Thanks Thanks:  0
Results 1 to 25 of 25

Thread: VG's in other uses

  1. #1
    Farmboy's Avatar
    Join Date
    Jan 2016
    Location
    Glens Falls, NY
    Posts
    697
    Post Thanks / Like

    VG's in other uses

    So here's a question for those that truly understand, or believe to understand the low pressure effects of vortex generators.

    There's nothing better than flying a cub with the door open, and while I enjoyed the wind in the back of a J-3, some of my passengers would prefer less wind/buffeting in the back of my -11.
    Has anyone played around with vortex generators on the fuselage, in front of the door? Some theoretical thoughts would be they might create more "turbulence" in the cockpit, but the counter thought would be they might stop the back seat from being such a parachute due to the vortex?...

    Thoughts?

    Pb



    Sent from my imitation glass cockpit using SuperCub.Org mobile app

  2. #2
    CamTom12's Avatar
    Join Date
    Jul 2015
    Location
    Huntsville, AL
    Posts
    345
    Post Thanks / Like
    Might work, but I don't think it will. VGs work by creating a vortex, which then expands. On a wing, it expands in 3 directions: upwards and to the side (because it can't go down, the wing skin is in the way). To the side is not that important, but when the vortex expands upwards, it entrains free-stream (high energy) air and then pulls it down into the boundary layer. Doing this re-energizes the boundary layer, delaying its separation and allowing the wing to maintain a higher angle of attack before stalling.

    If you put them on the side of the fuze, you might entrain free stream air and pump it into the cabin as the vortex expands in all 4 directions (not constrained from expanding into the cabin because there's no aircraft skin to keep it from doing so)...

    But the free stream air you entrain might give the boundary layer on the side of the fuselage enough energy to "jump" the open door. I'd be curious to hear your results either way.

    If the VG idea doesn't work, you might have good luck with a small (2-3") deflector, like you see in front of most car sunroofs when they're open.

  3. #3
    Farmboy's Avatar
    Join Date
    Jan 2016
    Location
    Glens Falls, NY
    Posts
    697
    Post Thanks / Like
    Thanks for the education. That's good info.
    I initially thought about the sunroof deflector idea, as it wouldn't be too much of a stretch to build one that popped out when you opened the door. But as I was thinking about this while I was installing VG's on the wing....

    I might throw a piece of tape on the side and stick some VG's to it just as test case, in front of the lower door. Maybe even a set on the inside of the door, which would be then outside.
    What is the trail length of the vortex at 85 mph? Affecting the tail ?


    Sent from my iPad using SuperCub.Org

  4. #4
    CamTom12's Avatar
    Join Date
    Jul 2015
    Location
    Huntsville, AL
    Posts
    345
    Post Thanks / Like
    Given the size of most VGs and at only 85mph, I don't think it'd be strong enough at all to effect your tail. I'm definitely interested in your results, though. Try building up your airspeed from a fast taxi to slow in ground-effect flight to slow forward flight to your cruise speed just to be safe.

    I like your tape idea!

  5. #5
    cubdriver2's Avatar
    Join Date
    Apr 2003
    Location
    upstate NY
    Posts
    7,786
    Post Thanks / Like
    I just let the wifie sit up front if she wants.

    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"
    Likes Farmboy, kestrel, JP liked this post

  6. #6
    skywagon8a's Avatar
    Join Date
    Mar 2008
    Location
    SE Mass
    Posts
    7,009
    Post Thanks / Like
    Pb,
    Place your mind in airfoil shape mode. The fuselage is an airfoil shape tuned on it's side. The air passes over the leading edge (windshield and nose) moving back along the fuselage sides as it does a wing. Tape some pieces of yarn to the windshield and along the side where you can see them. Then fly with the door closed and open to notice what happens to the airflow. After that tape some vortex generators in various locations to see what effect they have.

    Also I have seen deflectors as Cam Tom mentioned attached to the screws which hold the back end of the windshield. I don't know how effective it is?
    N1PA
    Likes BC12D-4-85 liked this post

  7. #7
    fobjob's Avatar
    Join Date
    Aug 2002
    Location
    Salt Lake City, Utah
    Posts
    1,916
    Post Thanks / Like
    Let's see....what have I had sucked out of the cockpit while leaving the upper door open?
    1. a camera
    2. all of my legal documents...
    3. a blue tarp(grabbed and reeled in before it draped itself across my tail)
    4. a dollar bill out of my shirt pocket....
    5. a jacket
    6. a map

    I don't leave the top door open any more...

    *I think you'd have better luck with a deflection vane along the leading edge of the door opening....
    Last edited by fobjob; 05-16-2017 at 11:37 AM.

  8. #8
    cubdriver2's Avatar
    Join Date
    Apr 2003
    Location
    upstate NY
    Posts
    7,786
    Post Thanks / Like
    Quote Originally Posted by fobjob View Post
    Let's see....what have I had sucked out of the cockpit while leaving the upper door open?
    1. a camera
    2. all of my legal documents...
    3. a blue tarp(grabbed and reeled in before it draped itself across my tail)
    4. a dollar bill out of my shirt pocket....
    5. a jacket
    6. a map

    I don't leave the top door open any more...

    *I think you'd have better luck with a deflection vane along the leading edge of the door opening....

    Never understood how you SC and CC guys can close the door. In my 4000+ Cub hours over 2500 of them are with the door open and a third of that in the backseat with the door open. Try it you'll like it, even on skis

    Look what you miss out on with the door closed. This is this Amish boys first view ( no TV ) of what we get to enjoy everyday



    Glenn
    Last edited by cubdriver2; 05-16-2017 at 01:27 PM.
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"

  9. #9
    kestrel's Avatar
    Join Date
    Aug 2013
    Location
    Southern NH
    Posts
    200
    Post Thanks / Like
    Quote Originally Posted by cubdriver2 View Post
    Never understood how you SC and CC guys can close the door. In my 4000+ Cub hours over 2500 of them are with the door open and a third of that in the backseat with the door open. Try it you'll like it, even on skis

    Look what you miss out on with the door closed. This is this Amish boys first view ( no TV ) of what we get to enjoy everyday

    Glenn
    Though not so much in the winter, back in my youth when I had a J-3 to play with I always flew with the door open if it was "warm enough". Hang your toes out, it feels great! I always enjoyed flying from the back seat so I could see how the passenger is doing, if they needed anything, and could slap them if needed. I once read an magazine article by a flight instructor who preferred Champs to Cubs. ...not getting into that, but... He preferred the door of a Cub, but liked the Champ better because as an instructor, he got to sit in the back of a Champ with the benefits I mentioned, and had to sit in the front of a Cub.
    --
    Bearhawk, RV-4
    Likes Farmboy liked this post

  10. #10
    Farmboy's Avatar
    Join Date
    Jan 2016
    Location
    Glens Falls, NY
    Posts
    697
    Post Thanks / Like
    I expect that 90% of us list the open door as one of the greatest benefits of a Cub, but I could be wrong. I know it is for me. Actually, I think this has already been discussed on this forum.

    Regarding the Windy-ness... Wife would not ride up front... she's ummm... not a happy flyer, and requires the back seat.
    I've not lost anything out the door, nor do I really find there is any sort of low pressure sucking out, (except when shutting both doors together) but I did have the rear seat leanback get blown forward against the rear stick one day. That woke me up and smartened up my takeoff checklist.

    For mine there is a big difference in rear seat wind from the lower door, but the window (upper door) isn't too bad.

    And it's a rare machine that doesn't have room for improvement to better suit an individual.

    pb
    Likes kestrel liked this post

  11. #11
    cubdriver2's Avatar
    Join Date
    Apr 2003
    Location
    upstate NY
    Posts
    7,786
    Post Thanks / Like
    Quote Originally Posted by Farmboy View Post
    I expect that 90% of us list the open door as one of the greatest benefits of a Cub, but I could be wrong. I know it is for me. Actually, I think this has already been discussed on this forum.

    Regarding the Windy-ness... Wife would not ride up front... she's ummm... not a happy flyer, and requires the back seat.
    I've not lost anything out the door, nor do I really find there is any sort of low pressure sucking out, (except when shutting both doors together) but I did have the rear seat leanback get blown forward against the rear stick one day. That woke me up and smartened up my takeoff checklist.

    For mine there is a big difference in rear seat wind from the lower door, but the window (upper door) isn't too bad.

    And it's a rare machine that doesn't have room for improvement to better suit an individual.

    pb
    Get her some headgear like your avatar. I've flown a lot of young ladies in both seats, it's a hair thing 90% of the time

    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"

  12. #12
    Farmboy's Avatar
    Join Date
    Jan 2016
    Location
    Glens Falls, NY
    Posts
    697
    Post Thanks / Like
    Lol.... no, she's just plain scared. If I cover her eyes she'd scream. Lol. Probably just needs someone like you to fly her around.
    Likes cubdriver2 liked this post

  13. #13
    cubdriver2's Avatar
    Join Date
    Apr 2003
    Location
    upstate NY
    Posts
    7,786
    Post Thanks / Like
    Yea don't foget to check the baggage before flying with the door open. Getting ready to mow about 7:45 this evening and one of the local kids thats had a rough life stops in. He's been bugging me all winter for a ride and I had told him to come over some calm warm evening. Quick preflight and I put him in the front seat and off we go with the door open. Nice warm evening flight, come back to land and I honk it into a hard slip on short final between the trees and something jumps out of the baggage and covers my face, I kept flipping it back off and it kept coming back. Darn red nylon windbreaker I keep back there. When I was preflighting I removed 2 tool pouches from the baggage that kept the windbreaker still.

    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"
    Likes Farmboy, kestrel liked this post

  14. #14
    BC12D-4-85's Avatar
    Join Date
    Feb 2016
    Location
    Fairbanks, AK.
    Posts
    324
    Post Thanks / Like
    A forward lip deflector on the door can work. I had one to help keep the cold out of my PA-18A in winter even with the door closed.

    However, folks flying Champs and Citabria/Scouts with boot cowl vents beware of air leaks. On one long game survey flight in a Scout I had emptied my small thermos and needed to go. No place to land nearby so I got smart and almost refilled the thermos. Thinking numb and dumb I started to empty the bottle out the vent in case there was more on the way.....guess what flowed back along the fuselage, right door, and sprayed into the rear cockpit? The passenger was not pleased. Dumb makes smart.

    Gary
    Likes Farmboy, CamTom12 liked this post

  15. #15
    hotrod180's Avatar
    Join Date
    May 2008
    Location
    Port Townsend, WA
    Posts
    1,352
    Post Thanks / Like
    That story makes me think that the old expression oughta be "too dumb NOT to pour piss out of a boot"....
    Cessna Skywagon-- accept no substitute!

  16. #16

    Join Date
    Dec 2011
    Location
    Kalifornia
    Posts
    195
    Post Thanks / Like
    I've often thought of experimenting with a row of VG's vertically along the aft edge of the cowl doors. Seems like it might help suck the hot air out and stabilize the turbulated air past the cowl and along side the fuselage....maybe the prop blast screws up any benefits to the VG's. Would be ugly, but what the hell...
    Likes Farmboy liked this post

  17. #17
    kestrel's Avatar
    Join Date
    Aug 2013
    Location
    Southern NH
    Posts
    200
    Post Thanks / Like
    Quote Originally Posted by Helmetfire View Post
    I've often thought of experimenting with a row of VG's vertically along the aft edge of the cowl doors. Seems like it might help suck the hot air out and stabilize the turbulated air past the cowl and along side the fuselage.
    I recently came across a post where someone had put a large saw-tooth pattern on the rear edge of their cowl flaps (or large fixed outlet lip?) to do exactly that. The teeth might have been 2-4 inches in size?
    --
    Bearhawk, RV-4
    Likes Farmboy liked this post

  18. #18

    Join Date
    Apr 2016
    Posts
    1
    Post Thanks / Like
    Quote Originally Posted by CamTom12 View Post
    Might work, but I don't think it will. VGs work by creating a vortex, which then expands. On a wing, it expands in 3 directions: upwards and to the side (because it can't go down, the wing skin is in the way). To the side is not that important, but when the vortex expands upwards, it entrains free-stream (high energy) air and then pulls it down into the boundary layer. Doing this re-energizes the boundary layer, delaying its separation and allowing the wing to maintain a higher angle of attack before stalling. If you put them on the side of the fuze, you might entrain free stream air and pump it into the cabin as the vortex expands in all 4 directions (not constrained from expanding into the cabin because there's no aircraft skin to keep it from doing so)... But the free stream air you entrain might give the boundary layer on the side of the fuselage enough energy to "jump" the open door. I'd be curious to hear your results either way. If the VG idea doesn't work, you might have good luck with a small (2-3") deflector, like you see in front of most car sunroofs when they're open.
    CT,

    FWIW I think one of the Seabee Mod's ( combined w/ many mods to the wings aka fences and flaps outboard, no I don't know the STC number ) had a vertical row of VG's behind the rear window about about 1/2 back of the remaining real-estate on the Fuselage, so conceptually VG's on the fuselage is nothing new, their are others that have utilized them as well. To buffet the wind, have you ever considered a partial screen that could be a small triangle placed in the front of the door that is reminiscent of the screens many off the assembly line convertibles use to reduce wind noise ( look a the Audi's in particular ).

    My best,
    Anthony

  19. #19
    cubdriver2's Avatar
    Join Date
    Apr 2003
    Location
    upstate NY
    Posts
    7,786
    Post Thanks / Like
    Pete does your girlfriend complain when she's in the Cub. Yes or No answer only

    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"
    Likes Farmboy liked this post

  20. #20
    kestrel's Avatar
    Join Date
    Aug 2013
    Location
    Southern NH
    Posts
    200
    Post Thanks / Like
    Quote Originally Posted by AJLiberatore View Post
    CT,

    FWIW I think one of the Seabee Mod's ( combined w/ many mods to the wings aka fences and flaps outboard, no I don't know the STC number ) had a vertical row of VG's behind the rear window
    The Glass Goose and I think the Osprey (both home built amphibs) use VG's in a similar manner. However, I suspect it will be difficult to compare using VG's to keep airflow attached to a surface, to using VG's to manage the flow where there is no surface for it to attach to.

    To buffet the wind, have you ever considered a partial screen that could be a small triangle placed in the front of the door that is reminiscent of the screens many off the assembly line convertibles use to reduce wind noise ( look a the Audi's in particular ).
    This is probably a better example to work from. Something that creates a controlled vortex and probably much larger than what we typically think of as VG's.

    --
    Bearhawk, RV-4

  21. #21
    cubdriver2's Avatar
    Join Date
    Apr 2003
    Location
    upstate NY
    Posts
    7,786
    Post Thanks / Like
    Take the bug deflector off your old truck and nail it to the front doorpost

    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"

  22. #22
    cubdriver2's Avatar
    Join Date
    Apr 2003
    Location
    upstate NY
    Posts
    7,786
    Post Thanks / Like
    Saw this this morning



    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"

  23. #23
    Farmboy's Avatar
    Join Date
    Jan 2016
    Location
    Glens Falls, NY
    Posts
    697
    Post Thanks / Like
    Those were very popular on semi truck cabs to help fuel efficiency (drag) between cab and trailer for a short time, then they somewhat moved on to fold out doors on the trailer tail and fixed curtain walls under the trailer.

  24. #24
    behindpropellers's Avatar
    Join Date
    Feb 2003
    Location
    NE Ohio
    Posts
    6,528
    Post Thanks / Like
    Quote Originally Posted by cubdriver2 View Post
    Saw this this morning



    Glenn
    Small world Glenn. I saw that truck a couple weeks ago.

  25. #25
    cubdriver2's Avatar
    Join Date
    Apr 2003
    Location
    upstate NY
    Posts
    7,786
    Post Thanks / Like
    Quote Originally Posted by behindpropellers View Post
    Small world Glenn. I saw that truck a couple weeks ago.
    SJs collecting data on the trouble makers on here. Will be in Jenks next week

    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"

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
  •