And yes, fine pitch - RPM lever fully fwd - does cause increased drag, and should be used for steep descents, throttle retarded... FLIGHT does model this.

 

The Prop adjustments in the p51 also translate correctly to cruise speed changes in FLIGHT!

For example, I'm wondering why the top speed at level flight is so slow in the Musting.

 

What airspeed are you talking about (IAS or TAS)? :Thinking:

 

If you compute the TAS, you will find that the Flight P-51 is performing in the ballpark of most commonly published figures.

 

For example, assuming standard conditions, 250 IAS = ~325 TAS at 15,000 feet and ~375 TAS at 25,000 feet.

Constant speed prop basics......

 

Nice to have at high altitude airports. Full forward, allows the engine to rev & produce as much horsepower as possible. Note: Prop governor usually set at redline (Lycoming 2700 rpm for instance). While in cruise, pull back the rpms. It's nice to have a quieter running airplane. If you really need the top speed, the prop knob will go forward again; to full forward ( a finer pitch) or close to it. This is where it differs from a car on the freeway.....in which a lower gear is used for higher speeds.

 

The advantage of C/S props over fixed pitch. Fixed pitch is a compromise. A good cruise prop with coarser pitch makes a lousy takeoff prop...........as the engine cannot achieve it's highest rpms. High rpms mean high horsepower. A good takeoff prop with a finer pitch, means that the airplane can't go full throttle without exceeding red-line. Therefor, most fixed pitch airplanes have settings in between.

 

The C/S prop also acts as a good air brake. I can easily head down hill, such as 2000 fpm, and loose airspeed...........while a fixed pitch doesn't have a chance.

 

Note: I'm keeping the explanations somewhat short. I've owned and used a Hartzell constant speed for years. C/S has always been my favorite, because I operate out of mountain airports. The advantage is not as noticeable at sea-level. I'll takeoff full forward, and pull back slightly for noise. Then usually back to 2350 in cruise. For descent, it can actually remain at 2350 and still has the braking effect. For climbs, it goes forward again. On short final, the blue knob goes full forward, otherwise, you'll notice a significant loss of power on a touch & go. Push it forward too soon, and it's like shoving a car or motorcycle into low gear at high speeds. Not good for the engine, and throws your body against the seat belts.

 

L.Adamson

Constant speed prop basics......

 

Nice to have at high altitude airports. Full forward, allows the engine to rev & produce as much horsepower as possible. Note: Prop governor usually set at redline (Lycoming 2700 rpm for instance). While in cruise, pull back the rpms. It's nice to have a quieter running airplane. If you really need the top speed, the prop knob will go forward again; to full forward ( a finer pitch) or close to it. This is where it differs from a car on the freeway.....in which a lower gear is used for higher speeds.

 

The advantage of C/S props over fixed pitch. Fixed pitch is a compromise. A good cruise prop with coarser pitch makes a lousy takeoff prop...........as the engine cannot achieve it's highest rpms. High rpms mean high horsepower. A good takeoff prop with a finer pitch, means that the airplane can't go full throttle without exceeding red-line. Therefor, most fixed pitch airplanes have settings in between.

 

The C/S prop also acts as a good air brake. I can easily head down hill, such as 2000 fpm, and loose airspeed...........while a fixed pitch doesn't have a chance.

 

Note: I'm keeping the explanations somewhat short. I've owned and used a Hartzell constant speed for years. C/S has always been my favorite, because I operate out of mountain airports. The advantage is not as noticeable at sea-level. I'll takeoff full forward, and pull back slightly for noise. Then usually back to 2350 in cruise. For descent, it can actually remain at 2350 and still has the braking effect. For climbs, it goes forward again. On short final, the blue knob goes full forward, otherwise, you'll notice a significant loss of power on a touch & go. Push it forward too soon, and it's like shoving a car or motorcycle into low gear at high speeds. Not good for the engine, and throws your body against the seat belts.

 

L.Adamson

Very well described indeed - thank you!

toedy, my only hands-on flight experience has been with fixed pitch props (C152).

 

I'm trying to understand how to fully use prop speed control with MS Flight.

 

For example, I'm wondering why the top speed at level flight is so slow in the Musting. It hits me that maybe the default prop control level position in MS Flight is firewalled (fine pitch) and that, although, this is proper for take off and landing, it won't be the best setting to squeeze the maximize level flight top speed.

 

So the point I missed is that we're not dealing with fully manual prop control. We're modeling consatnt speed props here.

 

My thoughts are that this is entertainment, which is cool

 

I'm sorry, but you clearly have a misconception of what constant speed props are for. They are not designed to make the plane fly faster... they are to make the plane fly more efficiently. Please read the link I provided earlier.

 

As noted by Oracle, your concerns about the Mustang's top speed is most likely due to not taking IAS vs. TAS into account.

RobRay, Misconception, yup, that nails it.

 

But,...... I just tried X-Plane and it works just as I would have thought. With everything firewalled, yes, your engine is screaming. Pull back a bit on the prop lever for a coarser pitch and RPM drops but airspeed nudges up..

 

Which is why I asked about MS Flight not representing airspeed change..

 

I appreciate your statement that constant speed props are not designed to make the plane fly faster. Having said that though, wouldn't you agree that having the ability to control pitch in flight fundamentally allows for a faster top speed? By that I mean you benefit from having a coarse pitch for top speed and yet can move to a fine pitch fot takeoff, otherwise, the prop angle of attack would be too high and most of the prop disk would be stalled out at lower airspeed (resulting in a longer ground roll)..

Yes, Larry provides an excellent explanation on CSP use & fixed pitch prop limitations.

 

Let me go a bit further w/o the hopes of not trying to muddle the issue.

 

"Normally," when you go to purchase or rent an airplane, you'll find included a POH (Pilot Operating Handbook) with the plane. Obviously not all planes have a POH. The Maule has limited info. I'm not sure the year... 1970s? when POHs came into existence like we see with today’s aircraft (there used to be "Operating Manuals" "Information Manuals" some better than others etc.)

 

At some point (a few decades ago) the FAA decided to make the POH mandatory in compliance... it is known as an AFM (Airplane Flight Manual) when it is specific to a airplane by serial number. The AV industry came up with a certain standardized format that manufacturers (typically) follow now.

 

For example... in a POH... Every "Section 3" is "Emergency Procedures"... Section 5 - Performance... Section 6 - Weight and Balance.

 

A pilot will thoroughly familiarize (him/herself) with the POH/AFM before checkout. That means much of the info you will know "cold" like Section 2 - Limitations... Emergency Procedures, Normal Procedures (Section 4).

 

Ok, enough with the history lesson and moving to the Section we cannot specifically memorize (which answer the OPs question) Section 5 - Performance.

 

(For those wanting "more" info on the above from the FAA: http://www.faa.gov/l... Chapter 08.pdf)

 

First find a POH (for an airplane that uses a CSP). Here is an example POH for the Cirrus SR22 (Serial Numbers 3026 and Subsequent). http://servicecenter...e13772-002E.pdf

 

Again, "normally" a pilot will choose a cruise power setting based on a number of factors. 65% power is typically chosen... usually 75% Power would be a max setting... if the engine capable of that % output for the chosen altitude.

 

So we have an altitude we have chosen... we decided since it such a short hop... say 6000'MSL. And I figure I don't mind burning some AVGAS today so I'll run at 75% power (or so). So we go to Section 5 (Remember? The Performance Section) and look for "Cruise Performance. Check out (if you have downloaded the SR22 POH) page 5-23 (Adobe page 160 for me).

 

I look at 6000PA on page 5-23 (Pressure Altitude) and know we are closest to "Standard ISA" Temp (remember... standard day is 29.92"Hg and 15°C / 59°F with a standard temp drop of a couple degrees C per 1000'... Adiabatic Lapse Rate for you Techies)...

 

And I see "oh cool... with an engine in tip-top shape... I can make 76% Power... TAS will be 177kts with a Fuel Flow of 18.1gph. I just need to set my MAP to 23.5" and RPM to 2500."

 

And there you have it... that is how that works. Go to page 5-25 for the "Range and Performance Profile" and based on the following conditions (Weight 3400lbs etc... Best Economy Mixture... Full Fuel... 45minute IFR Reserve Fuel) and I'll burn 2.0gal for the climb to 6000', have about 80gals for cruise with a 4.5hr range (or about 800nm). Side Note: Time is what I used. I start that engine... my clock starts as I WILL be back on the ground with an hour fuel remaining.

 

Let's say we are feeling a bit more frugal... ok then how about 65% Power? Chart says by pulling MAP back to 20.5" I will develop 64% Power... True at just 10kts less but burn 3gal/hr less that way.

 

How does Larry set his power?... I bet first he was at the Vans support forum reading as much as he could on the matter of performance. Found out as much as he could from his Engine Manufacturer. Bet he got involved with a local group of builders (if available) and became a part of EAA. Probably found 2350RPM as a reasonable setting for the (reduced) noise (full throttle at cruise sounds like), good TAS and FF, and as he said, a useful setting for descents.

 

Another example if you wish... Here's a POH for the Beech Baron (B55) http://www.flytaa.co...s/BE 55 POH.pdf You can see on pages 5-36 thru 5-39 Cruise RPM settings as High as 2450rpm to as low as 2100rpm. It all depends how hard you want to work the engine, what Fuel Flow / TAS you want for Altitude flown, and personal preferences like pulling RPMs lower for that "not so loud" whine or roar.

 

You follow the AFM first or what the Engine Manufacturer provides or in the absence of that (like the RV-6) talk to the pros like Larry.

 

-Rob

 

However, I see no increase in speed.

 

Because MAP will (or should) go up... you are getting all you are going to get... MAP + RPM = % Power. IRL that typically would not be good as you could very well cause Detonation to occur - with not so fun things resulting like the engine failing.

 

How do I set power in Flight Sim? Keep Everything shoved full forward as I want to go as fast as I can (typically). I don't have to worry about checking Performance Charts (even if I were to have the right ones) worry about blowing up an engine, paying for fuel, paying for decreased time between overhauls... maybe I pull the RPMs back now and then to limit noise.

But,...... I just tried X-Plane and it works just as I would have thought. With everything firewalled, yes, your engine is screaming. Pull back a bit on the prop lever for a coarser pitch and RPM drops but airspeed nudges up..

 

I don't know which model you're using, but don't count on X-Plane "in general" to accurately replicating a C/S prop. Most of the models don't perform the braking effects hardly at all, if at all. As to pulling the prop back for more speed............it's usually very little at the most, if at all. For instance, in my RV, it's like 50 rpm. That's not much. For those speed runs, when the prop lever is at full forward, and the throttle is at full.............it doesn't mean that the prop is at the finest pitch, that it would see on the takeoff run.

 

As to my preferred settings, my particular engine/prop combo has a limitation between 2000 & 2250 rpms. I'm not suppose to run very long between those rpm settings. I don't like running it below 2000, and would usually stick with around 2350.

As to my preferred settings, my particular engine/prop combo has a limitation between 2000 & 2250 rpms.

 

Larry that would be an IO or O-360 and Hartzell?

RobRay, Misconception, yup, that nails it.

 

But,...... I just tried X-Plane and it works just as I would have thought. With everything firewalled, yes, your engine is screaming. Pull back a bit on the prop lever for a coarser pitch and RPM drops but airspeed nudges up..

 

Which is why I asked about MS Flight not representing airspeed change..

 

I appreciate your statement that constant speed props are not designed to make the plane fly faster. Having said that though, wouldn't you agree that having the ability to control pitch in flight fundamentally allows for a faster top speed? By that I mean you benefit from having a coarse pitch for top speed and yet can move to a fine pitch fot takeoff, otherwise, the prop angle of attack would be too high and most of the prop disk would be stalled out at lower airspeed (resulting in a longer ground roll)..

 

I think you're still getting hung up thinking that moving the prop control directly affects the blade angle. It doesn't. The way the governor works isn't simple. There's a very complex relationship between the engine power, the RPM you've selected, your airspeed, air density, and probably some other variables I'm not even aware of. We're at the limits of my own understanding of this topic, so at this point I'll just have to defer to the experts like Larry who fly with them regularly. My own personal real-life experience is limited to fixed pitch props, except for some highly unofficial turboprop time (and that had an FE minding the engines for me).

 

I wouldn't want to fly a plane where I could directly control the blade angle... it seems like it would be quite easy to destroy your engine with a single ill considered push of the prop control lever. Think of putting your car in neutral and flooring the gas pedal...

Larry that would be an IO or O-360 and Hartzell?

 

0360/Hartzell 2 blade (and not the new blended tip model)

I think you're still getting hung up thinking that moving the prop control directly affects the blade angle. It doesn't. The way the governor works isn't simple.

 

Unless I am way off forgetting from my A&P course days... it's a balance between the oil pressure the governor supplies and whatever is trying to take the prop to high or low pitch (depends on the prop setup e.g. using counterweights to take to high pitch and oil pressure to take to low pitch).

 

(and not the new blended tip model)

 

Thanks sir...

 

LOL... that reminded me of the story when those "Q-Tip" props were new and someone was ramp checked and duly cited for having "bent prop tips".

 

 

Because MAP will (or should) go up... you are getting all you are going to get... MAP + RPM = % Power.

 

Thinking on this further... maybe there is some increase in prop efficiency? Higher MAP but with increased prop efficiency leads to a slightly higher TAS?

 

Been a long time... I have forgotten so much...

 

And if it does... we are really asking a whole lot out of our Sim...

Thank you everyone for your patience while helping me through this.

Thank you for asking! I'm sure I'm far from the only one who enjoys seeing this type of topic come up for discussion. I manged to learn some things myself.

Why is it that I read the articles at these links and I come out feeling like I know less than when I started? It was the same with the VOR information. I already know how to use a VOR, and I understand constant speed props, but the way they're explained seems like they're attempting to produce the most confusion possible.

 

I couldnt agree more ...It's as Einstein said .... "If you cant explain something simply, you simply do not understand it"