Slats and other mod questions

[Charlie Longley]

Correct; https://www.eaa.org/eaa/aircraft-bu...ently-asked-questions/non-builder-maintenance

I learn something new every day!

 

[bda]

Fatcub I would like to see pictures of those strakes!

Going back to the Slat gap discussion, The Wenzinger and Shortal Report (The Aerodynamic Characteristics of a slotted Clark Y wing...) on testing 100 different slat configurations gives an "optimum slat configuration for best lift coefficient and best AOA increase".

Slat Width - slat distance from leading edge (measured front edge to front edge) = 12% of wing Chord - or 7.2" for a Cub wing

Slat gap - back edge of slat to wing = 2% of wing chord = 1.2" for cub wing

Slat depth - below the chord line of the wing = 4% = 2.4" for a cub wing

They noted that lower slat placement and larger gaps resulted in higher lift and higher AOA but also resulted in large drag penalties.

 

[Colorado-Cub]

Fatcub I would like to see pictures of those strakes!

going back to the Slat gap discussion, The Wenzinger and Shortal Report (The Aerodynamic Characteristics of a slotted Clark Y wing...) on testing 100 different slat configurations gives an "optimum slat configuration for best lift coefficient and best AOA increase".

Slat Width - slat distance from leading edge (measured front edge to front edge) = 12% of wing Chord - or 7.2" for a Cub wing

Slat gap - back edge of slat to wing = 2% of wing chord = 1.2" for cub wing

Slat depth - below the chord line of the wing = 4% = 2.4" for a cub wing

They noted that lower slat placement and larger gaps resulted in higher lift and higher AOA but also resulted in large drag penalties.

For slat depth the measurement makes sense from the chord of the wing profile, but I am curious what the reference point of the slat was described as being? Measured from center line of slat, or from lowest part of slat?

Also, was there mention of the gap distance (mouth opening) between slat rear surface to wing profile leading edge? Or is that what the Slat Width reference is? Or, slat gap?

A diagram would be most helpful here.

 

[BC12D-4-85]

If interested in more, try "The Anatomy of Lift Enhancement" Chapter 10, p. 415 on from this text:

General Aviation Aircraft Design

General Aviation Aircraft Design, Second Edition, continues to be the engineer’s best source for answers to realistic aircraft design questi

shop.elsevier.com

There's lots of figures, text, and bibliography for reference.

 

[Colorado-Cub]

Great link, thanks for posting that.

This diagram comes out of the Wenzinger and Shortal Report which helped answer my questions:

 

[BC12D-4-85]

Yes, a figure like this with data is included in the linked text p. 424. Also see for a similar .PDF: https://ntrs.nasa.gov/citations/19930091481

Anyone that's serious about this stuff needs to own the book. It's that good and the bibliography of sources worth more than the cost.

Gary

 

[Colorado-Cub]

Such great information!

Here is a direct link to that Wenzinger report. It is short but really, really sweet:

https://ntrs.nasa.gov/api/citations/19930091473/downloads/19930091473.pdf

These guys were doing things in 1931 that captivate all of us to this day.

 

[skywagon8a]

Great link, thanks for posting that.

This diagram comes out of the Wenzinger and Shortal Report which helped answer my questions:

View attachment 107325

Not to be a contrarian but the above drawing of the Clark Y refence of the chord line appears to be inaccurate. This link seems to indicate it differently. http://airfoiltools.com/airfoil/details?airfoil=clarky-il Therefor the depth reference is in question. Is the depth dimension in reference to the chord line or the bottom camber of the Clark Y?

 

[Colorado-Cub]

I noticed that as well, and was initially confused.

I think the chord line as depicted is not attempting to indicate it is at the bottom of the wing, but rather that the leading edge profile has been modified (or not depicted) and the actual profile reaches below the chord line as we have become accustomed to.

Of course, I could be completely wrong.

 

[Colorado-Cub]

In other words, their slat profile is actually constructed by deconstructing the existing leading edge:



...where the standard chord line is easy to visualize.

It seems in the depiction to show "depth", the lower leading edge of the main wing profile is truncated with the profile continuing below the chord line like we would expect.



I agree it is confusing.

 

[skywagon8a]

I need to take the time to dig into this report.

 

[bda]

Yes that is confusing.

My discussions with those that have tested different locations for the Mackey slats thoroughly (I will let them name themselves) leads me to believe that the picture above shows it correctly.

2.5 to 3" below the bottom of the wing is optimal.

 

[Colorado-Cub]

The most interesting tidbit from it that I did not expect was the following:

Changes in the slot gap cause no appreciable differences in the highest maximum lift coefficient obtainable (fig. 30), the variations falling practically within the experimental error of the tests.

...followed by:

The highest angle of attack for maximum lift obtained with the largest slat gaps.

This flies in the face of some recent local testing which will take me some time to get my head wrapped around.

 

[Southern Aero]

For what it might be worth .................... I took measurements directly off a Helio wing when I first got in to this. I have since gone to the 2413.5 section and applied all info I have gathered into it.

It "appears" that the slat isn't super critical, it's just what configuration will be optimum?? This is why I am making this first slatted wing adjustable. And then ................. to throw some sh*t in to the game, another knowledgeable person asks me ...... Once you add a slat to the 23012 (or any) section you no longer have a 23012 section. You have an unknown section with a slot??? Where's your data for that section??

 

[Southern Aero]

I need to take the time to dig into this report.

It makes my head hurt................

 

[tedwaltman1]

I just walk in everyone’s shadow. When “Colorado Cub” announces the solution I’ll be the dummy test pilot…

 

[BC12D-4-85]

All this Slats talk made me order another read: https://mcfarlandbooks.com/product/the-helio-courier-ultra-c-stol-aircraft/

 

[bda]

Southern Aero my mock up on the cub airfoil with the numbers from above looks very much like your helio drawing.

As for data on the wing with slot and flap - that new CL and Cd are shown in the reports listed above.

What chord length are you using on your wing?

- Also from what I am understanding from these reports, Slat depth (below the wing) is very important to increase in lift, and the Slat gap on the trailing edge not so much.

 

[Southern Aero]

Southern Aero my mock up on the cub airfoil with the numbers from above looks very much like your helio drawing.

As for data on the wing with slot and flap - that new CL and Cd are shown in the reports listed above.

What chord length are you using on your wing?

- Also from what I am understanding from these reports, Slat depth (below the wing) is very important to increase in lift, and the Slat gap on the trailing edge not so much.

The drawing is of the 23012 section which already has a "drooped nose". The Cub section is actually slightly undercambered, close to flat like the Clark Y and with out checking, the numbers would have to be close to the same.

I'm using the 63" chord. I have the same feeling on the slat position as you just stated, the lower the slat (stagnation point) is more important (effective?) than the slot created ................. but how much and what is optimum? In my non-engineer brain it seems to me the the lower the slat the more undercamber is created, which would be a much higher lift airfoil without the slot. With the slot, it can provide lift at a higher AOA as with any other airfoil. Just because you CAN fly at this high AOA doesn't mean you Must or SHOULD.

The L14, which never made it into production, with Piper's slotted wing would have used this high AOA to climb to get out of ground fire to do it's observation job. It already had STOL characteristics without the slot. The slot didn't help it get off the ground any faster, just climb.

Again, this is why I am making this first slatted wing with adjustments built in. I can even change the radius and amount of travel of the tracks.

 

[BC12D-4-85]

I can see the value of LE devices if slow flight/loitering on station/turns is part of the liaison mission. That and flaps to add lift and drag w/o excessive AOA. Long gear/big tires or a combo is what makes it work from and to the ground if that's also required. Plus a long prop can then be safely used to add low speed thrust.

Gary

 

[bda]

Measured The SuperStol slats for reference.
SuperStol wing chord is 57"

Slat chord - 8.5"
Slat "width" or extension - 6.5"
Slat "gap" trailing edge gap - 1.375"
Slat "depth" - 2" down
Slat "cut-off" from leading edge - 1.5"