Tuesday, November 11, 2008

Science Museum Aircraft


The Science museum in London has a section on aircraft. This post will be about what I found interesting there.

This is the Supermarine S.6 Schneider Trophy winning aircraft of 1931. What I particularly like is that the aircraft has not been ‘restored’; look at the peeling paint on the fuselage. This aircraft was designed by Reginald Mitchell who later designed the Spitfire. From the design and construction of this aircraft he would have learned stuff that was of great benefit to him when he did the Spitfire. You can see the similarities in the design – particularly the tail. Very advanced construction methods such as countersunk rivets so the skin was smooth to reduce surface drag were pioneered on this aircraft.

Also there is the trophy itself. The competition was first flown in 1913 with the team that won it 3 times in 5 years being the outright winner and keeper of the trophy. Mitchell’s designs did that in 1927, 1929 & 1931. The trophy is much bigger than I realised; standing on the floor the fairy with dragonfly wings is almost level with your head. The fairy is kissing a water-nymph’s face in the foam of the wave. It is a big but very elegant trophy. Inside a glass case so my photo is poor but I had not known it was there and it was, for me, a very special thing to have seen. http://en.wikipedia.org/wiki/Schneider_trophy

This is the Rolls Royce R engine of the Supermarine seaplane. It is a V-12 engine of 36,7 litres. It developed 2530 HP (1887 kW). The huge centrifugal supercharger at the back was vital for making that amount of power then and Rolls used this system when they developed the Merlin engine.

This is a Supermarine Spitfire Mark 1 as used in the Battle of Britain. My uncle ‘Sailor’ Malan was the top scoring RAF pilot in that battle. http://en.wikipedia.org/wiki/Sailor_Malan.

The prototype Spitfire first flew in 1936. Mitchell died in 1937 so he did not witness the tremendous contribution his aircraft made. The Hawker Hurricane used the same engine and first flew just months before the Spitfire and it looked quite similar. The Hurricane was a then traditional design of bolted steel frame covered with wooden strips and doped cloth whereas the Spitfire was leading edge design with aluminium skin firmly attached to an aluminium frame so the skin was an important load bearing part of the structure. The design of the Spitfire was so sound and adaptable that it was still in use after WW2 when the engine power had doubled from 1000Hp to 2050HP whereas the Hurricane had to be given ‘light duties’ later in the war as it was then completely outdated (however it was the most successful fighter in the RAF during the Battle of Britain partly because the Spitfires had to engage the German fighters and keep them away while the Hurricanes attacked the bombers).

This is a Merlin of 1800 HP from much after the Battle of Britain. Note the big double supercharger at the rear of the engine. It was a 27 litre V-12 with 4 valves per cylinder, a new design but knowledge gained from the much bigger R engine of the seaplane must have been invaluable; particularly the supercharger. This engine served in such important aircraft as the Mosquito, Hurricane, Lancaster and Mustang besides the Spitfire. 150 000 of the engines were built including many by Packard in the USA.

Lessons learned and experienced gained in competing in the Schneider trophy had a major effect in the course of the Second World War.

This is the equivalent German engine in many ways. The Daimler-Benz DB605 used in the Messerschmitt ME109 fighters. It is also a V12 but has the crankshaft at the top which seems very strange to me as the oil will flow down into the cylinder heads. It had dry sump so that was actually no problem. It was considerably larger than the Merlin at 35,7 litres (as against 27) but the power was similar as it did not have as much supercharging. The power developed by an engine is not determined by the engine capacity; it is determined by how much air can be passed through the engine. The power comes from the fuel and it has to be mixed pretty precisely with the air for ignition to take place, so the more air that goes through the engine the more fuel that can be burned and the more power that can be developed. (In fact it is the amount of oxygen & that can also be increased by injecting nitrous oxide for example.) Three things determine the amount of air:
1. Engine capacity.
2. Engine speed
3. Air density.

Rolls Royce got the same power as Daimler-Benz from their smaller engine by increasing the air density significantly through supercharging. Two wonderful engines that achieved similar results by somewhat different means. The DB was fuel injected whereas the Merlin had a carburettor.


There is an interesting fact about a woman’s contribution to the success of the Spitfire. The British Government had supported the 1927 & 1929 British Schneider trophy effort but they withdrew support for the 1929 competition because the world was in the Great Depression.

Mitchell gave up all hope of there being a 1931 contest. Then, quite out of the blue, Lucy Houston, the widow of a millionaire ship owner, who made an unsolicited gift of £100,000. By now the 1931 Schneider Trophy was only seven months away and in that time Mitchell could not hope to produce an entirely new S.7. Instead, he decided to concentrate on making some changes to the S.6 design, with the primary aim of accommodating the more powerful version of the Roll-Royce "R" engine that raised the power output of the 1929 version from 1,900hp to 2,350hp.

Quote from: http://www.rjmitchell-spitfire.co.uk/schneidertrophy/1931.asp?sectionID=2
A much more complete version which includes details about the woman that really surprised me is here: http://bygonederbyshire.co.uk/articles/WWII:_Brewer%E2%80%99s_mistress_and_Spitfire_story

This is the first British jet engine, the Whittle WU of 1937, which was purely a test bed engine to test and develop the concept.

This is the second Whittle jet engine, Whittle W1, which powered the first British jet plane, the Gloster E29/39 in 1941.

The lower engine in this photo is the Junkers Jumo which powered the first operational jet aircraft, the Messerschmitt ME 262. (I don’t know what the upper engine is). Notice how much narrower the Junkers engine is compared to the Whittle engine; that is because the Whittle compressor used radial flow whereas the Junkers is an axial flow design.

This is the label attached to the Jumo engine. It points out the additional merit of the engine; its simplicity of construction. Every exhibit in the Science Museum has a label or board with information like this. It identifies the object then it always puts it into perspective telling you what is significant about it or how it compared to others or affected the development of the product. Most museums just put items on display and identify them; that is absolutely wrong as a museum is not a collection, it is a source of information and knowledge. The Science Museum is an excellent example of how it should be done.

This is the only photo I have of this very interesting rocket powered aircraft of late in WW2 but it was the most interesting of them all to me. (The other ‘plane is a Hawker Hurricane). It was designed to attack the US Flying Fortress bombers on daylight raids over Germany. It was the first aircraft to fly over 1000 kph, in 1941 and in 1944 that was increased to 1130 kph. Only in 1953 was that exceeded for the first time; by a British Hawker Hunter (I am talking about aircraft that had taken to the sky under their own power, not research aircraft dropped from a mother ship).

The operational speed and limited fuel resulted in these aircraft being not very effective; the pilot had to be an extremely good shot to hit a B17 when it was flying past at over 300 kph faster than the B17. I had never seen one before and was very interested to see it. Notice that it has no tailplane just a fin and rudder.

What I had not known was that it was designed by Alexander Lippisch. There was a long running photo quiz on ADVRider that I participated in called ‘ID this Fighter Jet’ (though it came to be any fixed wing aircraft). That is where I learned about Lippisch and I even later posted this picture of an aircraft based on his design.

Another of the extraordinary aircraft that came up in the quiz was the Collins Aerodyne. The panel for the ME163 showed me that Lippisch was responsible for both. Those informative panels at the Science Museum are wonderful. I include this especially for Klay at ADVRider who I will tell about this post but he is certain to have known the connection between these three aircraft.

This is the engine used in the Concorde (4 per ‘plane). Rolls-Royce/Snecma Olympus 593B. I think it is a significant engine. The engine behind is for a 747 Jumbo.

This is the Rolls-Royce RB211 jet engine. Originally developed for the three engined Lockheed TriStar it went on to be used by the Boeing Jumbo Jet (747). This engine was a big step up from the previous generation and it used much greater bypass than previously. The bypass fans were to be made of a carbon fibre composite. Rolls had lots of difficulty developing the engine and Lockheed and Douglas Aircraft beat Rolls-Royce down on the price. In the end Rolls-Royce went bankrupt through these problems and the company was nationalised to preserve the employment and export earnings. The new Rolls-Royce company re-negotiated the contracts with Lockheed and Douglas and the engine has become a wonderful success. It is the engine on the South African Airways Jumbos.

Both the Olympus and RB211 engines are developments from the German Jumo engine design. The Whittle design (radial compressor as against axial compressor of the Jumo) is not much used at present.


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