Rudder Alignment

[Lew]

While on X-country this weekend, after a year of maintenance, I noticed that I required a lot of right rudder to maintain heading.

Is it possible to revise the rudder to be closer to a neutral position?

Thanks

[Shadrach]

“Heading” is not the metric by which you gauge an aircraft’s rigging. Is the ball centered in level flight without rudder input? Is the ball centered on the ground with the aircraft stationery?

Hands off, coordinated, level flight does not guarantee that an aircraft is properly rigged but it’s the starting point.

[jlunseth]

Yeah, what Ross said. A crosswind will cause the aircraft to crab into the wind in level cruise so your heading will be different from your course (desired track or "DTK"). You should not use the rudder to try to match heading to DTK if that is what you are doing. That puts the aircraft in a cross-controlled status. Let the aircraft crab. Depending on the crosswind your heading may need to be anywhere from 5-15 degrees off your DTK and well into the wind. Its the ball that tells you whether you need rudder, not the difference between heading and desired track. Along with being cross-controlled, if you use the rudder to match heading to DTK the wind will then blow you left or right of your DTK, you will be making unintentional leeway. The ailerons are for turning, the rudder for slip-skid control.

That said, some use the rudder for fine directional control during an instrument approach, but that is another matter.

Edited October 3, 2022 by jlunseth

[A64Pilot]

Actually we don’t have a trim indicator, we only have a level, that’s why what Shadrack said is important before adjusting rudder trim, is the ball centered on level ground?

A piece of yarn taped to the windshield is an excellent trim indicator, just to validate things

But to answer the original question

 

[PT20J]

Shoptalk - rigging.pdf

[Pinecone]

28 minutes ago, A64Pilot said:

A piece of yarn taped to the windshield is an excellent trim indicator, just to validate things

That doesn't work that well on single engine planes.  It only shows the propwash direction.

GREAT on gliders and helicopter.

[Will.iam]

3 minutes ago, Pinecone said:

That doesn't work that well on single engine planes.  It only shows the propwash direction.

GREAT on gliders and helicopter.

Wouldn’t a helicopter have the same prop wash issue only at a different plane?

[Pinecone]

In a hover yes, but in forward flight, the rotor wash does not hit the windscreen.  At least not in an R-22.

[Will.iam]

I wonder if you brought the engine back to idle and setup for a glide if that would work. Humm might need to experiment and see at what point the yarn swings a lie compared to the o’l ball and turn. 
neighbor has a yarn on his twin and was complaining his rudder needed adjustment. After i pointed out he had a self induced fuel x-wind by not matching power of each engine the issue went away but not before teaching him power output matching needs to be precise or you will be flying in a slip even if only slightly. 

[A64Pilot]

1 hour ago, Will.iam said:

Wouldn’t a helicopter have the same prop wash issue only at a different plane?

No, the Army TH-55 used a piece of yarn as a trim indicator, and it worked on a Thrush, but the prop is 8 or 10 feet or more ahead of the window on a Thrush, I guess not on small airplanes.

We learned shooting rockets in forward flight on the AH-64 that the trim ball was just a level as the rockets missed, a single rotor helicopter in flight if you center the ball which levels the fuselage, your flying sideways due to thrust from the tail rotor pushing the aircraft to the right, that’s why a single rotor US helicopter hovers left side low, the push is called translating tendency.

We went back to the yarn and determined if we were one half a ball width out that we were in aerodynamic trim and the rockets would go straight, so we put it a half ball out to shoot. AH-64 was designed to shoot from a hover, but in the desert running fire was more useful than say in Europe’s forests or Steppes. 

‘French and Russian helicopters main rotor spins the opposite direction, so they hang right side low and require opposite pedal inputs.

A helicopter goes through translational lift at around 20 kts, this means the rotor system is flying in clean air and not affected by its own downwash, so the airframe is in undisturbed air at that point and the yarn works perfectly, below ETL you don’t look at the trim.

[Pinecone]

40 minutes ago, A64Pilot said:

below ETL you don’t look at the trim.

You CAN look it is, but it is fluttering around.

[Lew]

Well, to provide additional information, this plane had the entire rear from the bulkhead aft replaced due to a ground incident. The G5 and the turn & Bank showed 1/3 ball to the right.

[PT20J]

5 minutes ago, Lew said:

Well, to provide additional information, this plane had the entire rear from the bulkhead aft replaced due to a ground incident. The G5 and the turn & Bank showed 1/3 ball to the right.

The first thing I would do - before adjusting anything - is make a lot of careful measurements to determine if the empennage is “level, plumb and square” as the carpenters say. The factory might be of some help with exact dimensions, but a rough check would be comparing distance from wingtips to stabilizer tips on each side and stabilizer tip heights above a level surface with the airplane leveled. 

[Lew]

1 hour ago, PT20J said:

The first thing I would do - before adjusting anything - is make a lot of careful measurements to determine if the empennage is “level, plumb and square” as the carpenters say. The factory might be of some help with exact dimensions, but a rough check would be comparing distance from wingtips to stabilizer tips on each side and stabilizer tip heights above a level surface with the airplane leveled. 

That was completely done when the tail was installed. It was done by one of the better Mooney mechanics here. He gave me the rigging dimensions, And had shown me proof of the rigging, and they were spot on. The horizontal is level, as I've been able to trim for level flight without any issues.

[OR75]

isn't the easiest to check the plane is level to put a level (from Home Depot will work fine) across on the seat rails ?

Edited October 3, 2022 by OR75

[A64Pilot]

Some aircraft the stabilizers angle of incidence is adjustable ( Mooney isn’t I don’t think) Well I guess it is, but I mean rigging.

You can have the stabilizer way off and the aircraft will still trim, but it’s draggy because the stabilizer may be generating too much lift, that the elevator has to cancel out.

So being able to trim doesn’t mean much, but if your sure the airplane is square, I’d adjust the trailing edge of the rudder and go on, in fact I’d just do that anyway because if it’s not square your not making it so without a lot of money and pain and why subject yourself to that?

Most often an airplane that’s not “square” may have an evil stall, drop a wing heavily for instance. So if it doesn’t do anything scary then don’t  go looking for trouble?

[A64Pilot]

2 hours ago, OR75 said:

isn't the easiest to check the plane is level to put a level (from Home Depot will work fine) across on the seat rails ?

If the seat rails are the leveling datum, are they? I have no idea

[PT20J]

2 hours ago, OR75 said:

isn't the easiest to check the plane is level to put a level (from Home Depot will work fine) across on the seat rails ?

That’s the method according the the service manual.