Diiiau engine performance

[No.23_Starling]

All, does anyone have a link to any studies on the differences between the 1917 diiia engine and the 1918 overcompressed version? I’m curious to better understand what engine performance we have in game now (in game tests vs engineering data) - most ppl seem to think we have the 1917 model. Also, what difference would the upgrade make to the merc birds in game right now? Seems to me that most differences would be at higher altitude where the compression would help with thinner air.

PS it would be great if someone has already performed the kind of testing Baer ran on the SPAD XIII to show that the in-game engine performance matches the 200hp version rather than the stated 220hp, with clear comparative tables and sources quoted.

[J99_Sizzlorr]

Edited May 22, 2022 by J99_Sizzlorr

[SYN_Vander]

And the engine we have now in the Albatros DVa and Fokker DVII is the 180hp variant? I looked all this up for RoF, but that was a long time ago....  

Edited May 22, 2022 by SYN_Vander

[J99_Sizzlorr]

Since there is so much confusion about the engine and its variants, I wrote some things together to get a better picture of the situation

 

 

D.III           

Introduced late 1914
160hp
separate cylinders
rear oil pickup and sump
water pump mid height on rear accessory stack
compression: 4.5:1

 

 

D.IIIa (ingame in fighters)

An up-graded D.III introduced in 1917 rated at 170 hp (British rating 180 h.p.)

Introduced June 1917
170hp
separate cylinders
rear oil pickup and sump
water pump at bottom of rear accessory stack
compression: 4.64:1

 

D.IIIaü (ingame but only in the Halberstadt Cl.II 200 h.p.)

An unofficial designation, (ü for über), for D.IIIa engines with domed pistons, operating "over-compressed", (at a higher compression ratio). These engines were not able to operate at full throttle at sea level, utilising a self compensating carburettor. 180/200 hp

Introduced late 1917 early 1918
200hp high altitude version (according to British standards)
separate cylinders
rear oil pickup and sump
water pump at bottom of rear accessory stack
new carburation
new fuel blend
compression: 5.73:1

The aü model, which included upgraded D.III and D.IIIa engine blocks, was the most prolific German fighter engine of 1918 and designed into most fighter designs from late 1917 on. This included most of the entries in the First Fighter Competition at Adlershof in January 1918, notably the famed Fokker D.VII.

Confusingly, the "ü" was not an official part of the name. This leads to a number of problems in various references, which often confuse the IIIa with the IIIaü, listing the former as a 180 hp engine.

 

D.IIIav/ D.IIIavü

D.IIIa engines with the domed pistons made from Aluminium alloy giving the higher compression ratio as well as a higher operating rpm (1600 rpm) due to the weight lost and thus more power. 200 hp (200-217 hp)

Introduced in Oktober 1918

It is unclear if any av's saw service use. The increased use of Benzol in German aviation fuel may have helped this final upgrade of power, its higher octane rating being better suited for the higher compression ratio.

 

 

The D.III line of engines would find themselves eclipsed in performance by the BMW IIIa of 185 and then 200 hp (British rated it at 230HP) in 1918, however, the small number of BMW's produced ensured that the Mercedes D.III series would be the primary German fighter engine up to the last month or two of the war and it would still be seen in very large numbers even at the end. At the end of the war the D.IIIaü would still be the numerically predominant German fighter engine. As a result, the Fokker D.VII's (those not equipped with BMW IIIa's) and the Pfalz D.XII's would be engine-limited in performance (as opposed to "airframe-limited") and yet would still be formidable adversaries to their Allied counterparts. The D.IIIaü was considered the optimum engine for the Roland D.VI, Pfalz D.IIIa, and Albatros D.Va fighters, whose airframes were of an earlier, "all-wood" generation in design.

           

 

Edited May 22, 2022 by J99_Sizzlorr

[SYN_Vander]

4 minutes ago, J99_Sizzlorr said:

Since there is so much confusion about the engine and its variants, I wrote some things together to get a better picture of the situation

 

 

D.III

           

Introduced late 1914
160hp
separate cylinders
rear oil pickup and sump
water pump mid height on rear accessory stack
compression: 4.5:1

 

 

D.IIIa (ingame in fighters)

An up-graded D.III introduced in 1917 rated at 170 hp (British rating 180 h.p.)

Introduced June 1917
170hp
separate cylinders
rear oil pickup and sump
water pump at bottom of rear accessory stack
compression: 4.64:1

 

D.IIIaü (ingame but only in the Halberstadt Cl.II 200 h.p.)

An unofficial designation, (ü for über), for D.IIIa engines with domed pistons, operating "over-compressed", (at a higher compression ratio). These engines were not able to operate at full throttle at sea level, utilising a self compensating carburettor. 180/200 hp

Introduced late 1917 early 1918
200hp high altitude version (according to British standards)
separate cylinders
rear oil pickup and sump
water pump at bottom of rear accessory stack
new carburation
new fuel blend
compression: 5.73:1

The aü model, which included upgraded D.III and D.IIIa engine blocks, was the most prolific German fighter engine of 1918 and designed into most fighter designs from late 1917 on. This included most of the entries in the First Fighter Competition at Adlershof in January 1918, notably the famed Fokker D.VII.

Confusingly, the "ü" was not an official part of the name. This leads to a number of problems in various references, which often confuse the IIIa with the IIIaü, listing the former as a 180 hp engine.

 

D.IIIav/ D.IIIavü

 

D.IIIa engines with the domed pistons made from Aluminium alloy giving the higher compression ratio as well as a higher operating rpm (1600 rpm) due to the weight lost and thus more power. 200 hp (200-217 hp)

Introduced in Oktober 1918

It is unclear if any av's saw service use. The increased use of Benzol in German aviation fuel may have helped this final upgrade of power, its higher octane rating being better suited for the higher compression ratio.

 

 

The D.III line of engines would find themselves eclipsed in performance by the BMW IIIa of 185 and then 200 hp (British rated it at 230HP) in 1918, however, the small number of BMW's produced ensured that the Mercedes D.III series would be the primary German fighter engine up to the last month or two of the war and it would still be seen in very large numbers even at the end. At the end of the war the D.IIIaü would still be the numerically predominant German fighter engine. As a result, the Fokker D.VII's (those not equipped with BMW IIIa's) and the Pfalz D.XII's would be engine-limited in performance (as opposed to "airframe-limited") and yet would still be formidable adversaries to their Allied counterparts. The D.IIIaü was considered the optimum engine for the Roland D.VI, Pfalz D.IIIa, and Albatros D.Va fighters, whose airframes were of an earlier, "all-wood" generation in design.

           

 

 

Thanks! Yes, I was referring to the British rating of 180hp as in the test report.

So indeed the Albatros DVa and Fokker DVII we have in the game now are very strange creatures for 1918...

[No.23_Starling]

3 hours ago, J99_Sizzlorr said:

Awesome, thank you. 
 

How would this translate into speed and climb performance for say the Dva at various altitudes?

 

Probably most importantly, how would this impact speed and climb for the DVII at different heights?

 

Any ideas?

 

The DVII vanilla is crying out for a boost. It would also mean we could reduce the DVIIF count in servers to make up for the poorer engine performance. I also want to see what the 1918 Dvau vs Camel match up is like…

[SYN_Vander]

1 hour ago, US103_Rummell said:

Awesome, thank you. 
 

How would this translate into speed and climb performance for say the Dva at various altitudes?

 

Probably most importantly, how would this impact speed and climb for the DVII at different heights?

 

Any ideas?

 

The DVII vanilla is crying out for a boost. It would also mean we could reduce the DVIIF count in servers to make up for the poorer engine performance. I also want to see what the 1918 Dvau vs Camel match up is like…

 

Giving the Fokker DVII a DIIIau engine option is a no brainer for me. It will give it a little climb and speed boost, but not anything like the BMW.

 

For the Albatros DVa there is more at play. I find the overall maneuverability currently a bit suspect when I look at pilot assessments, so I wonder what we will end up with. Maybe it just needs to lower the roll rate a bit :

https://docs.google.com/spreadsheets/d/1N3uVPKS38BwZ4hufXgSuekn26NiPytZeMAshIqXAflY/edit#gid=0

 

 

Edited May 22, 2022 by SYN_Vander

[BMA_Hellbender]

5 hours ago, J99_Sizzlorr said:

D.III           

Introduced late 1914
160hp
separate cylinders
rear oil pickup and sump
water pump mid height on rear accessory stack
compression: 4.5:1

 

D.IIIa (ingame in fighters)

An up-graded D.III introduced in 1917 rated at 170 hp (British rating 180 h.p.)

Introduced June 1917
170hp
separate cylinders
rear oil pickup and sump
water pump at bottom of rear accessory stack
compression: 4.64:1

 

D.IIIaü (ingame but only in the Halberstadt Cl.II 200 h.p.)

An unofficial designation, (ü for über), for D.IIIa engines with domed pistons, operating "over-compressed", (at a higher compression ratio). These engines were not able to operate at full throttle at sea level, utilising a self compensating carburettor. 180/200 hp

Introduced late 1917 early 1918
200hp high altitude version (according to British standards)
separate cylinders
rear oil pickup and sump
water pump at bottom of rear accessory stack
new carburation
new fuel blend
compression: 5.73:1

The aü model, which included upgraded D.III and D.IIIa engine blocks, was the most prolific German fighter engine of 1918 and designed into most fighter designs from late 1917 on. This included most of the entries in the First Fighter Competition at Adlershof in January 1918, notably the famed Fokker D.VII.

Confusingly, the "ü" was not an official part of the name. This leads to a number of problems in various references, which often confuse the IIIa with the IIIaü, listing the former as a 180 hp engine.

 

 

2 hours ago, SYN_Vander said:

 

Giving the Fokker DVII a DIIIau engine option is a no brainer for me. It will give it a little climb and speed boost, but not anything like the BMW.

 

For the Albatros DVa there is more at play. I find the overall maneuverability currently a bit suspect when I look at pilot assessments, so I wonder what we will end up with. Maybe it just needs to lower the roll rate a bit :

https://docs.google.com/spreadsheets/d/1N3uVPKS38BwZ4hufXgSuekn26NiPytZeMAshIqXAflY/edit#gid=0

 

 

 

 

Here we go again, for no one in particular:

 

 

The early Fokker D.VII flew at Adlershof in January 1918 with a 160hp D.III, since all the 170/180hp D.IIIa(ü) were in use on production Albatros D.Va and Pfalz D.IIIa scouts. With these engines all of these machines had a top speed of around 180-185km/h at sea level, give or take. The Fokker D.VII reached a few squadrons in April 1918, still equipped with that same 160hp D.III, until Anthony Fokker could get his hands on 170/180hp D.IIIa(ü). Also of note that the early Fokker-built Fokker D.VII was of shoddy workmanship, until Albatros Flugzeugwerke in Johannisthal started building them.

 

The main production Fokker D.VII which reached Jastas around May (tragically after MvR's death) was equipped with the 170/180hp D.IIIa(ü). Top speed at sea level... 200km/h? It's wrong to think that the overcompressed D.IIIaü was somehow faster at sea level. Yes there would have been rickety-tickety-clink-clank (that's a technical term) of some sort happening due to detonation and eventual seizure, which would not have been the case at full throttle on a non-overcompressed D.IIIa. Still, at full throttle at sea level top speed would have been the same with both engines, simply not permitted/sustainable with the D.IIIaü. Speed drop off at altitude would have been slower on the D.IIIaü obviously, and at around 1500-2000m at full throttle is where the D.IIIaü was beginning to shine.

 

Both the Albatros D.Va and Pfalz D.IIIa we have had the 170/180hp D.IIIa(ü) from the very start. Again: top speed around 180-185km/h at sea level. Here's where we indeed run into problems, as @SYN_Vanderpoints out: these planes were trucks. They were heavy on the controls, slow to roll, "stalled sharply and spun vigorously". Their FM in the sim is about as accurate as that of the Nieuport 28, but in a positive way.

 

 

So if the devs ever wish to fix the game, they could do this:

 

• Same top speed for the Halberstadt CL.II and CL.II 200hp at sea level (175km/h sounds fine) with a slower drop-off in speed for the 200hp at altitude
   
• Give us the Fokker D.VII early with the 160hp Mercedes D.III engine (same as the Albatros D.II), a top speed of 180-185km/h ASL (current vanilla D.VII has around 190km/h) and weaker wings
   
• Give us both the Fokker D.VII and D.VII 200hp. Both have a top speed of 200km/h at sea level, only the 200hp risks detonation/seizure there at full throttle but maintains more power at altitude. It's a trade-off.
   
• Completely redo the Albatros FMs. All of them, including the D.II and D.III. Speak to the people at Old Rhinebeck, the WW1 Aviation Heritage Trust and the Vintage Aviator. I'm headed to New Zealand next year, but otherwise I've spoken to all of them in person and they all agree: it flies like a truck and stalls sharply, not at all what we have in the sim. When the FM is redone give them the same treatment as the Fokker D.VII / D.VII 200hp with the low altitude/high altitude trade-off split.
   
• Same for the Pfalz D.IIIa, redo the FM first and then same treatment as the Fokker D.VII.
   
• Fix that janky rudder in a dive on the Pfalz D.XII and again give it the same treatment as the Fokker D.VII. Current Pfalz D.XII can stay as Pfalz D.XIIf.

 

 

 

Edited May 22, 2022 by Hellbender

[J99_Sizzlorr]

2 hours ago, Hellbender said:

 

 

 

Here we go again, for no one in particular:

 

 

The early Fokker D.VII flew at Adlershof in January 1918 with a 160hp D.III, since all the 170/180hp D.IIIa(ü) were in use on production Albatros D.Va and Pfalz D.IIIa scouts. With these engines all of these machines had a top speed of around 180-185km/h at sea level, give or take. The Fokker D.VII reached a few squadrons in April 1918, still equipped with that same 160hp D.III, until Anthony Fokker could get his hands on 170/180hp D.IIIa(ü). Also of note that the early Fokker-built Fokker D.VII was of shoddy workmanship, until Albatros Flugzeugwerke in Johannisthal started building them.

 

The main production Fokker D.VII which reached Jastas around May (tragically after MvR's death) was equipped with the 170/180hp D.IIIa(ü). Top speed at sea level... 200km/h? It's wrong to think that the overcompressed D.IIIaü was somehow faster at sea level. Yes there would have been rickety-tickety-clink-clank (that's a technical term) of some sort happening due to detonation and eventual seizure, which would not have been the case at full throttle on a non-overcompressed D.IIIa. Still, at full throttle at sea level top speed would have been the same with both engines, simply not permitted/sustainable with the D.IIIaü. Speed drop off at altitude would have been slower on the D.IIIaü obviously, and at around 1500-2000m at full throttle is where the D.IIIaü was beginning to shine.

 

Both the Albatros D.Va and Pfalz D.IIIa we have had the 170/180hp D.IIIa(ü) from the very start. Again: top speed around 180-185km/h at sea level. Here's where we indeed run into problems, as @SYN_Vanderpoints out: these planes were trucks. They were heavy on the controls, slow to roll, "stalled sharply and spun vigorously". Their FM in the sim is about as accurate as that of the Nieuport 28, but in a positive way.

 

 

So if the devs ever wish to fix the game, they could do this:

 

• Same top speed for the Halberstadt CL.II and CL.II 200hp at sea level (175km/h sounds fine) with a slower drop-off in speed for the 200hp at altitude
   
• Give us the Fokker D.VII early with the 160hp Mercedes D.III engine (same as the Albatros D.II), a top speed of 180-185km/h ASL (current vanilla D.VII has around 190km/h) and weaker wings
   
• Give us both the Fokker D.VII and D.VII 200hp. Both have a top speed of 200km/h at sea level, only the 200hp risks detonation/seizure there at full throttle but maintains more power at altitude. It's a trade-off.
   
• Completely redo the Albatros FMs. All of them, including the D.II and D.III. Speak to the people at Old Rhinebeck, the WW1 Aviation Heritage Trust and the Vintage Aviator. I'm headed to New Zealand next year, but otherwise I've spoken to all of them in person and they all agree: it flies like a truck and stalls sharply, not at all what we have in the sim. When the FM is redone give them the same treatment as the Fokker D.VII / D.VII 200hp with the low altitude/high altitude trade-off split.
   
• Same for the Pfalz D.IIIa, redo the FM first and then same treatment as the Fokker D.VII.
   
• Fix that janky rudder in a dive on the Pfalz D.XII and again give it the same treatment as the Fokker D.VII. Current Pfalz D.XII can stay as Pfalz D.XIIf.

 

 

 

The early Fokker D.VII had both engines installed at Adlershof the D.III and the D.IIIaü the prototype just had a different name and an enlarged vertical tail. It was designated the Fokker V18 

[HagarTheHorrible]

Not to belabour a point, but the Mercedes IIIa 170/180 engines are power rated (as per Sizzlorr’s cutting) at 1400rpm.  When was the last time anyone took to the skies with the engine going that slow ?  The Mercedes engine normally runs at closer to 1500 rpm (the Pflaz DIIIa runs at 1540) and if memory serves, doesn’t drop much below it’s rating at any point in it’s operational regime.  What we have is essentially, an engine that is in near permanent boost, without any of the limitations, such as excess heat or engine damage.  Compare that to the Allied HS engines, none of which ‘boost’ and the Viper, which can only attain it’s engine rating in a dive, not to mention that it is often operating at a power disadvantage for most of it’s flight regime, even compared to Mercedes IIIa engine when operating at its rated rpm and power, let alone it’s boost power.

 

The whole engine thing is actually a little bit vexed and raises as many questions as new engines might answer. Where real, historic, top speeds achieved at rated rpm or boost rpm ?  How long could a boost be maintained ?  What was the ‘actual’ cruise speed at the rated rpm ?

[J5_Adam]

When Mikael Carlson was asked about his 200HP DIIIaü in his DVII, the discussion was something like:

 

"Why do you have a 'stop' on your throttle?"

"Because I don't go to altitudes where anything past that point is effective. Usually only to about 3000 feet."

"What would happen if you took the stop off and and used full power on the lever?"

"The engine would of course die due to an over lean mixture."

 

I don't believe there's be a "rickety-tickety-clink-clank" like Bender said. I think there would be a rather quick drop in power and then seizure as things heat up way too much

Edited May 22, 2022 by J5_Adam

[Holtzauge]

Another reason Mikael Carlson does not take out all he can from these engines is that he does not need to: There is a "160 PS" marking on one of the throttle rods (for the Siemens Halske Sh.IIIa in his Plfalz D.VIII) with a stop he has set up right now in order not to overtax the engine. In his Fokker D.VII there is a small wood stop in the throttle lever guide which would be easy to remove. If you look at the various videos on YouTube you can see that 160 hp is plenty for aerobatics as well. I had the good fortune to watch him putting his Fokker D.VII through its paces and it did not look like he was short on power to me. Running these engines at a fraction of what they are capable off to mollycoddle them seems like a good idea to me: After all, there are probably not that many old WW1 aero-engines left hidden away in old barns to be discovered these days are there?

[BMA_Hellbender]

13 hours ago, Holtzauge said:

Another reason Mikael Carlson does not take out all he can from these engines is that he does not need to: There is a "160 PS" marking on one of the throttle rods (for the Siemens Halske Sh.IIIa in his Plfalz D.VIII) with a stop he has set up right now in order not to overtax the engine. In his Fokker D.VII there is a small wood stop in the throttle lever guide which would be easy to remove. If you look at the various videos on YouTube you can see that 160 hp is plenty for aerobatics as well. I had the good fortune to watch him putting his Fokker D.VII through its paces and it did not look like he was short on power to me. Running these engines at a fraction of what they are capable off to mollycoddle them seems like a good idea to me: After all, there are probably not that many old WW1 aero-engines left hidden away in old barns to be discovered these days are there?

 

In multiplayer if going full throttle required an offering of blood to some unholy god and guaranteed eternal damnation, the only question would be which blood type gives the best performance.

[Holtzauge]

15 hours ago, Hellbender said:

 

In multiplayer if going full throttle required an offering of blood to some unholy god and guaranteed eternal damnation, the only question would be which blood type gives the best performance.

 

For sure! Also IRL I imagined they firewalled their throttles quite often (IIRC Göring talked about running the Fokker D.VIIF with all throttles wide open at SL for extended periods of time with no ill effects). After all, better to roll the dice with the engine than to die from "acute" lead poisoning.........

[Chill31]

On 5/22/2022 at 11:27 AM, Hellbender said:

• Completely redo the Albatros FMs. All of them, including the D.II and D.III. Speak to the people at Old Rhinebeck, the WW1 Aviation Heritage Trust and the Vintage Aviator. I'm headed to New Zealand next year, but otherwise I've spoken to all of them in person and they all agree: it flies like a truck and stalls sharply, not at all what we have in the sim. When the FM is redone give them the same treatment as the Fokker D.VII / D.VII 200hp with the low altitude/high altitude trade-off split.

 

The sharp stall...it isn't what you imagine.  It doesn't break off into wild spinning gyrations.  My recent Camel flight was enlightening, and I should have a video up soon along with a write up of my experience.  Now if I could just get my hands on an Alby...

[J99_Sizzlorr]

On 5/25/2022 at 4:03 AM, Chill31 said:

 

The sharp stall...it isn't what you imagine.  It doesn't break off into wild spinning gyrations.  My recent Camel flight was enlightening, and I should have a video up soon along with a write up of my experience.  Now if I could just get my hands on an Alby...

Maybe ask Kermit he has one...

 

 

Edited May 27, 2022 by J99_Sizzlorr

[Sgt_Joch]

Another point to remember is that all airplanes used propeller with a fixed pitch which has the same effect as basically running an engine with only one speed. The props, depending on pitch, worked best at a certain RPM, say 1300 rpm for example. At that point, it did not matter if the engine did, theoretically, develop its best HP at 1600 RPM, running it faster than the prop speed of 1300 RPM just wasted fuel without producing much more speed.

 

Prop pitch could be tweaked to produce more terminal speed or greater acceleration. Pilots generally aimed for the pitch that was most useful in combat, a compromise between decent speed and enough torque to maneuver easily in a dogfight.

 

Usually the HP rating you see for WW1 ACs are for the engine/prop combination, I.e. Mercedes DIIIa 180@1400 RPM.

 

Now on the issue of speeds, anyone who has tried to research this, especially German engines/aircraft, knows that there is too little data to make definitive judgment. Almost every German test has been lost. Those that remain all have issues one way or another. The most complete tests are allied tests of German aircraft. So called “anecdotal” evidence based on pilot experiences is all over the map, etc, etc, etc. The Devs made a best guess based on what available data there is and other than some minor quibbles, I don’t see any mistakes.

 

Now on the Alb. DV, performance may seem on the low side, but it was obsolescent by the spring of 1918. Let’s not forget that MvR himself enthusiastically picked the DVII as the replacement at the feb. 18 tests and he personally chose to go into combat with a DR1. The DV with the 160 hp DIIIa was too underpowered for its weight and I have not seen any compelling evidence that it was ever produced with the DIIIau engine.

 

Now, there are mistakes in the engine/AC matchup, for example we are missing the DVII with the DIIIau engine which most DVII would have been equipped with from June-July. Getting that engine combo would boost performance.

Edited May 29, 2022 by Sgt_Joch

[J2_Trupobaw]

Good summary, Joch, except...

 

1. The Entente tests, while most complete, describe captured planes (with months of battlefield use before they were forced down behind the lines). They are not 1:1 comparable with surviving tests of factory new machines (which is what Entente crates performance is based on).

 

2. From April 1918 on, every Mercedes D.III / Mercedes D.IIIa taken to Flugpark for regular overhaul was being upgraded to D.IIIau. While no D.Va was produced with this engine, by the July/August the D.Vas (and D.IIIs, and D.IIIas) still in service had been re-equipped with D.IIIaus - there were no untiuched D.IIIas left. Also, D.IIIau was not an official designation, just most up to date variant of D.III.

Edited May 29, 2022 by J2_Trupobaw

[HagarTheHorrible]

22 hours ago, Sgt_Joch said:

The Devs made a best guess based on what available data there is and other than some minor quibbles, I don’t see any mistakes.

 

Unless there is a certain wilful blindness, I don't know how you can draw that conclusion ?

 

The physics base of the FS has produced a very good series of sims, but, I suspect, it has also been a weight around it's neck (a bit of an Albatros), producing sometimes 'odd', conflicting, or unexpected results that are either ignored, ignored completely or fluffed.

 

The D VII is a case in point. If you cast your mind back to when it first appeared in RoF, it took some time to 'develop' the FM, it just didn't perform as the Developers expected, which is why the 'f' version was quickly produced, to rectify this 'error'.  Tweaking, with the various tools available to the engineer, within the physics based system, just couldn't make the vanilla D VII perform as expected.

 

Back to Mercedes D IIIa engine, with which you only have "minor quibbles", at maximum loading, it can produce an excess of power (1480 rpm, or 1500 rpm in the Pflaz), as it unloads, and accelerates to it's optimum comfort zone it actually loses rpm, dropping to a low of 1370, in the Alb, and 1415 in the Pflaz (at 70 mph).  My understanding, limited though it is, suggests this is wrong.  The D IIIa engine seems to operate with what seems to be closer to a constant speed prop (if imperfect), the engine being able to produce the 'designed' rpm, or close to, throughout it's operation range, rarely dipping, and in the case of the Pflaz (1415), never, dipping below it's optimum specified design rpm.  From my understanding it shouldn't be able to, or it is undesirable, for a fixed pitch propeller to produce maximum rpm at maximum load, for the simple reason that it will begin to overspeed as it unloads.  The engine then, once it passes through it's optimal range, slows down, as drag impeeds the propeller.  Obviously it was possible to tweak propellers, to maximize desired traits, (speed, acceleration, best power at certain speeds etc) but essentially the laws of physics remained the same, you could fiddle with them, but without variable pitch, you were limited to a fixed set of pre-adjustable traits.

 

I don't think I need to point out to you how at variance this is to that of the Viper engine, in the Se5a

 

Niether of these engines, in my estimation, 'performs' as might be expected.  Why this 'fudge' has persisted, over the years, I know not, whether it is a design 'feature' to overcome balance issues, or a physics engine limitation, or even just a fluff, I find it difficult to believe it is correct as is.

 

What I find difficult to get my head around is, how introducing 'new'  D III engine variants, without examining past inconsistencies, might improve things, it will just widen already existing inconsistancies, would it not ?

 

[Sgt_Joch]

well, it is easy to speculate, but what you need is hard data. What hard data exists is well known. The "Profile Publications" series that came out in the 1960s summarized every available German flight tests. I dusted some off.

 

1. aircraft profile no. 9, Alb Dva, 1965

170/185 hp DIIIa

top speed: 165 kmh

climb: 3000 meters in 14.8 minutes

 

2. aircraft profile no.55, DR1, 1965

110 hp Le Rhone engine

top speed: test 1 - 102.5 mph at 4000 meters

                   test 2 - 97 mph at 3000 meters

                              - 86 mph at 4000 meters

climb: 3000 meters in 10 min. 5 secs.

 

3. aircraft profile no. 25, DVII

engine: not clear if DIIIa or DIIIau

top speed: 189 kmh

climb: 3000 meters in 13 mins.

 

now on the DVII with the DIIIau engine, I did see an actual flight test from nov/dec. 1918 where the Germans recorded 189 kmh at 1,000 meters. It was not a flight test per se, but a test of their method to test flight speeds. The report was translated in english and is in the NACA archives. I read it years ago, but unfortunately lost the link.

 

DVIIF with BMW engine

top speed: 200 kmh

climb: 3000 meters in 9 mins.

 

as you can see all these figures are very close to the in game figures, so hard to say anything is wrong.

 

now one thing that would be very useful would be if someone could find the aircraft profile for the Pfalz DXII. I had  found it once but foolishly failed to download it. It included the Pfalz DXII data from the feb. 1918 tests in three configuration, with a DIIIa, DIIIau and BMW engine. As I recall, the top speeds were very close, i.e. the BMW was 10 kmh faster than the DIIIau which was 10 kmh faster than the DIIIa. 

Edited May 30, 2022 by Sgt_Joch

[HagarTheHorrible]

Aircraft performance is important, but I was under the impression we were discussing ENGINE performance, in particular that if the Mercedes D IIIa(u). 
Because of the limited real life data available, engine performance has to be painted in pretty broad brush strokes within the sim, and while they get much, broadly right, that is not to say there aren’t inconsistencies or question marks.

 

The average power available to the D IIIa engine, within the sim, (in this case the Albatros) across it’s full speed range 10mph -103mph is 102%, with a low point of 97%, (or 174 horses) at 70mph.  Maybe that is right, maybe it is wrong, I don’t know.  It does however look suspicious.  Not only does it look suspicious in it’s own right , but it looks especially suspicious when compared to that of the SE5a’s engine performance.  Maybe, I don’t know, just maybe the Germans had this fantastic engine, propeller combo, that allowed it to perform within an average plus or minus 3% of it’s optimal performance, across it’s total flight envelope.  Mean while, on the other side of the trenches, the much admired Hs8 (can’t, off the top of my head , remember if it’s the ‘a’, ‘b’ or indeed ‘ab’ ) Viper engine can only produce a measly 82% of it’s available power across it’s full flight envelope, with a low (at 70mph) of just 77.5%, or 155 horses.

…..and that is before we even get into the peculiarities of engine power retention, and drop off, with altitude.

[J2_Trupobaw]

9 hours ago, Sgt_Joch said:

well, it is easy to speculate, but what you need is hard data. What hard data exists is well known. The "Profile Publications" series that came out in the 1960s summarized every available German flight tests. I dusted some off.

 

1. These are not "hard data". These are tests of worn and battle damaged planes, maintained by crew untrained in type, running on fuel octane not intended for the engine (in case of Mercedes) and flown by pilots with no experience in the type. They are anecdotical data at best, showing low end of available performance - even if unmaintained and badly handled, the type performs no worse than that. There is also question whether IAS or TAS was used for speeds "tests".

2. Weren't Profile Publications debunked as inconsistent decades ago?

 

 

 

 

 

Edited May 30, 2022 by J2_Trupobaw

[Sgt_Joch]

1 hour ago, J2_Trupobaw said:

1. These are not "hard data". These are tests of worn and battle damaged planes, maintained by crew untrained in type, running on fuel octane not intended for the engine (in case of Mercedes) and flown by pilots with no experience in the type. They are anecdotical data at best, showing low end of available performance - even if unmaintained and badly handled, the type performs no worse than that. There is also question whether IAS or TAS was used for speeds "tests".

 

those are German tests of their own airplanes, not tests of captured planes.

 

1 hour ago, J2_Trupobaw said:

2. Weren't Profile Publications debunked as inconsistent decades ago?

no.

[J2_Trupobaw]

German test results of their own planes were destroyed in 1918. What could be recovered in 1920s was destroyed again in 1945. Only Entente tests of captured planesr survived.

[No.23_Gaylion]

Bruh this is a huge assumption you're making here. 

 

They captured the factories at the end of the war too, and were told to turn over all planes. Why would you test a beat up plane when you 100% had brand new ones captured at the end of the war? 

[J2_Trupobaw]

Germans handed over planes but destroyed documentations. The planes stayed around but no one cared much about measuring performance of old planes from defeated nation in post-war crisis anymore. It was time of surplus airframes, airforces downsizing, R&D decline. Germans reconstructed what they could in inter-war period, but destroyed that documentation again in 1945.

 

The period test results of German planes that survived are Entente war time tests of captured machines (suffering from all inconsistencies listed above). They were since used verbatim by publications like Profiles (inconsistencies and all).

Edited June 3, 2022 by J2_Trupobaw

[No.23_Starling]

On 5/31/2022 at 12:15 AM, J2_Trupobaw said:

1. These are not "hard data". These are tests of worn and battle damaged planes, maintained by crew untrained in type, running on fuel octane not intended for the engine (in case of Mercedes) and flown by pilots with no experience in the type. They are anecdotical data at best, showing low end of available performance - even if unmaintained and badly handled, the type performs no worse than that. There is also question whether IAS or TAS was used for speeds "tests".

2. Weren't Profile Publications debunked as inconsistent decades ago?

 

 

 

 

 

Can you cite sources for point one please?

 

I fail to believe that experienced test pilots and ground crews wouldn’t be able to get similar performance to a type than an average operational pilot. The engineering was far simpler then than even 10 years later.

 

If you’re implying that the surviving data understates performance materially, what do you suggest the developers do (not that they’re likely to do anything anyway)?