Data Showing Incorrect Engine Used In The SPAD XIII For Flying Circus & Proposed Engine Variants - Repost

[US103_Baer]

A re-post of original bug report, Oct 2021 to make the Data included more accessible to FC users (and Devs!) now we have dedicated forums for this kind of information.

 

 

Data Showing Incorrect Engine Used In The SPAD XIII For Flying Circus

& Proposed Engine Variants

 

 

Brief description: The SPAD XIII in FC uses a 200hp engine, not 220hp. This is provable through both Hispano-Suiza engine model documention, and historic flight test performance.
 

Detailed description, conditions:

 

- Section 1: Overview -

 

• The Spad XIII in Flying Circus is specified as a 220hp model using the Hispano-Suiza HS 8Ba.

 

• Using a variety of data sources collected from extant engines and published in peer-reviewed and widely well-regarded publications, we can show that the FC Spad XIII in fact uses a 200hp engine model and that its performance is in-line with that of a 200hp Spad XIII. (See section 2 and 3)

 

• This being the case, two recommendations are made to improve the Flying Circus simulator.

1. Leave the existing Spad in place and redesignate it as a 200hp HS8Ba powered SPAD XIII
2. To re-model a 220hp SPAD XIII with the HS 8BEc using the Ratmanoff 6727 propeller. This engine/airframe combination has excellent published data to support max hp, rpm and flight-tested speed and climb performance.

 

• Both these models should then align with published model numbers, specifications and performance data for both the aircraft and engine.

 

 

- Section 2: Engine Model -

 

• The HS 8Ba was a standard compression 200hp engine, not 220hp. See table 2 below. (Hispano-Suiza in Aeronautics: - Appendix II p481)

 

• The 200hp (4.7:1 compression) engines were known as Type 35. The 220hp engines were higher compression (5.3:1) Type 35Bis or 35S

 

• Table 2 (HS&A p481) below clearly lays out the Type 35 (Bis/S) engine development and power. The first of these 220hp engines is the HS 8Bc.

 

Table 2  (Screenshot of Appendix II - Hispano-Suiza in Aeronautics:Men, Companies, Engines and Aircraft, Lage, 2003, p481)

 

KEY POINTS

 

• Power naming designations like 200hp or 220hp SPAD are based on Nominal HP. It can be seen in Table 2 that the ‘200hp’ Type 35 engines actually produced a max 210-219hp at 2000 - 2240rpm. Likewise the 220hp engine would produce up to 238hp at 2240rpm.

 

• Table 2 does not give a max power/rpm for the initial model of Type 35Bis (220hp) engines (HS 8Bc), stating simply its nominal output of 223hp/2000rpm. Using the conservative 5% scaling achieved by the 200hp engines, that translates to an expected max of 234hp/2240rpm

 

• Note: Gearing 2000/1500 for fighters and 2000/1333 for twin-engined aircraft (HS&A p42)

 

220hp ENGINE OPTIONS

       The 220hp engine options for Flying Circus are therefore:

1. HS 8Bc achieving 234hp at 2240rpm (extrapolated performance from nominal hp - max hp scaling of earlier models)
2. HS 8BEc 238hp at 2240rpm
3. HS 8BEe at 238hp at 2240rpm.

 

- Section 3: SPAD XIII Speed/Climb Performance -

 

The table below collates and compares performance data from the published references listed, Flying Circus SPAD XIII Specifications and In-game testing. For easier comparison IAS speeds were converted to TAS using this well-regarded Aviation Calculator

 

 

 

KEY POINTS

• 218kph is the most commonly quoted top speed at 2000m. This aligns exactly with the September 1917 tests using the Ratmanoff 6727 prop and HS 8BEc engine.

 

• Max speed attained with Flying Circus in-game at 2000m is 208kph TAS (189kph IAS), Thus not reaching its spec speed which is itself lower than the published data provided. In-game tests were replicated with multiple pilots over sea using standard weather temps and atmos (Kuban autumn, clear weather.)

 

• Flying Circus in-game speeds are extremely close to the 200hp data from Soltan & Davilla, demonstrating that FC does not simply suffer from a typo regarding engine model.

 

Key Performance comparisons:  200hp performance, Actual In-game performance & common 220hp Spad performance.

 

 

- Section 4: Recommendation -

• The recommendation is therefore to modify the 220hp Spad XIII in FC to use the Hispano-Suiza HS 8BEc (238hp/2240rpm) with Ratmanoff 6727 propeller (Prop data provided below).

 

• Leave the existing Spad in place and redesignate it as a 200hp SPAD XIII

 

• Both these models should then align with published model numbers, specifications and performance data for both the aircraft and engine.

 

 

- Appendix: In Flight Test Captures-

 

Max speed 215kph IAS at 25m. Kuban, autumn, morning

 

 

 

Max speed 189kph IAS at 2000m (208.3kph TAS)  Kuban autumn morning

 

 

Spad Propeller Data - Screenshot from ‘AEF Catalogue’

 

 

 

- Acknowledgements-
The data presented is a result of efforts from a number of community members. Many thanks to @Garven / @94th_Vernon @US213_Talbot @US93_Larner @US213_Doolittle and @US28_Baer

Edited October 13, 2021 by US28_Baer