I am considering changing my flaps. With the same flap area, chord, and span - which would be better:

a) slotted flap, maximum extension 35 degrees?
b) plain hinged flap, maximum 52 degrees extension?

I can't decide which is better. A plain flap with more angle, or a slotted flap with less angle.

Two huge "barn doors" at 52 degrees create a lot of drag and some extra lift. Whereas 35 degree slotted flaps will almost certainly generate even more lift, and it'll be lift at the back of the wing which reduces the deck angle on approach to land, so visibility improves. But they won't create as much drag, so the plane could become harder to land well.

Background info:
I have figured out an easy way of using offset hinges to get slotted flaps, without making any structural changes to the wing or flap.

Basically I could imitate a Maule or a Husky flap hinge, then fair the inside of the slot with foam or fibreglass so it's aerodynamic. A pretty minor job which could have some handy performance benefits. But the unintended consequence of such a change, is the flap drive system in a Bearhawk 4-place doesn't have enough travel to push the slotted design to 52 degrees, because of the geometry of the adjusted hinge. So the flap would only move about 35 degrees with this mod.

One minor added bonus with slotted flaps is the ability to place miniature flap-VGs upon the flap's leading edge. These are hidden inside the slot while the flaps are retracted, and only exposed to the airflow when the flap is extended. This flap-VG mod has been tested on a Bearhawk 4-place and has been shown to noticeably reduce the deck angle during the approach to land, so visibility improves. There was a small stall speed reduction but not much. This was tested using normal non-slotted flaps, so the VGs could not be retracted into the wing. It had the unwanted side-effect of increasing landing roll because the wing would not stop lifting the plane after touchdown. So it would only work with slotted flaps, and manual flaps are desirable for a quick retraction to kill that extra lift upon touchdown.

Thoughts?

You've seen the vg'd slotted flaps on the new Shock Cub? Pretty wild......http://www.zlinaero.com/prodotti.php?id=17&lang=2

Look at the Husky flaps. They're very effective in both lift and drag, though their max deflection is 30 degrees +/-

MTV

Not sure of your terminology- hinged vs slotted flaps.
Maybe a couple photo examples please?

My old ragwing C170 had simple hinged flaps.
The Husky has what I call dropped hinges on the flaps, so they can roll back while they come down.
Cessna has what I've heard referred to as "semi-fowler" flaps-
they ride on on tracks so that they also roll back as they come down-
but (I believe) to a greater degree than do the Husky flaps.

Not trying to be a smart-ass!

There's a good nomenclature and description on Wikipedia.

https://en.wikipedia.org/wiki/Flap_(aeronautics)

Cessna flaps are Fowler Flaps, they have significant rearward travel.

Using an offset hinge (like the Shock Cub) creates a semi-Fowler Flap because it moves rearward a little bit as well as down.

Simple hinged flaps do not move rearward at all.

In case anyone is wondering what the difference is:


The Bearhawk comes with plain flaps. I am considering installing a slotted flap, but the mod will prevent the flaps extending as far as normal.

mtv wrote:Look at the Husky flaps. They're very effective in both lift and drag, though their max deflection is 30 degrees +/-

MTV

Good to know. Thanks!

EZFlap wrote:Cessna flaps are Fowler Flaps, they have significant rearward travel.

Using an offset hinge (like the Shock Cub) creates a semi-Fowler Flap because it moves rearward a little bit as well as down.

Yep that's right. I am basically intending to copy the offset hinge design (like Shock-Cub, Maule, Husky, etc).

If you wanted to get really technical, you could argue Cessna flaps are semi-fowler too. The Cessna ones open up a slot and move backward a little, but not all the way to the trailing edge. They are a nice compromise, a full fowler flap would need under-wing nacelles to house the moving parts.

A true fowler flap travels all the way to the trailing edge of the wing, like the Double-Ender's flap.

Those flaps must create SOOOO much torque on the rear spar... good thing it has a lift strut for each spar.