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How to do the Albatros series justice


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#41 MattM

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Posted 28 November 2011 - 22:30

No reason to apologize.

Your calculation makes sense. Thinking about it, if ailerons closer to the roll axis (or COG) would increase rollrate that much, they might've put ailerons on the low wings instead. I think except for the N28, i don't know any plane that has ailerons on the lower wing instead of the top wing. Not sure why that is though (except on the sesquiplanes and other biplanes with smaller lower wing, there it wouldn't make any sense at all to put them on the lower wing).

Did a short acceleration test between the D.Va with the Camel. Also added the SPAD VII 150 HP and D.VII just for the sake of it (their performance seems to be alright, plus they are somewhere in the ~180-190 km/h area)


Fully loaded, 90 km/h IAS to 150 km/h IAS at sea-level (used the lake-map :D).

I get,

11 seconds for the Camel
18 seconds for the D.Va
14 seconds for the D.VII
12 seconds for the SPAD VII

Not sure how i would rate that.

Power-to-weight (which doesn't need to say much about acceleration of course) is like this:

SPAD VII 5.00 kg/HP
Camel 5.07 kg/HP
D.Va 5.19 kg/HP
D.VII 5.33 kg/HP
(the weight of the D.VII varies quite a bit, i used 959 kg, which seems to be the most common take-off weight, but with the D.IIIa engine, it was most likely a bit lighter than that)

So it is definately a bit surprising. Of course drag, propeller pitch play a major role in this. The D.VII was supposedly less draggy than the Albatros and with D.IIIa engine, it probably weighted about the same (i think the D.IIIau was 25 kg heavier than the D.IIIa engine, not sure about that). Like most British planes, the Camel had "aerodynamic" wires, which greatly reduced drag and it also had a low-drag airfoil. Wingspan and -area are comparable to the D.VII and D.Va. The SPAD obviously had the smallest wingspan and -area, aswell as a low drag airfoil. That combined with the good power/weight ratio, should give i a decent performance. However, in top speed it's only marginally better than the Camel and it's slightly slower in acceleration (atleast 90 km/h to 150 km/h, maybe it switches at higher speed).
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#42 gavagai

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Posted 29 November 2011 - 00:29

959kg for the D.VII? I've never seen a weight like that.

The trend is clear: The Spad7 has better power:weight, better thrust:drag, and the Camel out-accelerates it. :roll:

Anyway, it's clear enough that the D.Va not only deserves a higher airspeed, but also a better climb rate, and a worse roll rate.

———-

P.S. Going back to those German PS ratings, I seem to recall that PS was not measured at full throttle?
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#43 NickM

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Posted 29 November 2011 - 02:03

How have you measured the thrust:drag ratio?
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#44 gavagai

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Posted 29 November 2011 - 04:13

I haven't measured it. I'm merely making use of the point that a faster aircraft has a better thrust:drag ratio than a slower one, where maximum airspeed is when thrust=drag.
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#45 Chill31

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Posted 29 November 2011 - 04:58

With regard to power, it is just a math conversion. 1ps is appx 1.013 hp

http://www.statman.i...ions/power.html" onclick="window.open(this.href);return false;">http://www.statman.i...ions/power.html

The numbers in the spread sheet are all derived from ROF in flight testing. The historical numbers for the pup come from 1916 flight test data for a brand new pup
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#46 gavagai

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Posted 29 November 2011 - 18:22

Wow Chill31, the Pup's climb to 3km is more than 20% better than the historical data you include in that chart! :0o: How was that thing ever released in such an erroneous state?
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#47 MattM

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Posted 29 November 2011 - 19:17

959kg for the D.VII? I've never seen a weight like that.
Profile Publications has that weight. It also seems to be the weight most people agree on on theaerodrome forums. I'm not saying that the weight is correct, definately not for a D.VII with D.IIIa, which is what we have in ROF.

The trend is clear: The Spad7 has better power:weight, better thrust:drag, and the Camel out-accelerates it. :roll:
It would probably need a few more tests to determain that. Like acceleration at different altitudes etc. But it does seem weird to me that the Camel accelerates that quickly (and it surprises me even more, that it has about the same speed as the 150 HP SPAD).

Anyway, it's clear enough that the D.Va not only deserves a higher airspeed, but also a better climb rate, and a worse roll rate.
Speed (at low level) and roll rate yes. Not sure about climb.


P.S. Going back to those German PS ratings, I seem to recall that PS was not measured at full throttle?
Engines were rated at higher altitudes, probably at the altitudes were they performed the best (which wouldn't be ground-level, because of the engine being leaned back at that altitude). The engine was tested with full throttle afaik (makes no sense to not use full throttle). Probably not the lever fully forward on the D.IIIau, because that would put the carburator in the high altitude setting and lower overall performance at low altitudes (and increase performance at higher altitudes obviously).

With regard to power, it is just a math conversion. 1ps is appx 1.013 hp
Yes, that's what i basically mean. We shouldn't really bother if we use HP or PS here. I have my doubts that the power tolerance of WW1 engines was closer than the difference between HP and PS.

The numbers in the spread sheet are all derived from ROF in flight testing. The historical numbers for the pup come from 1916 flight test data for a brand new pup
OK, i guess i found the same data in H. King Sopwith Aircraft 1912-1920:

Speed:

5,000 ft = 105 mph/169 kmh
11.000 ft = 101 mph/162 kmh
15,000 ft = 85 mph/137 kmh

Climb:
5,000 ft = 6 min 25 sec
10,000 ft = 16 min 25 sec
15,000 ft = 32 min 40 sec

And in O. Thetford British Naval Aircraft since 1912:

Speed:

5,000 ft = 105 mph/169 kmh
9,000 ft = 103 mph/165 kmh
15,000 ft = 85 mph/136 kmh

Climb:
5,000 ft = 6.5 min
10,000 ft = 16.5 min
16,100 ft = 35 min

Of course half of the data is basically identical, so it's likely that those numbers came from the same flight test.
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#48 Tom-Cundall

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Posted 29 November 2011 - 19:26

How was that thing ever released in such an erroneous state?

A simple reason. Quite often Beta-testers don't have long enough or as much influence as you may think:

Welcome to game development by the seat of your pants where you have to be perfect every time or your screwed…

This kind of stuff needs to be pointed out to us months in advance….

Jason

N.B. This is about a different issue but illustrates the pressure 777 are under and also the fact that by the time Beta-testers spot errors that aren't proper 'bugs' it is often too late to change anything.
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#49 gavagai

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Posted 29 November 2011 - 19:38

Anyway, it's clear enough that the D.Va not only deserves a higher airspeed, but also a better climb rate, and a worse roll rate.
Speed (at low level) and roll rate yes. Not sure about climb.

Give me a good reason why the D.Va should climb like a turd compared to other aircraft with similar powerloading. It would be one thing if there were a small difference, but we're looking at a huge gap that has to be explained. Without some profound explanation of a crucial difference, we are bound by inductive reasoning to expect similar climbrates.

P.S. Going back to those German PS ratings, I seem to recall that PS was not measured at full throttle?
Engines were rated at higher altitudes, probably at the altitudes were they performed the best (which wouldn't be ground-level, because of the engine being leaned back at that altitude). The engine was tested with full throttle afaik (makes no sense to not use full throttle). Probably not the lever fully forward on the D.IIIau, because that would put the carburator in the high altitude setting and lower overall performance at low altitudes (and increase performance at higher altitudes obviously).

I could swear that PS ratings were for something like 1500rpm, and no more. I can't remember where the thread is. But the fact remains that the British rated the Mercedes D.IIIa at 180hp, and the Germans rated it at 170PS. We have to compare apples to apples, so unless we have German ratings for an engine like the Clerget 9b, stick with 180hp.
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#50 gavagai

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Posted 29 November 2011 - 20:04

Here it is: Current ROF Airplanes Flight Model Discussion Topic.

As Imp reported:
174 bhp @ 1400RPM (180 bhp @ 1500RPM)

maximum power recorded 197bhp@1700RPM

So 170PS is only at 1400rpm.

And as Mig writes:

Power/weight ratio is misleading unless you know exact power at different alitudes. IE BMW engine could develope ~230hp at sealevel, but was rated to 185hp (by germans. By brits/americans it was 230hp engine). DIIIa engine could develope 197hp but was rated to 180hp. Viper engine could develope 220hp but was rated to 200hp, etc.

Entente versus German power ratings could very different! Let us keep that in mind before we compare the horsepower of a British aircraft to the German PS rating of another.
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#51 MattM

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Posted 29 November 2011 - 23:34

Give me a good reason why the D.Va should climb like a turd compared to other aircraft with similar powerloading. It would be one thing if there were a small difference, but we're looking at a huge gap that has to be explained.
The propeller makes a huge difference. Power/weight can't explain everything. Otherwise i wouldn't say that the D.Va most likely climbed noticably worse, but flew faster than the Camel.

A fixed-pitch propeller can be optimized for climb or speed or a compromise between those two and all that would also depend on altitude.

The DR.I has about the same powerloading as the D.Va with D.IIIa. I don't think those two planes had the same climbrate.

I could swear that PS ratings were for something like 1500rpm, and no more. I can't remember where the thread is. But the fact remains that the British rated the Mercedes D.IIIa at 180hp, and the Germans rated it at 170PS. We have to compare apples to apples, so unless we have German ratings for an engine like the Clerget 9b, stick with 180hp.
Again, what British rated German engines with, doesn't matter (to me), they replaced the carburettor on some D.IIIau engines, because they got too low power at low altitude (also says so in that topic). I guess because they didn't figure out the throttle/carburettor mechanism or they didn't know that the engine was deliberately leaned back at low altitude, because the Germans didn't concentrate on ground-level performance. I wouldn't call that very reliable.

I do have some info from a German (post-WW1) book. It rated the Mercedes D.III variants the following.

D.III : 170 PS @ 1400 RPM
D.IIIa: 180 PS @ 1450 RPM
D.IIIau: 160 PS @ 1400 RPM up to 1800 meters

It doesn't say at what altitude the D.III and D.IIIa were rated though (leaned back and all that).

This book also rated the Clerget with 130 PS (not HP) @ 1200 RPM.

So 170PS is only at 1400rpm.
The only reliable info i got for the D.IIIa which does include the altitude, says those 170 PS @ 1450 RPM @ 400 meters altitude i mentioned earlier. Perhaps it did reach 180 PS @ 1450 RPM @ 0 meters. I simply don't know that. But like i said before, i'm OK with using 180 HP for D.IIIa for comparison sake.

Afaik, engine power was always rated at maximum RPM, but not necessarily at ground-level. Would have to ask Mig about were he found his info in that thread. I'm pretty sure his and Imps posts in that topic can be considered obsolete though (because the info i'm talking about was not avaliable back then).

Of course the D.IIIa could reach god knows what power at ~1700 RPM or whatever, but that was not the maximum practical RPM. That was 1450 RPM.
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#52 gavagai

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Posted 29 November 2011 - 23:37

Give me a good reason why the D.Va should climb like a turd compared to other aircraft with similar powerloading. It would be one thing if there were a small difference, but we're looking at a huge gap that has to be explained.
The propeller makes a huge difference. Power/weight can't explain everything. Otherwise i wouldn't say that the D.Va most likely climbed noticably worse, but flew faster than the Camel.

A fixed-pitch propeller can be optimized for climb or speed or a compromise between those two and all that would also depend on altitude.

The DR.I has about the same powerloading as the D.Va with D.IIIa. I don't think those two planes had the same climbrate.

Yes, I agree with all those points. What do we know about the D.Va's prop pitch? If it's going to do less than 190kmh, then it can't climb like a turd at the same time.

Again, what British rated German engines with, doesn't matter (to me), they replaced the carburettor on some D.IIIau engines, because they got too low power at low altitude (also says so in that topic). I guess because they didn't figure out the throttle/carburettor mechanism or they didn't know that the engine was deliberately leaned back at low altitude, because the Germans didn't concentrate on ground-level performance. I wouldn't call that very reliable.

The point is that British and German power ratings of the same engine could vary wildly, and therefore it is dubious to compare a British rating to a German rating. Don't forget that this side discussion started because you wanted to compare the 170PS rating of the D.Va to the 130hp rating of the Camel to compare power:weight, and I wouldn't let you.
:D
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#53 NickM

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Posted 30 November 2011 - 12:04

The propeller makes a huge difference. Power/weight can't explain everything. Otherwise i wouldn't say that the D.Va most likely climbed noticably worse, but flew faster than the Camel.

A fixed-pitch propeller can be optimized for climb or speed or a compromise between those two and all that would also depend on altitude.

There are also aerodynamic properties to consider. A draggy aircraft may still have a poor maximum airspeed despite having a reasonable power/weight ratio. I believe that the Albatros series suffered from using round-section bracing wires unlike the steamlined-section RAF wire used on most British aircraft. Whether the difference was enough to significantly reduce the top speed of the Albatros aircraft, I don't know - but I would be surprised if it didn't make a measureable difference.

It's also worth pointing out that rate of climb depends on more than just excess power. The full formula includes a variety of terms relating to things like L/D, prop efficiency, etc.
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#54 gavagai

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Posted 30 November 2011 - 12:32

Yes Nick, I don't think any German aircraft used streamlined bracing wires.

Petrovich also takes ceiling into account when he tests the climbrates of the RoF aircraft. The logic seems to be that you can only expect the aircraft to climb so fast or so slowly with a certain maximum ceiling, and it seems like a reasonable assumption before all of the complications introduced in WW2 aircraft.

Various figures exist for the D.Va's ceiling, but 6250m (250m less than the D.V) is one I've seen that looks believable.
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#55 ImPeRaToR

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Posted 30 November 2011 - 12:48

D.IIIau: 160 PS @ 1400 RPM up to 1800 meters
You might need octane additives for this due to compression but they tested 177PS at 1000m and 1450RPM in Friedrichshafen. We also have figures for torque, somebody posted a formular for torque earlier but we actually have figures for this:

D.IIIa 117 kg m (circa* 1170 Nm) at 400m and 1450RPM
D.IIIa 105 kg m (circa* 1050 Nm) at 1000m and 1450RPM
D.IIIaü 122 kg m (circa* 1220 Nm) at 1000m and 1450RPM

*m kg ≈ 0.101 971 621 N·m


Imo these 160PS are very vague and we also know that originally the decompression valves were handled very conservatively at the beginning but later this was changed, so early tests of these engines would yield lower results.
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#56 Hellbender

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Posted 30 November 2011 - 22:55

Guys, this is all fascinating stuff An.Petrovich will hopefully be able to use, but you lost me and a bunch of others a few pages ago.

In short, regarding the D.Va: is the current model available in RoF (engine and all) in need of review (and if so: what's the consensus?) or do we absolutely need to have a new model added with a different engine to improve performance?
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J5_Hellbender


#57 gavagai

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Posted 30 November 2011 - 23:29

Bender,

In a nutshell:

The D.Va's airspeed could be increased to 187kmh @1km, but no one knows the origin of that figure. It's out there, and Chill31 and Mig-77 recommend it as the target airspeed. This would be with the regular "180hp" Mercedes D.IIIa engine.

The ceiling could be increased from 5600m to 6250m, and Petrovich can work out the implications for the D.Va's rate of climb.

The roll rate is definitely too good, and should be decreased to something like the Albatros D.III's roll rate. The smaller wing gap of the D.Va should have a negligible benefit for roll rate versus the D.III.

http://www.theaerodr...ifferences.html" onclick="window.open(this.href);return false;">http://www.theaerodr...com/forum/aircr … ences.html
It's interesting to see the incontrovertible Dan San say that the D.V used the 170ps Mercedes, and the D.Va used the 180ps D.IIIau. According to what Imp said, he seems confused on that point, and we know that the D.IIIau was not used until many months after the D.Va's introduction.
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#58 Hellbender

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Posted 01 December 2011 - 01:18

Thanks, gav, that cleared things up for me. I sincerely hope this happens soon.

Just to be clear, do you think that this is enough to make the D.Va viable against the Camel, or will the Central flyers still need a model with a better engine?

I'm not talking about being on equal terms with the Camel, just that someone can confidently climb aboard his D.Va and know that he can at least actively avoid 1 on 1 encounters with Camels, much like an SE5a pilot would avoid tangling with a Dr.I.
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J5_Hellbender


#59 gavagai

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Posted 01 December 2011 - 02:14

It's hard to say Bender. Our current Camel is a 190kmh machine on the deck. If it were modeled according to production model data and not the data from the F.1/3 prototype, then this new Albatros D.Va would have a slight edge in airspeed.

Another thing to look at in Camel FM review is its climbrate. Taking an average of climb times to 10,000ft from new, factory fresh Camels would be a fair and just way to model it, I think. We have those figures from that page piecost posted.

————–

Here Bender, this is a picture of what I'm talking about. The proposed Camel figures are from B2312, the D.Va figures use the 187kph figure and my estimation (imagination) of what might be (TAS in KPH):

Attached File  DVa&Camel.PNG   22.62KB   393 downloads
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#60 MiG-77

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Posted 05 December 2011 - 14:58

Afaik, engine power was always rated at maximum RPM, but not necessarily at ground-level. Would have to ask Mig about were he found his info in that thread. I'm pretty sure his and Imps posts in that topic can be considered obsolete though (because the info i'm talking about was not avaliable back then)

IF you mean mercedes DIIIa/DIIIau data. Those were british tests (I have original test data in digital format).

Attached File  180hp mercedes.jpg   150.83KB   349 downloads

Attached File  200hp mercedes.jpg   210.99KB   349 downloads
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#61 Mogster

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Posted 12 December 2011 - 12:04

These changes look great. I enjoy the Camel as is but chasing down Central scouts just doesn't feel right compared to the majority of historical accounts.

It'll be interesting to see how people react to these changes though :)
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#62 =FB=VikS

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Posted 12 December 2011 - 12:44

What about these two?

Attached File  D5a_engine_31102.jpg   313.48KB   432 downloads

Attached File  D5a_no5695-17.jpg   312.92KB   432 downloads


note, that 5695/17 are from late 1917 order batch (sept 1917).

Attached File  Albs_Serials.jpg   111.4KB   432 downloads

PS: any chance to find engine serial numbers?
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#63 MiG-77

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Posted 12 December 2011 - 13:59

PS: any chance to find engine serial numbers?


Other document list engine serial number to be 31102. In british "180hp mercedes aero engine" (DIIIa) test document their tested engine serial number was 35254 (taken from Albatros D.V captured November 14th 1917, serial number D4545). For some reason engine in that french Albatros was earlier production!? That raises way more questions tought (IE was engine mercedes DIIIa first place?)

As for mercedes serial numbers, I would suggest you to contact Dave Watts from aeredrome forum. He has very good material about mercedes engines (after all, he was the one who had those original german DIIIau test data which you now have ;) )
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#64 =FB=VikS

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Posted 12 December 2011 - 14:28

Other document list engine serial number to be 31102. In british "180hp mercedes aero engine" (DIIIa) test document their tested engine serial number was 35254 (taken from Albatros D.V captured November 14th 1917, serial number D4545). For some reason engine in that french Albatros was earlier production!? That raises way more questions tought (IE was engine mercedes DIIIa first place?)

As for mercedes serial numbers, I would suggest you to contact Dave Watts from aeredrome forum. He has very good material about mercedes engines (after all, he was the one who had those original german DIIIau test data which you now have ;) )


Yup, and note - both of them had almost exact performance (different take off weight?).
These are two different airplanes, and reports dated one march and other may of 1918.
They where so lucky to test two different D.Va`s with the early D.III engine fitted in 1918?
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#65 elephant

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Posted 12 December 2011 - 14:36

The engine in that 'French' Albatros was earlier because the plane was a D.V (not a DVa) and could have been produced earlier. (no Idflieg No is noted at the first document).
Also many earlier D.V-s were uprated with D.IIIa engines and structural lower wing reinforcements.
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#66 =FB=VikS

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Posted 12 December 2011 - 14:55

The engine in that 'French' Albatros was earlier because the plane was a D.V (not a DVa) and could have been produced earlier. (no Idflieg No is noted at the first document).
Also many earlier D.V-s were uprated with D.IIIa engines and structural lower wing reinforcements.

5695/17 - is D.Va, check for the table with attached serials.
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#67 MiG-77

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Posted 12 December 2011 - 15:08

The engine in that 'French' Albatros was earlier because the plane was a D.V (not a DVa) and could have been produced earlier. (no Idflieg No is noted at the first document).
Also many earlier D.V-s were uprated with D.IIIa engines and structural lower wing reinforcements.

5695/17 - is D.Va, check for the table with attached serials.

Elephant means the other document. No Idflieg serial number and it is listed as "D5 type C".
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#68 =FB=VikS

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Posted 12 December 2011 - 15:22

Elephant means the other document. No Idflieg serial number and it is listed as "D5 type C".

You mean that report with performance curves?
If yes - its still notes (second document) its serial number, and its D.Va, and it had no difference in climb data (which should be obvious in case of different engine).
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#69 gavagai

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Posted 12 December 2011 - 15:26

Really Viks? You want to rely on data from a captured aircraft? That is simply not valid; not when so many other aircraft in RoF are based on a factory fresh aircraft, or even a prototype.
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#70 =FB=VikS

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Posted 12 December 2011 - 15:33

Really Viks? You want to rely on data from a captured aircraft? That is simply not valid; not when so many other aircraft in RoF are based on a factory fresh aircraft, or even a prototype.

What else we should rely on???
Or you mean that one number from book - is better than this?
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#71 MiG-77

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Posted 12 December 2011 - 15:48

You mean that report with performance curves?
If yes - its still notes (second document) its serial number, and its D.Va, and it had no difference in climb data (which should be obvious in case of different engine).

I mean this:

Attached File  D5a_engine_31102.jpg   313.48KB   366 downloads

No idflieg serial number about plane (I cant see any). There is serial number of engine which indicate that it might have been originally mercedes DIII (which may have been upgraded to DIIIa standard).
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#72 gavagai

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Posted 12 December 2011 - 15:49

Viks

It is better if it is closer to the airspeed of a factory fresh Albatros D.Va.

You know enough about WW1 aircraft to know that performance declined dramatically after 24-48 hours of engine wear, both for rotary and liquid cooled engines (some were worse than others). A 10% decrease in airspeed in a worn-out engine was normal. If that is true in the case of the French Albatros D.Va, then you would have a catastrophic result for the RoF Albatros if you did not compensate for it.

~170kmh/.9= 189kmh

So we need only assume that performance might have dropped by 8 or 9 % to get something like the other airspeed figure.

170/.91= 187kmh
170/.92= 185kmh

——————-

The airpseed of the D.Va in RoF makes no sense compared to eye witness accounts. I know you don't like anecdotes, but who is faster is one of the easier things to judge accurately because pilot skill doesn't enter into the judgment.

Open your eyes. Read about what the RFC/RNAS pilots had to say about it. There's a serious mistake that's been made here.

————-

Mig-77, you mentioned German data for a captured SE5a once. How fast did they measure it?
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#73 MiG-77

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Posted 12 December 2011 - 16:08

Mig-77, you mentioned German data for a captured SE5a once. How fast did they measure it?

SE and there was no mention if it was plain SE5 or SE5a (test was made in 27th April 1918). Anyway, 93.95mph@8500ft (slower than D.VII at 9000ft in same tests 100.66mph).
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#74 gavagai

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Posted 12 December 2011 - 16:13

But even the British data for the 150hp SE5 has it faster than the Mercedes-engined D.VII.

Case in point: you need to be very careful when using data from a captured aircraft.

Viks?
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#75 elephant

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Posted 12 December 2011 - 16:21

I don't think the two French reports are on the same plane,
but on two different ones: an uprated D.V with unknown serial, (probably overpainted),
so the engine serial is listed instead and a D.Va with known serial, (5695/17).
Both types wore the same type of engine so no harm done.
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#76 ImPeRaToR

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Posted 12 December 2011 - 16:30

They have different props though.
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#77 elephant

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Posted 12 December 2011 - 16:41

The props are noted at the documants too.
Thanks Imp!
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#78 MiG-77

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Posted 12 December 2011 - 17:02

You cannot read text at the bottom of page what those 10,20,30,etc means. Are they climb times? If so, this one is faster in climb even when it is heavier plane:

Attached File  climb.jpg   492.24KB   293 downloads

That could explain it slower level speed (propeller optimized more for climb, not speed).
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#79 ImPeRaToR

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Posted 12 December 2011 - 17:11

Would make sense that the slower plane has better climb and vice versa, as they have different props.
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#80 MiG-77

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Posted 12 December 2011 - 17:17

This would fit to normal mercedes operation (mixture set to be optimal at ~1700m). Max level speed is virtually identical 0-2km alititude:

Attached File  speed.jpg   487.97KB   276 downloads

Also interesting to note is tha this plane is 10km/h slower at 5000m.
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