Takeoff Trim Setting - New to me 1970 M20F

[ProtoFly]

New to me 1970 M20F.  I've been flying with a CFI for meeting insurance minimums.  (note:  insurance first year is heavy, as I have no complex time, but about 400 hours and instrument rated).

Anyway, what I'm noticing is that when the flaps and trim are set at the 'takeoff' suggestions, the back of the plan wants to lift off, and ride the nose.  This doesn't seem 'right' to me.  When I lift off, I have to use a LOT of pull on the yoke to keep the nose up, and find that immediately trimming nose up really helps.  

Is this typical?  Seems odd to me, and I'm thinking the plane is out of rig.  Once trimmed up, and flaps up, it flies fantastic.  My CFI doesn't have a whole lot of hours in type, so he's not much help.  Is it possible the trim is out of whack, and need to be 'centered' properly?  When landing, I'm full up trim by touch-down.

I figured I'd ask the hive to see what direction I should go.  I either put the trim where I don't have to crank back on the yoke, or I figure out why it's doing this....

Overall, I'm quickly falling in love with the plane.  I picked this particular model (M20F) for its efficiency and useful load, and value for $ - in other words, it fits my mission, and short of spending A LOT more money, I'm not going to get anywhere faster or higher. 

-Darryl

[AndreiC]

I was told that many people set their trim indicator so its *bottom* edge (it is a white square in my plane, probably in yours as well) lines up with the *top* of the trim position marked on the window. You could try that to get a more nose-up trim position. But YMMV; I tried this in my plane and did not like it, so I reverted to getting the trim indicator properly aligned with the mark on the side.

[Hank]

13 minutes ago, AndreiC said:

I was told that many people set their trim indicator so its *bottom* edge (it is a white square in my plane, probably in yours as well) lines up with the *top* of the trim position marked on the window. You could try that to get a more nose-up trim position. But YMMV; I tried this in my plane and did not like it, so I reverted to getting the trim indicator properly aligned with the mark on the side.

That's what I do for most takeoffs, along with Flaps Up. But when loaded up near gross, then it's Takeoff Flaps and align the marks.

Check your CG with full fuel, no baggage and two adult males up front, you'll see why we put in a little Nose Up trim!

But absolutely use the trim wheel. That's what it's for, so the plane will fly hands off.

[AndreiC]

See page 6 of this thread (which started on an unrelated topic, but drifted).

 

[PT20J]

There are springs in the Mooney elevator system so it takes about a 5 lb pull to rotate for takeoff. When the trim is set to the proper position for takeoff, the springs should hold the elevator aligned with the stabilizer. If at this setting the trim indicator is not in the takeoff position then the indicator needs adjustment. 

[MikeOH]

For well under gross weight take-off (i.e. most of the time with just me, or me and my wife) it's take-off flaps and take-off trim set with the indicator up about half-way out of the 'box' marks.  I, too, have a 1970 M20F.

[47U]

59 minutes ago, ProtoFly said:

Is it possible the trim is out of whack, and need to be 'centered' properly?  When landing, I'm full up trim by touch-down.

With you and the instructor and no other (significant) weight in the back seats or baggage compartment, the CG will be forward.

When the trim is run full up and full down to the stops, how do the respective markings line up then?  

I’m almost always solo in my C and set the trim indicator about one bar-width above the takeoff mark.  When I have the back seats filled, it’s aligned with the takeoff mark.  

When solo, I also land with close to full nose-up trim.

[Barneyw]

Hi Protofly

When I picked up my aircraft back in March this year and despite having lots of hours including complex aircraft I wasn't foolish enough to jump in and have a go so arranged a dual check with an experienced Mooney Instructor. 

I have to say I was quite surprised by the amount of back pressure that was required to flare the aircraft to the point I felt I was running out of elevator authority. My third and last landing with the instructor was satisfactory and he got out and told me to go and practice. I flew home and again the landing was OK but I had to haul back on the elevator to make it so. Some of this was due to lack of appreciation of the amount of back trim required for landing with full flap.

A couple of things to note and I'm happy to be correct on this.

1. The Mooney's CG is quite forward.

2. The coupling between main gear and the nose wheel is quite short.

3. I set my trim about 1/8 inch above the take-off position - in fact there was already a mark on the scale - and that seems to work well.

4. I fly with up to 20 litres (about 5 US Gals 44lbs) of water ballast in the back - for solo I will fill it with 10 litres (22lbs) and 2 up 20 litres and that works well and balances the aircraft nicely. I use a heavy duty white chemical container marked and weighed and can be filled or emptied as required.

If you are doing touch and gos, and given that the trim is set quite aft for landing, you will be fighting a large pitch up force getting airborne making it interesting especially if you have manual gear. To combat this I have decided to develop a procedure which is basically "flaps up" then "flaps down" pump twice for take off flap, elevator trim two handfuls forward before setting power again. This works well for a less challenging wrestle with the machine after getting airborne. This will get easier when I get my aircraft back from the shop with an electric trim fitted. This has implication for IFR approaches in particular missed approaches where a lower flap setting is preferred through the FAF to avoid the gross pitch up forces.

Anyhow I hope that has been useful but would be interested to hear other peoples experiences.

Cheers

Barney

[Rusty Pilot]

Certainly, consider the weight of pilot and front seat passenger which may impact cg and require a slight trim adjustment.  Sounds like you may have a little forward cg, but I am by no means an expert.

[N201MKTurbo]

The take off indicator is just a reference mark. your experience will tell you where it needs to be for you. 

As far as rigging is concerned, as long as the trim indicator screw isn't limiting the trim travel , you cannot get off by very much. The physical limits of the tail travel and the limits of travel of the indicator, are very close to each other. 

As far as landing is concerned, I have been flying a mid body for a little over 40 years. I figured out on the second day of ownership that is easier to land with full up trim. I have been doing it that way ever since. 

As far as go arounds, missed approaches and T&Gs, I just advance the throttle until the back pressure gets to be a lot, then retrim and finish increasing the throttle. After a while it gets to be muscle memory. The amount of power to get a reasonable amount of back pressure is plenty to arrest the descent and start to climb.

[Shadrach]

I have lots of M20F time, the only time it’s ever wheel borrowed is when I have tried to delay lift off by “holding” the nose down to build more speed.  The trim indicator is simply a cable attached to a jack screw on one end and to an indicator lever on the other. After 54 years of maintenance, there's a reasonable chance that it’s out of adjustment.  Mid bodies tend to be forward CG when empty which is part of the reason that they can be loaded to gross with almost no worry of getting out of CG. Proper take off trim is important.  At a minimum, try running it to the stops in each direction and check the indication at max up and max down. 

[AJ88V]

My 1970C was set the same way, although I usually had 'pulled' the plane off the ground before the wheelbarrowing you describe happened.  Even with the plane at max gross and near rear CG needed a healthy tug if set to the indicator.

As others have said, you can either set the indicator off the mark, or you can adjust the indicator to read someplace more to your liking.  Unscrew the plastic cover and the little white plastic block just slides on the cable. Not that I would ever suggest you reset it.

[Shadrach]

2 hours ago, AJ88V said:

My 1970C was set the same way, although I usually had 'pulled' the plane off the ground before the wheelbarrowing you describe happened.  Even with the plane at max gross and near rear CG needed a healthy tug if set to the indicator.

As others have said, you can either set the indicator off the mark, or you can adjust the indicator to read someplace more to your liking.  Unscrew the plastic cover and the little white plastic block just slides on the cable. Not that I would ever suggest you reset it.

A third option would be to ensure that the indicator and flap position match factory specs.  

[N201MKTurbo]

The most likely way the indication gets messed up, is if you disconnect the trim drive shaft. It is easy to get them out of sync. If they get out of sync, you will notice the tail will hit its limit of movement before the indicator screw hits its stops. The indicator should be the trim motion limiter.  If you get it synced so the tail doesn't hit its limits, you will be pretty close to the factory settings

 

[Fly Boomer]

6 minutes ago, N201MKTurbo said:

The indicator should be the trim motion limiter.

Seems counterintuitive that the relatively massive tail, driven by a relatively powerful motor system would be limited in it's travel by a relatively flimsy indicator.

[Shadrach]

18 minutes ago, Fly Boomer said:

Seems counterintuitive that the relatively massive tail, driven by a relatively powerful motor system would be limited in it's travel by a relatively flimsy indicator.

It’s limited by the jackscrew that drives the indicator not the indicator itself.

[ProtoFly]

2 minutes ago, AJ88V said:

My 1970C was set the same way, although I usually had 'pulled' the plane off the ground before the wheelbarrowing you describe happened.  Even with the plane at max gross and near rear CG needed a healthy tug if set to the indicator.

As others have said, you can either set the indicator off the mark, or you can adjust the indicator to read someplace more to your liking.  Unscrew the plastic cover and the little white plastic block just slides on the cable. Not that I would ever suggest you reset it.

When I first 'felt' the wheelbarrowing, I started pulling back.  Wheelbarrowing isn't good no matter when it happens, IMHO.  So, from there, I started adjusting trim to lessen the tendency, and ended up with what seemed 'comfortable' - still requires pulling back, but not so much that it feels like 'too much'.  Just that the trim indicator was a bit above 'Take off'.

[MikeOH]

Just now, ProtoFly said:

 Just that the trim indicator was a bit above 'Take off'.

That sounds just about right to me

[AJ88V]

57 minutes ago, Shadrach said:

A third option would be to ensure that the indicator and flap position match factory specs.  

Splendid suggestion.  I've always wondered what it should be according to spec.  And 88V goes into annual next month, so this time I'll finally check it.

I've also wondered if Mooney intentionally selected a nose heavy trim setting so that you didn't have such a dramatic out-of-trim situation when retracting flaps on climb-out?

[N201MKTurbo]

2 minutes ago, AJ88V said:

Splendid suggestion.  I've always wondered what it should be according to spec.  And 88V goes into annual next month, so this time I'll finally check it.

I've also wondered if Mooney intentionally selected a nose heavy trim setting so that you didn't have such a dramatic out-of-trim situation when retracting flaps on climb-out?

I usually take off with no flaps. All these issues go away. You will use slightly more runway but the takeoff forces are much lighter. If you have the trim set right it will fly off hands free. I reserve takeoff flaps for short fields.

[MikeOH]

2 minutes ago, N201MKTurbo said:

I usually take off with no flaps. All these issues go away. You will use slightly more runway but the takeoff forces are much lighter. If you have the trim set right it will fly off hands free. I reserve takeoff flaps for short fields.

My technique is to always use take-off flaps as I like to standardize my procedures whenever possible.  For me, this whole trim force thing has just never been an issue so there is nothing to gain by making some takeoffs without flaps.

[Shadrach]

On 8/21/2024 at 2:02 PM, AJ88V said:

Splendid suggestion.  I've always wondered what it should be according to spec.  And 88V goes into annual next month, so this time I'll finally check it.

I've also wondered if Mooney intentionally selected a nose heavy trim setting so that you didn't have such a dramatic out-of-trim situation when retracting flaps on climb-out?

The "out of trim" scenario is real but is more perception than reality, just like when people describe a brief "sink" when retracting flaps (which is all perception).  When you retract the flaps, you change the chord line of the wing  As the trailing edge retracts, the wing seeks roughly the same AOA. Because the the effective angle of incidence is reduced as the flaps come up, the same AOA equates to a higher pitch of the longitudinal axis (fuselage). There is likely a marginal increase in drag from the increased angle of the fuselage to the relative wind, but the perception that some have that raising flaps shifts the airfoil significantly towards a stall is a misunderstanding, unless the aircraft is already on the ragged edge.  

[AJ88V]

Point well taken, Ross.  Perhaps 'out-of-trim' was sloppy language on my part.  I do know that I have to firmly hold the yoke forward to maintain pitch, then rapidly roll in trim to take off the pressure and let the plane accelerate for cruise climb.  But what you wrote is technically correct.  - Cheers, AJ

[PT20J]

1 hour ago, N201MKTurbo said:

The most likely way the indication gets messed up, is if you disconnect the trim drive shaft. It is easy to get them out of sync. If they get out of sync, you will notice the tail will hit its limit of movement before the indicator screw hits its stops. The indicator should be the trim motion limiter.  If you get it synced so the tail doesn't hit its limits, you will be pretty close to the factory settings

 

BTW, this can happen when installing a GFC 500 trim servo if the installer is not familiar with how the trim system works.

[Shadrach]

2 minutes ago, AJ88V said:

Point well taken, Ross.  Perhaps 'out-of-trim' was sloppy language on my part.  I do know that I have to firmly hold the yoke forward to maintain pitch, then rapidly roll in trim to take off the pressure and let the plane accelerate for cruise climb.  But what you wrote is technically correct.  - Cheers, AJ

Some time at a safe altitude with take off flaps deployed and the airplane trimmed for hands off climb at Vy, try raising flaps without trying to making pitch adjustments.  It is not so dramatic as it is while managing an accelerating aircraft in the airport environment.

I have done more than a few full flap, touch and goes and even the pitch change during the transition from full flaps to no flaps is quite manageable though the procedure is not something I'd recommend.  It's a fair amount of work coordinating pitch, initial trim, gear retraction, flap retraction and retrim at low speed.