Climbing performance of the SPAD VII

[Akaalias]

Hi all.

Just a quick question................

Does anyone have the performance times for the SPAD VII to reach 3000 and 5000 mtrs, with both the H-S 8Aa and the 8Ab motors?

Thanking you in anticipation.

Cheers.

[R Pope]

I have listings in feet, 6.40 min. to 6500 ft.,11.30 min. to 9800 ft, about 3000 meters, and19.30 min. to 13100 ft. Engine is listed only as 180 Hispano, no model #. Ceiling is 18000 ft. Not quite what you asked for, but some help, I hope.

Originally Posted by Akaalias

Hi all.

Just a quick question................

Does anyone have the performance times for the SPAD VII to reach 3000 and 5000 mtrs, with both the H-S 8Aa and the 8Ab motors?

Thanking you in anticipation.

Cheers.

Tough question, that. I have been looking for info on the VII's climb performance, too - but there's hardly anything trustworthy to be found. It seems clear, though, that the Spad VII had an extraordinary climb performance for her time.

[Akaalias]

R Pope:
Thank you for that. I wonder if those figures relate to the 8Aa (150 hp) version. I understood that, when the SPAD VII first arrived, it was faster than the latest Le Rhone Nieuports (24, 24bis and 27) and could easily out dive them. On the other hand, the Nieuports were more nimble and had a better rate of climb up to 5000 mtrs. Ray Sanger (Nieuport Aircraft of World War One) cites figures of around 21 to 22 minutes to reach this height. A figure of 19:30 minutes to reach 13100 feet means that it would take a lot longer than 22 minutes to reach 5000 mtrs., which makes me think that the 8Ab (180hp) would make it a bit quicker than the Nieuports.

Fileunderfire:
You're right, it is hard trying to find reliable information. The Osprey books - Allied Aviation of World War 1 and SPAD Aces of World War 1 have very little technical data. Dan-San Abbott's addition to a thread in April, 2001 provides the best info so far, but only up to 2000 mtrs. I'd like to find out if the Aviatik publications edition of the SPAD VII (Tomasz Gronczewski) can provide more info.

Cheers.

[YavorD]

Hi Akaalias,

James Davilla and Arthur Soltan in French Aircraft of the First World War
provide following data.

SPAD 7, 705 kg, 150 hp Hispano Suiza 8Aa:
2000 m .......... 6 min 40 sec;
3000 m ........ 11 min 20 sec;
Ceiling 5500 m.

SPAD 7, 705 kg, 180 hp Hispano Suiza 8Ab:
2000 m .......... 4 min 40 sec;
3000 m .......... 8 min 10 sec;
4000 m ........ 12 min 49 sec;
Ceiling 6553 m.

The same values are given for license built aircraft with Wolseley W.4A Python I (150 hp) and Python II (180 hp) engines.

Regards,
Yavor

[Bletchley]

I believe that the 180 hp H-S probably had the Zenith altitude-compensating carburettor, 55 or 58 D.C., or Claudel C7 (or Claudel Hobson HC7), which helps to explain the consistent climb rate above 2000m...

The 150 hp version may have been originally fitted with a non-altitude compensating carburettor, although altitude compensating ones could have been retro-fitted as they became available...climb rate above 2000m may therefore have varied, depending on carburettor type.

The 'vacuum' type altitude compensation carburettors used by the Allies were good up to around 6000m, although it varied, and they were introduced sometime in early-mid 1917 and were probably in general use by late 1917 early 1918.

If the aircraft had the altitude compensating type then a photograph of the cockpit should show a second 'mixture' lever next to the throttle lever.

Info. on HS carburettors from: Ministry of Munitions. Hispano-Suiza engines: notes for squadrons in the field, September 1918.

Bletchley

[Akaalias]

YavorD:
Thanks for those figures - they correlate closely to those affered by Dan-San in 2001. Thanks also for the reference - guess how I'm spending my Borders gift voucher?


Bletchley:
Interesting about the carburettor info. Could this partly explain why the SPAD VII was slower than the XIII (with the 8Ba) to 5000 mtrs by increasing equal amounts eg 20 secs slower to 3000 mtrs (Profile 17 - CF Andrews), 40 secs slower to 4000 mtrs and, if my guesstimate is correct about the time for the VII to reach 5000 mtrs (approx 19:30 mins), 60 secs slower to that height?

Cheers.

[Bletchley]

Possibly Akaalias, although the difference doesn't look that significant to me. The Spad XIII was a later type and so it probably did have an altitude compensating carburettor, but then some of the later versions of the Spad VII may also - it is actually very difficult to say, as these carburettors were, I believe, retro-fitted in the field as they became available (just as the higher compression pistons may have been on the H-S). The climb figures between 2000m and 6000m provide the best clue, as the manually operated altitude compensating device maintained a more nearly correct fuel/air ratio as the aircraft gained altitude and reduced the loss of power due to the over-enrichment of the mixture in the thinner air at altitude, although a good photograph of the cockpit that showed a second lever on or near the throttle quadrant is also a clear indication. On the later 300 hp H-S engines the mixture lever was mounted on the quadrant next to the throttle lever, and the two were calibrated together so that the pilot could grasp them both with one hand and pull them back together to open the throttle and close the fuel supply as the aircraft gained altitude (as the late war over dimensioned or higher compression engines were generally throttled back slightly at the lower altitudes), but this was with the later 65 D.C. Zenith carburettor - on the earlier ones the mixture lever may have been separate, but would most likely nevertheless be located somewhere near the throttle quadrant. I think a small consistent difference in the climb performance may have had more to do with weight differences, or aerodynamics, than with carburettor type.

This additional info. on the 300 hp H-S comes from: Ministry of Munitions. The 300 hp Hispano-Suiza aero engine (direct drive), December 1918.

Bletchley

[Akaalias]

Thanks Bletchley. I think I was looking for answers that weren't there. Interesting about the H-S......I didn't realize that it was subject to "altitude enhancement" a la BMW and Benz.

Cheers.

[Bletchley]

Yes, although the enhancement in this case was probably a high compression engine - the altitude compensating carburettor just prevented loss of power from unbalanced fuel/air mixture. Without checking I don't know if the 8ab had the higher 5.3:1 compression ratio. The high compression engines of both sides were supposed to be throttled back somewhat at the lower altitudes, to avoid over stressing and overheating them, although the H-S manual I referred to in my first post comments that they could be opened up beyond the 'safe' rpm "for a few minutes only" : there is anecdotal evidence from both sides that pilots used this low altitude "boost" as a form of WEP in combat, and extended the recommended time from "a few minutes only" up to half an hour (there was obviously some design tolerance built in), although this was officially frowned upon as it most certainly shortened the service life of the engines and could lead to engine failure, most commonly in the form of cracked cylinder heads and burnt exhaust valves. These engines needed good radiators.

More data for the 150 hp H-S Spad, taken from British flight test report No.96 dated April 1917:

Climb to 6,500 ft in 6.3 mins (climb rate of 810 ft per min)

Climb to 10,000 ft in 11.5 min (climb rate of 570 ft per min)

Climb to 15,000 ft in 24.5 min (climb rate of 240 ft per min)

Estimated ceiling: 19,000 ft (with comment that this is probably a slight underestimate)

I also checked the British test figures for the power output of the French built 150 hp/180 hp H-S and the British (Wolseley) ones, and they are almost identical (very slight variation, but negligible).

Also checked details of compression ratio for H-S engines, and this is from the 'Notes for Squadrons in the field':

"Two compression ratios are used on Hispano engines, viz., low compression 4.7 to 1 and high compression 5.3 to 1. The high compression is obtained by putting in pistons which are slightly longer from the gudgeon pin axis to the crown, viz. 50 mm. as against 45 mm. As the majority of engines are being converted to high compression, the compression of any engine must be obtained by reference to the Log Book or by actual measurement, but as regards engines as originally issued from the makers:-

All English geared machines were low compression. All Viper engines are high compression. All French 1170 engines are low compresssion. French 1500 geared engines were high compression, except Brasier up to 16450 inclusive, and Mayen up to cases. All Hispano Suiza engines are now converted to high compression when they have been overhauled"

Hope this helps

Bletchley