Trim during landings - Cessna 172?

Question

Okay, as an 8 logged flight hour student pilot, I'd like to try to get some advice from more experienced people regarding landings. I dont want hear from FSX fly boys, just people who fly real planes. At any rate, when you're abeam the numbers on downwind, and reduce your power settings, add in 10 degree of flaps, is it acceptable to start adding trim in to compensate for back-pressure that you need to maintain during your base and final turn? It seems like i'm having a hard time maintaining a decent rate that I feel comfortable with...i get the feeling my decent rate is too fast, 300-500ft/min seems ideal, but can i trim to help keep this so i dont have to keep so much backpressure to achieve it? Also, any advice anyone can give about where to look when leveling off and deciding to flare would be helpful as well. Thanks!

Answer 1

Lets leave the instructing to the instructors.... Ok?  

You NEED to use the trim in a 172 otherwise you'll just be fighting the airplane and you will NEVER be able to fly a stabilized approach. With full fuel, Student & CFI up front the CG is far forward making it feel nose heavy resulting in more control pressure required on the elevator. This makes the landing flare difficult for most new students who ignore or are sometimes incorrectly taught not to use trim.  If you have difficulty pulling back during the landing flare, get your CFI to throw a case or two of oil in the baggage. This will add 25-50lbs aft and make the airplane feel not as nose-heavy.  Have your CFI do a weight and balance with you to see the CG shift.

The sceret to trimming correctly: Put the nose where you want it on the horizon, hold that pressure, trim until the pressure is gone. The most common error is releasing the pressure on the elevator as you reach down to trim. Dont do that. Remember to hold off on trimming until after you apply flaps. In a high-wing like a 172 you will get a nose-up pitching moment when you apply flaps. So when you reduce power on the downwind to start your descent you'll get a nose-down pitching moment, hold the back pressure to slow the airplane down. The back paressure you're holding will almost be cancelled out when you add the first 10dg of flaps because of the nose-up pitching moment. Then trim....

Your sinkrate has nothing to do with trim. You pitch for the desired airspeed, trim, POWER as needed to control SINK RATE. Then make SMALL pitch, power & trim adjustments to stay stabilized.

Answer 2

Some of these folks have some good information.  I'll try to relay what i think...

Trim is used to relieve pressure on the controls.  You should not fly the plane with the trim control.  Make the input on the controls then trim.  I would not trim, though, until you have the proper combination of airspeed, attitude, descent rate, power, set up for each leg of the landing.

As to where to look, I generally look a little left of center and keep an eye on the runway, etc., as the nose will be in a fairly high position.  I'd get your instructor to make a landing and talk you through it, so you can figure out what's best for you though.

At you stage of training, rely on your instructor for most of your advice.  Build good habits, fly safely, and enjoy...

Answer 3

Trim to control your airspeed, use your power to control your rate of decent. As you change power settings at various points in your approach you may re-trim to help control the airspeed. It all results in a stable approach. The Cessna 172 is fairly light on the controls so after your final re-trim for short final you should be able to fly with no further trim changes as you r****d the power and enter the flare. On your initial approach pick point at the approach end of the runway such as the runway numbers or general area, if the point that you are looking at appears to rise in the windscreen then you are going to be short of your desired touchdown zone, if it seems to lower in the windscreen then you are overshooting your touch down zone. Maintain your airspeed with trim adjust your flight path as needed with small power changes. With the runway and your touchdown zone made reduce power and adjust your point of vision out beyond your touchdown zone. the initial flare to level flight should happen about five foot off the ground as the aircraft slows while flying in ground effect you continuously apply back pressure holding the main wheels off the runway as long as you can slightly nose high. You should be hearing the stall warning horn slightly before touchdown. With some practice you will see that airspeed and power settings are the key to a stable approach and a good landing.

Answer 4

Pull the carb heat if carbureted, if not pull the throttle, trim to best glide speed. As soon as you speed drops to flap speed apply 1 notch of flaps. Retrim with every configuration change.

Sounds like a lot to do, but it will come naturally with practice.

In a 172 it is not necessary to carry power all the way around base to final. If you get in the habit of doing that and the engine quits at some point you will be landing in the grass somewhere short of the runway.

Answer 5

300-500ft/min seems good.

Don't get hooked on trim, I used to try to fly the whole plane using trim...Bad thing.

Use trim to relieve pressure, of course you know that.

Yes you can use trim to relieve pressure, that's the point of trim....

Each pilot is different when it comes to flying.

Here's my advice.

When flaring i don't use the trim unless im diving towards the runways, which hardly ever happens anymore because I know can fly a smooth approach.

When leveling off trim is the key, especially to keep things smooth. Apply SOME trim when leveling off, while keeping pressure on the yoke.

Good Luck.

And don't you have a VASI  at your airport? Its my best friend when trying to keep a good descent rate on final.

Here's a great link about glide slopes and how to Maintain a perfect approach.

http://images.google.com/imgres?imgurl=h...

Answer 6

you are reducing the power too early. wait for your 45 degrees from the threshold then

1. carb ht on (if you're in a fuel injected engine then disregard this obviously)

2. reduce power to 1500RPM

3. 3 full nose up trim

4. lookout

5. turn to base

6. white arc F10 (this step can be done anywhere cos you're just looking for the speed to get into the white arc but it's usually around here)

7. reset power to 1500RPM (it's dropped due to your decreasing speed)

By this step you should be nicely trimmed out with your horizon cutting halfway down the windscreen and a descent rate of around 500fpm. good luck. remember attitude + power = performance. hold your attitude of the horizon cutting halfway down the windscreen and maintain 1500RPM and your descent rate will be perfect.

Answer 7

I find as I turn base, just after lowering 10deg, I wind back 3 winds of the trim wheel and as the airspeed reduces to 70 IAS it will be about right. On short final, it is helpful to trim bach hard to you are holding some foward pressure, when you kill the power and and enter the flare, the control pressure decreases. I also find it is much more controllable to strart the flare about 1 wingspan above the runway. This is pretty high but dont rip it straight into the flare, do it nice and slowly, this will kill off some speed and give you a better view of the end of the runway (where you should be looking), you can control the sink a lot better this way and you wont float halfway down the runway. Of course, this method works well when you are at 65 knots but it will be too high to flare if approaching at 50-55 knots. This is just advice on what I do, I'm not massivly experienced, I have 200 hours in 172's and I only learnt to land properly at 100 hours. You should listen to what your instructor has to say before you try any of the methods people are describing on this site. Good luck to you.

Answer 8

Much good advice here but I'll add my .02 cents.

Trim is used to relieve constant control pressure (not transients) so yes, you can trim for the downwind, base and final but...

At ANY of those positions you must be carrying enough altitude and airspeed to make darned sure you can make the airport if you have an engine failure at any given point.

If your low and slow, dragging it in on long final would you be able to make the airport if the engine quit? Always plan on turning final at an altitude you KNOW you can reach the airport with should your engine quit. Trim out the control forces as necessary.

Good work on your 8 hours! Solo should be coming up pretty soon! >12 hours

Answer 9

I recommend trimming any time you are exerting a more or-less constant pressure. That means many times during landing. Even during the roundout/flare if you want, though that's getting a little crazy.

The only thing I would warn you about is that you do trim all through the landing, it is very important that you understand that the pull up force required during a go around will be much different, you may even have to push the nose *down* hard. Also, it's super-important that you neutralize the trim when you clean up the plane (after pulling off the runway and stopping) or you may require some very unusual and unexpected forces during the next take off.

Try it and see what you like, but keep those two warnings in mind.

Answer 10

Trim is added any time you need to reduce control pressure, it your putting in a lot of pressure to hold the descent, add some nose up trim, but not try to fly the airplane by trim.  In the landing situtation, its common to adjust the trim everytime you change flight condtions, adding/reducing power or flaps.

Also, the view of the runway is one of the hardest things to get, and the trick is not looking right where you landing, but rather down the runway. Its not distance your eyes are judging, but persepecitve. Deceding on the flare is based on wind, the stronger the wind, the less ground speed, the shallower the flare. A good starting point is aiming for the second stripe before the touchdown aiming point, and when over that, slowly start the flare, and depending on the wind, should touch down right on or about  the aiming point.