Results 1 to 26 of 26

Thread: Question about additional horizontal fin

  1. #1
    RVBottomly's Avatar
    Join Date
    Sep 2017
    Location
    Asotin County Washington (KLWS)
    Posts
    1,005
    Post Thanks / Like

    Question about additional horizontal fin

    I saw an interesting PA 12 the other day. One thing stood out: it had extra horizontal fins on the fuselage just ahead of the trim opening.

    Click image for larger version. 

Name:	IMG-3976 crop.jpg 
Views:	138 
Size:	131.5 KB 
ID:	53634

    Click image for larger version. 

Name:	PA 12.jpg 
Views:	164 
Size:	138.7 KB 
ID:	53635

    It had vortex generators and bigger gear, but otherwise didn't seem heavily modified.

    Does anyone know why those fins would be added?

  2. #2

    Join Date
    May 2013
    Location
    Alberta Canada
    Posts
    67
    Post Thanks / Like
    I believe it is part of the vortex generator kit. Some have the small vg’s on the underside of the horizontal stab and other kits have the fin you show in the picture
    Thanks RVBottomly thanked for this post

  3. #3

    Join Date
    Dec 2015
    Posts
    3
    Post Thanks / Like
    Correct. This is part of the Cub Crafters VG STC. The entire thing, both strakes, clamps etc, including attachment hardware weighs in at almost 2.5 pounds.
    Thanks RVBottomly thanked for this post

  4. #4
    mvivion's Avatar
    Join Date
    Jun 2003
    Location
    Bozeman,MT
    Posts
    11,345
    Post Thanks / Like
    That kit was developed by Boundary Layer Air, which later sold the STC to Cub Crafters. The “strake” forward of the horizontal stab. helps keep the airflow “organized” across the underside of the stabilizer AND elevator, while the VGs mounted under the tail only affect flow over the elevators.

    MTV
    Thanks tedwaltman1 thanked for this post
    Likes Delta Cub liked this post

  5. #5

    Join Date
    Jan 2007
    Posts
    2,285
    Post Thanks / Like
    That looks to be a highly modified 12. Cub gear/tail, flaps, left side door, bushwheel/garr arrow tailwheel, suspect bigger engine. DENNY
    Likes Dave Calkins liked this post

  6. #6

    Join Date
    Dec 2015
    Posts
    3
    Post Thanks / Like
    Quote Originally Posted by mvivion View Post
    That kit was developed by Boundary Layer Air, which later sold the STC to Cub Crafters. The “strake” forward of the horizontal stab. helps keep the airflow “organized” across the underside of the stabilizer AND elevator, while the VGs mounted under the tail only affect flow over the elevators.

    MTV
    Mike,
    Thanks. I wonder if my Cub could benefit by the addition of VGs under the trailing edge of the horizontal stabilizer as well as the strakes. Or would that be redundant? I have temporarily removed the strakes to access the rear fuselage inspection holes, which were partially covered by the strakes, and was amazed at how heavy the installation is. Each strake weighs almost a pound and there is a lot of attachment hardware for them inside, nuts, screws, washers, clamps and bracketry securing it all to the upper longerons. Probably it all adds over two pounds.
    I have also wondered how much weird air comes from having the gap between the root of the horizontal stabilizer and the fuselage on a Cub.

  7. #7
    Jerry Burr's Avatar
    Join Date
    May 2002
    Location
    Sedro Woolley, Washington.
    Posts
    711
    Post Thanks / Like
    Hi MTV. I just can't let your comment go unanswered. The BLR kit was developed primarily to attempt to cure the moose stall, which was the rage of the day. BLR couldn't limit the elevator travel as it is a primary control with limits found in the TC. The next easiest would be to add to the surface area of the stabilizer, to simply overpower the elevator. It works. However if you have a heavy engine / prop the last thing you need are a pair of fins holding the tail up on landing. You suggest that the strakes keeps the airflow organized over the bottom of the stabilizer and elevator. Do you have data showing the bottom of the stabilizer completely stalled with or without the strakes? I have video of the same in a fully developed spin and the air flow over the stabilizer bottom is quite normal. Because of this continuity of airflow the vg's along the stabilizer trailing edge are doing their job along the entire span of the tail. Not just 2 or 3 feet in the center. I might add that during testing the number of vg's under the stabilizer were reduced from the original array, as they were not needed to do the job. Less vg's less maintenance. I don't mind you hyping your favorite brand, just don't diss the rest with unsubstantiated claims. Show me the data. Jerry
    Thanks mike mcs repair, Steve Pierce thanked for this post
    Likes MT12, Dave Calkins liked this post

  8. #8

    Join Date
    Oct 2006
    Location
    Seldovia, Alaska
    Posts
    208
    Post Thanks / Like
    The lift produced by the tail is in a downward direction. The vortex generators on the bottom allow the tail to continue generating lift in a downward direction at slower speeds. I’m aware that the strake is part of the boundary layer mod and I am assuming that the stc requires that they be there, I also assume they aid in the tails developing downward force at slow speeds.

  9. #9
    mvivion's Avatar
    Join Date
    Jun 2003
    Location
    Bozeman,MT
    Posts
    11,345
    Post Thanks / Like
    Quote Originally Posted by Jerry Burr View Post
    Hi MTV. I just can't let your comment go unanswered. The BLR kit was developed primarily to attempt to cure the moose stall, which was the rage of the day. BLR couldn't limit the elevator travel as it is a primary control with limits found in the TC. The next easiest would be to add to the surface area of the stabilizer, to simply overpower the elevator. It works. However if you have a heavy engine / prop the last thing you need are a pair of fins holding the tail up on landing. You suggest that the strakes keeps the airflow organized over the bottom of the stabilizer and elevator. Do you have data showing the bottom of the stabilizer completely stalled with or without the strakes? I have video of the same in a fully developed spin and the air flow over the stabilizer bottom is quite normal. Because of this continuity of airflow the vg's along the stabilizer trailing edge are doing their job along the entire span of the tail. Not just 2 or 3 feet in the center. I might add that during testing the number of vg's under the stabilizer were reduced from the original array, as they were not needed to do the job. Less vg's less maintenance. I don't mind you hyping your favorite brand, just don't diss the rest with unsubstantiated claims. Show me the data. Jerry
    ,

    Im not questioning the efficacy of the VGs under the tail. I’d suggest you visit with Penney Nixon, who did some pretty extensive flight test on various mods on the Super Cub, including the VG kits. I believe he very much liked the BLR kit. I’m not a Flight Test Engineer, or even a test pilot, Im certainly not qualified to explain the aerodynamics of these things, but he is.

    Years ago, I also visited with Bob DeReusch (I’m quite certain I butchered the spelling of his name) at Boundary Layer Research. We discussed this at length, but that’s also been 25 or 30 plus years ago, so my memory may not be perfect. I don’t take Prevagen. But he did show me several videos of the BLR kit, including of the tufted tail of a Super Cub. It was impressive. Have you seen those videos?

    I for one prefer the BLR kit. But diversity is good.

    Good to see you post on here. Please post more frequently.

    MTV
    Last edited by mvivion; 01-17-2021 at 06:53 PM.
    Likes tedwaltman1 liked this post

  10. #10
    RVBottomly's Avatar
    Join Date
    Sep 2017
    Location
    Asotin County Washington (KLWS)
    Posts
    1,005
    Post Thanks / Like
    Quote Originally Posted by DENNY View Post
    That looks to be a highly modified 12. Cub gear/tail, flaps, left side door, bushwheel/garr arrow tailwheel, suspect bigger engine. DENNY
    LOL. You are right, of course. It's just that I've never actually seen an unmodified PA 12, so I already don't know what to look for.
    Likes DENNY liked this post

  11. #11
    Jerry Burr's Avatar
    Join Date
    May 2002
    Location
    Sedro Woolley, Washington.
    Posts
    711
    Post Thanks / Like
    Click image for larger version. 

Name:	Untitled.png 
Views:	235 
Size:	116.8 KB 
ID:	53636This is the best I can do with windows 10. MTV, You were a lot braver than I in trying to spell Bob's name. I am the last person they would be willing to share info with. Take Care. Jerry
    Likes Dave Calkins liked this post

  12. #12
    mike mcs repair's Avatar
    Join Date
    Aug 2004
    Location
    chugiak AK
    Posts
    11,774
    Post Thanks / Like
    Quote Originally Posted by mvivion View Post
    , I’d suggest you visit with Penney Nixon, who did some pretty extensive flight test on various mods on the Super Cub,
    MTV
    He was one of our flight training instructors in Naknek, when he was Commander of the King Salmon air force base back in?? late 80's or early 90's...

    he got all excited when some of our January caribou hunters reported guys in all white on snow machines.... he said they were "sneaking up" to "attack the base"..... training games...

  13. #13
    mvivion's Avatar
    Join Date
    Jun 2003
    Location
    Bozeman,MT
    Posts
    11,345
    Post Thanks / Like
    Quote Originally Posted by Jerry Burr View Post
    Click image for larger version. 

Name:	Untitled.png 
Views:	235 
Size:	116.8 KB 
ID:	53636This is the best I can do with windows 10. MTV, You were a lot braver than I in trying to spell Bob's name. I am the last person they would be willing to share info with. Take Care. Jerry
    Thanks for trying. Glad to see someone else had an argument with Windows 10 today. I lost too.

    Take care.

    MTV

  14. #14

    Join Date
    Oct 2012
    Location
    Wolf Lake, AK
    Posts
    5,943
    Post Thanks / Like
    Penny Nixon flew the Supercub moose stall test flights in what, 1994-95? I don't recall Micro VGs being around back then. BLR had very little if any presence at that time, either.

    Does BLR use a tail strake on Cessnas? Any other aircraft types? I recall that early Micros didn't address the tail, or was it just the fin? My Cessna's Micros include stabilizer and fin VGs. Heck, I've read VGs don't help a Cessna, anyway, so I guess it doesn't matter. (Wrong!)

  15. #15
    Jerry Burr's Avatar
    Join Date
    May 2002
    Location
    Sedro Woolley, Washington.
    Posts
    711
    Post Thanks / Like
    Hi stewartb. I have the first Micro STC for the Piper Cub. It is dated Jan 4 1993. Obviously our testing was complete at that time. Early Micro's did address the tail because the stock tail would not stall the improved wing. You are correct BLR didn't come in until a couple of years later. Later changes to Micro were primarily influenced by marketing. Jerry
    Thanks stewartb, cubscout, Steve Pierce thanked for this post
    Likes mike mcs repair, Cubus Maximus liked this post

  16. #16
    Dave Calkins's Avatar
    Join Date
    Jul 2002
    Location
    Anchorage, Alaska
    Posts
    5,481
    Post Thanks / Like
    My PA11 had an early MicroVG’s kit on the wings. it worked.

    As I recall, Penny Nixon was a Husky Driver maybe?

  17. #17
    Crash, Jr.'s Avatar
    Join Date
    May 2015
    Location
    Anchorage, AK
    Posts
    413
    Post Thanks / Like
    After seeing those strakes on a couple 4 place cubs recently I asked Kirk Ellis about them. Apparently he is just now trying them and says they make a noticeable improvement in handling. Didn't really get more detail than that. Must help with heavier tailed Piper aircraft and pitch control.

  18. #18
    krines's Avatar
    Join Date
    Feb 2012
    Location
    Billings
    Posts
    73
    Post Thanks / Like
    Cubcrafter strake and VGs installed on my plane before I bought it. Went out to do stalls shortly after purchase. Plane wont stall. What happens is the wing is solid as a rock no instability. No pre-stall feel. No wing drop as occurs with stall. The plane drops like a rock in nose high attitude and remains that way until corrected. This was done with half tanks, power on and off and as I remember no flaps, just me the pilot and trimmed as I fly it. Might have tried all the flap settings but can't remember. I was thinking that as the angle of attack for the horizontal increased that tail strake would get hit by the relative airflow thus pushing the horizontal up and in some way counteracting maximum elevator authority. I am not an aeronautical engineer. Must say aflter all that testing it made me feel a lot more confident in the plane.

  19. #19

    Join Date
    Feb 2015
    Location
    Anchorage
    Posts
    71
    Post Thanks / Like
    Penny has a PA14 that’s been in his family for a long time....as well as a 180. Super interesting person to spend a few hours with.
    Likes Dave Calkins liked this post

  20. #20

    Join Date
    Mar 2015
    Location
    Anchorage, Alaska Carefree, AZ
    Posts
    310
    Post Thanks / Like
    Quote Originally Posted by Jerry Burr View Post
    Hi stewartb. I have the first Micro STC for the Piper Cub. It is dated Jan 4 1993. Obviously our testing was complete at that time. Early Micro's did address the tail because the stock tail would not stall the improved wing. You are correct BLR didn't come in until a couple of years later. Later changes to Micro were primarily influenced by marketing. Jerry
    I had an early Micro VG kit for my cub, did not have VG's under tail on mine on that kit, and on wings did not go inboard of fuel tanks back then. Micro sent me later version when we recovered the wings and now have them all the way inboard, and under the tail too.
    John

  21. #21

    Join Date
    Jan 2003
    Location
    nd
    Posts
    3,722
    Post Thanks / Like
    Quote Originally Posted by john schwamm View Post
    I had an early Micro VG kit for my cub, did not have VG's under tail on mine on that kit, and on wings did not go inboard of fuel tanks back then. Micro sent me later version when we recovered the wings and now have them all the way inboard, and under the tail too.
    John

    make a difference??in anything that you could notice??

  22. #22

    Join Date
    Mar 2015
    Location
    Anchorage, Alaska Carefree, AZ
    Posts
    310
    Post Thanks / Like
    Did a lot of testing, before and after install on original Micro VG set back in the day. Basically about 20%+ reduction in stall speeds back then. And much firmer feel on controls at slow speeds.
    Made so many changes to the cub when we put the revised set on hard to tell. Added big tailfeathers, flaps to fuselage, Airframes/Keller flaps. Doubt I could tell anything different after all those mods with just a few more VG's. The flaps are the biggest improvement to me on a cub, expensive but big change in stall speeds and attitude. Really almost just sinks now at slow speeds, hard to stall.
    John
    Likes mike mcs repair, BC12D-4-85, KevinJ liked this post

  23. #23

    Join Date
    Sep 2004
    Location
    Illinois & Wisconsin
    Posts
    754
    Post Thanks / Like
    Doesn’t Charlie Center’s 180 hp mod also require the tail strakes?

    After all, that is a PA12.

    Or am I wrong again?

  24. #24

    Join Date
    Oct 2012
    Location
    Wolf Lake, AK
    Posts
    5,943
    Post Thanks / Like
    When I talked to Charly about -12 mods he had a relationship with Micro and used slightly larger than normal Micro VGs. I don't recall anything about a strake. He does have the STC for the beefed-up tail yoke and recommends that for high power -12s. That adds a lower strut to the stabilizer, not a strake.
    Last edited by stewartb; 01-22-2021 at 09:02 AM. Reason: Sp
    Likes mike mcs repair liked this post

  25. #25

    Join Date
    Sep 2004
    Location
    Illinois & Wisconsin
    Posts
    754
    Post Thanks / Like
    Stewartb: that’s what I remember. Wasn’t there a airplane magazine with his green and white 12 on the cover with a photo of the tail showing the strake and the mini-struts to the front of the horizontal? So was that was a combination of Charlie’s struts and VG’s strakes?

    Quote Originally Posted by stewartb View Post
    When I talked to Charly about -12 mods he had a relationship with Micro and used slightly larger than normal Micro VGs. I don't recall anything about a strake. He does have the STC for the beefed-up tail yoke and recommends that for high power -12s. That adds a lower strut to the stabilizer, not a strake.

  26. #26
    mvivion's Avatar
    Join Date
    Jun 2003
    Location
    Bozeman,MT
    Posts
    11,345
    Post Thanks / Like
    Memory fades, but comes back in very short bursts.....

    One of the things I recall about talking to Bob at BLR about the strakes was the turbulence that comes off the inboard end of the flaps in a stock Cub. He actually fabricated temporary extensions to see what extending the flaps in to the fuselage did to that turbulence. He found that doing so actually increased that turbulence that spun down the side of the fuselage and affected the horizontal stabs.

    As I recall the discussion, that was what led to the strake initially, at least....to better organize the flow over the inboard sections of the tail. I can't recall if there were other things the strakes address, but I believe that was what originated the idea of the strakes. His before and after strake videos were quite convincing as well.

    MTV
    Thanks Bill Rusk thanked for this post

Similar Threads

  1. Horizontal stab reinforcement question
    By tamarack in forum Cafe Supercub
    Replies: 15
    Last Post: 06-25-2020, 05:20 PM
  2. PA-12 additional inspection rings on fuselage
    By Frogdad in forum Tips and Tricks
    Replies: 11
    Last Post: 10-09-2015, 01:05 PM
  3. Replies: 9
    Last Post: 03-02-2005, 03:35 AM
  4. Additional memories of my Army life
    By AlaskaAV in forum Alaska Av Memories
    Replies: 0
    Last Post: 07-24-2004, 07:47 PM

Bookmarks

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •