The 109... questions

[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.

[robtek]

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