Trim wheel very hard to turn

[N201MKTurbo]

Tails have down lift in flight. If the tail departed it would go down first.

[N201MKTurbo]

3 hours ago, cnoe said:

Here's a question for those of you with aerodynamics expertise. And if anybody else wants to chime in your comments will be noted.

Does anybody know "how much" downward force is applied to the horizontal stabilizer during level flight at cruise? And do you believe that said force is "less, equal, or more" than the weight of the tail assembly itself?

My observation has been that when trimming the tail on the ground using the electric trim it seems to struggle just a bit when trimming up because it is effectively "lifting" the weight of the tail. But when trimming down the weight of the tail "assists" the motor.

So the reason for my question is this...

I can't "hear" the trim motor in cruise and I'm wondering if it is still struggling when trimming up, or whether the aerodynamic forces on the tail might lessen the load on the motor.

Any thoughts on this?

You can tell how much the motor is struggling by turning the wheel by hand and feeling how much effort it takes.

[cnoe]

1 hour ago, Yetti said:

It's a wing, it's flying so would not lift, drag and weight be in play.  If the tail cleanly separated from the plane in flight  I would think it would go up first before down.

My understanding is that the horiz stab is providing a downward force in level flight.

[cnoe]

16 minutes ago, N201MKTurbo said:

Tails have down lift in flight. If the tail departed it would go down first.

A pleasant thought indeed!

It always amazes me how few 1/4-28 bolts there are between joyous flight and certain doom.

[cnoe]

17 minutes ago, N201MKTurbo said:

You can tell how much the motor is struggling by turning the wheel by hand and feeling how much effort it takes.

Yeah, I wish I'd said that.  It makes sense.

Off the top of my head I'd say it takes less force on the trim wheel in flight to trim "up" than it does on the ground. So I'll assume that forces on the tail aren't that great (in level flight).

[Yetti]

4 holding the engine mount on

[Shadrach]

4 hours ago, cnoe said:

My understanding is that the horiz stab is providing a downward force in level flight.

It does! Think of a seesaw - the center of lift is the fulcrum and the weight of the engine and the down force of the tail as balancing each other.  The amount of down force will vary with weight and CG.  In terms of pounds, I would bet it's a range between 150lbs-350lbs but that's a guess.

If the CG were so far aft that the tail was producing positive lift, you would have an unstable airplane.

In such a case, at high AOAs if the tail would stall first increasing the AOA of the wing insuring a deep nose up stall. Conversely, in a steep dive the increase in speed would cause a flying tail to produce more lift steepening the dive.

That is why the positive lift tail is rare in aircraft.  With a conventional inverted lift tail plane, the aircraft will naturally return to stable flight. A stall causes the nose to drop and a dive causes the nose to pitch up.

Edited January 15, 2016 by Shadrach

[Hank]

It's more of a three-legged seesaw. The engine weight pulls down at front. The fulcrum is the CG. The center of lift pulls upwards, which pushes the nose down. So the tail has to pull down in order to support the nose.

[Shadrach]

2 hours ago, Hank said:

It's more of a three-legged seesaw. The engine weight pulls down at front. The fulcrum is the CG. The center of lift pulls upwards, which pushes the nose down. So the tail has to pull down in order to support the nose.

Pretty sure the center of lift is always the fulcrum. The CG just determines how much and what type of force is required from the tail.  I think if you give it a second thought you'll revise your thinking.

Edited January 15, 2016 by Shadrach

[Hank]

No. Basic statics. All forces act on the body around the CG. Lift is a force upwards at the center of lift, weight is a force downwards at the center of gravity.

So I will revise and take weight of the engine out. Lift pulls up, weight pulls down, the tail pulls down (upside down airfoil generating negative lift). When all balance, you are in level flight. That's how you can climb or descend by moving the tail up or down. In power on descents, push the yoke forward (less tail downforce) and start down; as airspeed increases, lift increases and descent rate is reduced unless you give more down yoke or trim. Reducing tail downforce results in a descent; increasing tail downforce results in a climb.

This is simplified in PPL training by eliminating the negative tail lift, and using a single Lift arrow pointing up and a single Weight arrow pointing down. But vectors are additive, so the Lift arrow is really Lift = Wing Lift - Tail Downforce. Sorry, for a minute there I operated outside of my engineering mind. 

I may need to draw a picture, it's very obvious that way.

[N201MKTurbo]

The faster you go the more down force on the tail which makes the nose point up, slowing you down. That way you get dynamic stability. The center of lift of the wing is slightly ahead of the CG so the faster you go the more it lifts the nose which also makes the plane stable. 

[Shadrach]

49 minutes ago, Hank said:

No. Basic statics. All forces act on the body around the CG. Lift is a force upwards at the center of lift, weight is a force downwards at the center of gravity.

So I will revise and take weight of the engine out. Lift pulls up, weight pulls down, the tail pulls down (upside down airfoil generating negative lift). When all balance, you are in level flight. That's how you can climb or descend by moving the tail up or down. In power on descents, push the yoke forward (less tail downforce) and start down; as airspeed increases, lift increases and descent rate is reduced unless you give more down yoke or trim. Reducing tail downforce results in a descent; increasing tail downforce results in a climb.

This is simplified in PPL training by eliminating the negative tail lift, and using a single Lift arrow pointing up and a single Weight arrow pointing down. But vectors are additive, so the Lift arrow is really Lift = Wing Lift - Tail Downforce. Sorry, for a minute there I operated outside of my engineering mind. 

I may need to draw a picture, it's very obvious that way.

Please do... Just saying "basic statics" does not provide much explanation for what you've said. To be clear, the only thing I'm disagreeing with you on is the fulcrum being the center of lift and not the center of gravity. 

So you're suggesting that when the aircraft is on jacks with the tail weighted to raise the nose that the fulcrum is not the jack points but the CG?

In your drawing please use a forward CG (as in front of the CL) and demonstrate how the aircraft pitches about the CG (your fulcrum) with both up (wing) and down (tail) force behind the so called fulcrum.

Edited January 15, 2016 by Shadrach

[Hank]

If the plane is on jacks, there is no lift from the center of lift on the wing, instead there are two upward forces from each jack below the wings, and a downward force from the tail tie down. (Or an upward force from the engine hoist). Both act around the CG of the plane.

I'll break out my pencil, paper and scanner tomorrow.

[Shadrach]

11 minutes ago, Hank said:

If the plane is on jacks, there is no lift from the center of lift on the wing, instead there are two upward forces from each jack below the wings, and a downward force from the tail tie down. (Or an upward force from the engine hoist). Both act around the CG of the plane.

I'll break out my pencil, paper and scanner tomorrow.

Your saying the plane pivots around the CG and not the jacks? Clearly the jacks are the fulcrum and clearly the CG is in front of the fulcrum. Is the fuselage not a lever with the jacks acting as fulcrum?

 

[Shadrach]

 

"In the diagram above, the fulcrum of an aircraft in flight is the centre of lift. Generally the CG is forward of the Centre of Lift, causing the aircraft to naturally want to "nose down". The elevator located at the aft end of the aircraft provides the counter-balancing force to provide a level attitude in normal flight. Normally, the pilot will "trim" the elevators, by use of the trim tab control in the cockpit, to cause the elevators to provide the correct elevator balance force to relieve the pilot from constant elevator control."

http://www.pilotfriend.com/training/flight_training/aero/principa.htm

We need to get to work correcting all of the misinformation out there. Everyone from NASA to the FAA and many flight schools have published data stating that the fulcrum of an aircraft in flight is the CL and not the CG as you have stated.

 

Edited January 15, 2016 by Shadrach

[carusoam]

Additional observations:

0) Has anybody heard from Leesh, the OP?  It's been a while...

1)  In the POH, Mooney uses a term called MAC in the WnB section.  The C's POH has it.  The R's POH has it and probably two sentences to describe it... (Insert what it means here?)  Cg is in front of Cl. During an ordinary stall, the main wing begins to stall first, lowering the nose to return to controlled flight.

2) The scale of the force on the tail plane, as a couple of people have pointed out, is measured in pounds.  Roughly, how much weight does it take to hold the tail down when jacking the plane up?  The Jack points are not exactly at the Cl and the bucket of used hardware and cement is usually in abundance of what is needed.

This is also visually represented by most SE Cessnas on the ramp after a heavy snowfall.  6" of snow and they all point skywards.

3) The canards, like the Long EZ, don't waste energy using a tail to provide negative lift for dynamic stability.  The canard wing provides lift like the main wing, working together.  During a stall, the canard is designed to stall first dropping the nose.

The Long Bodies use the canard theory when jacking up the plane.  There is a third Jack point on the pilot side of the engine mount on the bottom.

4) Why this is important to know:

Getting the WnB correct are both important.  The W part (in some cases) can be off by a couple hundred pounds.  The B part is measured with inches.

Getting weight, lift, center of lift and center of gravity is pretty easy in the hangar...

Knowing what changes the WnB, Lift and Cl in flight is important.  Fuel usage for some planes.  This time of year... Ice. Thrust and drag are also effected when ice builds on surfaces of the prop and everywhere else.

5) Engineers: Use the science of Statics to describe the balance, simplified down to the model of a teeter-totter.   The science called dynamics describes how fast control is lost after the WnB gets outside the envelope.

6) Other things that are dynamic: Lift is a function of speed and AOA. Wings are designed so the stall occurs in stages, in less important areas first.

7) what makes it challenging: Statics in aviation can only be achieved when the plane is in motion.  No motion=no lift.  

8) what makes this work with small fasteners holding the whole thing together: Maneuvering speed.  The speed that can be used so the fail safe mechanism works.  A stall occurs before the forces can build up strong enough to break things...

9) when a stall sounds like a good idea, that's a dynamic situation!

Good morning,

-a-

[Yetti]

The horizontal stabilizer on a mooney pretty symmetrical so does it provide lift? Or just keep all the other forces in balance, or is it neutral until needed to change direction. I think I remember the CG point is 29" aft of the nose gear.     If the CG was perfectly above the center of the lift produced by the wing, would the elevator be neutral with no down weight or lift?  Would it change with level flight vs other flight.

I don't think jacking the plane has anything to do with in flight.  More of a function of where there was a piece of angle alum. to support jacks.

My business degree fails me, but I am going say the downforce or lift on the horz stab depends on the loading of the plane which is why we have a trim wheel and the tail can move.

 

Edited January 15, 2016 by Yetti

[mpg]

36 minutes ago, Yetti said:

The horizontal stabilizer on a mooney pretty symmetrical so does it provide lift? Or just keep all the other forces in balance, or is it neutral until needed to change direction. I think I remember the CG point is 29" aft of the nose gear.     If the CG was perfectly above the center of the lift produced by the wing, would the elevator be neutral with no down weight or lift?  Would it change with level flight vs other flight.

I don't think jacking the plane has anything to do with in flight.  More of a function of where there was a piece of angle alum. to support jacks.

My business degree fails me, but I am going say the downforce or lift on the horz stab depends on the loading of the plane which is why we have a trim wheel and the tail can move.

lots a folks have writ lots of dumb stuff about what they think makes a mooney not fall from the shy,,  but

most of what they wrote is junk.     I try really hard to ignore the stupid err, dumb err, a unknowledgeable posters ravings.

I agree with your simple straight forward thoughtful and Correct explanation!!  

36 minutes ago, Yetti said:

 

 

[Shadrach]

1 hour ago, Yetti said:

The horizontal stabilizer on a mooney pretty symmetrical so does it provide lift? Or just keep all the other forces in balance, or is it neutral until needed to change direction. I think I remember the CG point is 29" aft of the nose gear.     If the CG was perfectly above the center of the lift produced by the wing, would the elevator be neutral with no down weight or lift?  Would it change with level flight vs other flight.

I don't think jacking the plane has anything to do with in flight.  More of a function of where there was a piece of angle alum. to support jacks.

My business degree fails me, but I am going say the downforce or lift on the horz stab depends on the loading of the plane which is why we have a trim wheel and the tail can move.

 

Don't get hung up on the shape of the airfoil. For the purpose of this discussion "flying" is due mainly to AOA (AOA is what makes a wing fly, Bernoulli makes it more efficient). 

If CG and CF were the same the H stab would be neutral. This is why TAS goes up slightly with aft CG.  As CG goes aft, less AOA is needed for the H Stab to keep the plane level. Less H Stab AOA means less induced drag. Less induced drag means more speed!

 

[Yetti]

Not sure about "induced drag"  But there is always drag created by the horz stab by it's mere presence on the back of the plane.  The tail feathers depending on their up or down position could create lift.  The tail trim could create a neutral balance.

Spent lots of time racing Sunfish learning not to move the rudder to go faster.  But you could steer the boat based on shifting your weight. 

  People get excited about engine monitors.   A $10.00 strain gauge on the tail hinge and some electronics to the cockpit would make for some serious fun.  Moving around the stuff in the baggage compartment telling people to lean forward then retrimming to get a couple extra knots.   Maybe having some water ballast with some pumps to move it around.

[Johnnybgoode]

On January 14, 2016 at 7:37 AM, INA201 said:

Anyone have a recommendation for a mechanic that would be familiar with our Mooney trim systems near upstate SC? Mine is pretty stiff and I would like it gone through. I've heard mention of a guy at KEHO or KMRN but can't remember.  Thanks in advance.

Lynn at KMRN.

[mike_elliott]

11 hours ago, Hank said:

No. Basic statics. All forces act on the body around the CG. Lift is a force upwards at the center of lift, weight is a force downwards at the center of gravity.

So I will revise and take weight of the engine out. Lift pulls up, weight pulls down, the tail pulls down (upside down airfoil generating negative lift). When all balance, you are in level flight. That's how you can climb or descend by moving the tail up or down. In power on descents, push the yoke forward (less tail downforce) and start down; as airspeed increases, lift increases and descent rate is reduced unlessu give more down yoke or trim. Reducing tail downforce results in a descent; increasing tail downforce results in a climb.

This is simplified in PPL training by eliminating the negative tail lift, and using a single Lift arrow pointing up and a single Weight arrow pointing down. But vectors are additive, so the Lift arrow is really Lift = Wing Lift - Tail Downforce. Sorry, for a minute there I operated outside of my engineering mind. 

I may need to draw a picture, it's very obvious that way.

Give a Moment diagram, Hank.

[Shadrach]

1 hour ago, mike_elliott said:

Give a Moment diagram, Hank.

I'm looking forward to it. If seems logical (all other things being equal) that theoretically speaking if the CG and the fulcrum were at the same place, there would be no need for a horizontal stab as the fulcrum would be at the balance point. 

 

Edited January 15, 2016 by Shadrach

[Shadrach]

2 hours ago, Yetti said:

Not sure about "induced drag"  But there is always drag created by the horz stab by it's mere presence on the back of the plane.  The tail feathers depending on their up or down position could create lift.  The tail trim could create a neutral balance.

Spent lots of time racing Sunfish learning not to move the rudder to go faster.  But you could steer the boat based on shifting your weight. 

  People get excited about engine monitors.   A $10.00 strain gauge on the tail hinge and some electronics to the cockpit would make for some serious fun.  Moving around the stuff in the baggage compartment telling people to lean forward then retrimming to get a couple extra knots.   Maybe having some water ballast with some pumps to move it around.

Induced drag is drag that is created by producing lift. 

[N201MKTurbo]

11 hours ago, carusoam said:

 

1)  In the POH, Mooney uses a term called MAC in the WnB section.  The C's POH has it.  The R's POH has it and probably two sentences to describe it... (Insert what it means here?)  Cg is in front of Cl. During an ordinary stall, the main wing begins to stall first, lowering the nose to return to controlled flight.

MAC = Mean Aerodynamic Cord. Usually %MAC for CG. Used in transport aircraft, not very often for GA.