ATA vs RPM

[SpaydCBR]

Hello all, newbie here.

 

I just recently started learning to fly aircraft without any automatic engine management like the bf-109 has, and I'm starting with the JU-87. I followed Requiem's guide and I seem to be doing fine but I still get an engine failure here and there. I think my problem is I'm not so sure I understand what ATA and RPM do and when to increase or decrease each one. I assume RPM just makes the propellers spin faster, and I actually have no idea what ATA is. I guess I was wondering if one of you could explain what each one is and what their relationship is.

[JimTM]

This page may help. The last paragraph tells you how to handle the controls when increasing and decreasing power. 

[Habu]

First, you have to check what is the limit of the plane you fly with.

 

When you take off, you have gaz, pitch and mixture at maximum (except for the P40).

 

As soon you take off, you have to set the engine to the climb setting, and when you are at the right altitude, you set it to the cruise speed.

 

If you don't respect the engine settings, you'll break or damage the engine.

 

To help you, you can display the technochat and tips.

 

 

RPM and ATA are link.

 

Main control of RPM is the gaz, but increasing Pitch will increase RPM a little bit.

 

Main control of ATA is the Pich, but increasing Gaz will increase ATA too.

[L3Pl4K]

 

 

I'm starting with the JU-87

You can use this for the stuka:

http://www.deutscheluftwaffe.de/archiv/Dokumente/ABC/j/Jumo/Jumo%20211/Jumo%20211%20F%20Faltkarte.pdf

Page 9

[JtD]

Ata are "technical atmospheres absolut". They give you the pressure at which the air is being pumped into the engine. This determines the torque the engine generates. And roughly speaking, ata multiplied with rpm are equivalent to power output. Rpm are the rotations per minute of the engine, not the propeller, though these are linked.

 

If you think of it as a car, increasing ata is like flooring the throttle, whereas increasing rpm equals shifting down a gear.

[Jade_Monkey]

If you think of it as a car, increasing ata is like flooring the throttle, whereas increasing rpm equals shifting down a gear.

 

This!

Very roughly in my limited understanding:

 

ATA is the accelerator.

 

High RPM is like low gears, a lot of traction (good to climb) and pulls the plane, like whe you drive in 2nd gear

Lower RPM is better for cruising, like driving on higher gear on the highway. There is less 'grip' but more flow.

 

Combiantion of high ATA and High RPM will blow your engine if you do it for a long time.

Turn on the technochat, and play around the engine settings to see how they work. You want to have the engine on combat mode for less than 5 min most of the time, ideally on continuous mode for cruising.

[6./ZG26_Klaus_Mann]

I don't know how basic I have to get here, but I'll try to explain it in simple terms. 

All ingame Aircraft have Supercharged Internal Combustion Engines. 

 

Internal Combustion requires a certain ratio of Fuel, in our Case Aviation Grade Gasoline, and Air. Normally the perfect ratio of Air to Fuel in an ideal engine is 15:1, or 15 Weight Units of Air for one Weight unit of fuel. This can however vary, for example the Choke on a Car or the Primer on an Aircraft can reduce this to 3-5:1 for Startup, as the fuel doesn't fully vaporize at these low temperatures, while at very high temperatures in a hot running Air Cooled engine you can reach Mixtures of up to 25:1, but 15:1 is still the optimum you want. 

 

This means that in order to generate power you have to Mix large amounts of Air with very small amounts of fuel through means of a Carburettor in which the fuel is mixed into the intake Air and vapourizes in it. 

Getting the small amounts of fuel there thus is almost no Challenge, so the quest is for the greatest Amount of Air to maintain roughly a 15:1 Mixture. 

Now a Naturally Aspirated engine is limited to whatever it can suck in at Ground Pressure, which is why you often see Ludicrously Large  Air Intakes on Naturally Aspirated Sports Cars and American V8 Muscle Cars. 

 

This automatically leads us to Manifold Pressure, units are ATA for Germans (ca 1.0 ata at Ground Level), mm in Mercury for Russians (ca. 750mmHg on the Ground) and Inches in Mercury (29.92 InHg on the Ground). 

 

The Airflow in the Intake Manifold is controlled by the Throttle Valve in the Carburettor. At 0% throttle this Valve is almost closed, so the Cylinders can suck in only very small amounts of Air-Fuel Mix, creating low pressure in the intake. This is called "Idle". At Idle the Airpressure inside may be as low as 10% of the surrounding Air, when the throttle is wide open,  the pressure inside the Manifold will almost equalize with the Ouside Pressure. 

 

Now here is the Problem with Naturally Aspirated Engines, especially in Aircraft. In our Atmospehere the Pressure at 5500m is half as much as on the Ground, at 11000m it's 25% and so on, and at the same rate engine power would decrease as well. This means your performance would drop sharply the higher you got, you would really struggle with 5000m and more. 

 

In the end the only solution to get more engine power at higher alitudes then is to get more air into the intake. In WWI some German engines were equipped with a Second Throttle which when opened at 1500m would supply the engine with a bit more air, but this wasn't very effective. 

 

One Option was to pump more of the Surrounding Air into the Engine through means of a Compressor driven by the Engine. This Compressor could Charge more Air into the Manifold, even at high Altitude it could provide the engine with as much Air as it would have on the Ground.

 

So instead of your German Engine having 0.5 ata at 5500m, you still could use 1.0 ata at that altitude, thus providing you with 4 times as much power at that altitude as your Naturally Aspirated Counterpart. 

You could even use that Compressor to Boost you Power at Lower Altitude, since it could deliver much more than Ground Pressure into the intake.

This Compressor is the "Supercharger"

 

This was a huge leap and engine power rose sharply before the War. You were suddenly able to make much smaller, lighter, yet more powerful engines which could cruise higher and farther, since you the drag at high altitude is much lower. 

For Example the Normally Aspirated Wright R-790  could only produce 220hp for take-off, it's later cousin, the Supercharged R-760 despite it's slightly smaller displacement could produce 350hp for take-off and had much better performance at altitude. 

 

All that to get to the simple point of: ATA indicated how much pressure that Supercharger is producing in your intake Manifold. 

RPM are simple "Revolutions per Minute" of the Engine, in other words how many Rotations the Crankshaft makes in a Minute. 

This is regulated by the Propeller blades being adjusted to a finer or coarser angle. I'll put in an Illustration below. 

 

1.4 ata@2600RPM are appopiate for take-off (don't forget to open all radiators fully)

1.3 ata@2400RPM are the appropiate setting for climbing. You can use them for 30 Minutes.

1.15ata@2200RPM are the Maximum Cruise Power you can use for eternity (or until fuel runs out)

 

It's a Two Speed Supercharger, so at 3000m it automatically switches up to 2nd gear, which is the high altitude gear. 

Don't forget to switch down Manually when you dive, or you may Over-Rev your engine. 

Also remember to make only gently movements on the throttle. 

 

The big, snail looking thing is the Supercharger, basically a Big Fan. 

 

 

[SvAF/F16_Goblin]

Very nice explanation mate. Thumbs up and rep inbound

[Bearfoot]

Very, very, very, nice explanation, @6./ZG26_Klaus-Mann!

 

Very nice!

[Jade_Monkey]

I learnt a lot! Thanks!!

[SCG_Limboski]

I was curious as to how BOS calculates the damage an engine takes due to having too high of an RPM and/or ATA.  Is a power rating combining the two variables being used?  I've noticed in Cliffs of Dover, the critical variable for damaging engines seems to be RPM only.  That is, basically, you can run at maximum manifold pressure for long periods without damage as long as you keep the RPM low enough.  You will damage your engine if you try this in BoS.

[6./ZG26_Klaus_Mann]

I was curious as to how BOS calculates the damage an engine takes due to having too high of an RPM and/or ATA.  Is a power rating combining the two variables being used?  I've noticed in Cliffs of Dover, the critical variable for damaging engines seems to be RPM only.  That is, basically, you can run at maximum manifold pressure for long periods without damage as long as you keep the RPM low enough.  You will damage your engine if you try this in BoS.

It should be the other way round. Revs don't really hurt an engine, the load does. 

High MAP at low RPM can lead to detonation and Pre-Ignition. 

[JG13_opcode]

It should be the other way round. Revs don't really hurt an engine, the load does. 

High MAP at low RPM can lead to detonation and Pre-Ignition.

Excess RPM absolutely can hurt an engine. As your RPMs increase the stresses on the piston connecting rods become excessive. You also run into limits of spark timing, valve float, pre-ignition, etc.

 

Engines have "red lines" for a reason.

Edited August 16, 2016 by JG13_opcode

[SpaydCBR]

Nice write up Klaus_Mann! One question that is probably stupid, it sounds like by "increasing/decreasing RPM" I'm just changing the pitch of the propeller blades, is that right? If so then why is there a separate propeller pitch control in the game?

[Aap]

Because by changing the prop pitch you are able to increase/decrease RPM. 

Simpy put, your RPM depends on both your power and prop pitch. If you are flying level with a certain RPM and want to increase RPM, you either add throttle, so more power for engine, or change pitch, so it is "easier" for engine to run. Or take an example of riding a bicycle, if you are moving your feet 10 RPM and are starting to go uphill, you either need to do more work - put more pressure on pedals to keep the RPM, or you change gear, so it is easier to keep that RPM, but your speed will drop.

Now, different planes have different automation levels for these things. For Bf-109 with auto pitch, you control both ATA and RPM by just moving your throttle lever. Most other planes have constant speed propeller, which means that you set a desired RPM and then with throttle you just control the ATA, while plane will automatically change the pitch to keep the desired RPM, if physically possible. And then there is the manual pitch control, where you control both the ATA (throttle) and pitch angle directly.

[6./ZG26_Klaus_Mann]

Excess RPM absolutely can hurt an engine. As your RPMs increase the stresses on the piston connecting rods become excessive. You also run into limits of spark timing, valve float, pre-ignition, etc.

 

Engines have "red lines" for a reason.

Of course, moviing the RPM above safe limits will shorten the life of the engine considerably (or Murder it outright). But when operating within the limits and you want more power it is always advisable (of course within reason) to increase RPM first and then increase the Load. Same is true for Super and Turbocharged Cars. You shouldn't put full Load on an engine at Low RPM since it puts a ton of stress on Bearings and Seals. 

[216th_Jordan]

In most planes you do not set prop pitch but rpm. This means a point on the lever for rpm corresponds to a given rpm and a prop governor adjusts the angle of the blades according to the power output of the engine to keep the engine on that rpm.

[6./ZG26_Klaus_Mann]

In most planes you do not set prop pitch but rpm. This means a point on the lever for rpm corresponds to a given rpm and a prop governor adjusts the angle of the blades according to the power output of the engine to keep the engine on that rpm.

The P-40 is the weirdest of all with a Constand Speed Setting AND Manual Prop Pitch. 

[1PL-Husar-1Esk]

Would be there any real benefits by using (fine tuning) manual pitch on 109 during extending in horizontal plane or climb, divie against auto pitch for best results?

[6./ZG26_Klaus_Mann]

Would be there any real benefits by using (fine tuning) manual pitch on 109 during extending in horizontal plane or climb, divie against auto pitch for best results?

Yes, especially at high altitude. Since the Supercharger is driven mechanically by the engine, the higher the engine revs, the higher therefore the Supercharger as well, and thus can deliver more air even at altidues normally considered "critical" , in other words, where the Supercharger cannot provide enough air to maintain the wanted Manifold Pressure. 

 

Take the Bf109E-7 for example. Normal Combat mode for it is at 2350-2400RPM and 1.23-1.3 ata. This works up to roughly 5000m, however the engines were uprated in late 1940 to be able to run up to 2600 enabling it to maintain full boost pressure up to 6000m. 

This is why the Bf109E-7 has such a large difference between Combat Power and WEP at these altitudes, because at 2350 RPM it simply cannot provide the high boost pressure, but as soon as you go into WEP and 2600RPM it suddenly can produce full boost again. 

So at 6000m its maximum at 2400RPM is maybe 1.1ata (should be 1.23) but once you go to full throttle it produces 1.3ata again at 2600rpm. This means an enormous Power Increase. 

 

Look at the provided PDF and you will see the large difference between WEP and Combat Power in the E-7 at high altitude, much larger than at lower altitudes. 

http://forum.il2sturmovik.com/topic/24384-just-made-little-fm-test-after-patch/?p=376748

 

In the 109G-2 you gain up to 15kph in Level Speed at Low Alt and more than 30 at high alt when using manual Prop Pitch for 2800RPM.

Edited August 16, 2016 by 6./ZG26_Klaus_Mann

[1PL-Husar-1Esk]

Thanks Klaus!

[6./ZG26_Klaus_Mann]

Thanks Klaus!

Ecclesiastes 3:8

 

A time to love, and a time to hate; a time of war, and a time of peace. A time to troll, and time to be serious.  

[69th_chuter]

The P-40 is the weirdest of all with a Constand Speed Setting AND Manual Prop Pitch. 

 

Wouldn't it be the same as the German planes?  They're all electric and the German planes have governors too.

Would be there any real benefits by using (fine tuning) manual pitch on 109 during extending in horizontal plane or climb, divie against auto pitch for best results?

 

Not really, the governor should hold max rpm for you.  Some German pilots, though, reported using manual control to slightly over-rev the engine for more power, so there's that.  Good luck there - lol.

Edited August 16, 2016 by chuter

[6./ZG26_Klaus_Mann]

Not really, the governor should hold max rpm for you.  Some German pilots, though, reported using manual control to slightly over-rev the engine for more power, so there's that.  Good luck there - lol.

 

 

I'd disagree. The DB605A was rated for 2800RPM originally (unfortunately the switch plain bearings required extra lubrication, this wasn't possible with the DB601 derived pump leading to overheating Oil --> Fires and the reason for the 1.3ata/2600rpm until at least 1943) and by manually controlling the Pitch you get a bit more power low down and much more at above the current critical altitude of 5.7km. (With Ram Air 6km). 

 

 

Just did a quick test. At 7k at 2600rpm you get 1.15ata, at 2800 you get 1.3. 

Observe the difference in Top Speed as well. The higher you get, the bigger the difference. 

 

 

 

 

Edited August 16, 2016 by 6./ZG26_Klaus_Mann

[JtD]

Since you are exceeding rated rpm and thus over-revving the engine, I'd say you and chuter in fact agree with each other.

 

Anyway, good explanation up there, and also nice to see that there appears to be quite a bit of interest in this subject.

[6./ZG26_Klaus_Mann]

Since you are exceeding rated rpm and thus over-revving the engine, I'd say you and chuter in fact agree with each other.

 

Anyway, good explanation up there, and also nice to see that there appears to be quite a bit of interest in this subject.

It's not really over-revving in that case, since the engine is designed for 2800RPM. It's basically tricking the throttle Stop for slight Performance gain. 

 

According to the june of 1942 Manual it was recommended to use Manual Prop Pitch for Cruise and there are several reminders not to forget to put the prop back to Automatic when necessary (in Combat, especially before diving).

According to Manual 2800 shouldn't be exceeded, according to Daimler Benz 3200RPM were the Structural Maximum, what they consdidered Overrevving. 

 

Page 17 applies to diving "Put throttle onto white Marker, maximum allowable RPM in a Dive are 2800 per Minute"

http://www.deutscheluftwaffe.de/archiv/Dokumente/ABC/m/Messerschmitt/Me%20109/Bf%20109%20G-2.pdf

Edited August 16, 2016 by 6./ZG26_Klaus_Mann

[Mac_Messer]

Does the game tolerate 2800rpm?

[6./ZG26_5tuka]

Just tested it, 2800 RPM at 1.3 ata will kill your engine after some time (mechanical failure, not overheating) in the G-2.

Edited August 17, 2016 by 6./ZG26_5tuka

[6./ZG26_Klaus_Mann]

Just tested it, 2800 RPM at 1.3 ata will kill your engine after some time (mechanical failure, not overheating) in the G-2.

Roughly 5-10 Minutes. 

[9./JG27golani79]

Would be there any real benefits by using (fine tuning) manual pitch on 109 during extending in horizontal plane or climb, divie against auto pitch for best results?

One thing you´d also could benefit from using manual prop pitch would be that sometimes the automatich governor needs to much time for the adjustments.

So if you know what you want to do you can adjust the pitch faster than the governor.

 

I´ve tried to fly with manual pitch for some time but switched back to automatic mode cause in the heat of a dogfight you can kill the engine pretty fast if you are not careful :D

Edited August 17, 2016 by 9./JG27golani79

[Mac_Messer]

I´ve tried to fly with manual pitch for some time but switched back to automatic mode cause in the heat of a dogfight you can kill the engine pretty fast if you are not careful :D

Depends on circumstances. If you have 1 minute overrev engine death limit then yes, too dangerous to use. Now if we could go realistic and some overrev was allowed, you get TrackIR and you assign the right buttons to prop pitch control then changing pp can become instinctual. Some people were even a bit TOO good doing it. Hence what we have in this game, I suppose.

One thing you´d also could benefit from using manual prop pitch would be that sometimes the automatich governor needs to much time for the adjustments.

So if you know what you want to do you can adjust the pitch faster than the governor.

 

Yeah, I land on manual regulary, both in 109 and fw190. I seem to remember it was in the official 109 manual somewhere, if I`m not mistaken.

[6./ZG26_Klaus_Mann]

Yeah, I land on manual regulary, both in 109 and fw190. I seem to remember it was in the official 109 manual somewhere, if I`m not mistaken.

In the Emils the Governor tended towards the overregulating side and quick changes in throttle could lead to Engine Braking due to the engine overrevving at first, then the Governor would step in brutally and coarse the Prop Pitch very quickly while the Wastegate opened at the same time reducing power again, resulting in too Low RPM and too high Prop Pitch, which it would then correct again and so on, all of which could lead to the aircraft banking sharply resulting in Crashes.