Flaps vs other Stol devices

[dplunkt]

hello,

relative newbe here. I read a lot about VG's, leading edge cuffs and slats, wing tips and extentions but I have not seen much about flaps. The reason this interests me is that it would seem that modifying flaps could have as great an impact on STOl capability as say VGs. And I like the fact that it does not require (theoretically) as much nose up attitude. I think I saw some interesting experimental flaps on someone at Valdez (can't remember who or where). I also vaugely remember something about an L shaped piece added to the trailing edge of the flap?? Anyway, any thoughts on flaps adn flap mods?

[highroad]

This may be what you were refering to. Doug Keller out of the PDX area.

http://www.supercub.org/forum/showthrea ... lap+design

[d.grimm]

The L shaped pieces are called Gurney Flaps.
Lot's of good discussion over the years @ www. Supercub.org
Dave

[EZFlap]

You gotta remember that any mods to the flaps are also affecting the ability of the stabilizer/elevator to keep the airplane from pitching over. So any bigger, badder, more powerful, "inrease your length and width with this pill", bigger-nastier Fowler track, or double-slotted-deHavilland-ness you add to the flaps will very probably require some more available power in the up-sy down-sy flipper on the back of the airplane.

But when your Max Manhood Muscle Flaps are retracted, now you probably have too much pitch authority on the back of the airplane, and over-G'ing the airplane, or jittery handling, or having a 60 MPH maneuvering speed becomes something to think about.

NOT that super flaps are a bad thing... but that they require engineering attention to be paid on the other end of the airplane to do it safely. That is why the tails on airliners are bigger than your backyard. It's to balance out those even bigger three-section Fowler Flaps.

The L shaped extrusion is something that is a quickie-dirtie way of adding effective camber to a wing using nothing more than a pop rivet gun. A banner tow guy (early PA-18) told me it works fairly well to slow down an airplane that does not have flaps built into it.

[akflyer2001]

I have a set of large flaps on my Stinson. A long with the VGs and the drop tips.
With the mods I have landing the plane at slow speeds is not impossible. It handles quite well
at the slower speeds. They enable me to take off in shorter distance and respond well in the air.

I would recommend them ..

Ken in Alaska

[lesuther]

I had never heard of Gurney flaps before.

http://www.dept.aoe.vt.edu/~mason/Mason_f/AIAA2007-4175.pdf

A 46% increase in Cl means a 20% decrease in stall speed. That's pretty cool.

[porterjet]

Interesting read. I liked the part about putting a strip on the trailing edge of the Sweringen jet rudder for better dutch roll control. When I flew the early Citations that had that same strip on the rudder we always thought it was to keep the sea gulls from bending the rudder when they hit us from behind.

[hotrod150]

I have a set of large flaps on my Stinson. .....

Please elaborate-- "large flaps" being longer span, longer chord, more deployment, and/or ??? Also, STC'd, field approved, or "under development"?
I find it interesting that the Stinson 108 has a stop built into the elevator pushrod that limits up elevator when the flaps are not deployed. Although a friend of mine's 108-3 doesn't appear to have this feature- whether broken off or removed, I don't know.

[akflyer2001]

I have a deeper chord. I added 4 inch to the depth. I took the flap skin of the 185 and added to the flap of the Stinson after removing the old skin from the Stinson flaps.

[soggyc]

I had never heard of Gurney flaps before.

http://www.dept.aoe.vt.edu/~mason/Mason_f/AIAA2007-4175.pdf

A 46% increase in Cl means a 20% decrease in stall speed. That's pretty cool.

They are pretty effective in what the do, just watch out for the drag increase if you go too big.

[JimC]

The L shaped devices were called wickerbills before Dan Gurney made them famous on the race track. On a Cub, they should protrude downward between 5/8" and 3/4". They work by increasing circulation.

[flightlogic]

For the ST part of the STOL equation, it is common to yank more than 20 degrees of flap on a 185 to get off the water or gravel bar. It is brief but effective. No mod needed, just timing and technique.

[dplunkt]

If gurney flaps work, and motorsport testing and other testing suggests they do; then why are they not used more. For example, I would think that since they are so inexpensive and simple every back country pilot would want to use them. In addition they seem to complement VG's in that they keep the air attached at higher angles of attach.

Any opinions as to why I don't see more of them on cubs, and other stol aircraft? someone suggested above that these could reduce your stall speed by 20%. That would be nearly 10mph for my PA-22. I can't see that happening.

[lesuther]

Neither can I, but the paper was written for the Cessna wing section, and that's what the data shows.

A delta Cl of 42%. If L=1/2(dens)(A)(Cl)(V^2), then delta V would be proportional to (1/Cl^.5). The numbers show a Cl increase of up to over 50%. That translates to about a 18% decrease in airspeed. Not bad. Looking at lower Re, the increase in Cl is more modest...around 20%. This translates to around a 9% decrease in airspeed.

The lift/drag ratio really deteriorates rapidly as the size of the flaps increase much above .5%-.1% of chord.

It also shows a rather large pitching moment for the Gurney, and a large rearward shift in Cp for both the Tee and the Gurney.

Neither of these would be welcome at all, for example, in my 182.

However, putting a Tee strip on the trailing edge of the elevator might eliminate some of the 'heavy nose' syndrome significantly for the small tailed 182's. My 182E can't get anywhere close to a stall unless I have the CG more than 75% of the way to the rear...and even then it is just a moderate wing drop and nose drop...not a real break. Getting the CG back that far requires people in the back and something significant in the baggage area.

It makes me want to try a .5% Gurney back there out of curiosity.

[dirtstrip]

Any opinions as to why I don't see more of them on cubs, and other stol aircraft? someone suggested above that these could reduce your stall speed by 20%. That would be nearly 10mph for my PA-22. I can't see that happening.

This is a demonstration of theory and not a practical application. The theory is valid of course but difficult to add to existing aircraft. The wing used in the demo has the Gurney flap angle attached to the trailing edge and only has room to do its work creating the large vortex behind it because it lacks ailerons and flaps. This demo wing has none of that to interfere with the vortex. A practical question is how will the Cub handle without them? I have seen one aileron lost in flight from an Arctic Tern but never a Cub.

Maybe a large enough gap can be created at the trailing edge for the vortex to do it's work by dropping the hinge point for the flap or aileron below the lower surface of the wing as in the flaperron system of the Avid Flyer, Kitfox or CH 701. Another possibility is the gap created behind the trailing edge of the wing by lowering a Cessna Fowler flap or the gap created by the lowered trailing hinge of the Tundra Fowler flap. The effect would be created then only when dropping flaps, which might work provided the additional forward pitch of the Gurney and the normal forward pitch of full flaps do not create an unmanageable imbalance to a plane that might already be near the end of its up elevator and trim. If so, then you have more of the same work to do by making a fowler style elevator hinge in order to use the Gurney there also.

This calls for some work by EZ Flap. He could work this into the Mountain Hawk conversion then the rest of us could just copy it.

[lesuther]

More fuel for the fire. Way better paper for Gurney data, none for Tee designs...

http://digitalcommons.calpoly.edu/cgi/viewcontent.cgi?article=1554&context=theses&sei-redir=1&referer=http%3A%2F%2Fwww.google.com%2Furl%3Fsa%3Dt%26rct%3Dj%26q%3Dgurney%2520flaps%26source%3Dweb%26cd%3D12%26cad%3Drja%26ved%3D0CGEQFjAL%26url%3Dhttp%253A%252F%252Fdigitalcommons.calpoly.edu%252Fcgi%252Fviewcontent.cgi%253Farticle%253D1554%2526context%253Dtheses%26ei%3DtaA-UL3HKoPmiwKa3YDoCQ%26usg%3DAFQjCNGr-k5QBL_Tc3FJ3u5dxKDkrsu3Qw#search=%22gurney%20flaps%22

[JimC]

Wickerbills will increase the maximum lift coefficient on a flapped Selig S1223rtl by about 5%.

[EZFlap]

Wickerbills will increase the maximum lift coefficient on a flapped Selig S1223rtl by about 5%.

Selig is doing airfoils on full size aircraft??

As for the Gurney flap, I'm sure they have to make some drag compared to properly cambering the airfoil. Maybe not much drag, but it has to be something. Air does not like 90 degree corners, pretty much period.

Sorry Dirtstrip, there will be none of those zip-flaps in the taildragger 172 kit... I'm giving you an almost airfoiled landing gear, that's not flying at a 5 degree AOA in level flight like OEM does. Be happy with that. Last time I improved the aircraft wing flap, I got redneck keel-hauled.

[hotrod150]

.........Last time I improved the aircraft wing flap, I got redneck keel-hauled.

Aaaarrrrr, y'all.

[xcalibursword]

Zenith Aircraft produces a StOL plane that has flaperons...no independent ailerons and flaps all one flap/aileron combo.