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Flying the Sonex Sport Acro

During a recent visit to Wisconsin I made a point to stop by Son-ex Aircraft to see John, Betty and Jeremy Monnett and the rest of the Sonex Team. It had been four years since my last visit to Sonex so I was anxious to get caught up with them and see the progress they’ve been making on some of their newest projects, including the new modified Sonex they call the Sport Acro. During my last visit to Sonex in 2004, I had been so impressed with the AeroVee powered Sonex, Waiex and Xenos that my father and I decided to build an AeroVee powered Sonex of our own. As of this writing it is approximately 60% complete.

I was given the opportunity to fly the Sport Acro if I would give them honest feedback on it’s handling qualities and my impressions on the modification to the ailerons to improve the roll rate for sport aerobatics. I gave them an immediate “YES.” This article is that feedback.

To get re-acquainted with the flying qualities of these aircraft and Oshkosh’s Wittman Field, Jeremy and I first took the Waiex out for a short flight. I had not flown the Waiex since I did the basic spin testing on it in 2004, so it was fun to get back into this little gem as it is a blast to fly.

The main objective of the flight with Jeremy in the Waiex (other than just getting current) was to evaluate the roll rate. Doing bank-to-bank rolls 60o to 60o takes about 2 seconds at 120MPH, so I estimate the roll rate at 55-60o degrees per second at this speed. The roll rate was slightly faster when I later flew it solo, so I estimate it at 65-70o per second at 120MPH.

We went back to Wittman field where Jeremy coached me through a standard Sonex / Waiex pattern and landing: below 100MPH (max flap speed) on down wind lower the first notch of flaps and fly 90MPH, on base fly 80MPH, turning final lower full flaps and fly 70MPH until letting the speed slow to 65MPH approaching ground effect and then throttle to idle and it just about lands itself. How simple is that?

I dropped off Jeremy and went back out west of the field for a little Waiex fun on my own, again to look at the roll rates and light acro such as lazy-8’s and wing-overs with one person on board as that would be more comparable to the Sport Acro, which is set up to fl y solo.

The Sport Acro, set up to fly solo from the center, makes for a very roomy cockpit with great visibility left, right and over the nose. The stick, in the center is approximately 3 inches longer in anticipation of the added hinge moment forces for the longer ailerons, which are approximately 16 inches longer inboard making the flaps about 16 inches shorter. I was curious how this would affect roll rate and stall speed, which was the reason for the evaluation.

I spent a few minutes getting used to the cockpit controls for the wheel brakes, flaps, trim, radio, engine and flight instruments as well as a very nice-to-have video recording system so we could provide those interested in the Sport Acro some video. I taxied out thinking about the takeoff and reminding myself that the ailerons are much longer and they may be “over sensitive” on takeoff so do not “over control.” This concern proved not to be an issue. Yes they are more responsive, but I had no tendency to over control on takeoff.

I went out west of the field and checked the roll rate of the Sport Acro, again at 120MPH in bank-to-bank rolls 60o to 60o. This time it was close to 1 second so I estimate the roll rate at this speed at 110 – 120o per second. So that means we have an increase in roll rate of approximately 60% (approximately 40o per second faster divided by 65o per second). I also ran though what I would consider a common set of proficiency acro maneuvers (loop, cloverleaf, Cuban-8, split-s, Immelmann, aileron roll and barrel roll, etc.) The mission of the “Sport Acro” is to be an entry-level acro aircraft for the Sportsman category and just a fun acro machine that is also an all around Light Sport Aircraft that can be flown as a two place with some re-arranging of the interior.

The Sport Acro has hit the mark! Workload for the pilot during acro is very low. The aircraft is very easy to fly during acro with good control harmony, which means that the forces and deflections in pitch and roll are favorable to the pilot and properly proportioned. The differential ailerons assist the pilot, as only small amounts of rudder are needed to coordinate rolls. A loop is accomplished by starting a slight dive for 140MPH then smoothly pulling it up into a 2.5 – 3g loop using approximately 300 ft. Other acro maneuvers such as an aileron roll, barrel roll, and Cuban-8 are a piece of cake and will be available to view thanks to the three camera video system. Please remember these are my first attempts at these maneuvers in this aircraft.

Stalls were also accomplished in the Sport Acro. There is no difference in stall characteristics with noticeable buffet before the stall and the speed is within a few knots of the standard model at approximately 40MPH. Returning back to the pattern at Wittman field I used the same techniques described above in the Waiex and the pattern and landing were very easy using those procedures.

Once again Sonex has found a good balance of performance, flying qualities and cost to meet the desired task and mission. The Sport Acro is a sweet little acro machine!

Roger Tanner is an Air Force Test Pilot at Edwards Air Force Base flying, among other things, missions evaluating F-16 spin recovery with asymmetrical wing ordinance and fuel loading. Roger also is a part time CFI-G at Mountain Valley airport in Tehachapi, CA.

Light Aviation Edition October 2008

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