Installation of Gear Leg Fairings on a Long EZ

 

The shape of the standard, fiber glass gear leg for a Long EZ presents, during flight, an airfoil with a high angle of attack.  The high angle of attack creates both drag and downstream turbulence that can interfere with prop efficiency.  The airfoil shape can easily be changed by anyone familiar with composite construction.  The following description of the technique I used to modify my gear leg airfoils was explained to me by Gary Hertzler – a recognized Go-Fast Guru.  The application of the gear leg fairings gained me at least two things:

1)      My cruise speed increased by about 5 kts.

2)      My climb performance dramatically changed – i.e.  I can now climb at about 800 fpm at 110 kts.

 

Here are the stepwise procedures I followed (as laid out by Gary Hertzler).  Hopefully, they will be of help to those desiring to increase the efficiency of their Long EZs.  Drawings are available by CLICKING HERE.

 

 

SETUP

1)      You will need to make out of plywood, a vertical reference plane approximately 24”x24”mounted on a flat base.

2)      Elevate the nose of the plane so that the longerons are 2 degrees above horizontal.  This simulates the position of the aircraft in straight and level flight.

3)      Cut blocks approximately 8”x7” from two-inch-thick, brown, urethane foam.

4)      Shape the foam blocks to conform to the upper surface of the gear leg from the fuselage down to the top of the wheel pant.  This is easily accomplished by folding a piece of 60 grit sandpaper over the top of the gear leg and rubbing the foam block to conform it to the top of the gear leg.  A caution here – make sure that: a)  the trailing edge of the foam block is at least level to the earth (with the longeron elevated two degrees up) or a little higher, b)  the block extends below the trailing edge of the gear leg, and c)  there is enough foam extending beyond the trailing edge of the gear leg to allow formation of the full chord length of the new air foil.

5)      Shape the abutting edges of the foam blocks so that there are no gaps between the blocks (do not add micro between the foam blocks).  Make sure you leave a space 0.125” to 0.250” between the fuselage and the upper most block of foam.  That can be accomplished by placing a piece of poster board on the fuselage at the gear root.  Cover the poster board with polyethylene sheet and tape it to the fuselage around the root of the gear leg.  Make sure the tape is applied beyond where any fiber glass is to be applied.  If done correctly, the poster board can easily be removed after your fiber glass layup has been completed.  The transition between the gear leg fairing and the fuselage SHOULD NOT be made with a radius.  The transition should be blunt.

6)      Attach the foam blocks to the gear legs using micro made with a fast setting epoxy such as the fast setting version of the West System.

 

SHAPING THE GEAR LEG FAIRING

 

1)      Elevate the nose of the airplane to provide a two-degree-up orientation of the longerons.

2)      Position your vertical reference plane either in front of or behind the gear leg.  The vertical reference plane must also be oriented normal to the centerline of the aircraft.  Vertical does not mean at right angles to the floor, but at 90 degrees to spirit level.

3)      Clamp two carpenter’s squares together to make a caliper that will touch both the upper and lower surfaces of the gear leg.  The separation will have to be varied to accommodate the change in gear leg thickness as you move down.

4)      Sand a level line above and below the gear leg with the reference being the upper and lower surface of the gear leg.  This relieved area will be where you place the carpenter’s squares.

5)      Mark the desired trailing edge of the foam blocks.  The chord of the new airfoil should be four times the thickness of the airfoil.  I found that this ratio up near the root of the gear leg was insufficient to permit the shaping of a symmetrical airfoil, so I increased it to 5.5 times the thickness, and then transitioned the chord from 8.5 inches at the root to 6 inches further down.

6)      Make a vertical, square cut along the trailing edge of the foam blocks.

7)      Place the vertical leg of the carpenter’s squares against the vertical reference plane with the horizontal legs touching the upper and lower surfaces of the gear leg.

8)      Mark the midpoint between the horizontal legs of the squares on the trailing edge of the foam with a magic marker.

9)      Shape the bottom of the foam to produce a smooth transition from the lower surface of the gear leg back to the marked centerline of the trailing edge of the foam blocks.  The objective is to produce a completely symmetrical airfoil.  At this point you can, using usual construction procedures (micro over the foam and application of two plies of BID) glass the lower surface.  Or you can go ahead and shape the upper surface (carefully so as not to spoil your day by breaking off a chunk of foam) and assure yourself that you will have the airfoil you are attempting to produce.

10)  After you have glassed the lower surface, you can shape and prepare the upper surface for glassing.  Prior to glassing the upper surface, trim the trailing edge of the lower glass layup to conform to the desired final trailing edge.  Then remove about ¾” of trailing edge foam and replace it with epoxy and flox to form a stable trailing edge.  Complete the airfoil with a layup of two plies of BID on the upper layer.

11)  Finish and paint to your specifications.

 

You should be able to complete this operation in about 8 hours (not including the cure time of the layups).