At higher RPM the prop pitch will be lower, generating less lift, at lower RPM (but still at max throttle) you'll get a higher pitch, producing more lift and making you go faster.

 

Generally lower RPMs = Less power (it depends on the RPM range where the engine produces max HP)

 

If you reduce RPMs your engine is not able to transfer as much energy to the air, so the net result is less thrust. This is the reason why all the checklists say to push the prop control to full forward. By keeping the RPMs for peak HP, you will ensure that you are getting max thrust.

 

The tradeoff for max thrust is lower fuel efficiency. Lowering RPMs gives up some power, for fuel savings. The net bigger bite of air causes the engine to turn slower, but it also prevents the engine from developing maximum power.

 

Think of what happens when you press on the gas in a car which develops max HP at a high RPM range (5K+). Disregard the gears in this case. When the care is at low RPM, it will accelerate slowly and gradually accelerate faster until you get near that peak HP RPM range at which point it will begin to accelerate much more quickly. Always keeping the engine at this peak RPM range will result in the best acceleration. However, it does not result in very good fuel economy.

There is some good material here too. http://flysafe.raa.asn.au/groundschool/propeller.html

Surely the same people are asking how a P51 Mustang can break Mach 1?

 

Strangely, I don't think it ever came up.

Actually, there has been a pretty steady stream of "why can't the Maule get up to it's claimed service ceiling" questions since Day 1.

 

Yet that is the one thing the "improvement" doesn't fix.

I haven't really had a chance to play around with it since the update, but my understanding is that this is closer to the way CS props should work. As someone mentioned earlier in this thread, full RPM does not mean max power. At higher RPM the prop pitch will be lower, generating less lift, at lower RPM (but still at max throttle) you'll get a higher pitch, producing more lift and making you go faster.

 

In order for the engine to develop it's rated horsepower (at sea-level), it must turn it's rated RPM's (2700 as an example). If you're flying along in cruise, the engine isn't working as hard as the climb, just like a car. However, we still want the most horsepower available, so the throttle will still be full forward. And, we still need those 2700 rpms to get that horsepower. Therefor, while the prop is turning at 2700 rpms........because we set it there with the blue knob, the pitch is actually coarser than it was for the climb mode. If you were to suddenly climb, the load becomes higher on the engine, just like a car. But the prop governor (not the blue knob) will reduce the pitch on the blades automatically, in order to keep the prop spinning at 2700. That means........just because the RPM's are higher, it doesn't mean the blade pitch will always be finer, as you've read somewhere.

 

As we gain altitude, the available horsepower drops. At 18000', it's somewhere around half, because the air molecules are less dense. But, you still want the prop & throttle full forward, to get the plane to it's highest ceiling possible. Anytime that the rpms are reduced, the available power is reduced, because the engine is a "pump" that's pulling in less air per revolution. If you look at some POHs, you'll find numerous prop & throttle settings, to achieve the same thing.

 

Note: I own a plane with a constant speed prop. I've flown them for many years. For my setup, I takeoff with full RPM & full throttle. I'll reduce rpms a bit on the climb for noise. I then cruise at 2350 to 2400 & leave it there, unless I want to climb quickly. I'll leave it at that 2350 to 2400 for the entire flight, until the throttle has been pulled back, and I'm on final approach. At that point, I'll push the blue knob full forward in case of a go-around or touch and go. My engine/prop comb has limitations between 2000 &2250 rpms. You can't keep it in that range for much time (harmonic vibration). I never like using it below 2000 rpms, and never run it that way.

Note: I own a plane with a constant speed prop. I've flown them for many years. For my setup, I takeoff with full RPM & full throttle. I'll reduce rpms a bit on the climb for noise. I then cruise at 2350 to 2400 & leave it there, unless I want to climb quickly. I'll leave it at that 2350 to 2400 for the entire flight, until the throttle has been pulled back, and I'm on final approach. At that point, I'll push the blue knob full forward in case of a go-around or touch and go. My engine/prop comb has limitations between 2000 &2250 rpms. You can't keep it in that range for much time (harmonic vibration). I never like using it below 2000 rpms, and never run it that way.

 

Larry, so, independent of the aircraft, I believe we can surely say that, specially on climb, pulling (retarding) the blue knob should NEVER account for a speed increase=power increase, and even less so abrupt like the one we are observing in the Maule after the patch....

 

I did a few tests with the RV-6 and I find that if climbing at full power (firewalled MP and RPM), I retard the prop lever, speed increases a knot or so for a couple of seconds and then begins to drop, and the nose starts to drop too...

Larry, so, independent of the aircraft, I believe we can surely say that, specially on climb, pulling (retarding) the blue knob should NEVER account for a speed increase=power increase, and even less so abrupt like the one we are observing in the Maule after the patch....

 

I

 

Yes, we can surely say that. As to your RV-6 observation, it's close enough.

Ok, so, might I suggest that we email MSFlight's Team about this, and other issues that came with the patch :-)

 

I did already ;-)

Full Power doesn`t mean full speed!!!!

 

Heimi, it would be good to be a little bit more specific with this statement.

 

Statement 1: If you were saying, "using Max (available) BHP (brake horsepower) or Max MAP (manifold pressure) "doesn`t mean full speed"... I'd say, "doesn`t necessarily mean full speed" as it will require max rpm.

 

Statement 2: If you were saying, "using Full Power (as in "Takeoff Power", a function of Max MAP and RPM) doesn`t mean full speed... that is incorrect (as Larry talked about).

 

After reading your first paragraph a number of times (a half dozen or so) I think you mean Statement 1.

 

I am not sure what you are trying to say in your second paragraph... one thing tho: when you talk of reduced power settings it has nothing to do with better speed.

 

If I don't pull back the prop speed, climb and top speed take a hit.

 

Definitely categorized in the "Twilight Zone POH".

 

 

Considering the cost of Flight, I think the flight models are pretty good.

 

This is pretty much the sum of the matter.

 

Now... I used to do the same thing in FSX from high altitude airstrips. When you take off from 11,300 feet you have to pull the prop back right away or you won't get off the ground.

 

How bizarre... I've never noticed this in FSX... a fun quirk to be aware of...

 

 

@ Larry A. Thanks for some "real world" injection (posts 33, 34 & 80) and writing some very lucid explanations.

 

Btw guys... some time ago I posted a link to a RW Cirrus POH. Here's the challenge for you (for those not accepting RW observation). Go to Section 5... find the "Cruise Performance" Chart... now show me an example where MAP is unchanged, RPM setting decreases and KTAS increases...

 

(Here is one link that works if you do not have it: https://wiki.umn.edu...rrus_Manual.pdf Btw... A lot of good info in that manual... worth the time to save it & to take some time to peruse it.)

 

You will not find it (KTAS increasing w/ lower RPM). Max MAP + Max RPM = Max Hp (probably could call Max Hp -> Max THP or Max Thrust HP if one takes into account engine and propeller losses). And simply put, More Hp = More Speed.

 

Go to any POH for that matter... and see...

I haven't really had a chance to play around with it since the update, but my understanding is that this is closer to the way CS props should work. As someone mentioned earlier in this thread, full RPM does not mean max power. At higher RPM the prop pitch will be lower, generating less lift, at lower RPM (but still at max throttle) you'll get a higher pitch, producing more lift and making you go faster.

 

Aside from oddities, like damaged props, extreme engine wear, or weird airframe/prop harmonics, the most thrust, for a given throttle-setting, is generated at the highest RPM setting. So yes, full RPM does mean max power.

 

There is no direct relationship between blade-pitch, and prop RPM. Blade-ptich continuously adjusts to maintain the pilot-set RPM.

 

Example: Takeoff with full-throttle, and max RPM (2700 for this discussion)... at the begining of the takeoff roll the blade-pitch will be near minimum.. as airspeed picks up, the prop RPM wants to increase too... the constant-speed prop mechanism will begin increasing pitch in order to maintain 2700RPM, and continuously adjust blade-pitch during the climb to maintain 2700RPM (or something lower, if the pilot so chooses, but that's beside the point)... Then, as the aircraft levels for cruise and gains airspeed, the constant-speed prop will adjust blade-pich, to maintain the selected RPM... Then, as cruise-speed is reached, and/or the pilot retards the throttle for cruise, the the blade-angle will settle in, to whatever is needed to maintain selected RPM.

 

To the point... You can takeoff with the prop-control full forward.. climb, cruise, descend, and you will have likely put the prop-blades through their entire pitch range, without ever touching the prop-control..

LHookins, on 25 June 2012 - 12:45 AM, said:

 

 

Now... I used to do the same thing in FSX from high altitude airstrips. When you take off from 11,300 feet you have to pull the prop back right away or you won't get off the ground.

 

 

How bizarre... I've never noticed this in FSX... a fun quirk to be aware of...

 

I've never noticed this either.. having devolped a few, Native FSX freeware light props (c177rg, c310, Bonanza P35).. I have uncountable hours testing this stuff (lots a real time in all three).. every possible combination of MP/Mixture/RPM you can imagine, for every possible scenario.

 

This scenario has mixture written all over it (having to pull it back for takeoff power at high altitude) ... perhaps there is a corruption in control assignments ?

This scenario has mixture written all over it

 

It sure would explain "things" except the... did not someone say a 10-20kt boost in performance?

 

the constant-speed prop mechanism will begin increasing pitch in order to maintain 2700RPM

 

And if I understand "thangs" correctly... this is one reason why you can only go so fast with a prop (like the realm of P-51 speeds)... pitch "runs out"... or maybe better... pitch which produces effective thrust runs out (am a little fuzzy on this tho i.e. I need some schooling here)

This scenario has mixture written all over it (having to pull it back for takeoff power at high altitude) ... perhaps there is a corruption in control assignments ?

 

Unfortunately I don't think it is the case, because the problem happens at SL airstrips, and using manual mixture I have tested that after the patch the mixture is still working properly at various levels, although, as we all know, mixture has never been the best modelled feature of reciprocating engines in MSFS... Anyway, for testing pouposes, pick the Maule, takeoff and climb at a given fixed speed, preferably using the mouse for easier triming. Then, above 3500/4000' start leaning and superimpose your mouse to the VS indicator. While IAS keeps more or less constant as you lean, VS increases as it should (more power available) and it drops if you push the mixture "knob". This is OK, so, the problem is in the CS Prop/Reciprocating engine model. It could also have it's root in a change on the prop mass and or gear ratio...

 

It is probably something MS FLIGHT team tried to corretct in the reciprocating engine model but got wrong. We also notice that the prop takes a lot of time now to come to a stop/accelerate when the engine is quit/started.

 

I look forward for a patch. It'll most probably get fixed.

It sure would explain "things" except the... did not someone say a 10-20kt boost in performance?

 

 

 

And if I understand "thangs" correctly... this is one reason why you can only go so fast with a prop (like the realm of P-51 speeds)... pitch "runs out"... or maybe better... pitch which produces effective thrust runs out (am a little fuzzy on this tho i.e. I need some schooling here)

 

Yeah, mixture is the logical deduction... and yes, you "outrun" a prop, but in a common, light-single, it would likely require a dive...

 

Unfortunately I don't think it is the case, because the problem happens at SL airstrips, and using manual mixture I have tested that after the patch the mixture is still working properly at various levels, although, as we all know, mixture has never been the best modelled feature of reciprocating engines in MSFS...

 

It is probably something MS FLIGHT team tried to corretct in the reciprocating engine model but got wrong. We also notice that the prop takes a lot of time now to come to a stop/accelerate when the engine is quit/started.

 

I look forward for a patch. It'll most probably get fixed.

 

Yes, sounds like a 'Flight' patch bug.. but the poster I was quoting says it happened in FSX..

Heimi, it would be good to be a little bit more specific with this statement.

 

Statement 1: If you were saying, "using Max (available) BHP (brake horsepower) or Max MAP (manifold pressure) "doesn`t mean full speed"... I'd say, "doesn`t necessarily mean full speed" as it will require max rpm.

 

Statement 2: If you were saying, "using Full Power (as in "Takeoff Power", a function of Max MAP and RPM) doesn`t mean full speed... that is incorrect (as Larry talked about).

 

After reading your first paragraph a number of times (a half dozen or so) I think you mean Statement 1.

 

I am not sure what you are trying to say in your second paragraph... one thing tho: when you talk of reduced power settings it has nothing to do with better speed.

 

I also don`t understand what you want to tell me with that.

Maybe I generalized/simplified my description too much.

 

This what i wanted to say: http://stoenworks.co...xtures and.html

 

Especially the PROP section