Turn Coordinator and KAP-140

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Rich
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Re: Turn Coordinator and KAP-140

Post by Rich »

Rick wrote:FWIW, my KAP140 always did 3/4 rate turns, too. There's no adjustment for that in the KAP, either. :(
So has mine. But my T/C is a traditional panel mount. Timing the rate of turn shows it's like 2/3 standard rate BUT the T/C incorrectly shows it as standard rate throughout. The A/P is doing what it's being told by the T/C.
2002 DA40-180: MT, PowerFlow, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210, Orion 600 LED, XeVision, Aspen E5
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Russ B
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Re: Turn Coordinator and KAP-140

Post by Russ B »

Our 40 started drifting left, kept getting worse to the point we could not use the AP. Tried nulling, did not help. Replaced the Turn Coordinator and tried nulling, did not fix it. Had to replace the roll servo. Just got down from nulling it and every thing works great.

Russ
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Gasser
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Re: Turn Coordinator and KAP-140

Post by Gasser »

Well, its good to know at least its working normally, just not optimally.
Before I had the null valve centered it would turn standard to the left and 1/2 standard to the right.
Jeff

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Gasser
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Re: Turn Coordinator and KAP-140

Post by Gasser »

Russ B wrote:Our 40 started drifting left, kept getting worse to the point we could not use the AP. Tried nulling, did not help. Replaced the Turn Coordinator and tried nulling, did not fix it. Had to replace the roll servo. Just got down from nulling it and every thing works great.

Russ
will yours hold a standard rate turn using the heading knob in heading mode?
Jeff

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2005 DA40 SOLD
2006 SR22, A/C, TKS, AVIDYINE PFD/MFD, IFD 540/440, AXP322 remote ADS-B TRANSPONDER, AMX240 AUDIO PANEL, MLB100 ADS B in.
168 KTAS 9,000' msl @ 13.6 gph LOP. 1005 pound useful load.
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Jean
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Re: Turn Coordinator and KAP-140

Post by Jean »

Ours does
40.446, G1000, KAP 140, Hartzell Metal
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40flyer
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Re: Turn Coordinator and KAP-140

Post by 40flyer »

My 2005 DA40 will only do about 60% of a standard rate turn in HDG mode, either left or right, causing overshoots on all turns greater than about 45 degrees. The TC was overhauled but the problem remains. There is no wing walk. Is KAP 140 or roll servo the likely cause?
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Rich
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Re: Turn Coordinator and KAP-140

Post by Rich »

Some new data on mine, testing specifically the A/P feedback signal:

1. In a left turn, rate displays in Foreflight as 2 deg/sec. Display on the TC shows it clearly less than standard rate (~2/3 - 3/4 deflection).

2. In a right turn, rate displays in Foreflight as 4 deg/sec. Display on the TC shows it just a smidge more than standard rate.

3. Set A/P in ROL mode. This is most interesting. Plane is in an obvious slight right bank, TC display a very slight right turn. FF display shows 0 deg ROT. And plane definitely is in a constant, low-rate rotation to the right. Bank doesn't steepen or anything scary,

The system intercepts/tracks heading/course OK, but the implication is the TC is emitting a signal biased to the left. That is, it thinks it's left-turn component is more than it actually is.

The No. 3 situation is the most concerning. ROL mode is something I've almost never used. But in nice, milky IMC if one gets distracted this very slow rate of turn (probably less than 1/2 deg/sec) could go undetected for awhile. I know that the TC outputs a voltage signal that varies from 0-<some value> so it would seem this could be recalibrated, which I'll look into. It's unclear to me whether the "brushless" version address this signal or the gyro drive mechanism. I'm still mystified no one has a digital replacement for this instrument. :scratch:
2002 DA40-180: MT, PowerFlow, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210, Orion 600 LED, XeVision, Aspen E5
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Rich
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Re: Turn Coordinator and KAP-140

Post by Rich »

Digging more. It looks like there is an offset adjustment in the KAP140 that would influence at least the ROL behavior. It's setting the pitch and roll NULL points.
2002 DA40-180: MT, PowerFlow, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210, Orion 600 LED, XeVision, Aspen E5
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Re: Turn Coordinator and KAP-140

Post by Colin »

That setting of the nul points require a factory rep to stop by my avionics shop (where the plane was for a third time hunting this problem). He zero'd them and it was great from then on.
Colin Summers, PP Multi-Engine IFR, ~3,000hrs
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Steve
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Re: Turn Coordinator and KAP-140

Post by Steve »

This thread made me curious. I had never noticed anything unusual about the autopilot-directed turns in my airplane, but I cannot say that I actually watched to quantify them. So, today I did. In both HDG and NAV mode, turns were precisely standard rate. I guess I lucked out, and the NULL adjustment is correct. I keep expecting my TC to fail, since it is original to the airplane (18.5 years old).
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