PDA

View Full Version : Alright, plz explain prop pitch to me



XyZspineZyX
08-16-2003, 09:14 PM
i dont really understand how to use prop pitch. i know that lower pitch means lower rpm's but thats about it. why would you want to lower it? does your ideal prop pitch depend on you altitude? it just seems like when ever i lower the pitch, i just lose airspeed. so how do you use it correctly in combat? i understand that its better to use a lower setting while cruising, but i dont see why you would ever want to change in during combat. plz help.

"diplomacy is saying 'good doggie' until you can find a really BIG rock."

XyZspineZyX
08-16-2003, 09:14 PM
i dont really understand how to use prop pitch. i know that lower pitch means lower rpm's but thats about it. why would you want to lower it? does your ideal prop pitch depend on you altitude? it just seems like when ever i lower the pitch, i just lose airspeed. so how do you use it correctly in combat? i understand that its better to use a lower setting while cruising, but i dont see why you would ever want to change in during combat. plz help.

"diplomacy is saying 'good doggie' until you can find a really BIG rock."

XyZspineZyX
08-16-2003, 09:39 PM
Nose down in a dive, roll it 70 to 60% even 50% for the big hoggs.

Nose steep up in a climb, 90 to 100%

Level in hot pursuit or on the run, 75 to 85% depending on plane.

Rough guide to get you started. If your always flying a favorite like the P-47, consider swapping your prop pitch onto your throttle. Set throttle to 100% power and leave it there with radiator closed for better speed. It won't overheat for quite some combat time, than just 20% open on the rads, no more.

The reason your engine boggs down is the prop is moving more air, you want that for best speed, but not too much that your engine can't keep up. If your losing airspeed, you've gone too far.


If your engine is winding up with high RPM's and doesn't seem to want to go any faster, but holds right where it's at, you don't have enough prop %.

Use the settings above as a rough guide. Higher your nose goes up, the higher % you dial in. Lower the nose goes, lower the %.

For your specific plane, level it out, set the power to 100% with radiator closed, than play prop % up and down to get best speed. Be patient and let it have a minute or two to stabalize after making an adjustment. When you figure out fastest possible speed setting %, remember it for combat time. When you need it, dial above it a bit to prevent any sort of bogg down, than as your plane speeds up dial slowly tword the magic number and you'll smoke em good as it gets.

XyZspineZyX
08-16-2003, 09:48 PM
Hey GeneralD,

I am by no means an expert, but I've been flying an Emil for 12 hours straight now, and have picked up the basics/i/smilies/16x16_smiley-happy.gif

(note that all of the following doesn't apply to constant speed props, such as all the Allied aircraft. It only applies to Variable Prop Pitch aircraft, which basically means Bf109's, and even they have the option to use Kommandoger¤t, or auto-pitch. That's not nearly as cool, though. /i/smilies/16x16_smiley-happy.gif )

Think of it as a car with a stick shift. You might as well ask: "Why would I want to shift up from 1st gear in a car? High RPMs are good, right?" Of course, as you know this isn't true. Get too high RPMs, and you wreck the engine. It's the exact same thing with prop pitch.

Come with me on an imaginary flight:

We start in our trusty Emil. We have just made takeoff. Pitch is at 100% and throttle is at 100%. We're still going fairly slow. We are picking up speed. If you watch the RPM gauge, you will see it increasing. Now it is getting near its recommended maximum: 2400 RPM is combat speed. Any faster, and you may damage the engine. But, I hear you ask: "We're still going pretty slow. Don't tell me a Bf109E can't go any faster!"

Of course it can. You just have to do the exact same thing that you do when you shift up in your car. You "coarsen the pitch", that is, bring it to, say, 75%.

The RPMs will drop, but the Emil will continue to accellerate. The prop is now pushing more air per revolution than it did before. It produces more thrust for the same RPMs.

Let's keep coarsening the pitch until the RPMs won't go any further. For an Emil that happens at about 60% pitch. With 100% throttle, 60% pitch and 2500 RPM we're going 450 kph at sea level, which, incidentally, is this aircraft's rated maximum for level flight! /i/smilies/16x16_smiley-happy.gif See, you couldn't have reached that speed at 100% pitch. Just as you couldn't have reached 80 mph in your car in first gear.

Now when you're in a dive, you can go much faster. Then you have to coarsen the pitch even more, to stop the engine from over-revving on you.

The analogy to a manual shift car goes even further. Just as in a car, you can use the engine on a "low gear" to "brake" the aircraft. If you go too fast, for instance for a landing approach, and just throttle back, not much will happen. But if you also bring the pitch back up towards 100%, your speed will drop rapidly. It's just the same as if you were driving a car down a steep slope. You'd put it in a low gear, so the engine itself would slow down the car and spare the brakes.

Whew, I hope all of that made sense. /i/smilies/16x16_smiley-happy.gif I'm a bit enthused today, see, because I have grokked prop pitch, and it is truly cool that FB models it. /i/smilies/16x16_smiley-very-happy.gif /i/smilies/16x16_smiley-very-happy.gif


--
Joques
Ok, so you've got a Yak
That don't impress me much

XyZspineZyX
08-16-2003, 09:51 PM
The controllable pitch propeller can also be called a constant speed propeller, since the propeller knob controls the engine RPM at the normal cruise power settings. Once this RPM is set, the prop will continually rotate at this constant speed.


The throttle controls manifold pressure (MP) and (indirectly) pitch of the prop. Increasing throttle increases the manifold pressure (the pressure of the air/fuel mixture going to the engine) and the prop tries to turn faster.

On planes with auto pitch control the prop controller resists faster RPM by increasing the "bite" of the blades in the air. This increased pitch and angle of attack of the blades causes more thrust, but also causes more drag, resisting an increase in RPM. In a sense, throttle only increases the torque of the engine, and then the prop governor increases the pitch of the blades to produce more thrust and drag. This happens quickly and automatically, so no change in RPM is noticed.


So, the throttle controls the MP/engine torque/prop pitch, and the prop knob regulates engine/prop RPM.

If you are flying a plane without auto pitch control during a dogfight you will need to constantly adjust pitch, as required, to keep your propeller in the proper speed range for the model you are flying. The IL2 manual on the game CD's provides some information on the proper rpm range for each plane, which you can use as a rule of thumb.

If you overspeed the prop, you eventually burn up the engine. If your prop pitch/rpm is too low, you slow down/loose efficiency.


Hopefully this answers the mail


All the best, Don

XyZspineZyX
08-16-2003, 09:55 PM
ok a fixed pitch propeller is efficent at a set speed it equates to when the forward motion of the prop through the air sets the optimum angle of attack of the advancing prop blade.

Now as the plane accelerates this angle in effect reduces as the forward speed increases, so the prop becomes less effective and and in effect the pitch goes fine. to get round this a variable pitch prop was introduced, as the forward speed increases and the prop angle of attack reduces, then the propeller coarsens up to maintain the optimum angle and hence maintains the maximum thrust over a larger airspeed range. hope that helps you.

At cruise you are in effect flying at a slower speed, when in combat you want the maximum speed and hence power available so you coarsen the prop as your airspeed builds up.

Modern piston aircraft like the Beech Baron you use the prop lever to set its operation at a given rpm then when you open the throttle this becomes a power lever and the RPM remains stationary but the boost increases and the prop coarsens via the CSU (Constant speed unit) to increase power, ie thrust

XyZspineZyX
08-17-2003, 12:12 AM
Wow joques -

I've never quite had it explained that way - very simple and to the point - I always wondered why I couldn't get my Emil to go over 260km/h at 100% pitch, 100% throttle.

Thanks for the simple yet powerful example!


<center> http://www.autumnhullphoto.com/fbsig.jpg

.

XyZspineZyX
08-17-2003, 12:24 AM
Prop Pitch ? what Prop Pitch We dont have Prop pitch anymore
we have some fantasy Pitch that dosent allow the Engines to induce drag so now you canot decelerate to land or force overshoots Real Prop pitch can actualy be used as an airbrake as it did in version 1.0 and as it does in real LIFE

The new Patched prop pitch is not Prop pitch at all its some kind of bad Joke

I like the sim overall But the Sound the Prop-pitch & the throttle all need to be re-worked

<center><FONT COLOR="white">ӚFJ-M œ R D ˜ ӡ[/i]</font>

<center> http://www.onpoi.net/ah/pics/users/ah_109_1059752328.jpg </center>

<center><FONT COLOR="white">The "Ace Edge"(c).
With my incremental trim
I am actually able to turn so quickly that, I never turn at all.
In Fact the Planet Earth rotates around the Axis of My PC, thus giving me the optimum turn rate and insuring that you
the bandit are promptly fraged !!!
In memory Of Ray R.I.P.[/i]</font>

XyZspineZyX
08-17-2003, 01:06 AM
alright. cool, thanks fellas. relating prop pitch to the gears in a car really helped me alot since my car is a stick. i think i got it, i just need to get used to using it correctly. anyhow, thanks again

"diplomacy is saying 'good doggie' until you can find a really BIG rock."

XyZspineZyX
08-17-2003, 02:57 AM
Very informative and easily understood answers ....am I on the right board?

"We make war that we may live in peace."

Aristotle

XyZspineZyX
08-17-2003, 08:01 AM
AFJ_Murdoc wrote:

- we have some fantasy Pitch that dosent allow the
- Engines to induce drag so now you canot decelerate
- to land or force overshoots Real Prop pitch can
- actualy be used as an airbrake as it did in version
- 1.0 and as it does in real LIFE

You are not correct. This works in FB, I do it all the time (see my example above)





--
Joques
Ok, so you've got a Yak
That don't impress me much

XyZspineZyX
08-17-2003, 08:22 AM
TheGeneral_D wrote:
- alright. cool, thanks fellas. relating prop pitch
- to the gears in a car really helped me alot since my
- car is a stick. i think i got it, i just need to get
- used to using it correctly. anyhow, thanks again

Glad you liked it /i/smilies/16x16_smiley-happy.gif Just note that what I said only applies to VPP aircraft, which means Bf109 and FW190, and they even have auto options available (esp. FW190).

Constant Speed props (nearly every other aircraft in the sim) is something else entirely. Then you use the "pitch" controls to set RPM directly. 100% "pitch": highest RPM. 0% "pitch": Lowest RPM.

I put "pitch" in inverted commas because even though you aren't really adjusting pitch directly in these aircraft, that's what the game tells you that you are doing. Kinda confusing at first. /i/smilies/16x16_smiley-happy.gif


--
Joques
Ok, so you've got a Yak
That don't impress me much

XyZspineZyX
08-17-2003, 12:04 PM
Joques Go take A Dora 44 up & tell me that the PP is right

Or the A9 ??

If it works for you & its not for me then maybe I need reinstal of the sim

I know how PP is suposed to work & it seams Very wrong for Dora & A9 ?

Please reply

<center><FONT COLOR="white">ӚFJ-M œ R D ˜ ӡ[/i]</font>

<center> http://www.onpoi.net/ah/pics/users/ah_109_1059752328.jpg </center>

<center><FONT COLOR="white">The "Ace Edge"(c).
With my incremental trim
I am actually able to turn so quickly that, I never turn at all.
In Fact the Planet Earth rotates around the Axis of My PC, thus giving me the optimum turn rate and insuring that you
the bandit are promptly fraged !!!
In memory Of Ray R.I.P.[/i]</font>

XyZspineZyX
08-17-2003, 12:16 PM
AFJ_Murdoc wrote:
- Joques Go take A Dora 44 up & tell me that the PP is
- right
- Or the A9 ??
- If it works for you & its not for me then maybe I
- need reinstal of the sim
- I know how PP is suposed to work & it seams Very
- wrong for Dora & A9 ?
-
- Please reply

You're right, there something odd with prop pitch in a D9. Or at least, it doesn't work like in an Emil. I really don't know enough about the theoretical workings of prop pitch to say it is "borked" in D9, (or A9, didn't try that one), but you just might be on to something here. My best recommendation: Use Oleg's bug report form. Just keep your cool, test thoroughly, compile data and present your test data in a level-headed manner. That's your best bet to have it fixed (if indeed it is wrong) /i/smilies/16x16_smiley-happy.gif



--
Joques
Ok, so you've got a Yak
That don't impress me much

XyZspineZyX
08-17-2003, 01:12 PM
The best explanation I've ever heard, is the "scuba diver" reperetoire.

Imagine you are a scuba diver under water, with the "duck feet". You are propelling yourself through the water by pedalling your feet.

Now, imagine an "economy cruise" while swimming. You don't have to pedal too fast to achieve this.. just give a rythmical, slow pedalling.. scoop lots of water with the duck feet and propel yourself forward.

Then, you meet a shark suddenly. You decide to get the hell outta there full speed. What do you do?

You pedal your feet as fast as possible.. your duck feet don't scoop up as much water as in the 'cruise', but it picks up and pushes little amounts of in a very rapid interval. As you pedal madly away from the shark, you feel yourself getting tired - your heart is pumping, you have trouble breathing, and your muscles become tense.

...

The water as air, duck feet as propellers, your heart as engine, your heartbeat as RPM, your breath and lungs as the radiator system.

Voila, now you understand the relationship between the engine, engine RPM, cooling system, propeller and the air.



-----------
Due to pressure from the moderators, the sig returns to..

"It's the machine, not the man." - Materialist, and proud of it!

XyZspineZyX
08-17-2003, 06:16 PM
For this explanation attempt assume we are looking at a plane traveling <----- in level flight.. the prop is rotation clockwise and we're looking at the TIP of the prop blades as they spin. They start out looking like this / So, the bottom forward edge is trying to grgab into the air as it spins.

The important factor is the Blades AoA (Angle of Attack) The AoA is the angle made between the prop blade and the relative air flow (which at low speed or zero speed is close to | And a higher AoA is better for efficiency. So the AoA is the angle between / | which for argument sake is 45' Now, as forward speed increases, the airflow over the prop increases in speed (same speed as the plane is moving forward assuming no wind) and the "realtive Airflow" is now coming from the direction the plane is heading since the plane is moving through the air at some speed.

As the relative Airflow vector approaches /, the AoA between the prop blade / and the relative airflow / become almost ZERO..since they are the same angle.. This is a bad thing for a prop. Since you can't control the airflow, the solution is to make the props more coarse.. or move the blade angle from / to something closer to horizontal..thuus keeping a good gap (or AoA) between the airflow and the blade pitch..

Or simply put, as speed increases you want the leading edge of the blade to be angled into the wind..at low speeds you're taking small bites of slow air with every bladee.. as the air moves faster you angle the blades forward so you can take bigger gulps of faster moving air.

This would be easy with diagrams <G>

Check here for diagrams

http://142.26.194.131/aerodynamics1/Performance/Page8.html

XyZspineZyX
08-17-2003, 07:18 PM
The prop pitch setup for FW190's is correct (at least for FW190A's, I have less information on D series, but I assume they would be similar, more modern than the Bf109's).

The FW190A series used a Constant Speed Prop (like P47 or La5), in conjunction with a complex apparatus (Kommandererat) that adjusted RPM, Manifold Pressure, Spark Advance, Mixture, and Supercharger automatically with 'one lever' up to its critical altitude (where it began to function less efficiently). What we have in FB1.1 is a very reasonable simulation of this (of course it could be more complex, but come on). The FW190 could also be operated manually, in which case the Constant Speed Prop operated very similarly (the same) as the P47 for example.

Though I don't know about the FW190D series, I would assume they would continue to use what is considered the best and most modern technology, the Constant Speed Prop.

Murdoc, don't forget that you can't directly adjust the Prop Pitch on a constant speed prop, so the 'speed brake' you speak of is not possible in the manner you describe.

XyZspineZyX
08-17-2003, 08:09 PM
ZG77_Lignite wrote:
- Though I don't know about the FW190D series, I would
- assume they would continue to use what is considered
- the best and most modern technology, the Constant
- Speed Prop.
-
- Murdoc, don't forget that you can't directly adjust
- the Prop Pitch on a constant speed prop, so the
- 'speed brake' you speak of is not possible in the
- manner you describe.

This is a surprise to me. According to the early version of the aircraft tables at Tailspin's site, the FW190 had a VPP underneath the kommandoger¤t. I see now that in that latest version of the table, this has been updated to CSP/Auto.

Intriguing. Is it a well established fact that FW have a CSP (it certainly handles that way in the game), or is it a debated issue? Does anybody have confirmation that this is in fact true?


--
Joques
Ok, so you've got a Yak
That don't impress me much

XyZspineZyX
08-17-2003, 08:42 PM
Previous table was wrong. It was CSP.

Explaining CSP with VPP is confusing.

RPM governor sets RPM, and pitch will adjust automatically for current environment. (Kommandogerat controls it better.)


Just think it simple.
When you need high speed at low speed and power situation, rpm up! (game calls it 100% pitch)
If you got enough speed in air, full rpm won't provide effective power. (can even cause resistance.)
Then pilot adjusts RPM down. That's why cruise RPM and combat RPM exist.

In a harsh combat, you may need 100% rpm all the time except when B in BnZ and dive attck.

--------------------------------------
I hate angry, yelling 'New User'.

XyZspineZyX
08-17-2003, 08:52 PM
TheGeneral_D

I'm guessing your flying a Russian/American plane? If that's the case. They have constant speed props. Just leave it on 100% for best performance.

The only plane that you use like a tranny in a car would be the 109's.

25th_Buzz
------------------------------------------------------------------------------------------------------------------------------------------------------------------
<center>
http://www.vfa25.com/sigs/buzz.jpg