The Development and Deployment of the SPAD S.XIII
by
Daniel
During April, 1917, the first SPAD S.XIIIs arrived on the Western Front for evaluation.[1] The goal of the SPAD S.XIII was to allow the French and Americans to maintain air superiority over current and future German fighters. The SPAD S.XIII was the successor to the older SPAD S.VII. The SPAD S.XIII had excellent performance and was the technological equal or superior of all German fighters until the Armistice on November 11, 1918. It was faster than all German fighters in both level flight and in a dive.[2] It was capable of reaching 135 mph in level flight and over 200 mph in a dive; could reach an altitude of 22,000 feet; and had a rugged airframe, which allowed it to safely dive at the speeds it did.[3] The SPAD S.XIII was one of the most produced fighters of the war; 8,472 were built by the Armistice.[4]
[Image pending permission for use]
Fig. 1. SPAD S.XIII, National Museum of the United States Air Force
In the Spring of 1917, the French SPAD S.VIIs were technologically superior to the current German fighters. However, the SPAD S.VII, was no longer new, and it would soon become outclassed as a top fighter.[5] To partially remedy this issue, a higher compression version of the Hispano-Suiza engine was installed, which was able to output 180 hp, 30 hp more than the previous version. This modification would allow the SPAD S.VII to remain competitive until the end of the war. However, this was only a partial solution and there was still a need for a new fighter in order to maintain the size of the technological gap between French and German fighter technology. This danger would materialize as two aircraft, the Albatros D.V in May 1917,[6] and the Fokker Dr.I in October 1917,[7] but by then the French had fielded the SPAD S.XIII, which was far superior to both the Fokker and the Albatros.[8] The SPAD S.XIII was a direct continuation of the SPAD S.VII, with the addition of a second machine gun and a more powerful 220 hp Hispano-Suiza engine.[9] These improvements gave the SPAD S.XIII its capability as a gun platform and its high top-speed.
[Image pending permission for use]
Fig. 2. SPAD S.VII, National Museum of the United States Air Force
When it was first introduced, the SPAD S.XIII was a huge success, giving its primary users, the French and Americans, a fighter that could best all German fighters from then to the end of the war if flown by a talented pilot who knew in what manner to fly it. Luckily, the SPAD was flown by such pilots, such as Captain Edward Rickenbacker and Lieutenant René Fonck, who used the SPAD’s abilities to wreak havoc upon German fighters. The SPAD’s structural strength, high speed in level flight, and unmatched dive speed allowed it to escape from any German fighter if the pilot desired.[10] Unfortunately, the SPAD S.XIII was only available in small numbers until 1918. Only 151 machines had reached the front by December 1917 due to reliability issues with the engine.[11] Because of this, the SPAD’s abilities were only glimpsed in repelling the Kaiserschlacht (German Spring Offensive of 1918). On July 25, 1918, shortly after the end of the Kaiserschlacht, the SPAD began to play a larger role in the war, when United States Air Service pilots scored their first victories in SPAD S.XIIIs, which had just replaced their Nieuport 28s.[12] It was not until the Allied Meuse-Argonne Offensive that the true extent of the SPAD’s abilities were shown. On September 26, the first day of the offensive, Rene Fonck downed six German aircraft in one day, three of which were Fokker D.VIIs, the SPAD’s main opponent in the struggle for air superiority.
The SPAD S.XIII was the second fastest production fighter during World War 1, behind the Royal Aircraft Factory SE.5.[13] An experimental supercharged variant of the SPAD was capable of 139 mph, faster than the SE.5.[14] This raw speed came from 1) its smooth fuselage, whose forward half was tightly formed around the engine and radiator assembly, then covered in metal sheeting; and 2) its powerful 220 hp engine with a gear ratio that enabled it to turn a large propeller at an efficient speed.[15] The reduction gear on the engine increased the efficiency of the propeller because it enabled the engine to turn a larger propeller at a slower speed. This increased the efficiency of the propeller in multiple ways, other than simply allowing the use of a larger propeller (Appendix A).
The SPAD’s high dive speed and powerful engine called for a reinforced structure, which increased the weight, and in turn further increased its dive speed and all around survivability.[16] A weakness resulting from these elements of the SPAD’s design was that it could not fly at low speeds or perform extremely tight turns. The advanced nature of the SPAD’s design allowed it to outperform its competitors in both 1917 and 1918, when used for diving upon its enemies and diving away from engagements.[17] The durability possessed by the SPAD enabled it to withstand incredible punishment, both from enemy fire, and high speed dives.
The SPAD S.XIII was an excellent fighter that allowed the Allies to gain air superiority over the Germans once it became available in significant quantities. The design of the SPAD S.XIII was a continuation of the SPAD S.VII, with a large number of improvements to the best features of the SPAD S.VII in order create a superior fighter that did not compromise its predecessor’s most valuable assets. Even though the SPAD S.XIII was potentially the best fighter of World War I, it had its limits, such as it could not be flown in a turn-fight at low speeds.[18]
Appendix: The reduction gear and propeller efficiency
A low pitch, large diameter propeller spun at a low speed is more efficient than a faster rotating, higher pitch, small diameter propeller during low speed flight. This is because for a low pitch, large propeller, the propeller is able to move more air at a lower velocity, as in addition to the direct increase in thrust due to the larger diameter, its blades are operating at a more efficient angle of attack, which decreases drag and allows for a larger propeller, or a slightly higher rotation speed. The decrease in angle of attack can also come from the motion of the plane and its propeller, as when the propeller is turning on a plane in flight, the propeller’s blades are moving forward and horizontal, relative to the surrounding air, due to the aircraft’s speed in flight, and the propeller’s rotation.
This motion relative to the air is determined by how fast the propeller is spinning, and how fast the plane is moving. This can be seen in two scenarios, where the speed of the plane and the pitch of the propeller are the same in both, but the speed at which the propeller rotates is different. The pitch of the propeller will be for this example 45 degrees, which realistically would never happen, but helps for visualization.
In the first scenario, the tips of the propeller are moving horizontally at twice the speed of the aircraft. Assuming the air is completely stationary relative to the ground, the direction of the air’s motion perpendicular to the aircraft’s fuselage, would be half of the propeller’s pitch, or 22.5 degrees. This gives an angle of attack that is also 22.5 degrees, as the angle of attack can be found as the difference between the propeller’s pitch, and the angle of the airflow.
In the second scenario, tips of the propeller’s blades are moving just 10% faster than the aircraft’s forward speed. Using this data, the angle of the airstream perpendicular to the aircraft’s fuselage would be 40.9 degrees, which then gives an angle of attack of 4.1 degrees, which is similar to the cruise angle of some aircraft. These scenarios are able to show the effect of propeller speed on efficiency.
[Image pending permission for use]
Fig. 1. SPAD S.XIII, National Museum of the United States Air Force
In the Spring of 1917, the French SPAD S.VIIs were technologically superior to the current German fighters. However, the SPAD S.VII, was no longer new, and it would soon become outclassed as a top fighter.[5] To partially remedy this issue, a higher compression version of the Hispano-Suiza engine was installed, which was able to output 180 hp, 30 hp more than the previous version. This modification would allow the SPAD S.VII to remain competitive until the end of the war. However, this was only a partial solution and there was still a need for a new fighter in order to maintain the size of the technological gap between French and German fighter technology. This danger would materialize as two aircraft, the Albatros D.V in May 1917,[6] and the Fokker Dr.I in October 1917,[7] but by then the French had fielded the SPAD S.XIII, which was far superior to both the Fokker and the Albatros.[8] The SPAD S.XIII was a direct continuation of the SPAD S.VII, with the addition of a second machine gun and a more powerful 220 hp Hispano-Suiza engine.[9] These improvements gave the SPAD S.XIII its capability as a gun platform and its high top-speed.
[Image pending permission for use]
Fig. 2. SPAD S.VII, National Museum of the United States Air Force
When it was first introduced, the SPAD S.XIII was a huge success, giving its primary users, the French and Americans, a fighter that could best all German fighters from then to the end of the war if flown by a talented pilot who knew in what manner to fly it. Luckily, the SPAD was flown by such pilots, such as Captain Edward Rickenbacker and Lieutenant René Fonck, who used the SPAD’s abilities to wreak havoc upon German fighters. The SPAD’s structural strength, high speed in level flight, and unmatched dive speed allowed it to escape from any German fighter if the pilot desired.[10] Unfortunately, the SPAD S.XIII was only available in small numbers until 1918. Only 151 machines had reached the front by December 1917 due to reliability issues with the engine.[11] Because of this, the SPAD’s abilities were only glimpsed in repelling the Kaiserschlacht (German Spring Offensive of 1918). On July 25, 1918, shortly after the end of the Kaiserschlacht, the SPAD began to play a larger role in the war, when United States Air Service pilots scored their first victories in SPAD S.XIIIs, which had just replaced their Nieuport 28s.[12] It was not until the Allied Meuse-Argonne Offensive that the true extent of the SPAD’s abilities were shown. On September 26, the first day of the offensive, Rene Fonck downed six German aircraft in one day, three of which were Fokker D.VIIs, the SPAD’s main opponent in the struggle for air superiority.
The SPAD S.XIII was the second fastest production fighter during World War 1, behind the Royal Aircraft Factory SE.5.[13] An experimental supercharged variant of the SPAD was capable of 139 mph, faster than the SE.5.[14] This raw speed came from 1) its smooth fuselage, whose forward half was tightly formed around the engine and radiator assembly, then covered in metal sheeting; and 2) its powerful 220 hp engine with a gear ratio that enabled it to turn a large propeller at an efficient speed.[15] The reduction gear on the engine increased the efficiency of the propeller because it enabled the engine to turn a larger propeller at a slower speed. This increased the efficiency of the propeller in multiple ways, other than simply allowing the use of a larger propeller (Appendix A).
The SPAD’s high dive speed and powerful engine called for a reinforced structure, which increased the weight, and in turn further increased its dive speed and all around survivability.[16] A weakness resulting from these elements of the SPAD’s design was that it could not fly at low speeds or perform extremely tight turns. The advanced nature of the SPAD’s design allowed it to outperform its competitors in both 1917 and 1918, when used for diving upon its enemies and diving away from engagements.[17] The durability possessed by the SPAD enabled it to withstand incredible punishment, both from enemy fire, and high speed dives.
The SPAD S.XIII was an excellent fighter that allowed the Allies to gain air superiority over the Germans once it became available in significant quantities. The design of the SPAD S.XIII was a continuation of the SPAD S.VII, with a large number of improvements to the best features of the SPAD S.VII in order create a superior fighter that did not compromise its predecessor’s most valuable assets. Even though the SPAD S.XIII was potentially the best fighter of World War I, it had its limits, such as it could not be flown in a turn-fight at low speeds.[18]
Appendix: The reduction gear and propeller efficiency
A low pitch, large diameter propeller spun at a low speed is more efficient than a faster rotating, higher pitch, small diameter propeller during low speed flight. This is because for a low pitch, large propeller, the propeller is able to move more air at a lower velocity, as in addition to the direct increase in thrust due to the larger diameter, its blades are operating at a more efficient angle of attack, which decreases drag and allows for a larger propeller, or a slightly higher rotation speed. The decrease in angle of attack can also come from the motion of the plane and its propeller, as when the propeller is turning on a plane in flight, the propeller’s blades are moving forward and horizontal, relative to the surrounding air, due to the aircraft’s speed in flight, and the propeller’s rotation.
This motion relative to the air is determined by how fast the propeller is spinning, and how fast the plane is moving. This can be seen in two scenarios, where the speed of the plane and the pitch of the propeller are the same in both, but the speed at which the propeller rotates is different. The pitch of the propeller will be for this example 45 degrees, which realistically would never happen, but helps for visualization.
In the first scenario, the tips of the propeller are moving horizontally at twice the speed of the aircraft. Assuming the air is completely stationary relative to the ground, the direction of the air’s motion perpendicular to the aircraft’s fuselage, would be half of the propeller’s pitch, or 22.5 degrees. This gives an angle of attack that is also 22.5 degrees, as the angle of attack can be found as the difference between the propeller’s pitch, and the angle of the airflow.
In the second scenario, tips of the propeller’s blades are moving just 10% faster than the aircraft’s forward speed. Using this data, the angle of the airstream perpendicular to the aircraft’s fuselage would be 40.9 degrees, which then gives an angle of attack of 4.1 degrees, which is similar to the cruise angle of some aircraft. These scenarios are able to show the effect of propeller speed on efficiency.
Sources
- Guttman, Jon. SPAD XIII vs. Fokker D VII: Western Front 1918, Oxford: Osprey, 2009.
- Jackson, Robert. The Encyclopedia of Military Aircraft, London: Parragon, 2009.
- Leinburger, Ralph. Fighter: Technology, Facts, History, London: Parragon, 2008.
Footnotes
[1] Guttman, Jon. SPAD XIII vs. Fokker D VII: Western Front 1918. (Oxford: Osprey, 2009). 8-9.
[2] Jackson, Robert. The Encyclopedia of Military Aircraft, (London: Parragon, 2009), 341-42.
[3] Ibid.
[4] Ibid.
[5] Ibid.
[6] Ibid., 20.
[7] Ibid., 155.
[8] Ibid., 341–42.
[9] Ibid.
[10] Guttman, Jon. SPAD XIII vs. Fokker D VII: Western Front 1918. (Oxford: Osprey, 2009). 35.
[11] Ibid., 13.
[12] Ibid.,. 8–9.
[13] Jackson, Robert. The Encyclopedia of Military Aircraft, (London: Parragon, 2009), 322-23.
[14] Ibid., 341-42.
[15] Ibid.
[16] Guttman, Jon. SPAD XIII vs. Fokker D VII: Western Front 1918. (Oxford: Osprey, 2009). 13.
[17] Ibid.,. 28-9.
[18] Ibid., 29.
[1] Guttman, Jon. SPAD XIII vs. Fokker D VII: Western Front 1918. (Oxford: Osprey, 2009). 8-9.
[2] Jackson, Robert. The Encyclopedia of Military Aircraft, (London: Parragon, 2009), 341-42.
[3] Ibid.
[4] Ibid.
[5] Ibid.
[6] Ibid., 20.
[7] Ibid., 155.
[8] Ibid., 341–42.
[9] Ibid.
[10] Guttman, Jon. SPAD XIII vs. Fokker D VII: Western Front 1918. (Oxford: Osprey, 2009). 35.
[11] Ibid., 13.
[12] Ibid.,. 8–9.
[13] Jackson, Robert. The Encyclopedia of Military Aircraft, (London: Parragon, 2009), 322-23.
[14] Ibid., 341-42.
[15] Ibid.
[16] Guttman, Jon. SPAD XIII vs. Fokker D VII: Western Front 1918. (Oxford: Osprey, 2009). 13.
[17] Ibid.,. 28-9.
[18] Ibid., 29.