Bearhawk STOL mods

[zkelley2]

700fpm is a normal landing with something like TK1's. You still don't bounce. People not used to such things think you'll bounce hard, but any airframe should be able to handle it.
I've certainly put large jets on the runway at 700fpm. It's an arrival and everyone asks if the runway is now 10ft lower, but it works.

[JimParker256]

Well, 700 FPM sounds like a lot, but 700 FMP is only 7.95 MPH...

The Cirrus web site says following a CAPS deployment, the airplane will be descending at 17 mph (or roughly 2X the 700 FPM described above. So far, there have been zero fatalities from ground impact after a Cirrus parachute deployment.

Of course, the Cirrus' seats are designed to absorb a good bit of the G-forces from that vertical impact. That "vertical g-force absorption" is a big part of why I'm using multiple layers of different density foam in my seat cushion.

Frankly, I'm more concerned about the 30-40 mph forward velocity at impact – another good reason to land into the wind, aim between trees, etc...

[svyolo]

Dave Roberts is a promoter of VG’s. Flew his Bearhawk with an O540 without VG’s....didn’t like how it flared...loves VG’s now that he’s installed them. And if you ever get a chance to do short field landings with him...flat eff’n impressive!

A friend of mine with a 207 installed VG’s on his Horton STOL equipped airplane..left off the vertical stabilizer VG’s. Could get air borne before having good directional control...after vertical stabilizer VG’s he had great control. He also feels that if light with an engine out he can keep the yoke in his lap all the way to the ground at 700 feet per minute decent rate...says in emergency at 700 feet per minute hitting the ground is something he can walk away from.

I have them on my Pacer and Marv has them on his...improved elevator authority during flare. Shorter take off...maybe better aileron control when hanging on the prop during slow speed maneuvers. Almost eliminates moose stall...

Really good info.

[schu]

I thought of that, but for CG and cost reasons I’ll probably stick with a metal prop unless I find that I can land significantly shorter than I can take off and I’m looking for more thrust.

My airplane has extensive modification so I’m waiting to see where the CG ends up.

[Nev]

Schu,

You could add a light weight prop to your list perhaps. It is rotational weight, not sure if it has a greater effect than “fixed” weight.

[Battson]

700 ft/min is a serious crash

[Mark Moyle]

Dave Roberts is a promoter of VG’s. Flew his Bearhawk with an O540 without VG’s....didn’t like how it flared...loves VG’s now that he’s installed them. And if you ever get a chance to do short field landings with him...flat eff’n impressive!

A friend of mine with a 207 installed VG’s on his Horton STOL equipped airplane..left off the vertical stabilizer VG’s. Could get air borne before having good directional control...after vertical stabilizer VG’s he had great control. He also feels that if light with an engine out he can keep the yoke in his lap all the way to the ground at 700 feet per minute decent rate...says in emergency at 700 feet per minute hitting the ground is something he can walk away from.

I have them on my Pacer and Marv has them on his...improved elevator authority during flare. Shorter take off...maybe better aileron control when hanging on the prop during slow speed maneuvers. Almost eliminates moose stall...

[svyolo]

Have you guys done it? Noticeably improvement at low speed/high AOA?

[Mark Moyle]

Bottom side of the horizontal stabilizer forward of the hinge...about 4”. Since experimental you can also use VG’s on the vertical stabilizer just forward of the rudder hinge line...at some distance...maybe 4” as well?

[Battson]

Under the tail, just in front of the elevator.

[svyolo]

Where do you put the VG's on the tail? Top on the leading edge, bottom just forward of the hinge line?

[Battson]

When Battson brought up the topic of flap changes a couple years ago I began to wonder if using a exterior flap track like used on the Quest Kodiak would be an effective way to go.

I've gone as far as designing flap tracks for the Bearhawk, for a true Fowler system. It was based on the tracks used by the Sherpa Turbine. They are expensive to have machined, so I started looking deeper before progressing.
The problem I found was the bending moment / torque on the rear spar. This would need more steel braces between spars to avoid cracking the wing skin from fatigue. That work would require opening the wing skin. Too invasive for a "working" plane, it would be out of action for many months!

The beauty of the slotted flap or double slotted flap is they can be retrofitted with just a few simply mods to the trailing edge of the wing (non-structural), plus a new hinge which can be bolted on. They also create less torque on the rear spar.

The price of the Airframes Alaska flaps is high, but that's just aviation. I hope the tailwings are large enough with VGs and gap seals installed. Alternatively, they could easily be replaced.

[svyolo]

Fowler types always have some external actuators/support/support. If you look at the bottom of any airliner you will see multiple fairings sticking out the bottom of the wing. Some planes they are huge. I was surprised how little hangs down in the pictures of the Keller flaps that I have seen.

They do add drag, as well as weight and complexity.

[whee]

When Battson brought up the topic of flap changes a couple years ago I began to wonder if using a exterior flap track like used on the Quest Kodiak would be an effective way to go.

KODIAK-100-sn-100-0155-exterior-right-762x456.jpg

Jump to 12:00 min and you get a decent view of the Kodiak flaps deploying:

[svyolo]

Any of the flaps that move aft as well as down and increase the wing are also move the center of pressure aft. That means you need more tail downforce to compensate, including in the flare. I can definitely see running out of flare authority, especially at forward CG.

I like the idea of this type of flap, but you would definitely need a test program to see not just how much slower you stall, but controllability when you are doing it, at various CG's.

But, I like it.