Gustav questions about weight and pressurization

[istari6]

I've just started a Career flying the Bf 109 G-2 at Stalingrad.  Having flown the Friedrich (F-2 and F-4) previously, I've been looking forward to learning the differences in the famous Gustav.  Coming into this campaign, I knew the Gustav series was heavier than Friedrich, being increasingly optimized for 4-engined bomber interception.  I also knew the German pilots rated the Friedrich the best overall flying experience, while the Gustav was increasingly "warped" by the weight, power and torque issues.  

 

When I looked at the Aircraft Performance information in Battle of Stalingrad, I wasn't surprised to see the G-2 has a SL turn time of 22.2 sec compared to just 20.3 sec for the F-4.  That fits with a significantly heavier aircraft.  Yet when I compared the actual weights, here's what I came up with:

 

WEIGHTS	Bf 109 E-7	Bf 109F-4	Bf 109G-2
Empty	2049 kg	2382 kg	2486 kg
Standard	2614 kg	2890 kg	2994 kg
Maximum TO	2893 kg	3189 kg	3283 kg

 

For Empty or Standard, the G-2 is only 104 kg heavier than the F-4.  That's just 4.3% heavier, yet it has a turn rate almost 10% slower.  In contrast, the Friedrich was much heavier than Emil, yet pilots talked of it's sparkling performance and handling.  

 

Why did Gustav suffer such a decrease in turn rate for what seems a very modest weight increase?  Can 104 kg have that big an effect on an airframe?  If so, it would seem that the relative fuel load would be one of the most important facts in dogfights, considering the 109 has 304 kg in fuel alone.  

 

Also (unrelated question on the Gustav)... 

 

Why was pressurization pursued so halfheartedly in the G series?  Learning about the different variants, it seems the odd-numbers (G-1, G-3, G-5, etc) were meant to be pressurized, while even-numbered (G-2, G-4, G-6...) were not.  Yet the non-pressurized ones were built in vastly greater quantities.  Was pressurization a technology that just didn't work properly?  Were the B-17s and Lancasters not flying high enough to need pressurization, and this was more future-proofing against the B-29? 

 

 

 

[unreasonable]

On the pressurization point - before the B-29 very few bomber aircraft could fly at an altitude high enough to make pressurization necessary, generally only long range recce versions like the Ju86P.  Bombing heights were rarely above 15,000 - 20,000 ft and often considerably lower: fully loaded RAF bombers would unable to get above that and even some of the USAAF bombers, with their lighter bomb loads, found that in practice accuracy drops off so badly at higher altitudes that it was pointless.  Over Japan, even the B-29s eventually changed their tactics and dropped from 5-10,000 ft at night!

 

So you only needed a few interceptors capable of operating at extreme heights to catch recce flights, or pressurized versions of fighters with cameras installed to do recce themselves.  

Edited August 21, 2019 by unreasonable

[Kurfurst]

10 hours ago, istari6 said:

Yet when I compared the actual weights, here's what I came up with:

 

WEIGHTS	Bf 109 E-7	Bf 109F-4	Bf 109G-2
Empty	2049 kg	2382 kg	2486 kg
Standard	2614 kg	2890 kg	2994 kg
Maximum TO	2893 kg	3189 kg	3283 kg

 

For Empty or Standard, the G-2 is only 104 kg heavier than the F-4.  That's just 4.3% heavier, yet it has a turn rate almost 10% slower.  In contrast, the Friedrich was much heavier than Emil, yet pilots talked of it's sparkling performance and handling.  

 

As per the German weight sheets, the actual standard take off weight was 3037 kg for the G-2, and 2890 kg for the F-4 (clean, fully fueled and loaded fighter configuration).

Not much of a difference, however note the early Fs with the 601N engines were considerably lighter than the F4 (2600-2700-ish IIRC). I believe the comments in how much lighter the Fs were are largely based on the first impressions on the early F models.

 

The difference between the F-4 and G-2 were much lower in practice, given that the weight of light metal plates (32 kg) behind the fuel tank were not counted in the F4, and in all probability neither was the external armored glass, as these were retrofits on the F4 but standard on the G2. The rest came down by slightly heavier prop and engine and ancillaries (bigger oil cooler), landing gear, and the strengthened wing structure of the G2.

 

In fact overall the late F-4s and the early G-2s were largely similar, the G2 was more of a facelifted F4, so much so that the G series part manuals refer back to the F series part manuals, as the parts were interchangeable to a large extent.

 

10 hours ago, istari6 said:

 

Why did Gustav suffer such a decrease in turn rate for what seems a very modest weight increase?  Can 104 kg have that big an effect on an airframe?  If so, it would seem that the relative fuel load would be one of the most important facts in dogfights, considering the 109 has 304 kg in fuel alone.  

 

Its probably an error in turn specs. The Russians tested both captured F4s and G2s, and the turn times were iirc measured as 20 sec vs 20,5 sec at 1000 m.

 

Speed wise, in 1942 there wasn't much of a difference either (660-670ish), which is logical given the F4s fully rated (1.42) 601E had very similar power output to the derated (1.3) early 605As. The latter had slightly better altitude output though.

 

Personally I believe the practical difference between an F-4 and the G-2 was pretty slim in 1942, given the F-4s actual take off weight was probably within 100 kg from the G-2 when all the extra armor was retrofitted, power output, weapons and aerodynamics being practically the same as well. 

 

10 hours ago, istari6 said:

 

Also (unrelated question on the Gustav)... 

 

Why was pressurization pursued so halfheartedly in the G series?  Learning about the different variants, it seems the odd-numbers (G-1, G-3, G-5, etc) were meant to be pressurized, while even-numbered (G-2, G-4, G-6...) were not.  Yet the non-pressurized ones were built in vastly greater quantities.  Was pressurization a technology that just didn't work properly?  Were the B-17s and Lancasters not flying high enough to need pressurization, and this was more future-proofing against the B-29? 

 

 

There was not much need for such high altitude aircraft. Pressurization was vital for any extended operation at higher altitudes, i.e. 7000-8000 m and up, but there were few such targets, mostly just lone PR aircraft. Russian aircraft were for low and medium altitude, and the RAF's medium bombers at the time, and in fact, for the entire war were either rated for rather modest altitudes (4000m), or were already bombing by night. That pretty much leaves you with the odd PR Spitfires and the odd medium bomber struggling at high altitude, which at this time (1942) presented lone, but relatively fast moving targets that could not shoot back. In short, apart from a few specialized high altitude Staffeln on the Western front, there wasn't much need to operate - and provide replacement for - special high altitude interceptors. The pressurized cockpit was a must for these planes due to human limitations, but for good measure GM 1 boosters were added to the mix to provide truly terrific performance at altitude, very useful indeed considering the fast cruise speeds and high cruising altitude of PR aircraft.

[-=PHX=-SuperEtendard]

@JtD has tested the turntimes for most of the planes planes and could achieve 20 seconds with both the F-4 and G-2, but with the F-4 he was using 1.3 ata, so 110 HP less than the G-2 and turning just as well. With 1.42 ata it would turn better. The efficiency he calculated was very similar between the F-4 and G-2 though, so it seems that those 104 Kg difference between both planes in stock configuration in game (no extra armor for the F-4) almost explain the difference in turn performance, maybe the rest is down to the propeller, but I don't know the differences between them.

The worst turner is the 109 F-2 though, even being really light at 2789 Kg stock configuration, the turn time is slower at 22.4 seconds with 1175 HP according to his tests, and you can really feel it in game. The plane becomes rather sluggish at low speeds compared to the F-4 for example. I guess it has to do with the propeller. At low speeds the F-2 prop can't mantain the high RPM, it needs around 185 km/h in the take off run to reach 2600 RPM with 1.35 ata. The F-4 and G-2 props can achieve their rated RPMs for 1.3 ata while standing still.




 

Edited August 21, 2019 by -=PHX=-SuperEtendard

[istari6]

On 8/20/2019 at 8:02 PM, unreasonable said:

On the pressurization point - before the B-29 very few bomber aircraft could fly at an altitude high enough to make pressurization necessary, generally only long range recce versions like the Ju86P.  Bombing heights were rarely above 15,000 - 20,000 ft and often considerably lower: fully loaded RAF bombers would unable to get above that and even some of the USAAF bombers, with their lighter bomb loads, found that in practice accuracy drops off so badly at higher altitudes that it was pointless.  Over Japan, even the B-29s eventually changed their tactics and dropped from 5-10,000 ft at night!

 

So you only needed a few interceptors capable of operating at extreme heights to catch recce flights, or pressurized versions of fighters with cameras installed to do recce themselves.  

 

So do we know if the Gustav was an attempt by the RLM to "future-proof" against B-29s?  Or were they facing threats already that required pressurization in 1943?  I've heard the Mosquito was a high-flying reconnaissance airplane, but I don't believe it was pressurized.  Thanks for the info.

On 8/21/2019 at 12:34 AM, VO101Kurfurst said:

There was not much need for such high altitude aircraft. Pressurization was vital for any extended operation at higher altitudes, i.e. 7000-8000 m and up, but there were few such targets, mostly just lone PR aircraft. Russian aircraft were for low and medium altitude, and the RAF's medium bombers at the time, and in fact, for the entire war were either rated for rather modest altitudes (4000m), or were already bombing by night. That pretty much leaves you with the odd PR Spitfires and the odd medium bomber struggling at high altitude, which at this time (1942) presented lone, but relatively fast moving targets that could not shoot back. In short, apart from a few specialized high altitude Staffeln on the Western front, there wasn't much need to operate - and provide replacement for - special high altitude interceptors. The pressurized cockpit was a must for these planes due to human limitations, but for good measure GM 1 boosters were added to the mix to provide truly terrific performance at altitude, very useful indeed considering the fast cruise speeds and high cruising altitude of PR aircraft.

 

The idea of a few specialized 109s for high-altitude PR intercepts makes sense when you look at the numbers of G-1 (167) or G-3 (50).  I guess even the G-5 at 475 is <5% of the G-6 (12,000+).  So that all fits with the idea of a tiny fraction of the total production being for anti-PR work, while gaining experience with pressurization ahead of the coming B-29.  

On 8/21/2019 at 12:34 AM, VO101Kurfurst said:

Its probably an error in turn specs. The Russians tested both captured F4s and G2s, and the turn times were iirc measured as 20 sec vs 20,5 sec at 1000 m.

 

Speed wise, in 1942 there wasn't much of a difference either (660-670ish), which is logical given the F4s fully rated (1.42) 601E had very similar power output to the derated (1.3) early 605As. The latter had slightly better altitude output though.

 

Personally I believe the practical difference between an F-4 and the G-2 was pretty slim in 1942, given the F-4s actual take off weight was probably within 100 kg from the G-2 when all the extra armor was retrofitted, power output, weapons and aerodynamics being practically the same as well.

 

Interesting, I hadn't considered the possibility that the data in the Aircraft Specifications is a typo.  Having flown both the F-4 and G-2 in the game, the G-2 definitely "feels" heavier and mushier in a turn, with more nose instability.  The F-4 feels like it turns on a dime with better precision in pointability.  But that might be placebo effect since I'm interpreting how they feel through the bias of the specification data. 

 

Agree that the don't feel very different overall, but for me, the huge advantage of the G-2 is slamming the throttle to full power and fighting for 30 minutes.  The F-4 might have higher peak power, but it's only usable for short bursts, always babying the engine.  The G-2 feels better for energy tactics since I can just hold the engine at max available power and work the vertical.  

On 8/21/2019 at 8:50 AM, -=PHX=-SuperEtendard said:

has tested the turntimes for most of the planes planes and could achieve 20 seconds with both the F-4 and G-2, but with the F-4 he was using 1.3 ata, so 110 HP less than the G-2 and turning just as well. With 1.42 ata it would turn better. The efficiency he calculated was very similar between the F-4 and G-2 though, so it seems that those 104 Kg difference between both planes in stock configuration in game (no extra armor for the F-4) almost explain the difference in turn performance, maybe the rest is down to the propeller, but I don't know the differences between them.

The worst turner is the 109 F-2 though, even being really light at 2789 Kg stock configuration, the turn time is slower at 22.4 seconds with 1175 HP according to his tests, and you can really feel it in game. The plane becomes rather sluggish at low speeds compared to the F-4 for example. I guess it has to do with the propeller. At low speeds the F-2 prop can't mantain the high RPM, it needs around 185 km/h in the take off run to reach 2600 RPM with 1.35 ata. The F-4 and G-2 props can achieve their rated RPMs for 1.3 ata while standing still.

 

That's really interesting!  Never considered the possibility that the prop could play such a key role in turn performance.  I've always heard about the value of the late-war "paddle blades" for better extracting power at high altitudes.  One of the great things about this hobby is that even after 30 years, still so much to learn.  

 

[unreasonable]

27 minutes ago, istari6 said:

 

So do we know if the Gustav was an attempt by the RLM to "future-proof" against B-29s?  Or were they facing threats already that required pressurization in 1943?  I've heard the Mosquito was a high-flying reconnaissance airplane, but I don't believe it was pressurized.  Thanks for the info.

 

 

I very much doubt thoughts about the B-29 had anything to do with it, did the Germans even know about the programme?  From the Mk XVI onwards, both PR and bomber versions of the Mossie were pressurized, so from roughly 1944 onwards. The Mosquito was an exception to my earlier remarks about bombers, BTW: high level bombing by them did not need to be particularly accurate: they were essentially just keeping everyone awake and in shelters and harassing the emergency workers with nuisance bombing.   TBH I just forgot about them.

 

Not that chasing Mosquitoes with Gustavs would get you very far, pressurized or not.

[MasserME262]

On 8/20/2019 at 6:13 PM, istari6 said:

That's just 4.3% heavier, yet it has a turn rate almost 10% slower.

Man I am no aerospace engineer or something like that but I doubt its as easy as "if 4.3% heavier -> 10% slower".

[FTC_Cule]

Turn rate involves lots of factors. Engine power is one of them, because with higher angles of attack in the turn, a more powerful engine will deliver more centripetal force, assisting in the turn. F2 (in comparison to F4 and Gs) has weaker power at combat and continuous settings, and if I remember correctly the turn times are calculated using such power settings. This could probably be the important disparity when the devs calculated it.

 

However, a good indicated best turn time does not mean a plane will turn tighter in a combat situation, where energy is bled through drag to assist the turn. F2 can turn very well at lower speeds, though not sustained. Another thing to note is that some planes turn to one side much better than the other due to the engine torque. A right hand side turn in a yak vs 109 will result in the yak gaining the upper hand even if it has a slower indicated turn time, that is because the yak's torque favours the right turn whereas the 109 is hindered by it and would rather turn left.

 

P.S. When the 109 G2 was conceived, it was not yet intended for better intercepting 4-engine bombers.