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Aircraft Topics related to WWI aircraft, aircraft engines and armament

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Old 5 June 2004, 05:44 AM   #1 (permalink)
wingedwarrior
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Hi everyone,

I have a question regarding the Spad VII, but it probably pertains to other WWI aircraft as well. I have read reports on the range and endurance of the Spad VII, and I was wondering if someone knows how the manufacturer would determine these performance statistics? I believe that these figures are highly dependant on flight regime, and piloting skills. In a dogfight, I am sure that the pilot would expend more fuel, as he would be in and out of full throttle for a period of time. I wonder if the range and endurance stats take this into consideration, as these were fighting machines, and were not meant for leisurely fights of fancy.

If the manufacturer only tested the airplane with a particular throttle setting and in a straight line of flight, then I suppose that the figures would be useless when trying to determine if a pilot in a real life situation would have enough gas to stay afloat for x amount of hours. Granted, the condition of the aircraft, both airframe and engine, weighs in heavy here , so that's why I am talking about a factory fresh airplane. What are your thoughts on this?

Also, does anyone have reliable figures of endurance/range for the Spad VII, both with the 150hp & 180hp HS engine, something akin to factory figures?

regards
 
Old 5 June 2004, 12:49 PM   #2 (permalink)
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Range and endurance have always been an enlightened guess, for exactly the reasons you stated. The factory would operate one at its best cruise and use these figures.The pilot was expected to allow for differences in the way he flew the plane. A lot like EPA mileage, few in the real world ever seriously expected to achieve these figures.
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Old 6 June 2004, 02:02 PM   #3 (permalink)
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Wingedwarrior:
Endurance for fighter is based on fuel consumption of the engine at full power at a specific altitude.
If you look at the the specification fora an engine they give the fuel consumption at so much grams, ounces or lbs per horse power per hour.
For example the 160 Ps (hp) Mercedes D.III data sheets gives the fuel consumption @ 230 grams or 230 / 1000 =.023kg per hour per hour and the oil consumption at 20 grams per Ps(hp)
You are the designer and you want your fighter to have a two hour flight duration at full power, it will require:
Fuel
2hrs x .230kg x 160 ps = 73.6 kg fuel.
Oil
2 hr. x .02 kg x 160 = 6.4 kg. oil generally engineers use 1/10 of the fuel to determine the oil require or in the case 7.2 kg of oil.
The 150 hp Hispano-Suiza Model A engine has a fuel consumption of .52 lbs per hour hour per hp =
150 x .52 = 78 lbs.
Gasoline weighs 7.2 lbs per gallon, 78/ 7.2 = 10.83 gallons or gallons x 4.545 = liters, 10.83 x 4.545 = 49.2 liters per hour.
If the fuel tank capacity is known you can then determine the duration.
The Spad VII DATAFILE on page 24 , gives tha endurance as 1 1/2 hours, by dropping the rpm from 1450 to a cruise rpm of1300 would lower the fuel consumption, horse power and extend the length of duration.
An aside The Spad VII with the 150 hp Type 8A Hispano-Suiza was a marginal fighter aircraft, it was too heavy. The problem was solved when SPAD went to the 180 Hp Hispano-Suiza Type 8Ab engine, then it WAS a fighter!
Blue skies,
Dan-San
P.S. I just got back from Vintage Aero Annual picnic. It was great! 11 P-51s 10 Ds and 1 H model. The Navy was well represented also, and a F-18 Hornet. It was well worth the drive.
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Old 7 June 2004, 03:05 PM   #4 (permalink)
wingedwarrior
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Hi,

I appreciate the detailed information. The formulas for determining endurance is interesting. I would think then that in normal flight, with ingress, combat and egress, a pilot may get a somewhat longer flight duration then what is stated by the manufacturer (in a well maintained bird). This is due to the fact that he would probably not fly at full throttle during normal flight (non-combat), once the required altitude is reached and the enemy has not been sighted (but this is only an opinion of mine). True, the pilot may opt to fly at full throttle to engage the enemy formation, or use all the speed he could muster to escape an uncomfortable situation. All in all, conservation of full would seem vital, especially if you find yourself heading for home having to escape an enemy formation and, at the same time, fight a 20 knot headwind!


BTW, those Mustangs must have been a real sight..... Just a single P-51 at an airshow usually gets the crowd to take notice!

regards
 
Old 8 June 2004, 05:33 AM   #5 (permalink)
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Dan san--I very much doubt that endurance would be calculated at full power. The figures would be a mere percentage of what would be expected at part throttle. Modern fighters are rated assuming a set percentage of cruise, with so much combat time, and then cruise home, but WW1 builders wouldn't have used such niceties. After all , "endurance" was meant to show what one might expect from the ship in the real world. Experience would show the pilot more accurately what he could expect, but he had to have some idea of what to expect initially.
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Old 8 June 2004, 09:12 AM   #6 (permalink)
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RPope:
Endurance is calculated on the fuel supply with the engine runnying at full power. All combat is flown at full power.( with some exceptions.)
Blue skies,
Dan-San
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Old 9 June 2004, 08:06 PM   #7 (permalink)
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Sure, combat is at full power, but stooging up and down the front waiting for someone to come up and play, you'd be at cruise speed.
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