Bearhawk STOL mods

[500AGL]

I've not installed VG's nor test flown various settings on the Ribblett airfoil of the Bearhawk. But regarding VG's in general, Jerry Burr is pretty much the authority on them, having spent likely hundreds of hours testing, learning and understanding what worked the best. I believe the graph below from him was on a SuperCub wing. The most common installation error in my opinion is simply that they are mounted too far back on the chord. The idea is to keep the airflow attached at high(er) AOA, and as his graph shows, it's almost impossible to put them too close the leading edge.

[Gerd Mannsperger]

Yes that was my information as well

[FastLaneAK]

92 VG's on leading edge and 58 VG's on leading edge of flap. Slotted flaps they work fine and help alot.

[FastLaneAK]

I have a Lake Buccaneer. The VG’s are on both the leading edge and the huge slotted flaps as per STC. I’m not sure who said that they don’t work on both as they do. Also used on Shane Madison’s cub slotted flap hangers with great success.

[Cguy]

VGs on the leading edge of semi fowler flaps work extremely well but you can do either that or the VGs on the leading edge not both.

The leading edge VGs give the benefit of better control while the VGs on the flaps just lower stall speed with a reduction in slow flight control.

The reduction in stall speed is very close to the same in both instances, if in doubt go for improved controllability.

I believe the Cessna Caravan comes with VGs on the flaps stock.

That is also what MicroAeroDynamics told me. A long time, 20 years, user of their VG's on two different Rans S-7's, on the wings and the bottom of the horizontal stab., I had an idea to use them to "enhance" my flaps, and was told in no uncertain terms that it was not a good idea, and was not needed as the LE VG's were already "getting the job done."

[svyolo]

Putting the flaps down with powerful flaps (fowler or semi-fowler) also causes a big change in center of pressure - i.e. big trim change. Doing it at a slower speed makes it a lot less unpleasant for the passengers.

[Gerd Mannsperger]

As long as there are known upgrades and fixes for known problems you are good togo.
Fatigue is a tough target to design for when dealing with aircraft that need to be light.
Just keep that in mind when you build, take extra care when you build the attach structure to save yourself a repair later.
This is just a heads up for anyone upgrading to bigger more powerful flaps.

Also watch your flap extension speeds especially in rough air, a few MPH lower Flap extension speed dramatically drops the induced forces on the flap,
These Forces on your flaps increase exponentially with speed they go down the same when you slow down.

[Battson]

The mod has been fully tested using CAD processes with stress analysis, or such is my understanding. The torque on the rear spar and stresses transferred to the wing skin are known problems.

[Gerd Mannsperger]

One bit of caution on fowler and semi fowler flaps. They generate a lot of force into the back spar and attachments. The early Cessna 206 aircraft used to bend the back spar , never a issue with the less powerful 185 flaps, later versions of the 206 had spar doublers. On the Found Bush hawk we used to have Barn-door flaps that were activated by a simple lever--when they build the semi fowler flap the stall speed dropped by 7 knots and the approach was nice and flat, but it was impossible to activate by hand and a 2 tone electric flap jack( a bit of overkill) was installed.
My point is better make sure the engineering on the attache structure is up to the task. Extra weight (Attach structure and the flap) as well as added complexity are the negative side effects of fowler flaps.

[Gerd Mannsperger]

That is correct

[Battson]

This is the latest I heard about the Fowler flaps modification:

Final approach - estimated prevailing deck angle was in fact about 7 degrees. Ample visibility over the nose till the last couple of seconds and the round out.
This compares to about 14 degrees in a Bearhawk 4 place A model flown at the same approach speed / profile. This is a big deal, and the main benefit which we would hope for - as well as the speed reduction. We are talking flying at the slow speed limit here, certainly nothing like a 50kt approach.

That touchdown actually was concurrent with a full stall just as the stick hit the stops. It will take more time to really master it, results are still preliminary.
The roll-outs are now very benign from the reduced energy touchdowns, the pilot has said it makes the roll-out a very relaxing experience.

He is trialling some crosswind landings, noting the icy condition at the time this was reported. The pilot's view is that with the slotted flaps there is much less weather-cocking than the 52 degrees of barn door flaps. Crosswind control appears to have improved compared to the normal flaps.

I've touched base for a further update.

[Bcone1381]

Please clarify something for me. Are you saying VG's can be done either on the flap or the wing, but not both?

[Gerd Mannsperger]

VGs on the leading edge of semi fowler flaps work extremely well but you can do either that or the VGs on the leading edge not both.

The leading edge VGs give the benefit of better control while the VGs on the flaps just lower stall speed with a reduction in slow flight control.

The reduction in stall speed is very close to the same in both instances, if in doubt go for improved controllability.

I believe the Cessna Caravan comes with VGs on the flaps stock.

[Westward_Flyer]

Battson extra detailed information sounds great!

[Battson]

Optimistic given the current conditions! There is no news. I can probably share some extra detailed information not previously posted, though.