Proper way to trim?

[clamman]

I seem to have a lot of trouble gatting aircraft to trim properly. Seems I go to much one way than too much the other way. Is the trim wheel supposed to be real sensitive or do I need to adjust it some how? Also if I notice I am starting to drop altitude should I be using trim to bring it back or should I pull back on the yoke than trim afterwards? Thanks for any advice>

[xxmikexx]

clamman,

The correct way to trim is to do it until you don't have to apply any control forces to fly straight and level. After that you would control rate of climb/descent trend with power. However ...

The required amount of trim required will change with airspeed. Another complicating factor is that if the autopilot is on it will control angle of attack by operating the elevator trim, effectively negating any manual trim elevator inputs you may have made.

For the benefit of those of you who fly props aircraft, the first thing you should do is to use rudder trim to remove any yaw tendency. (Check the ball in the turn/slip indicator.) Then you should trim the elevators. Finally, if there is any residual rolling moment you should counter it with aileron trim though you're not likely to encounter the need for this -- typically only if there were a fuel imbalance in wing tanks.

I hope this helps,

[tigisfat]

IT's a matter of choice whether you use trim or elevator pressure to correct smal errors during cruise.

Personally, once the aircraft is trimmed out, I use small amounts of elevator to counteract pithc moments in cruise. The reason is, you're likely to have to set the trim back to where it was in a short minute. Thermals and descending air greatly affect small aircraft with high wing-loading under 10,000 feet. While it may seem that the aircraft has gone out of trim; it hasn't. You merely need to get to the other side of the phenomena causing the small climb or descent.

Think of every trim setting having a specific speed and drag configuration that it's good for. If you're perfectly trimmed out for 90KIAS for an approach and you add power, you'll get an initial 2-3 knot increase in airspeed as the nose pitches up. The nose will go further than it needs to because of the extra knots. A true instrument pilot will know how far it needs to go up and 'guide' the aircraft's nose to the right place while letting your trim setting do most of the work. The added power but unchanged with trim will eventually have you climbing at 90KIAS. The same is true about descents.

In an aircraft that is both statically and dynamically stable longitudinally will always try to return to a flight attitude that makes your speed and trim agree. It may porpoise (very slowly, and only up and down 30-40 feet) a few times, but that's only if you fail to help it find the right attitude without overshooting. What causes porpoising and overshooting is extra and too little speed. If you're trimmed out for 90KIAS and you enter a thermal, you'll get high and slow. Because of the reduced lift and trim setting, the nose will drop. Going below your cruising altitude now, the aircraft picks up speed that is too fast for the trim setting and the nose rises. You now climb slightly past your desired cruising altitude. This will go on and on a few times, high and low, until the aircraft settles pretty close to where you initially set up your trim and at the right speed.

Set MSFS up with no winds and give it a shot. These concepts are most true in small, stable propeller-driven aircraft when in normal weather conditions. Once you see how it all works, you'll probably develop your own technique.

When in airliners, I rarely touch the elevators except for the flare. At those speeds and departure (from level flight) rates, I find trim is all I need to gently maintain altitude.

[xxmikexx]

tigisfat,

I agree with you completely about making small corrections with elevator. That's why I used the word "trends", which is where power changes come in.

[tigisfat]

Where it gets REAL fun is this:

aircraft with high wing loading and excess power have different rules. I fly a seminole pretty often, and I set power once for the whole approach. I know it well enough that 18" manifold pressure will yield me blueline at 88KIAS with a certain trim setting and 25 degrees flaps will add the correct descent at around 500FPM. All changes in airspeed and descent are made by pitch only. I had a conversation with a DC-10 pilot about such a technique, and he admitted that it was his secret to the perfect approach as well.

[bstolle]

clamman,

You have to take into account that when using the elevator (or stabilizer) trim there is a considerable lag.
You have to trim a bit, wait a few seconds and then trim further.
If you try to crank in the correct amount at once you are likely to trim too much, hence the impression that the trim is oversensitive.

E.g. in IRL I NEVER use the stab trim during the approach for small corrections but this implies that the plane has been perfectly trimmed initially.

When using elevator/stab trim I most of the time even let go of the yoke/stick for a second or so after trimming, to make sure that the plane is perfectly in trim.

tigisfat

Confirmed, as long as the speed is within plus or minus 5kts of my target speed I don't touch the thrustlevers or stabilizer trim (in the 767)

[clamman]

Thanks for the suggestions guys. I think my biggest mistake is making too big of an adjustments instead of small ones and waiting. Now if I could just land without crashing I'd be all set.:D

[lnuss]

Thanks for the suggestions guys. I think my biggest mistake is making too big of an adjustments instead of small ones and waiting. Now if I could just land without crashing I'd be all set.:D

A couple of common mistakes in landing are in flying the approach too fast and in trying to "land" the aircraft. Approach speeds in airliners will typically be in the 120 to 150 knot range, depending on the aircraft and its weight, and for light single engine aircraft approach speed is typically in the 70 to 90 knot range, again depending on the aircraft.

You don't actually land an aircraft. Instead, you want to descend to a foot or so off the ground and maintain that altitude by gradually increasing back pressure until (with power way reduced or at idle, depending on the aircraft) the aircraft settles to the ground of its own accord. And, if you are using autothrottle you must disengage it separately from the autopilot. It takes practice to perfect the landing, of course...

[xxmikexx]

lnuss,

I will add to your remarks that a spot landing typically must be a "wheels" landing, in which the aircraft is driven onto the runway at a planned spot at a low rate of descent.

I will also observe that wheels landings are easier to perform than classic full stall landings. So maybe clamman could start out with wheels landings and work his way up to doing it right.

[bstolle]

I disagree. In a tailwheel aircraft my spotlandings are always 3 pointers.
Only in conventional planes with a nosewheel I never do threepointers ;)
E.g. a few weeks ago I flew a tailwheel motorglider which MUST be landed in a threepoint attitude as the single mainwheel suspension too rigid for a wheel landing.
Furthermore in a threepoint attitude you are slower, also not bad for a spotlanding ;)

If you do a full stall landing the plane naturally stays on the ground, but you can screw up a wheel landing quite easily.

[tigisfat]

I gotta be honest Mike, I do three pointers when I do my power-off 180's to a specific spot in taildraggers. I plan on being in the flare for the last 100 feet or so, like any other landing. You are right though, it is harder. My thought process is this: If I'm doing a wheel landing, it means I've got a crosswind or a long runway. I have 1,900 feet for the Aeronca Champ I fly, and I don't trust wheel landings on grass anyway.

[xxmikexx]

tigisfat,

From my viewpoint three point landings are much easier to bring off in the real world than in the sim because of all the available cues that are absent in FS -- peripheral vision, control sloppiness, slipstream noise come to mind.

So I don't wear a hair shirt, I just drive the sucker on in a controlled way at a reasonable airspeed. Furthermore ...

The only full stall landings I have experienced in airliners mainly were in props -- Connies, Electras, etc. I have sat through many attempts at grease jobs in airliners. Some pilots can bring it off, some can't. I can't, at least not anymore.

[bstolle]

Mike, if I look at the geometry of an Electra etc... it's impossible to 'stall' this plane during landing.
I've never flown a connie etc.. but I doubt that someone intentionally lands any airliner in a stalled condition!

[xxmikexx]

bstolle,

I'll not insist that I'm right about full-stall landings in airliners. I should have said "grease job", though I would like to hear from skylab, who has Connie and DC-6 time.

Regarding full-stall landings in an Electra, you sure could have fooled me, but what aspect of the aircraft geometry are you referring to? The overwing exhausts? Because with power applied and flaps down this would create something of a blown flaps effect and would certainly delay the stall though I don't see how this could eliminate it.

I used to ride the old time Eastern Airlines Shuttle during the days when they operated Electras between Newark and Boston. I rode it so often, and I was so impressed with his skills, that I still remember the name of the captain -- Ed Stark -- who could consistently land the Electra at least semi-stalled if not fully stalled, resulting in consistent greasers.

I suppose the impressions of passengers riding back in the cabin regarding stalled/not may be misleading, but let's hear from skylab.

Now ... Did you bring back that chicken curry I requested? :D

[lnuss]

Mike,

A "grease job" doesn't result from a full stall (or semi-stall) landing. It results from having a very minimal rate of descent at touchdown. A stalled landing would result in a heavy thump if the stall was just above the surface, or a much harder landing if the aircraft were higher.

So in a "grease job," the aircraft is still flying, but (in a tri-gear) has a high enough pitch attitude to keep the nose wheel off the ground at touchdown, and the pilot has reduced the rate of descent JUST before touchdown to almost nil, settling the last few inches in the ground effect cushion. Usually (unless the pilot is lucky), this will chew up quite a bit more runway than a light "thumper" landing, and often (not always in light singles) requires that the pilot carry a touch of power all the way to touchdown. Granted, however, that once in a while a pilot will luck into a "grease job" from a more normal approach and landing.

Even the most skilled pilot in the most benign of aircraft, in TRYING for a "grease job," will occasionally thump it on, and for some pilots that "have we touched down yet" feeling is from a rare instance of luck.

I might add that the pitch attitude which, power off in flight, gives a stall in a light aircraft in level flight, isn't a stalled attitude when in ground effect.

[xxmikexx]

lnuss,

Let's ignore terminology, which I'll concede to you guys. Now ...

When you slide an Electra in from a foot above the runway it's a very gentle and extremely skilled landing whatever label you care to apply. Captain Stark's method was to float with the main wheels barely above the runway and then to reduce the residual thrust. I imagine that one could do the same with any propliner -- a smooth power reduction while floating above the runway. Skylab will tell us.

And yes, I'm aware of ground effect.

[skylab]

OK, Mike wants me to chime in here so.....

I don't think I've EVER landed an aircraft from my first hour of dual in a Piper Super Cruiser to my last landing in a DC-8-71 in a stalled condition. What's the point?! Sure, conditions permitting, you want to be slow so as not to use up too much runway if you're runway limited, but other than that, what are you trying to prove? That you're some kind of hot shot?

The only way you're gonna land at stall speed is to fall out of the sky the last inch or more otherwise how would you know if you were at stall speed? The book might say such and such will stall at XX kts at such and such weight, but it won't do it every time. You might even land below what stall speed is "supposed" to be, but that doesn't mean you landed in a stall. To land "in a stall", you have to drop out of the sky; not too smooth as far as I'm concerned, especially with passengers on board.

"Greasing" an aircraft on does not necessarily mean you've landed at or near stall speed. I've greased many of 'em on, prop and jet, as I'm sure others have, and we were not always near stall speed. I've also 'bounced' a few. It's easier to grease one on the faster you're going. Naturally, it's nice to have lots of runway available. I've also landed quite close (within 5 knots or so) to stall speed many a time but ONLY if runway length was a problem, or we wanted to avoid a long taxi. Usually did this in the Connie or DC-6 series. Maybe a time or two in a 737, but probably never got closer than 10 knots to stall speed in the DC-8. Reference speeds in the jets these days kinda preclude you landing too close to stall speed unless you use up a lot of runway or "duck under" the G/S.

The main thing to remember is.....the conservative approach is usually the safest approach. Especially with airline transports. Now in your "sport" planes, go ahead and do what you want as long as you are the only one that will suffer any consequences.

My "technique" (learned very early on in the Connies) was to close #1 & 4 throttles before the flare. That kept some power on until landing assured. Worked like a charm, even on the DC-8s. Kinda hard to do in FS though. That's another advantage of FOUR engines! Scares me now to think I flew single and twin-engine aircraft.

And, Mike, I've ridden on many Electras, and I agree with you; some of the best landings.....and they were slow most of the time. Not at stall, but pretty slow. But, it can be done in the Connie, DC-6, 737 and DC-8 as well. I've ridden on a couple of 747s where I couldn't even tell we were on the ground, the landing was so smooth. 90% is probably luck and conditions.

Next.....

[xxmikexx]

sky,

It is possible in FS to retard thrust on 1 and 4. Here's how ...

Very rapidly type E 1 4. This will select 1 and 4, and then any thrust/throttle changes you make will affect only the selected engines. To get back to normal simply type E 1 2 3 4 rapidly.

But you raise an interesting point. If I can just get back to flying I'll try killing #2 in my 727. (Did angels355 recommend that last winter?)

[skylab]

sky,

It is possible in FS to retard thrust on 1 and 4. Here's how ...

Very rapidly type E 1 4. This will select 1 and 4, and then any thrust/throttle changes you make will affect only the selected engines. To get back to normal simply type E 1 2 3 4 rapidly.

But you raise an interesting point. If I can just get back to flying I'll try killing #2 in my 727. (Did angels355 recommend that last winter?)

Ya.....I know about that, but it's just a little too awkward. Then gotta go back and re-do it. I just close 'em all in the sim.....no problem.

I've seen guys do that in the RW 727 tho (close #2). Don't like that airplane.....but you know that!!

[bstolle]

Concerning geometry.

In the Electra a tailstrike occurs at roughly 12deg pitch attitude.
The outboard wingsection is a NACA 0012 (inboard 0014) which stalls at around 16deg AoA.
Hence my impression that you can't land this plane in a 'stalled' condition.

Concerning thrust reduction.

You do the same e.g. in the 767.
If you are at Vref +5 or slightly faster, most pilots make a small (let's say 5" thrustlever movement) thrust reduction at 50ft (on both engines ;) )

[xxmikexx]

So okay -- you crash-land it in a stalled condition. :D

[bstolle]

Good idea. If you know that you will crash you want to minimize the energy on impact.....

[xxmikexx]

I have an idea ...

Let's require that they all be full-stolle landings. :) That should cover a wide variety of circumstances.

[skylab]

There was a man who entered a local paper's pun contest. He sent in
ten different puns, in the hope that at least one of the puns would
win. Unfortunately, no pun in ten did.

[NikeHerk67]

Caution: A humor blog!

One of my CFI's once said jokingly:

"There are three simple rules for making a smooth landing: Unfortunately, no commercial pilot knows what they are."

No offense here, but one time when landing at KPIT, as we touched down the aircraft leaned over so far to one side one of the wings almost touched the ground. If you ever wanted to see some pail looking passengers that was the time to look around. :)

A veteran commuter sitting next to me said in all the landings he'd ever experienced, that was the worst. As I looked at it, as long as we walked off the airplane, it was a great landing. :)

OK, having said that, I must confess.
The very first landing that I made all by myself I hit the RW, bounced off into the grass, and then bounded back on the RW. After coming to a stop Chuck B, my CFI with nerves of steel, just looked at me and said with a smile, "When they tell you to sides-step the RW that isn't what they'll mean."

[xxmikexx]

You win, sky. :)