What do these do?

Homebuilt Aircraft & Kit Plane Forum

Help Support Homebuilt Aircraft & Kit Plane Forum:

davidb

Well-Known Member
Joined
Jun 3, 2008
Messages
1,731
Location
Vacaville, CA
46D99A43-6BC3-433A-8B3A-4341BF1FE87F.jpeg
Not a good picture but these look like large vortex generators stuck on the pylon of the Icon. They are about 4-5 inches long and stick out about 3 inches. I’m just wondering how they improve the aerodynamics. Do they somehow contribute to yaw stability? Thoughts?
 

Vigilant1

Well-Known Member
Lifetime Supporter
Joined
Jan 24, 2011
Messages
6,194
Location
US
Last edited:

Riggerrob

Well-Known Member
Joined
Sep 9, 2014
Messages
1,952
Location
Canada
looks like those vortex generators smooth airflow around the aft half of the pylon/cabin.
Many small amphibians - with pusher propellers - suffer similar problems. Consider that most taper down from 4 feet (rear seat) to zero thickness in a short space (maybe 8 feet). That short space is needed for balance ... to avoid mounting the prop and engine too far back.
For example, the Glass Goose suffered yaw problems because airflow would briefly attach to one side of the pylon and yaw the airplane to that side. Then the boundary layer would stall and it would yaw in the other direction, rinse and repeat.
VGs help keep flow attached on both sides of the pylon.
 

bmcj

Well-Known Member
HBA Supporter
Joined
Apr 10, 2007
Messages
13,776
Location
Fresno, California
A friend built a Mermaid amphibian and found that putting VG’s on the aft fuselage just ahead of the major taper did a lot to improve airflow through the prop and increase the effectiveness of the rudder.
 

davidb

Well-Known Member
Joined
Jun 3, 2008
Messages
1,731
Location
Vacaville, CA
Thanks for all the replies and links. I see this has been discussed in various threads.

I’m still wondering what dictates the size of these things. I guess for this application something that doesn’t stick up far enough wouldn’t be effective. What is the process for determining the needed height? Is it just multiple tuft tests until one finds the right size and placement?
 
Top