Engine technology free-for-all

[J.A.W.]

D-B did an up-camming 'hot-rod' type tune - as applied to their V12 fighter mills.

http://www.enginehistory.org/German/daimler-benz.shtml

The German V12s DB 605/Ju213 were of ~ equivalent swept volume as the British Griffon & Sabre liquid cooled mills.

[J.A.W.]

T-C wrote.. btw a former co-worker ex-Napier said that of compressor tests eg critical to N's failed engine design that killed the Rotodyne
the compressor was driven by a naval steam turbine controlled by viewing an oscilloscope and manually turning the steam valve[/quote]


AFAIR, spinning a multi-stage compressor turbine up on test takes a fair drive input,
& employing a steam turbine donkey wasn't all that unusual..

[gruntguru]

The interesting bits in the D-B article are:
1. The low boost pressures tolerated by the DB601. The power-up raised the boost from 4.25 psi to 6.0 psi. Apparently piston "weakness" was the limiting factor. Cylinder filling would have improved more than the 9% attributable to boost increase alone, thanks to the "hot cam" and "port & polish" mods that were also part of the power-up.
2. The massive increase in valve overlap from 42* to 105*. Probably to increase scavenging as much as anything. Increased scavenging would cool the combustion chamber (including the "weak" pistons). Direct injection of course permits unlimited scavenging without loss of fuel.

[J.A.W.]

For the Jumo 213, the Germans used increased rpm (to TBO threatening piston speeds) as a means of power-boost.

& @ T-C, re: the sorry saga of the Rotodyne..
..This was another (sadly typical) British example of snatching defeat from the jaws of victory..
..by political, rather than technological reasons..
The Napier Eland was killed by R-R - after their take-over, & again - due to non-technological reasons..

http://www.flightglobal.com/pdfarchive/ ... 00336.html

[wuzak]

The interesting bits in the D-B article are:
1. The low boost pressures tolerated by the DB601. The power-up raised the boost from 4.25 psi to 6.0 psi. Apparently piston "weakness" was the limiting factor. Cylinder filling would have improved more than the 9% attributable to the boost increase due to the "hot cam" and "port & polish" mods that were also part of the power-up.
2. The massive increase in valve overlap from 42* to 105*. Probably to increase scavenging as much as anything. Increased scavenging would cool the combustion chamber (including the "weak" pistons). Direct injection of course permits unlimited scavenging without loss of fuel.

The other thing limiting boost was the higher compression ratio favoured by Daimler-Benz. While th eMerlin ran 6:1, the V-1710 6.5:1 (later ones had 6:1) and teh Sabre 7:1, Daimler Benzes typically ran between 8 and 9:1. IIRC the DB 605 had 8.6/8.8:1.

[wuzak]

For the Jumo 213, the Germans used increased rpm (to TBO threatening piston speeds) as a means of power-boost.

& @ T-C, re: the sorry saga of the Rotodyne..
..This was another (sadly typical) British example of snatching defeat from the jaws of victory..
..by political, rather than technological reasons..
The Napier Eland was killed by R-R - after their take-over, & again - due to non-technological reasons..

http://www.flightglobal.com/pdfarchive/ ... 00336.html

Suggest it was for commercial reasons.

Rolls-Royce had the slightly more powerful Tyne in production. They would be competing for essentially the same market.

FWIW, Eland was a single shaft turboprop, which means no separate power turbine, whereas the RR Tyne used two shafts and a power turbine.

[J.A.W.]

Yes W, that seems a reasonable explanation.

Per the Germans..
The Germans mostly relegated their V12 aero-engines to running on lower octane spec B4 fuel,
- due to their air-cooled BMW radials needing the available high test C3 juice..

The higher static comp ratio also allows a more efficient low boost cruise consumption/endurance/range..

[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 production Vulture used a different system to the ealier pivoted type. It was in two pieces with 4 clamping screws. The faces of the master rod and cap were serrated, so no movement between them should have been necessary.

The bolts remained small and short, which limited the amount of preload which could be applied. The bolts were the weak point of the design.

Wright engines used single piece master rods and built up crankcases.

Pratt & Whitney used the same method for their single row engines, but went for a one piece crankshaft for R-1535 and R-1830, but a single piece master rod and built up crank for the R-2800.

Naturally the R-4360's crank was too long to be built up, so it was one piece and the master rod in 2 pieces.

[wuzak]

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..

Don't think Vulture's troubles were related to harmonics.

Weakness in the connecting rod system was the last major issue - the bolts were the weak point, which could also cause the bearing to fail.

Other issues the Vultuire suffered from include:
Relative movement of the two crankcase halves - slved by fitting dowels.
Cavitation in the cooling pumps - there were two pumps, which could lead to cavitation on one side - the solution was to fit a balance pipe.

[wuzak]

This is the bottom end of an R-2800 master rod.



Note that the clamping bolts go through two of the slave rod pin holes.

And this is the single piece rod form an R-2800



Rolls-Royce could have done sonething similar for the Vulture. Instead, the bolts fitted between the slave rod pins.

[J.A.W.]

R-R (& others) were keen on X-configuration mills but none ever really made the cut..
A radial is a 'different kettle of fish', & 4-stroke radials such as the R-2800 run odd-numbered sets/banks of cylinders.

W, do you know how the R-R Pennine big-end/con-rod arrangements differed from the Vulture?
Curious that R-R seemed to admit defeat & went to a twin crankshaft scheme for their last 24cyl..

[wuzak]

R-R (& others) were keen on X-configuration mills but none ever really made the cut..
A radial is a 'different kettle of fish', & 4-stroke radials such as the R-2800 run odd-numbered sets/banks of cylinders.

W, do you know how the R-R Pennine big-end/con-rod arrangements differed from the Vulture?
Curious that R-R seemed to admit defeat & went to a twin crankshaft scheme for their last 24cyl..

No, I do not know what they did for the Pennine. Though it was capable of 2800hp @ 3500rpm early in development.

To put that in perspective - it was the same hp as the very best R-2800 running on 100/150 fuel (the Pennine on 100/130 fuel) and similar to the Sabre at that time (1945).

The Pennine post-dated the Eagle 22.

[J.A.W.]

Did the Pennine ever make production status, pass a 'type-test' or even fly?

It was ~same swept volume as the R-2800, ~ 10 litres more than the Sabre.. which in the event..
.. was the only 'hyper' type liquid cooled mill to make it into service/'mass' production..

Much of the issue with increased Sabre power output - was in the availability of propellers - able to hack it..

See a stripped Sabre laid out for inspection - below in this link..
http://www.aviationshoppe.com/sabre-ii- ... p-256.html

[riff_raff]

The R-R Pennine used a master/slave type conrod.

The focus of post-war aircraft piston engine development was more about increased reliability/service life and reduced fuel consumption. Plus there was little money available for developing new engines. So the obvious approach was to improve the best existing engines. In the UK that meant the Merlin/Griffon and Hercules/Centarus, and in the US that meant the Pratt R2800/R4360 and Wright 3350.

[J.A.W.]

There were a number of factors..

A, There were tens of thousands of cheaply available ex-military engines & airframes suitable for transport use.

B, High performance fighter-aircraft piston engines were largely passé due to the advent of turbo-jets..

C, Post war Britain was broke & had to eke out some viable productive use from its service dependant industries,
but compared to ~125,000 2,000+hp R-2800s built in USA..
.. Britain all told - made fewer than 20,000 Centaurus/Griffon/Sabre 2,000+hp aero engines.