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Zenith 601 HD

I’ve owned our Zodiac/Zenith 601 UL TD for three and a half years and I should have installed VGs four years ago. The plane weighs 550 lb empty but always flew nose high, not anymore. I installed the VGs as per your instructions on the wings and also added two on each side facing slightly downward about two inches above the wing near the leading edge, plus one where the fuselage curves inward. I also placed 14 VGs on top of the canopy to help keep the airflow attached and prevent turbulence.

A 10 mph drop in stall speed is a huge improvement. Now every landing is tailwheel first and the plane flies like it is on rails. Thanks for a great product.
Ron, British Columbia, Canada 

Installing Stolspeed VGs on a 601XL

Wing Placement:

  • Measure from a vertical at the leading edge of the wing when the aircraft is at flying attitude.

  • At the wing root, mark a point 110 mm back from that vertical.

  • At the wing tip, mark a point 85 mm back from that vertical.

  • Run a string line between these points.

  • Set the VGs with their front tips along the line.

  • Start at each wing tip with a spacing of 60 mm for the first 15 VGs, then use 90 mm spacing for the rest.

Horizontal Stabilizer:

  • Place the VGs on the underside with their front tips 100 mm in front of the hinge line.

  • Space the VGs at 30 mm.

Installing Stolspeed VGs on the 601HD (UL) Wing

  • Wing placement
    Position the front tips of the VGs along a line 310 mm in front of the main rivet line on top of the spar. From the wingtip: first 15 VGs at 60 mm spacing, then the rest at 90 mm spacing.

  • Horizontal stabilizer
    Place VGs on the underside, 100 mm in front of the gap between the stabilizer and elevator. Spacing: 30 mm.

Positioning the Stolspeed VG's on the 601HDS

On the center wing:
Place the front tips of the VG's 310 mm in front of the main rivet line on top of the spar.

On the tapered portion of the wing:
Start at 310 mm at the join to the center section and go to 188 mm at the wingtip.

Spacing for the main wing:

  • 60 mm for the first 15 VG's in from each wingtip

  • Then 90 mm spacing for the remainder

Horizontal stabilizer:
Place VG's 100 mm in front of the gap between the stab and the elevator.
Spacing for the horizontal stab is 30 mm.

Results

Stalls: Much safer now. Before, the 601 would abruptly pull leftward. Now it behaves normally
Landings: Require about 10 km/h less speed than before
Takeoff: With two people on board, 60 km/h (35 knots) is now possible
Climb: At 100 km/h (55 knots), climb rate is 1200 ft/min in calm air
Cruise: Level flight is easier with less drag and lower fuel consumption

We are very pleased with these VGs. The improvement in safety alone makes them worth it.

Catherine & Daniel, France

Zenity 601 HDS

I have a new airplane and I am absolutely impressed and surprised by the results. I never expected such improvements!

The VGs are a big advantage for both safety and operation. I demonstrated my airplane to 601 flyers and to the German Zodiac dealer. My test results with photos will be shared with experimental builders in Switzerland, and later in Germany and England. I also hope they will appear on the ZENAIR homepage. Everyone is impressed and plans to install your VGs.

Installation

  • Wings: 38 VGs on each wing

  • Elevators (lower side): 33 VGs on each side

  • Total: 142 VGs installed according to instructions

Take-off:

  • Lift-off speed: 40 kt (before above 50 kt)

  • From high-altitude airport Samedan LSZS (5600 ft, OAT 15°C) with 2 persons and 72 L fuel: lift-off speed was 42 kt

  • Take-off distance with 2 persons and 50 L fuel: ~130 m (more than 20% reduction)

Climb:

  • Rate of climb is much better across all speed ranges

Cruise:

  • Maximum power cruise speed remains the same (rarely used)

  • Typical cruise power (12–15 L/h) shows an increase of 2–3 kt at the same power

  • Nose is 3° lower, reducing drag

  • Stall strings (“stallfäden”) installed on the wing confirm airflow improvements; similar tests planned for 601 HDS without VGs

Stall:

  • Stall speed with max power: 35 kt (high angle of attack)

  • Stall speed with power off: 40 kt (very comfortable)

Maneuverability:

  • 360° turn at 58 kt IAS in only 15 seconds (circle diameter <150 m)

  • Flight characteristics at high altitude up to 13,500 ft improved significantly

  • Approach speed: 55 kt (before 65 kt)

  • Touchdown speed: below 50 kt, limited by tail contact

Flight controls:

  • Elevator and other controls now feel much more comfortable

  • Safety margin improved across the entire flight envelope

Installing VGs is the best modification I have ever made, even for a small investment. The only mistake was not installing them 800 flight hours earlier.

HB-YKV Viktor