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Heck

Made a couple of changes to my Fokker DVII and DVIIF

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I gave the Fokker DVII the same power as an Albatros DV, SLPowerDry=130497.5. For some reason the DVII's original power was about 119000.0, which was way to low. She flies much better now. About the same performance as an Albatros (same engine), but more handy.

 

I also inserted a minus sign in front of the cnb value for the fuselage of both the DVII and DVIIf. It seemed to be the only aircraft where the value was positive. Was Cnb=0.0016, now Cnb=-0.0016 This cured the excessive yaw both the planes displayed on take off. If you extract the data ini's and make these changes, I think you'll find both fly much better. I think so anyway.

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weird numbers on TKs originals... :dntknw:

from the pre-addon

D.Va SLPowerDry=119312.0

D.VII SLPowerDry=119312.0

D.VIIf SLPowerDry=137954.5

 

maybe its a balance thing... but those aircraft never had a 160hp engine (even the alb D.III didn't i think)

and why they would be lower now after the addon....?

 

from a few sources...

 

all rated at 1400Rpm (german rating system) most were capable of another 200ish rpm/40-50ish Hp for shortish periods/or at certain (high) altitudes

 

Mercedes DIII = 160hp = 119312 watt

Mercedes DIIIa = 170hp = 126769 watt....Albatros D.III and D.V (the engine was upgraded to DIIIaü spec when possible)

Mercedes DIIIaü = 180hp = 134226 watt ....Most Fokker D.VII and most Albatros D.Va

Mercedes DIIIaüv = 200hp = 149140 watt ....Very late production Fokker D.VII

BMW IIIa = 185hp = 137954.5 watt ...Fokker D.VIIf

 

BMW was lighter, had better high Alt performance, and better +1400rpm power (1600 rpm = 254hp)

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Guest Charles

I'm pretty sure the first Fokker D.VIIs did have the 160hp Mercedes DIII engine, which would make TK's figure of 119312 watts correct. Later production models had the BMW IIIa 185hp, which is the 137954.5 figure for the D.VIIF

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Albatros D.I/II/III used the 160 hp Mercedes D.III engine. The D.V and D.Va's began incorporating the Mercedes D.IIIa after March 1918.

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I would have to respectfully (and gently) disagree with you Charles

 

The engine was certainly (confusingly) called the Mercedes 160 hp (that according to a datafile is the Mercedes class name)

But was continually improved through out its life (life starting from midish 1916 with the Albatross D.I)

 

I don’t think the D.VII ever saw front line service with the old DIII engine (nor the D.V or D.Va or the D.III that stuck around for long)

maybe in prototype form… I only have references (not that many :blush: ) referring to the latter types of engines in D.VII’s

 

As an aside

The Albatross D.III Oef was built till the end of the war by the Austro-Hungarians

Powered by Austro-Daimler engines (heavier than the Mercedes)

I don’t know if the Austro-Hungarians rated their engines at 1400rpm like the Germans (and the Mercedes engines are all capable of more then 1400rpm)

 

Depending on the D.III Oef series number…

Austro-Daimler

185 hp = 137954.5 watts

200 hp = 149140 watts

225 hp = 167782.5 watts

 

@ Tex

Yes of course, and I haven’t done any tests on the D.VII

But there are many more subtle ways IMHO (and areas that are greyer in terms of published info) of adjusting those performance parametres (CD0, PropEfficiency etc) than depriving it of at least 12% of its power

And considering engine power is used when estimating aerodynamic coefficients when published material is scarce, the whole plane could be out of whack…

 

Whether it’s worth it if the D.VII is performing in balance with the other craft is another matter :wink:

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According to data from Fokker, source Militair Luchtvaart Museum Soesterberg (Dutch Air Force Museum) which also has one of the surviving D VII's in the collection, the early D VII's had the Mercedes DIIIa, later models had the BMW engine.

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Guest Charles

Well, you live and learn, thanks, P10ppy.

 

I have a copy of Jane's "Fighting Aircraft of WWI" (2001 release, but based on the 1919 edition), and it says that the Fokker D.VII had a "Mercedes 160 h.p" engine, so it looks like a long-standing misconception. The section on engines at the back of the book mentions Mercedes engines of 100, 160, 180, 200, 220, 230 and 260 hp, but says of BMW engines only that they "appear to follow general Mercedes design...", which is not very informative.

 

The discussion at the Aerodrome looks informed, so it looks like 180hp for the D.VII, and 185 hp with the lighter BMW engine for the D.VIIF.

 

Uprating the engine power in the sim is easy, although the mass and inertia figures of the aircraft should also be increased, as well as the mass fraction of the nose.

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Anybody else terribly confused? :crazy:

 

Perhaps if a consensus is reached the definitive SLPowerDry (Watt) values and engine mass parameters for the INIs can be posted?

Very interesting thread...

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Anybody else terribly confused? :crazy:

 

Perhaps if a consensus is reached the definitive SLPowerDry (Watt) values and engine mass parameters for the INIs can be posted?

Very interesting thread...

 

I don't think there is any definitive value, Bandy. I'm really just adjusting things to suit my own personal experience from sources I've read and things I've seen. The only reason I posted this here was because I saw another member say that he thought the Fokker DVII was rather sluggish. I had to agree with him, because the behavior that I saw in the sim didn't match what I saw years ago at Old Rhinebeck Aerodrome where they were flying an original rebuilt Fokker with an overcompressed Mercedes of 180hpr. So I changed it, and posted it here in case other members here found it useful.

 

The Germans at this time were experimenting with different ways to wring more horsepower out of their well tested Mercedes 6 cylinder inline. One of the ways was to overcompress the engine by fitting oversized pistons. They managed to get between 10-20 more horsepower out of the straight six they were using, but there was a cost. The engines had a shorter life, and couldn't be run at full throttle at low altitude, because you'd overheat them and blow them up. I read once that American pilots testing a Roland DVIb nearly did that, because they didn't know you weren't supposed to run the engine at full throttle low down, and the German pilots who turned it over after the Armistice didn't tell them. :biggrin: The engines were in fact fitted with a compression release valve, because you couldn't swing the prop to start them unless you released the compression.

 

The same lack of definition applied to airframes. According to James Norman Hall and Charles Woodruff, a French pilot flying in 1917 wanted to be assigned a Spad/Spad, Hisso/Hisso, meaning a Spad 7 or 13 airframe built by Spad, and a Hispano Suiza built by Hisso, because the subcontractor's versions of both engines and airframes were not well trusted by the pilots. Variation was widespread, because a subcontrator was handed a copy of drawings to work from, and were on their own after that. Some were good, some not so good. Airframe construction especially was more of an art form than an industrial process. If you can find someone who still makes complex wooden furniture by hand, watch them some time and you'll see what I mean. The guy who built your piano before the war was often the guy building your airframe during the war. :biggrin:

 

I know this probably makes this more muddy, but that's my point. The world of WW1 aviation was a very muddy place indeed, and anyone who thinks they know exactly how a Fokker DVII flew is really only kidding themselves, because any German pilot of the time would know that his Fokker wouldn't behave or handle like Von Bratwurst's, two places down the flight line. If something in this sim doesn't suit you, experiment with it and change it, that's the true beauty of TK's sims, and makes it truly the best engine to simulate the muddy, muddy skies of WW1. I hope I haven't offended anyone with this spiel, it's just the ravings of a madman who's read way to much over the years to believe that he knows anything at all for certain.

 

And you think you're confused.... :rofl:

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Agrees with Heck

 

Add to all of this that the Germans certainly did fly at above 1400 Rpm (especially in combat) and it gets hard to model indeed (no "overpower" parametres that I'm aware of)

 

A brief speed test of the stock addon D.VII (speed was never its strong point tho)

Seems to indicate that it could use more power imho

Climb seemed weak too but I never tested it in any rational way… so I may be mistaken:blink:

The D.VII's big advantage was its cantilever wing with the thick high lift airfoil section…and its relatively viceless handling

I haven't flown the Addon anywhere near enough to make balance judgments

But the D.VII (both) should have the best sustained climb performance of all the stock Aircraft and be good at low speed maneuvers IMHO

 

note: ive seen many differing performance figures for the D.VII

Alt------KIAS----KTAS----KPH-IAS--KPH-TAS-----D.VII-"RL"----D.VIIf-"RL"-
sl-------99.2----99.5----183.7----184.274--------185----------205----------
500------98.2----101-----181.8----187.052----------------------------------
1000-----95.5----100.5---176.8----186.126----------------------------------
2000-----87.5----97.2----162.05---180.0144-------183----------200----------
3000-----80.2----93.5----148.53---173.162----------------------------------

sorry about the horrible table

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hello

 

from some book

british test D.IIIa mercedes at 180 hp

D.IIIau mercedes at 200 hp

D.III BMW at 185 hp

 

but for me the auther advantage of BMW it was lighter so D.VII weight 680 with it and 700 with mercedes

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