Issues with G-2, G-4 & G-6 high altitude WEP

[HandyNasty]

I wanted to test the 109G-2 performance at 2800RPM at high altitudes (above FTH) and I found following results :

results are in INDICATED airspeed (the velocity the game gives), map is Kuban Autumn, rads automatic, full fuel.

 

ALT         auto 100% throttle            100%throttle + manual 2800rpm

8km    :      417                                                     437

9km    :      387                                                     408

10km  :     357                                                      380

11km  :     322                                                      343

 

Note a +- 20kph increase IAS.

 

 

Now when I did the same for the G-4 (comparing "combat mode : 80% throttle" , "boosted mode : 100% throttle" and finally "80% throttle where I put RPM at 2800 manually")

ALT         auto 80% throttle                          auto 100% throttle                           80%throttle + manual 2800rpm

8km    :     406                                                    419                                                  426

9km    :     378                                                    390                                                  399

10km  :     347                                                    360                                                 371

11km  :     311                                                    325                                                 335

 

Note a +- 12kph indicated difference between column 1 and column 2, and a roughly 20kph indicated difference between Column 1 and Column 3 (on par with differences seen in case of G-2)

 

 

For the case of the G-4, I would have expected that full throttle (column 2) and column 3 would give same top velocity.  Additionally at 10km alt, I have 0.92 ata and 2800RPM for both Column 2 and Column 3 (see images), but there is a speed difference of +-11 IAS (at that alt, that's roughly 19kph).

 

Is this supposed to be like that? From what i know about engines and aerodynamics column 2 and 3 for the G-4 should gives same velocities as they have same rpm and ata, no?

Also, a quick test on the F-4 showed me no difference between 100% throttle and 80% throttle + manual 2700RPM at 10km alt. Another quick test showed same issue with the G-6 at 9km alt (379kph vs 388kph indicated).

 

Can someone shed some light here?

 

 

 

 

 

[=EXPEND=13SchwarzeHand]

Does seem strange...

One thing though, full combat in the G4 is 85% throttle not 80%.

The G4 also has the non retractable tail wheel and the wing bumps which give it increased drag compared to the G2, so it is generally slower, when on full combat

 

21 minutes ago, =FSB=HandyNasty said:

For the case of the G-4, I would have expected that full throttle (column 2) and column 3 would give same top velocity

 

I don´t think that is the case. The Kommandogerät chooses the optimal prop to rpm setting, so by just increasing rpm manualy you do not get the same power output as by having it in auto. So this is correct AFAIK. Ata is linked to power output so you cannot increase power output by only increasing rpm.

I don´t understand why ata is the same for 100% and 80% though.

 

Edited April 12, 2019 by =EXPEND=SchwarzeDreizehn

[HandyNasty]

Additional tests for G-4 at 10km alt

 

80% throttle + 2800rpm : 371 kph

85% throttle + 2800rpm : 368 kph

90% throttle + 2800rpm : 364 kph

95% throttle + 2800rpm : 360kph

100% throttle (and auto 2800RPM)  : 360kph

 

In all cases, ata is 0.92..., ergo in all cases the engine regime is the same, yet top speed is different

 

[=EXPEND=13SchwarzeHand]

13 minutes ago, =FSB=HandyNasty said:

Additional tests for G-4 at 10km alt

 

80% throttle + 2800rpm : 371 kph

85% throttle + 2800rpm : 368 kph

90% throttle + 2800rpm : 364 kph

95% throttle + 2800rpm : 360kph

100% throttle (and auto 2800RPM)  : 360kph

 

In all cases, ata is 0.92..., ergo in all cases the engine regime is the same, yet top speed is different

 

 

 

I do not know what the Kommandogerät does to the angle of the prop blades when the rpm governor is turned off. I think finding that out will give the solution to the problem.

 

Because same ata and same rpm should give the same speed when the prop is set the same way for both scenarios.

If the prop adjustment differs when changing the throttle this might lead to some skewed results though

Edited April 12, 2019 by =EXPEND=SchwarzeDreizehn

[Bert_Foster]

DB engines don't have Kommandgerat. In the DB engines the ATA/RPM AUTO relationship is controlled pretty simply as a function of throttle position.... no magic analog KG type device.

With Prop pitch manual you drive the blade angle directly via the thumb switch. There is no Constant speed function in manual, RPM will vary as a function of TAS for any given ATA. If TAS is constant RPM will be constant.

Edited April 12, 2019 by Bert_Foster

[JtD]

This is truly not as it should be...can you do a few more runs and check at which point the aircraft gets slower? 70%? 60%?

 

Have you checked the radiators? Is it possible that they are more open at full throttle than they are at lower throttle settings?

 

Differences between having the throttle position at full and at combat in real life would be:

- ignition timing (which is connected to throttle lever position), could lead to small differences in engine temperatures and power output

- positions of the throttle regulation system, which in case of emergency power is also actuated mechanically, while in case of combat power it is only actuated hydraulically (should have no net effect on boost pressure)

[=EXPEND=13SchwarzeHand]

1 hour ago, JtD said:

(should have no net effect on boost pressure)

 

Sorry, I don´t understand, there should be no effect on boost pressure between combat and emergency due to the difference in mechanical and hydraulic actuation, but there should be a difference in boost pressure overall right?

Edited April 13, 2019 by =EXPEND=SchwarzeDreizehn

[HandyNasty]

Other test :

 

at 10km altitude,  full boost in the G-6. When arrived at top speed I fix the prop pitch. Then, when I reduce throttle to 80%, the RPM changes to ~2900 and ata increases from roughly 0.92 to 0.96. Subsequently, the plane accelerates a few kph.

 

Why would, for fixed prop pitch at high alt, reducing throttle a bit (which should not change ata, since 80% throttle tends to 1.3 ata if there was enough outside air pressure) increase engine revolutions (and thus supercharger revs and thus increase ata a bit)?

[JtD]

47 minutes ago, =EXPEND=SchwarzeDreizehn said:

but there should be a difference in boost pressure overall right?

 

Not at high altitude (10km), no.

 

The DB605 boost pressure regulation system is a bit odd. It uses two different throttles, one for automated boost regulation that compensates outside pressure changes, and one manually regulated for actual manifold pressure.

 

The first throttle regulation was set up in a way so that it would always regulate to 1.3ata - you go up into thinner air, it opens up, you go down into thicker air, it closes. This was done, as per usual, with an aneroid that operated a hydraulic valve, and the hydraulics controlled the throttle position. It worked up to an altitude where 1.3ata were no longer achievable by the supercharger. At this altitude the throttle would be fully open.

 

The second throttle was mechanically linked to the power lever. This direct linkage is possible, because the automated boost regulator would always provide 1.3ata no matter the altitude (up to critical altitude), so setting the pilots power lever to 40° would have the same effect at 1km at it would have at 5km - reducing the 1.3ata from behind the supercharger to 1.2ata going into the manifold. The throttle was fully open at combat power setting.

 

Now in order to achieve 1.42ata take off/emergency boost, you would have to override the first throttle, so that the aneroid would no longer limit the boost to 1.3ata. The second throttle was fully open already, after all. For this, a cable existed between the pilots power lever and automated boost control unit. If the pilot pushed the lever beyond combat power into emergency, this cable would move the linkage between the aneroid an the hydraulic control valve, essentially tricking it into believing there were less than 1.3ata - and the regulation would open up to 1.42ata. The second throttle, still fully open, would allow this to go directly into the manifold.

 

So at high altitude, both throttles would be fully open, both at combat and emergency power. The second throttle should be closing below combat power (80ish%), and boost should fall off.

The throttle regulation would be in tricked state at emergency, and in normal state at combat, but both conditions would just cause the first throttle to open fully.

Edited April 13, 2019 by JtD

[HandyNasty]

Subsequent tests with G-6 at 11.5km alt, all tests have 2800RPM, varying throttle position.

 

60%  throttle and 2800rpm : 300kph (with ata ~0.738)

66%  throttle and 2800rpm : 300kph (with ata ~0.738)

75%  throttle and 2800rpm : 299kph (with ata ~0.738)

80%  throttle and 2800rpm : 299kph (with ata ~0.738)

85%  throttle and 2800rpm : 295kph (with ata ~0.738)

90%  throttle and 2800rpm : 291kph (with ata ~0.738)

100% throttle and 2800rpm: 287kph (with ata ~0.740)   (slightly higher than other throttle settings)

 

 

If I'm not misunderstanding your post above JtD, this is wrong behavior? Below 80% throttle, ata should drop right?

 

[JtD]

Thanks for testing, and yes, it should.

[Velxra]

This is definitely incorrect behavior. I hope it gets fixed "soon" and very informative information everyone. 

[E69_geramos109]

very well modelled

[Willy__]

Just out of curiosity, how much time can you maintain 2800rpm before the engine blows up ?

[Guest deleted@50488]

Are the Devs aware ?

 

This should be fixed...

[HandyNasty]

25 minutes ago, cagari-cagarou said:

Are the Devs aware ?

 

This should be fixed...

 

It would indeed be great for them to acknowledge this issue. Additionally, the behavior I noticed here above is only for the G versions of the 109's, the F and K don't have this issue. I suspect therefore that this is indeed a bug / not-correctly-modelled-feature. It shouldn't be that hard to correct?

 

However, I do not rule out the possibility that it is correctly modelled and that we are overlooking something in the workings of the DB605. Yet if that's the case, I'd very much like to know (from the devs) where I (we) were wrong.

 

 

11 hours ago, Willy__ said:

Just out of curiosity, how much time can you maintain 2800rpm before the engine blows up ?

I do my tests with "unbreakable" on where engine does not blow up if you abuse the engine settings.

[Dakpilot]

Perhaps it would be prudent to formulate this in a proper bug report in the correct section. 

Cheers, Dakpilot 

[Velxra]

4 hours ago, =FSB=HandyNasty said:

I do my tests with "unbreakable" on where engine does not blow up if you abuse the engine settings.

 

With normal damage settings turned on. Does the engine self destruct? Perhaps that is why this issue has gone unnoticed until now.

[HandyNasty]

1 minute ago, Geronimo553 said:

With normal damage settings turned on. Does the engine self destruct? Perhaps that is why this issue has gone unnoticed until now.

With the "unbreakable" setting off I obtain the same (I just need to do the tests in a smaller time window as to avoid engine destruction due to high engine setting for too long a time)

 

[E69_geramos109]

I made this quick test. I set the pitch on manual and i realice that when i take out power the Ata increases. It looks that something is weird here

 

Edited May 8, 2019 by E69_geramos109

[HandyNasty]

@E69_geramos109

 

Thank you for doublechecking and coming to same conclusion and ty for vid as well, makes it more visually clear what the test gives as results.