AtlantaFalcons
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aviator23
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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?
If your throttle slips at full tight, you need a new throttle cable.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.
Might also be the throttle's friction packing (assuming a 172 also that kind of set up). That was the issue with a Comanche I used to fly.If your throttle slips at full tight, you need a new throttle cable.
If your throttle slips at full tight, you need a new throttle cable.
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.
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.
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.
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.
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.
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.
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.