“Normal” planes have a trim tab on the elevator. This is driven from a jackscrew which is rotated by means of a cable which runs forward to the cockpit and is wrapped around the trim wheel.
If there is an electric trim, there is an electric motor which can also move this cable along. Usually, however, electric trim is delivered with an autopilot which includes pitch trim; see below.
It is this wheel which a Cirrus does not have, so clearly they have a purely electrical (motor) means of doing the trim.
I didn’t realise there is no trim tab on an SR22. That is really surprising. “Something” must be handling a big aerodynamic force during flight.
Now, speaking of autopilots, if you have an autopilot which has a pitch trim, the autopilot has a pitch trim servo which also has the above mentioned cable wrapped around its capstan. So either the pitch trim servo, or the trim wheel, can rotate the jackscrew.
BUT then we have e.g. this thread which talks about a pitch trim. It is clear that somebody (probably most owners) doesn’t know what is actually installed in an SR22 and how it is driven. You can find other threads with a search like e.g.
SR22 AND TRIM
but this is slightly digressing from the trim wheel topic.
Many of the Rotax powered trainers are designed that way, without a trim tab, e.g. the Aquila. The elevator is actuated by a pushrod with two springs attached. The springs are connected to a center piece which is moved back and forth by an electric motor. There is no way to move it manually by a wheel.
And „normal“ planes move the whole empennage like Mooneys do ;-)
JasonC wrote:
How many people on here have lost electric trim in flight? While I like having one, I doubt its absence is a serious problem.
Did happen to me. Can’t tell whether it was an issue or not as I used the manual trim to sort myself. However, once I forgot to trim out before take off and started the run with trim being at the “nose up” position, it wasn’t fun.
Peter wrote:
I didn’t realise there is no trim tab on an SR22. That is really surprising. “Something” must be handling a big aerodynamic force during flight.
Is that the case? There are aircraft which require a lot of control pressure if not correctly trimmed, and those that dont. Isnt it a good idea to fly a new to you aircraft way out of trim to get a sense of the potential loads? It seems to me the loads on the control stick in a Cirrus are not that substantial should needs must. In some aircraft it seems to me loads can be almsot unmanageable. Personally in the DA42 I found flying the aircraft on one engine produced very high loads on the leg if these are not trimmed out, to the extent that I would have thought anyone a little weak of leg would struggle to do so for any length of time.
Is there actually something handling a big aerodynamic load?
From SR20 G1 POH:
Electric Trim/Autopilot Failure
Any failure or malfunction of the electric trim or autopilot can be overridden
by use of the control yoke If runaway trim is the problem, de-energize
the circuit by pulling the circuit breaker (PITCH TRIM, ROLL
TRIM, or AUTOPILOT) and land as soon as conditions permit.
1. Airplane Control ………………………………….. MAINTAIN MANUALLY
2. Autopilot (if engaged) ……………………………………………..Disengage
If Problem Is Not Corrected:
3. Circuit Breakers………………………………………… PULL AS Required
• PITCH TRIM
• ROLL TRIM
• AUTOPILOT
4. Power Lever ………………………………………………….. AS REQUIRED
5. Control Yoke…………………………… MANUALLY HOLD PRESSURE
6. Land as soon as practical.
And „normal“ planes move the whole empennage like Mooneys do ;-)
Yes 
and I think the Mooney solution is equivalent to the THS (trimmable horizontal stabiliser) on an airliner.
I know the PA38 Tomahawk also didn’t have a trim tab and had springs instead and the trim wheel just changed the spring preload. It is a horrible mechanism which only barely works. I have 20hrs in the PA38…
Is there actually something handling a big aerodynamic load?
AFAICT there is no way to implement (other than a THS) a trim-tab-less solution without “something” applying a lot of force during flight, continuously. Whether the pilot feels it is what a “trim” is about.
So far, nobody has said what mechanism the Cirrus actually uses, and I suspect it is not common knowledge among owners. We had another long thread on the autopilot implementation there where it was claimed that the autopilot pitch axis merely drives the pitch trim and there is no separate pitch servo as such. That would work although with a sub-optimal transient response because the jackscrew effectively integrates the pitch signal, so the AP computer has to differentiate it first, to compensate for the integration, and that is prone to various issues (like wearing out the servo). But there might be no jackscrew – because there is no trim tab. OTOH the elevator needs to be driven somehow…
How many people on here have lost electric trim in flight? While I like having one, I doubt its absence is a serious problem.
We once had a trim runaway in the Aquila. It uses the spring-loading system and has no manual trim. The pilot returned to land safely and found it only uncomfortable.
Since that event, everyone flying our Aquilae has to fly a pattern with a plane trimmed fully forward or backward with an instructor to be prepared for this. Hasn’t happened since, the trim switch was found to be faulty.
Because the spring-load-system leaves you with the full evelator authority (unlike as with a moving stabiliser) I found it is only unpleasant, but not scaring.
Bear in mind the Aquila has a MTOW of 750kg, therefore the overall control forces are probably lighter than in other aircraft.
I have no Cirrus experience, it might be different there.
One Aquila is in a check right now, and the trim system is one of the items. I could take some pictures of the assy, if the forum is interested.
Peter wrote:
So far, nobody has said what mechanism the Cirrus actually uses, and I suspect it is not common knowledge among owners.
I’m pretty sure anyone who flies a Cirrus knows how it works!
The mechanism is really simple – there’s a spring which always wants to centre the control yoke. The other end of the spring cartridge is attached to the trim actuator. So basically all it does is move the ‘centre’ point of the spring.
>>es and I think the Mooney solution is equivalent to the THS (trimmable horizontal stabiliser) on an airliner.
Correct even though only half the story. The whole empenage moves including the vertical stabilizer.
Consequently the manual trim wheel is very welcome in such a case.
The VS movement is surely just an unavoidable side effect.
