Manned aircraft autopilot system

Hey everyone,

This might sound like a bit of a crazy idea, but that’s what we’re here for! Anyway, I’d love to build an autopilot system for my (manned) light aircraft (Zenith 601 HDS) . Here’s a link to give you an idea of what the plane looks and performs like (http://www.zenithair.com/zodiac/601-hds.html).

For those that are unfamiliar with the “Experimental” class of manned aircraft in the US; basically, if you build it you can fly it - which differs drastically from the “Certified” class of aircraft, in which each part has to undergo rigorous testing before you’re allowed to used it. So, the assumed liability for any parts being used is on the pilot in an experimental.

All that said, there are several companies that produce autopilots for the experimental class of aircraft, here are a few links to several of those:


http://www.mglavionics.com/
http://www.dynonavionics.com/

There is one company in particular (TruTrak - http://www.trutrakap.com/) that has released a different style of autopilot for light aircraft. The “Standard” setup for aircraft autopilots is to have a panel mounted control system, and two servos mounted inside of the airplane that are attached to the control surfaces via their cable/pushrods (one on the ailerons for roll and one on the elevator for pitch). These servos basically take over control of the airplane when they are engaged. The servos have to be very strong, thus heavy in this configuration.

The “Eco Autopilot” by TruTrak basically uses ’ trim tabs’ attached to each control surface (ailerons and elevators) that are controlled by large RC aircraft servos (a ton lighter than the traditional A/P servo) - there is a panel mounted control unit that can communicate with an external GPS system (like a Garmin) to follow a ground track.

In aviation, iPads are becoming more and more popular for navigation and flight planning (there are tons of apps for that…Foreflight, FlyQ, WingX…). There are also several companies that make AHRS/ADSB systems that work with these apps (Stratus, StratusX, iLevil…) Surprisingly, I haven’t found anyone capable of controlling autopilot with an iPad! Call me crazy, but I think it’s possible to do!

I’m new to the navio system (I’ve got a good amount of experience with the Reach RTK system), so I’m not sure if this is the right unit to do something like this with - so I ask you, the experts - is it possible to mimic a system like the “Eco Autopilot” by TruTrak by creating a flight plan in a flight app (Foreflight), and have my airplane follow it as I fly along using the navio as the autopilot computer and RC aircraft servos to steer the plane?

I look forward to hearing your thoughts!

Thanks!
Chad

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that’s totally crazy, irrensponsible and dangerous - i love it!
but primarily, i believe, you should invest in a parachute system that saves your life first!
well in your position i would check how big g-forces can become on your airplane and how much navio2’s sensors can handle (i’m not sure if I remember correctly 16g);
i’m not sure how vibrations on your plane occur - but i believe you would have to come up with something that does reduce vibrations on your frequency significantly;
navio(2) puts out pwm signals, you will need a device that turns pwm into fuel injection on your plane;
i found 200kg servos on aliexpress (i don’t have the slightest clue what power for rudders you would need on your zodiac ch 601 hds) - but that would be plug and play!
i’d like to hear some more about your project!

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I figured I could find some like minded people here!!

My particular airplane isn’t designed for aerobatics and probably won’t see over 4g’s, so no need to worry there…also, the “experimental” category brings with it lots of freedom to do as you please, but when a kit plane like Zenith, Vans, Sonex, etc., is built according to the factory specs they are extremely strong and safe! My particular plane has flown for 205 trouble free hours, and there are thousands just like it safely flying, so I do have confidence in the plane.

As far as the autopilot goes, having ‘auto throttle’ would be amazing, but that’s a lot of engineering and is usually only found on very expensive, bigger planes.

Typically, in a small plane like this, it’s the responsibility of the pilot to maintain airspeed, so the autopilot system would just control pitch and roll.

I have nothing to offer than I think this is very cool and if you did decide to continue, keep us updated!

It looks like there have been a few people to come up with a similar design. Here is a forum post that has a very similar design (R/C servos to power trim tabs), yet has a fundamentally different “brain” than what I’m talking about building. In the first post, “Pops” mentions his servos has a torque rating of 375 inch oz. which is a good spec to to start with. Anyway, reading that post gives me some confidence that this can be accomplished.

It seems as though the Navio unit can talk to servos pretty easily, and I can size the ‘trim tabs’ easily enough.

The part I don’t understand is how to get my iPad to talk to the Navio. Like I said, my ideal autopilot would just control roll and pitch and my GPS signal/attitude information would be coming from an external unit (Stratus 2S), and my flight plan would be coming from an app on my iPad - so i’m not sure how that information is relayed to the navio. I’m not a programmer by any means, and this whole concept is pretty new to me. The App that I use for navigation (foreflight or FlyQ) can reccommend an altitude based on wind direction/speed at different altitudes, but in no way includes this information in the ‘flight plan’ (which is no more than a straight 2D line on a map that goes from waypoint to waypoint). Is it possible that I would have to write a new app that would somehow take my flight plan from foreflight, add an altitude and relay it to the Navio? Is it easier to use a different AHRS unit/GPS reciever?

Thanks again for any input you guys have. I think all this is possible, I just don’t have the right skill set to pull off all the really hard stuff! :slight_smile:

Are you planning on using any Ardupilot? If so you can talk to ArduPilot over mavlink.

I’m not quite for sure if Ardupilot is up to what you want to do with the flight plan, maybe a ArduPilot expert can chime in.

I’m not dead set on any hardware (or software), as I am still figuring out what sort of pieces need to come together in order to make this thing work.

Admittedly, I am a “complete dummy” as to what sort of components and programming it is going to take to accomplish this.

Thanks for recommending I take a look at Ardupilot - I’ve got lots of reading to do!

the ios app is: MAV Pilot by Communis Tech
best thing would to create an wifi hotspot on the raspberry pi 3 (which is under your navio)

navio with ardupilot does provide you with accelerometer and gyro for roll and pitch; ardupilot in airplane mode can rely on a magnetometer (compass) but (i never used ardupilot in airplane) i believe ardupilot does calculate heading from gps; if you don’t have a pressurized or sealed cabin you can also use the barometer to measure height (together with gps) navio already includes a gps (2.5m accuracy at best should be enough - or not?)

i suggest trim tabs are just for small changes for rudders to “center” them according to loading of the airplane; if servos get powered - but no pwm signal, some can start to tremble up and down (imagine that happens during landing) you need servos that do not tremble upon out of range pwm signal, and if there is a trim position you couldn’t land safely, you need servos that move freely when you shut off the power to the servos;

the apps I personally use (tower for android, mission planner for windows) are very intuitive and easy to create waypoints; of course they don’t take wind speed/direction into consideration; (does foreflight take windspeed/direction for safety or efficiency into consideration? with pitot tubes or from an online source?)

Thanks for your response!

My cabin is not pressurized, so I could definitely use the on board GPS/barometer for altitude. 2.5m is more than enough accuracy for my application. In fact, I think a standard vertical tolerance for an autopilot is 25 feet. The purpose of that is so it doesn’t jerk the plane around trying to fix on an exact altitude. I think that also plays into the use of the ‘trim tabs’ - Basically I would want them to be in a neutral position when they aren’t engaged (I will be hand flying the take off, climb out to about 1,500’, as well as the landing procedures - so autopilot will not be engaged at this time). They would be sized such that in the neutral position, they would have a very small effect on the handling characteristics of the plane.

My goal of the autopilot (which is different from some others) is to reduce pilot load while in cruise - especially when traversing complicated airspace where controllers are barking orders like mad. I guess, to that end, if I just had lateral guidance and could hold an altitude that would be just fine with me!

When doing a flight plan in ForeFlight, wind speed and direction is reported from an online type source.

What’s really nice about an aviation app (vs a drone mission planner) is to have an “aeronautical sectional chart” as the basemap rather than a google maps photo. Also, they have an airport database that shows airports and other navaids as waypoints, so you can type in the code of an airport or navaid and it will show up on the map. Anyway, there’s lots of reasons to use one of these apps vs a drone mission planner.

mmmh;
should we introduce a deadman’s switch?

Seriously, any updates?

I would like updates too. I saw a similar request like this a while ago on ardupilot forms and it was a blood bath.

No updates just yet, but I do plan on pursuing this eventually. I think the experimental aircraft community would love a system like this.

I think for safety, it would be important to have the tabs return to neutral in the event of a failure. That said, in the case of a failure while stuck at full deflection, the trim tabs would be sized such that they could be overridden by manual control inputs on the stick and the plane could be flown safely. Autopilots are always wired on their own fused and switched circuit, so if anything were to go wrong, the pilot can shut it off (traditional autopilots usually have shear pins that can be broken by heavy control inputs in the case of a servo failure to regain control over the aircraft).

337, I saw that forum as well, that’s why I figured I would give this board a go :wink:

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what if your servos/servoarm etc fail/break and get loose? it could rattle from side to side until it rips apart and potentially hit something else?
also you might want to invest in some good servos and a fire extinguisher if a servo goes on fire and a place where you can reach the servos; (that’s probably aircraft regulation anyway to have a fire extinguisher);

and very important: pics when you think it’s time for pics!

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Your Idea of using servos commanding tabs is sensible. Ordinary servos actuate the Control cables directly and depend on clutches to disengage. Your solution is in principle safer If tabs are properly sized so that regardless of their deflection you can override them. As for the hardware, I would use Arduíno, perhaps more than one unit, and use components such as IMU, pressure sensors and GPS. But Bear in mind that dynamic systems like this are not that simple to program. Especially to ensure attitude stability. Filters like the so called Kalman Filter may have to be embedded in the software.