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frapeforte1
11-11-2004, 10:10 AM
I was just wondering if anybody can explain to us new guys about the ins and outs of Fuel Mix, and prop pitch? How do you know when and how to change these parameters????

Thanks

frapeforte1
11-11-2004, 10:10 AM
I was just wondering if anybody can explain to us new guys about the ins and outs of Fuel Mix, and prop pitch? How do you know when and how to change these parameters????

Thanks

Buzzer1
11-11-2004, 10:35 AM
Here is a good guide:
http://people.ee.ethz.ch/~chapman/il2guide/cemguide/intro.htm
Must say the manuals are seriously lacking regarding engine management etc.
Just says you have to adjust mixture, pitch etc for best engine performance! Great...

While here - can anyone tell me the purpose of the radiator and cowl flaps?
To cool engine more? I usually open radiators during TO and landings...no idea if it is correct procedure though http://forums.ubi.com/images/smilies/16x16_smiley-surprised.gif

theaircobra
11-11-2004, 10:56 AM
well i am no expert, but i think the radiator lets more air into the engin. therefore cooling it. the only problem is it decreseases proformance a little.

Fliger747
11-11-2004, 10:59 AM
The real F4U has three levers on the right side pannel, forward for 'cooling'. Cowl flaps, oil cooler shuters and supercharger intercooler.

For ground ops and takeoff and slow speed usally the cowl flaps are open, and adjusted in cruise as necessary to keep a desired cyl head temp. What they do with a radial engine is control the amount of airflow past the cylinders. Cooling causes a lot of drag, so it is reduced when not necessary.

In the 'game' we don't have seperate controls for all three, so to keep it simple, open for takeoff, landing pattern and ground ops, adjust toward close in cruise, you may need them a bit open.

The prop pitch is set to max RPM for takeoff, landing and combat, when maximum power is or may be needed. For other operations RPM is reduced to conserve fuel and prolong engine life. There was a climb/cruise schedule of RPM and manifold pressure vrs altitude and airspeed (which I don't have). The procedure it to first reduce the MP (throttle) and then the prop RPM. Going the other way RPM and then MP.

In a real aircraft, bringing the prop to max RPM on approach is both really audible, and can brake the aircraft quite a bit, a little like downshifting in a car.

e2michaelb
11-11-2004, 02:13 PM
Question from a novice (old newbie): isn't the "Prop Pitch Auto Mode" setting supposed to take care of all this automatically? I tried to set it before taking off in a Spitfire and got no response. Then, as I entered the landing pattern, I found that the RPM's stayed up, even though my throttle (Saitek X45)was at idle. http://forums.ubi.com/images/smilies/16x16_smiley-sad.gif What have I missed?

Snootles
11-11-2004, 03:38 PM
On using Fuel Mixture: Generally I keep this at 100%. As you reach higher altitudes you will need to gradually decrease the mixture to compensate for thinner atmosphere. Otherwise your engine will run at decreased power and leave smoke trails behind it from incomplete combustion. When running full emergency power, add more fuel (120% mix at sea level) to get the most out of it.

Nige_Reconman
11-11-2004, 05:27 PM
Mixture.

Okay mixture controls the amount of air/fuel mix in the piston chambers of the engine. Add more fuel and you get more powerful combustion, less fuel and you get weaker combustion.

Mixture with a high setting is known as "rich" (ie rich in fuel) a low setting is "lean" (ie lean in fuel).

A mixture at rich offers more performance at the expense of greater fuel usage. A mixture at lean offers low power, but less fuel usage. So rich is good for when you require power - takeoff, combat, climbing. So lean is used for fuel conversation such as maintaining a cruise.

An increase in altitude requires a reduction in mixture ie make it more lean as you get higher Keeping it rich would flood the engine with fuel at higher altitudes (due to less air pressure).

Auto rich is the power user setting, auto lean is for a cruiser. The cutoff position cuts fuel flow to the engine shutting down the engine.

Prop Pitch.

It requires a plane with a variable prop for starters as a fixed prop cannot be changed.

Prop pitch is the angle at which the propellor cuts the air.

A fine/high prop pitch allows the greatest amount of power to be applied ie in combat/takeoff/landing and infact a high prop pitch can create more drag and reduce your landing run.
A low prop pitch takes larger bites at the air and is good for reducing drag and cruising where power is not immediately required.

When you start playing with prop pitch you should really be also using the throttle with it except in the case of landing (until you get into trouble and need to ram the throttle forward).

I = Fine pitched prop blade (not completely vertical mind you)

/ = Course prop pitch

- = feather prop pitch (used to reduce drag in the event of engine failure)

All up for maximum range go for moderate throttle settings, lean mixture with low RPM. For maximum performance open throttle, rich mixture, high RPM.

While i'm at it...

Throttle.

Controls the airflow into the engine (measured by the manifold pressure gauge). Essentially increasing throttle increases pressure on the engines cylinders forcing more air into the cylinders increasing the amount of fuel that can be burned - hence increasing the ability of the propellor to grab air and pull the craft forward faster.


Gee i hope i got that all right. I'm sure someone will point out the errors. http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif

Fliger747
11-11-2004, 05:40 PM
Life gets complicated once you get past 16....

The main reason for a very rich mixture at high power settings was COOLING! The evaporation of the unburned fuel caused a much greater heat and mass flow out of the engine at very high power settings. Water methanol injection was used for COOLING. The methanol was in there mostly to keep the stuff from freezing in it's tank!

The atmosphere decrease by another 1/2 in pressure about every 18,000'. So only 1/2 as much fuel for a given 'volume' of air is needed at 18,000'. Of course this all gets more complicated as these engines were supercharged, with often more than one stage. Cylinder head temperature, and especially exaughst gas temperature (EGT) are affected by the mixture, and could be used to 'lean the engine'. EGT will rise as the engine is leaned. Best economy is typically 25C on the rich side of the peak temperature and best power perhaps 75C. Cyl head temp works in the same way, but has a lag, and may not pick up a lean cylinder (the one you are burning up).

Nige_Reconman
11-11-2004, 05:45 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Fliger747:
Life gets complicated once you get past 16....

<HR></BLOCKQUOTE>

?? Is that some sort of shot at my age?!


Nice explanation by the way http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif http://forums.ubi.com/images/smilies/25.gif

x__CRASH__x
11-11-2004, 05:59 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Fliger747:
Life gets complicated once you get past 16....

The main reason for a very rich mixture at high power settings was COOLING! The evaporation of the unburned fuel caused a much greater heat and mass flow out of the engine at very high power settings. Water methanol injection was used for COOLING. The methanol was in there mostly to keep the stuff from freezing in it's tank!

The atmosphere decrease by another 1/2 in pressure about every 18,000'. So only 1/2 as much fuel for a given 'volume' of air is needed at 18,000'. Of course this all gets more complicated as these engines were supercharged, with often more than one stage. Cylinder head temperature, and especially exaughst gas temperature (EGT) are affected by the mixture, and could be used to 'lean the engine'. EGT will rise as the engine is leaned. Best economy is typically 25C on the rich side of the peak temperature and best power perhaps 75C. Cyl head temp works in the same way, but has a lag, and may not pick up a lean cylinder (the one you are burning up). <HR></BLOCKQUOTE>

This is why people get jumped. They have their heads buried in gauges trying to get the best performance out of their engines, next thing you know, you have lost a wing, and it all doesn't matter.

Ok, here is my down and dirty for playing this game (Not based on historical data or any mechanical comprehension):
PROP PITCH American Aircraft = DON'T TOUCH THE PROP PITCH. It doesn't do a thing for you. The ONLY plane I use manual pitch on is the 109 because it can make a difference in a fight.
FUEL MIX If its available, the use it. Below 2000 meters I keep it at 120 for max performance, but it can run hot. The higher I go, I start dropping it down. 80% at about 4000m, 60% at 6k, 40% at 8k. I LISTEN TO THE ENGINE! What does the bird like? You can tell, cause she will talk to you. She will tell you when she doesn't like the mix. Some Russian aircraft like the LAGG will actually smoke out the exhust when you get it wrong.
SUPERCHARGER Stage 1 below 3km. Stage 2 3km-7km. Stage 3 7km and above

Radiator and cowl flaps allow more air to flow past the cylinders faster, thus cooling the engine. However, they create drag. SO I open it to full at take off and leave it there, but close them when I stir it up in the s**t, unless I start really overheating, then I will open it up again.

Hope this helps.

Athosd
11-11-2004, 07:38 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by e2michaelb:
Question from a novice (old newbie): isn't the "Prop Pitch Auto Mode" setting supposed to take care of all this automatically? I tried to set it before taking off in a Spitfire and got no response. Then, as I entered the landing pattern, I found that the RPM's stayed up, even though my throttle (Saitek X45)was at idle. http://forums.ubi.com/images/smilies/16x16_smiley-sad.gif What have I missed? <HR></BLOCKQUOTE>

The "prop pitch auto" mode is only available if the plane had the feature. Most types in the game have manual pitch so hitting auto will have no effect.
For those that do have automatic pitch control - it is on by default and you can disengage it to make manual adjustments.

Note that there are several different types of air screw modelled in the game (Variable pitch, constant speed (most common) etc) - and the effect of prop pitch is somewhat abstracted for game purposes.

To find out if your ride has auto pitch control just try adjusting the pitch when you first get in the cockpit - if nothing shows up in your Hud Log (info display on the right side of the screen) then its currently automatic (or the aircraft has a fixed pitch prop).

For manual types refer to the material already posted above.

Cheers

Athos

lindyman
11-11-2004, 11:46 PM
Just to add a bit on the radiator flaps. I've only flown one plane that has radiator flaps, and that's not exactly a high performance fighter, but rather a bening and very pleasant Cessna 177RG Cardinal.

The rule of thumb for that one is radiator flaps open during takeoff and climbs, and closed otherwise. However, during level flight, you keep an eye on the oil-temp and cylinder head temp, and if they climb unpleasantly high, you check the EGT. If the EGT is high too, you've leaned it too much, so you give it a richer fuel mix. If EGT is not too high, you open the cooling flaps a bit (this really shouldn't happen, unless it's very warm weather.)

When descending for landing, you double and tripple check that the cooling flaps are shut. You don't, really don't, want the engine on idle and cooling flaps full open, since that shock cools the engine, and severely shortens its life.

It can be that they used them for drag on the fighters, knowing very well that the expected lifetime of the fighter wasn't very long anyway, so shortening the life of the engine wasn't a big deal. Can be, although I don't think so.
_
/Bjorn.

VVS-Manuc
11-12-2004, 03:18 AM
That shows that the "complex engine management" in PF (and before this in FB/AEP) is far away from being complex...

Buzzer1
11-12-2004, 03:53 AM
This vid confirms what Bj¸rn said above.
Cowl flaps are 2/3 open during TO, and closed during landings (ie F4U vice):
http://www.zenoswarbirdvideos.com/F4U.html

effte
11-12-2004, 10:06 AM
Water/meth does indeed act as a coolant, but not as much of the engine as of the air in the combustion chambers. In an engine, you try to add energy to the mixture and thus increase the pressure. This is done by burning fuel, together with oxygen. There is a limit to how much fuel/air mixture you can get into the cylinders though. We squeeze in more of it through using superchargers and turbochargers to increase the manifold pressure (MAP), but there€s always that wish for just a bit more isn€t there? There€s also a point where the pressure and heat will make the metal fail. This is when the piston heads suddenly turn into works of modern art. Afterwards, they work better as conversation pieces on the mantelpiece than as pistons.

So, you want even higher pressure but you are limited by MAP and/or the temperature in the chambers? Well, put some water in the cylinders with the fuel and air. The water will evaporate. As it does, it cools off the air in the cylinder allowing you to burn more fuel without the air in the cylinders getting too hot. Water vapour also takes up a lot more volume than water in a liquid state, which means that as it evaporates and cools the air, it will also increase the pressure in the cylinders tremendously (as gas tends to do, when it wants to be at a bigger volume than what is available).

Those of you familiar with intercoolers will recognize the effect.

Now, to make use of all that water you need to push more fuel into the cylinders with it, as evaporating the water will take more energy. Do you really want to reschedule your fuel injection or modify your carburator? That€s a lot of work.

No, instead you put meth in the water. Besides keeping the water from freezing at altitude, the meth will also contain the energy needed to evaporate the water, if mixed in the right proportions. And Viola (why does she always come in just as I€m making my point?), you have more power without redesigning your engine... hm, except for making sure that the gaskets, pushrods, bolts holding the cylinder heads etc will be able to cope with the pressure, of course. Blowing the cylinder heads out through the cowling has an adverse effect on the performance of an aircraft.

Cheers,
Fred

Jason Bourne
11-12-2004, 01:05 PM
um, just so you know, if you do the water/menth injection in the wrong proportions or at the wrong temp, you WILL blow the head off your cylinder/engine. or you will start bending the connecting rods/crank. because if it is to cold in the engine or there is to much water, it will not evaporate and instead will remain a liquid, which will not compress, throwing your engine into hydraulic lock, which means basically that you will never be able to use that engine again.