Bearhawk STOL mods

[Battson]

For avoidance of doubt, this is not my plane we are talking about. This is a STOL modified machine in the midwest USA.

[Cguy]

This has been tried and the results are known.
It makes a large difference, but there were some unintended consequences which were more annoying than the benefits were worth. I believe it made the plane really floaty in the flare.

I talked with MicroAeroDynamics about this (more vg's in front of the flaps, a month ago, as my Rans S-7S also has "plain" flaps, like the BH designs. I have been using their vg's for 20 years on my wings, and had my credit card out and was hot to trot. They talked me out of it, I'd be messing with the ALREADY vg-ized (energized maybe was the term) airflow caused by the existing vg's on the LE, no need to put more on plus there was something said about "control reversal possibilities", and that's when I tagged out. The idea comes up from time to to time, but near as I can tell there is a good reason why we don't see vg's in front of the flaps.

Way to go Battson on the Keller flaps! I too look forward to your numbers on how they work.....

[Isilverone]

Great news, are you waiting on permission from the builder?

[svyolo]

Excellent. I can't wait to hear the whole story.

[Shopperly]

This is excellent and exciting news, and is truly a great example of the experimental aviation world. Kudos to those involved in this project!! I’m very much looking forward to hearing more. Thank you!

[AKKen07]

Fantastic! Looking forward to the rest!

[schu]

Thanks for the update. Would love to know more.

[Battson]

I am excited to confirm the new Airframes Alaska double-slotted fowler flaps have flown on the Bearhawk 4-place.

Positives:

• There was a significant improvement in approach speed. Yet to be confirmed, but we are talking about a reduction of 6 knots or more and a 'rock-solid' approach.
• Reduced stall speed, improvement yet to be confirmed.
• There was an even more significant improvement in deck angle and forward visibility when landing. Angle is yet to be confirmed, but more importantly the point of touchdown was clearly visible even at the stall speed, no neck-craning required.

Negatives:

• There was a small reduction in elevator effectiveness at extremely low airspeed. This only occurred at speeds previously unreachable by a 4-place on final approach.
• When the plane stops flying, it really stops. The transition was sharp.

I am looking for permission to post the first-hand account, possibly video which I also have.

[zkelley2]

Any other side effects than floaty in the flare?

[Battson]

With the Bearhawks plain but huge flaps, I have always wondered if VGs placed near the front of the flaps would give you partial flow attachment and improve performance. Might be something I try once flying and comfortable with the plane.

This has been tried and the results are known.
It makes a large difference, but there were some unintended consequences which were more annoying than the benefits were worth. I believe it made the plane really floaty in the flare.

[Battson]

Considering we have the "plain flap" shown above, I am expecting good things. Cubs have a slotted flap and it makes a big enough difference for them.

[AKKen07]

Awesome! That is a great illustration. Thanks for the information. I’m in the edge of my seat waiting to see how these things work!

[rodsmith]

With the Bearhawks plain but huge flaps, I have always wondered if VGs placed near the front of the flaps would give you partial flow attachment and improve performance. Might be something I try once flying and comfortable with the plane.

[Battson]

Pardon my ignorance but can you please explain what you are saying about the first notch not being “blown” due to the pocket being imperfect? Do you mean that the slot won’t get extra airflow at that setting as the lower skin blocks it or something to that effect?

Yes you have it Ken, I assume that both sections of the flap needed attached airflow right around their surface to generate maximum lift. However the truth may be different, it all depends on how the design has been done though.

I have always thought they worked like this, so that the airflow was blowing smoothly over both segments of flap:

image_121.png
However, in researching this response, I found this literature which suggests that the double-slotted flap still works without a streamlined flap pocket. So-call Douglas double slotted flap.

I love this stuff

A26_Av_4505_flaps_dwg_p160_W.png

[AKKen07]

Pardon my ignorance but can you please explain what you are saying about the first notch not being “blown” due to the pocket being imperfect? Do you mean that the slot won’t get extra airflow at that setting as the lower skin blocks it or something to that effect?