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Bottom side of the horizontal stabilizer forward of the hinge...about 4â€. 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?
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Have you guys done it? Noticeably improvement at low speed/high AOA?Comment
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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...Comment
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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... -
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. -
Yes I mixed up acceleration and velocity. My bad. I was thinking same as dropping a plane 10 ft off the ground, but that give the right average velocity - not the right instantaneous velocity at touchdown.
The correct analogy is dropping a plane from 5 ft off the ground. Still a hard impact, but not a "serious crash".
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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.Last edited by Nev; 11-27-2018, 10:24 AM.Nev Bailey
Christchurch, NZ
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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.Last edited by schu; 11-28-2018, 05:44 PM.Comment
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The current price of the double slotted experimental flap from Performance STOL/Airframes is between $6400 and $8400 depending on the number of hangars required. Has anyone taken the leap and built or modified a Bearhawk wing to accept this system? Is it possible to mount these on a QB wing kit?Originally posted by Battson View PostComment
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Someone is doing this at the moment.Originally posted by Shopperly View Post
The design will allow Airframes AK to offer a standard bolt-on solution for Bearhawk aircraft wings, hopefully they do.
The issue (big unknown) is the pitching moment. Bob has advised that the tail may not be large enough to overcome the increased nose-up pitching forces created by the double slotted flaps. The ultimate solution will be larger tail wings, if gap seals / VGs / greater control deflection don't solve it first.Comment
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The speed range of the BH range is the equal of anything. But that comes with limitations at both ends of the speed spectrum.Twitchy at the high end, run out of control authority at the low end. I bought the kit because of the compromise.
How much would I pay for a 4 mph reduction in landing speed? If I can't control it, zero. If it works, I will get in line, price dependent.
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I agree this is a concern. However, a Bearhawk with plain flaps pitches down when flaps are deployed while a Cessna with slotted flaps pitches up. The plain flap produces less down-wash over the tail than a slotted flap. There is a chance that the increased angle of flow over the tail will counter balance the increased pitching moment of the wing and the problem will correct itself. I can't wait to see results of a test as we won't know until that happens.Originally posted by Battson View PostComment
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Question: Will slotted flaps allow for a more nose down approach and touchdown when flying at minimum airspeed?
I’m beginning to understand why others have wanted a Fowler flap or a semi-Fowler like a Cessna. When practicing max performance landings I touchdown in a very nose high attitude which someday will result in something broken in the tail.
Second question: Will VGs allow the plane to fly at a slower speed for a given AOA when in the slow flight regime?Scratch Built 4-place Bearhawk. Continental IO-360, 88" C203 McCauley prop.Comment
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Q1: About 8 to 10 degrees improvement could be expected, based on the results for other aircraft.
Q2: VGs make a big difference throughout the whole approach. They transform the wing when installed properly. I have the benefit of flying two sister-ship Bearhawk 4 places, to compare the differences with and without.
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Trailing edge devices facilitate a lower nose on approach - the more efficient they are (ie: slotted vs straight), the lower the nose. Have a look at the video here https://youtu.be/NZ9I61UGwcg for a comparison of deck angles on a Super Cub with stock flaps and Keller flaps.Originally posted by whee View Post
To me, safety is the most important benefit to slotted flaps. While it is dramatic to see a slow approach at a high deck angle and slow airspeed, the pilot usually is blind to the landing zone in the final stages of the approach. In the Airframes PSTOL video, it is clear that the deck angle is substantially lower with the slotted flaps compared to straight flaps.
A nice additional benefit is a slower approach speed leading to a shorter landing roll.
VG’s (and other leading edge devices like slats and slots) will lower the stall speed at high AOA by energizing the flow over the leading edge and keeping it attached for more of the wing chord.Comment
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I am really hoping these flaps work out on a BH because I am interested. Controllability might be a huge issue, and not just running out of elevator authority at low speed. The BH has comparatively large area flaps, so they will be very effective, but that might include a lot more unpleasantness as well. Huge pitch changes can happen in only 5-15 knots of speed change.
A go around could get interesting really quickly, and not in a good way. Most big airplanes have huge and very effective Trimmable Horizontal Stabilizers that can handle the change in CP quickly. With the flaps down some of them make the trim motors run much more quickly to help deal with it. But it is always an issue. The second step of every go around is raising the flaps (to less than half). Part of the reason is to reduce drag. A big part is to reduce the pitch change from when accelerating.
I hope they work out great.Last edited by svyolo; 09-20-2019, 12:11 PM.Comment
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Most likely yes. More flap usually results in a higher max lift coefficient, but at a lower angle of attack.Originally posted by whee View Post
No. VG's allow flying to a higher angle of attack but normally produce the same lift for the same AoA.Second question: Will VGs allow the plane to fly at a slower speed for a given AOA when in the slow flight regime?
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