Throttle adjustments

Your CFI is wrong. Your hand should be on the throttle at all times in the pattern except for flaps, gear (if applicable) and trim. There is no reason to have two hands on the yoke in the pattern.
 
My throttle on the 182 and on the 172 I trained in has a ring on it that controls how hard it is to push in and out. I have always kept my as tight as possible because that is where I like it. Others like it loose, so check that. As for keeping your hand on the throttle, that is how I was trained. I always have my right hand on the throttle, unless it is doing something else, such as changing frequencies, changing mixture, using the G1000, etc. In the pattern I change my throttle at downwind abeam the numbers, and then on flare as I land. Depending on the wind, and other thing I may make minor adjustments, but I am not good enough to have a completely stabilized approach without some tweaking of the throttle on final so my hand is still there.
 
As the aircraft slows down, the reduced forward motion of the airplane will increase the angle of attack of the propeller blades and increase the drag, thus the RPM will decrease. That's why you can only get about 2200RPM at full throttle on the ground at a standstill.

As for cruise flight, you'll see variations in RPM due to turbulence as well as the aircraft's natural tendency to oscillate up and down (and thus faster and slower).
 
I was taught to fly with my hand on the throttle all the time. Especially while on takeoff, pattern and landing. Could just be the normal changes that happen when you pull power back? If your expected RPM is 1700, try pulling back to 1800 and see if it settles in around 1700 for you. Whats your CFI have to say about it?

edit. btw, 1500 is a pretty good setting for the 172. :)
 
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In the pattern, throttle in your hand. Close enough to the runway that if you lose the engine you can make the runway, none of this 3 mile pattern BS. Fly the plane like it is yours with no insurance.. :yes: :rofl:
 
AtlantaFalcons said:
I'm flying C172P's for training, and the throttles seem to have a tendency to slip to higher/lower RPMs (gradually) throughout the flight. Not dangerous or anything, just something that seems to require adjustment during the usual "scans". I tighten the throttle friction as tight as it'll go but it still creeps.

So I've developed a habit of flying with my hand on the throttle all the time. Not a big deal in cruise, when I am keeping straight and level and a constant RPM and only need to adjust infrequently.

The bigger issue is in my pattern work, when I am finding myself constantly tweaking the power after I start the descent. My CFI thinks I should "peg" it at a certain RPM level and concentrate on the altitude/airspeed, but I'm looking at the tach and it goes from 1700 (preferred descent setting) to 1500 or less on its own and I don't feel like I can trust it without manually keeping my hand on it at all times.

That results in very uneven descents and (usually) coming in high/low turning base, and having to make major altitude/speed adjustments on the base leg prior to turning final. Anyone else fly planes with creeping throttles and tips for it?
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There is no need to "tighten as much as you can". The friction lock just needs to barely be snug, if it slips at snug, it will slip at full crank tight. That's probably what happened, someone over tightened and then pushed the throttle.

As others have said, keep your hand on a loose throttle. Pitch for airspeed control, adjust power for descent, small adjustments as needed. A 200 rpm change from 1700 to 1500 should not make a large difference.

Steady glide airspeed control is a key. Go fly a glider, no throttle, just drag device to adjust. Pitch controls airspeed, drag (throttle) controls rate of descent to the threshold.
 
My hand is always on the throttle in the pattern except if I'm using it to trim or actuate flaps or carb heat.

I can't imagine anyone would suggest that no throttle adjustments are needed once the descent starts. Very rarely is it the case that I don't need to adjust the throttle from abeam the numbers to the runway made point.

The one exception is when the CFI pulls your throttle to idle abeam the numbers for an engine out simulation. That's fun in a 172 with 40 degrees of flap available:D
 
My first CFI used to chant:

"Two Bits, Four Bits, Keep your hand on the throttle.
For Every second off, you owe me a dollar"

And there was one longer TnG lesson where I earned him an additional $15 to his gratuity for f
 
It is particularly important to keep a hand on the throttle whenever there is a CFI in the right seat. They have a nasty habit of pulling unattended throttles when least expected. :D
 
BillTIZ said:
There is no need to "tighten as much as you can". The friction lock just needs to barely be snug, if it slips at snug, it will slip at full crank tight.
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If your throttle slips at full tight, you need a new throttle cable.
 
Tom-D said:
If your throttle slips at full tight, you need a new throttle cable.
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:yeahthat:



A lot of these old planes flying around have junk throttles that should have been reoplaced 15 years ago, but this is obviously not right.
 
Your instructor's idea of pegging the RPM at a given value and leaving it alone makes no sense to me because the throttle is a flight control just like the elevator, ailerons, and rudder. Ask to see documentation that supports his policy.

Bob Gardner
 
bnt83 said:
:yeahthat:
A lot of these old planes flying around have junk throttles that should have been reoplaced 15 years ago, but this is obviously not right.
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I may need the throttle cable in my 172 replaced. Any idea what I should expect my A&P to quote me? He generally charges about $75/hr (I always get 10% off for some reason) and I have never found him to gouge me. He often goes to my hangar to check out minor things and doesn't even charge.
 
JOhnH said:
I may need the throttle cable in my 172 replaced. Any idea what I should expect my A&P to quote me? He generally charges about $75/hr (I always get 10% off for some reason) and I have never found him to gouge me. He often goes to my hangar to check out minor things and doesn't even charge.
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~ 2 hours labor + parts...

McFarlane probably sells PMA'ed cable for you serial # which can run anywhere from $350 a pop and up. The Cessna 177 cable is around $480..
 
Z06_Mir said:
Your CFI is wrong. Your hand should be on the throttle at all times in the pattern except for flaps, gear (if applicable) and trim. There is no reason to have two hands on the yoke in the pattern.
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My CFI is teaching me the above as well, and certainly on short final. We can have deer or other critters on the runway (especially in the evening), and my hand is ALWAYS on the throttle in case I need to power up and do a go-round at any time...
 
AtlantaFalcons said:
The bigger issue is in my pattern work, when I am finding myself constantly tweaking the power after I start the descent. My CFI thinks I should "peg" it at a certain RPM level and concentrate on the altitude/airspeed, but I'm looking at the tach and it goes from 1700 (preferred descent setting) to 1500 or less on its own and I don't feel like I can trust it without manually keeping my hand on it at all times.
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These numbers look kinda suspicious....

Are you sure the throttle is creeping? The tach is not a throttle position sensor. With fixed pitch, it will drop on its own with airspeed, at constant throttle.

In particular, in a 172, 1700 at 80 knots and 1500 at 60 knots are the same throttle position. You expect to set the throttle to 1700 to begin the descent at 80 KIAS and have it drop to 1500 by short final.

With a CS prop, the RPM won't change at all with throttle position (until you run out of travel for prop pitch).

While throttle adjustments during descent are both normal and advisible, it's important not to overcontrol the throttle. And if you're behind the power curve, it may require a lot more throttle (and a simultaneous pitch adjustment!) than if you're in the normal control regime.
 
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MAKG1 said:
These numbers look kinda suspicious....

Are you sure the throttle is creeping? The tach is not a throttle position sensor. With fixed pitch, it will drop on its own with airspeed, at constant throttle.

In particular, in a 172, 1700 at 80 knots and 1500 at 60 knots are the same throttle position. You expect to set the throttle to 1700 to begin the descent at 80 KIAS and have it drop to 1500 by short final.

With a CS prop, the RPM won't change at all with throttle position (until you run out of travel for prop pitch).

While throttle adjustments during descent are both normal and advisible, it's important not to overcontrol the throttle. And if you're behind the power curve, it may require a lot more throttle (and a simultaneous pitch adjustment!) than if you're in the normal control regime.
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Now that you mention it, this sounds like whats going on.

Fixed Pitch prop - At any given throttle setting, RPM will increase if airspeed increases or vice versa.
 
Not just fixed pitch, just not goverened. I flew for years with a controllable non-constant speed prop. When you leveled out after a climb you just knew to dial the prop back a little bit. My wife never knew different having never flown a CS prop until we converted ours.
 
Another thing that can cause throttle creep is a loose cable housing clamp at the engine end. Might be worth checking before spending a bunch of money is spent on new parts that aren't necessary.

Dan
 
FWIW, this does not sound like the throttle is slipping This simply sounds like the result of the world not being perfect and several factors can cause RPM changes. If you're dumping flaps, changing your airspeed, etc right after you set the throttle the RPM is indeed going to be different than what it was right before you changed your speed.

Your CFI is probably trying to get you to not obsess over the RPM, not change power every second, and instead just look out the airplane and land it. You should listen to him. There is no reason to be looking at the tach again after you make your initial power reduction to start your descent from pattern altitude. You make your power changes based on what you see outside the window. The RPM itself has no significance.
 
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This is good advice, I think. I don't look at that tach after the initial pullback abeam the numbers. Try not to get so caught up in the details that you forget the overarching goal: make the airplane do what you need it to do.

FWIW: I was too timid and too detailed when I first started out. I was letting the plane fly me instead of vice versa.

jesse said:
FWIW, this does not sound like the throttle is slipping This simply sounds like the result of the world not being perfect and several factors can cause RPM changes. If you're dumping flaps, changing your airspeed, etc right after you set the throttle the RPM is indeed going to be different than what it was right before you changed your speed.

Your CFI is probably trying to get you to not obsess over the RPM, not change power every second, and instead just look out the airplane and land it. You should listen to him. There is no reason to be looking at the tach again after you make your initial power reduction to start your descent from pattern altitude. You make your power changes based on what you see outside the window. The RPM itself has no significance.
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Whatever the cause of these rpm changes, the bottom line is that if you have the vertical speed (and direction) and airspeed you want, it doesn't matter... unless it's an extreme change (which would indicate a mechanical problem).

Flying fixed pitch, the only times I (briefly) look at the tach are on the takeoff roll and abeam the numbers... or if I hear a dramatic change (like silence, lol). Last few times I've flown power in the pattern, I was in the back seat of some tandem airplane, so I really couldn' t even see the tach. It's not a big deal. The result is what matters, just like jjockeying spoilers in a glider to control descent rate and glide angle. There are no "book" settings for spoiler operation, and for 172s and such, the recommended tach numbers are guidelines-not carved in stone. If the airplane's doing what you want it to, and the prop is turning, but below redline, forget the tach.

But definitely "guard" that throttle in the pattern, when landing or departing.
 
Well, if you get behind the power curve, you'll need big changes in throttle to get out of it. Not that unlikely to drag it in like that for a student.

You use what throttle you need, and don't fixiate on the instruments. Airspeed is important, but everything else can be seen out the window. Even airspeed can come from pitch, but that's best left for post-solo.
 
jesse said:

Your CFI is probably trying to get you to not obsess over the RPM, not change power every second, and instead just look out the airplane and land it. You should listen to him. There is no reason to be looking at the tach again after you make your initial power reduction to start your descent from pattern altitude. You make your power changes based on what you see outside the window. The RPM itself has no significance.
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And what you hear.

You can hear the tone of the engine and get pretty close to any particular gross RPM setting.

I could probably nail 1700 within. +-50 without looking.
 
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