Monday, July 4, 2011

Britain - 1917 Airco D.H.9

Sometimes Newer is Not Better

Sometimes an aircraft will look like a winner and fly like a brick.The ill-fated DH-9 was one of those aircraft. Despite a sleek streamlined fuselage it fell victim to a poor choice of its power plant. The large order for this plane was based on the success of the reliable and versatile DH-4 which served admirably in many of the Allied air corps.

The Airco DH.9 (from de Havilland 9) - also known after 1920 as the de Havilland DH.9 - was a British bomber used in the First World War. A single-engined biplane, it was a development of Airco's earlier, highly successful DH.4 and was ordered in very large numbers for Britain's Royal Flying Corps and Royal Air Force.

Its engine was unreliable, and failed to provide the expected power, giving the DH.9 poorer performance than the aircraft it was meant to replace, and resulting in heavy losses, particularly over the Western Front. The subsequently-developed DH.9A had a more powerful and reliable American Liberty L-12 engine.

The DH.9 was designed by de Havilland for the Aircraft Manufacturing Company in 1916 as a successor to the DH.4. It used the wings and tail unit of the DH.4 but had a new fuselage. This enabled the pilot to sit closer to the gunner/observer and away from the engine and fuel tank. The other major change from the DH.4 was the choice of the promising new BHP/Galloway Adriatic engine, which was predicted to produce 300 hp (224 kW) and so give the new aircraft an adequate performance to match enemy fighters.

By this time, as a result of attacks by German bombers on London, the decision was made to almost double the size of the Royal Flying Corps, with most of the new squadrons planned to be equipped with bombers. Based on the performance estimates for the DH.9 (which were expected to surpass those of the DH.4), and the similarity to the DH.4, which meant that it would be easy to convert production over to the new aircraft, massive orders (4,630 aircraft) were placed.

The prototype (a converted DH.4) first flew at Hendon in July 1917. Unfortunately, the BHP engine proved unable to reliably deliver its expected power, with the engine being de-rated to 230 hp (186 kW) in order to improve reliability. This had a drastic effect on the aircraft's performance, especially at high altitude, with it being inferior to that of the DH.4 it was supposed to replace. This meant that the DH.9 would have to fight its way through enemy fighters, which could easily catch the DH.9 where the DH.4 could avoid many of these attacks.

While attempts were made to provide the DH.9 with an adequate engine, with aircraft being fitted with the Siddeley Puma, a lightened and supposedly more powerful version of the BHP, with the Fiat A12 engine and with a 430 hp (321 kW) Napier Lion engine, these were generally unsuccessful (although the Lion engined aircraft did set a World Altitude Record of 30,500 ft (13,900 m) on 2 January 1919) and it required redesign into the DH.9A to transform the aircraft.

The first deliveries were made in November 1917 to 108 Squadron RFC and first went into combat over France in March 1918 with 6 Squadron, and by July 1918, nine squadrons operational over the Western Front were using the type.

The DH.9's performance in action over the Western Front was a disaster, with heavy losses incurred, both due to its low performance, and engine failures (despite the prior de-rating of its engine). For example, between May and November 1918, two squadrons on the Western Front (Nos. 99 and 104) lost 54 shot down, and another 94 written off in accidents. The DH.9 was however more successful against the Turkish forces in the Middle East, where they faced less opposition, and it was also used extensively for coastal patrols, to try and deter the operations of U-boats.

References

  1. From Wikipedia Airco DH.9, "http://en.wikipedia.org/wiki/Airco_DH.9"
  2. Barnes, C.H. Handley Page Aircraft since 1907. London:Putnam, 1976. ISBN 0 370 00030 7.
  3. Bruce, J.M. " ;The De Havilland D.H.9 Historic Military Aircraft No. 12, Part I". Flight, 6 April 1956. Pages 385-388, 392.
  4. Bruce, J.M. "The De Havilland D.H.9 Historic Military Aircraft No. 12, Part II". Flight, 13 April 1956. Pages 422-426.
  5. Gerdessen, F. "Estonian Air Power 1918 - 1945". Air Enthusiast No 18, April - July 1982. Pages 61-76. ISSN 0143-5450.
  6. Jackson, A.J. British Civil Aircraft since 1919 Volume 2. London:Putnam, Second edition 1973. ISBN 0 370 10010 7.
  7. Jackson, A.J. De Havilland Aircraft since 1909. London Putnam, Third edition 1987. ISBN 0 85177 802 X.
  8. Mason, Francis K. The British Bomber Since 1914. London Putnam Aeronautical Books, 1994. ISBN 0-85177-861-5.
  9. Winchester, Jim, ed. Bombers of the 20th Century. London Airlife Publishing Ltd., 2003. ISBN 1-84037-386-5.

2 comments:

The Angry Lurker said...

Still it's a good design, strange that when the engine was changed there was no improvement?

W. I. Boucher said...

That may have been due to an overstatement of performance numbers and an understatement of the weight by the engine manufacturing company.