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Capabilities of a two-axis autiopilot


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What are the capabilities of a two-axis autopilot? The 2006 CTSW I looking at taking lessons in has one and I didn't think about asking when I saw the plane. The plane has steam gauges and a Garmin 296. Below are the specification for the CTSW.

 

LSA Flight Design CTSW

 

2006 composite construction w/ Rotax 912ULS

Garmin SL-40 com with intercom

Garmin 296

two axis Autopilot

34 gal capacity with less than 5 gph burn

375 pound payload

BRS parachute system

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Hi Lindenberg,

 

With the 296 the AP can fly you on a multiple route and or just a straight destination and hold your altitude. Throw a Garmin 696 in there and it can even butter your bread. Once you take off the 696 can fly you out of the pattern and completely to your destination and into the pattern.

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from wikipedia.. "A two-axis autopilot controls an aircraft in the pitch axis as well as roll, and may be little more than a "wing leveller" with limited pitch oscillation-correcting ability; or it may receive inputs from on-board radio navigation systems to provide true automatic flight guidance once the aircraft has taken off until shortly before landing; or its capabilities may lie somewhere between these two extremes. A three-axis autopilot adds control in the yaw axis and is not required in many small aircraft.A two-axis autopilot controls an aircraft in the pitch axis as well as roll, and may be little more than a "wing leveller" with limited pitch oscillation-correcting ability; or it may receive inputs from on-board radio navigation systems to provide true automatic flight guidance once the aircraft has taken off until shortly before landing; or its capabilities may lie somewhere between these two extremes. A three-axis autopilot adds control in the yaw axis and is not required in many small aircraft."

My Two-axis Trutrak can read a flight plan from the Garmin 296, including multiple legs, and climb and descent. However, I generally use it to fly current track (one-button push), or fly the current direct-to in the GPS (two button pushes).

tim

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Most likely it is a Tru track autopilot. These have a couple different modes and capabilities. The first is it will maintain a ground track based on information from the 296. this is the mode it starts in when you turn it on. What ever ground track your currently flying will be the one it maintains until you tell it to do something else. This could be a new ground track command using the knob or a GPS route track command by pressing the mode button. In the GPS route mode the autopilot will maintain the track between two waypoints in the GPS keeping the cross track error needle centered. At the same time it will maintain the altitude you were at when you turned it on and some models will maintain a rate of climb or descent based on a foot per minute command using the knob.

 

It also has a backup mode in case the GPS fails or is off in which it maintains a bank angle command up to 15 degrees as set by the knob.

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I have found TruTrak to be very proactive as far as providing service for all issues I've had - which has been my display showing lines and having pixel dropouts. TruTrak serviced my unit and provided an unexpected software upgrade during the repair with no charges and with a quick turnaround. I am very happy that my plane has the TruTrak 2 axis A/P. It performs extremely well coupled to my Garmin 495.

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  • 7 months later...

I have what may be a (nearly) dumb question. I've sent my Trutrak control head back to Arkansas to try to fix it. When I pulled the control head out the vacuum line was connected to one of two idential screw-in ports, one labed "P" and one labeled "S". I assume that stands for Pitot and Static. Since the autopilot hasn't worked right since the control head was replaced about a year ago I can't help but wonder if the vacuum line was attached to the wrong port. It was attached to the "P" port.

 

I've searched every document on the aircraft I have and it doesn't talk about which port to use. Can someone tell me this before I re-install the unit?

Thanks very much.

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Tom,

Very interesting and, unfortunately, mine appears to be different. You said that factory installations have both lines connnected. Mine only has one line. I followed this line backward and it runs into a "t" intersection, each other line going a different direction. There was only one line coming toward the Trutrak control head.

 

So, do I have an incorrect installation? It hasn't worked right since the control head was replaced last year because of the intermittant alphanumeric display. I thought maybe it had been installed incorrectly.

 

Lucas at Trutrak is returning the control head with an updated OS that is supposed to help. I just didn't want to put the thing back in incorrectly.

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Tom,

Very interesting and, unfortunately, mine appears to be different. You said that factory installations have both lines connnected. Mine only has one line. I followed this line backward and it runs into a "t" intersection, each other line going a different direction. There was only one line coming toward the Trutrak control head.

 

So, do I have an incorrect installation? It hasn't worked right since the control head was replaced last year because of the intermittant alphanumeric display. I thought maybe it had been installed incorrectly.

 

Lucas at Trutrak is returning the control head with an updated OS that is supposed to help. I just didn't want to put the thing back in incorrectly.

 

Ron, that "T" intersection you traced it to one line goes to the pitot, and the other should go to the instruments. If it gets hooked to the static line, but goes to the one marked "P" on the autopilot head it will do funny things. Don't ask me how I know this. If it worked before you swapped out the head, then there are a few things you should check. Go through and make sure all the settings in the autopilot are correct. If you have updated the GPS check to make sure the setting for the GPS are correct. One other thing is I've seen the connections in the plug push out and not make contact, so pull the plug and look to make sure that hasn't happened. What is it that the autopilot isn't doing correctly?

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Tom,

I sure appreciate the advice but being mechanically challenged I'm not sure I quite understand. Some background: about a year ago the control head was switched out for a new one as the alphanumerics were faint and intermittant. It hasn't worked right since then and has gotten increasingly worse. It wanders off the assigned heading, either directly input or coupled to the Garmin696. For a long time it would hold altitude just fine, now it won't do that either. I first went to a very knowledgeable guy at Garmin and we explored the problem from the GPS side and made some minor changes to the GPS. I've written off-and-on to Lucas at Trutrak for about six months. He noted that he and his co-workers were "banging their heads against the wall" trying to figure this out. Again, I made all suggested changes from him. I then took it to an avionics shop authorized to work on Garmin and Trutrak and he said the GPS was communicating normally to the autopilot (though I don't know if he checked the autopilot connections.) Finally, Lucas said to send it in and he just advised me two days ago that they updated the software and that he thought that would solve the problem. It's due back in two days.

 

All that said, I didn't quite understand your sentence "If it gets hooked to the static line, but goes to the one marked "P" on the autopilot head it will do funny things." Let me explain again and please tell me if I have this right. There is a t-intersection. One line (at the top of the T) appears to be coming from the Pitot tube or Static port (can't tell), Another line at the top of the T appears to be going into the instruments, and the line at the bottom of the T goes to the back of the Trutrak. So, should that line to the Trutrak be screwed into the "P" hole or the "S" hole?

 

For all I know this line could have been plugged into the wrong hole for the entire time this newer control head was installed.

 

So, the two questions are: screw it into the P hold or the T hole, and why do you have two connections to the control head and I only have one?

 

Your answers will be VERY welcome.

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Ron, on the back of the A/P head you should have 2 screw in ports marked P and S. The "P" is for pitot, and the "S" is for static. Having the static open to cabin pressure does not hurt anything, but they are hooked up on factory installed A/P's. The A/P will work just fine without either line hooked up, except the Min. and Max. airspeed function will not work. When you trace the line back to the "T" fitting it should have been installed in the pitot line. One side will go into the airframe, and the other will go to the Dynon, and "T" off again to the airspeed ind.

The other thing I was talking about is the plugs that connect to the A/P head and servos. each wire that comes into these plugs has a small gold plated terminal attached to the wire. These terminals are pushed into the plug in thier respective holes, and they should lock into place. I have seen these terminals push out of the plug during installation. When this happens they have poor or no contact. By looking at the plug with a light, and maybe some magnification you can see if any of these are pushed back.

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OK, Tom. I think I have it now. I can't help but wonder if the original owner or his mechanic changed things? I say that because my A/P was factory installed (on one of the equipment lists) so why is only one side hooked up: S or P? Mystery to me. I sorta figured that the 25 pin connector coming out of the A/P head went to the servos but I haven't been adventurous enough to dig behind the panel to find it. (OK, I'm not even sure what servos look like.)

 

However, if this software update doesn't work as expected I'll got straight to a qualified technician and have him check the servo plug-ins. Thanks again for your advice.

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Hi Ron,

 

I'm pretty confident this will cure your problem. Having the pitot line connected to the S port on the autopilot will really take you for a ride in pitch though. As Tom suggested, it's best to actually trace the lines and see where they go so you can get them connected in the right places.

 

While it's ok to fly the AP with the S port open (it won't hurt anything), any change of cabin pressure due to opening or closing an air vent will also take you on a short roller coaster ride. Please don't hesitate to give me a call, email, or post here for help. Thanks!

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Hi Lucas,

 

The autopilot head arrived in less than 24 hours. Great Service!

 

I'll try to get it installed and flying in the next two days, but after that I'll be gone for a month. I'll e-mail you one way or the other of success.

 

Thanks again,

Ron

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Ron, you'll maybe be pleasantly surprised on how well the TruTrak A/P functions if you have not used this system before. Setting waypoints with your Garmin GPS is a nice function of this system. Basically all you need to do is monitor the airspeed. If conditions are convective, occasional throttle adjustment is required to maintain constant airspeed as the A/P changes up/down pitch to hold altitude. The TruTrak controls this so smoothly the airspeed changes are sometimes hard to sense if one isn't looking at the airspeed indicator. The tip-off is engine sound change.

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Gentlemen!

 

I DO remember when my autopilot worked properly. But it hasn't for nearly a year now. From my last post today, I received the control head back from Lucas at Trutrak this morning. I took it to the airport this afternoon and installed it, hooking up the vacuum(?) line to the P port. After take-off, reaching altitude, and setting a waypoint to fly toward (the nose pointed directly toward the waypoint), I engaged the autopilot. The plane went into an immediate 45 degree turn to the left and I finally stopped the turn after 450 degrees. It wouldn't hold altitude as it did before either. So, I pulled the panel and changed the vacuum wire to the S port and took off again. Same symptoms. So, I returned to the airport and unhooked the vacuum line completely, taped it shut and put the panel back. Same symptoms again. In all three cases it would not hold or turn to a manually entered course either. I am now at a loss about what to do. Garmin says everything is fine, Trutrak says everything is fine. I'll have to leave it for a month while we travel. I'll try to think of something then. ANY ideas appreciated.

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Roger,

 

I may bring the thing to Ryan just so you can figure it out! My buddy at Garmin gave me new settings for the 696. Before I sent the control head back to Trutrak I reset everything to factory settings. They updated to the newest software version, calibrated airspeed and altimeter, function benchtested, and noted that all readings were within current manufacturer's specs.

 

I'm starting to think about trying Voodoo.

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Hi Ron,

 

This is a copy of my email as it may be important to other users as well.

 

Something is definitely amiss here. When do you power up the autopilot? Is it after take-off? The AP master needs to be turned on after the engine is started but before you move the aircraft. And, you need to not move the aircraft until you see AP OFF on the display. Let me know. Thanks!

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Hi Ron. Here are some comments and please note that I am not an expert on this subject. I am sending this in hopes that it may provide you some information that you may be able to use. As far as I know, our CT's do not have any vacuum lines that contol our instruments. There are just two plastic lines that go to the instrument panel, pitot (pressure induced by movement of the plane thru the air) and static (atmospheric pressure). In order to properly resolve your concern, you will first need to sort out which line is pitot and which is static. I took this photo during my rubber replacement at which time I had my A/P serviced by TruTrak and re-plumbed this to the new manifold configuration it came back to me in. I don't have my notes with me but looking at the attached picture of the A/P (lower right part of the picture), I would say that the right port is for pitot and the left is for static. If sorting out the correct lines do not fix the problem, I would then look into electical connections to servos and the data line to / from GPS. If all else fails, you may have to spend some time on the phone with Lucas or another person at TruTrak. They are patient and are truly experts in all things pertaining to their hardware.

post-24-0-84694200-1327692832_thumb.jpg

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Here is part of my response to Lucas at Trutrak. He's one of the good guys and I'd recommend him to anyone with these issues.

 

 

My autopilot is powered through the avionics master switch. So the engine is always started before electronics are powered up and well before the aircraft is moved. Yes, also, I see the AP OFF on the display every time. I have never engaged the autopilot until in the air. Now, personal thoughts, I'm guessing but think that the autopilot system consists of the control head, the computer cable connecting to the servo mechanism, and the links to the control surfaces. The autopilot causes the aircraft to climb and descend (and occasionally hold altitude) as well as causes the ailerons to move causing turns. So, the servo mechanism and control links to airfoils appear to work appropriately. The fact that the control head causes the servo unit to react they way it does implies that the problem is in the control head or in the connecting cable. The current control head was replaced during my last annual inspection (completed 5/19/2011) because the original unit worked fine but very weak lighted alphanumerics with dashed lines running through the letters and numbers. From that flight home on 5/19 the autopilot did not work correctly. I had to recycle the button in and out of the "GPS" mode at least 10 times in a two hour flight. It has been intermittantly erratic since that time and mostly inoperative for the last several months. Yet, your folks said the unit was "bench tested" last week. What other parts are there to cause a problem?

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