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Discussion in 'Pilot Training' started by einepilotin, Dec 23, 2017.
Does anybody have PITCH POWER setting table for C172?
Thanks in advance,!!
Full power for take-off and most climbs to a higher altitude. Maintain Vx or Vy for airspeed as needed.
When I did my instrument I tried to record them... the problem is in a 180 hp STOL it's all over the place depending on weather/temp/load and such... I gave up and just did what I needed to do to maintain a 500 or so foot descent. If that's what you're asking about....
Pitch/Power Table Cessna 172:
Takeoff: Pitch up/Power full
Cruise: Pitch level/Power full
Descent: Pitch down/Power full
Landing: Pitch up/Power idle (if headwind exceeds 5 kts, Power full)
To be technical, fixed pitch props change pitch and, hence, rpm, when you change deck angle. A 172 in a full power descent may well redline.
@einepilotin, I assume you are talking Instrument flight settings. Your best bet is to find them in flight yourself. Most of us fly a 172 about 90kts for approach level and instrument descents (but your CFII may have a different preference). You may already know the one for approach level - it may be the same one you use for downwind in the traffic pattern.
You really want to fly totally by paint by numbers?
I don't think having a setting in mind that is usually close is a bad trait. Set it to x RPM's and y flaps for each segment of the approach and then adjust as needed.
I've posted elsewhere my "setup grid." It's a good tool.
But your comment also has merit. Don't want to be sitting in the ambulance saying "my power and pitch were spot on."
Did anyone say "totally"? Even the most elaborate pitch/power table and I personally find many of them way to complicated) is just a bunch of ballpark targets.
It's always good to have a few known pitch/power combinations in your back pocket. I wish more jet guys would figure that out...when one degree of pitch change starts pushing 500 ft/min, the "chasers" struggle.
I have a power pitch table, I have vx, vy, vbg etc and I pitch till I get them (within logical reason) lol
It's a good idea to have a starting point. The numbers may not be exact but it gives you a starting point. A couple of things to keep in mind, for precision flying,
pitch+power=performance, you trim for airspeed and reduce control pressure.
About the only power setting I worry about is my initial setting when setting up for landing. I typically set 1800RPM and set airspeed for 75KIAS/80MIAS and pitch for 500fpm at key position or on a 3mile straight-in. From there, I manage pitch and power to hit my airspeed and decent rates.
If I'm flying an instrument approach, I'll shoot for 2100RPM, 90KIAS, and 450fpm decent. Again, adjust accordingly.
I guess I'm a moron. I can't use rpm to determine much of anything in a fixed pitch prop plane. You pull back the throttle, rpm drops, nose drops, rpm picks back up. wtf is the point.
For VFR, not a big deal (although my teaching preference is controlled descents at predetermined targets settings).
For IFR, well, I might agree with you (not the moron part; I don't know you well enough to comment ) except, well, I've seen (A) instrument-rated pilots flying 172s and Warriors under the hood hunting for their approach speed and the glideslope, getting a bit behind the airplane in the process. I've been able to compare them with (B) pilots who learned to trim for a level approach at 90 KTS with 2100 or 2200 RPM, reduce to 1800-1900 as they intercept the glideslope or FAF, and let go of the yoke as the pre-trimmed airplane does the rest. And yes, once starting down they do have to move the throttle a few millimeters or twist the vernier a bit as the descent stabilizes.
Typical response when I show the B method to someone in the A group? "Why the heck was I working so hard?"
Unless you're at high alitude or flying a rental, you don't typically leave the knob firewalled throughout the flight.
You don't use the throttle to control pitch...that's what the yoke is for. Change the power and then use the trim wheel to get the airplane to hold a given airspeed. While the 152 can pretty much be thrown around without worrying about the trim, the 172 is a lot better off if you work the trim wheel after each configuration change.
None of this is rocket science, it's all in the "book" (POH).
Of course in Denver, we just used WOT until we were abeam the numbers on downwind, and then we brought it back to 1700RPM.
When I got checked out at Sea Level after learning to fly in Colorado, I was flying around for about three or four minutes when the instructor asked if I intended to reduce power. I said "There's an interesting concept..."
One of the first things you train for in IFR is the power and pitch settings for climb, level flight, and descent. Get those down. Takes some practice. Hours.
Yep, best explanation is in Peter Dogan's book. He defines six regimes of flight where you set power/pitch/configurations (the command) and the expected performance for these.
This is what I made for my instrument training. Tables for a 172 SP
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Outside the pattern at SL, or in it?
I don’t see any limitation in the Skyhawk POH that would indicate any need to slow down from WOT in cruise. Didn’t buy/rent this silly airplane thing to go slow.
In the pattern at SL, sure... might as well fly the normal pattern speeds of all the other bugsmashers.
Was the instructor afraid you’d get to the practice area 20 seconds sooner? LOL.
Fixed-pitch prop pitches don't change. Their angle of attack changes with RPM and airspeed. Not the same thing as propeller blade pitch change.
If you define "pitch" exclusively as the angle of the prop relative to the longitudinal axis of the airplane, you are correct.
AH, FULL RENTAL POWER.
There are a number of reasons why you don't want WOT. At lower altitudes, you're probably not doing anything good for the engine to run it continually there. You certainly are using up a lot of fuel pulling that drag puppy through the air at a tiny increase in airspeed.
I'm curious about this and have no idea what the answer is. I do know the tips of the prop bend forward when producing power. In a fix pitched prop, does the amount of bend change only with RPM, or does the angle of attack also impact it?
Our 172n has an rpm limitation of 2500 under 5000’ so as I’m learning instruments, we use 2,400 as cruise rpm to avoid a bust, as it’s an actual “limitation”
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I certainly agree with the first sentence. I haven’t been able to find a single sentence from either the engine maker or Cessna that supports the second if the engine is operated inside published limits.
Speaking specifically about the venerable Skyhawk here, And stock engines, of course.
Many years ago someone challenged me to prove that oft-repeated pet idea. I dug for quite a while for manufacturer data, certification data, numbers from how TBO was determined, or even anecdotal data to hang that hat on. Couldn’t find anything quantifiable.
Desired airspeed, noise, fuel burn, etc etc etc all reasonable reasons to reduce power in cruise in a Skyhawk, but I couldn’t find anything limiting WOT ops because anything bad was happening to the engine.
Eventually I took off the hat. If limits (usually temperature) aren’t exceeded, there’s no “there”, there.
It’s been a while since I did all that digging but I couldn’t even find a limit on continuous power level in the POH, as I recall. I do remember that most of my search was limited to POHs and not AFMs since they weren’t as prevalent online at the time, and I didn’t have one handy.
Maybe there’s words in one of those that will support the assertion. Or a manufacturer’s SB. If you know of one, please share.
Maybe I can go find that old stickler for backing up teaching from publications, who liked killing these “words of wisdom” that turn into “truthiness” around the airport and stick my tongue out at him and tell him he owes me lunch. Ha.
Here's kind of what is happening in terms of comparing the two (decidedly non-technical and, BTW, @Dan Thomas is correct and I'm wrong - "technically" prop "pitch" is used to define the blade angle with respect to the airframe, not its AoA with respect to the relative wind).
With a fixed pitch prop, the angle between the blade and the airframe remains constant. It doesn't twist at the hub. But when the airplane's AoA changes along with its associated change in airspeed, we get a change in RPM as well. You can demonstrate this easily enough. Go to level cruise, set your rpm and do some normal climbs and descents without moving the throttle. You also see the same effect when maintaining level flight in up- and downdrafts, for the same reason.
We typically talk about constant speed props in terms of setting it to high rpm to give us addition thrust for takeoffs and climbs and then a cruise setting for efficiency and vibration dampening. But another effect is, unlike the fixed pitch prop with rpm varying with the airplane's airspeed, with the constant speed, we set rpm where we want, and the blades twist at the hub to maintain it despite those same aircraft AoA changes.
There's a pretty good description of the difference in some videos on the Hartzel website, http://hartzellprop.com/whats-the-difference-between-a-fixed-pitch-and-variable-pitch-propeller/
Cool. An actual limit. I can “do” actual limits. I can even agree that “bad things” might happen above the limit.
So it’ll actually turn above 2500 RPM when WOT below 5000’ in level flight? Or are you more concerned about busting the limit in a descent?
Obviously they’re such dogs up here as @flyingron mentioned, that there’s little chance of one over-revving on anything but the coldest days of the year.
To match up with Ron’s story, the RPM would have had to have been approaching or exceeding the limit for the instructor to ask to reduce power as it sped up in cruise, I assume.
THAT I can see happening if they’ll overspeed in stock configuration (no climb prop, etc) below 5000’ in level flight.
my eye hasn't happened to have ever noticed that maybe, depending on your viewing angle, that tachometer in some way, perhaps, might have been over 2,500 below 5,000 MSL.
it is also marked off on the tach for 2,500 = <5,000 ft, 2550 up to 10,000 and 2600 above 10,000
I've had it over 10,000, but it's tough in a o320 Skyhawk with 2,500 SMOH
For an older 172 (possibly L or M model), they tell you that max cruise is normally limited to 75% power. The TCDS for the O-320-E2D doesn't state that limitation. In fact, it says that maximum continuous power is 150 HP at 2700 RPM at sea level. http://www.airweb.faa.gov/Regulator...fa23b886257b63006ba6a4/$FILE/E-274_Rev_22.pdf
It will just make lots of noise and burn lots of fuel at that seting at low levels. I've done it as recommended by Lycoming as part of their break-in procedure.
Now, look at that chart: You aren't going to get even 75% power at full throttle much above 7500 feet. The first RPM given at each altitude will be a full-throttle setting if the installed propeller is the one specified for the airplane. Manufacturers of fixed-pitch airplanes typically have the propellers made and pitched to give redline RPM at full throttle in level flight at sea level, and that principle tends to hold true until you get above 5000 feet. I've seen redline at 6000'.
All that is based on an accurate tachometer. They start underreading as they age (years, not hours) and I regularly find them 60 RPM low or worse. In Canada we have to test them annually and they must be within 4%, which is around 100 RPM at 2500.
I just check them in the sodium vapor lights after dark.
It depends of what pitch attitude you are talking about.
You can find more information here: http://www.studyflight.com/climbing/
Pitch controls airspeed. Pitch attitude will be higher for Vx than for Vy. Don't need to worry about pitch angles.
Of course Dan, but he wasn't clear about it in his first message.
Dan got it. In simple planes like the 172, we adjust the pitch angle for the target airspeed for that phase of flight, and we usually don't care about the actual angle. Most of us here understand the difference between Vx and Vy, and those that don't should look it up if they wish to fly a plane. Most of us also know there is a point where Vx = Vy for most of the planes we fly, but we heretofore left that out of the discussion for simplicity. Determination of that point is left as an exercise for the student. I looked at the link you placed in your other message, and it does correctly show the difference between Vx and Vy.
Even flying IFR, I would trim the plane for 90 knots since that speed matches one of the options on the approach plates (not going to go into further details about plates). Once a plane is trimmed to maintain a certain airspeed, it will tend to maintain that speed no matter how the power is set. To descend, just reduce power; the plane descends at 90 knots. Below the glide path? Just add power. Reduce power if above. I didn't know (nor care) what pitch angles made 90 knots.
For planes like the C172, it is much better to monitor and control airspeed through the various phases of flight and let pitch take care of itself, and that seems to be what CFIs hammered into me when learning.
Even large airplanes benefit from this basic bit of airmanship. Better monitoring and control of airspeed may have prevented this: https://www.ntsb.gov/news/events/Pages/2014_Asiana_BMG-Abstract.aspx