Stall Strips - has anyone tried them?

[karmarepair]

I've searched the forum, and found nothing.

Your experience with stall strips is what I'm after.

[Bryan Cotton]

Vortex generators:
viewtopic.php?f=21&t=3043

There have been a couple references to stall strips over the years.

[NWade]

I'm curious what the intended usage/benefit would be. To put it another way: *Why* are you interested in stall strips on a Sonex?

--Noel

[WaiexN143NM]

hi all,
i tried the search window aircraft spruce, for stall strips. found nothing, but did find some raw stock on ebay
$19 a foot plus shipping. Next time at local airport will look around the ramp. lots of certified planes have them.
will measure dimensions. would be interesting for someone to experiment and see what the results would be on a sonex.


WaiexN143NM
Michael

[NWade]

I reiterate:

What are you all trying to achieve with stall strips?

[radfordc]

Stall strips are often added to correct undesired stall characteristics after a design has been test flown. I see no benefit to adding them to a Sonex. How much more benign stall could you want?

[MichaelFarley56]

I've never seen stall strips on a Sonex.

I have flown a bunch of airplanes that have them, including Cirrus's, Bonanza's, etc.

Back when I was flying Hawker 800XP's, I was part of a flight crew that would perform post maintenance test flights and occasionally we would perform stall tests after the airplane had its wing leading edges removed to check for underlying corrosion. On that airplane, it was equipped with stall strips that could be adjusted a small amount and extreme care was taken to ensure they were reinstalled in the exact same location to prevent control issues during a stall. Thankfully I never had a problem on any of the test flights I completed but heard plenty of stories about other test flights where one stall strip was out of position and, as the stick pusher recovered the airplane from a stall, the airplane would roll nearly 90 degrees.

The moral of the story is, if you decide to try them on your Sonex, proceed with caution. If they aren't lined up properly you may find the stall characteristics of your airplane to be much worse than before.

[Scott Todd]

For those not familiar, stall strips are intended to energize the boundary layer to allow the wing to go to a higher angle of attack thus delaying the stall. This allows the airplane to slow down a bit more. In real life, airplanes can see a stall speed reduction of a few knots. This is important for STOL airplanes but it really serves no function on a well behaved airplane like a Sonex.

Lets take my new Onex which has about 30 hours now and about 90 landings. It starts to show stall signs at 44 IAS and really breaks around 40. FWIW, I have the white arc marked at 45. I have done approaches coming over the fence at 60-65 and its a bit nerving. Its a lot of stick pressure and the nose is above the horizon. it floats a hundred feet or so before settling in and I can usually stop in another 600-800 ft without abusing the brakes. I have the Sonex Hydraulic brakes. I really like coming in around 75. The gusts don't bother it as much and it's just more comfortable. I turn final at 100, put the flaps out and it goes down to 75 in 5 seconds or so. Its a very comfortable approach attitude and the float is maybe 100 feet longer. I can easily slow to the 60's as I cross the field boundary but usually don't. I like rolling to the 2000 foot turnoff to go easy on the brakes and its usually the mid field mark at the airports I operate at.

So what would stall strips do? Lower the stall speed 5mph? That's over 10%, which seems huge. It might change my roll out by a hundred feet, if I modified my approach speeds accordingly. For STOL people, this is the world (I've been flying/teaching in my Kitfox for almost 25 years now). For a Sonex operating on normal runways of 2000 ft+, its fluff. I would not teach or recommend anyone approach at slower than 60 in a Sonex unless they were a highly qualified pilot with tons of time in type. And if that's you, none of this matters. I don't consider the average Sonex pilot previously reported here of 500 hours as 'highly qualified' unless its all in a Sonex or similar.

Could I land in 500 feet like Sonex advertises? Probably with some practice, but why? That's what the Kitfox is for. Same weight, 50% more wing area, full span flaps, bigger wheels, bigger brakes, and a bigger prop creating more drag. But that's not the mission of the Sonex. Its well designed and refined for its mission just as it is :)

[karmarepair]

I'm curious what the intended usage/benefit would be. To put it another way: *Why* are you interested in stall strips on a Sonex?

--Noel

To provide a tactile (shaking, buffeting) warning of an incipient stall.

[NWade]

For those not familiar, stall strips are intended to energize the boundary layer to allow the wing to go to a higher angle of attack thus delaying the stall. This allows the airplane to slow down a bit more. In real life, airplanes can see a stall speed reduction of a few knots. This is important for STOL airplanes but it really serves no function on a well behaved airplane like a Sonex.

Folks, let's all make sure we're talking about the same thing here.

• Stall Strips are large objects attached on the leading-edge of the airfoil, usually shaped like a triangle/wedge. They do not energize the boundary layer. They do not lower stall-speed. They are designed to change the shape of the airfoil's leading edge such that at higher angles of attack they force the wing to have separated airflow (i.e. stall) at a specific and repeatable angle. They are either used as a "band-aid" to help fix bad stall behavior, or to ensure that specific FAA certification margins are met with respect to stall/spin characteristics, or as a manufacturing trade-off to substitute for other techniques that would be more-costly to implement while ensuring aileron authority in slow-flight (such as wash-out/wing-twist). Wikipedia actually has a fairly accurate and concise description of them: "A stall strip initiates flow separation on a region of the upper surface of the wing during flight at high angle of attack. This is typically to avoid a tendency to spin following a stall, or to improve the controllability of the airplane as it approaches the stall. A stall strip may be intended to alter the wing’s stall characteristics and ensure that the wing root stalls before the wing tips."
• Vortex Generators are very small vanes that are attached on the top or bottom surface of an airfoil which are designed to stick up through the boundary layer of air flowing over the airfoil and create small vortices. This mixes free-stream air into the boundary layer, forcing the airflow to be turbulent (instead of laminar) while helping to prevent laminar bubbles or airflow separation from the airfoil (i.e. stall). For wings/airfoils that are not achieving laminar flow across a high % of the wing chord, vortex generators can also improve airfoil performance at higher angles of attack, delaying airflow separation (i.e. the stall) and allowing for slower flight.

--Noel
Sonex #1339
(and ASG-29. As a sailplane pilot I care a great deal about things like laminar flow, drag, and slow flight!)