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SE5a FM - review & fixes!


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#81 piecost

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Posted 03 September 2011 - 23:32

We still do not know if the SE5a stall speed was corrected but the above posts give an idea of the magnitude of the ASI error.
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#82 Bullets

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Posted 04 September 2011 - 08:40

I know this has not got much to do with the climb rate but this video shows a very important feature that needs to be fixxed with the SE5a,
I wasnt aware of this until i stumbled upon it, please let me know if you agree :lol: :D

http://www.youtube.c...feature=related" onclick="window.open(this.href);return false;"> … re=related
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#83 MattM

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Posted 04 September 2011 - 13:52

Hey good find. I'm pretty sure noone has mentioned the glass engine of the SE5a in this forum before. Ever.

However, Mr. Petrovich already posted that he fixed that already for the next update.
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#84 Josh_Echo

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Posted 04 September 2011 - 16:21

Hey good find. I'm pretty sure noone has mentioned the glass engine of the SE5a in this forum before. Ever.
However, Mr. Petrovich already posted that he fixed that already for the next update.

I narrowly avoided a coffee-on-monitor moment here. [g]
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#85 Bullets

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Posted 04 September 2011 - 17:02

Hey good find. I'm pretty sure noone has mentioned the glass engine of the SE5a in this forum before. Ever.

However, Mr. Petrovich already posted that he fixed that already for the next update.

:lol: no need for the sarcasm…. I not being an aeroplane fanitic didnt know what the cause of the "Glass engine" was, and on seeing this and the amount of views i didnt think many others did, Was trying to be helpful :cry:
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#86 MattM

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Posted 04 September 2011 - 18:39

Sorry Ben, was only kidding.

It's just that the "glass engine" thing of the SE5a is probably the most common issue regarding flightmodels in ROF.

I didn't mean to sound rude. :S!:
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#87 Josh_Echo

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Posted 04 September 2011 - 20:36

Aye, if MattM says something like that, read it as said with a grin and a wink, not a glare and a smirk.
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#88 An.Petrovich

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Posted 05 September 2011 - 09:50

great sense of humor, guys :)


BTW, Ben, this video shows wrong airscrew properties, not the absence of braking effect of engine. You can sure at this if switch off the engine on the ground - it will stopped.

EDIT: moreover, SPAD XIII has a reduction gear, but S.E.Va has no.

Sincerely,
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#89 Josh_Echo

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Posted 05 September 2011 - 15:28

Andrey, I understand that you're concentrating on the S.E.5a at present, but I had a few questions about some of the other aircraft. The Fokker Dr.I flies level with a very nose-down attitude, and the Fokker E.III is very resistant to accelerated stalls. Do you know why they do this?

The funny thing about the Dr.I flying so nose-down (so it climbs a great deal when the chord is level with the horizton) is that Mikael Carlson's accurate replica Dr.I does not do this in level flight at full power, and he said that he rigged his exactly according to the original Dr.I specifications. Also, our Dr.I requires that the elevator be deflected sharply down for level flight at full power, while Mr. Carlson's elevator is level under the same approximate conditions. I think that this nose-low attitude (so that the velocity vector is pointed well above the gunsight at most velocities) is the main reason why our Fokker Dr.I bounces so much on landing compared to all other aircraft (including the Sopwith Triplane, which has three wings, and the Sopwith Camel, which has a short tail).

As for the Fokker E.III, I can't understand why I can yank the stick back all the way at almost all airspeeds without suffering an accelerated stall. According to the store stats, the E.III has ~95% of the weight of the D.H.2, but only ~74% of the wing area. Furthermore, the E.III has a moving stabilizer instead of only an elevator, so I expect that it isn't that the E.III doesn't enough elevator authority to exceed maximum A.o.A. The two aircraft have the same power, and, finally, the E.III surely has less drag, but I'm not seeing why this would mean that the aircraft shouldn't accelerated stall except at the very slowest of speeds.

If you could explain why these phenomenon happen, I would appreciate it.
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#90 gavagai

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Posted 05 September 2011 - 15:32

Josh,

Because of the DH2's lousy gap:chord ratio, it only produces 80% of the lift compared to a monowing of the same shape and area. Ultimately, its recalculated wing loading is within 5% of the E3! We had a whole thread about this a while back if you can find it with google.
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#91 Josh_Echo

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Posted 05 September 2011 - 15:33

So the primary reason why the E.III can pull full back-stick without stalling at most speeds, while the D.H.2 can't, is that the E.III has lower drag but approximately the same lift, power, and weight?
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#92 gavagai

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Posted 05 September 2011 - 15:36

So the primary reason why the E.III can pull full back-stick without stalling at most speeds, while the D.H.2 can't, is that the E.III has lower drag but approximately the same lift, power, and weight?

Hmmmmm… Let's go back a few steps. I don't know why its stall behavior is as it is. Honestly, I am not qualified to explain that stuff.

But, yes, the DH2 and E3 have about the same wingloading and power, but the E3 has less drag.
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#93 Josh_Echo

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Posted 05 September 2011 - 15:38

Of course, not all wings are created equal, and so on. I just find it puzzling that I can haul away with the elevator fully deflected and never suffer an accelerated stall except for when I'm very near my slow stall speed.
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#94 gavagai

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Posted 05 September 2011 - 15:38

I agree.
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#95 Bullets

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Posted 05 September 2011 - 15:43

great sense of humor, guys :)


BTW, Ben, this video shows wrong airscrew properties, not the absence of braking effect of engine. You can sure at this if switch off the engine on the ground - it will stopped.

EDIT: moreover, SPAD XIII has a reduction gear, but S.E.Va has no.

Sincerely,

Will google what that means :lol: :S!: but ok, you say wrong ? does this mean it will be fixxed!? :D
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#96 NewGuy_

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Posted 05 September 2011 - 15:54

I think I suggested this before, but how about asking the Vintage Aviator team about the SE5a? It would be nice to see greater coopreration and collaboration among the ROF team, Old Reinbeck team, the Vintage Aviator team, Shuttleworth team, etc, if this is not happening already. :S!: MJ
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Something something SPAD. Something something then dive away. 


#97 piecost

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Posted 05 September 2011 - 18:36

Air Speed Indicator Calibration for British Aeroplanes in WW1

Find attached extracts from R&M 266 which gives the method for measuring the ground speed of aeroplanes. It had been used to calibrate air speed indicators. This was report published in July 1916 and states that the method has been in use for about a year.

I conclude that it is likely that from July 1916 (and maybe even back in the summer of 1915) the airspeeds given in R&M reports are calibrated for position error. Hence, I believe that the stall speed of 54 to 56 mph for the SE5a in R&M 603 was corrected.

Also See attached R&M 289 - this seems to be where the British adopted the standard position of the Pitot Static as halfway up the outer wing strut.

I do not know if it became standard practice for all British production aircraft to have a standard method of calibration for airspeed indicators but it may be the case. I strongly believe that for planes with the pitot static mounted on wing struts the ASI will be calibrated.


A Method of Measuring the Speed of an Aeroplane at a Height

Reports & Memoranda No. 266

&

The Velocity of the Wind in Front of the Wing Tips of a Biplane in Flight

Reports & Memoranda No. 289

Attached Files


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#98 piecost

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Posted 05 September 2011 - 18:44

Biplane Effect on RAF15 Wing Section

Reports & Memoranda No. 366

[wind tunnel test of SE5 wings - early raked tips]

Attached Files


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#99 piecost

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Posted 05 September 2011 - 18:47

Maximum Lift of Biplanes

The Design of the Aeroplane, Darrol Stinton

extract from: Engineering Aerodynamics, Walter Diehl

Attached Files


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#100 =IRFC=AirBiscuit

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Posted 07 September 2011 - 16:42

Of course, not all wings are created equal, and so on. I just find it puzzling that I can haul away with the elevator fully deflected and never suffer an accelerated stall except for when I'm very near my slow stall speed.

You mean like all Central aircraft in this game, except for the D.XII? :)
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=IRFC=Air Biscuit

http://quetoo.org


#101 ImPeRaToR

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Posted 07 September 2011 - 18:10

Bullshit, go to the QMB, pick the D.VII and airstart 3000m. Initiate a bit of a dive and speed up to something around 200km/h and then pull up quickly, but just smoothly enough so you don't rip off your wings. One wing will drop and stall (I think the right one), followed by the other one.

You can even do this with keyboard :P
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#102 Josh_Echo

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Posted 07 September 2011 - 20:51

Isn't it odd, though, that you need to be going around 200 K.P.H. before you have enough elevator authority to exceed maximum A.o.A.? That's my point. It's very strange that you don't suffer an accelerated stall when you pull back all the way at normal speeds. I could understand if the elevator were very, very weak, but that isn't the case. These aircraft have good elevator authority at normal speeds. I'm not saying it's wrong; I don't know much about biplanes, but it's definitely worth looking at.
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#103 An.Petrovich

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Posted 08 September 2011 - 12:15

Andrey, I understand that you're concentrating on the S.E.5a at present, but I had a few questions about some of the other aircraft. The Fokker Dr.I flies level with a very nose-down attitude, and the Fokker E.III is very resistant to accelerated stalls. Do you know why they do this?

I write the answer once in "SE5a climbrate" thread and let's finish offtop here:

The attitude of any airplanes in level flight is mostly depend on airfoil performances and wing incidence. The Fokker Dr.I has a thick airfoil (CL=0.52 at AoA=0 for aspect ratio = 6) and has wing incidence from 2.3° (inner) to 2.5° (outer wing). That's why it flies level with a very nose-down attitude. You can calculate yourself the required IAS for level flight with level attitude (or with level chord). So I'm not sure that "Mikael Carlson's accurate replica Dr.I does not do this in level flight at full power". Likely, the speed was not maximum.

The resistant to accelerated stalls is not depend on wing area, airplane weight and drag. The type of elevator is important, of course, but you lose sight of CoG position. It's the most important thing when we're speaking about the pith balance and the airplane ability to do much AoA at enough IAS. If CoG posithion is too forward - you never can do stall at normal IAS, until you lose IAS and airplane is stalling (increasing AoA) because it go down (when the trajectory is changing much w/o notable changes of attitude position).

Sincerely,
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#104 Josh_Echo

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Posted 08 September 2011 - 12:41

So I'm not sure that "Mikael Carlson's accurate replica Dr.I does not do this in level flight at full power". Likely, the speed was not maximum.

Hmm. I had thought that I saw someone on this forum quote him as saying that he was flying at full power at that point in the video, but I can't find that now. Maybe whoever contacted Mr. Carlson could ask him next time.

you lose sight of CoG position. It's the most important thing when we're speaking about the pith balance and the airplane ability to do much AoA at enough IAS. If CoG posithion is too forward - you never can do stall at normal IAS, until you lose IAS and airplane is stalling (increasing AoA) because it go down (when the trajectory is changing much w/o notable changes of attitude position).

Thanks for the explanation.
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#105 An.Petrovich

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Posted 08 September 2011 - 13:37

Welcome :)
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#106 An.Petrovich

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Posted 09 September 2011 - 07:11

gavagai,
would you mind if I rename this thred as "SE5a FM review & fix" ?
I'm going to write a mini-report here about final results of this work.
Sincerely
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#107 gavagai

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Posted 09 September 2011 - 10:43

By all means, go ahead!
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#108 BullpupBarrie

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Posted 09 September 2011 - 20:44

OFF TOPIC

So I'm not sure that "Mikael Carlson's accurate replica Dr.I does not do this in level flight at full power". Likely, the speed was not maximum.

Hmm. I had thought that I saw someone on this forum quote him as saying that he was flying at full power at that point in the video, but I can't find that now. Maybe whoever contacted Mr. Carlson could ask him next time.

Thanks for the explanation.

Don't forget that the RoF DR1 goes a bit too fast at full power doesn't it?

If it does fly faster than a real one, then the RoF model will fly with a lower angle of attack in level flight because the increased speed generates more lift. Further, if it was slowed down to the speed of a real one, it would surely fly with a higher angle of attack and hence more nose level attitude. Maybe.

So possibly what Josh has observed is a knock-on effect of the speed issue?


Please note I don't claim to have a clue about aerodynamics beyond schoolboy physics and any resemblance to facts in the above post are purely coincidental.
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#109 =Fifi=

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Posted 09 September 2011 - 20:54

Any chance to see same topic for N17, An.Petrovich? :mrgreen:
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#110 piecost

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Posted 10 September 2011 - 00:52

A bit late perhaps, but I just remembered that I posted this table a while ago.

Attached Files


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#111 An.Petrovich

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Posted 10 September 2011 - 15:12

Hi guys! :S!:

So, I have some good news for you: the fixed S.E.Va finally is already under beta test now, and at last I’d like to make a summary report here about its final performances.

As you know, the main S.E.Va FM problem was a wrong engine revolutions («glass engine» in the dive), and also it had a very fast climb, and a little high stall speed. For fix these issues I had to revise many performances, as they all depend on each other. It was really hard research (as usual for any airplane) because many sources contain conflicting data (as usual again). I think I’ve found the compromise which seems like a true, but many questions still not answered.

Now, some facts from the 777 hangar:

180 (200?) h.p. Wolsely W.4A Viper engine.

As I wrote before, we have 2 different sources with the engine power curve,
the first source:

Attached File  HS Viper 200 hp.JPG   154.17KB   1813 downloads

And the second source:

Image

This difference is due to the different compression ratio. I've tested both engines in RoF, and chose the high compression engine, because it provides the best fit of all the characteristics of the aircraft. As a result, the maximum error of Viper power in RoF does not exceed 0.5 BHP (0.3%) against the source curve from 1200 to 2200 RPM.

BTW, the heat balance of engine has also retuned.

Airframe aerodynamics

Many thanks for piecost, who found the polar curve of S.E.Va! So, the aerodynamic performance have also retuned, and now our S.E.Va in RoF has Drag and Lift the same to the real airplane:

Attached File  Polar.jpg   136.87KB   1812 downloads

Attached File  Drag.jpg   143.77KB   1812 downloads

(Note: the Drag curve on this picture has recalculated for 2050lb. weight, although the S.E.Va in RoF has 1940lb. gross weight; moreover, the stopped airscrew in RoF has 52.5lb. of drag at 100f.p.s, exactly according to this source, with error less than 0.9%).

The maximum CL, in accordance with our discussion (started here), has been refined using this source. Taking into account the stall speed 54-56mph for 2050lb. the average CL_max value is 1.09. Finally, the stall speed of S.E.Va in RoF is about 45-48mph on the airspeed indicator w/o thrust, and less than 40mph at full power.

Since aerodynamics of the wing have been modified (according to new CL and CD curves), then the roll rate (aileron performance) is also changed as a consequence. Now the roll rate is worse then before.


Airscrew

After airframe aerodynamics and engine performances have been modified, all I can do to ensure the right characteristics of the aircraft (I mean the climbrate and speed) - this is an airscrew tuning. All the more that «glass engine» was because wrong blade aerodynamic performances.

The general geometry of the airscrew I've taken from this source:

Image


After analyzing the drawing I put into the RoF basic geometric parameters of T28118 – as an original airscrew for S.E.Va with Viper engine:

Attached File  Airscrew.zip   23.72KB   52 downloads

And then I’ve done many iterations to found aerodynamic performance of blade (CL and CD polar curve) that match general performance of typical British 2-blades fixed pitch wooden airscrew:

Attached File  BritishAirscrewPower.jpg   535.43KB   1812 downloads

Attached File  BritishAirscrewThrust.jpg   849.67KB   1812 downloads

Selected CL and CD curves for the blade provide a good agreement between the results of tests in the game and calculations of thrust and RPM using charts above:

Attached File  RPM.jpg   182.93KB   1812 downloads

Attached File  Thrust.jpg   179.67KB   1812 downloads

And most important, this airscrew gives needed performance of airplane in general…


Airspeed, climb rate and ceiling

Well, guys, as we have already discussed about the maximum speed, I just publish the test results here:

Attached File  Speed.jpg   335.72KB   1812 downloads

The climb rate… yea, it’s a really most hard task, because as usual every source data is uneven, they often contradict each other, roughly approximated, and we very seldom know anything about the conditions (the weather, airplane weight, fuel, ammo, etc.) or when the timer started: in the moment when the pilot set full throttle, or when wheels were up from runway, or may be when the pilot started climb after level flight at some altitude? We don’t know anything. So, this is a always investigation, painstaking research and walking around strange puzzle, analysis and many trying to know the truth. The same words about the ceiling, but the climb rate, of course, is more important for gameplay.

For determine what data can be trusted and what are not I do always analysis the time data from each source: study how its derivative depend on altitude, calculate several theoretical climb paths, with taking into account the various vertical velocity at sea level, and various ceiling (as is known, the climb rate often very close to linear function of altitude). I combine some data from different sources each other, shift all of them on the same time for acceleration or deceleration the beginning of climb, to obtain a uniform vertical velocity dependence on altitude, w/o the time, which may be was spend for moving on the runway, or on the contrary add the time, which may be need to spend for takeoff and for climbing to some altitude. After this analysis sometimes it becomes clear, that airplane can't climb to some altitude so fast, because the time in the source is from level flight, not from start on the ground, f.e. Or sometimes it becomes clear, that climb time to some altitude can't be so much, because then the ceiling must be too low (may be this data for the airplane with bombs, or it's a mistake and value is for the other engine, etc.). I write this to you just for your understanding, that sometimes the source contains data that cannot exist together, because so many reprints, errors, and speculations have accumulated in the books.

Attached File  British-Aeroplanes.jpg   217.61KB   1812 downloads

Attached File  Profile.jpg   866.29KB   1812 downloads

Attached File  AE_Complete.jpg   1.06MB   1812 downloads

As usual, if airplane FM is developing and tuning in accuracy, the climb rate doesn’t need for additional tuning, and it is quite close to some of sources. In this case I usual believe this source, and finish work. But sometimes I have to spend much time for understanding: what’s wrong? Is here our mistake, or maybe it’s a wrong source data? Nobody knows.

Anyway, the new S.E.Va climb rate seems quite close to the one of combinations of source data. It is a bit faster all the time, about 10 seconds for any altitude, except 10’000ft (there is a bit delay). I don’t know why this time shift is present, may be because in real life pilot is starting easier, and moving throttle smooth or something else. The most important is that vertical velocity is quite realistic at any altitude. However, the theoretical ceiling of S.E.Va in RoF (where is the level flight is possible yet) almost w/o fuel is 6700m (with accuracy less than 25m), and it seems very-very close to 22’000ft (error does not exceed 18ft, 0.1%). That’s why I don’t believe in 19:55 or 20:50 to 15’000ft with full fuel loading (I note, that we test climb rate in RoF from the start with the place with full fuel loading for all airplanes). If 19:55 would be possible, then ceiling must be much higher, but I’ve never read anywhere about ceiling more than 22’000ft for S.E.5. Moreover, the theoretical ceiling of S.E.Va in RoF with full fuel loading is 5900m (with accuracy less than 25m), and it again seems very-very close to 19’500ft (error does not exceed 143ft, 44m, 0.7%). Magic? I don’t know. So, the climb rate for S.E.Va in RoF is:

Attached File  Climb.jpg   257.1KB   1812 downloads

Of course, I clearly understand that it’is climbing to 5000ft up to 14 seconds faster, and the error is 5.1% (this is the biggest error here). I have tried many ways to fix it and spend about 3 days over the plan for this job – but I have no good result. Each method corrupts other performances more than improve climb rate. And to the end, I don’t understand one more thing: how is it possible: if S.E.Va in RoF has a right engine power curve; has a right Drag and Lift with and w/out aircrew; has right performances of T28118 airscrew, with consider an its slipstream and additional drag for airplane parts which are in the slipstream; and at last, S.E.Va has a quite right horizontal speed at any altitude, has right ceiling and almost right climb but.. look at this yourself:

Attached File  Climb_T28118.jpg   333.32KB   1812 downloads

- is here some another S.E.Va with another Viper engine??? I don’t understand it all… No any weight loading or low engine compression can give the same result to the this source. On this picture the airplane is dramatically slow and it's a very pure climbing. May be somebody tell me - how is it possible?.. and… welcome to the club, who has read all until this line. :)

(and sorry for my English, maybe I wrote something not clear here…)

Sincerely,
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#112 NewGuy_

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Posted 10 September 2011 - 15:33

An.Petrovich,
Well, I would like ot first thank you for your great job on the Spad 7. She is a real masterpiece and so utterly enjoyable to use. Given your great skill, I am sure that we are all in for a great experience, using this new and improved FM; for the SE5a. Thank you for putting so much hard work into the SE5a and I look forward to seeing your efforts implimented in 1.22. :S!: MJ
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Something something SPAD. Something something then dive away. 


#113 mozza

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Posted 10 September 2011 - 15:50

An. Petrovich and team.

Simply Incredible response and attention to detail - Brilliant and I can't wait to see the results !

Attached File  P1040240.JPG   2.96MB   1744 downloads
Attached File  P1040241.JPG   3.05MB   1744 downloads

Don't know if you have this data from RAE Farnborough tests that I found at Public Records office in Kew , London. I have some more written report on these tests and also some handwritten RAE reports on French built 150/180/200 geared Hisso's if required.

Huge thanks for all this great work - I can't wait to try the new SE5a FM !

Mozza
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#114 Wad

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Posted 10 September 2011 - 15:59

The links to the second source of engine power curve and the source of general geometry of the airscrew is not available for me at least.
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#115 SYN_Mike77

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Posted 10 September 2011 - 16:08

Oh happy days! Put this fix in with the stutters fix for ATI cards and call it 1.021b and you will have some very happy customers!
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#116 BuddyWoof

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Posted 10 September 2011 - 16:20

Sounds awesome. Thanks An.
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#117 gavagai

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Posted 10 September 2011 - 17:09

Since aerodynamics of the wing have been modified (according to new CL and CD curves), then the roll rate (aileron performance) is also changed as a consequence. Now the roll rate is worse then before.

I had wondered about this. The current SE5a is in the category of super-rollers with the N28, and Albatros D.II/Va.
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#118 FlyingShark

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Posted 10 September 2011 - 17:19

Oh happy days! Put this fix in with the stutters fix for ATI cards and call it 1.021b and you will have some very happy customers!
Indeed, good idea.

:S!:
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#119 Rivet

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Posted 10 September 2011 - 17:55

An. Petrovich and team.

Simply Incredible response and attention to detail - Brilliant and I can't wait to see the results !
Mozza

+1 :S!:
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#120 HotTom

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Posted 10 September 2011 - 18:05

Thank you for such a deep analysis!

It should be a very accurate model now!

:S!:

HT
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