Setting Kodiak elevator trim during cruise

[argee 0]

To all,

I’d appreciate advice about elevator trimming during cruise with the Kodiak. When I try to do that with no wind, the nose pitches up and down slowly. The altitude rises and falls slowly with this, and the best I can get is an up-down range of around 200 ft, and even getting the range that narrow takes a lot of gentle manipulation of the trim wheel.

This happens at different amounts of torque and RPMs, different altitudes, different centers of gravity, and whether I use the Honeycomb Bravo (with low sensitivity) or turn that off and just mouse over the trim wheel.

(FWIW, the altitude stays completely level when I use AP, and doesn’t change when I turn AP off – the bobbing only starts if I change altitude or speed and try to retrim).

Is this normal, or is there something I should do differently?

Thanks!

[Bobsk8 12,702]

3 minutes ago, argee said:

To all,

I’d appreciate advice about elevator trimming during cruise with the Kodiak. When I try to do that with no wind, the nose pitches up and down slowly. The altitude rises and falls slowly with this, and the best I can get is an up-down range of around 200 ft, and even getting the range that narrow takes a lot of gentle manipulation of the trim wheel.

This happens at different amounts of torque and RPMs, different altitudes, different centers of gravity, and whether I use the Honeycomb Bravo (with low sensitivity) or turn that off and just mouse over the trim wheel.

(FWIW, the altitude stays completely level when I use AP, and doesn’t change when I turn AP off – the bobbing only starts if I change altitude or speed and try to retrim).

Is this normal, or is there something I should do differently?

Thanks!

Try adjusting your altitude or speed with your elevator first , once you get it stabilized then trim out any control pressure. 

[Stearmandriver 2,295]

The trim is too sensitive. This is true of many aircraft in this sim.  If you use an axis, try an extremity dead zone of around 25% - 30%.  You will never need more trim authority than that, and it'll make handflying more enjoyable when you can trim more precisely. 

[argee 0]

Thanks, everyone, I really appreciate the responses.

Bobsk8, I’m able to first stabilize the altitude and speed with my joystick – but I can’t find a trim wheel setting that keeps it stable when I take my hand off the joystick. I always get the slow bob of +/- 100 feet. So I think the problem is being unable to stabilize using the trim wheel.

Stearmandriver, I don’t think I’m using an axis. The Honeycomb Bravo treats the trim wheel as a button, and I’ve got it set at a low sensitivity so each turn of the Bravo wheel moves the sim wheel less than a click. And I’ve tried this with the Bravo disconnected, only moving the sim wheel using my mouse, with the same result.

So I’m wondering if others are able to trim the Kodiak in cruise, without AP, and get a constant altitude without any bobbing, and I'm doing something wrong – or if this is the normal behavior and I should expect it.

Thanks again for your ideas!

[Bobsk8 12,702]

9 minutes ago, argee said:

Thanks, everyone, I really appreciate the responses.

Bobsk8, I’m able to first stabilize the altitude and speed with my joystick – but I can’t find a trim wheel setting that keeps it stable when I take my hand off the joystick. I always get the slow bob of +/- 100 feet. So I think the problem is being unable to stabilize using the trim wheel.

Stearmandriver, I don’t think I’m using an axis. The Honeycomb Bravo treats the trim wheel as a button, and I’ve got it set at a low sensitivity so each turn of the Bravo wheel moves the sim wheel less than a click. And I’ve tried this with the Bravo disconnected, only moving the sim wheel using my mouse, with the same result.

So I’m wondering if others are able to trim the Kodiak in cruise, without AP, and get a constant altitude without any bobbing, and I'm doing something wrong – or if this is the normal behavior and I should expect it.

Thanks again for your ideas!

Probably a good question to ask on their Discord Page. 

 

[PIC007 82]

Trim is used to remove pressure on the yoke........

Once you have your airspeed stable adjust the trim to remove any pressure from the yoke/stick.....that's all there is to it.  If/when you change airspeed you will need to re-trim.

[tup61 1,560]

I usually fly on AP but whenever I don't:

1. I finetune the trim using the throttle. So after setting the trim as close as possible I increase or decrease power just a little bit and usually that does the trick. The throttle usually has a finer range than the trim wheel, so it seems.

2. I accept a slight deviation and only correct it every now and then OR I jst let the plane fly (after doing step tip 1) and it will usually keep a certain altitude after a short while. Maybe not the exact altutide I want but who cares. 😉

[fppilot 4,368]

19 hours ago, argee said:

(FWIW, the altitude stays completely level when I use AP, and doesn’t change when I turn AP off – the bobbing only starts if I change altitude or speed and try to retrim).

Is this normal, or is there something I should do differently?

The unrealistic element here is that in the simulators the altitude stays completely level and does not change when turning the AP off.  I have experienced that with every simulator I have flown. Flight conditions over time are staying relatively constant.  But as soon as you change something with the aircraft, such as speed or altitude, the sim begins to react.

When hand flying in a sim I just try to stay within +/- 200 ft of a planned altitude by making small adjustments with both trim and power.  Then if I climb toward the top of that envelop I make a small reduction in power.  Conversely if I descend toward the bottom of that envelope I make a small power increase.  I have found that when using trim I begin to chase the needles more rapidly.  What is needed varies by aircraft model, airspeed being maintained, and even planned altitude.

Maintaining level altitude when hand flying an actual aircraft takes constant effort because conditions are always changing.  Lift caused by airflow over the control surfaces changes constantly, affecting the aircraft with both lateral and vertical forces.  ex. as wind speed and direction changes. Only in these simulators the wind and temperature at an altitude is staying constant over periods of time, changing only occasionally.  The autopilot senses/measures the changes and constantly adjusts.  When you come off of autopilot in the sim flight conditions are usually staying constant over a period of time,

Compare it to driving a car on a straight segment of roadway.  Let go of the wheel and the car may or may not continue straight, reacting to the pavement, crown of the road, and other conditions such as wind.  But if the surface is perfectly level, and conditions do not change, the car will continue straight and true for a significant distance.

I once read a great discussion, I believe in the book "Fly the Wing" by Jim Webb.  It explored the age-old argument of do you control altitude with pitch, or with power.  He referred to deep discussions in segments of well known books such as Wolfgang's "Stick and Rudder", and Hoyt's "As the Pro Flies". His deduction was that you control altitude, and level flight, by continuously making changes with both, as needed.  If your windspeed or direction, or both change, that changes your airspeed, and perhaps yaw.  When your airspeed and or yaw changes, so does lift. When lift changes it affects airspeed.  When airspeed changes, lift changes.  Thus chasing the needles....

Here is an excerpt from an article in Aviation Safety in 2019.  https://www.aviationsafetymagazine.com/features/pitch-trim-principles/

"Upon reaching your cruise altitude, lower the nose to level flight and allow the airplane to accelerate. As indicated airspeed increases, the airplane—following the principle of trim—will pitch up to try to slow down to the airspeed for which it is trimmed. You’ll have to apply nose-down pressure as speed builds, trimming off the pressure as you go. It won’t all happen at once…the airplane accelerates, you hold forward control pressure and trim a little nose down to relieve that pressure; the airplane accelerates some more, you hold more forward pressure and trim the nose down more; the airplane accelerates more yet and you hold more forward pressure and trim even more nose down…all the way until the airplane stabilizes on cruise indicated airspeed."

"If you reduce power for cruise, you’ll need to trim the elevator up slightly to maintain level flight. The higher you fly, the lower your indicated airspeed will be (although your true airspeed may be higher), so the pitch trim setting in cruise flight will usually be more nose-up at higher altitudes and/or lower engine power. As fuel burns off, the center of gravity may change, requiring you to re-trim the airplane slightly. As you should know, if the airplane is trimmed for an indicated airspeed (IAS) slower than your current IAS, it will tend to nose up. If the airplane is trimmed for an IAS faster than your current IAS, it will tend to nose down."

Edited April 4, 2022 by fppilot

[Bert Pieke 7,585]

3 hours ago, argee said:

So I’m wondering if others are able to trim the Kodiak in cruise, without AP, and get a constant altitude without any bobbing, and I'm doing something wrong – or if this is the normal behavior and I should expect it.

I find that the default weather in MSFS has small wind gusts all the time.  This makes the airplane go up and down.  As I see Frank explained in detail above.. 🙂

Edited April 4, 2022 by Bert Pieke

[Bobsk8 12,702]

2 hours ago, Bert Pieke said:

I find that the default weather in MSFS has small wind gusts all the time.  This makes the airplane go up and down.  As I see Frank explained in detail above.. 🙂

Same thing happens in a real aircraft with real weather. 

[argee 0]

Thanks everyone for these great ideas – all very helpful. I’ll try working more with the throttle and less with trying to fine tune the trim to keep a reasonably stable altitude.

(FYI, I had posted this question first in the Simworks Studios Discord before here – the discussions there are also very lively and thoughtful - but no one responded, which made me think the problem was most likely just with me!)

[Glenn Fitzpatrick 3,798]

The advise to fly with yoke and then trim to remove pressure rather than try and "fly with the trim wheel" is correct.

Also check your CG as an out of bounds CG can exasperate oscillations.

Edited April 5, 2022 by Glenn Fitzpatrick