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OL_Maverick
04-01-2005, 09:00 AM
What is it? And is it worth adjusting?

OL_Maverick
04-01-2005, 09:00 AM
What is it? And is it worth adjusting?

IAFS_Painter
04-01-2005, 09:10 AM
It controls the angle (pitch) of your prop blades

and - sometimes.

If you fly LW types, you'll learn not to set 100% throttle and 100% pitch.
(Try it and see why, but do it off-line http://forums.ubi.com/groupee_common/emoticons/icon_wink.gif)

In an IL2, 80% throttle, 80% pitch can be faster than 100% both!

Ummm - setting pitch does help the engine run cooler, and (theoretically - I haven't tested) saves fuel.

BuzzU
04-01-2005, 09:47 AM
100% throttle with 100% pitch works fine in a steep climb.

NHawk52
06-06-2006, 09:59 AM
In general, for most planes, does 100% translate to "more pull" as well as higher temps? Is 80-90% generally a "better" setting?

Also, the control reference card references "Prop Pitch Auto = Shift+0"; in my plane, this doesn't appear to change anything. ??

han freak solo
06-06-2006, 11:38 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by OL_Maverick:
What is it? And is it worth adjusting? </div></BLOCKQUOTE>

It's your gearshifter, just airpane style.

100% is finest pitch which is like 1st gear in a car.

The lower your pitch %, the higher the gear # and the potential lower RPMs on the engine for a given throttle setting.

You can acheive faster level speeds with a lower than 100% pitch.

It is very usable in the game!

vocatx
06-06-2006, 06:31 PM
I have tested, and yes, it does increase range. I can get 800 km. out of a Spit V or Hurri II.

WTE_Galway
06-06-2006, 07:54 PM
i find the simplest way to work manual pitch is dial in a throttle setting and then vary the pitch slider to keep engine revs at optimal.

If there is a better way of doing it I would be interested.

Aardvark184
06-06-2006, 09:09 PM
I think I may have the whole procedure bass-ackwards, but here goes...

Prop pitch at 100% is when the prop blades are closest to perpendicular to the fuselage, i.e. they lay flatest. They spin faster due to less drag. As pitch is decreased, the blades turn out more, for example (not accurate) they are 45 degrees off perpendicular when at 45% pitch. They have much more pull, and spin slower. Slower spinning blades cause lower RPMs in your engine, which means you are getting more power put towards pulling your plane at lower RPM's... this'll save your engine from blowing up, and better fuel mileage. Higher percentage prop pitch can help you accelerate, and climb. If you have an airplane with adjustable pitch (and they don't all have it) try decreasing the percentage as you dive, and increasing it when you climb. I always try to keep the engine RPM between 2000 and 2500 in the 109's. With 80% power, I just use the prop pitch to change speed. That's just my style; everyone's got their own way of doing it. Experiment, and figure out your own way of doing it.

Someone PLEASE tell me if I'm backwards on this!

Cheers!

Tim

NonWonderDog
06-06-2006, 09:35 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by han freak solo:
It's your gearshifter, just airpane style.

100% is finest pitch which is like 1st gear in a car.

The lower your pitch %, the higher the gear # and the potential lower RPMs on the engine for a given throttle setting.

You can acheive faster level speeds with a lower than 100% pitch.

It is very usable in the game! </div></BLOCKQUOTE>

This is a common misconception, but still wrong. A gearshift in a car is used to keep the engine in the (one) desired rev range at various speeds, while the RPM control in an airplane is used to select different rev ranges for different modes of flight.

In addition, there are several types of prop control. The first, and most common, is a Constant Speed Propeller governor, in which the propeller pitch is automatically governed and the pilot merely selects the RPM of the engine. A couple planes in the sim have a Variable Pitch Propeller, where the angle of the blades must be adjusted directly -- with care taken not to overspeed the engine. I believe only the Bf-109 models still have this type of system in the sim, and then only when switched to "manual" mode. The German planes in the sim mostly use a proprietary system that ties the throttle and rpm controls together. This lets you ignore propeller settings altogether, but you're supposed to turn it off for landing (switch to manual mode in the 109 or CSP mode in the 190) -- more on that later. (Incidentally, I've heard that the Kommandgeraet system had a special takeoff/landing mode that is not present in the sim. I don't really know about that, but I *do* know that I don't want idle RPM during landing.)

Just like a car engine, aircraft engines have a specific RPM setting at which they develop maximum power. However, unlike in a car, the RPM of a constant speed propeller equipped aircraft engine is (more or less) independent of throttle setting. What this means to you is that you have two levers (actually three, including mixture) that directly control the power the engine produces. For takeoff you want maximum power, so you set your engine to full throttle and the peak-power RPM. This should be 100% RPM or close to it for every CSP-equipped plane in the sim.

Simply said, the RPM knob controls how fast the cylinders cycle, while the throttle lever controls how much fuel/air mixture is pumped into the cylinders every cycle. (The mixture knob controls the ratio of fuel to air in the combustion mixture.) Even more simply, the RPM knob chooses your base power level (on a non-linear curve), while the throttle determines (~linearly) how much of that power and heat you actually get. All of these affect fuel consumption, power, and heat.

The complicated bit is that the propeller also generates more (backwards) air drag the faster it spins. While 100% RPM should always lead to the most power, it will not necessarily cause the plane to be faster than at 90% RPM. Higher RPM will, however, always result in better accelleration at low speed.

This air drag is especially important during landing. You should ALWAYS use 100% RPM during landing. If you're flying a German plane, MANUALLY force the engine to a high RPM. This is for two reasons. First, and most importantly, it creates orders of magnitude more drag than at minimum rpm. People used to complain constantly that it was impossible to slow the FW-190 down to landing speeds (I believe it's since been changed), but it was EASY to land if you switched it to CSP mode first and chose 100% RPM. The corollary to this is that you can maintain a greater throttle opening during the approach because of this drag. This helps you to settle the plane once it's in ground effect -- a three-point landing is impossible if you can't decrease the throttle to drop the plane onto the runway. Secondly, keeping a high RPM setting decreases the spool-up time for the engine in case of a go-around. Since you're already at max RPM, you don't have to wait for the engine to spool up.

For cruise, you should pull back both the throttle and RPM in order to keep heat down and get good mileage. Another consideration is that there are two throttle and RPM settings combinations for nearly every power level. The engine may make the same amount of power at, say, 80% throttle and 2200 RPM as it does at 65% throttle and 3000 RPM. In nearly all cases the high-throttle, low-RPM setting is preferred. It will lead to less wear, less drag, and an equivalent amount of heat.

For dogfights, just choose 100% RPM and leave it there. You want all the power and accelleration you can get. If you find yourself in a high-speed dive, however, you will find it beneficial to reduce RPM first. I'm not really sure about the proper procedure here, though, since you're generally NOT supposed to reduce RPM when at full throttle (although the real-life consequences of such an action are not present in the sim).

DHC2Pilot
06-06-2006, 10:12 PM
Operators manuals almost always have engine power charts which (in graph form) show the best throttle (manifold pressure) settings to use with a particular prop (R.P.M.) setting. These charts will show you the best performance settings for both climb and cruise. Unfortunately FB/PF doesn't have this information in the documentation. So, as stated above 100% throttle / 100% pitch should generally be used during initial takeoff/climb (High power, flat pitch), then level off at altitude, throttle back to cruise power (this varies depending on the engine - usually about 60 or 70%), and begin increasing the prop pitch. Your RPM's will drop off and your manifold pressure will (should) rise. Keep in mind that with a constant speed prop governor the engine regulates the prop pitch according to throttle setting (it attempts to maintain a constant RPM by adjusting the blade pitch). Of course there are limits to the range of adjustment, and once the throttle is beyond the range that the governor can compensate the RPM for, the RPM will increase or decrease accordingly. The pilot would refer to the engine charts to determine the best RPM / Manifold pressure for a given flight situation.

erco415
06-06-2006, 11:22 PM
I don't know if it would matter in-game, but in rl you would adjust power as follows: When increasing power you increase mixture, then prop and lastly throttle. When decreasing power it's reversed - throttle, prop, mixture. Using a high power setting (manifold pressure with constant speed props) with a too-low prop rpm is an excellant way to blow the cylinder heads off your engine or cause other damage. There is an excellant discussion of all this (and more) on www.avweb.com (http://www.avweb.com) in the 'Pelican's Perch' columns.

WTE_Galway
06-06-2006, 11:51 PM
Problem is the auto pitch mechanism in IL2 are not necessarily constant speed props . .teh 109 auto pitch is definitely not !!

erco415
06-07-2006, 11:26 AM
WTE_Galway is correct about not all IL2 aircraft using constant speed props. From the fixed pitch props of the Gladiator to adjustable and constant-speed units to the sophisticated efforts to automate engine management made by the Germans, we've got it all! So one technique won't cover all, but outside of the early engine/prop control automation efforts the basic operation is the same.

Here are a few links to John Deakin's 'Pelican's Perch' columns that might be interesting...
This one about engine operation
http://www.avweb.com/news/columns/182045-1.html
About engine controls, throttle, prop, mixture
http://www.avweb.com/news/columns/182081-1.html
http://www.avweb.com/news/columns/182082-1.html
http://www.avweb.com/news/columns/182084-1.html
http://www.avweb.com/news/columns/182084-1.html
About flying the Constellation (for a certain fish...)
http://www.avweb.com/news/columns/182087-1.html
Everything you wanted to know about turbocharging
http://www.avweb.com/news/columns/182102-1.html
http://www.avweb.com/news/columns/182103-1.html
http://www.avweb.com/news/columns/182104-1.html
http://www.avweb.com/news/columns/182105-1.html
http://www.avweb.com/news/columns/182106-1.html
http://www.avweb.com/news/columns/182107-1.html
Flying the Bearcat
http://www.avweb.com/news/columns/182122-1.html
Detonation
http://www.avweb.com/news/columns/182132-1.html
Flying the Liberator (C-87)
http://www.avweb.com/news/columns/182133-1.html
And the B-29
http://www.avweb.com/news/columns/182150-1.html
And the Zero
http://www.avweb.com/news/columns/185354-1.html
http://www.avweb.com/news/columns/185520-1.html
The Hurricane
http://www.avweb.com/news/columns/185674-1.html
http://www.avweb.com/news/columns/185849-1.html

Some of these articles are focused on operation of general aviation aircraft, but it mostly all still applies to any propeller-driven aircraft. Also, some might notice that there seems to be a hint in these articles that not everyone agrees how to best operate piston engines. This is most certainly true. I believe the proof is in the pudding, and in any case, overhauling your engine in IL2 is inexpensive and cheap!

antifreeze
06-07-2006, 03:47 PM
I would probably refute the idea that some constant-speed-propeller aircraft go faster with a setting less than 100% throttle and 100% pitch (at below 5000m anyway). I did some extensive testing a couple of years ago in the game, and concluded that the apparent gain in speed was due to the nose dropping very slightly when cutting throttle or pitch. If you weren't watching your height extremely carefully and compensating for the drop in the nose, you'd be forgiven for thinking that you were getting an extra 10-20 km/h out of the aircraft. I'd need to see a track before I reconsidered this 'myth'.

OMK_Hand
06-07-2006, 04:09 PM
Maybe not faster, but almost as fast as flat out with reduced settings.

The model has changed in the last couple of years.

erco415
06-07-2006, 04:42 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by OMK_Hand:
Maybe not faster, but almost as fast as flat out with reduced settings. </div></BLOCKQUOTE>

This is correct, though I haven't checked to see if this is reflected in game. You get most of the speed for less fuel, heat, etc. A prop at 100% pitch is a far more effective airbrake than one at, say, 75%. (This assumes that the engine is being turned by the prop) So if you want to glide with your engine out, a stopped prop is best followed by one at low pitch/rpm with the high pitch/rpm causing the most drag.

ot, but for giggles, let's see what school y'all been to. What are the four cycles (strokes) in a four stroke engine?

Sillius_Sodus
06-07-2006, 05:01 PM
What pitch setting does the sim use when flying with complex engine management OFF?

Good Hunting,
Sillius_Sodus

NHawk52
06-07-2006, 09:39 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by erco415:
ot, but for giggles, let's see what school y'all been to. What are the four cycles (strokes) in a four stroke engine? </div></BLOCKQUOTE>

Intake, compression, combustion, and exhaust (backyard automotive school in the pre-muscle car era)

Stackhouse25th
06-07-2006, 10:52 PM
WHY is it each of these posts is just a fraction of knowledge, cant anyone put detail and time into their posts?

This thread needs only 1 response, 2 at most.

look it up on Google.com It saves on gas, and increases the range of your plane. 100% for climb, 100% for landing, 50-90% during cruise depending on power settings. Avoid low RPM's and high power settings.

NonWonderDog
06-08-2006, 09:10 AM
I really thought my 797 words was more than "a fraction of knowledge."

I guess I'll have to try harder next time. http://forums.ubi.com/images/smilies/1241.gif

mortoma1958
06-08-2006, 09:25 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by NonWonderDog:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by han freak solo:
It's your gearshifter, just airpane style.

100% is finest pitch which is like 1st gear in a car.

The lower your pitch %, the higher the gear # and the potential lower RPMs on the engine for a given throttle setting.

You can acheive faster level speeds with a lower than 100% pitch.

It is very usable in the game! </div></BLOCKQUOTE>

This is a common misconception, but still wrong. A gearshift in a car is used to keep the engine in the (one) desired rev range at various speeds, while the RPM control in an airplane is used to select different rev ranges for different modes of flight.

In addition, there are several types of prop control. The first, and most common, is a Constant Speed Propeller governor, in which the propeller pitch is automatically governed and the pilot merely selects the RPM of the engine. A couple planes in the sim have a Variable Pitch Propeller, where the angle of the blades must be adjusted directly -- with care taken not to overspeed the engine. I believe only the Bf-109 models still have this type of system in the sim, and then only when switched to "manual" mode. The German planes in the sim mostly use a proprietary system that ties the throttle and rpm controls together. This lets you ignore propeller settings altogether, but you're supposed to turn it off for landing (switch to manual mode in the 109 or CSP mode in the 190) -- more on that later. (Incidentally, I've heard that the Kommandgeraet system had a special takeoff/landing mode that is not present in the sim. I don't really know about that, but I *do* know that I don't want idle RPM during landing.)

Just like a car engine, aircraft engines have a specific RPM setting at which they develop maximum power. However, unlike in a car, the RPM of a constant speed propeller equipped aircraft engine is (more or less) independent of throttle setting. What this means to you is that you have two levers (actually three, including mixture) that directly control the power the engine produces. For takeoff you want maximum power, so you set your engine to full throttle and the peak-power RPM. This should be 100% RPM or close to it for every CSP-equipped plane in the sim.

Simply said, the RPM knob controls how fast the cylinders cycle, while the throttle lever controls how much fuel/air mixture is pumped into the cylinders every cycle. (The mixture knob controls the ratio of fuel to air in the combustion mixture.) Even more simply, the RPM knob chooses your base power level (on a non-linear curve), while the throttle determines (~linearly) how much of that power and heat you actually get. All of these affect fuel consumption, power, and heat.

The complicated bit is that the propeller also generates more (backwards) air drag the faster it spins. While 100% RPM should always lead to the most power, it will not necessarily cause the plane to be faster than at 90% RPM. Higher RPM will, however, always result in better accelleration at low speed.

This air drag is especially important during landing. You should ALWAYS use 100% RPM during landing. If you're flying a German plane, MANUALLY force the engine to a high RPM. This is for two reasons. First, and most importantly, it creates orders of magnitude more drag than at minimum rpm. People used to complain constantly that it was impossible to slow the FW-190 down to landing speeds (I believe it's since been changed), but it was EASY to land if you switched it to CSP mode first and chose 100% RPM. The corollary to this is that you can maintain a greater throttle opening during the approach because of this drag. This helps you to settle the plane once it's in ground effect -- a three-point landing is impossible if you can't decrease the throttle to drop the plane onto the runway. Secondly, keeping a high RPM setting decreases the spool-up time for the engine in case of a go-around. Since you're already at max RPM, you don't have to wait for the engine to spool up.

For cruise, you should pull back both the throttle and RPM in order to keep heat down and get good mileage. Another consideration is that there are two throttle and RPM settings combinations for nearly every power level. The engine may make the same amount of power at, say, 80% throttle and 2200 RPM as it does at 65% throttle and 3000 RPM. In nearly all cases the high-throttle, low-RPM setting is preferred. It will lead to less wear, less drag, and an equivalent amount of heat.

For dogfights, just choose 100% RPM and leave it there. You want all the power and accelleration you can get. If you find yourself in a high-speed dive, however, you will find it beneficial to reduce RPM first. I'm not really sure about the proper procedure here, though, since you're generally NOT supposed to reduce RPM when at full throttle (although the real-life consequences of such an action are not present in the sim). </div></BLOCKQUOTE>Very nice explaination but the thing you missed is the biggest reason for them developing constant speed and variable pitch blades to begin with.
It was developed simply because the air gets thinner the higher up you go. The higher you go the bigger the "bite" you need to make up for the thinning air. You need a bigger bite to be as efficient and go as fast as you were down lower, as the air molecules are farther apart up there.

With fixed pitch props, manufacturers had to make the blade pitch optimized for take off or landings and low altitude in general, or lower the pitch for better cruise efficiency up at high altitudes. Either that or make one that compromised between the two needs. This was not the best solution, so ways to vary pitch were developed. Direct variable prop pitch and then the constant speed system were invented. So more than anything the whole concept was not done for fuel efficiency nor was it for reducing operating temperatures or even reducing engine wear. Those were just nice benefits/advantages that went along with it. It was by far mostly done for speed effiency in the whole altitude range of a particular aircraft. From down on the ground up to the maximum ceiling.

In fact having a type of variable pitch system can in of itself increase the ceiling ( and top speed ) of an aircraft, over having just a fixed "compromise" prop. So it's more for eeking max speed/efficiency/altitude out of an aircraft. Not for reducing temps and getting better fuel economy, though it does that too.

NHawk52
06-08-2006, 12:09 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Stackhouse25th:
WHY is it each of these posts is just a fraction of knowledge, cant anyone put detail and time into their posts?

This thread needs only 1 response, 2 at most.

look it up on Google.com It saves on gas, and increases the range of your plane. 100% for climb, 100% for landing, 50-90% during cruise depending on power settings. Avoid low RPM's and high power settings. </div></BLOCKQUOTE>

Thank you, Sir! Short, direct, and applicable to the sim. Anything more just confuses the question.

Viper2005_
06-08-2006, 12:09 PM
Actually mortoma, variable pitch is all about speed range, not altitude range.

First, some definitions.

Pitch = the distance which the blade would advance during a single revolution if turning in a solid medium (just like a screw). <span class="ev_code_red">Pitch is a distance, not an angle.</span>

So, let's imagine that the air is a solid medium and that there is no slip.

It follows that speed will vary in proportion to the product of airscrew pitch and airscrew rpm.

In order for the airscrew to be efficient, it should have constant pitch throughout its diameter. In otherwords, it must be helical, like a spiral staircase. Thus, the blade angle at the root must be "steeper" than the blade angle at the tip.

This has some important consequences when we try to use the airscrew in air.

The design of a practical airscrew is constrained by several factors.

i) Tip Mach number; supersonic airscrews tend to be inefficient. This places limits upon the relationship between diameter, rpm and aircraft speed.

ii) Static thrust; the aeroplane must be constrained to flight at the design speed; it must be able to accelerate from a standing start.

Since engine power varies with rpm, it follows that if possible we want to remain as close as possible to the optimum rpm at all times.

So, for the sake of argument, let's design an airscrew for high-speed flight. The design speed is 450 mph, and the design engine rpm is 3000. We'll put it through a reduction gearbox with a ratio of 0.42:1, so that the airscrew is turning at 1260 rpm or 21 revolutions per second.

450 mph is 660 feet per second.

Therefore the required pitch is just over 31.4 feet.

If the airscrew has blades of this pitch then they will slice through the air at zero angle of attack. &lt;&lt;Of course in reality, you want the blades to have an angle of attack, so having calculated the helix angle associated with the design pitch you then add however many degrees angle of attack you require.&gt;&gt;

Now let's imagine slowing down to 45 mph. The pitch required is only 3.14 feet.

It is possible to calculate the angle at which the blades will meet the air with some simple trig; but I'm on holiday, so I can't be bothered. Anyway, because the blade angle varies helically from root to tip, it follows that the "off design" when flying too slowly, the roots of the blades will see a higher angle of attack than the tips.

If you go slowly enough, the whole blade will be stalled. Not very useful - stalled blades produce very little useful thrust, and so the chances are you'll have difficulty taking off.

In fact, this was the limiting factor for the Schneider Trophy racing seaplanes - they had very little useful thrust at low speed (but bags of torque), and as a result takeoff was marginal at best.

The solution is of course to reduce pitch. Unfortunately, this reduces top speed, and the only way to get back to the design performance you first thought of is to increase rpm or pitch. Increasing rpm is generally impractical due to tip Mach number effects.

Therefore, designers cried out for variable pitch.

Unfortunately, variable pitch is impossible, because pitch implies a helical, twisted blade. So instead, we've ended up with variable blade angle. This has the effect of varying the pitch of the blade, but due to trigonometry, the pitch of the root and the pitch of the tip vary at different rates!

Since most of the useful work is done at about 70% of the way from the root of the blade to its tip, what generally happens is that the pitch at around this point is about right for the speed being flown, and the pitch at other stations isn't, except when flying at the design point, when everything lines up.

The variable pitch airscrew is therefore something of a misnomer, but it sounds better than variable blade angle.

Of course, shortly after the invention of the variable blade angle airscrew, it was noticed that the increased pilot workload required to operate the blade angle control caused problems, and so some bright spark came up with the constant speed airscrew.

This simply exploits the fact that the greater the angle of attack of the airscrew blades, the greater the drag they exert. This means that over the normal operating range it is quite simple to construct a mechanical governor which will control engine speed by manipulating blade angle.

This isn't very aerodynamically elegant* a lot of the time, but generally the aerodynamics of the airscrew are less important than the thermodynamics of the engine! Operating the engine at low rpm with an open throttle offers considerable improvements from the thermal efficiency viewpoint if you're after long range. More importantly for the pilot, it is possible to fly in a carefree manner without fear of the engine overspeeding in a dive or cutting out in a stall.

*Essentially it uses the airscrew as a replacement for the water or electric brake generally employed on engine test-stands.

justflyin
06-08-2006, 01:08 PM
Nice write-up, Viper.

Some of your always level-headed and accurately informative posts might get lost on certain individuals around here, but I'd just like to take a second to acknowledge your efforts, as they are very much appreciated by me.

There are a few around here just like you that I truly enjoy reading from and always find their posts to be helpful, spot-on accurate and very even-keeled in attitude. Thanks for being you.

No need to respond, just keep doing what you do best. http://forums.ubi.com/images/smilies/25.gif

mortoma1958
06-09-2006, 10:37 AM
Wow Viper, that is truly a complicated explaination. I just know the simpler stuff, not that much detail!! I also know what I have read over the years and what I was taught in my pilot training material. Maybe there is some misconception and therefore innaccurate informantion in pilot training manuals then. Anything is possible I suppose. Do you have a degree in aeronautics per chance??

mortoma1958
06-09-2006, 10:58 AM
Not trying to disprove, demean or otherwise disrespect anyone. But I have found a place on
one of Nasa's webpages that indeed discusses propeller pitch and it's stated that altitude performance does in fact have a good bit to do with it, as my pilot training had taught me.

However, I'm waiting for permission from Nasa to post the info in here......I'll be back. It does seem to behoove the powers that be to train real world pilots such as myself with a proper understanding of how things work and why they work, concerning aircraft. If I don't understand propeller pitch properly, then should I even be flying?? In my case I fly mostly trainers with fixed props but I have flown a Cessna Cardinal and Beech Bonanza, just not very much time in them.

Despite the eloquence of Viper's post and his going into complex physics and trigonomety and such, he still fails to mention the effects of various densities of air on the overall equation. The lowering density of air as one goes higher does seem to have an impact on the matter.

mortoma1958
06-09-2006, 02:32 PM
Ok nevermind, my message to them was undeliverable, so I did not get permission to post it. So the next best thing, which I didn't think of for some reason ( Doh! ) at the time is to just link to the website. The paragraph I'm referring to is the fourth one down and mentions that variable pitch/CS props were not needed at first, weren't in demand until planes were made that went faster and <span class="ev_code_RED">higher</span>!!
I think Nasa, of all organizations, should know this stuff. Not trying to rub anyone's nose in the dirt, or crowing/bragging about being right either, just wish to teach correct principles of flight.

Here's that link:
http://www.centennialofflight.gov/essay/Evolution_of_Te...ogy/props/Tech14.htm (http://www.centennialofflight.gov/essay/Evolution_of_Technology/props/Tech14.htm)

As an aside, I'd like to point out that if you took a fixed pitch plane, such as a Cessna 172 or a Piper Warrior and added a CSP mechanism, the added weight penalty of the system would do much to negate the improved altitude performance!! It would still probably go higher, maybe a bit faster up there too but not as much as you might think.

erco415
06-09-2006, 03:41 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by NHawk52:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by erco415:
ot, but for giggles, let's see what school y'all been to. What are the four cycles (strokes) in a four stroke engine? </div></BLOCKQUOTE>

Intake, compression, combustion, and exhaust (backyard automotive school in the pre-muscle car era) </div></BLOCKQUOTE>

You are correct, but easier to remember is what we learned in A&P school:
Suck, Squeeze, Bang, Blow http://forums.ubi.com/groupee_common/emoticons/icon_razz.gif

Viper2005_
06-09-2006, 05:16 PM
This is in danger of turning into a discussion of semantics.

If an aeroplane has excess power, a choice may be made to either fly higher or fly faster.

It may be shown that (all other things remaining equal) brake power requirement varies as:

Thrust*Velocity

Since at Vmax in level flight:

Thrust = Drag

And at EAS values greater than that for maximum L/D:

Drag = 0.5*roh*v²*CD*S

it follows that at constant roh, brake power requirement varies as the cube of velocity.

Now let's climb instead.

If we hold constant EAS, it follows that drag will remain constant. Since air density (roh) is decreasing, it follows that TAS will increase.

We go faster at constant drag.

Therefore the power required only varies with the first power of velocity rather than the third.

<span class="ev_code_red">We generally fly higher in order to fly faster, not the other way around.</span>

Unfortunately, the power available to a naturally aspirated piston engine also varies with roh. Therefore the equivalent sea level power requirement actually varies with the square of velocity. Still, since squares are smaller than cubes, it makes sense to fly higher in order to fly faster.

We can get some extra help though. Ram effect raises inlet manifold pressure by a few "Hg at high speed, and then of course there's supercharging. Of course, if you were to power your aeroplane with an electric motor then the first power relationship would apply (until you get high enough for compressibility to bite...).

Practically, if your aeroplane is going to fly over a large altitude range, it follows that it will have a large speed range. It is the speed range (and thus the range in advance ratio) rather than the altitude change per se that makes a variable pitch airscrew worthwhile.

However, if for some reason you were going to vary altitude without varying TAS there would be no case for a variable pitch prop. There might be a case for a variable solidity prop, or a variable area prop, but that's another matter...

I can start thowing NACA reports around if you really want, but frankly life's too short!

BTW, if your 172 or Warrior is fitted with a cruise prop, you'll see no useful speed improvement. However you will see an improvement in rate of climb.

If it's fitted with a climb prop then going to constant speed will make it faster, but won't substantially improve climb rate.

The major benefit will be seen in range flying when you can control output by regulation of engine rpm rather than BMEP; this allows for quite dramatic SFC improvements. If you swapped out the Cessna for something aerobatic, you'd also see a substantial reduction in cockpit workload when making large attitude speed and power changes. You can just set your power, set your rpm and leave them alone. Even flying in the circuit in a 152, at the end of the downwind leg you'll be doing perhaps 90 knots. At that point you'll need to throttle back to start going downhill. Set 1700 rpm at 90 knots and you'll have about 1500 rpm by the time you're established on short final which is about right. In an aeroplane with a constant speed prop, you don't have to be as far ahead of the aircraft. Assuming that you're already at high rpm ready for your a missed approach, you can just set the power required and leave it alone; no guess work or judgement based upon experience needed. Wonderful!

WWMaxGunz
06-09-2006, 08:55 PM
Does Reynolds number design elements effectively change with air density?
Just seeing as how it has to do with properties of the air?
I know there's allowances, etc, where perhaps high alt wings differ and I wonder if the
considerations work out the same as if the Reynolds number had changed.

Just wondering.

Viper2005_
06-10-2006, 08:54 AM
Yes, Reynolds number is affected by changes in altitude.

http://aero.stanford.edu/StdAtm.html

The higher you go, the lower the Reynolds number.

Props escape some of the really nasty low reynolds number effects because of engine vibration, but never the less, there be dragons if you go high enough (though you'd probably need to use an electric motor to get yourself into real trouble...).

Kernow
06-10-2006, 03:56 PM
The prop doesn't need to bite more air because the air is thinner at height. At height a given IAS equates to a greater TAS than it does lower down. It's the TAS that matters. The airflow relative to the prop blade depends on TAS and prop speed of rotation.

Imagine some point on the blade where TAS is same as speed of the blade:

A
^
^
^
^
B&gt;&gt;&gt;&gt;&gt;&gt;&gt;C

AB represents TAS, BC prop rotation.

As they're the same here, angle ACB is 45 degrees. Prop pitch at this point needs to be greater than 45 degrees to produce any thrust. If pitch &lt;45, the airflow drives the prop, causing drag and possibly engine damage.

If the engine is producing any power the CSU would increase the blade angle so that there is a positive 'angle of attack' and the power gets transfered to the airflow, ie you get thrust. If you closed the throttle and left demanded rpm the same, the angle would reduce until the airflow was driving the prop at the demanded rpm. As the engine is no longer providing power the only way for the CSU to maintain the desired rpm is to take energy from the airflow to drive the prop, ie you get drag and the prop is a windmill.

Basically you alter the pitch to keep the blade meeting the airflow at a positive angle of attack, so that energy from the engine ends up doing useful work.

Demanding less than 100% rpm means you don't get full power, so you don't go faster... or turn better, or climb better or do anything, which requires power, better.

IL2-chuter
06-11-2006, 02:43 AM
Yay, Kernow. I've been a pilot my whole life and found it interesting reading all the posts. 100% throttle + 100% prop = 100% power. Only manually controlled blades need constantly adjusted . . . to hold 100% RPM. The 109 does have a manual mode but in RL they didn't get any more thrust out of it, they just had to work harder at it in manual. (In auto the RPM went in steps. They probably got better cruise economy manually, however.) http://forums.ubi.com/images/smilies/16x16_smiley-indifferent.gif

And what the hell is with the 190's total lack of takeoff accelleration? It bogs along like its got a fixed pitch cruise prop. That commando thingy should run the prop/throttle out to max for takeoff. http://forums.ubi.com/images/smilies/blink.gif

PS. I've flown the Porsche commando unilever thingy (c.1977ish). . . found it a little gimmicky - I'm a old taildragger pilot. (They had no idea BMW had come up with it in WW2 and were surprised to hear about it).


Have a nice day. http://forums.ubi.com/images/smilies/16x16_smiley-happy.gif

Kernow
06-11-2006, 05:48 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by IL2-chuter:
...

And what the hell is with the 190's total lack of takeoff accelleration? It bogs along like its got a fixed pitch cruise prop. That commando thingy should run the prop/throttle out to max for takeoff. http://forums.ubi.com/images/smilies/blink.gif

</div></BLOCKQUOTE>

Yea, that's always annoyed me - the engine only seems to really pick up well after you get airborne, which I guess is a sure sign the prop pitch isn't where it should be.

I've always run the 109 & 190 in auto - save sometimes for the E model, early versions of which had a manual system, I believe - as that ought to give best performance. However, maybe I should start trying manual in the 190.

Kocur_
06-11-2006, 06:00 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">And what the hell is with the 190's total lack of takeoff accelleration? It bogs along like its got a fixed pitch cruise prop. That commando thingy should run the prop/throttle out to max for takeoff. </div></BLOCKQUOTE>

Well thats obvious: because it was fascist invention, and since they lost, it must have been useless and stupid. Simple, isnt it.

Xiolablu3
06-11-2006, 06:23 AM
I never used Prop Pitch in my life, am I missing much speed/climb ability by not using it?

Viper2005_
06-11-2006, 10:46 AM
In the Fw-190A you'll see a substantial performance improvement from using 100% "prop pitch". You would also see a substantial improvement in the Dora were it not for the fact that it causes fatal engine overheating within seconds.

WWMaxGunz
06-11-2006, 12:20 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by IL2-chuter:
And what the hell is with the 190's total lack of takeoff accelleration? </div></BLOCKQUOTE>

Prop strongly designed for high speed is not so great at low speed?

Kernow
06-11-2006, 03:28 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by WWMaxGunz:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by IL2-chuter:
And what the hell is with the 190's total lack of takeoff accelleration? </div></BLOCKQUOTE>

Prop strongly designed for high speed is not so great at low speed? </div></BLOCKQUOTE>

Yes. Thats why they designed variable pitch props, like CSUs or the Kommandojobber in the 190.

WWMaxGunz
06-11-2006, 10:45 PM
Even with variable pitch you only get so much range. Contrary to some seeming belief the
range of rotation is not 90 degrees or even nearly so. For prop to feather takes extra
mechanism not found on most fighters but yes found on many VSP bombers. Once feathered
they do not revert back in flight.

Where did I learn of props optimised for high speeds or other uses? Oleg post and then a
good bit of searching. So unless you think that he makes these things up?

justflyin
06-12-2006, 10:22 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Kocur_:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">And what the hell is with the 190's total lack of takeoff accelleration? It bogs along like its got a fixed pitch cruise prop. That commando thingy should run the prop/throttle out to max for takeoff. </div></BLOCKQUOTE>

Well thats obvious: because it was fascist invention, and since they lost, it must have been useless and stupid. Simple, isnt it. </div></BLOCKQUOTE>

As I highly doubt that is the reason why, I have often wondered why some planes take so long to get rolling, even with 100% pitch, WEP and full throttle. FW certainly one of them. A couple of the japanese planes as well. As Arte might say, "Veeeeeddy Interesting".

Kernow
06-12-2006, 12:48 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by WWMaxGunz:
Where did I learn of props optimised for high speeds or other uses? Oleg post and then a
good bit of searching. So unless you think that he makes these things up? </div></BLOCKQUOTE>

Make things up? Surely not.

Some props are optimized for climb, cruise or high speed, but the ones I've read about were fixed pitch ones. By varying the pitch you get around the problems of being optimized for one specific flight regime. I'm not a prop engineer, so can't be certain there is no other optimization that could be done, but that Kommandothingy should give a decent performance for take-off, unless the low pitch stop is really at a pretty high angle. However, as manual control does give a good take-off (according to Viper) a suitable blade angle clearly is obtainable.

Incidentally, the Pe-2 (in-game version) doesn't have a feathering mechanism. Seems unlikely in a modern twin-engined design, so I reckon the real one could feather the prop on a failed engine; maybe they made that up.

WWMaxGunz
06-12-2006, 08:21 PM
Sigh....................

First thing I wrote last post, the range of blade angle is not zero to ninety degrees.
You can't get everything out of VSP alone.
WWII planes in dives had to be controlled to prevent overspeed and busting the prop hub
which did happen and also happened in the highspeed record attempts.

Here's a link, scroll down to the subtitle "Hitting the Stops". Use Edit-&gt;Find if you need,
it's in Big Black Letters without the double quotes.

http://www.avweb.com/news/columns/182082-1.html

And don't bother with drivel about websites before you check John Deakins credentials and
those of the AVWeb site.

Then THINK a bit. If the prop blade rotation is limited then how you get more efficiency
at higher speed? You start with the prop blade at a higher angle is one way. You make the
blade shape higher efficiency at faster speed is another --- same as thin wings versus thick.

Years ago one reply about Rechlin data on an FW not matching the sim got the reply of what
prop was used on the exact plane the data was from (we saw one page of many posted, Oleg has
the entire report) is not the prop in the model simulated. Then there was text about prop
differences but not much detail, just the facts of differences and which was used.