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Sonex Sport Acro

Flying the Sonex Sport Acro
August 25, 2008: Tested and Written by Roger Tanner

See the Sport Acro in Action!

Watch the video below to see Roger Tanner's initial flight evaluation of the Sonex Sport Acro, along with footage of Sonex Founder and President John Monnett flying the Sport Acro with air show smoke. More videos showing more Sport Acro manuevers will be coming soon!



During a recent visit to Wisconsin for a family wedding near Oshkosh I made a point to stop by Sonex 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 the electric aircraft motor, the e-flight initiative as well as 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.  By the way, the Y-tail of the Waiex seems to have very normal spin and recovery characteristics.  One and two turn spins to the left and right recovered in less than a turn.

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 60° to 60° takes about 2 seconds at 120MPH, so I estimate the roll rate at 55-60° degrees per second at this speed.  Due to the differential aileron it takes only small amounts of rudder to coordinate the roll.

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?

Sport Acro center seating single-place cockpit.

John Monnett familiarizes test pilot Roger Tanner with the Sport Acro's cockpit.

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 fly solo.  The roll rate was slightly faster so I estimate it at 65-70° per second at 120MPH.  Back to Wittman field for a few patterns and landings using the same procedures as stated above and I was ready to fly the Sport Acro.

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.  For reference (from my set of plans) the standard ailerons on the Sonex / Waiex are approximately 39 inches long and the flaps are approximately 72 inches long.  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 set up by Mark Schaible 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 60° to 60°.  This time it was close to 1 second so I estimate the roll rate at this speed at 110 – 120° per second.  So that means we have an increase in roll rate of approximately 60% (approximately 40° per second faster divided by 65° 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. 

Thanks to Jeremy, John and Mark for the opportunity to fly the Sport Acro.  Once again you have 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!

A personal note about the author and this test:  Roger Tanner is a full time test pilot and a part time CFI-G at Mountain Valley airport where he enjoys sharing the joy of soaring with others. Roger originally performed Xenos Spin Testing for Sonex Aircraft, LLC in 2004, along with some Spin Testing of the Waiex. Roger and his father Perry are now building Sonex SN 1063. Roger has requested and received no payment for his help with this testing. See a report about a recent flight test project Roger Tanner conducted for the Air Force.

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