how would it not reach about 500 after a modest dive ?
no doubt there would be a placarded speed limit, at altitude, related to compressibility effects on trim and control

and I have found my RR Heritage Trust No 21 (Crecy) book - brilliant !

British 'Pilots Notes' & the US 'placards' give tables/graphs of Vne speeds in IAS over the altitude range,
with correction factors for pitot errors & warnings for compressibility speed zones/handling advisories.
& engine settings (MAP/boost, rpm, temp, time limitations & associated fuel consumption/speed/range data.
No doubt other forces had their own equivalents.

Interestingly, a German B-25 equivalent, the Do 217 - was cleared for a Vne of 700kmh - due to being design stressed
for the dive bombing role, giving it a valuable potential evasion tactic option.