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The Fokker DVII


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#361 Panthera

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Posted 22 March 2012 - 20:07

Bletchley and Dave Watts only provided original documents. How Kacey did provide more convincing source materials? He just calculated speed, etc (quite convising I might add). It is not source material at all tought…

I was talking about the engine power outputs, where Kacey relied purely on original source material for his argument, not the top speed of the aircraft where Kacey made the right approach of not trusting in the wildly contradicting original sources on that subject.
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#362 Panthera

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Posted 22 March 2012 - 20:10

And it is good that we also have britihs test and they only got ~186HP@1600rpm and sealevel (wiht its own carburettor) :)

But hold on, what fuel was used ? And was it even actually a D.IIIaü ? There were so many different versions of this engine that the British easily could've mixed it up, and according to Kacey it wouldn't have been the first time either.
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#363 MiG-77

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Posted 22 March 2012 - 20:11

I was talking about the engine power outputs, where Kacey relied purely on original source material for his argument, not the top speed of the aircraft where Kacey made the right approach of not trusting in the wildly contradicting original sources on that subject.

And we do have those original source materials. No "200hp mercedes"….
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#364 Panthera

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Posted 22 March 2012 - 20:13

177PS @ 1km and 1450 RPM, but that would be during a climb. In level flight at top speed RPM would be around 1550 RPM.

True, but as we are comparing HP ratings and engines almost never were rated in their max RPM. almost all engines could have had more HP ;)

It still doesn't explain how the British rated the regular D.IIIa at 180 hp, and the BMW IIIa at 232 hp.
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#365 MiG-77

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Posted 22 March 2012 - 20:14

But hold on, what fuel was used ? And was it even actually a D.IIIaü ? There were so many different versions of this engine that the British easily could've mixed it up, and according to Kacey it wouldn't have been the first time either.

They used their own fuel (which is better than german normal fuel, but not as resistant to detonation as fliegerbenzin). And yes it was DIIIau. Compression ratio and function of carburettor is quite clearly explained.
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#366 MiG-77

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Posted 22 March 2012 - 20:15

It still doesn't explain how the British rated the regular D.IIIa at 180 hp, and the BMW IIIa at 232 hp.

Why should it explain it? DIIIa could reach ~200hp@1700RPM and BMW could have +250HP depending how you measure it.
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#367 NewGuy_

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Posted 22 March 2012 - 20:18

Even the Goering account can be explained, without the DVIIf being faster than the 220 hp SPAD XIII or 235 hp SPAD XIII. Goering and the SPAD pilots are low to the ground, right? The DVII, according to French pilots, claiming to encounter DVIIs frequently, is at best, according to them, as fast as the 220 hp SPAD XIII and we would guess, but not know for a fact, slower than the 235 hp SPAD XIII. The DVIIf can out climb the SPAD XIII and has Camel like maneuverability, no? Your best defense against such attributes, as a SPAD pilot, is your ability to dive away, but you are low to the ground, so you cannot dive. If you are the SPAD pilots, are you in a hurry to catch Goering, at low altitude or sea level? No way, because Goering will just climb over you and go right on your tail, using his Camel like maneuverability and 220 hp SPAD speed performance. Still, where are Allied accounts of super fast, high altitude DVIIs, running down 235 hp SPAD XIIIs, in straight and level flight, at combat altitude, exempting engine trouble or other malfunction of the 220 hp or 235 hp SPAD XIII? :?
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Something something SPAD. Something something then dive away. 


#368 Panthera

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Posted 22 March 2012 - 20:19

I was talking about the engine power outputs, where Kacey relied purely on original source material for his argument, not the top speed of the aircraft where Kacey made the right approach of not trusting in the wildly contradicting original sources on that subject.

And we do have those original source materials. No "200hp mercedes"….

With use of Flieger Benzin ?

I'm asking because the British did rate the Merc D.IIIa at 180 hp, the aü at 200 hp and the BMWIIA at 232 hp, i.e. a lot higher than the Germans. And while I understand that the aü was using a different carburettor the fuel used would've been different as-well (Allied fuel).
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#369 Panthera

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Posted 22 March 2012 - 20:21

But hold on, what fuel was used ? And was it even actually a D.IIIaü ? There were so many different versions of this engine that the British easily could've mixed it up, and according to Kacey it wouldn't have been the first time either.

They used their own fuel (which is better than german normal fuel, but not as resistant to detonation as fliegerbenzin). And yes it was DIIIau. Compression ratio and function of carburettor is quite clearly explained.

In that case shouldn't it also be quite possible that the D.IIIaü was a 200 hp engine with use of Flieger Benzin ?
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#370 SYN_Vander

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Posted 22 March 2012 - 22:32

In any case, Mikael Carlson's Fokker DVII is powered by the Mercedes DIIIau or in his own words: "Engine is a Daimler High compression 200hp".

Hmm… no, Mikael Carlson's aircraft is fitted with the std. 160 hp D.IIIa as also listed on his own website.

That's odd, the quote came from an email he sent me!
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#371 hq_Jorri

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Posted 22 March 2012 - 23:12

Well, unless he measured it, he probably doesn't actually know how much power output his own engine has?
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#372 gavagai

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Posted 23 March 2012 - 03:37

How much you want to bet that Carlson didn't make his own website?
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#373 hq_Jorri

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Posted 23 March 2012 - 07:37

….something that Achim Engels could learn from ;)
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#374 MiG-77

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Posted 23 March 2012 - 12:14

Even the Goering account can be explained, without the DVIIf being faster than the 220 hp SPAD XIII or 235 hp SPAD XIII. Goering and the SPAD pilots are low to the ground, right? The DVII, according to French pilots, claiming to encounter DVIIs frequently, is at best, according to them, as fast as the 220 hp SPAD XIII and we would guess, but not know for a fact, slower than the 235 hp SPAD XIII. The DVIIf can out climb the SPAD XIII and has Camel like maneuverability, no? Your best defense against such attributes, as a SPAD pilot, is your ability to dive away, but you are low to the ground, so you cannot dive. If you are the SPAD pilots, are you in a hurry to catch Goering, at low altitude or sea level? No way, because Goering will just climb over you and go right on your tail, using his Camel like maneuverability and 220 hp SPAD speed performance. Still, where are Allied accounts of super fast, high altitude DVIIs, running down 235 hp SPAD XIIIs, in straight and level flight, at combat altitude, exempting engine trouble or other malfunction of the 220 hp or 235 hp SPAD XIII? :?

If we belileve Goering account that D.VIIF could outrun SPAD XIII (and given time of encounter, it most likely was with high comperesses HS) at low level, it most definately would outrun them even higher altitude. Now anecdotal accounts always are little questionable as all depends on circumstances (planes dont cruise at full speed and it takes time to accelerate to max speed). In dive SPAD XIII was superior so they could always "outrun" D.VII by diving.
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#375 MiG-77

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Posted 23 March 2012 - 12:19

With use of Flieger Benzin ?

From memory, fuel is not mentioned.

I'm asking because the British did rate the Merc D.IIIa at 180 hp, the aü at 200 hp and the BMWIIA at 232 hp, i.e. a lot higher than the Germans. And while I understand that the aü was using a different carburettor the fuel used would've been different as-well (Allied fuel).

Yes, but as their fuel was better than normal german one their test are good aswell (British fuel could run engines with 5,3 compression ratio wihtout problems). Also those test are very similar to germans test, so we have 2 original test that show only about ~185HP at sealevel. So either fliegerbenzin didnt have enought of adventage (because of small fuel jets RPM could not actually get as high) or they simply did not use it in D.VII (Flieger benzin was mainly reserved for BMW anyway).
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#376 MiG-77

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Posted 23 March 2012 - 12:21

In that case shouldn't it also be quite possible that the D.IIIaü was a 200 hp engine with use of Flieger Benzin ?

Not really, as even german test it had about 185HP at sealevel. If it would have benefit with flieger benzin that much, Im sure they would have used it in their tests. Limiting factor in DIIIau max sealevel power was its carburettor that was designed for high altitude.
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#377 Panthera

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Posted 24 March 2012 - 01:47

In any case, Mikael Carlson's Fokker DVII is powered by the Mercedes DIIIau or in his own words: "Engine is a Daimler High compression 200hp".

Hmm… no, Mikael Carlson's aircraft is fitted with the std. 160 hp D.IIIa as also listed on his own website.

That's odd, the quote came from an email he sent me!

Well in that case I'd trust that over the website, also it would explain the rather fast cruise speed of 176 km/h, which normally means running at 75% throttle, which in the case of a 200 hp Merc D.IIIau would be around 160 hp.
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#378 Panthera

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Posted 24 March 2012 - 02:00

In that case shouldn't it also be quite possible that the D.IIIaü was a 200 hp engine with use of Flieger Benzin ?

Not really, as even german test it had about 185HP at sealevel. If it would have benefit with flieger benzin that much, Im sure they would have used it in their tests. Limiting factor in DIIIau max sealevel power was its carburettor that was designed for high altitude.

Why would they necessarily have been using Flieger Benzin in that test MiG_77 ? Flieger Benzin was in very limited supply, Flug Benzin being the most commonly used fuel, and as such tests with Flug Benzin would've been necessary as-well in order to establish the performance of the aircraft with the fuel it would most likely be using 90% of the time.
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#379 MiG-77

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Posted 28 March 2012 - 18:57

Why would they necessarily have been using Flieger Benzin in that test MiG_77 ? Flieger Benzin was in very limited supply, Flug Benzin being the most commonly used fuel, and as such tests with Flug Benzin would've been necessary as-well in order to establish the performance of the aircraft with the fuel it would most likely be using 90% of the time.

Because as they were measuring its power it would be logical to use flieger benzin if it would have made noticable perfomance increase. As I said before, most limiting factor was carburettor, regardless of fuel used (british "200hp" test were done almost twice larger fuel jets than DIIIau own carburettor-> 250cc per min standard jet vs 450cc per min test jet).


EDIT: Now checked german DIIIau tests. Test were done with both "benzin" and "benzol". Power curves are almost identical from air density of 1,2kg/m3 (roughly 200m) to 0,7kg/m3 (roughly 5500m) after that benzol start to be better fuel. Power was measured at constant 1450RPM
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#380 Panthera

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Posted 29 March 2012 - 13:19

To me it seems most logical to test an engine with the fuel it will most likely be using in the field, and performance testing was required with use of Flug Benzin. So unless it is specifically mentioned that Flieger Benzin was used then we can't really be sure.

An interesting note is that tests with a D.IIIav engine revealed a ~15 hp increase in horsepower with use of Flieger Benzine, going from 203 PS to 217 PS.
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#381 MiG-77

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Posted 29 March 2012 - 14:05

To me it seems most logical to test an engine with the fuel it will most likely be using in the field, and performance testing was required with use of Flug Benzin. So unless it is specifically mentioned that Flieger Benzin was used then we can't really be sure.

It specifically says both benzin and benzol was tested. Benzol is specifically fuel that gives higher octane rating (IOW Flieger Benzin). -> It made no difference at 1450RPM at ground level.
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#382 Lieste

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Posted 29 March 2012 - 14:30

Which still says not very much about relative performance at 1600 rpm and a lighter loading, where the increased power, heat, and steeper pressure gradients may alter the detonation threshold a little..? Or not… but that test is still not conclusive.
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#383 MiG-77

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Posted 29 March 2012 - 14:43

Which still says not very much about relative performance at 1600 rpm and a lighter loading, where the increased power, heat, and steeper pressure gradients may alter the detonation threshold a little..? Or not… but that test is still not conclusive.

Yes, but british test say (they tested it at 1600RPM -> 186HP). German and British test are very close each other in HP ratings when you look britihs test with DIIIau own carburettor.
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#384 Panthera

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Posted 30 March 2012 - 14:29

To me it seems most logical to test an engine with the fuel it will most likely be using in the field, and performance testing was required with use of Flug Benzin. So unless it is specifically mentioned that Flieger Benzin was used then we can't really be sure.

It specifically says both benzin and benzol was tested. Benzol is specifically fuel that gives higher octane rating (IOW Flieger Benzin). -> It made no difference at 1450RPM at ground level.

Well Flieger Benzin is a mix, it's not just pure Benzol (Flieger Benzin featured ~60% Benzol), so unless the percentage of Benzol is listed then we still don't know for sure :) But I admit am beginning to lean more in your direction, the aü being a 180-185 PS engine.

Anyway if a speed of 176 km/h is achieved with around 150 PS (cruise), then another 30 PS could certainly result in a 195-200 km/h top speed and a very high climb rate.

The climb rate of the ingame D.VII corresponds to that of a 160 ps Merc D.III powered variant, taking 3 min 38 sec to 1 km and 7 min 40 sec to 2 km. The climb rate with the 180 PS Merc D.IIIaü would probably be closer to 3 min straight to 1 km and 6 min 20 sec to 2 km, as-well as supplying a ~200 km/h top speed.

The ingame D.VIIF seems spot on in climb performance, but too slow in top speed, where the real thing reportedly was capable of 200+ km/h, and as much as 225+ km/h with use of alt throttle.
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#385 MiG-77

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Posted 30 March 2012 - 21:03

Well Flieger Benzin is a mix, it's not just pure Benzol (Flieger Benzin featured ~60% Benzol), so unless the percentage of Benzol is listed then we still don't know for sure.

Yes I know that, but in that test I get feeling that "benzol" means actual flieger benzin, not pure benzol (altought in test they just mention fuels as "benzol" and "benzin"). Anyway that misses the point. Point was that Benzol is the fuel that give much better octane rating and resist detonation better -> should give better results if fuel would be the limiting factor.

The climb rate of the ingame D.VII corresponds to that of a 160 ps Merc D.III powered variant.

D.VII didnt have 160PS mercedes ever (in actual power) as DIIIa did produce more power than that. In name, all mercedes DIII engines were officially "160PS", even DIIIau.
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#386 Panthera

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Posted 31 March 2012 - 03:28

Yes I know that, but in that test I get feeling that "benzol" means actual flieger benzin, not pure benzol (altought in test they just mention fuels as "benzol" and "benzin"). Anyway that misses the point. Point was that Benzol is the fuel that give much better octane rating and resist detonation better -> should give better results if fuel would be the limiting factor.

Well it might, and it might not, seeing as there will be an optimum mix, which is where it gets confusing. Mr. Kacey for example puts the D.IIIaü at around 200 PS at SL when using Flieger Benzin.

I just find it abit strange if the higher octane fuel didn't have any effect on the D.IIIaü's performance when it so significantly affected that of all the other engines.

D.VII didnt have 160PS mercedes ever (in actual power) as DIIIa did produce more power than that. In name, all mercedes DIII engines were officially "160PS", even DIIIau.

That is true, in actual power the "160 PS" D.IIIa put out about 170 PS, which just makes the climb rate figures even stranger. And if I remember correctly the top speed of the first D.VII's was around 185 km/h, where'as the speed of the D.VII's with the over-compressed merc engine (D.IIIaü) was reported as around 200 km/h.
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#387 MiG-77

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Posted 31 March 2012 - 07:43

Well it might, and it might not, seeing as there will be an optimum mix, which is where it gets confusing. Mr. Kacey for example puts the D.IIIaü at around 200 PS at SL when using Flieger Benzin.

But point is that benzol, even its pure form, has much better detotanion resist that benzin, but it didnt give better perfomance for DIIIau (at sealevel). Kacey figures are only calculations and they are not in line with historical test reports. Altough I respect Kacey calculations, I trust more actual test reports.

I just find it abit strange if the higher octane fuel didn't have any effect on the D.IIIaü's performance when it so significantly affected that of all the other engines.

Higher octane fuel didnt have any effect as carburettor limited max RPM engine could achieve -> With DIIIau carburettor, benzin and benzol could achieve same max RPM without detonation. Main throttle altitude position could not be used at sealevel as it leaned mixture too much and engine simply stopped if the throttle was fully opened.
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