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Home>Aircraft Using Stolspeed Vortex Generators>Allegro

 

Allegro 2000

 

First test flight with Stolspeed VGs.

 
3 flights, total time about 2.5 hrs flown with instructor Michael Peare
Density alt 2,600'
CG close to forward limit
Weight 490 KG
Pictures and info for VGs at www.stolspeed.com
 
 
Test 1 - VGs half span
Test 2 - VGs full span
Test 3  - VGs full span but leave gap of 80cms at wing root
 

 

POWER OFF

 

POWER ON

 

3000 RPM

 

(Flap setting)

 

0

 

15

 

48

 

0

 

15

 

48

 

 

 

 

 

 

 

 

NO VG

 

45

 

40

 

36

 

44

 

38

 

35

 

HALF SPAN VG

 

43

 

36

 

36

 

43

 

37

 

34

 

FULL SPAN VG

 

41

 

36

34

 

38

 

36

 

34

 

 

 

 

 

 

 

 

Stall speed reduced

 

4

 

4

2

 

6

 

2

 

1

 

       Airspeeds in knots – Dynon and ASI both calibrated

 

 
No VGs
Aircraft breaks and drops right wing. Significant wing drop with power on.
Little buffet just before stall. Ailerons ineffective close to stall. Needs some rudder to correct wing drop.
Ailerons a little heavy.
 
Test 1 - VGs half span and VGs on vertical stabiliser
Ailerons lighter, more effective.
A lot of buffet warning
Power off - no break, no wing drop. Stick full back, aircraft nose high and buffets
Power on - mild wing drop, quick recovery.
Can be rolled 30 left 30 right a few knots before stall. Stable.
Ailerons can be used to roll level after stall.
Can fly 40 degree banked turn few knots before stall. Aircraft buffets and purpoises but does not break.
Small reduction stall speed except power off reduced 4 kts @ half flap
 
Test 2 - VGs full span
Ailerons same as test 1.
Reduced buffet
Power off - mild wing drop, quick recovery. At zero flap, no break, descends 500'/min
Power on - break and mild wing drop, quick recovery
Significant reduction in clean stall speed, power on/off.
Aircraft can be trimmed to fly at 38 knots full flap with very high nose angle. Stable.
 
 
Test 3 - removed VGs at the wing root (approx span of the elevator) to try to get the strong buffet in test 1 with half span VGs. Made no difference.
 
Notes.
Factory stall warning gave good warning under all tests. For example power off, full flap the stall warn sounds @ 42, buffet @ 37 and stall 34
Right wing drop even from left turn with left rudder 34 kts 3,800 RPM
Increasing RPM to 4,000 full flap, stall speed same, 34 kts, wing drop not significantly worse with more power (very different to standard config with no VGs)
Stall speeds in POH say 43 - 39 - 35 kts
An interesting test might be to fit the VGs closer spaced over 75% span to try to combine the low stall speeds of full span but large buffet and reduced wing drop of half span.
 
 
Conclusion
The VGs on the tail did not seem to give a noticeable difference in handling.
Results broadly similar to many aircraft i.e. large difference in clean stall speed, less so in approach configuration.
Half VGs gave the best handling but a small reduction in stall
Full VGs gave good reduction of stall speed but less buffet and more wing drop than half span
The Allegro has powerful 48 degree flaps. The inboard span stalls long before the outboard and the VGs cannot help much.
Big difference in aileron response. Much nicer to fly. Although Allegro has 11m wingspan, it feels light in roll.
Surprisingly, removing the VGs close to the wing root did not bring back the buffet that was present with half span VGs
These VGs were a simple and inexpensive way to improve safety and handling
 
Regards
 

Paul

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