I owned a Cessna 150 with a Lycoming 320 engine before building the Zenair. I sold the Cessna to be able to buy the engine, instruments and rest of the aircraft components. There is no comparison for this airplane's performance vs the Cessna 150/150. Everything is so different. One thing to note is that I was not getting the maximum horsepower from the engine. During the installation I missed the instructions for connecting the Carb Vent Tubes. When I added them during my first Condition Inspection ("Annual Inspection") in November 2005 I found them and picked up 15 knots right away.
Zenair says carb heat is not required for the 912S when using the Zenair cowling; since the air chamber had inlets for carb heat I connected it anyway. I have never needed to use it.
I am flying the airplane without wheel pants so cruise speeds are lower than ideal by about 5 kts indicated.
My airplane is equipped with Micro Aerodynamics vortex generators kit for experimental aircraft, therefore, its low-speed handling will be greatly different than that of the standard 601 HDS aircraft.
N905KM handles nicely during low-speed taxi. Steering is immediate via the hard-tied rudder pedals. The turn radius can be rather tight using differential braking. I can easily turn the aircraft around in less than a 15-foot radius (wheels only, not counting the wingtip). Once I got used to the direct-linked "Piper-style" steering, ground control is easy to master. The Cessna 150's nose gear was not directly connected, therefore, there was a delay in ground steering. The 601 pilot needs to be aware in a crosswind landing that the aircraft might swerve upon contacting the ground if holding cross-controlled aileron and rudder. This is easily mastered if the pilot straightens the pedals just before the nosewheel contacts the ground.
At speeds higher than 40 kts the nosewheel shimmies an objectionable amount. This is not an issue as the elevator is powerful enough at this speed to hold the nosewheel off of the ground.
N905KM is equipped with brakes on both sides. The brakes are adequate to quickly stop the airplane but will not hold the airplane during engine run-up. Rotax recommends checking the magnetos at 4,000 RPM; at light loadings the airplane can barely be kept in place at 3,600 RPM.
N905KM doesn't have a great deal of aileron control at low taxi speed. When lightly loaded in a strong cross wind it can get pushed sideways (tire skittering).
N905KM's elevator isn't very effective at low speeds. During transition from taxi to takeoff speed the elevator appears to be non-existant, then suddenly "comes alive" somewhere below the airspeed indicator's minimum 40 kts indication. Lightly loaded, N905KM will rotate very quickly, and the tail can contact the runway without immediate control correction. This is not a dangerous problem but one that must be mastered. If the pilot keeps the nosewheel on the runway until about 40 kts then rotation is more predictable.
At very light loadings (one pilot, no baggage, low fuel load) N905KM will fly in ground effect at unindicated airspeeds (the A/I needle doesn't reach the numbers). Aileron control is minimal at best. At light loads and no wind the airplane will accellerate from a stop to rotation in less than 3 seconds and fly in ground effect after a couple hundred feet ground roll.
At heavier loads almost to gross weight N905KM will rotate and fly in ground effect at about 40 kts indicated. It will accellerate quickly in ground effect and fly out a speed comfortably above stall within 2-3 additional seconds. The airplane will fly in ground effect at heavier loads after about 500 feet of ground roll.
Once the aircraft has reached sufficient air speed the best climb speed is at 70 kts indicated. Let the speed increase or slip by only 5 kts then the rate of climb decreases by at least 300 feet per minute.
Once airspeed is 60 kts indicated or more the ailerons, rudder and elevator become extremely effective. During most turns up to about 45 degree bank angle the rudder is not required (the ball in the electric turn coordinator is less than one ball diameter out of the lines). At steeper turns a little rudder correction is required.
Aileron and elevator controls seem to be fairly balanced. Very little actual movement of the stick is required to "point" the nose where the pilot wants. This makes the airplane a bit "darty," but it's easy to control by anchoring the elbow on the arm rest.
The airplane rolls quite quickly and doesn't appear to overshoot the roll angle. It requires positive application of aileron to roll back to level flight. I have not attempted bank angles greater than 60 degrees.
The airplane is extremely sensitive to left/right balance. With an empty weight of half that of a Cessna 150, shorter wingspan and wider cabin, the airplane will tend to roll towards the side of a single pilot. In a level and trimmed flight the airplane can be rolled by the pilot leaning towards either side of the aircraft.
The airplane is equipped with an electric aileron trim tab. With a balanced load of fuel and one pilot the trim must be set almost fully wing down on the side opposite of the pilot to maintain hands-off level flight. As the fuel burns off the trim must be readjusted every 10 minutes or so. The airplane is easily controllable in a fully untrimmed flight.
If the pilot prefers neutral aileron trim then the airplane may be leveled for single-pilot use with ballast in the opposite wing baggage locker. A ballast of about one-seventh of the pilot's weight, secured to the outer rib of the baggage locker, is about right.
The airplane is equipped with an electric elevator trim. For 95% of my flying to date I have set it for hands-off level flight then don't touch it for the remainder of the flight. It is fully controllable throughout the flight in any trim condition. (I used to stay on the 150's elevator trim during the entire flight. The 150 took too much yoke pressure to be comfortable during long climb outs or descents to fly untrimmed, and was too risky to fly at very low airspeeds untrimmed as it would either drop the nose or raise the nose and stall).
I am currently getting about 95 kts indicated cruise speed with a tach reading of 4800 RPM at about 2,000 MSL. In this speed range the indicated cruise speed is very close to actual speed, as measured by GPS tests. 5000 RPM yields about 100 kts indicated with a fuel burn of about 4.5 gallons per hour. 5,400 RPM gives me about 105 kts (121.5 MPH).
I have performed stall tests both with light loading and with the aircraft ballasted to nearly its certificated gross weight of 1200 lbs. At light loading the airplane will fly at less than 40 kts indicated. Aileron control is almost non-existant but level flight can be maintained with the airspeed indicator needle oscillating irregularly between 0 and 40 kts. At nearly gross weight the airplane can maintain level flight at 40 kts indicated. Aileron control is almost non-existant at these speeds. Elevator control is sufficient. Letting speeds dip below 40 kts indicated the airplane will quickly lose altitude but will not drop the nose or a wing. Airspeed can be regained with application of power and/or forward stick. (I was able to fly my 150 fully loaded at about 49 kts indicated. It, too, had very sloppy controls at its lowest airspeed but would eventually stall with a drop of the nose and possibly a wing, too.)
The airplane will lose airspeed quickly in a steep turn without application of power. I have flown it at bank angles in excess of 45 degrees at speeds of less than 60 kts indicated with constant altitude and full control (no hint of stall).
Power off, the airplane has a fairly steep glide angle. I have used 70 kts indicated as best glide speed.
I have flown the airplane to 7,000 MSL and have calculated an absolute ceiling of about 10,700 feet. This test was flown before the Carb Vent Tubes were connected. More cruise and climbs tests will probably give me a higher absolute ceiling.
At a pattern altitude of 800 feet AGL I generally cut the power to 3600 RPM about one-half mile abreast of the runway end. From there I can make a short, rounded "rectangular" pattern directly to the runway with no additional power. If any additional distance in the pattern is needed the power must be added. The airplane will not glide further at a different airspeed; it will only sink faster.
I normally come over the fence at about 60 kts indicated and float in ground effect until the airplane is too slow to fly any more. It will contact the ground on its own at less than 40 kts indicated, resulting in a greaser landing. Faster speeds in this airplane will result in a rather pronounced bounce or excessive float in ground effect. Slower airspeeds will result in the airplane dropping out of the air. I keep the nose wheel off the runway as long as possible to avoid nosewheel shimmy.
Once the airplane contacts the ground it can generally be stopped in a few hundred feet. Landings with gentle braking to a full stop typically take less than 1,000 feet from the start of the runway.
I certificated this airplane at 1,200 lbs gross, as per designer recommendations. It is stressed to 6 Gs positive and negative (absolute). Although capable of moderate aerobatics, I have not flown any to date. (Mr. Heintz says it was not designed or intended for aerobatics and I respect that.)
For very cold weather the heater installation is inadequate. I am currently getting too much draft air through the nosewheel steering arm slots and along the canopy hinge. These can be corrected with better boots and/or weatherstripping. The large, tinted bubble canopy does little to protect the occupants from the sun. The pilot should wear a hat for long flights (I've experienced mild sunburn from the cockpit). Ventilation in flight is adequate (at least for April weather) through the two NACA air ducts on the sides of the fuselage. Ventilation on the ground is non-existant. For prolonged ground operation I recommend that the pilot leave the canopy open but secured until ready to depart.
The airplane is extremely maneuverable and fully controllable throughout its flight envelope. The visibility is outstanding. I am very surprised by its low speed capabilities, as it will fly much slower than the vortex generator manufacturer expected. Its cruise speed is lower than promised by the designer, though. There are at least two factors under my control that are contributing to the lower than expected cruise speed (vortex generators, no wheel pants, and the canopy is installed higher than designed for more headroom). I think that I can get 5-10 more knots with some aerodynamic cleanup, but if I get to 115 kts (132 MPH) it is still a bit slower than the advertised 140 MPH cruise speed.
Overall I am very happy with the airplane. Like most homebuilts it is a work-in-progress. After 107 enjoyable hours of flying I am now working on customized touches. It has no bad habits and is comfortable for flights of a couple of hours. I wish I had enough money to build another just like it; I like it that much. But if I never get to build another airplane I will be happy with this one for a very long time.
Page Created April 7, 2005      Last Updated December 1, 2005
Copyright © 2005 Michael Mossman. All rights reserved.