Fokker D.VIIf calculations

[HagarTheHorrible]

I've been in touch with the chap who compiled all of the information at "aircraftinvestigation.info".  He has very kindly come back to me.  I haven't time to go through it just yet, but thought i would post his response, for your perusal -

 

From Bert Zalm,

 

"I like to discuss about the figures :-), because I also don't have all the information and deduct figures from limited data/sources

For my calculations I try to keep to calculate on common standard.

 

 

But for the engine performance I see on Wikipedia :

SE5a Powerplant: 1 × Hispano-Suiza 8 or Wolseley Viper water cooled V8 engine, 150 hp (110 kW)   110/150= 0.73333

SPAD S.XIII : Powerplant: 1 × Hispano-Suiza 8Ba, Bb or Bd Water cooled 8-cylinder vee-type, 150 kW (200 hp) = 0.75

 

So on Wikipedia the conversion from HP to KW is not consistent also ☹

In my calculations I have made adjustment now to converse HP to KW with ratio 0.7457 (and not with the German 0.7355 for PS), below extract from Wikipedia :

British horsepower ratings apparently differed. Postwar British tests put the rating of the BMW IIIa at 230 hp. This corresponds to British ratings of the Mercedes DIIIa engine being rated by the British as 180 hp (German rating of 170 hp) and the DIIIau at 200 hp (German-180 hp). This discrepancy may explain the significant difference in performance of the BMW IIIa equipped Fokker D.VIIF both against Mercedes powered D.VII's and their Allied opponents. The standard German Pferdstärke metric horsepower unit was expressed in the early 20th century as being a unit of almost exactly 735.5 watts, while the British unit for mechanical horsepower was based on the older 33,000 ft-lb/min figure, which translates to 745.7 watts instead. 

But the difference between 0.7457 and 0.7355 is making not to big difference in performace for the DVIIF.

 

For the performance calculations it is based on following information I find on Wikipedia and literature for the BMW IIIa engine :

Wikipedia / Fokker D.VII

1 × 137.95 kW (185 hp) BMW IIIa 6-cyl. water-cooled in-line piston engine (180 kW (240 hp) rating at low level, emergency only, risk of engine damage.)

Because the BMW IIIa was overcompressed, using full throttle at altitudes below 2,000 m (6,600 ft) risked premature detonation in the cylinders and damage to the engine. At low altitudes, full throttle could produce up to 179 kW (240 hp) for a short time.

 

Wikipedia / BMW IIIa :

. It enabled the engine, now dubbed BMW IIIa, to develop a constant 200 horsepower (150 kW) up to an altitude of 2000 meters – a decisive advantage over competitors' engines.

German and British horsepower ratings apparently differed. Postwar British tests put the rating of the BMW IIIa at 230 hp.

 

 

so 230/240 hp at low altitude gave premature detonation was for emergency only at low level, and I cannot use for climbing performance.

for calculation I use for the BMW IIIa : 

201 hp / 149.9 KW/ 203.8 PS at 1400 rpm constant power from sea level up to 2000m > full throttle at 2000m , above 2000m the engine performance will slowly drop due to the lower density of the air which now longer can be compensated by more opening the  "altitude throttle" . below formula gives the drop in performance with height for an piston engine :

 

 

 

for aircooled American radial engine value for c = 0.132

 

 

I attached information  for a supercharged engine, but compares to the over-compressed altitude engines of WWI in my opinion.

 

 

The figure of 185 hp, if for me unclear, is this the normal rating at low altitude ?? at what rpm ? for my calcultaions I don't use 185 hp, I calculate with 201 hp constant to 2000m,

185 hp would give even lower climbing performance

 

 

 

 

Also attached information regarding the thickness of an aerofoil influence of the maximum stall angle.

It is in German I hope you can understand :-)...

 

 

The thicker profile gives a more gentel/ slow  stall, a medium thick wing will have a more abrupt stall, so I think but I am not sure that a SE5a was more likely to a sudden/abrubt stall at great altitude, and  just  "fall out of the sky"  and that a DVII pilot would get more notice from the airplane behaviour for an apparent/aproaching stall, but I must say this is more a feeling then that I can prove..

 

 

The thinner wing probably  attributed to the SE5a having a higher max.speed of 203 km/u at 1000m  compared to the Fokker DVIIF 189 km/u at 1000m

 

 

 

I look forward to your opnion / reaction

 

 

 

Edited May 5, 2020 by HagarTheHorrible

[No.23_Starling]

I thought the Viper engine was 200hp?

[US63_SpadLivesMatter]

[HagarTheHorrible]

57 minutes ago, No.56_Waggaz said:

I thought the Viper engine was 200hp?

 

I think that is this  "110/150".   The 110KW is the 150hp and the 150KW is the 200hp, I assume.  I don't know if it should effect the "= 0.73333" figure ?

[76SQN-FatherTed]

7 minutes ago, HagarTheHorrible said:

 

I think that is this  "110/150".   The 110KW is the 150hp and the 150KW is the 200hp, I assume.  I don't know if it should effect the "= 0.73333" figure ?

He's basically saying that if you divide KW by hp you should get the same quotient whatever the numbers.

[NO.20_Krispy_Duck]

On 5/5/2020 at 10:34 AM, No.56_Waggaz said:

I thought the Viper engine was 200hp?

 

The knock on the original SE5 as it debuted was two-fold: that it wasn't as nimble as the Nieuport 17 and that the 150 Hispano Suiza left it somewhat underpowdered. The SE5a upgraded to the 200 Hispano Suiza but there were issues with the gearing mechanism on the motor (the Spad XIII also struggled early on with the geared Hispano Suiza, to the extent pilots were reluctant to give up their uprated Spad VIIs with the 180 hp direct drive Hispano Suiza). Eventually the 200 Viper was found as a solution to Hispano Suiza availability and the gearing issues were overcome.

 

To make things even more complicated, there was also the lesser-known SE5e which had a 180hp American Wright-Hispano engine. One of the more interesting aspects of the late war period was the prospect of the USAS moving to American-made SE5 variants that would have become available in 1919, and perhaps mixed with purchases of the prospective Nieuport-Delage 29.

[HagarTheHorrible]

Fokker VII, Lethal Weapon

[J5_Adam]

You've probably seen this before but it's a good one. In here he talks about the BMW IIIa as well as the Hispano Suiza 200HP   @US103_Baer @US93_Furlow @US93_Larner