Supercharger....

[Anatoli-Kagari9]

- Intentionally left blank -

Edited August 17, 2015 by jcomm

[Narushima]

Completely different engines and superchargers.

 

Dora:

 

Anton:

[Anatoli-Kagari9]

Thank you very much Narushima

 

Completely different engines and superchargers.

 

[RAZBAM_ELMO]

Climbing through 2800m and 3100m I can definitely see an ATA and RPM shift in the Dora I don't know if you missed that.

[Anatoli-Kagari9]

Climbing through 2800m and 3100m I can definitely see an ATA and RPM shift in the Dora I don't know if you missed that.

You're right - it happens around 2800m.

But I tried with a Winter, cold day, -15ºC surface temp, and it changed at exactly the same indicated altitude, while I believe if it's density-based, it should have changed above it because it's colder / denser atmosphere... ( ? )

 

pressure altitude = (standard pressure - your current pressure setting) x 1,000 + field elevation

 

and

 

density altitude = pressure altitude + [120 x (OAT - ISA Temp)]

 

And from my tests, DCS DOES MODEL Density Altitude, as we can simply check by modifying a mission with an airstart, from Winter -15ºC, to Summer 30 ºC, with the same QNH of 760 mm. Climb to the same altimeter reading, and check from F2 view the true "height", a lot lower in Winter than ion Summer with that 45º difference!

Edited July 6, 2015 by jcomm

[Weegie]

Your long name control system on the BMW was the Kommandogerat, I believe, I don't know what control system the Jumo used as I have precious little info on German aircraft.

 

The BMW 801 was a single stage 2 speed supercharger, the Jumo a 2 stage 2 speed, from the info I've come across.

 

Now as for what switches the supercharger, that topic raised a pretty huge "discussion" over on the BoS forum for the A3 a while back.

 

Ideally it should be density but I'm not sure if it was. My understanding was in general at that time, pressure was usually the trigger via some sort of aneroid capsule.

 

However if anybody has more information I'd love to know more

[Anatoli-Kagari9]

Your long name control system on the BMW was the Kommandogerat [...]

However if anybody has more information I'd love to know more

 

Exactly! Thx, and yes, would also like to read more about it...

[RAZBAM_ELMO]

From what I concluded from the pilots manual in my belonging, it was a set altitude determined by a solenoid, I could be wrong with the translations but I myself went and tried different baro and air prssure settings to the best of my knowledge in the M.E. but found my results to be the same all varying between 2800 and 3100m so maybe it is or maybe it isnt, alls I know is its autoimatic and I dont have to worry hans' head off about changing it lol

[Anatoli-Kagari9]

From what I concluded from the pilots manual in my belonging, it was a set altitude determined by a solenoid, I could be wrong with the translations but I myself went and tried different baro and air prssure settings to the best of my knowledge in the M.E. but found my results to be the same all varying between 2800 and 3100m so maybe it is or maybe it isnt, alls I know is its autoimatic and I dont have to worry hans' head off about changing it lol

 

 

I also tested it yesterday, and indeed it depends on power settings, but for a fixed throttle setting, it always occurs more or less at the very same altimeter read, which differs from the density altitude.

 

Density altitude is somehow modeled in DCS too. We can pretty much acknowledge this changing the weather in a mission from Summer to Winter and varying OAT from, say 30 ºC to -15 ºC, for a fixed QNH of, say, 760 mm Hg. You will notice that although your altimeter reads the same altitude, from an outside view ( F2 ) you'll be able to notice a huge difference in the true height / alt, shown in the lower info bar.

Edited July 7, 2015 by jcomm

[Mobius_cz]

Your long name control system on the BMW was the Kommandogerat, I believe, I don't know what control system the Jumo used as I have precious little info on German aircraft.

 

The BMW 801 was a single stage 2 speed supercharger, the Jumo a 2 stage 2 speed, from the info I've come across.

 

Jumo 213 A1 used in FW-190 D9 also had single stage, two speed supercharger like BMW 801D. Jumo 213 is using hydro-mechanical engine control device called "Bediengerät"

[Anatoli-Kagari9]

Jumo 213 A1 used in FW-190 D9 also had single stage, two speed supercharger like BMW 801D. Jumo 213 is using hydro-mechanical engine control device called "Bediengerät"

 

AH! Thx for making that clear for me.

 

But I do notice a change in ATA around 2800m alt ( QNH ). Is that the two speed turbocharger kicking in ? Do you confirm it is dependent on pressure, and not on density ?

[Weegie]

Ahh so I was probably looking at a later Jumo derivative, thanks for the info and setting me right.

 

Its a pity there isn't a good source book for the axis engines, that I've seen anyway like the "Allied Aircraft Piston Engines" by Graham White, for the Errr Allied side.

 

Recommend that book to anybody with an interest in aero piston engines

[Flying-Kane]

There is a good book about german engines, but it is in german. :D

 

Jumo 213 A - two-speed one-stage supercharger - critical height: 5800m

 

Jumo 213 E/F - three-speed two-stage supercharger - critical height: 9600m

 

 

The A version was used by the Dora 9.

The E/F versions were used by D-11/D-13 and Ta152H-0/1.

Edited July 8, 2015 by Flying-Kane

[RAZBAM_ELMO]

AH! Thx for making that clear for me.

 

But I do notice a change in ATA around 2800m alt ( QNH ). Is that the two speed turbocharger kicking in ? Do you confirm it is dependent on pressure, and not on density ?

 

Yeah thats the supercharger changing into second speed, it should also be heard audibly if you're climbing at a fixed throttle or ATA setting during that time. I find it more noticeable audibly with Diveplane's sound mod, helps when you're in the thick of it and don't want to glance down at you're gauges for reference. One of those nifty things you learn after flying a bird for a while lol.

[Weegie]

There is a good book about german engines, but it is in german. :D

 

Jumo 213 A - two-speed one-stage supercharger - critical height: 5800m

 

Jumo 213 E/F - three-speed two-stage supercharger - critical height: 9600m

 

 

The A version was used by the Dora 9.

The E/F versions were used by D-11/D-13 and Ta152H-0/1.

 

:megalol:

 

Interested though I am, not so interested to take a course in technical German first.

 

Thanks for the info

[Mobius_cz]

Ok guys,

 

1) Supercharger is driven by engine itself (crankshaft i believe), Turbocharger is driven by exhaust gases. So i hope we are on the same level even before i mentioned it :)

 

2)

a) Because of Bediengerat (hydro-mechanical engine control unit) i really do not know how this engine works exactly. I hope you can help me with my thoughts. Good example is V-1650-7 engine in the mustang. You have one lever which operates engine RPM so throttle lever is controlling directly supercharger or whole air intake system am i right?

 

b) Jumo 213 A1 and V-1650-7 have two speeds superchargers. Two speed supercharger means precise revolutions? Like 6000 per minute, 8000 per minute.. (random numbers). My conclusion is that you are controlling how much air is going into the supercharger but supercharger RPM are still the same. Am i right or not?

 

c) Density of air is problem. Because you can not measure density directly (for gases). For density you need to measure pressure, tempreture and even volume or mass flow rate. Even in these days you need digital technology which measure these thing and compute density for you (or you can compute it by yourself of course :smartass: ). And the most important is...for most aplications which are using air or any kind of gases you are using pressure or temperature, flow rate but almost never density. These engines were designed and built in the 40s.. IMO switching speed of a supercharger is based simply on pressure (maybe some kind of membrane i really do not know).

 

 

Everything what i have said is based only on what i really think how this works and i believe if i am completely wrong you will corect me as much as needed.

[Weegie]

I'm interested too, but don't know anything about the Jumo or the Bediengerat

 

Here is all I've gathered from reading about allied engines, the Merlin in particular

 

1) Agree, but the drive for the supercharger would be through shafts, possibly quill shafts, gear box, couplings and in the case of 2 speed units a clutch

 

2)a) Were the levers not usually mixture and boost? I would imagine on the Dora by that stage it was fully automated with just a single throttle lever

 

2)b) Not sure what you mean there. My understanding is that the Supercharger gear ratio did change, so for a constant engine RPM the supercharger impeller would be turning faster

 

2)c) This raised a real furore over on the BoS Forum but I cannot find the thread. Some insisted on the A3 it was corrected air density others air pressure.

 

From what I've read on the allied engines it was pressure operated by an aneroid capsule, but it would have been possible to include into a mechanical control some form of temperature measurement to arrive at density. Although from what I've read it just wasn't implemented that way. Maybe too costly, not worth the effort, or would have been too complex either for ruggedness or maintenance purposes, but I'm in the realms of conjecture now.

 

I'm hoping Flying-Kane will chip in with some gems from his book. If he does I'd also be interested in what its called and who wrote it, I still might try to grab a copy if possible.

 

I don't put myself forward as an expert either, although I have read quite a few books on the allied engines

[Mobius_cz]

From Wikipedia :-D

"In the 1930s, two-speed drives were developed for superchargers. These provided more flexibility for the operation of the aircraft, although they also entailed more complexity of manufacturing and maintenance. The gears connected the supercharger to the engine using a system of hydraulic clutches, which were initially manually engaged or disengaged by the pilot with a control in the cockpit. At low altitudes, the low-speed gear would be used in order to keep the manifold temperatures low. At around 12,000 feet (3,700 m), when the throttle was full forward and the manifold pressure started to drop off, the pilot would retard the throttle and switch to the higher gear, then readjust the throttle to the desired manifold pressure. Later installations automated the gear change according to atmospheric pressure."

 

Well this seems quite logical for me, probably it is true :smilewink:

[Art-J]

Density is not a problem, really, because, as You noticed, it can be determined indirectly. Let's use warbird carburetors as example.

 

In Bendix-Stromberg pressure carbs, common in Allied planes, high dynamic pressure, measured by tubes in the air inlet works with low static pressure measured in inlet venturi, so that together they move diaphragm closed in a can. Density is "hidden" in both of these pressures. Diaphragm pushes a poppet valve, to which another can with second diaphragm is attached. That one is pulshed the other way by the fuel pressure from the pump. Balance between diaphragms ensures poppet valve meters correct amount of fuel for given conditions.

 

Late marks of Merlins and Allisons used SU/Rolls-Royce density carburetors, which didn't even have a venturi, but measured pressure difference between intake and exhaust manifolds plus intake temperature (there's Your density). Input from pressure diff (via aneroid capsule), coupled with input from temp measuring device (pushrod + thermometer) moved a diaphragm in a can, which balanced a valve pulled to the other side by the centrifugal engine-driven governor (similar to the one controlling the propeller). Balance of the forces opened the valve just enough to provide necessary amount of fuel.

 

Generally, WWII carbs and boost controllers are based on bunch of aneroid capsules and cylinders with diaphragms, all linked together by pipes and rods. No fancy electronics required here. I don't know how German engine regulators worked, but they couldn't be very different.

 

On a sidenote, the usual impeller-to-engine RPM ratio for first speed of superchargers on US engines was 5:1, while for second speed it was 8:1. In todays engines it varies between 7 and 11.

[Yo-Yo]

Density is not a problem, really, because, as You noticed, it can be determined indirectly. Let's use warbird carburetors as example.

 

In Bendix-Stromberg pressure carbs, common in Allied planes, high dynamic pressure, measured by tubes in the air inlet works with low static pressure measured in inlet venturi, so that together they move diaphragm closed in a can. Density is "hidden" in both of these pressures. Diaphragm pushes a poppet valve, to which another can with second diaphragm is attached. That one is pulshed the other way by the fuel pressure from the pump. Balance between diaphragms ensures poppet valve meters correct amount of fuel for given conditions.

 

Late marks of Merlins and Allisons used SU/Rolls-Royce density carburetors, which didn't even have a venturi, but measured pressure difference between intake and exhaust manifolds plus intake temperature (there's Your density). Input from pressure diff (via aneroid capsule), coupled with input from temp measuring device (pushrod + thermometer) moved a diaphragm in a can, which balanced a valve pulled to the other side by the centrifugal engine-driven governor (similar to the one controlling the propeller). Balance of the forces opened the valve just enough to provide necessary amount of fuel.

 

Generally, WWII carbs and boost controllers are based on bunch of aneroid capsules and cylinders with diaphragms, all linked together by pipes and rods. No fancy electronics required here. I don't know how German engine regulators worked, but they couldn't be very different.

 

On a sidenote, the usual impeller-to-engine RPM ratio for first speed of superchargers on US engines was 5:1, while for second speed it was 8:1. In todays engines it varies between 7 and 11.

 

Ventury tube does not measure pressure - it measures air volume flow, if it is a Bendix-Stromberg carburettor. Then a gas filled aneroid box measures a complex of pressure and temperature so it is possible to use it as a nonlinear density function. Air flow and this density function passes through a kind of analog multiplier giving a value proportional to air mass flow.

Bosch injectors used a series combination of vacuum and gas-filled aneroid boxes that gives air density value more precisely.

The same idea added with the atmospheric pressure box was used in Jumo-213 to maintain constant air mass flow instead of manifold pressure.

[Art-J]

Yes, "measures" was not the most fortunate word I used in this context. You know what I meant, though :D.

[Crumpp]

The BMW801 D2 KG changed the supercharger gearing based on density altitude not pressure altitude.

 

Read the manual published by BMW. It explains it well. Read them and refer to Yo-Yo's post in this thread.

 

:smilewink:

[MiloMorai]

Ventury tube does not measure pressure - it measures air volume flow

 

But the pressure differential is used to 'calculate' the flow volume.