I have a 1980 Sundowner and was considering some type of autopilot. I know there are different levels of what they control and the prices appear to be all over the map. What is the least expensive type and what does it control, who makes it etc. I can start from there. I am having a difficult time understanding the differences and equipment needed. Is there somewhere I can go and get information for dummies on autopilots?
Thanking you in advance, Al
Brittain made the autopilots and still rebuild and ship them and/or install them. I talked to them last month and was quoted a price of $1573.60 for the wing leveler, uninstalled. This is their e-mail to me.
“The Brittain BSS (wingleveler), refurbished with rudder servos, runs $1573.60. Installation is available for an additional labor charge, on our ramp here in Oklahoma. The kit price does include complete installation manuals as well as Flight Manual Supplements and the STC.”
Here is their web address: http://www.brittainautopilots.com/
Good Luck with your search, and please keep me posted as to what you find. I am also interested in a autopilot.
Brian Foote
EDITOR’s NOTE; BASIC AUTOPILOT PRIMER:
With respect to the class of planes in our group, here is the basic list of autopilot capabilities, in approximate order of cost and relative necessity:
1. Wing leveler
2. Heading tracking (heading bug).
3. Heading tracking plus radio coupler-selector, for course tracking.
4. Add altitude hold.
5. Add altitude hold with altitude pre-select.
There are some vagaries in how the various APs work in real life, as well as what they use for course guidance, and how they detect and correct for any course deviation.
A wing leveler is exactly what it says it is. If activated, it keeps the wings level. It does not normally detect and correct for any variation from a compass heading, or from a desired course line (ground track). It is of somewhat limited usefulness, except when the pilot is facing a heavy workload, or during general recreational flying.
Heading tracking adds the capability to maintain a set direction, usually as selected by a heading bug on what is often referred to as an “autopilot directional gyro”. This is very useful for travel, but the pilot must make corrections in the heading for any wind drift that is encountered, along with the usual DG corrections for gradual precession.
Heading tracking that includes a radio coupler-selector adds a major capability to an AP. It means that a primary nav radio can be selected as a source of course deviation information. This brings several new features. Wind correction is automatic. Approaches can usually be coupled. Course intercepts can usually be automatic, within certain limitations that vary by brand and model. If the primary radio (usually #1) is a Garmin GNS430, and is it set for course sensitivity of 0.3 NM, the AP will hold the desired ground track within a variation of 20-30 feet when in GPS mode; vastly more accurate than any VOR tracking. Yet it allows selection of VOR mode (on the Garmin), for tracking using a VOR, or for coupled approaches.
Depending on the brand, and the sensing instruments, the above capabilities are termed “single-axis” or “two axis” APs (roll and yaw). This is a bit misleading, as most of the low-end models don’t include yaw-damping; something of value on a plane like the Model 35 Bonanza. Some models use a yaw control servo for wing leveling; most use an aileron servo for course control.
There is a clear distinction in course control capability between traditional course sensing and correction, versus the newer “GPSS” capability (GPS Steering). Traditional APs can’t tell exactly where they are relative to a course change waypoint, until they cross over it. That means that either the pilot needs to anticipate any required turn, and “lead the turn” with the next heading, or else the plane will fly past each waypoint before the next one is activated (or dialed in). GPSS capability means that the AP uses the “smarts” in the GPS unit that tells how far the plane is from the next waypoint, often coupled with knowing the plane’s ground speed. This allows the GPSS logic to anticipate the turn, and enables the AP to smoothly roll the plane onto the next course leg, without pilot intervention. It requires GPS capability that is either in the primary nav radio, or which is integrated in the AP unit itself.
The “third axis” is usually meant to be altitude control. These units use independent servos for elevator/stabilator control, and usually contain their own internal altitude-sensing device to detect altitude deviations. The basic type simply seeks to hold the current altitude where it is engaged. The more expensive and more complex type allows “preselection” of the desired altitude, whether higher or lower. This feature can be integrated in the primary autopilot control unit, or it can be an independently-installed unit.
Altitude hold and preselect is handy on long cross-country flight, but is not really needed in our planes; it’s a “nice to have” capability. Our planes are normally quite altitude-stable when properly trimmed, in reasonably smooth air. It takes them a little while to deviate, which gives the pilot time to detect and correct altitude changes. They don’t climb fast enough to make it too easy to “bust” an assigned altitude. On the other hand, altitude hold in the simple forms in our planes can be dangerous, if not carefully monitored. If the plane isn’t kept in good trim, and the AP is holding a large corrective pitch control force, you can get banged into the seat or the ceiling when it is disconnected. If you are experiencing a gradual and undetected loss of power, and you don’t see the declining airspeed, the AP can hold altitude right into a stall. Many people have been killed by APs that they did not fully understand, and failed to use properly (or failed to disconnect in time).
There are large variations in AP designs, capabilities, and costs. This overview is intended to just give you a basic understanding of what to consider and investigate when you are considering an installation or upgrade. In the price range we all tend to be operating in, you are usually better off to buy a plane that already has one, if you want one. On the other hand, if you have your air-baby TLC’d to death already, and a decent AP would be the icing on the cake, by all means take a look at what is out there. Right now Brittain and STEC seem to be the primary players in our price range.
Please let me know of any comments or corrections in this write-up.