No manual trim - do you care?

With more than 250 planes out there, I was wondering how people felt about the lack of manual trim? We had one Lancair that has/had a bug somewhere in the trim system - and people starting talking about the lack of manual trim. I’m not sure what to think of the issue and I thought the Cirrus Body might have some perspective.

Dean

The electric trim is not precise enough to trim for hands off operation. The best you can do is periodically change which direction you have to hold pressure on the yoke. When we picked up the plane the instructor said the best way to set the trim was turn on the autopilot for a minute or so until it settles down and then the trim will be set. If my autopilot worked I wouldn’t care about the trim in the first place.

In reply to:


With more than 250 planes out there, I was wondering how people felt about the lack of manual trim? We had one Lancair that has/had a bug somewhere in the trim system - and people starting talking about the lack of manual trim. I’m not sure what to think of the issue and I thought the Cirrus Body might have some perspective.


Hi Dean,

To me there are two reasons for potentially wanting manual trim.

One reason is that the current electric trim system is pretty sensitive, especially in pitch. It’s sometimes hard to get the plane trimmed exactly as you want it, without resorting to letting the A/P trim the plane (as Art mentioned above). So for this reason, I believe a manual trim system could be poentially useful, though not necessary. If it adds complexity, I would definitely say it’s not worth it.

The other reason (which is I believe the issue raised on the Lancair board) is safety. If there’s an A/P problem or runaway trim, does it pose a safety-of-flight concern. I have never flown the Cirrus with full trim in any direction. However, I admit a couple of times forgetting to shut the A/P off and trying to “fight” it. (Usually I would turn the Alt Hold off, and forget that I didn’t shut the heading/track off also). In those cases, it was absolutely no issue whatsoever in overpowering the A/P and trim system. (Again, it didn’t run the trim to the stops so maybe in that condition it might be an issue.) So it would seem that from a safety issue, manual trim would not be required.

Just my $0.02.

Steve

Hi Dean, nice to see you again.

On various points:
– Actually, almost 350 planes out there now;
– Agree with Art P (who wudda thunk?) about the trim being hard to set precisely. Requires some tuning, and it IS easiest to set pitch trim by putting the A/P on Alt Hold for a minute or two;
– Completely disagree with Art P (yet again) about the need to hold pressure constantly. I find that after I get it trimmed up I can fly for very long periods with light pressure. (I base this on 280+ hours in a Cirrus).
– Agree with Steve Lin that it is no physical problem to override the trim. When I’ve forgotten that the A/P is still engaged, I find myself working harder, but there’s never a doubt about who’s going to prevail, ie my arm or the autopilot.

So, I’d like a trim system that was slightly easier to make fine adjustments in, but from what I’ve seen there’s no real safety concern about runaway trim.

Like the others I would like a manual trim because the current system is VERY sensitive. I taught my wife how to land (if anything should happen to me I thought landing was preferable to parachuting) and the thing she found most difficult about flying the Cirrus was getting it trimmed correctly. The problem I think is that the “trim” system is really not trim at all. Other than the soon to be discontinued rudder system on the 22 all the trim does is set the spring mechanism on the stick to regulate where the stick want’s to sit without pressure. It can be overpowered in an emergency.
To put a manual trim tab system in would add significantly to the complexity. Whether a manual system could be rigged to alter the spring tension I don’t know. I think the reason it’s so sensitive is that in order to be effective at low speeds it has to be very sensitive at high speeds.

Manual trim on small aircraft is a net positive in my opinion. It adds some failure modes to the aircraft that need to be balanced against some of the failure modes eliminated. Actual accidents in which the manual trim system were a contributing cause are extremely rare. Actual accidents in other aircraft designs have occurred as a result of their electric trim systems. Almost all that I am familiar with were the result of an errant AP combined with electric trim. The most meaningful examples I can think of off the top of my head are the MU-2 runaway trim situations with several separate fatal crashes and many more survivable ones, and the King KFC-200 runaway trim problem. The KFC-200 is thought to have caused a few fatal crashes also. The problem seems to have been solved by a circuit board redesign. Those who have faced runaway electric trim in IMC will usually comment that a major factor in their recognition of the problem was the visual reference to the large trim wheel, or the actual feel of the wheel turning as they reached to check it.Clark Jernigan

Yesterday–beautiful severe clear–I practiced slow flight in my SR-22. I was able to trim the airplane at 65 knots–horn on continuously–and do 360’s (in both directions) completely hands free (except for trimming in opposite bank at the turns).

I note placing my thumb on the side of the stair step portion of the hat allows for very small adjustments. Versus pushing against the side of the side edge of the hat.

I have no special flying skills and am at best an intermediate pilot.

sps

Absolute codswallop! I’m starting to wonder how many of your “squawks” are just user error, Art. The trim does require some initial practice, but it doesn’t take too long before trimming to fly hands-off becomes instinctive.

One additional comment. On the preflight check list (Wings Aloft version) you switch on the AP and overpower it. I have never had any problem either during this test or in flight even with full deflection.

I agree with Jim almost entirely, but feel that a two speed trim system would alleviate all of the complaints. If it were somehow speed sensitive or with a switch, then a slower setting would make it mush easier to precisely trim. I understand that this is not impossible and more a matter of cost

2!5 hours in the '22

Marty

Very interesting discussion from my perspective. 350 planes worth of experience as well! I’m going to try at some point tomorrow to summarize any experience here on the Lancair board. As you may or may not know, (and as you may or may not remember from days of Cirrus passed) with less than 50 Lancairs flying, position holders are dying for anything to talk about. We had one pilot experience with AP sending his trim to the stops - and we’ve been talking about it ever since!

Personally, I’d just like a way to neutralize the trim to zero/center with the touch of a button if the AP went nuts and the trim computer went with it. Though I’m not sure what would have to happen for all that to go wrong.

Thanks

Dean

In reply to:


I think the reason [the electric trim] is so sensitive is that in order to be effective at low speeds it has to be very sensitive at high speeds.


I was told by an old FAA salt that trim rate is predicated on performance at maneuvering speed. I nosed around FAR 23 and didn’t see anything to that effect (see below). I would be very interested to hear from anyone familiar with FAR 23 certification procedures or with the Cirrus certification about why the pitch trim rate on the Cirrus seems way too touchy, especially when levelling at cruise.

My Bonanza 36 has the opposite problem - trim rate too slow. Not too big a deal except for trimming after configuring the airplane for landing. I always have to resort to a couple twirls of the manual trim wheel on final.

Maybe this is a hint as to the speed choice in the Cirrus. Those of you who actually have the airplanes (as opposed to us mere position holders) - if the trim rate was slower would the transition to full flaps and final approach speed be awkward?

SFAR 23.11 Electric trim tabs.
The airplane must meet the requirements of FAR 23.677 and in addition it must be shown that the airplane is safely controllable and that a pilot can perform all the maneuvers and operations necessary to effect a safe landing following any probable electric trim tab runaway which might be reasonably expected in service allowing for appropriate time delay after pilot recognition of the runaway. This demonstration must be conducted at the critical airplane weights and center of gravity positions.

23.677 Trim systems.
(a) Proper precautions must be taken to prevent inadvertent, improper, or abrupt trim tab operation. There must be means near the trim control to indicate to the pilot the direction of trim control movement relative to airplane motion. In addition, there must be means to indicate to the pilot the position of the trim device with respect to both the range of adjustment and, in the case of lateral and directional trim, the neutral position. This means must be visible to the pilot and must be located and designed to prevent confusion. The pitch trim indicator must be clearly marked with a position or range within which it has been demonstrated that take-off is safe for all center of gravity positions and each flap position approved for takeoff.

(b) Trimming devices must be designed so that, when any one connecting or transmitting element in the primary flight control system fails, adequate control for safe flight and landing is available with -
(1) For single engine airplanes, the longitudinal trimming devices; or
(2) For multiengine airplanes, the longitudinal and directional trimming devices.

© Tab controls must be irreversible unless the tab is properly balanced and has no unsafe flutter characteristics. Irreversible tab systems must have adequate rigidity and reliability in the portion of the system from the tab to the attachment of the irreversible unit to the airplane structure.

(d) It must be demonstrated that the airplane is safely controllable and that the pilot can perform all maneuvers and operations necessary to effect a safe landing following any probable powered trim system runaway that reasonably might be expected in service, allowing for appropriate time delay after pilot recognition of the trim system runaway. The demonstration must be conducted at critical airplane weights and center of gravity positions.

Yesterday–beautiful severe clear–I practiced slow flight in my SR-22. I was able to trim the airplane at 65 knots–horn on continuously–and do 360’s (in both directions) completely hands free (except for trimming in opposite bank at the turns).

Try that straight and level at cruise speed.

I learned this “thumbnail technique” from Walt Conley and it was a definite improvement in trim control. In addition, after a few hours early on of difficulty controlling the plane by reference to instruments, I found I was inadvertently in addition activating the aileron trim when trying to adjust only pitch trim. Once I made sure that my pitch trim adjustments were aligned exactly along the proper “axis” and not at an angle, I had no problem. Knowing my ability to find the wrong way to do something when few others can, perhaps I’m the only one to have experienced this!

I’m somewhat relieved to hear others have difficulty (impossible ?) trimming Cirrus to hands off at cruise speeds, though I list electric trim as one of the many, many benefits of Cirrus aircraft. The speed shouldn’t be an issue, however. I didn’t have any problem trimming a T-38 for long periods of hands-off at Mach .95.

Art, for once we agree - it is indeed completely impossible to do 360’s while straight and level!!

I’m somewhat relieved to hear others have difficulty (impossible ?) trimming Cirrus to hands off at cruise speeds

Although some are claiming that trimming the plane is easy and those who can’t do it are not good pilots. I think it is another “emperorÂ’s new cloths”.

Doug, your experience with jets interests me because I’ve flown with other experienced pilots who can trim a Cirrus at cruise, including mine, when so often the best I can do leaves me wondering – and wandering. There seems to be something “experiential” or even “zen-like” about trimming my plane. Bill Graham’s comments about technique seem to comes closest to what works for me – the plane is so responsive to roll inputs that if I manhandle the trim it goes everywhere but where I want it to go, yet if I relax and encourage the trim with alternating left/right inputs then it doesn’t take me very long before I can let go and enjoy a stable ride. Unfortunately, I can’t pull that off all the time, yet, but the more I relax and become “one with the plane” then the easier time I have. Fight it and it fights back, relax and think it and it does the right thing. Weird, eh?

Cheers
Rick

I agree, Clyde. It just takes a little getting used to. Try giving it little bumps; make sure you are bumping orthogonally and in line with the side stick handle.

I agree. With some practice and being careful to use small inputs (the small bump method works for me) I have no trouble trimming my SR22. I would not use a manual trim if it were available. However, I wouldn’t mind a little less sensitivity on the trim control.

Two other trick that might help are:

  1. Pre takeoff, I find adjusting aileron trim by looking at both ailerons relative to the wing tips gets very close. From there I rarely need more than one small bump on the hat.
  2. For elevator trim, note the position of the trim indicator when you are trimmed properly for each of your main flight configurations. For example, I find that after every good landing (stable, full flaps, 80 knots) the elevator trim indicator is at about the same spot. So as the flaps are going to 100%, I can trim to that point on the indicator. From there the needed corrections are minor, and the big over corrections are eliminated. Similar for the usual cruise setting, there is a spot that gets me close and then I can make small adjustments. Take off is already marked.