Robin
Well-Known Member
- Joined
- Aug 23, 2011
- Messages
- 249
- Reaction score
- 72
I've noticed in the discussion of gap seals a preference for the tape aileron gap seals that are installed on the upper side of the wing. I had that preference myself about 32 years ago, and applied tape to the gap on the top of the wing in my Seneca's ailerons.
But then I made a set of under-wing aluminum seals and did not look back. They gave around 3 mph more speed, and should last forever, instead of needing periodic renewal.
I never thought of looking up the difference in an academic way until today. But today I thought I'd research the difference in Dr. Sighard Hoerner's Fluid Dynamic Drag. This is the authoritative book on low speed aerodynamics... the range in which we fly. (Under 400 mph). This is the same guy who developed other modifications that are found on our Pipers - ever heard of Hoerner wing tips?
Chapter 5 Verse 10 ( this is the bible of aerodynamics), states " the drag caused by transverse gaps or grooves is a function of their width and depth...
There's more detail, but in the gap between the aileron and the wing, the coefficient of drag is .29 of the open area.
Well, the open area on the upper side of the wing on my Arrow II is .2 inches. 0.2 inches times 54 inches = 10.4 square inches. (thats the amount of open square inches, with 10 inches deducted for the hinges, which are 5 inches wide each.) Multiply by .29 and you get the drag caused by the upper aileron gap which is 3.016
The lower side of the gap is 1.3 inches wide. This is 8 times wider than the uppers side (which was only 0.2 inches). 1.3 inches times 64 inches = 83.2 inches.
83.2 inches times the drag coefficient is 0.29 = 24.128
So sealing the lower part of the wing is 8 times more effective in reducing drag than sealing the upper wing gap. No wonder I chose the performance gains of the under wing seals.
But there's more... Hoerner goes on to say that upper side drag number must be multiplied by 1.14, while the lower side needs to be multiplied by 1.42.
This makes the difference in effectiveness even greater, actually, 9.965 times greater.
So It may be true that the tape gap seals are easier to install, and never ice up; but the under wing ones are 10 times more effective at reducing drag according to Hoerner. .
I have tested and demonstrated metal gap seals on the underside of the wing and they have reliably shown a 3.0 mph increase in airspeed as well as improvements in slow speed handling. If we go by Hoerners numbers, this is nearly 10 times more effective than sealing the upper part of the gap. The Laminar Flow Systems gap seals are coated in the entirety of their contact area with a layer of HDPE. This is the stuff ice cube trays are made of... because ice won't adhere to them. Similar to Teflon, but actually better. Under the extremely rare conditions where ice could form on the gap seal, a tap on the control wheel will free the aileron just as it would an ice cube tray. As neither your Cherokee or these gap seals are approved for known icing, this point is academic, but it is nice to know.
For a 3 mph speed increase Laminar Flow Systems charges about $100 LESS than the tape gap seals, with a lifetime guarantee on the parts and a 60 day money back satisfaction guarantee.
But then I made a set of under-wing aluminum seals and did not look back. They gave around 3 mph more speed, and should last forever, instead of needing periodic renewal.
I never thought of looking up the difference in an academic way until today. But today I thought I'd research the difference in Dr. Sighard Hoerner's Fluid Dynamic Drag. This is the authoritative book on low speed aerodynamics... the range in which we fly. (Under 400 mph). This is the same guy who developed other modifications that are found on our Pipers - ever heard of Hoerner wing tips?
Chapter 5 Verse 10 ( this is the bible of aerodynamics), states " the drag caused by transverse gaps or grooves is a function of their width and depth...
There's more detail, but in the gap between the aileron and the wing, the coefficient of drag is .29 of the open area.
Well, the open area on the upper side of the wing on my Arrow II is .2 inches. 0.2 inches times 54 inches = 10.4 square inches. (thats the amount of open square inches, with 10 inches deducted for the hinges, which are 5 inches wide each.) Multiply by .29 and you get the drag caused by the upper aileron gap which is 3.016
The lower side of the gap is 1.3 inches wide. This is 8 times wider than the uppers side (which was only 0.2 inches). 1.3 inches times 64 inches = 83.2 inches.
83.2 inches times the drag coefficient is 0.29 = 24.128
So sealing the lower part of the wing is 8 times more effective in reducing drag than sealing the upper wing gap. No wonder I chose the performance gains of the under wing seals.
But there's more... Hoerner goes on to say that upper side drag number must be multiplied by 1.14, while the lower side needs to be multiplied by 1.42.
This makes the difference in effectiveness even greater, actually, 9.965 times greater.
So It may be true that the tape gap seals are easier to install, and never ice up; but the under wing ones are 10 times more effective at reducing drag according to Hoerner. .
I have tested and demonstrated metal gap seals on the underside of the wing and they have reliably shown a 3.0 mph increase in airspeed as well as improvements in slow speed handling. If we go by Hoerners numbers, this is nearly 10 times more effective than sealing the upper part of the gap. The Laminar Flow Systems gap seals are coated in the entirety of their contact area with a layer of HDPE. This is the stuff ice cube trays are made of... because ice won't adhere to them. Similar to Teflon, but actually better. Under the extremely rare conditions where ice could form on the gap seal, a tap on the control wheel will free the aileron just as it would an ice cube tray. As neither your Cherokee or these gap seals are approved for known icing, this point is academic, but it is nice to know.
For a 3 mph speed increase Laminar Flow Systems charges about $100 LESS than the tape gap seals, with a lifetime guarantee on the parts and a 60 day money back satisfaction guarantee.
