The 109... questions

[Blackdog_kt]

Originally Posted by adonys

I've found out it's rather hard to exceed 400 IAS in Bf109E3, but sometimes you can do it.

Combat (full power settings - bold settings are your main goal):
- oil radiator almost closed 30% open (between 20-40% open, I'm modifying it all the time) - keep an eye on oil's temp all the time
- prop pitch anywhere around 90% (between 80-100%, I'm modifying it all the time, accordingly with oil rad modifications, and trying to keep the RPM in the desired area)
- throttle kept modified (accordingly with the above oil rad and prop pitch settings and trying to keep the RPM in the desired area)
- RPM around 2500 (between 2000 and 3000)
- speed over 400 IAS
- water rad fully open

Don't forget to lower/cut the the throttle in dives (and eventually ease your prop pitch too), and get it back once leveled.

Cruise (economy settings - bold settings are your main goal).
- water radiator fully opened
- oil radiator fully opened
- prop pitch 100% (between 90-100%)
- throttle around 45% (between 45-55%)
- RPM around 2000
- speed over 300 IAS
- manifold pressure as lower as you can manage it (to conserve fuel while keeping a reasonable speed)

Excuse me for saying so, but i tend to do cruise a bit different, lower the throttle and then drop the RPM. Reducing the pitch has the effect of raising the manifold pressure again, so i re-adjust the throttle which again affects the RPM (throttle affects RPM only on the German aircraft and on the RAF aircraft that don't have a constant speed prop, aircraft with a CSP keep the RPM steady on their own) and so on...but after a couple of back and forths it settles into a steady situation.

However, i use lower RPM (in fact i use the settings stated in the manual) with 1.2 Ata, since i think that RPM has a bigger effect on fuel consumption. For example, the Hurricane has a "cruise mode lock" on the propeller once you pull it fully back and it uses 1800 RPM or so for extra fuel economy.

Using 1.2 Ata, 2300 RPM and bit of trim i can easily cruise at 380-400 km/h with the water rads full open and the oil rads about 70% open.

The reason i'm using mid-range values for MP and RPM instead of high RPM with low MP is that every single aircraft checklist i've seen (both for combat and civilian planes) tells the pilots to use lower RPM in cruise to conserve fuel.

MP also has an effect in fuel consumption as the more air getting sucked into the engine the more fuel the metering valves/injection system/carburetors drop into he mix.

The thing is that using lower RPM lets you get more speed from the same amount of MP, as long as we're talking about cruise in level flight. After all, the reason RPM drops is because the prop is in coarse pitch and getting a bigger bite out of the air, making it more efficient for straight and level flight.
It's like going to 6th gear on a car when driving on a highway and dropping your RPM to 2500 without changing the amount of throttle you use: you won't accelerate/decelerate fast if you change how much you press the gas pedal, but you are sure getting where you want to go fast and with lower fuel burn, as long as you don't need fast responses from the engine.

Going low Ata with RPM is like doing the same speed in that car but instead of using 6th gear and 2500 RPM you use 4th gear and 6500 RPM: it's going to burn much more fuel and it's not even sure you'll get the same speed in the end.

The way it works is very different, but the end results are very similar so that it's easy to think of prop pitch and RPM like gears in a car. For example, whenever the car goes uphill we down-shift to increase our RPM and the engine's responsiveness, whenever the aircraft climbs we can go to high RPM to do the same.
During slow driving we use low gears that give us high RPM and fast response at low speeds, during the landing circuit we use fine pitch and high RPM for the same reason. Just like lifting your foot from the gas pedal will slow your car down via the gears if you are in low gear, using high RPM with low MP in an aircraft will do something similar. In this case however the braking is not only a function of the gearbox absorbing part of the energy, but mostly the propeller acting as an airbrake.

If you are on fine pitch/high RPM and the engine is not making enough power to turn that prop then it's getting turned by the air and windmills while at fine pitch (ie, the prop is almost flat, face-on to the incoming airflow)-->extra drag.

So, by using that analogy you can think of many useful scenarios.
What do you do to speed up in the dive faster or just let it pick up speed more efficiently? The same thing you'd do to speed up when driving a car downhill, progressively switch to higher gears/lower RPM while pressing the gas pedal or just go high gear and let it roll on its own. In our aircraft, this means coming back on the RPM a bit.

What if you want to go slow in the dive? Well, it's similar to what you'd do to keep your car from speeding up too much when driving downhill, use a lower gear/higher RPM while coming off the gas pedal. So, just chop the throttle and go to high RPM and the prop windmilling effect will give you the drag you need.

I'm not an expert or a real pilot and i certainly don't want to play it smart on you, i'm just surprised that your method is so different and that makes me want to compare notes.
You know, like a couple of pilots talking about "how to get that extra bit of performance" between sorties. Cheers

[Winger]

Originally Posted by Blackdog_kt

Excuse me for saying so, but i tend to do cruise a bit different, lower the throttle and then drop the RPM. Reducing the pitch has the effect of raising the manifold pressure again, so i re-adjust the throttle which again affects the RPM (throttle affects RPM only on the German aircraft and on the RAF aircraft that don't have a constant speed prop, aircraft with a CSP keep the RPM steady on their own) and so on...but after a couple of back and forths it settles into a steady situation.

However, i use lower RPM (in fact i use the settings stated in the manual) with 1.2 Ata, since i think that RPM has a bigger effect on fuel consumption. For example, the Hurricane has a "cruise mode lock" on the propeller once you pull it fully back and it uses 1800 RPM or so for extra fuel economy.

Using 1.2 Ata, 2300 RPM and bit of trim i can easily cruise at 380-400 km/h with the water rads full open and the oil rads about 70% open.

The reason i'm using mid-range values for MP and RPM instead of high RPM with low MP is that every single aircraft checklist i've seen (both for combat and civilian planes) tells the pilots to use lower RPM in cruise to conserve fuel.

MP also has an effect in fuel consumption as the more air getting sucked into the engine the more fuel the metering valves/injection system/carburetors drop into he mix.

The thing is that using lower RPM lets you get more speed from the same amount of MP, as long as we're talking about cruise in level flight. After all, the reason RPM drops is because the prop is in coarse pitch and getting a bigger bite out of the air, making it more efficient for straight and level flight.
It's like going to 6th gear on a car when driving on a highway and dropping your RPM to 2500 without changing the amount of throttle you use: you won't accelerate/decelerate fast if you change how much you press the gas pedal, but you are sure getting where you want to go fast and with lower fuel burn, as long as you don't need fast responses from the engine.

Going low Ata with RPM is like doing the same speed in that car but instead of using 6th gear and 2500 RPM you use 4th gear and 6500 RPM: it's going to burn much more fuel and it's not even sure you'll get the same speed in the end.

The way it works is very different, but the end results are very similar so that it's easy to think of prop pitch and RPM like gears in a car. For example, whenever the car goes uphill we down-shift to increase our RPM and the engine's responsiveness, whenever the aircraft climbs we can go to high RPM to do the same.
During slow driving we use low gears that give us high RPM and fast response at low speeds, during the landing circuit we use fine pitch and high RPM for the same reason. Just like lifting your foot from the gas pedal will slow your car down via the gears if you are in low gear, using high RPM with low MP in an aircraft will do something similar. In this case however the braking is not only a function of the gearbox absorbing part of the energy, but mostly the propeller acting as an airbrake.

If you are on fine pitch/high RPM and the engine is not making enough power to turn that prop then it's getting turned by the air and windmills while at fine pitch (ie, the prop is almost flat, face-on to the incoming airflow)-->extra drag.

So, by using that analogy you can think of many useful scenarios.
What do you do to speed up in the dive faster or just let it pick up speed more efficiently? The same thing you'd do to speed up when driving a car downhill, progressively switch to higher gears/lower RPM while pressing the gas pedal or just go high gear and let it roll on its own. In our aircraft, this means coming back on the RPM a bit.

What if you want to go slow in the dive? Well, it's similar to what you'd do to keep your car from speeding up too much when driving downhill, use a lower gear/higher RPM while coming off the gas pedal. So, just chop the throttle and go to high RPM and the prop windmilling effect will give you the drag you need.

I'm not an expert or a real pilot and i certainly don't want to play it smart on you, i'm just surprised that your method is so different and that makes me want to compare notes.
You know, like a couple of pilots talking about "how to get that extra bit of performance" between sorties. Cheers

Excellent. What are you in RL? Teacher? NO - should consider changing your job. Thanks for the writeup!

Winger

[adonys]

Originally Posted by Blackdog_kt

Excuse me for saying so, but i tend to do cruise a bit different, lower the throttle and then drop the RPM. Reducing the pitch has the effect of raising the manifold pressure again, so i re-adjust the throttle which again affects the RPM (throttle affects RPM only on the German aircraft and on the RAF aircraft that don't have a constant speed prop, aircraft with a CSP keep the RPM steady on their own) and so on...but after a couple of back and forths it settles into a steady situation.

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?

[Geronimo989]

Ok a quite simple and maybe stupid question: Does more RPM always mean more power on the 109, with the risk of breaking the engine when exceeding the limit? Or do you get maximum power when staying in certain RPM range (2500) and you actually LOSE power when you exceeding it?

[II./JG1_Krupinski]

Originally Posted by Geronimo989

Ok a quite simple and maybe stupid question: Does more RPM always mean more power on the 109, with the risk of breaking the engine when exceeding the limit? Or do you get maximum power when staying in certain RPM range (2500) and you actually LOSE power when you exceeding it?

Absolutely not... However, power is dependent upon RPM. That is power is a "rate" of work being done.

Use the Prop Pitch control to regulate the engine load by maintaining a certain RPM. At a high pitch, it's harder for the engine to swing it than at a lower pitch.

All internal combustion engines produce power on what's called a power curve, named because the relationship between torque output and RPM is not linear - it's a curve. Hard to describe but imagine an engine running at idle may produce an increasing amount of torque at an increase of RPM (with a constant load) up to a peak.

Then any additional RPM beyond that peak will start reducing the torque output, even though RPM's are increasing. (Side Note: In internal combustion engines, the power and torque numbers are equal at 5252 RPM)

A dynamometer, is used to measure the power parameters of an engine. The dynamometer operator will increase the throttle from idle to max throttle and measure the RPM and torque output.

Using a variable pitch prop [bf109] or fixed pitch prop [tiger moth], the propeller can represent the constant load (assuming you don't change the variable pitch) exerted on the engine, and taking the throttle from idle to max throttle will exercise the engine across it's power curve.

If the propeller is a constant speed propeller (spit) then the propeller will adjust its pitch (adjust its load) automatically to maintain a certain load. Since the engine produces power on a power curve, you can stick the RPM to the peak level and then worry about one less thing. As you increase throttle, the engine RPM will increase until there is enough power to swing that prop at the given setting. A constant speed prop makes it easy to keep the engine at the best RPM for a given situation, such as MAX performance, or MAX economy.

A variable pitch propeller the pilot must adjust the propeller pitch to do the same thing, as an increase in throttle will increase the RPM of the engine, unless the pilot increases the load on the engine.

A fixed pitch prop, the pilot must adjust the RPM's with the throttle.

Usually, aircraft manuals aren't published with detailed power curves, but what they do have is settings for varying scenarios. The CoD manuals have some values published, but I've seen more detailed tables in other game manuals (such as the shockwave A2A Bf109 manual - which you can view online)

Here is a nice web page that discusses power and torque.

http://www.epi-eng.com/piston_engine...and_torque.htm

[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.