Kodiak Trimming Question

[RandallR 444]

Real world autopilots maintain the trim (attitude) that was current at the time the AP was engaged, so this is correctly mimicking the real world. If you attempt to over-ride with adjustments to the trim while the AP is still engaged, you are forcing the AP to retrim and "fight" you to maintain the previous attitude. This is not a good thing to do, as you can come out of AP with the trim totally out-of-whack and be placed in a difficult (if not impossible) control situation (as you have discovered) :-) In the Kodiak's case, it goes to AP-trim nuetral, which may require some input from you in the form of Alt-hold engage or a change of the AP's own trim control, so you can maintain a climb or descent while also maintaining heading or NAV-following. The Cessna AP, on the other hand, is a simpler version that has no attitude/elevator control, so you can trim it with the AP on and hold or release back pressure with the yoke.The ALT Hold is just that - it will lock and maintain the current altitude. Without it on, the AP will maintain the current attitude/trim setting.The best way to trim with the Kodiak AP ON is to use the AP's own Trim Rocker on the throttle quadrant. Just click the Up or DOWN switch as many times as you want to decrease or increase the up and down trim - works great!The AP is the unit on the throttle quad - the panel unit is an annunciator for the AP, to remind you of what is or is not active. However, to make things a little easier, TRI made the main AP functions such as On/Off, NAV, HDG, APPRCH switchable from this unit, though I find them just a little to small and difficult to use. I use the main unit on the quadrant, set to an instant hotkey view. If necessary, I will undock the appropriate instrument so I can see the VSI, Altimeter, etc. when going to that view for an AP setting.

[Guest]

OK, that all makes sense. I had tried that rocker but wasn't sure what it did. So when you want to ascend or descend on the AP do you just use the rocker to manually retrim the aircraft to ascend/descend at whatever rate you want? Is there a way to determine how many "clicks" it takes to get, say, a 500fpm descent. Or do you just hit the button a few times and then go back up to the cockpit view to check the results? That seems a very slow way to do it. Is there a way to set that rocker to open buttons on my Wingman Extreme joystick? Thanks Again,John

[Roger Mazengarb 0]

G'day Randall,Great post, very informative. Just back from a very enjoyable flight in the Kodiak.For an aircraft to maintain straight and level flight the aerodynamic couples of lift/weight and thrust/drag must be in equilibrium. This is the designers nightmare as all four parameters are variables. On the Kodiac at 30"/2400 the thrust/drag couple (pitch up )is much larger than the lift/weight couple (pitch down ). In order to achieve equilibrium and maintain level flight you have to increase the pitch down couple by appling an upwards force on the tailplane. This is of course achieved by the use of nose down trim. I set the trim manually and it takes a hefty 50% nose down trim(approx) to maintain level flight. Can anyone verify that the Navajo actually does require this or is this just a quirk of TRI's Kodiac. As an experiment I reduced power to 20"/2000 which reduces the thrust/drag (pitch up) turning moment and fair enough as expectedI had to reduce the amount of nose down trim to 40% to maintain straight and level flight.If you don't trim manually but engage the auto pilot and then use the up/dn control on the command module the auto pilot will take control and trim the aircraft to also 50 (approx) to maintain straight and level flight. If you then disengage the auto pilot the aircraft flie like a dream as it is perfectly trimmed. Jcheyney's lack of elevator authority had nought to do with the trim condition of the aircraft and everything to do with his not having the correct control settings. At 50% trim settings the elevators should still have perfectly adequate authority to safely handle the aircraft.So my only concern with this whole trimming thing is:Is the 50% downtrim figure realistic?Any Navajo pilots on this forum able to shed light??Cheers,Roger @YSSY

[RandallR 444]

Roger,It is my understanding that the flight model of the Kodiak is probably the worst of the default aircraft, as far as matching the real world performance of the Navajo. Doesn't mean it isn't fun to fly, just not realistic as to performance. I know that flight modeling work is very complex, but I certainly hope someone with Rob Young type savvy can eventually give us a good model for this great aircraft.If comparison to the settings Rob qualified for the v88 version in Fly!2K have any merit, I have to go with higher settings to get anywhere close to his stated performance.The Navajo (at 10,000') should run at about 183K True at 29.8"/2300 or 198K True at 33"/2400. To come close to that, I have to run at about 35"/2400 - quite a difference.You've got me quite curious as to the trim amount for those settings at level flight - guess it's time to take a test flight. :-)

[RandallR 444]

John,I find about 2 spaced clicks gives me a 500' rate. I don't have to go back to cockpit view to set this, as I sinply undock the VSI so I have it right in front of me and only go back to cockpit view when I have the rate established.I'm not sure that the AP "rocker" can be programmed to keys or joystick - guess it's time to go back and check out the key assigns.

[Roger Mazengarb 0]

G'day Randall,Yes, I enjoy flying the Kodiac as well. :-)The whole business of stating trim as a percentage has me baffled.A percentage of what???Every aircraft I've had anything to do with simply uses "units of trim".Cheers,Roger @YSSY