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Aircraft Topics related to WWI aircraft, aircraft engines and armament

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Old 8 January 2011, 05:56 AM   #11 (permalink)
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Bletchley, Al, Thanks for positive comments; I used to blog when I worked for a living and I was never sure it was worthwhile till I stopped!
I am busy banging out the 'essay', while I am 'charged' up and will start adding any refs shortly. Some of ithe next sections originate from chats I had with the engineers that helped Frank Nixon write his RAeS Centennial piece published in Jan.1966. As an apprentice interested in history he sent me around to talk to Fedden and Fell, Sammy Wroath and others some of whom were in WW1, or worked for people from that era. My notes take some interpreting as I haven't looked at them for 40 years! But onward and upward as the supercharger people used to say!
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Old 11 January 2011, 02:55 AM   #12 (permalink)
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advance is all about people and knowledge...

Fortunately for the nascent Edwardian aero engine industry the Engineering schools of some of our universities were producing graduates that were not only interested in internal combustion engineering but had acquired the competences necessary to make some impact on the practical problems facing the pioneers. The Victoria University of Manchester had its origins in the Owens College setup in 1851 as a non-sectarian seat of learning to provide facilities for research and education to support the industrial and cultural activities of a booming area. A number of eminent Manchester engineers, including such notables as William Fairburn, Joseph Whitworth and Charles Frederick Beyer, endowed the chair of engineering at the university and Osborne Reynolds, at the age of 25 became the first professor to fill the chair, retiring in 1905 when he was succeeded by Joseph E. Petavel. Reynolds work on turbulence and flow through conical nozzles had an immediate impact on local and eventually in the form of Re-the Reynolds Number- transformed global industry.
The Royal Aircraft Factory began to take more than a passing interest in aero engines after their facilities had been used for the trials of engines entered into the Patrick Alexander Prize competition, held in 1909-10. The engines entered turned out to be problematic and even though the Green engine won the £1,000 prize people realised how much of a gap there was between aspiration and delivery of overall performance. In order to drive on the development Alexander offered another £1,000 prize for trials to be undertaken late in 1911.
The RAF under Mervyn O’Gorman suggested that they should undertake complete engine design led by F. M. Green who had been recruited as head of Engine Design. Eventually after the very ordinary results from the second prize entrants permission was given in Dec, 1911, to undertake engine design and development. The first engine was based on the Renault 80 hp V8 aircooled engine and was designated the RAF1, first running in January 1913 and delivering 100 hp. Used to develop their ideas, by February 1915 it became the RAF1a.
Meanwhile three recruits to the team were making great inroads into the problem of providing a lightweight, relatively reliable prime mover. They were Arnold Hartley Gibson who previously researched flow in conical diffusers, under Reynolds, who teamed up with Samuel Dalziel Heron to lay down the basic principles for designing radial engine cylinder heads. The third member was James Edwin Ellor, who studied under Petavel and became a leading light in supercharger development. Before Ellor arrived Green had initiated supercharger investigations, using piston compressors and Roots blowers but nothing came of these and they moved onto what we now regard as a normal configurations.
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Old 11 January 2011, 05:47 AM   #13 (permalink)
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Today we are familiar with the three basic forms of impeller design:


The most popular form generally used was the open bladed design which has the merit of being easy to machine and at that time lightweight. Putting a disk at the rear improves the aerodynamics and the structural static strength and alters the dynamic response. The closed design by fully defining the radial passage can offer the greatest pressure increase at the best efficiency, and is more tolerant to axial positioning as the sensitivity to running clearances is lower, but with a manufacturing and structural strength penalty. Both Rateau, in France and Sandford Moss, in the USA, favoured the open configuration. The Germans, who were adapting existing industrial designs that favoured closed impellers, naturally continued in that vein.
James Ellor explored all 3 configurations in his designs over the next few years.
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Old 11 January 2011, 06:05 AM   #14 (permalink)
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Ellor's first experiment.

James Ellor's first try at supercharging was a direct drive single-stage design that was fitted to the RAF1a engine mounted in a B.E.2c aeroplane towards the end of 1915. This DERA photograph taken in December 1915 shows the supercharged engine mounted below the fuel tank in the aeroplane.

[My copy of the photo has not arrived yet so I am cut and pasting a scan from The Aeroplanes of the Royal Aircraft Factory by Paul Hare]. My notes which I believe come from a reading of ICE 230 indicate that it was a debatable improvement
"A BE2C biplane powered by an RAF1a air-cooled eight-cylinder engine took 35 minutes to climb to 8,500 feet. With the gear-driven supercharger, it climbed to 11,500 feet in a similar time." Samuel Heron was heard to comment “A. J. Elliott, a pilot engineer, acting as the observer on the test flight, sat forward with his feet under the fuel tank and over the supercharger’s gear drive. The gears were quite inadequate and the pinion failed in flight, producing showers of sparks and a feeling of distinct concern.”
A look at The Vintage Aviator's B.E.2c build photos reinforces Heron's words!
The real innovation that Ellor applied to this supercharger was the move from an open to a semi-closed impeller design, improving the effectiveness of the system.

Last edited by tartle; 12 January 2011 at 12:12 AM. Reason: added observer's name
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Old 11 January 2011, 03:48 PM   #15 (permalink)
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Good evening,

"it was a debatable improvement"

Not too sure about that, tartle, 35 minutes to 8,500 feet, with the gear-driven supercharger, 11,500 feet in a similar time seems like an appreciable improvement, given the context of the time. Looking forward to more.

With regards,
Mike.
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Old 12 January 2011, 12:53 AM   #16 (permalink)
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Quote:
Originally Posted by tartle View Post
James Ellor's first try at supercharging was a direct drive single-stage design that was fitted to the RAF1a engine mounted in a B.E.2c aeroplane towards the end of 1915. This DERA photograph taken in December 1915 shows the supercharged engine mounted below the fuel tank in the aeroplane. ....
Thank You for the story, tartle!
I must admit a significant gap in my knowledge about early engine development in UK.
Just a small note - R.A.F. 1a supercharger shown on the picture is gear-driven (geared-up), not direct drive. R.A.F. 1a propeller shaft was rotating at one-half crankshaft speed. Do You know the impeller speed (or supercharger gear ratio)?
Regards,
Yavor

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Old 12 January 2011, 05:31 AM   #17 (permalink)
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deabatable improvement or promising line of development/

Mike,
What I meant was the trade-off between increased performance and safety of the actual device was weighted in favour of finding a solution to the gear drive problem. Because the RAFactory was really an experimental establishment that also managed development and production, people like Ellor, Gibson and Heron were looking for the scientific and engineering rules that determined how to improve the engines, etc. Today we would think of that B.E.2c flight as a proof of concept demonstration.
Whilst this work was going on the Team at Farnborough were looking at possible engine configurations to take forward to evaluation. Way back in 1913 after working with single and two row Gnome rotaries Green had initiated work on the RAF.2 - a 120hp 9-cylinder single row radial engine with the same bore and stroke as the RAF.1. Design work was complete by October, 1913 and work commenced on a test engine, but never completed as the funding was never easy to find.
In 1915 the RAFactory were taken by the demonstration of the Smith radial engine for which Heenan & Froude had a licence, Vickers wanted to use the engine but constant problems meant it never made it into production. [not found a pic or dwg of it.. haven't looked too hard yet..anyone got a lead?].
The feature that Ellor was excited by was the 'direct drive' supercharger which did not increase mass flow or pressure appreciably but improved fuel distribution to the cylinders.... more on this shortly.

Yavor... used the term to mean not turbine driven... but you are right to say gear-driven.. my original draft dated 26.4.1966 has a note to agree on a definition of terms... with all you helpers will be able to do it now!
Awaiting more data on the RAF1a supercharger.. will share when it is in my hands!

Last edited by tartle; 12 January 2011 at 05:37 AM. Reason: add comment for Yavor
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Old 12 January 2011, 04:09 PM   #18 (permalink)
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Good evening,

Thanks for the clarification, tartle.
Ellor (Lr) was one of the heroes of the British supercharging effort. The picture of the Bristol Jupiter supercharger impeller in Gunston's book, page 126, is what Ellor was aiming at originally.
If I may make a suggestion, you might use the term supercharger to specifically denote a mechanically driven blower and turbocharger to denote an exhaust driven unit. This should alleviate confusion.
As one of my old lecturers used say. " every turbocharger is a supercharger, but every supercharger is not a turbocharger".

With regards,
Mike.
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Old 16 January 2011, 11:03 AM   #19 (permalink)
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By Jupiter!

Mike (dirtyshirt),
Yes, I was amazed to realise that Bristol stuck with a 'simple' impeller for so long... I guess it had to do with space.
I have copied a couple of pages from my Jupiter VII manual to make it clear what an open impeller looks like in practice...


This shows the blower unit and below is a picture of the impeller itself:
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Old 17 January 2011, 05:55 AM   #20 (permalink)
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Raising the power of radials

The RAFactory first worked on a radial engine in 1913, completing the design of a 9-cylinder 120 hp air-cooled RAF2 on 13th October. crankshaft rpm was 1600 with a prop speed of 900. The bore and stroke were 100x140 mm. Building of the engine started but the ascendancy of the rotaries of that time meant it was better to allocate resources to other projects and the RAF2 was never tested.
After Ellor, Gibson and Heron's arrival at Farnborough work picked up on engines.
Influenced by the Smith Radial, they worked on design ideas for the improving the radial engine to make it more competitive.
one idea Ellor worked on was to combine the supercharger and make the inner diameter of the inlet as small as possible so that it was easier to arrange a uniform injection of fuel to be mixed with inlet air and distributed to the cylinders. This resulted in GB patent number 122,536 whichwas applied for on Mar 6th 1918 and accepted Jan 30th 1919.

This is a summary of the patent.
F. M. Green and S. D. Heron, with Ellor's growing expertise on superchargers, went on to design the RAF8 14-cylinder 2 row air cooled radial. With a bore and stroke of 4.75x5.5 inches, the design was not built at the RAFactory as the management saw more potential in the V's they were developing. When F. M. Green left for Siddeley Deasy he took the design with him.

This drawing of the RAF8 was published in Norman MacMillan's article 'Recollecting Radials' published in Shall Aviation News No 323 probably in 1965.
Norman recalled that in January 1917 Commodore Murray Sueter and Commander Wilf Briggs and his technical supervisor Major Evans evolved a specification for a 300 hp 42 inch diameter 630 lb weight air cooled radial. This Air Board Scheme A requirement needed responses by April. Green's departure can be seen as no coincidence and the RAF8 evolved into the Jaguar; the other engine that was developed to the spec. was the Bristol Jupiter.
The geared drive for the Jaguar supercharger (with a speed of 18,000 rpm) turned out to be beset with torsional vibration problems and although Heron, who had also migrated to Siddeley's, and Green designed a centrifugal clutch design that solved the problem, in the short term they reverted to a mixer fan layout. This picture shows a similar fan on the Lynx (one row of a Jaguar)

A section of the Lynx showing the fan is below


By 1926 the company now known as Armstrong Siddeley had developed the supercharger on the Jaguar, a diagram of which is shown below:

The centrifugal clutch design was patented by Green and Heron and is incorporated in the supercharger drive layout.
Canadian patent 201486 has a simple explanation of principles and a drawing:
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