Longitudinal Stability of the Sonex Line

[GWMotley]

Just a quick poll of those who are flying the Sonex line of aircraft. Hope you will play. ;)

[radfordc]

My plane will not recover to level flight by itself. If you trim the plane as well as you can so that no force is required on the stick for level flight, and if you then take your hand off the stick the plane will eventually enter either a climb or dive. If you don't do anything the plane won't recover to level flight...it will just keeping pitching away from level.

[N111YX]

Mine stays where last put. I have always heard that's how Pete and John designed it.

[MichaelFarley56]

Same here. Regardless of airspeed, once the plane is trimmed it stays right where it's pointed.

[GWMotley]

So far most us seem to agree that stability is neutral at best. While it does make it nimble it is also a handful for longer flights. Thus, how many of you guys would opt to install an auto pilot?

[radfordc]

So far most us seem to agree that stability is neutral at best. While it does make it nimble it is also a handful for longer flights. Thus, how many of you guys would opt to install an auto pilot?

Not me. The plane isn't tiring to fly...it just needs attention. My buddy Bob installed a wing leveler when he built the plane. He never used it and finally took it out and sold it.

[MichaelFarley56]

This is just my opinion but I don't think I'll be messing with an autopilot for a few reasons...
1. Added weight and cost.
2. I won't be doing a whole bunch of really long distance flights. For reasons already stated above, I feel my plane is best suited for a one hour, local, fun flight rather than a long distance XC cruiser.
3. Once trimmed out, the plane is still plenty comfortable and really easy to hold heading and altitude. I've never had any issues even if I'm tuning a radio, looking at a map, or writing down information. Just point the nose on the horizon and it stays there!!

Best of luck either way!! :)

[Andy Walker]

I'm curious who voted "negative dynamic stability." If I'm remembering my aerodynamics correctly, that means that if you put the aircraft in an oscillation state (say, but 'flicking' the stick back and then releasing it), it will continue the oscillation (in this example, pitching first up, then down), in ever increasing amplitude, until actively corrected or until the airframe can no longer handle the forces acting on it.

This is the worst possible handling trait for an aircraft, and is very dangerous. I certainly have never seen this kind of behavior from a Sonex/Waiex/Xenos. I have always heard of the Sonex described as having neutral stability on all axes, and in fact recall John Monnett stating that is how the airplane is designed to behave.

Am I wrong or have my definitions confused?

[chris]

Andy I believe that you are correct. Negative dynamic stability means oscillations increase after the equilibrium is disturbed.

I also noticed that neutral dynamic stability is missing from the poll.

Static stability is the initial tendency after equilibrium is disturbed and dynamic stability is the overall tendency. That makes them independent of one another so I believe we should be able to pick one of each in the poll and neutral dynamic should be added as an option.

Edit:
I changed the poll to go along with my thoughts in this post. This is the first poll I've had to edit so I wasn't aware that editing it would erase the existing votes. Sorry. If I am off about needing two votes somebody let me know.

[N111YX]

I have flown one aircraft that exhibited negative longitudinal stability and that was a Titan Tornado II. When the pitch was changed (be it pilot or turbulence) the nose would accelerate to the displaced direction. Talk about a labor-intensive cross country machine... :? Attempting to unfold a chart could cause the pilot to float out of his seat or a pitch up to aerobatic attitudes in a matter of seconds. On the same note, the Challenger II design is bad in directional stability. If it yaws, it stays crooked! The worst flying fixed wing that I have flow is a Mitchell Wing A-10. Conventional inputs into the 3-Axis machine brought about unconventional results. That and the owner killed himself in it two weeks later... :cry:

The Sonex handling is in a league way above many designs in my opinion...