Porpoising With my KFC-150

[Marauder]

David/Marauder - Can you confirm your installation costs for the Aspen and who did it? This is probably my next move for my Ovation.

 

I went to a number of shops for quotes (8 in total if I remember correctly). As you might guess, they were all over the map. The highest density was in the $3200 range just for the installation of the Aspen. It was being interfaced to a Garmin GTN 650, PS 8000BT, my Narco Mark 12D+ and off course the pitot/static system. 

 

The Garmin had it's own installed price, so did the PS 8000BT. Let me know if you need specifics. There are a lot of "gotchas" and you need to ask the questions or you'll get the surprises later.

[Marauder]

David/Marauder - Can you confirm your installation costs for the Aspen and who did it? This is probably my next move for my Ovation. 

 

Here are some pictures of my upgrade. The close up pictures of the Aspens shows the GPS signal loaded up on the PFD (the plane was in the hangar so the actual GPS signal isn't there) and the VOR signal from the Narco is on the MFD. The last picture is the autopilot reversion switch that Aspen provided the specifications for. Let me know if you have any questions.

[Bennett]

I posted a comment on the Avionics Forum page this morning that applies to my KAP150 "bobbing", but not really porpoising, in that altitude did not change when in altitude hold.  Turned out to be the AI (after a good deal of bench testing). The cost of an overhauled AI (by Mid-Continent was not unreasonably expensive - about $2,700, with guarantees and warranties), but all the testing, calibrating, and re-installation of everything certainly ran up the costs. Hate spending money on repairs as opposed to new gear, but that's aircraft ownership. 

[David Mazer]

I don't know how long your warranty will be but the one I had was only about 90 days.  Worthless.  Especially since the AI went out again in about a year and they wanted another $2,500 to rebuild it again.  That is when I broke down and upgraded the Aspen.

[Mark89114]

I will give you my experience and bad mouth Autopilot Central in Tulsa justly so.

I took my Ovation with KFC225 for them for a slight porposing, nose would go up and down slowly, airspeed would build up and then would go opposite direction.

APC tested the pitot static, tested the AI, tested the computer and finally decided it was a gizmo (forgot the name of part in the pitch servo), they replaced it and the problem still existed.  I said stop and told them you guys clearly don't know what you are doing after spending $4000 or so.  I was just going to live with it, till I was flying along one day on AP and the aircraft deviated nose up aggressively, hit the big red button and got plane under control.  Continued my flight hand flying the plane, almost declared an emergency or two (sarcasm font).  Finished my trip and started looking around for another avionics shop.  Found a guy nearby who diagnosed the failure, the gizmo had a cold solder joint, so Autopilots Central can't even solder correctly.  He then continued the diagnosis and determined that the motor in the pitch servo took too much voltage to start moving, I guess the computer sends voltage and waits to see what happens, it continues to crank up the voltage and then all of a sudden it starts to work and it just takes time for the system to equalize.  Motor should start moving with 1 volt and was taking almost 2.5 to 4 to start moving.  Replaced the pitch servo and it has been working perfectly.  

Don't know if this is going to be helpful or not.

Good luck.

   

[Tim Jodice]

I just had this problem with my KFC150. It over the past 5-6 months it kept getting I took it to Griffin Avionics in Hyannis, MA about 2 weeks ago. A overhauled trim servo, repaired pitch servo and $3600 it is works great. Based on the way it works now it was never right from the day I bought the airplane. 

[LANCECASPER]

Buried earlier in the thread Jose mentioned to make sure and lubricate the yoke control shaft. If it binds that can also be a cause. Go for the simplest fix first.

I firmly believe that most shops don't have a clue on autopilots and make it worse by digging into it. Call an expert, Bob Weber @Bob Weber

https://webairconsulting.com/services/ 

[Greg_D]

I had a similar problem in my Ovation with a KFC-150.  I was also having problems getting the system to pass a preflight check.  Lots of guessing ensued.  I had the KI-256 overhauled and also had the HSI overhauled.  The problem persisted.  At this point it was determined that the KC192 computer needed to be looked at.  While it was out of the airplane being repaired, I had a pitot static check completed.  When I got the KC192 computer back and installed, the preflight checks worked perfectly.  And the autopilot worked well...when flying low (<3,000 ft).  Anything higher and I would get un commanded pitch changes.  Troubleshooting lead me to believe I had a pitot static blockage or a faulty alternate static valve.  I looked at everything else...rigging, jackscrew lubrication, yoke shaft, etc.  After comparing the pitot static plumbing to a plane just a few months newer than mine, we found that the alternate and instrument lines on the alternate valve were reversed.  I thought it might be a quick fix, but on subsequent flights the pitch excursions then became wild, forcing me to disconnect the autopilot.  I decided to remove the glare shield and take a look behind the panel.  I found a disconnected static line by the airspeed indicator and when talking with my avionics guy learned that he had removed a T connection in the system near that location that didn't seem to go anywhere.  Well, it was supposed to go somewhere....to the KC192 that had been removed for repair.  Although I disagreed, he doubted that it would make that much of a difference and put the connection back in.  The system now works perfectly in all modes!  Altitude pre-select capture is spot on and the entire system operates better than it ever has in my 14 years of ownership.  Anyway, a long way of saying to check the entire pitot-static system carefully.

[PT20J]

3 hours ago, Hyett6420 said:

I love Mooneyspace, 7 years ago someone had an identical problem to mine (which has just happened).  I do. A quick google search and lo and behold this thread comes up.  
 

We have just had a lot of panel work done, bits of the static system were replaced.  The AI was faulty so an exchange unit was fitted.  The exchange unit was more modern than the one it replaced.  The AP now porpoises up and down, the flight director goes up 5 degrees, then down, up amd down and the plane follows.  No more than 200-300 feet at a time but its a brand new fault.  
 

So my logic is that its either:-

1. a static fault
2. a software level fault in the KFC150 
3. an issue with the replacement AI. 
    

So reading this I feel it is more likely to be 1 or 3.  Does anyone have any other thoughts?  Before we spend lots of money investigating.  
 

Andrew

A lot to unpack here.

First, after everything was put back together, did you have a pitot static check done? (It would be required for IFR flight under 91.411 since the static system was opened). If so, that should eliminate static issues as a cause.

Second, does it do this in pitch hold mode, altitude hold mode, or both? If it does it in altitude hold and it's due to a static system issue, you should see simultaneous indications on the pressure instruments.

The autopilot should follow the command bars and since you see them move, it appears that he autopilot is doing it's thing. 

It could be something with the KC 192, but since you changed out the KI 256 just before this happened, that would be the first place that I would look. When you change the gyro, I believe that the procedure calls aligning the gyro and computer together on the bench. I don't know if this is the issue or not, but it would isolate the problem to the computer or the gyro. Another thing worth checking is the connector to the KI 256 for any wiring issues since it was disturbed.

Skip

[jaylw314]

4 hours ago, Greg_D said:

I had a similar problem in my Ovation with a KFC-150.  I was also having problems getting the system to pass a preflight check.  Lots of guessing ensued.  I had the KI-256 overhauled and also had the HSI overhauled.  The problem persisted.  At this point it was determined that the KC192 computer needed to be looked at.  While it was out of the airplane being repaired, I had a pitot static check completed.  When I got the KC192 computer back and installed, the preflight checks worked perfectly.  And the autopilot worked well...when flying low (<3,000 ft).  Anything higher and I would get, un commanded pitch changes.  Troubleshooting lead me to believe I had a pitot static blockage or a faulty alternate static valve.  I looked at everything else...rigging, jackscrew lubrication, yoke shaft, etc.  After comparing the pitot static plumbing to a plane just a few months newer than mine, we found that the alternate and instrument lines on the alternate valve were reversed.  I thought it might be a quick fix, but on subsequent flights the pitch excursions then became wild, forcing me to disconnect the autopilot.  I decided to remove the glare shield and take a look behind the panel.  I found a disconnected static line by the airspeed indicator and when talking with my avionics guy learned that he had removed a T connection in the system near that location that didn't seem to go anywhere.  Well, it was supposed to go somewhere....to the KC192 that had been removed for repair.  Although I disagreed, he doubted that it would make that much of a difference and put the connection back in.  The system now works perfectly in all modes!  Altitude pre-select capture is spot on and the entire system operates better than it ever has in my 14 years of ownership.  Anyway, a long way of saying to check the entire pitot-static system carefully.

Hey wait a minute, I don't think the KC192 has a static air line input?  I think it has its own pressure sensor for altitude hold functions.  The KAS 170B altitude preselector takes its altitude data from an altitude encoder, not the static line as well.

[PT20J]

[LANCECASPER]

51 minutes ago, jaylw314 said:

Hey wait a minute, I don't think the KC192 has a static air line input?  I think it has its own pressure sensor for altitude hold functions.  The KAS 170B altitude preselector takes its altitude data from an altitude encoder, not the static line as well.

Do you mean the KAS 297B?

[carusoam]

Common AP issues around here... causing porpoising in flight...
 

1) Altitude hold always requires some connection to the static line... electronic or a piece of tubing... (Skip indicated tubing in this case, the sensor is in the control head)

Often, in some installations around here... a rubber hose was used. The rubber hose would degrade within a few years and lead to the cabin pressure being used...

cabin pressure has a tendency to change for a variety of reasons... enough the Alt hold would clause porpoising...

 

2) Servo clutches wear... and computing power of the 90s technology lead to a mismatch... the Servo in charge of Alt hold can have difficulty in choppy air... its response time lags what it needs and the porpoising begins...

Hand fly for a moment when this occurs, re-engage the Alt hold... it holds pretty well until the chop gets too strong again...

3) Cleaning and lubing the controls is a great way to start... the extra drag on the system will be working against the slow computer’s logic skills...

 

PP thoughts only, not a mechanic...

Best regards,

-a-

[jaylw314]

2 hours ago, LANCECASPER said:

Do you mean the KAS 297B?

Holy smokes, I must have had small stroke, I'm not sure where the 170 came from! 

[jaylw314]

2 hours ago, PT20J said:

You know, I've looked at that page several times before and never noticed that!  TIL...

[carusoam]

Mixed memories....

KX170B is a real thing... a very strong memory...

KAS297B is a lesser known memory...

Welcome to the world of memory challenges!

Think before you speak takes on a whole new meaning...   

Best regards,

-a-