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31" Dessers mounted.
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For what it's worth, I was stalling clean at 48 KIAS. I put some STOLSPEED vortex generators on my wings and tail. It dropped the clean stall speed to 41KIAS. My full flap stall speed went from 44 to 41 also. I'm certain that my tail is stalling first... I'm sure my forward CG with just me is contributing to this. I'm gonna play with gap seals and ballast for aft CG next.
Another observation is that my current 3-point attitude doesn't allow me to take advantage of the slower speed. I need bigger tires to help take advantage of it.Comment
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Hey Bobby, did you manage to get a slightly lower stall speed with power on ? I found mine was losing elevator authority at CG forward of 15 inches. I could get it to stall just around 38 KTAS at light weights and forward CG (F3 or F4), by keeping power on. The power on gives airflow over the elevators and keeps them active, allowing the wing to stall first. If the CG is aft of about 15 inches, then the wing will stall first with power off.
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This is a relevant observation for practical STOL work.Originally posted by swpilot3 View Post
- Leading edge devices like slats and VGs don't improve practical STOL performance at the touchdown or take-off. They do improve the safety margin during climb-out and approach, allowing for slower flight in those regimes. They increase stall angle and stall aggression.
- Trailing edge devices like slotted flaps or fowler flaps will improve practical touchdown speed and shorten take-off. This is the most practical STOL outcome.
They lower the deck angle, reduce Vso, and improve visibility by generating lift near the trailing edge and moving the centre of pressure (CP) aft.
- Wingtip devices can produce more lift, but don't move the CP much, so the stall angle of attack remains unchanged.
The most practical additions to any STOL Bearhawk will be some form of blown flap (slotted or fowler), followed by the wingtip.Comment
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Interesting observation that your tail is stalling first. I hadn't heard that one before, but again, I don't have a lot of light aircraft time, and zero bush plane time.Originally posted by swpilot3 View PostComment
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Tail stalling first - not a good thing as it's going to lead to a pitch up........Comment
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Paraphrasing Jared here – when the tail stalls in a nose-high angle-of-attack, the down-force being provided by the tail is reduced, causing a forward-pitching moment. This tends to reduce the pitch of the tail, resulting in it regaining aerodynamic effectiveness (and thus the down-force). The result can be a "nodding" action as the tail stalls and un-stalls. In some aircraft, and especially if allowed to fully develop, this may result in a quite rapid "mushing" descent (not specific to Bearhawks - just in general).
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Now there's an idea! Blown flaps, but like on the C-17 and US-2. Something like how Cessna experimented with it in the 50s on the 170.Originally posted by Battson View Post
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Bill, what I'm talking about is mass air injection from an motor or the like. The C-17 and US-2 use bleed air from their APU for takeoff. The Cessna 170/O-1 design from the 50's was using a hydraulic air pump getting power off the accessory case of the engine. Holes on the top side of the wing where boundry layer separation occurs first are made and air is injected to re-attached the airflow.
Its is extremely effective.Comment
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I wasn't referring to that impractically heavy experimental technology. I meant to summarise the family of flaps including slotted, fowler, semi-fowler, etc. which work like an aerofoil at the back of the wing. Sorry for the confusion.Originally posted by zkelley2 View PostBill, what I'm talking about is mass air injection from an motor or the like. The C-17 and US-2 use bleed air from their APU for takeoff. The Cessna 170/O-1 design from the 50's was using a hydraulic air pump getting power off the accessory case of the engine. Holes on the top side of the wing where boundry layer separation occurs first are made and air is injected to re-attached the airflow.
Its is extremely effective.Last edited by Battson; 11-25-2018, 04:58 PM.Comment
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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.Comment
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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:
Scratch Built 4-place Bearhawk. Continental IO-360, 88" C203 McCauley prop.Comment
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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.Comment
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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.Originally posted by whee View Post
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.
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