StolSpeed Aerodynamics - Performance Enhancement for Light Aircraft

Because I have a private airstrip ( indeed it´s a little patch of green farmland) length 150 m , I could really feel the difference of "no-vortex" and "vortexed wing". I could get the the take-off distance down about 25 m. The climb-rate didn´t change, but the climbspeed is much better now.

Also the max speed is now in the average about 15 km/h more than before, at the same fuel consumption.

The datas:

Sonex aircraft with 90 hp Subaru EA 81 custom made installation

cruise before 185 km/h now 200 km/h

stall speed 92 km/h 80 km/h

Take off distance 300 m 275 m

TO distance in my field 140 m 110 m

landing distance

on my field (Uphill) 100 m 70 m

Climbrate is 650 ft/min

Result: Absolutely positive!

Klaus, Germany

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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)

NO VG

HALF SPAN VG

FULL SPAN VG

Stall speed reduced

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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Fisher Dakota Hawk

Second test of plane with entire wing covered with Feathers.

All airspeeds unless noted as GPS are direct readings off the airspeed indicator. They are not corrected for angle of attack or or other possible calibration errors.

During first test I found it not possible to get a full stall at 1000 rpm and slow deceleration with full back stick. Although airspeed finally stabilized at 34mph indicated on Air Speed indicator.

Before second test I measured full up elevator to be 18.9 degrees. The maximum design up limit is 25 degrees. I increased elevator up throw to 22.9 degrees.

The next flight test I found the following:

Slow deceleration with engine set at 1000 rpm I still could not get enough angle of attack for a full stall but did get more. Finally speed stabilized at 31.5 mph ! Yes 31.5mph! At this speed there was still aileron control but it was diminished to about the same as it was prior to Vgs at 40 mph.

I let the airspeed increase to 35mph and found very good aileron response. Rolls from left to right to 30 degrees either way while keeping the ball centered were very positive. Quick stick movements of full aileron left to right without waiting for a bank to increase more than about 5 degrees showed definite and positive aileron response. This latest was a good demonstration of aileron control one can expect when at a three point landing is made in strong and turbulent cross winds are encountered.

Prior to feathers Vgs at 35 mph there would be very minimal aileron authority.

Now at 35mph there is strong aileron authority.

27 miles per hour!!!

Next test was to set rpms at 1550 rpm and continue with slow deceleration to minimum airspeed or stall which ever occurs first.

Very surprisingly the airspeed bottomed at 27 mph at full back stick. The rate of climb meter showed a steady 200 fpm down but the plane would not stall. Keeping the ball centered continue controlled flight. There was still some aileron control remaining, but no longer strong. Using coordinated rudder and aileron I was still able to make turns left and right to any heading I wished.

On the upper end of speed at cruise I wished to determine if increased drag there would be a penalty. Using routine 4 way gps testing techniques the speed at 2350 rpm (my cross country cruise rpm) at 4,000 msl and 43 degrees F the following:

102 average mph. This very closely matched the speeds of the first tests after vg’s. Where the speed was 102.5 mph. It therefore looks like a drag penalty of 1.5 to 2 mph at cruise speeds.

On the taxi strip coming back in to the hangar area I was taxiiing at about 10 mph into a 10 mph wind. The airspeed indicator was bouncing between 20 and 22mph. I decided to look for the aileron effect at this speed. Oscillating full left and full right with the stick the wing tips could be rocked an estimated 4 inches up and down (total excursion of 8 to 12 inches, the more significant when it is understood that my gear is quite stiff and wide. It has the Fisher spring kit. No doubt this is added evidence that there is considerable force available to the pilot to counter wing lift situation (wing lifts in a cross winds, is a major reason for experienced tail dragger pilots to still have a loss of control on landings. In that case a crosswind gust can lift a wing and full aileron will not be enough force to bring it down. If this continues for just a very short time loss of directional control is almost sure to follow.

I had in previous times worked this same exercise and could just barely see a response at the wing tip.

................

Today I flew in calm weather shooting several takeoffs and landings most on asphalt and the last on grass.

While at altitude I tried a near full power (2400 rpm ) stall straight ahead. Slow decelleration until stall, indicated airspeed 24mph and plane at a vertical pitch attitude so extreme as to be disconcerting. I felt it was near 60 degrees. The break when it finally came was very sharp, ( the bottom just dropped out). It did drop straight ahead.

I have been flying for a long time and and a cfi for a good part of that time. I was not greatly surprised by the quite dramatic downward pitch as I expected it, however it was the most complete and full break I have ever experienced. The Mfgr of Feathers vgs told me that when a full stall occurs with vgs it will result in a "sudden break". He is correct.

I guess this is not surprising as vgs keep the air attached to the entire wing more than is ever possible with out them. So when finally the break occurs it is complete and total across the entire wing.

The recovery was without incident as the pitch down was straight ahead. I did not observe the altitude loss. In due time I will perform it again with more care to watch rate of climb or loss just prior to stall break or the altitude loss.

Later I practiced stall approaches at 1500 rpm and it again repeated to be 27 mph indicated air speed. and 1000 rpm and again it repeated to be 31.5 rpm. In these last two I full back stick with constant rpm would not get a stall break.

Tom Marsom, Wisconsin, USA. (A very thorough test pilot!)

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Pazmany

Did the Pazmany (PL4a) tests last week. The Pazmany had the stall drop only 1 or 2 knots (about as expected) but the stall behaviour was considerably improved. It no longer drops a wing (20 degrees or so), and can be held at the stall with pretty reasonable aileron control remaining. With my short strip, every little bit helps.....

Roger, South Australia