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Roger Mazengarb

Kodiak Trimming Question

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I have just started on twin-flying with the Kodiak. I have found that once I get up to altitude and set the autopilot the plane flies with about 45% nose down trim. (This is with the recommended settings of 30inHg/2400rpm). The problem is when I try to come off autopilot to climb the aircraft won't because it has so much nose down trim, even using full throttle/full rpm. I am use to the Sahara where you use the automated ascend/descend system. This is also really a pain when I come off autopilot to land. It doesn't seem realistic that you would have remove all the trim and then try to climb, so clearly I am missing something. What am I doing wrong here?

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I don't have the answer, as my trim seemed to move also with auto-pilot after I pre-trimmed for straight and level.Did find something unusual though, although maybe everyone else already knows.....The trim indicator is marked "DN" towards the aft direction. This is opposite of what's usual, even in the other FLY Pipers. But if I spin the wheel foward for down trim, the indicator does travel backwards to down. I fired up the old FLY on my other CPU to check this out. The trim markings are just like FLYII, but now the indicator arrow runs the correct direction with the trim wheel.If Piper just decided to go opposite with the markings/pointer movement on this particular aircraft is unknown to me. But if so (which I doubt), the the pointer direction between FLY/FLYII is opposite.L.Adamson

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G'day Jcheyney,Mate something is wrong.I just did a flightclimbed out of KSFO.engaged auto pilot (hdg mode)climbed to 9000 ftengaged Alt holdset up 30/2400after a few minutes checked trim and found it to be very similar to your setting 54% nose down.then disengaged AP and Alt hold.The aircrft flew like a dream - perfectly trimed "hands off" in level flight.Joystick control was smooth and positive. I could wind the ROC pointeroff the clock IN BOTH DIRECTIONS.You had a problem.Sometimes when you select an aircraft the joystick exponential is not 100%, but way way down low. This would explain your problem of lack of elevator authority. Try the flight again but this time Click aircraft/options and check that the joystick exponential is 100%.Cheers,Roger @YSSY

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I should mention that I didn't have elevator control problems after disconnecting auto-pilot either. But with 54% down trim in level flight................ it's probably time to do some serious horizontal stab re-adjustment! :)L.Adamson

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I did the same flight tonight. Sure enough the plane trims itself to 45% down when you hit the autopilot. I too noticed the trim wheel direction thing but REGARDLESS of which way I turn the wheel it trims down, and it takes 10 or so turns of the wheel to get any change at all. I have to use the mouse on the trim wheel: The keyboard keys don't work. The plane flies level without autopilot without much trouble. Also, the plane seems to try to trim itself without the autopilot on. As I change the power settings the trim settings change themselves. I am still at a loss. I did find the exponential settings set to 0% during the flight and changed them without effect. I know each setting has to be redone for each aircraft but do you have to exit the program and reenter it for the change to take effect? I did a topic search here and did find a similar question from back in April. One responder suggested to trim the aircraft to stable flight and only then hit the autopilot. I will try that too.I'd really like to fix this, because it seems like a fun plane to fly but I essentially have to "crash" land at a stall with stick full back and hope it holds.Thanks again.

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G'day Larry,I'm not a pilot and the figure does at first appear to be high. A few aircraft I am familar with require a sustantial amount of up trim for straight a level cruise.Just maybe the Kodiac requires this nose down trim to maintain level flight? I dunno but I agree with you about the confusion over the trim controls.Cheers,Roger @YSSY

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If you haven't already done it, you may want to start "clean" with this plane: delete the 22059.HST file to get rid of any anomolies, restart Fly!II and reset the options for this aircraft to Trim Steps 1 and all Exponential to 100%, then give her another try.

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G'day Jcheyney,It surprises me that you even get airborne, it must be a real dog to fly.Ok you do not have to exit anything!!!! As soon as you select the Kodiac go straight to aircraft/options and check that the keyboard settings are 1 and that the joystick exponentials are 100% for all axes.I am not sure of the effect if you do this in mid-flight but I suspect it should still work!.The indicator will take a small time before it starts working when using the mouse.The keyboard numpad keys 7 (nose down) and 1 (nose up) do operate the trim pointer and aircraft does respond to the trim.The Trim Wheel however DOES NOT RESPOND to the keyboard.Finally a silly question?Are you patched to 2.5.240 (the final patch?)Cheers,Roger @YSSY

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>I'm not a pilot and the figure does at first appear to be >high. A few aircraft I am familar with require a sustantial >amount of up trim for straight a level cruise. Hello -- Roger,I just made my comment with regards to actual aircraft building which I've been involved with for a number of years now. An example is the horizontal stab in cruise flight with the CG within limits. During the test phase, if your crusing along, trimmed for level flight, and look back (or chase plane) and notice the elevator trailing in an up or down position due to the trim tab, then it takes a shimming adjustment of the leading horizontal edge to fix the problem (other ways too). Otherwise, the up/down elevator is in effect creating additional drag, lower top speed, and more fuel consumption.There are all kinds of tricks when dealing with control surfaces. If a wing is "heavy", you can actually squeeze or "fatten" the trailing edge of the ailerons to correct this. The whole idea is to get the ailerons to trail with the same cord-line of the wing. Anything that's off, is just more drag. If you need to account for heavy passengers, fuel tanks, etc. then you just live with the penelty of of slightly offset ailerons.L.Adamson

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>I have to >use the mouse on the trim wheel: The keyboard keys don't >work. The plane flies level without autopilot without much >trouble. Also, the plane seems to try to trim itself >without the autopilot on. As I change the power settings >the trim settings change themselves. As Randall suggested, I would delete the .hst file for this A/C and start again. You also might check the assignments of your keys, buttons and axis. With the autopilot off, your trim settings should not be moving with the throttle. The Kodiak IS a fun plane to fly and for a default A/C, it is pretty good. It is one of my favorites. I hope you get it flying right!Dean Karis

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G'day Larry,I'm a maintenance guy not a pilot.I don't disagree with a word you have said ..( a first time for everything :-) ). Specifically I was referring to the fokker f27 and the Aerocommander, both high wing twins. They have quite strong downsprings that hold the elevators down. These aircraft need up trim (ie tab down) to hold the elevator faired in flight. It is a form of anti-stall measure. If the aircraft slows then the aerodynamic load on the tab can no longer hold the elevator faired and the downsprings lower the elevators which reduces angle of attack and prevents stalling. Some aircraft have a minimum drag speed. Above that speed drag increases and below that speed drag increases. From that you can see that an aircraft can have a speed instabilty around its minimum drag speed. Speed slows- drag increases which slows speed which increases drag which slows speed and whhhoooppss we stall. The down springs stop this.Yes tabs on moveable controls are a drag problem and many aircraft have resorted to other forms of trimming. Variable incidence stabilizers, all moving tailplanes or varying C of G have all been used with various designs. Of course trim tabs are only a feature for manual controls. With powered controls the whole surface is trimmed.Sack whoever is doing your rigging :-)I wouldn't start playing around too much with the angle of incidence of the stabilizer just to fair the elevators. You will be changing the stability and flight characteristics of the aircraft.Cheers,Roger @YSSY

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Actually, it isn't a silly question. Yes I am patched all of the way. I am going to delete the .hst file and reset the exponentials and fly again today. I am also glad to know the trim wheel won't turn with the keyboard commands, so I know it isn't broken. It just seems like it takes forever to make any significant change.John

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>Sack whoever is doing your rigging :-) >I wouldn't start playing around too much with the angle of >incidence of the stabilizer just to fair the elevators. You >will be changing the stability and flight characteristics of >the aircraft. >Fear Not!!!! :) It is I, who shall re-rig if nessesary. Hopefully, I won't. But never the less, the approach is an enginerred and "scientific" one. Not just a matter of playing around.-My Bird-

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G'day Larry,Absolutely gorgeousCan't wait for the upload to the library :-jumpy :-lol :-lolCheers,Roger @YSSY

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I flew the Kodiak today and found something interesting. I set the exponentials to 100 on all three axes and the keyboard trim steps to 1, and prior to the flight deleted the .HST files. It seems that whenever the autopilot is on the trim is inoperable from anywhere (mouse or keyboard). This happens regardless of whether the altitude hold is on or not. So what was happening was that when the autopilot was engaged (even in heading mode only) the auto trim would take over. When I came of autopilot on final I was trying to fly an aircraft trimmed massively nose down. The only way to get trim control back was to completely shut off the autopilot. This is a pain because you have to try to hold heading steady while fighting the trim problem. This doesn't make any sense to me. Why would the autopilot maintain trim control when the altitude hold isn't on? Is this normal or is something still wrong. One other question. There is an autopilot control on the top of the control panel above the artificial horizon. Some of these controls are operable and some seem ot be merely advisory lights. There is another autopilot control on the throttle quadrant. The two seem to be entirely separate form each other, although both seem to work. Why is this? Which one am I really supposed to use?

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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.

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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

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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

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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. :-)

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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.

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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

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