The 109... questions

[meplay]

Originally Posted by Blackdog_kt

I use the settings specified in the manual with CEM and temperature effects enabled. I can exceed the RPM limit briefly with no problems as long as i keep temps in the normal range.

Generally speaking, manifold pressure is a measure of the pressure within the engine manifold intake where the fuel and air get mixed, just before they are fed to the cylinders for ignition. At least this is how it's measured in engines using a carburetor, i'm not sure where it's measured in the 109's injection system, but the general idea is the same. It might sound funny, but what it does is show you how hard your engine sucks at any given time

If the intake is full open it's sucking the maximum amount of air, you get higher manifold pressure values on the instruments and more air means more fuel/air mixture to burn which translates to more power. It's what your throttle lever does, controlling that gate/valve in the intake to restrict or allow airflow to the engine.

So, with the throttle at idle your MP gauge will actually read less than the outside air pressure because the engine is starved for air, but with the throttle at full it will show the exact outside pressure. If you have a supercharged engine like the fighters in CoD have, it will even show more than the ambient pressure because the supercharger compresses the air even further before feeding it to the engine.

Depending on the aircraft you fly, it's measured in different ways. German aircraft measure it in atmosphere/bar units and that's what your Ata gauge reads, 1 Ata is actually the air pressure at sea level on an average day.

Since the 109 is fitted with a supercharger, you can go higher than that to 1.3-1.4 Ata. As you climb higher, the air outside is thinner so it gives less pressure, but thanks to the supercharger you can have sea level performance of 1 Ata pressure at 3-4 km of altitude (approximately, don't remember at what altitude exactly it starts to drop off). Going even higher, even the supercharger can't keep up with how thin the air is so you will notice it dropping below 1 Ata at some point.

This is the fundamental difference between real aircraft (which CoD now models accurately) and how we used to do things in the previous IL2 sims: full power is not always full throttle. Power is a combination of throttle and RPM, even mixture if we want to go really complex on the matter.
In fact, there are WWII fighters where going full throttle while on the ground or at low altitude could destroy the engine in a couple of minutes, because full throttle at low altitude can exceed the engine's maximum rated power. They were built to generate a lot of "reserve pressure" to compensate during high altitude flight, but if that reserve was added to an already high-pressure starting point (when low, with a high ambient pressure) it could blow the engine to bits.

Full power is the amount of pressure the engine can tolerate at a certain RPM value that generates the maximum horsepower. For the 109 it's around 1.4 Ata (i think). When on the ground, you can easily achieve 1 Ata with the throttle pushed mid-way, when flying at 6km of altitude you will be hard pressed to achieve the same value with the throttle wide open due to the drop in the outside pressure: the engine can only work with what its given-->the air it sucks from outside the plane.

Also, if climbing/diving you can see the Ata value decrease/increase without even moving your throttle: it's the outside air changing in pressure that affects the amount of pressure in the engine induction system.
Finally, reducing prop pitch too much has the effect of transferring resistance from the blades to the engine and this increases the pressure. That's only a rough and by no means accurate description of the effect, just be wary that reducing RPMs too much while on high throttle settings might push your Ata over the limit.

So, with all that out of the way, let's see some usable values.

For climb and combat i usually set the throttle for 1.3-1.35 Ata, which is what the manual specifies. If i don't make any drastic altitude changes during the fight it tends to stay relatively steady, so i spend most of my time baby-sitting the RPMs.
This is quite hard to control in precision, so i just focus on maintaining the 2500 RPM redline limit. According to the manual, the actual never exceed RPM during dives is 3000 RPM so you have some wiggle room. I have used 2700 RPM on occasion, either by mistake or to get some extra "pull" from the prop during combat and the engine didn't die on me. It's doing fine as long as you don't leave it there but bring it back to 2500 RPM within 5-10 seconds.

I have not experimented with the oil cooler too much, but i can safely run combat power settings (1.3 Ata and 2300-2700 RPM) with the oil cooler about 3/4 open. Maybe it's possible to make do with closing it a bit and gaining some extra airspeed but i haven't tested it yet.

The one that's hard to get right in the 109 is the water cooler. Water seems to heat up and also cool down faster than oil, so power changes have a much more immediate effect. I might suddenly need to increase power and risk having it overheat, or i might chop throttle during the dive and have it cool down too much. As a matter of fact, i always give it 2-3 keypresses of the "close water rad" command before going in a protracted dive and increasing it afterwards.

This is made a bit harder by the way we get feedback from the control. While it's easy to judge the position of most controls by looking at the cockpit levers or the overlay panel, the water cooler cockpit control is a rotating crank whose position is hard to judge (it turns more than a full circle so you can't just look at it and know its position) and the info window with the engine controls doesn't display actual position either. It just displays if it's in motion: up when you are pressing the open key, down when you're pressing the close key and center when you are not messing with it.

Due to these reasons, for the most part i run with the water coolers almost all the way open during combat. In the 110's info window the water cooler is depicted similar to the other controls (the slider shows actual position) so it's easier to set precisely and gain some extra speed.

I'm sure that if they changed the info window display on the 109 to be like the 110 i could manage the water coolers better and maybe gain some extra airspeed. Currently, keeping the RPM at the right place (within limits but not too low to deliver useful power) is already taking up most of my attention so that i can't afford the guesswork involved with the water cooler's position and i just leave them fully open.

For example, when diving i reduce prop pitch a couple of clicks, increasing it again during the pull out, but both the blade angle (visible on the clock-like instrument) and the RPM still take some time to adjust, so you actually need to be thinking ahead and applying changes before the start of your maneuver.

I spent 15 minutes chasing an AI hurricane in a climbing scissors fight yesterday, gaining on him and then having me overtake me, until i realised that i was making a mistake with my prop management. As soon as i started paying more attention to maintaining as close to 2500 RPM as possible, i was able to easily close up on him and shoot him down.


Sorry for the marathon post, this sim has so much depth at high realism settings that describing a simple boom and zoom bounce takes 2-3 paragraphs to explain what controls to use, how and why

Nice Blackdog , was gonna go bed, but ooh il give it another hour

S!

[JG53Frankyboy]

watch the wings, there you see little sticks that show you the watercooler setting...

[Blackdog_kt]

Originally Posted by adonys

it's the same thing I said. I was writing from memory (haven't checked exactly in the game), yet I've said throttle back and low RPM (around 2000, but actually going down towards 1800), if the high prop pitch rises the RPM, then you'll lower it until you get around the needed RPM.

Which is the RPM you're using for cruising, isn't something between 1800-2000?

The two important causes for fuel consumption are throttle RPM and fuel pressure. I said throttle RPM, because RPM going higher because of the wind forcing a faster rotation of the propeller shouldn't accelerate your fuel consumption. using the same car analogy, if you let it loose downhill, faster rotation of wheels because of the gravity won't make you consume more fuel to acquire it.

That's what I believe, I'm also no pilot, just using logic and knowledge. So, don't worry, I don't have any problem arguing or being corrected (I'm not stupid enough to think I'm always right, I'm not God), on contrary, these kind of discussions improves the knowledge of all of us, and that's a good thing, isn't it?

That's a good point you're raising there, if the engine "rolling downhill" consumes as much fuel as when it's working normally at the same RPM, to which i don't know the answer

In cruise i use the values stated in the PDF manual for CoD (1.2 Ata and approximately 2300RPM) and this easily gets me 390km/h IAS at low altitudes (2km or so).

There are also different kinds of cruise and we don't know which one the manual gives. Endurance cruise gives the most amount of flight time per liter of fuel.
Economy cruise is different and gives the biggest amount of distance traveled per liter of fuel.

Assuming i'm flying a cessna, let's say it has an economy cruise of 25 inches Hg manifold pressure and 2500 RPM and an endurance cruise of 20 in Hg and 2200 RPM:
If i use 25"/2500 RPM, my fuel will last a shorter amount of time but in that time i will have traveled a bigger distance.
If i use 20"/2200 RPM, my fuel will last longer but the total distance travelled will be less.

Applying this to the 109, i suppose the values states in the manual give the best range and not the best endurance/loiter time. This is a pure guess on my part, i'm just guessing that a sleek fighter will have a relatively high economy cruise speed and since i'm getting almost 400km/h it seems reasonable.

If we wanted to maximize time over London we would combine both, economy cruise to the target area, endurance cruise while patrolling and economy cruise back to base

[adonys]

The cruise I've posted up in there was done at lower RPMs than the one in manual/yours (1800-2000 compared with 2300), and it is exactly for the lowest consumption of fuel/distance covered, therefore should be an economy cruise, not a fast (as I believe the one from manual to be, at 2300 RPM you're almost in the full power 2500 RPM area) or an endurance cruise (maximize the time staying in the air).

PS: yet, using the manual 2300 RPM for cruising.. isn't as being a lower RPM compared with my 2000(1800) one, as you said when we've started this discussion.. as it is actually a higher RPM, isn't it?

[Blackdog_kt]

Of course. I just went by the assumption that the manual states maximum range cruise. Maybe it's fast cruise and yours is more economical, i will probably try out your settings during the weekend

[Hellbender]

Question: So far the Fuel mixture in the 109 could be set by me only @ 0 % or 100%. At high altitude, I see smoke coming out of the Exhaust which vanishs by using Mixture 0% which is giving me almost no engine power.
In british planes I can set up the fuel mixture from 0-100% , but i only got 2 extremes on the 109.

[JG52Uther]

I think mixture in the 109 is bugged at higher altitudes.

[robtek]

afaik there is NO mixture adjustment for the 109!
Always "auto-rich"

[adonys]

yeah, the mixture of 109 is auto, you shouldn't fumble with it.

[JG52Uther]

When I get the time I will take off from France and fly to London at cruise settings,to see how much fuel is left.
I think in real life they had 10 minutes or so combat time over London,so it must have been pretty hair raising trying to get back while avoiding enemy fighters. I already flew one mission out in the channel,got a fuel leak and only just made it back to base with empty tanks and the fuel light on! That was bad enough,and no one was shooting at me!