Bearhawk STOL mods

[Bdflies]

Like he said! 😎

[Battson]

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.

https://en.wikipedia.org/wiki/Blown_flap

Its is extremely effective.

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.

[zkelley2]

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.

https://en.wikipedia.org/wiki/Blown_flap

Its is extremely effective.

[Bdflies]

Aviat describes the Husky flaps as "Slotted semi Fowler". The inboard portion of those flaps is in the prop blast, thus 'Blown flaps'. They are extremely effective!

Bill

[zkelley2]

The most practical additions to any STOL Bearhawk will be some form of blown flap (slotted or fowler), followed by the wingtip.

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.

[PaulSA]

You're right, of course - duh! - the HS "lift" is down........

[swpilot3]

Very good summary; This is turning into a very informative thread!

[swpilot3]

You're exactly right, Jared and Jim. That's inline with what I'm seeing.

[swpilot3]

I have the stock BH wingtips. I'll look at the ones Battson recommends!

[JimParker256]

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).

[jaredyates]

When it stalls in a "nose up" elevator situation, the flow that was causing the tail to go down separates and the tail now goes less down, which is the same as the nose going more down. That may be the most confusing sentence I've ever written. But what I mean to say is that in this case the nose either drops or stays about where it is as the plane just mushes along. Another way to put it is at forward CG, if we try a power-off stall, we can get the plane to a point where it steadily descends under control, but the stick is all the way back and the wing is not fully stalled yet (see the video link in the previous post).

[PaulSA]

Tail stalling first - not a good thing as it's going to lead to a pitch up........

[jaredyates]

https://www.youtube.com/watch?v=NB0kh3Z4OVM

[svyolo]

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.

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.

[Battson]

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.

This is a relevant observation for practical STOL work.

- 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.