M20C elevator position in cruise

[carusoam]

Elevator trim range is designed around the plane’s WnB envelope...  both Cg (gravity) and Cl (lift) will require variations in trim.  Speed and weight also have some considerations...

1) moving toward the back of the balance envelope will lessen the trim required.

2) flying faster will lessen the trim required.

3) keeping the flaps up will lessen the trim required.

 

4) it seems that the plane design is always very forward in its balance envelope.  So it has a low risk of falling out the back of the envelope accidently.  Falling out the back will be bad...

5) I have never run out of forward trim...

6) with regards to weight... when the plane is heavy, it uses a higher AOA to maintain level flight. The higher AOA uses trim to hold it... when the plane is light... it uses less AOA, and less trim in level flight...

7) descent will also add to the trim being forward for max forward speed...

 

So... to see the minimum elevator trim used in level flight... fly fast, light, and with a rear most balance, trimmed down for the ASI to be at Vne....  (smooth air only, within the WnB limitations, do not exceed anything...)

PP thoughts on trim, not a mechanic or CFI.

Best regards,

-a-

[PT20J]

Certainly the tail down force is a function of weight, CG and TAS, and if you didn't adjust the trim, the elevator position would vary with these parameters also. However, when you trim, you're changing the angle of incidence of the stabilizer. If there were no trim assist bungees, the stabilizer angle would trim the airplane and the elevator would trail in its neutral position. However, the trim assist bungees on the J and previous models bias the elevator to move along with the stabilizer to reduce the amount of stabilizer travel required to effect the full trim range (that's likely why Mooney called them trim assist bungees). This spring pressure causes the elevator to be slightly out of trail when trimmed at cruise speed. 

 

[65eTurbo]

So, I did some experiments with this and my autopilot in my E.  I was solo, not sure fuel status or CG.  Since the elevator is controlled by the autopilot (century 2000) and the tail trim is the jackscrew that moves the tail, I engaged altitude hold and then adjusted the trim such that the elevator was aligned in trail.  Once stabilized, this was good for a couple of knots.  Problem was that disengaging the autopilot, IIRC, resulting in a sudden zoom climb due to out of trim condition.  I suppose it is better than a sudden zoom dive, but I decided it was a practice best reserved for air races and the like.

[PT20J]

21 minutes ago, 65eTurbo said:

So, I did some experiments with this and my autopilot in my E.  I was solo, not sure fuel status or CG.  Since the elevator is controlled by the autopilot (century 2000) and the tail trim is the jackscrew that moves the tail, I engaged altitude hold and then adjusted the trim such that the elevator was aligned in trail.  Once stabilized, this was good for a couple of knots.  Problem was that disengaging the autopilot, IIRC, resulting in a sudden zoom climb due to out of trim condition.  I suppose it is better than a sudden zoom dive, but I decided it was a practice best reserved for air races and the like.

Great test. I can’t do that in my J because the KAP 150 has autotrim and I can’t fly it precisely enough when it’s that far out of trim to note any airspeed change. 

It’s kind of interesting that the bungees align the elevator at the takeoff trim setting rather than cruise. As @carusoam noted, we never run out of nose up trim. 

[kmyfm20s]

On 2/1/2019 at 2:21 PM, Yetti said:

Has anyone experienced getting the nose down like you are riding a wave or getting it on a plane like a boat.

 

Yep! Pretty impresive KIAS and KTAS for a NA plane at 15K

[65eTurbo]

3 hours ago, PT20J said:

Great test. I can’t do that in my J because the KAP 150 has autotrim and I can’t fly it precisely enough when it’s that far out of trim to note any airspeed change. 

It’s kind of interesting that the bungees align the elevator at the takeoff trim setting rather than cruise. As @carusoam noted, we never run out of nose up trim. 

Funny thing about our trim.  If you pull the power in an E and then slowly roll the trim to the up stop, and use the rudder to keep the ball centered, you'll stay just above stall clean.  A CFI taught me this as a last ditch way to deal with an engine failure with no vis (night, low IFR, etc.).  If you hit at that speed with a shoulder harness, you'll likely survive... that's the theory anyway.

[carusoam]

10 hours ago, 65eTurbo said:

Funny thing about our trim.  If you pull the power in an E and then slowly roll the trim to the up stop, and use the rudder to keep the ball centered, you'll stay just above stall clean.  A CFI taught me this as a last ditch way to deal with an engine failure with no vis (night, low IFR, etc.).  If you hit at that speed with a shoulder harness, you'll likely survive... that's the theory anyway.

Want a Mooney example...?

A particular M20C... Driven by a particular MS pilot... we can call him Dan... was trimmed early in the climb...

As Dan lost consciousness, the wing leveler kept the cleanside up. The trim maintained the forward speed,  ...and altitude as long as fuel was flowing.... things get dicey as the fuel runs out, the plane descends at the climb speed... the plane has no way to find an open field...

 

To Find Dan’s Story... search on CO monitor.

 

if conscious... get slowed before hitting anything... do not stall...

A good GU landing has an amazingly short roll out...

+1 for good seatbelts...

 

PP thoughts and stuff I learned reading MS...

Best regards,

-a-

[Marauder]

Want a Mooney example...?
A particular M20C... Driven by a particular MS pilot... we can call him Dan... was trimmed early in the climb...
As Dan lost consciousness, the wing leveler kept the cleanside up. The trim maintained the forward speed,  ...and altitude as long as fuel was flowing.... things get dicey as the fuel runs out, the plane descends at the climb speed... the plane has no way to find an open field...
 
To Find Dan’s Story... search on CO monitor.
 
if conscious... get slowed before hitting anything... do not stall...
A good GU landing has an amazingly short roll out...
+1 for good seatbelts...
 
PP thoughts and stuff I learned reading MS...
Best regards,
-a-

Do you know if Dan’s plane had ADS-B? I think that would have made for an interesting ADS-B track profile.




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[carusoam]

I believe there is a Flight Following trail provided by FlightAware to go with that...

Requesting if @DanM20C can help point us in that direction..? 

Best regards,

-a-

[65eTurbo]

Love the wing  leveler concept for that reason.

[DanM20C]

3 hours ago, carusoam said:

I believe there is a Flight Following trail provided by FlightAware to go with that...

Requesting if @DanM20C can help point us in that direction..? 

Best regards,

-a-

Here is the end of the track log from Flightaware.  I was trimmed for about 120mph climb.  Winds Aloft were light and variable that night.  With full power and full mixture 12.5K was as high as it would go in that configuration.  Elevation at the crash site was about 1250msl, so the last radar return I was just over 1000ft agl.  It interesting that my vertical speed slowed so much in the last 2 returns, thank god for that.

Cheers,

Dan