4-place Landing Techniques

[Nev]

Ok this is all good to know. I got to see (hear) Battson’s AOA in action and it seemed intuitive having the audible beeps.

[swpilot3]

I'm curious why people say the profiled tail doesn't do well with VG's on the underside. I have them and it seems to do very well. What is it that people think isn't good?

My tail has always stalled before my wing at typical CG, which is fairly forward. So, making the tail more effective has allowed me to fly slower.

[rodsmith]

Good data point!

[Bcone1381]

This thread below, post #13 records a report of a Patrol builder that removed them after testing.

https://bearhawkforums.com/forum/bearhawk-general-discussion-news/28944-stolspeed-vg-s

[swpilot3]

Thanks Bcone. Looks like lsilverone has both a patrol and a 4-place. He dislikes the VG's on the tail for the Patrol, but likes them for his 4-place. Interesting!

[John Bickham]

I have the same question Bobby. I have 100 hours on her now. I'm still in the early stages of learning. Goal this year is CONSISTENT 500 foot, hard surface landing distance with airframe friendly touchdowns. Like Whee, I can slow it down with plenty of control left. My issue is the high rate of descent and transition at the bottom. I plan to go into some narrow backcountry runways and over nose visibility is a must for my comfort level. VG's are on the short list. Want to establish a baseline first. Lots of slow flight and landing practice to go.

[swpilot3]

Well... perhaps a test is in order. I put VG's on my wing (A wing) and tail (profiled) at the same time. It reduced my stall by 5 knots or so and made it much much more stable at slow speed. I really liked the results so I just left it that way. But, perhaps it's worth a test to remove them from the profiled tail and see the difference.

[rodsmith]

Do you have gap seals or just the VGs on the tail?

[swpilot3]

I have gap seals also

[Nev]

I really liked the results so I just left it that way. But, perhaps it's worth a test to remove them from the profiled tail and see the difference.

This would make for a very interesting comparison. Keep us posted if you do it Bobby.

[whee]

swpilot3, we should meet somewhere and do some testing. I don’t have VGs on my plane and haven’t felt the need for them but I’m thinking about adding them. I’ve never noticed my tail stalling either. I’m obviously not pushing the limits of the airplane. A wing and profiled tail.

Mark Patey did an interesting VG test and posted it to YouTube. His method for observing if the tail stalled vs the wing was simple. I’d never though about the mechanics of the tail stalling vs the wing during power off stalls. I thought about doing the same test if I install VGs and a elevator gap seal.

I’m pretty sure lsilverone has a flat tail on his BH.

[Bcone1381]

My understanding is lsilverone loved the results of VG's on his Four Place Model A with slab stabilizer. He also has a Patrol. All Patrols have the profiled stabilizer. He had negative VG experience on the Patrol using the Stolspeed VG's that effected both feel and performance.

[swpilot3]

Yeah, whee, I'm up for meeting some where and doing some testing. Perhaps the BH fly-in you're coordinating.

[swpilot3]

I've been reading a lot of articles and trying to deepen my understanding of aerodynamics. I can't for the life of me envision how VGs could make aerodynamics worse. Does anyone have an idea of how VGs could make feel and performance of the horizontal stab worse? Too much adhesion? I can't see a scenario where VG's create less adhesion. Why would a profiled stab make any difference as it relates to VGs?

Does anyone know of any documentation that shows a negative effect of VGs?

[whee]

I've been reading a lot of articles and trying to deepen my understanding of aerodynamics. I can't for the life of me envision how VGs could make aerodynamics worse. Does anyone have an idea of how VGs could make feel and performance of the horizontal stab worse? Too much adhesion? I can't see a scenario where VG's create less adhesion. Why would a profiled stab make any difference as it relates to VGs?

Does anyone know of any documentation that shows a negative effect of VGs?

if I remember correctly lsilverone felt like VGs on the tail of his Patrol made it very pitchy. I could see that being possible since VGs can improved the effectiveness of flight controls. Making light controls lighter may not be favorable to some.

[m.mooney]

if I remember correctly lsilverone felt like VGs on the tail of his Patrol made it very pitchy. I could see that being possible since VGs can improved the effectiveness of flight controls. Making light controls lighter may not be favorable to some.

I have a different conclusion regarding VGs under the patrol stab. I’ve flown mine for 350 hours now, 300 with VGs, both wing and stab. Everyone flys differently and I’m not one to say that my way is best. My observations are; The airfoil is so efficient that it just doesn’t want to quit flying, it’s best to be done flying when the wheels are rolling down the strip. For me, this means full flaps, every time, to fly the slowest approach speed. That’s a lot of drag and those monsters can generate a huge sink into the flare. My observations were that the patrol ran out of elevator authority rather early in this type of flare. This is obviously par for the course for a slow speed STOL landing but I thought it was more pronounced than other types, thanks to the barn doors. Adding VGs under the stab produced much more control effectiveness in this type of flare. I was still not satisfied and decided to try gap seals on the horizontal stab. Again, a definite improvement, in my opinion. I’ve never been an analytical type of pilot, just an operator, so I can’t give you numbers, charts, graphs, aerodynamic conclusions. All I can say is that my butt has a fair amount of flight time under it and I’m no stranger to precision flying, getting the most out of the aircraft. My butt tells me that VGs and gap seals are outstanding improvements to the Patrol tail and VGs on the wing should be considered mandatory if you intend to get the most out of the wing. It is not too sensitive in pitch, it’s just right. Just an opinion, of course.
Mike

[whee]

I’ve been thinking about elevator authority and how many of you guys say it runs out when doing max performance landings. This isn’t something I’ve noticed and I can only think of two reasons: 1. I’m not flying the airplane close enough to the edge to notice. This is the mostly likely reason. Still, I don’t know how I could land the plane any slower; I already feel like a slatted cub that lands tail first and plops the mains down from 4ft up.

2. My longerons are extended 2” in the tail section. Perhaps this little bit of extra leverage is enough to make a difference in elevator authority?

[Nev]

I watched Battson’s video of his Bearhawk performing at a STOL competition last year (and won), and I noticed that on very short finals the elevators appear to be at maximum upward deflection against the stops. This is with the CG at nearly the forward limit (1 POB vs 2 POB). A question in my mind is whether this is the perfect scenario where the elevators lose authority just before the main wings stall. Either way, the fact that the Bearhawk outperformed others on the day implies that even without VG’s, it’s holding enough pitch authority to fly at a slower speed than other STOL aircraft.

I’m very curious to know with VG’s under the tailplane, does it provide enough authority to get into an undesirable pitch attitude at slow speed, or does it just improve the already great slow speed handling ?

[Battson]

You need power on to keep the tail down, in that configuration with CG hard forward. If you close the throttle, the nose drops and airspeed increases, limiting the performance of the aircraft.
It would be hard to fly into a stall for this reason.

[jaredyates]

In my experience, when the elevator is running out of authority, a little bit of thrust brings it back. The flow is in the propwash, so you get some induced flow that is greater than the wing airspeed.

[m.mooney]

I feel that the VGs and gap seals did in fact increase control authority and certainly improved the slow speed handling. I don’t feel that you can get yourself into an undesirable pitch attitude as a consequence of these additions, you simply run out of elevator in most slow landings, even with the VGs. All of these approaches and landings are power on, it’s the only way to make it happen when you’ve run out of elevator, like Jared mentions. As has been discussed elsewhere, the real game changer will be double slotted flaps. I started down the path last fall, after speaking to the gent that just sold the 4 place with them on it. It’s certainly not that difficult to do but it will cost a good chunk of change. Still contemplating it though.

[zkelley2]

I really don't think elevator authority is ever the issue. It's the tail first landings and high pitch where you can't see anything on touchdown, or alternatively the relatively high airspeed required for a wheel landing.

[Battson]

if I remember correctly lsilverone felt like VGs on the tail of his Patrol made it very pitchy. I could see that being possible since VGs can improved the effectiveness of flight controls. Making light controls lighter may not be favorable to some.

I flew a Bearhawk 4-place on Sunday with VGs under the tail wings.
It was a Bravo with the profiled stabilizer.
It was not pitch sensitive at a middling CG location, in fact I didn't even realize there were VGs installed until after the flight. We did not get a chance to fly with full aft CG.