Glad to hear the discussion has helped! Best of luck with your continued learning and training.

 

Scott

True, but I'm trying to "keep it simple" for him! LOL!!

 

Ken

 

No need, I get density altitude...

Good report, mryan. I guess you've hit the nail on the head on what that simulator game can do, supporting some rw training stuff or even offering new impressions to then learn about.

 

Yeah, I've gotten way more out of this "simple" question than I expected! Good stuff!

Which aircraft you are flying? Those data you found should be specific for an altitude. 75% of power will give you 24 inHg at certain altitude. If you fly higher, the number could be less than 24inHg. This is also the same for the engine RPM. At sea level you may get 2700rpm fro full throttle, but at 5000ft you may only have 2500rpm. It's quite normal.

 

Since it was mentioned, that it's a constant speed prop to start with, the prop/engine should still see a full 2700 rpms....... at 5000', if the prop control is full forward. The engine isn't producing sea level power of course, but it's plenty enough to let the prop governor spin at 2700. My RW point of view is from a 4600' airport, where density altitude can be much higher. I can always get the full 2700, and still could,quite a bit higher. I have not tried to an altitude point, in which the engine "says forget it".......it's not going to happen.

i don't want to start an argument here but i always thought that the Carenado Saratoga was a bit underpowered, even taking under consideration every word discussed in this topic.

So i modified the max_rpm_mechanical_efficiency_scalar= line in the aircraft.cfg to something closer to 1.0. Maybe a lower figure could represent a fatigued or not well maintained engine (my speculation). Obviously, i won't discover the gunpowder if i say 1.0 equal 100% mechanical efficiency.

Let me say that i fly normally in warm and low altitude regions.

 

Best regards,

Ignacio

Since it was mentioned, that it's a constant speed prop to start with, the prop/engine should still see a full 2700 rpms....... at 5000', if the prop control is full forward. The engine isn't producing sea level power of course, but it's plenty enough to let the prop governor spin at 2700. My RW point of view is from a 4600' airport, where density altitude can be much higher. I can always get the full 2700, and still could,quite a bit higher. I have not tried to an altitude point, in which the engine "says forget it".......it's not going to happen.

 

Yes, this is totally true. Not until you pull the power way down would there be any chance you could not achieve red line on the RPM, and frankly on any complex aircraft I have flown, even with the MP down to 10 to 12 inches, with the prop control levers full forward, the governor was still able to achieve and hold 2700 RPM (which is red line on my 310R). Not unless I was on the ground standing idle or in taxi would I see the RPM gauge below 2500 and this was with the MP gauge showing something less than 7 inches.

 

This is precisely why when you suffer inflight engine failure that both the manifold pressure gauge and the RPM gauge will lie to you! Both gauges will indicate that the engine(s) are producing full power! The manifold gauge will revert almost immediately to outside air pressure. The RPM will show something at least in the 2500 range or higher. Therefore, to discern a failed engine there is only one gauge that won't lie to you and that is the EGT (exhaust gas temperature). The other thing that won't lie is the sudden quiet on a single engine plane and the lurch in yaw that comes from a single engine failure on a piston twin!

 

Ken

i don't want to start an argument here but i always thought that the Carenado Saratoga was a bit underpowered, even taking under consideration every word discussed in this topic.

So i modified the max_rpm_mechanical_efficiency_scalar= line in the aircraft.cfg to something closer to 1.0. Maybe a lower figure could represent a fatigued or not well maintained engine (my speculation). Obviously, i won't discover the gunpowder if i say 1.0 equal 100% mechanical efficiency.

Let me say that i fly normally in warm and low altitude regions.

 

Best regards,

Ignacio

 

You know, I have to say I thought the same thing. I didn't get nearly the climb performance out of it (nor the speed) that I was expecting.

 

On the fuel burn issue, again, I was seeing about 12 gph with the prop at 2,400 RPM and the manifold pressure at 21.7 inHg. I was expecting more like 16 gph at cruise speed. Any thoughts on that? I guess I'll have to go up again in the thing and mess around with different settings and see what I get in terms of speed and fuel burn.

 

A funny side-note: I get to the end of the 2-hour cross country and get configured for the landing. As I put in the second notch of flaps this horn starts going off. At first I'm wondering if it's coming from the NAV radio, signaling the outer marker or something, and I'm trying to get this annoying horn to stop blaring (can you tell where this is going). But I don't want to go around because I'm right on glidescope, perfect speed, etc. So I say screw it, I'll figure out what that is after I land. Which I did. On the belly

 

Like I said, simulators are great for some things.

 

Yes, this is totally true. Not until you pull the power way down would there be any chance you could not achieve red line on the RPM, and frankly on any complex aircraft I have flown, even with the MP down to 10 to 12 inches, with the prop control levers full forward, the governor was still able to achieve and hold 2700 RPM (which is red line on my 310R).

 

Pardon me again, Ken, if this is a stupid question, but as was stated above, full throttle at altitude doesn't necessarily mean full power. So is it ok to keep the throttle firewalled if I'm getting 21.7 inHg as I was and 2,400 RPM, or should you back the throttle down to 75% (or some lower setting)? Is it bad for the engine to have the throttle at 100% if you're not getting 100% engine power? On this flight I just left the throttle in full, backed the prop to 2,400, and putted along.

Still on the throttle, eh? :P Perhaps your instructor should show you what that throttle actually does, next time being on the plane. I really mean the mechanical ways of that lever and where it ends. Differs a bit on the fuel injected engines, but perhaps it's an eye opener.

 

I always read some 'I'm worried about over-stressing the engine' into your statements, mryan and, while I like the cautious attitude, seeing that you may relate engine stress levels to the position of the throttle lever alone.

 

Well, that MP gauge is your power instrument on that kind of plane. Together with the rpm, those are your factors of defining how much power you are actually getting out of that engine. See both red lines? Match both and you will receive the rated engine power, your 100% defaulting to some HP value. You may not always be able to achieve it or, at colder days, you may be able to overshoot more or less.

 

So while you are ascending, the achievable MP will reduce, as described in the previous posts. With that, you are getting away from the max MP while the rpm may stay at max for way longer as the prop arrangement adjusts itself for the lower engine output, keeping the rpm steady.

This means that you yield lower than 100% either way. With the throttle lever fully opened, you allow for 100% of 'what's there' or 'what's left' which is perfectly save at altitude or even very shortly after climbing away from your starting point as the pressure drop within e.g the first 5000ft is very noticeable.

 

So there is no need to worry as long all your gauges show nice temps, nice oil pressure levels and a MP and rpm combination being within the limits the manufactures has defined. For example, the stuff does not like high MP settings with low rpm running, due to the torque levels developing in that situation. So there's a certain envelope (plane specific) to keep in mind. To find out about that one, the POH is the very fist source of data.

 

On the fuel burn. I don't know how accurate the Carenado plane is, but your table shows that you will achieve those 16 gal/hr up to 7000ft on a standard ISA day. Anything higher or warmer will reduce it as your achievable MP will drop, while lower and colder may be able to increase it because you can run a higher MP there.

 

Also mind the mixture setting of yours. You have to lean to get more power out and also see a rise in fuel flow. This may sound counter-intuitive at first. If you stick to the mixture levels from the takeoff and climb to 7000 feet, you will lose some more power just by running to much fuel in comparison to the volume of air.

 

Some 'smart' engines lean by themselves, but I guess yours has an extra lever for that one. And FSX needs a huge amount of leaning, perhaps too large in comparison to the rw engines.

And FSX needs a huge amount of leaning, perhaps too large in comparison to the rw engines.

 

An excellent point here, along with a lot of other good advice. FSX exaggerates how much leaning needs to be done, so you're going to find you'll have to pull the mixture back more than you would in reality. But even in the real world, you're going to be running fairly lean at these kinds of altitudes and the available power settings.

 

Power and heat are what your engine cares about in terms of stress and should be what you care about - you really, really (really, really!) need to stop worrying about the position of the throttle lever and pay attention to MP/RPM, and setting them according to the POH for your desired power. 75% power is 75% power (65 is 65 and so on) in terms of engine stress. Watch your leaning technique and cowl flap settings to help manage temps and you're good to go. The gauges are what you pay attention to - the physical throttle lever ends up where it ends up - and that's usually firewalled at altitude in a normally aspirated plane). "75% throttle" is meaningless.

 

Oh, and on the gear-up landing - sorry if this sounds preachy, but as you're in training, yes the sim is great but it can also teach you bad habits. A quick GUMPS check would've saved you here. If you're going to use the sim as a trainer don't allow yourself to develop bad habits and forget standard procedures. :-)

 

Scott

I liked the part with the gear up landing. Makes me forget about mine. ^_^

You have to lean to get more power out

 

True enough...

 

and also see a rise in fuel flow.

 

you mean decrease in fuel flow... ?

The full context was.

Also mind the mixture setting of yours. You have to lean to get more power out and also see a rise in fuel flow. This may sound counter-intuitive at first. If you stick to the mixture levels from the takeoff and climb to 7000 feet, you will lose some more power just by running to much fuel in comparison to the volume of air.

This is compared to the too rich mixture setting, assuming he took off and left the mixture lever alone all the way up e.g. 7000ft.

 

So, if he forgets about leaning, the actual mixture will become more and more rich as the plane ascends. The engine will develop less power, being further and further away from the max power mixture setting. This will decrease the actual fuel flow, adding to the power loss of the sheer altitude gain.

 

Back on my sentence. If he then grabs the mixture lever and leans until reaching the max power setting, the fuel flow will increase and, later, the true airspeed.

 

I may add that the sim's rendition of the fuel flow may be power based. So FSX may give you the max FF at the max HP developed, which happens at the fuel/air ratio for best power.

 

I've just checked a few of my planes and they all come up with that behaviour. As mentioned before, on the sheer amount of leaning being necessary in the sim, I wouldn't want to vouch for FSX when it comes to rw magnitudes.

Back on my sentence. If he then grabs the mixture lever and leans until reaching the max power setting, the fuel flow will increase and, later, the true airspeed.

 

Aha... you are referring to an FSX aircraft... (save the bump in airspeed).

you mean decrease in fuel flow... ?

 

No, increase.

 

As CoolP mentions, this can be counter-intuitive, but try it for yourself. Climb to a reasonable altitude (something over, say, 4,000') with the mixture full rich. As you climb, fuel flow will decrease and as the mixture becomes overly rich, flow will decrease below full efficiency, as the engine is simply choking on the too-rich mixture and won't take as much air or fuel. Now lean and watch fuel flow. The flow will actually increase until you're roughly in the correct range as the mixture results in more engine efficiency and increased intake of both air and fuel, and then decrease as you lean further.

 

Aha... you are referring to an FSX aircraft... (save the bump in airspeed).

 

Real world and sim.

 

Scott

The rw stuff has it's quirks too. For instance, the ways of how to measure fuel flow, especially on the smaller GA planes. This must not mean that something is attached to the lines and really is 'in the flow', like on the turbine based meters. You can also measure pressure (differences) and relate that to a flow for example.

 

Now that's actually an elegant way to do it, but may for example lead to false 'high' FF readings in the case of an clogged injector, actually meaning that less fuel enters the engine. So that may be the part which just stresses the need for some knowledge about the actual plane and systems in use.

 

And back on the sim. I'm happy that it sends the right signal. Lean for power at altitude. Well, if even it mixes up (nice pun, eh?) some magnitudes, I'm ok. The gain still is that it has rendered me aware about the need to lean. Not bad for a game.