One question on Tomahawks and Kittyhawks

[343KKT_Kintaro]

Hi all. Why do the flashcards instruct not to exceed 54 inches (Tomahawk) nor 56 inches (Kittyhawk) on the tachometer if the gauge doesn't go further than 50 inches?

[FTC_Karaya]

Because that is the actual max boost on both models, you cant reach more than that. The flashcards only show the maximum attainable boost in the sim.

[343KKT_Kintaro]

15 hours ago, Karaya said:

The flashcards only show the maximum attainable boost in the sim.

 

 

Well, maybe, but the gauge in the cockpit stops at 50... same as in the Great Battles series and, most likely, same as in historical P-40s. So... I don't get it yet.

 

 

[Thundercracker]

I would guess the boost figures  supplied are max as Karaya said. The pressure gauge was updated In later models with revised engines.

 

Here's the p40 kittyhawk they found in Egypt, showing a max readable figure of 50 (as in game).

 

And here's a private owned Curtiss P-40 Kittyhawk IV ZK-CAG Cn 28492 (ex-RAAF A29-448) at Ardmore NZAR, with a gauge that goes to 75.

Edited April 14, 2021 by Thundercracker

[I/JG54_chuishan]

For the Allison V-1710-F3R, or V-1710-39 series engines installed on Tomahawks and Kittyhawks, the manifold pressure that can be pulled from them depends on the automatic manifold pressure regulator installed and its setting.

 

I'm quoting this from the Handbook of Operation and Maintenance for Allison V-1710 "F" Type Engines 3rd Edition issued by Allison Division, General Motors Corporation.

 

 

 

 

 

 

 

 

It is therefore clear that the limit applied by the regulator directly impacts the maximum manifold pressure which can be pulled from the engine. And also there's always a limit for the regulator itself. A metal plate on the regulator states the maximum manifold pressure it can manage. As stated in this handbook, if the engine is not meant to be operated for War Emergency Ratings (or W.E.R), but only Standard Emergency Ratings then the maximum manifold pressure for the engine should be 52in. Regulators with limits of 52in or higher can be installed therefore, and their settings duly adjusted to match the desired engine operation limit of 52in.

 

As also listed in the handbook, it is possible to adjust the limit of the regulator from a minimum of 50in to a maximum of 60in, depending on the intended rating of the engine. It's therefore possible for frontline units to re-adjust the setting of the regulator to achieve higher manifold pressure.

 

Then why in our game the limit is set to 50in? I guess it is intended for getting matching results as it is said in the Pilot's Note, which shows as follows:

 

 

 

 

As you can see what listed in the Pilot's Note went well under 50in for safe operation and engine longevity.

 

For Tomahawk with V-1710 "C" Type engines the limits were even lower:

 

 

 

Although I am also a bit confused for why Curtiss did not provide manifold pressure gauge that supported this kind of flexibility of adjustment of maximum limits in the first place... But hope the above information is helpful.

Edited April 14, 2021 by I/JG54_chuishan

[I/JG54_chuishan]

1 hour ago, I/JG54_chuishan said:

why Curtiss did not provide manifold pressure gauge that supported this kind of flexibility of adjustment of maximum limits in the first place...

 

It was possible that in the pre-war and early-war years Standard Emergency Ratings were considered sufficient for V-1710, so the manifold pressure gauges were designed accordingly, with a maximum reading of 50in. 

 

1 hour ago, Thundercracker said:

with a gauge that goes to 75.

 

BTW, in reality it is also possible for P-40s with V-1710-F3R and F4R types of engines to run without an automatic manifold pressure regulator. According to a letter written by Mr. R. M. Hazen, the Chief Engineer of the Allison Division, General Motors Corporation, Pilots in the Middle East and Australia managed to continuously operate V-1710-F3R and F4R types of engines at over 70in of boost with regulators removed. It was reported that the engines were able to perform normally at this kind of boost for about 20 minutes before overheating. It is thus explained that why late model P-40s had a boost gauge with higher limits up to 75in.

 

It also proves that the so-called 'glass engine' Allison V-1710 modelled in BOX without automatic manifold pressure regulators simply does not exist in reality. This type of engine is way tougher than how it was modelled in the BOX game. It was also why soviet pilots can press so much of the performance out of this engine and made it a fierce weapon against the Luftwaffe at low altitude.

 

 

 

 

Edited April 14, 2021 by I/JG54_chuishan

[FTC_Karaya]

7 hours ago, 343KKT_Kintaro said:

Well, maybe, but the gauge in the cockpit stops at 50... same as in the Great Battles series and, most likely, same as in historical P-40s. So... I don't get it yet.

 

A gauge is a gauge. Just because it stops somewhere doesnt mean you cannot exceed its values.

[343KKT_Kintaro]

Thank you guys, Thundercracker and Chuishan, for all the precious documentation. You were great help.

 

 

On 4/14/2021 at 6:17 PM, Karaya said:

 

A gauge is a gauge. Just because it stops somewhere doesnt mean you cannot exceed its values.

 

 

My question dealt with exact numbers, 54 and 56 supposedly not having to be exceeded... on a gauge that doesn't go further than 50! Thus, my question was with no doubt relevant. I accept what you say, Karaya, but your answer makes sens only if the throttle's maximum displacement cannot make the manifold pressure goes up to the levels that cause the engine to break down. I don't think it was the case in those P-40 Bs, Cs and Es, back in the early 1940s.

 

I proceeded with more tests in both simulators, the Great Battles series and the Dover series.

 

1) Great Battle series. There's a P-40 E in the Great Battles series because the aircraft served during the defense of Moscow. There's something in this IL2GB P-40 that is very odd: to obtain the lesser prop pitch you need to set 0% when manual and 100% when automatic (automatic is constant speed). In my opinion this is very odd. Otherwise, the constant speed mode blocks the RPM at 3000. You can exceed those 3000 by diving, for example, by this causes the engine failure within 40 seconds more or less. Same thing when you are flying with the prop pitch manual mode: you manually set 0% of prop pitch (the lesser pitch in manual mode) so that you can easily go over 3100 RPM if you push enough the thrust (in the GB series a red mark indicates that limit on the tachometer, not in the Dover series) but, again, after 30 or 40 seconds, this causes the engine break down.

 

2) Dover series. In the Dover series, the P-40 E is the Kittyhawk. Same as in the Great Battles series, the constant speed mode blocks the RPM at 3000. I did one test on manual mode and, because it was so boring, I stopped after 10 minutes, but the fact is I didn't encounter any problem with flying (at levelled flight) at 42 inches on the manifold pressure indicator, and with 3300 RPM on the tachometer. 42' and 3250/3300 for 10 minutes minimum. Other tests broke my engine within a few tens of seconds, like in the Great Battles series P-40 E... but in the Dover series, in the Kittyhawk, this happened over 3500 RPM, not over 3100 RPM as in IL2GB.

 

I prefer the Dover series P-40, it behaves more reallistically, but there are at least two features that are better in the Great Battles series P-40: the mixture lever correctly moves all allong the four potential positions (idle, automatic lean, automatic rich, full rich) while in the Dover series the mixture lever is either lean or rich, impossible to set it in the middle. Second, when you switch to manual prop pitch in the Great Battles series, the constant speed lever is locked (this seems to me to be correct), but not in the Dover series P-40s. Other thant that, the P-40s in the Dover series behave correctly on the ground... and in the air. And not only dealing with the engine performances...

 

Edited April 15, 2021 by 343KKT_Kintaro

[343KKT_Kintaro]

Oh dear... Steam just announced that version 5.019 is coming, with this (among other improvements):

 

-  -  -  Quotation  -  -  -

 

Adjusted engine physics to better simulate use of higher than the normal rated rpms on power generation. Applies to all engine types.
Please note: Use of higher than maximum recommended rpms will continue to greatly increase the chance of overheat, higher rpm use only recommended as per the specific guidelines for aircraft types. As for example, for Bf-109E types, use of 2600 rpm for DB601A and DB601Aa over 6000 meters, and use of 2800 rpm for DB601N over 6000 meters is allowable for limited periods.

 

-  -  -  End of quotation  -  -  -

 

So now... I need to do all the tests again... LoL!

 

[Buzzsaw]

Thanks to Chuisan for his generally correct explanation.

 

In BLITZ and TOBRUK, although theoretically it would be possible to set the maximum boost levels at higher than what they currently are, we have made a decision to go with the levels in the game based on what was generally used at the time... and pilots and Squadron Commanders would generally follow the suggestions of their Flight Engineers and set the levels according to their recommendations.

 

If we continue with the Kittyhawks, then you will see a late model Kittyhawk Mk IA with 60 inches of boost.

 

Regarding the sometimes use of 70 inches in the Mk IA's F-3R/1710-39, this was achieved by running the engine at 3200 rpm... and this was done without official authorization, and when the engineers at Allison heard about it, they recommended the practice stop.  60 inches and 66 inches were used also, and the level was finalized at 60 inches and 3000 rpm in the fall/spring of '42/'43.  The early Allisons, i.e. the ones which equipped the Tomahawks and Kittyhawk Mk IA, (1710-33/1710-39) had a smaller diameter Supercharger impeller than the later models... so the superchargers could be run at the higher 3200 rpms without coming as close to the point of potential damage/overboost.  Later versions of the Allison, as equipped the Kittyhawk Mk III/IV had a supercharger with a larger diameter impeller, so if the engine was run at 3200 rpm, excess boost could be easily generated... so more care had to be taken... the engineers at Allison were quite concerned about this.

 

Eventually when 100/150 octane fuel became available in NW Europe, (115/145 in the Pacific) thus allowing the safe use of higher boost, these late model Allisons were run at 70 inches.  Aircraft Squadrons in the Mediterranean never officially received 100/150 fuel, (although some Crew Chiefs concocted their own brews) so they were limited to lower levels.

 

The Canadian Squadrons based in Britain in late '44 and early '45 which continued to use the P-51A, updated with late model Allisons at 70 inches, found their aircraft were extremely fast at low/medium altitude when using this level of boost... even Tempests were hard pressed to keep up.

[343KKT_Kintaro]

Again, thank you guys, thank you Buzzsaw, as all of this was indeed very helpful.

 

Only for those who are interested in learning the results, here are my new tests today after installation of patch 5.019. The Kittyhawk flashcard instructs, during a cruise flight, not exceeding 42 inches of manifold pressure nor 2600 RPM. So, I created three different Kittyhawks and I overated their engines all along three different tests... as follows:

 

a) At levelled flight, constant speed mode, 3,000 feet, 45 inches of MP, 3000 RPM = engine failure after 13'50''.

 

b) At levelled flight, manual mode, 3,000 feet, 45 inches of MP, 3000 RPM = engine failure after 35'20''.

 

c) At 3,000 feet, manual mode, exceeding 3500 RPM caused an almost immediate engine failure (within less than 30 s).

 

My flight parameters fluctuated a bit during the manual prop pitch mode test (see above test "b"), going sometimes bellow 45in/3000 RPM and sometimes over 45in/3000 RPM... so this is why, I guess, the engine failure came later (also, maybe in this game the flight model and the damage model introduce elements that randomly intervene in engine breakdowns, I dunno...).

 

At any rate, I'm very happy with your responses as I'm very happy with our Tomahawks and Kittyhawks in "Desert Wings - Tobruk". Now I only need to learn to fly them in combat situations...

 

Cheerio!