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How to do the Albatros series justice


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#1 gavagai

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Posted 24 November 2011 - 14:04

This was an idea I had in correspondence with Mattm. I think it's a good idea in response to the lack of good data for the Albatros series: what sort of performance should it have in Rise of Flight? While there is knowledge of the propellers the Albatrosses used, and their weights, dimensions, and the power curves for the Mercedes engines; all of the data for its performance comes from captured aircraft, and those tests disagree with consistent eye witness accounts from both sides of what the aircraft was actually like. So it is possible that the captured aircraft were in bad shape, were not tuned properly, etc. No one would want RoF to use German test data from a captured aircraft to model the SE5a, as the result would be exactly what has happened to the Albatros in Rise of Flight.

Therefore:

Pretend that we had no data whatsoever for the Albatros series, no data from captured aircraft, nothing at all. Judging only what we know from eye witness accounts, what would we infer?


Some very basic points seem clear enough about the Albatros series:

* that it was slower than the SE5a and 180hp Spad 7, and could not match them in climb or dive.

* that it was faster than the Sopwith Pup at medium and low altitude, e.g. 18000ft is where the Sopwith Pup was better in most respects.

* that it was faster than the Clerget 9b Sopwith Camel. Here we have that one quote from Strahle that describes the Camel as being faster on the deck, but we have no idea about what kind of Camel he faced, i.e. what engine it had. The rest of the eye witness accounts are consistent and unequivocal.

* that its climb was slightly inferior to the N17, with mixed accounts comparing its climb versus the Camel.

* that it was superior in dive acceleration versus Entente rotary engined scouts.

* and we know from historical accounts and descriptions of the vintage aviator replica that its roll and yaw response were mediocre, but with an overly sensitive elevator. Control balance was not one of its strong points. At the same time, the gentle stall it exhibits in RoF is, at worst, only slightly too generous.

Taking it as a given that the data for the Albatros series is crap, the above is how we should approach an estimation of its performance. Its speed should be in between the 180hp Spad7 and the Sopwith Camel. Its climb would be worse than the N17, comparable to the Camel, and better than the Pup's.

Pick some numbers that fit this trend, and you would have a good estimation of how the Albatros should perform in RoF. After all, I think Mig-77 and Chill31 are absolutely correct when they say that relative performance is what matters. The OAW D.III and D.Va should be very similar (same engine, after all), with the D.II being a bit less powerful, but still faster than a Sopwith Pup at medium and low altitude.

Please consider the above when it is time to review the Albatrosses, thanks! :S!:
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#2 hq_Jorri

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Posted 24 November 2011 - 14:39

Good initiative. Some thoughts:

Is it a good idea to throw all the Albatros versions on one heap with these comparisons?

Is it a good idea to also collect all the quotes here and archive them under subject (all quotes saying its faster than the Camel, all quotes saying it's slower than the SE5a, etc).
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#3 gavagai

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Posted 24 November 2011 - 14:45

Here are some Camel pilot quotes. They mostly describe the Camel in general terms as being a slow scout relative to its opponents, which would undoubtedly include the Albatros.

I at once turned but they did not wait, one of the horrible characteristics of a Camel
being… that it is unable to catch any other machine with the exception of the Fokker
Triplane on the level.

Captain Edgar Mcloughry, 4 Squadron AFC.

If we were only able to encourage the enemy to get in a dogfight, things were easy, as
a Camel could out manoeuvre anything.

Captain Arthur Cobby DSO DFC, 4 Squadron AFC

One word on the Camel: There is not one pilot in the squadron who would not argue
to the end for a Camel. Although slow, she could get around anything, also one could
not run away from anything, which rather aimed for success.

Captain Edgar Mcloughry DSO DFC, 4 Squadron AFC.

[One] had to shoot down all the Huns to get home himself, for there was no chance
to run for it.

Captain Henry Winslow Woollett, 43 Squadron RFC.

Our Camels were excellent fighting planes. Although they were slower in climb and
speed than the Albatros Scouts, they could outmanoeuvre the heavy-engined German
planes on a turn. We seldom had the initiative in a scrap but we very quickly took it
over once the scrap began.

Captain Norman Macmillan, 45 Squadron

—————-

SE5a pilot:
Compared to the Albatros, the SE5a might have been slightly faster.
Chidlaw Roberts

—————-

Albatros D.V pilot:
In the past Four weeks three new types of enemy aircraft have appeared. They are without
a doubt far superior in their ability to climb than the best D V They are the new English
SE 5 single-seater, the 200hp SPAD and the very outstanding Brisrol Fighter two-seater.
While the Albatros D III and D V come near in their ability to climb with the Sopwith
and Nieuport, and even surpass them in speed, it is almost impossible for them to force
an SE5 or a 200hp SPAD to fight because the enemy is able to avoid it by the ability of
his craft to outclimb the Albatros
von Tutschek

—————

What saved us from being being shot down in droves like B.E.s and R.E.s and F.E.8s and D.H.2s and Sopwith and Nieuport two-seaters was the Pup's agility at all heights, which made us a difficult target in a dogfight…but once engaged in a fight, we couldn't withdraw, for the Pup was slower than every other German fighter.

At 8,000[ft] the Pup is completely outclassed by the Albatros. You can't get away, you've got to fight it out with one gun against two.

I admit, I prefer to meet Huns at 17,000 ft upwards, for then we no longer fight at a disadvantage
Arthur Gould Lee (Pup Pilot and Air Vice-Marshall)
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#4 SYN_Vander

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Posted 24 November 2011 - 15:11

…While there is knowledge of the propellers the Albatrosses used, and their weights, dimensions, and the power curves for the Mercedes engines; …

I agree. Also, with the known data and accurate airfoil characteristics it is possible to do a fairly accurate calculation of both max speed and climb. I'm guesing Andrey could do this easily, if he hasn't done this already. This will be another good indication.
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#5 gavagai

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Posted 24 November 2011 - 15:32

But drag coefficients are measured, unit-less quantities, isn't that right? I like the idea of 'engineering' the aircraft from what is known, but there are limits to the validity of that procedure. Some sort of balance between the engineering approach and the eye witness accounts is necessary here.
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#6 SYN_Vander

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Posted 24 November 2011 - 15:40

But drag coefficients are measured, unit-less quantities, isn't that right? I like the idea of 'engineering' the aircraft from what is known, but there are limits to the validity of that procedure. Some sort of balance between the engineering approach and the eye witness accounts is necessary here.

Yes, they can be measured, but they can also be calculated quite accurately. I've designed an airfoil once for my Masters thesis and back then (1995) the algorithms and programs were already quite advanced, including calculations for Low Reynolds numbers (small aircraft/ low speeds) where air viscosity does complex things to the airflow.

The software I used on a mainframe was developed at MIT and years later I found it on the internet, free download and could be used on a simple PC then. I'm sure Andrey has something better already. :)
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#7 Hellbender

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Posted 24 November 2011 - 15:49

Agreed 100% on the relative performance part.

Agreed somewhat on the "Pretend that we had no data" part.

Hope with all my heart that Albies become better performing, yet harder to fly planes.

In forum speak: from underperforming UFOs to decently performing WWI aircraft.
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#8 =IRFC=AirBiscuit

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Posted 24 November 2011 - 16:06

+1 with this thread. Very well put, Gav and MattM.
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#9 J5_Rumey

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Posted 24 November 2011 - 16:21

Agree 100%

All good things here, would love the albie Dva to feel less generic. Right now it has no peaks but also no quirks, it feels bland to me. Off course that is a lot of feeling and I guess it does not belong here. :shock:

Real good initiative! I applaud you gents. :S!:
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#10 gavagai

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Posted 24 November 2011 - 16:22

Agreed 100% on the relative performance part.

Agreed somewhat on the "Pretend that we had no data" part.

When I say data, I mean performance data only. Prop pitch, weights, dimensions, and other things that can be calculated still stand, of course.

I'm serious about throwing out the performance data. I could just guess some figures and come closer to the truth than the "data" that is currently out there. 165kmh for the D.II? No way.
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#11 MattM

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Posted 24 November 2011 - 17:44

Just talking about performance (with that i mean speed, acceleration, climb, engine-on-dive):

I know that the devs have quite a bit of good info about the Mercedes D.IIIa and D.IIIau engine (and probably also about the D.III, not sure about that). But to sum some things up, the D.III and D.IIIa had a fixed mixture, it was not adjustable (the D.IIIau kind of was, but i leave that engine variant out of this discussion, because it wasn't the main engine of the Albatros).

This that a direct comparison of engine power or power-to-weight ratio with Entente planes which do have mixture control doesn't work (ie, the Pup had a weaker engine, so it was autoatically slower etc.).

(using the D.III / Pup comparison, because it explains things relatively well and it more often than not is very specific about the engines those planes actually used)

The engine was leaned down at ground-level to provide the best power output at about ~1200-1500 meters (i haven't found a source that narrows that in completely and it might've even changed between the D.III and D.IIIa engine). If they wouldn't have leaned it down at ground-level and instead used the optimum mixture at that ground-level, it would quickly run too rich (basically already after the take-off) and thus lose power at higher altitude.

Of course even with the mixture being leaned down at ground-level, it would still reach some point at which the engine would run too rich and thus lose power. This is why you can usually read, that the Pup was almost hopeless at low and medium altitude (because that's the altitude were the Albatros engine had a huge advantage over the small LeRhone of the Pup), while at very high altitude (15,000 ft), the Pup would gain the advantage, because unlike the Mercedes engine, the LeRhones mixture can be adjusted to give good performance at that altitude, while the Mercedes engine was running rich. So the relatively big performance gap, which did exist between the Albatros D.III or D.V(a) and Pup at low altitude, didn't show up as badly, and the Pup could outturn the Albatros very well at any altitude.

Now this fixed mixture is basically true for all German planes using that engine (talking about ROF, those are all Albatros, the Pfalz D.IIIa and the Fokker D.VII). This is not modelled right now. Instead, the Albatros does quite well at high altitude (only losing ~10 km/h of its overall maximum speed of 177 km/h), both compared to the Pup, aswell as other planes like the SE5a or any of the SPADs, which do suffer a lot more from higher altitudes.

That picture is basically reversed at lower-altitude. There the relatively good performance of the Mercedes engine (performing best around the 1500 m altitude mark) gets completely nullified, because the Pup has the same speed (and climb, but unlike the speed, the climb has been confirmed as an error in the FM).

Now, i do not think that the ~177 km/h topspeed of the D.III in ROF at ~1500 m altitude is THAT far off for an early 1917 Albatros D.III (which would encounter Pups, probably more often than a late 1917 Albatros D.Va). While i do agree that it is likely, that the Entente scouts with rotary engine had a very hard time catching (and that's what's usually written in pilot reports, they had trouble catching Albatros planes), that doesn't mean that the Albatros was actually the noticably faster plane. To catch somebody, you need to be faster. You don't need to actually be slower, to be unable to catch someone.

However, were anecdotal evidence does add up (from both sides), is that the Sopwith Pup was generally slower than the Albatros. For instance, Werner Voss, who similarly to Manfred von Richthofen, does say that the majority of Entente planetypes in 1917 were superior to the Albatros in dive, climb, speed and maneuverability, clearly states that the Pup was indeed slower. Gordon Taylor, Pup pilot, basically says the exact same thing in his "Sopwith Scout 7309" book. One could argue that a Pup pilot would automatically say that his plane is too slow, but someone like Werner Voss (who really showed no reason to make his own plane look superior to the enemies) would say that aswell and be wrong about it, makes very little sense.

Anyhow, this would probably become a too long post (if it isn't already).

What i would prefer right now, is that not just the Albatros now get lots of attention, but also the planes who are clearly superior to any of the Albatrosses (and not just the Albatrosses, but also later planes) in basically everything should also get a closer look at the same time (Pup and Camel for instance).

And i don't think that it should stop at comparing the performance, but also advantages (and disadvantages) of planes that don't show up that clearly yet.

This is something like gunnery, including accuracy, jams, necessity to reload drum magazines, rate-of-fire (synchronizer gear) etc.

Of course maneuverability is again a completely different matter. However, atleast the Albatros D.III (which is consider more "believable" than the D.II and D.Va) does not really outmaneuver planes it should outmaneuver and doesn't get outmaneuvered by planes it shouldn't get outmaneuver from (that's obviously my subjective opinion).

Also talking about D.III and the D.Va in ROF, it should be made clear what planes they should actually represent. If we should take the OAW D.III as an OAW D.III (which would obviously make sense), we have to conclude, that it had a better performance than a early 1917 Johannisthal D.III. And if it gets a performance of a OAW D.III, a D.III variant for the first half of 1917 would be totally necessary.

The same can be said about the D.Va. It either had the D.IIIa or (possibly) later in 1918 the D.IIIau engine. Unless it gets both engines, the FMs would need to get adjusted to one of the two engines and that would need to be agreed on, before people actually present sources.
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#12 gavagai

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Posted 24 November 2011 - 18:03

Matt, what IAS are you reading for the D.III at 1500m to get 177kmh TAS?
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#13 JoeCrow

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Posted 24 November 2011 - 18:34

The problem with using this method is that you arrive at an FM by comparisons (relative performances) and this throws up yet another problem: you first have to make the assumption that all the other FMs are approximately correct relative to each other. To use this approach you would need to establish some rudimentary base-line by which all FMs are judged. In other words, you would need to choose an aircraft (arbitrarily if you like) and deem it to be correct ( a base-line by which all other FMs would be established by relative performance).

The need for a base-line arises because there are other aircraft beside the Alby with equal claim for revision. The same problem arose when reviewing the Se5a FM. No plane is an island.

I hope that this is seen as constructive rather than destructive.
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#14 Chill31

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Posted 24 November 2011 - 18:38

I think we already have the data needed to fix the albs. It is just a matter of doing it.

180 hp alb, regardless of d5 or d3, should be a 186 kmh airplane. The 160 hp should be 175 kmh with d2 maybe 172 on the slow side. This is al from data that we currently have!

One thing that I don't remember if it is modeled right now in ROF is that as you climb with a fixed pitch prop your rpm increases with altitude so that you rpm limit is the deciding factor in your max speed. For example, if the rotary engine is calibrated at sl to give 110 hp at 1250 rpm with a rev limit around 1350 or 1400, he has to throttle back and lose horse power before an inline engine that might be calibrated around 1400 with a 1650 rev limit. This is one reason the rotaries "lose" power faster than inlines capable of higher revs.

Roll rate is also something we can deduce based on relative design. Since inertia increases exponentially with wingspan, you need expnentially larger ailerons on aircraft with long wings to achieve the same roll rate. Since we know the wing Spanish an control surface area, we can figure out relative roll performance to some degree.

With this info, we can use data and, to some degree, science to make sure they behave correctly.
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#15 JimmyBlonde

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Posted 24 November 2011 - 18:41

Most fixed pitch props are calibrated for top speed aren't they?
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#16 Chill31

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Posted 24 November 2011 - 18:46

Jimmy, yes but at what altitude? If you go for max sl performance, you will lose speed as you climb at a faster rate that an airplane with slow sl speed due to increased prop pitch.
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#17 JimmyBlonde

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Posted 24 November 2011 - 19:08

Presumably the altitude where the highest speed can be reached Chill, I'm no expert obviously but that would make sense.

However it works there must be documentation for that which is pretty clear at least since it was common practice until well into the 30's.
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#18 MattM

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Posted 24 November 2011 - 19:23

Matt, what IAS are you reading for the D.III at 1500m to get 177kmh TAS?
Just checked again. I'm reading 163 km/h IAS. Which is actually closer to 176 km/h TAS. :P

The problem with using this method is that you arrive at an FM by comparisons (relative performances) and this throws up yet another problem: you first have to make the assumption that all the other FMs are approximately correct relative to each other.
That's the main reason, why i think that a FM revision of the Albatros, without a revision of other planes which are probably more likely less accurate than the Albatros series, will probably not statisfy people who are looking for an "improved" Albatros series.

Of course they need to start somewhere. Getting rid of the "auto-mixture" for the Albatros (or the Mercedes D.III/D.IIIa engines in general) would be a good start imo.

One thing that I don't remember if it is modeled right now in ROF is that as you climb with a fixed pitch prop your rpm increases with altitude so that you rpm limit is the deciding factor in your max speed.
Is this also true with the relatively weak engines which lose power at altitude quite quickly?

Also with the number of "power-on-dives" etc., i highly doubt the RPM was the limiting factor in fully throttle level-flight in any WW1 plane.

180 hp alb, regardless of d5 or d3, should be a 186 kmh airplane. The 160 hp should be 175 kmh with d2 maybe 172 on the slow side. This is al from data that we currently have!
Based on what sources and, more importantly, at what altitude?

And why would a D.V (or do you mean D.Va if you say 180 hp engine?) would be just as fast as a D.III, with shorter struts and a completely redesigned fuselage. I just don't see how those planes would share the same speed, especially not narrowed down to an exact number like "186 km/h".

Since we know the wing Spanish an control surface area, we can figure out relative roll performance to some degree.
Well, iirc, you're a pilot, but i'm not aware of any formula that would allow something like this, without knowing the exact characteristics of the airfoil aswell (the airfoil of the Albatros sesquiplane changes along the wingspan, with slightly longer chord were the ailerons are). Then of course the deflection angles of the ailerons is important to know, again, not sure if there is hard data on this.
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#19 RAF74_Winger

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Posted 24 November 2011 - 20:22

One way to go about it would be to do 2D CFD analyses of the biplane cell along the span, that would give you Cl & Cd values, and you could also look at the effects of aileron deflection.

I'm not sure, but perhaps a 3D mesh of the whole aircraft could give you an estimate of roll damping - that would be rather a task to complete though.

The important thing would be to make sure that the CFD was 'calibrated' against a known good model - SE5a perhaps, we've a lot of data for that airframe.

W.
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#20 Hellbender

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Posted 24 November 2011 - 20:39

I think we already have the data needed to fix the albs. It is just a matter of doing it.

180 hp alb, regardless of d5 or d3, should be a 186 kmh airplane. The 160 hp should be 175 kmh with d2 maybe 172 on the slow side. This is al from data that we currently have!

Chill, wouldn't that still make it slower than the Camel, or is the Camel too fast at 190km/h at sea level?

Maybe we'd still need the D.IIIau engine variant to be a real match for the Camel.
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#21 piecost

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Posted 24 November 2011 - 21:39

A Theoretical Approach

As Winger says, all theoretical methods should be calibrated against wind tunnel, or preferably flight test data. Vander mentioned a code developed at MIT (XFOIL?) which would provide better 2D sectional data than some of the contemporary low Reynold's number sectional data we have. The difficulty is applying this to the 3D biplanes, that is not so easy.

For instance; A panel method or full-blown 3D CFD may be needed to estimate the induced drag (impact on climb and energy bleed in turns). In addition, the maximum lift cannot be lifted directly from these 2D graphs, 3D details such as the lovely wing-fuselage fairing on the Pfalz versus the crude lower wing attachment on the Albatross DVa may impact the stall. I would not be shocked if those upper wing radiators acted as a stall trigger.

With regard to roll rate; A crude model can be done quite easily to predict roll damping and rolling moment due to aileron (called strip theory). I have posted roll damping data from Bristol Fighter wind tunnel and lots of aileron rolling/yawing moment data for Fighter and SE5a. Also full scale measurements of SE5a roll rate. Unfortunately, aileron aerodynamics are very sensitive to details such as the gap at the hinge line (30% reduction in rolling moment on SE5a type ailerons with a large gap relative to sealed). Also, we should account for the forces required to move the ailerons (hinge moments), the Bristol Fighter suffered from high stick forces giving the impression of slow response, this cannot be adequately accounted for in the sim. Again, the small details such as hinge gap would have a massive impact on aileron hinge moments.

So, I would tend to work from the qualitative comparison of the Vintage Aviator Albatross and SE5a ailerons.

I do not believe that it's practical to simulate the overall aircraft drag polar by the theoretical means available to hobbyists or small software companies. Even with access to industrial computational methods, a large aircraft company would probably perform a wind tunnel test or, better still, to try to partner with the Vintage Aviator to test one of their replicas.


Back to gavagai/Mattm idea

I like the gavagai/Mattm approach, and probably do not need to mention the known difficulties with the comparison aircraft. but I will state them anyway; which Camel to compare it to? the one with the most numerous engined type, factory fresh example or an old tired one? Since anecdotes mainly relate to combat between flights rather than individual aircraft there is a high chance that any Camel fight was slowed down more by their degraded Camels than Albatros flights by their older planes.

I like the iterative approach to flight model changes with any model only being considered as finished when historic tactics can be applied against our datum aircraft. Could the Beta testers try out a range of modified Albatros and pick the best one? Am I being naive in assuming a consensus would be reached?
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#22 SYN_Vander

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Posted 24 November 2011 - 22:43

Yes Piecost, besides airfoil analysis you also need a 3d panel method based program to calculate total lift and dag (I forgot which one we used). Do note that I do not expect accurate results for rollrate, stall behaviour etc. but top speed and -climb should be fairly realistic. Then again, you need to test this first against another model for which you have measured values.
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#23 MattM

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Posted 24 November 2011 - 23:01

Chill, wouldn't that still make it slower than the Camel, or is the Camel too fast at 190km/h at sea level?
Yes it is. It's about 10 km/h too fast (talking about Clerget Camel here).

Maybe we'd still need the D.IIIau engine variant to be a real match for the Camel.
Not sure what would make it a match. But i don't think that really matters.

I like the gavagai/Mattm approach, and probably do not need to mention the known difficulties with the comparison aircraft. but I will state them anyway; which Camel to compare it to? the one with the most numerous engined type, factory fresh example or an old tired one? Since anecdotes mainly relate to combat between flights rather than individual aircraft there is a high chance that any Camel fight was slowed down more by their degraded Camels than Albatros flights by their older planes.
It's not really about anecdotes (if possible, no anecdotes should be considered anyway), it's more about what makes sense if you look at the data, in this case, engine data. Because even though data about the performance of many of the planes in ROF is scarce, data about the engines being used in those planes is actually very detailed.

And then it's also about features that don't make much sense. Like the D.Va being slower than the D.III and rolling better. Just can't figure out why this should be the case.

But yes, i would actually prefer it, if it would be cleared, what the D.Va (for instance) in ROF supposed to be. Is it a D.Va with D.IIIa engine (would make the most sense).

Now to be honest, i'm not sure what this discussion will lead to. The devs surprised me with the recent N17 FM review. Now i'm not sure if they got it perfectly right (because like i said, info about a plane like that practically doesn't exist or can't be confirmed, especially regarding maneuverability), but it is believable.

The performance of the D.Va in comparison to the Pup or Camel just isn't believable for me.
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#24 hq_Jorri

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Posted 24 November 2011 - 23:20

Well, if we were to believe 777: if the plane was modeled correctly, with the right dimensions and centre of gravity of every part, and the engine and prop modeled accurately, the whole flight model will sort out itself. And either ROF can claim to benchmark these planes and actually be a source of data about these historical planes, or it's a bit of a hoax.

Isn't that one of the elephants in the room?
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#25 =NFF=Rock

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Posted 24 November 2011 - 23:25

An other issue with the testing of a captured aircraft is the Fuel , The fuel that the Germans had was at a higher Octane than the fuel that the British/French/ Americans used .
On the British side the Octane was around 50 and at times a little higher . The German Octane was around 60 or more depending on the quality . This was caused by the natural state of the making of the fuel and where it came from !

The pilots saw that after the war there aircraft ran better when they used the German fuel.
I do not know how but I think this should also be mixed in with the outcome of the FM .
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#26 gavagai

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Posted 25 November 2011 - 00:36

Chill31,

A 175kmh D2 is still slower than our Pup, and, therefore, 175kmh is not correct, unless the Pup is slowed down (for medium and low altitudes).

Similar logic applies to the OAW D3 and DVa.
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#27 ImPeRaToR

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Posted 25 November 2011 - 00:51

Actually, imo it does make sense that the D.Va rolls faster than the D.III because the top wing - and thusly the ailerons - is closer to the roll axis and a smaller wing gap also improves this.
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#28 Chill31

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Posted 25 November 2011 - 02:17

With regard to the Pup vs Alb, I would submit that the SL performance might be close with performance difference increasing with atltitude in favor of the Alb.

For example, if I add 10kmh to the speed of the alb D2 at every altitude, it is faster than the pup at all altitudes above SL by 4-8 mph. I would consider this in line with the Pup being slow as anecdotal evidence suggests.

The same goes for the AlbD3/D5.

Finally, for the Pup, if the climbrate was fixed, it would not be the super lethal chase you down and kill you machine that it is.

I still say we have the right data and that if it gets fixed the way I have it in my mind, we will have very nice FMs that mirror history.
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#29 gavagai

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Posted 25 November 2011 - 02:26

Actually, imo it does make sense that the D.Va rolls faster than the D.III because the top wing - and thusly the ailerons - is closer to the roll axis and a smaller wing gap also improves this.

This is an obvious point, and I'm mad that I didn't think of it.

——————

A historical representation is what I want chill31. If you can help deliver that, you have my gratitude!
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#30 Chill31

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Posted 25 November 2011 - 02:32

Take a look at this excel sheet.

It makes it painfully obvious where we have gone wrong in the FMs for ROF. Look at speed. Look at the climb rate. if Petrovich polishes these details, we cant help but have historically accurate FMs.

Attached Files


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#31 elephant

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Posted 25 November 2011 - 07:09

I approve of this post!

:S!:
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#32 Cptn_Goodvibes

Cptn_Goodvibes
  • Posts: 255

Posted 26 November 2011 - 00:56

G'day Gavagai and others,


I've just got home from work (on nightlink driving buses and picking up drunks) and saw your post. I do appreciate your initiative and obviously agree with this direction. Am hoping that 777 is observing this, particularly in light of the recent message about limited resources and importances of finances in the scope of things. Importantly, the Albatros D.Va (along with the SPAD 13) are the aircraft which are "showcased" in the free download version of ROF. In this respect, it is particularly important and worthwhile to leave a favourable impression upon prospective new clients. Unbalanced aircraft models won't do this.

Now I know this is a wide generalisation, but I tend to look at the evolution of the Mercedes D.III and German airframes in the following way.

Phase 1: Mercedes D.III early from Aug 16, 160hp - Albatros D.I, D.II, maybe some D.III?
Phase 2: Mercedes D.III late from Feb 17, 175hp - Albatros D.III & D.V
Phase 3: Mercedes D.IIIa from Sep 17, 180hp - Albatros D.V & D.Va
Phase 4: Mercedes D.IIIau from Mar 18, 185hp? - Fokker D.VII, Pfalz D.XII, some overhauled Albatros D.Va
Phase 5: Mercedes D.IIIauv from Nov 18 ?hp and too late to be of consequence.

However, it does indicate a gradual (glacial compared to the Entente) increase in power and performance over the life of the Albatros series.

Not withstanding what Chill31 has found, the other day I was tinkering around with figures and references to the Albatri speed from various sources. Though they do not always appear to be on a consistent basis, especially in regard to "at what altitude", I do see 109mph (175kph) mentioned for the D.II, some references to the D.III being a touch faster, say 112mph (180kph) and sources quoting the D.Va at 116mph (187kph). Given this, what would be the consensus of opinion if we anchored these speeds to each of these Albatros models at sea level and then extrapolated the existing altitude performance decrement adjustments by the same percentage from the existing reference page to arrive at an appropriate speed? Admittedly, this is "quick and dirty", totally unscientific, but I did this exercise out of curiosity and is as it looks below.

Alb D.II 160hp, TOW 898kg, SL 175kph, 1000m 166kph, 2000m 158kph, 3000m 148kph, 4000m 138kph
Alb D.III 175hp, TOW 885kg, SL 180kph, 1000m 173kph, 2000m 164kph, 3000m 155kph, 4000m 145kph, 5000m 133kph
Alb D.Va 180hp, TOW 915kg, SL 187kph, 1000m 178kph, 2000m 169kph, 3000m 160kph, 4000m 149kph, 5000m 136kph

Nieu17 110hp, TOW 560kg, SL 165kph, 1000m 155kph, 2000m 145kph, 3000m 135kph, 4000m 117kph, 5000m 95kph
SPAD7 150hp, TOW 705kg, SL 193kph, 1000m 181kph, 2000m 169kph, 3000m 156kph, 4000m 141kph
SPAD7 180hp, TOW 705kg, SL 219kph, 1000m 206kph, 2000m 191kph, 3000m 177kph, 4000m 162kph, 5000m 145kph
SPAD13 220hp, TOW 820kg, SL 220kph, 1000m 208kph, 2000m 195kph, 3000m 181kph, 4000m 167kph, 5000m 153kph

SE5a 200hp, TOW 886kg, SL 222kph, 1000m 208kph, 2000m 194kph, 3000m 179kph, 4000m 165kph, 5000m 149kph
S Pup 80hp, TOW 556kg, SL 176kph, 1000m 166kph, 2000m 156kph, 3000m 146kph, 4000m 132kph
S Tri 130hp, TOW 699kg, SL 185kph, 1000m 175kph, 2000m 164kph, 3000m 153kph, 4000m 141kph
RE8 150hp, TOW 1235kg, SL 171kph, 1000m 160kph, 2000m 148kph, 3000m 135kph

Included others from ROF reference page for comparison, but discounted others with suspected speed issues. Am sure that things are not as simple as this, but kind of like some of the comparisons that I'm seeing here.

I haven't touched upon climb or manuverability and leave this to those with the specialised aerodynamic engineering prerequisites. If I must say anything on the Albatros series, I think that being "stationery engined" they were definetly easier to fly, more stable, maybe less time incentive than rotary engined machines, though less manuverable. In its time, I think the Albatros D.II was much like a less powerful but more heavilly armed SPAD 7. Not what we have in ROF. The D.III introduced more manuverabilty at the expense of compromising its lower wing structures. The D.Va added some speed, but was a dead end in terms of development compared to the Fokker D.VII. But for a time, they were a competitive and "cutting edge" series of fighters. Unfortunately, we don't really see this in ROF.

Thats me done and I now defer to the much more profesional aerodynamic engineers within the community.


Regards to all,
Vibes
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#33 gavagai

gavagai
  • Posts: 15542

Posted 28 November 2011 - 12:45

In multiplayer yesterday I was conversing with Chill31 about the D.Va. Is it true that no one knows the origin of the 187kmh @ 1km figure for the Albatros D.Va? Is it just as likely that it came from a captured aircraft as from a German test?

I'd also like to point out that power:weight is slightly better than the Camel, and I wonder what sort of climb rate we can expect from a revised D.Va?
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#34 MattM

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  • Posts: 2595

Posted 28 November 2011 - 17:03

Actually, imo it does make sense that the D.Va rolls faster than the D.III because the top wing - and thusly the ailerons - is closer to the roll axis and a smaller wing gap also improves this.
Yes that could improve rollrate, as could the slightly higher weight.

Question is if that would increase the rollrate by 25%, which it does now.

And why in this case, the D.Va can turn tighter than the D.III, dispite heavier liftloading.

Anyhow, yes it could be that the D.Va rolled slightly faster than the D.III. It's also very possible that the D.II rolled faster than both the D.Va and D.III (mostly because of the shorter wingspan).

Take a look at this excel sheet.
Excel sheets count as sources now?

Where did you find those numbers you put in that excelt sheet and are they reliable?
I'd also like to point out that power:weight is slightly better than the Camel, and I wonder what sort of climb rate we can expect from a revised D.Va?
For power-output, i have 130 HP at ground-level for the Clerget and 170 PS at 400 meters for the D.IIIa.

Weight of the D.Va was ~935 kg loaded, ~715 kg empty (that's for the Johannisthal D.Va, the OAW D.Va was ~15 kg heavier).

Weight of the Camel was ~660 kg loaded, ~420 kg empty (Clerget engined Camel F1).

Thanks to the big fuel tank of the Camel, the power/weight ratio with fully loaded planes were indeed comparable, still the Camel was slightly better (even if we assume 180 PS at ground-level for the D.IIIa engine, which is doubtful). With less fuel, the Camel has the much better power/weight ratio by far. The D.IIIa does have a slightly better compression ratio (4.64 to 4.56), but most of that advantage was probably nullified by leaning the mixture at ground-level and running rich at higher altitude.

Not sure what the climbtime for a D.Va with D.IIIa would be. The D.XII (not the same plane as the D.Va, it was ~30kg lighter) with D.IIIa reached 3000 meters in 13.1 minutes at Adlerhof. The Roland D.VIa (still not the same plane as a D.Va, about 100 kg lighter than the D.Va) took 11 minutes to 3000 meters.


Anyhow, the power/weight ratio of the fully loaded Camel and D.Va is comparable. Yet in ROF, the Camel accelerates much faster (10 seconds to 15 seconds from 110 km/h to 150 km/h for instance), is quite a bit faster (~20 km/h) and climbs much better (2.5 minutes less to 3000 meters), all that with full fuel load.
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#35 ImPeRaToR

ImPeRaToR
  • Posts: 7902

Posted 28 November 2011 - 17:09

Prop pitch and tourque are very important for acceleration if I am not mistaken.
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#36 gavagai

gavagai
  • Posts: 15542

Posted 28 November 2011 - 17:27

Where did you find those numbers you put in that excelt sheet and are they reliable?
I'd also like to point out that power:weight is slightly better than the Camel, and I wonder what sort of climb rate we can expect from a revised D.Va?
For power-output, i have 130 HP at ground-level for the Clerget and 170 PS at 400 meters for the D.IIIa.

Weight of the D.Va was ~935 kg loaded, ~715 kg empty (that's for the Johannisthal D.Va, the OAW D.Va was ~15 kg heavier).

Weight of the Camel was ~660 kg loaded, ~420 kg empty (Clerget engined Camel F1).

Come on Matt, what you write is here a red herring.

Why would you compare the Mercedes in PS versus the Clerget in HP? And why at different altitudes? If the British measured one to be 130hp, and the other 180hp, then in this case it's nice that we have their figures. Empty weights are meaningless because it's the standard around here to measure climb time with a full tank of gas. You also use different loaded weights than what is at the store page.

Just KISS and see here:

D.Va: 915kg/180hp = ~5.1kg/hp
Camel: 700kg/130hp = ~5.4kg/hp

Or, if you insist on using 660kg for the Camel contra the store page, then that is also 5.1kg/hp.

While I appreciate your lack of bias regarding German aircraft in light of your citizenship, sometimes I think you carry it further than necessary almost to prove a point. ;)

This is more like it:
Anyhow, the power/weight ratio of the fully loaded Camel and D.Va is comparable. Yet in ROF, the Camel accelerates much faster (10 seconds to 15 seconds from 110 km/h to 150 km/h for instance), is quite a bit faster (~20 km/h) and climbs much better (2.5 minutes less to 3000 meters), all that with full fuel load.
All that distraction to reach the same conclusion? :S!:
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#37 gavagai

gavagai
  • Posts: 15542

Posted 28 November 2011 - 18:01

Actually, imo it does make sense that the D.Va rolls faster than the D.III because the top wing - and thusly the ailerons - is closer to the roll axis and a smaller wing gap also improves this.
Yes that could improve rollrate, as could the slightly higher weight.

Question is if that would increase the rollrate by 25%, which it does now.

Ok, here is my estimate.

Assume ~4.4m from the middle of the top wing out to the middle of the aileron, and assume that the roll axis is .6m above the lower wing.

With a 1.54m gap for the D.III, and a 1.432m gap for the DVa, the D.III's wing is .94m above the roll axis, and the D.Va's wing is .832m above the roll axis. So the angle of force to the D.III's lever arm is 77.9 degrees, and the D.Va's is 79.3.

Now, remembering from high school physics (JayDolan) that Torque = r*F*sint, and doing a little algebra (r and F are the same for both aircraft), with the D.III being "1" and the D.Va being "2":

T2/T1 = sin t2 / sin t1 = ~1.005

Therefore, the difference in roll rate would be less than what we can measure with a stopwatch, far less.
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#38 elephant

elephant
  • Posts: 1156

Posted 28 November 2011 - 19:01

Could be the performance of the Vintage Aviator's replicas, ever taken under consideration?

http://thevintageavi...tes-flying-d-va" onclick="window.open(this.href);return false;">http://thevintageavi....co.nz/projects … lying-d-va

Just an idea…
I don't know how much reflects the real thing…
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#39 MattM

MattM
  • Posts: 2595

Posted 28 November 2011 - 20:12

Prop pitch and tourque are very important for acceleration if I am not mistaken.
Indeed. I guess we would need to check acceleration from 0 to top-speed (or top-speed of the slower plane), that should give a good insight of overall acceleration.

Torque would be slightly worse for the Camel. Again, less likely that the Camel would accelerate much faster.

Clerget: 570 lb/ft (130 HP @ 1200 RPM)
D.IIIa: 630 lb/ft (180 HP @ 1500 RPM)
(Pup's LeRhone, just for having a laugh: 350 lf/ft (80 HP @ 1200 RPM)

Btw, the formula is:

torque = power / (2x π) / RPM * 33000

Only need to insert power and RPM.

BTW, there are also different numbers floating around for the Clerget. I read up to 140 HP and up to 1250 RPM. But most of the time when i read about the Clerget, i read 130 HP and 1200 RPM.

The Mercedes engine does have the highest torque of most engines btw., 20% better than that of the Viper (~525 lf/ft) for instance. But the Clerget has higher torque than the Viper aswell.

This should give the plane a pretty good climbrate and acceleration, if the plane would not be that heavy. Which the Albatros D.Va unfortunately is. That's very visible if you compare a Roland D.VI (which was actually a light plane compared to most other inline-engine fighters) performance with that of the SE5a.

Why would you compare the Mercedes in PS versus the Clerget in HP? And why at different altitudes? If the British measured one to be 130hp, and the other 180hp
What the British measured the D.IIIa engine with, doesn't mean to be correct.

I trust German tests of a German engine and they give 170 PS at 400 meter. They don't give any data for ground-level. Regardless, even if we just use 130 and 180 (HP or PS or HP and PS or whatever doesn't matter). Because,

Or, if you insist on using 660kg for the Camel contra the store page, then that is also 5.1kg/hp.
i do insist on using realistic weights, not those on the store-page. 700 kg for the Camel is completely wrong, so i don't use that. I see no reason to make the plane weight 40 kg more (and the D.Va 20 kg less), if it didn't.

While I appreciate your lack of bias regarding German aircraft in light of your citizenship, sometimes I think you carry it further than necessary almost to prove a point. ;)
The Albatros D.Va is probably my favorite WW1 plane (definately my favorite Central WW1 plane that's also in ROF). I'm not trying to make it look worse than it was and i definately want a performance boost for the D.Va, because that plane really makes no sense now and i only fly it when i have to, but i'm also against making it better than it actually was.

If you ask me if i think that the D.Va with D.IIIa was usually faster than the Camel, then i would say yes. I don't think that the Albatros climbed better though.

All that distraction to reach the same conclusion? :S!:
I didn't realise that it was your conclusion that they share the same power/weight ratio, i thought you had the opinion that the D.Va had the better power/weight ratio.


Some interesting books about aviation engines, mostly about WW1 engines. Definately worth taking a look.
http://www.archive.o...ge/n72/mode/2up" onclick="window.open(this.href);return false;">http://www.archive.o...tream/aviatione … 2/mode/2up
http://www.archive.o...e/n133/mode/2up" onclick="window.open(this.href);return false;">http://www.archive.o...tream/airplanee … 3/mode/2up

Now, remembering from high school physics (JayDolan) that Torque = r*F*sint, and doing a little algebra (r and F are the same for both aircraft), with the D.III being "1" and the D.Va being "2":

T2/T1 = sin t2 / sin t1 = ~1.005

Therefore, the difference in roll rate would be less than what we can measure with a stopwatch, far less.
Thanks for checking. No idea if that is correct, but it would kind of confirm my opinion that it wouldn't have a huge impact on the rollrate, certainly not the day/night difference we have in ROF.
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#40 gavagai

gavagai
  • Posts: 15542

Posted 28 November 2011 - 20:37

Matt, my post was more snarky than I intended; it was only supposed to be a little bit snarky. :D Accept my apology for that.

Adjusting the roll axis up or down a few centimeters isn't going to change much. If you want to be confident that what I deduced is correct, here is the derivation, where F=force, r=radius, and t=angle of the force to the torque lever arm:

T1 = F*r*sin(t1)

T1/sin(t1) = F*r

T2 = F*r*sin(t2)

T2/sin(t2) = F*r

T1/sin(t1) = T2/sin(t2)

T2/T1 = sin(t2)/sin(t1)

You can see by inspection that angles t1 and t2 are going to be very close, and therefore the difference in torque will be very, very small.

————-

Anyway, I think its best to call it 180hp because that way we have the same people measuring both. Or if you have a German test of the Clerget 9b, then it would be fine to compare that against the German test of the Mercedes. That makes sense, doesn't it?
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