ChuckA
Aug 21, 2007, 12:35 AM
I did not include the spoiler installation in the Building Without Plans Or Lasercut Ribs thread. Since then I have seen several inquiries about spoilers so I decided to post a spoiler thread here.
My first sailplane back in 1971 did not have spoilers until after encountering the first killer thermal. I managed to get it out of the thermal and into sink in time to save it and didn’t fly it again until I had added spoilers. That first model used torque rods to actuate the spoilers from a servo in the fuselage. Since then, I have used servos in the wing or pull strings to actuate the spoilers from a fuselage mounted servo. Pull strings are easier and cheaper as well as being just as effective so that is what I use if possible.
The first LilAn had the spoilers in the outboard wing panels in order to keep the wake of the spoilers from impinging on the stab. This required spoiler servos in the outer wing panels and servo plugs in the wing joint. The limited space in the wing made spoiler linkage more difficult to install and adjust. Therefore, I decided to move the spoilers to the center panel and go back to pull strings to actuate the spoilers. This removes the servos from the outboard wing panels where the weight isn’t needed and use a single larger servo in the nose where the weight is needed. The original Lilan with outboard spoilers didn’t require elevator mixing. Moving the spoilers to the center wing panel did require elevator mixing but much less that my Ava’s one piece spoiler.
The drawing shows the spoiler installation I have been using since 1975. The spoiler must be located far enough aft of the spar shear web to clear the spoiler horn. For the LilAn, I followed Mike Drela’s advice and extended the top sheet further aft and placed the spoiler hinge line at the aft edge of the top sheeting. The distance from the spoiler hinge line to the actuating link attachment point (dimension A) should be slightly less than the distance from the center of the servo arm to the point at which the pull string or pushrod is attached to the servo arm. The angle between the actuating link and a line from the spoiler hinge to the actuating link attachment point should be 45 degrees when the spoiler is closed to insure that the spoiler can extend to 90 degrees when opened.
A simple jig fabricated from a scrap of wood and a short piece of 1/16 inch music assures that the horns on both spoilers are identical in length and angle relative to the hinge.
The hinge tape has enough spring to close the spoiler when the pull string slacks off and a magnet holds the spoiler closed. I swiped refrigerator magnets from the kids but lately I have been buying the smallest magnets for holding cabinet doors closed from Lowes. (Yes, kids could have magnets back then). I found a small oval magnet that is almost the right size except that I had to cut it in half to reduce the strength to insure smooth operation. The pull string should have no elasticity. In the early days, we used radio dial cords but radios haven’t used dial cord for many years so I now use 65 pound Stren fish line.
A polythene spoiler string guide tube is installed in the wing. I didn’t take a photo of the LilAn spoiler tube installation so used a photo from one of my older models
For three panel wings, the pull string guide tubes exit the bottom of the center wing panel inside the fuselage
¼ inch aluminum guide tubes carry the spoiler strings through the bulkhead ahead of the wing. The spoiler strings are hooked to 4-40 screws that clamp wheel collars to the spoiler servo pushrod. The rear of the spoiler servo pushrod slides through a guide hole in the aft bulkhead.
Tie a loop in one end of a 36 inch length of Stren fish line and push the other end through the wing polyethylene guide tubes. Fish the end of the string with the loops thought the aluminum guide tubes and bolt the wing on the fuselage. Hook the loops in the string over the wheel collar screws and pull tight. Extend the spoiler servo and clamp the spoiler fully open. Pull the spoiler string through the spoiler horn and insert a short piece of tooth pick to hold the string in place. Close the spoilers and adjust the wheel collars until both spoilers start to open at the same time. The spoiler strings should have a little slack when closed to avoid loading the servos when the spoilers are closed. After all adjustments are completed, lock the toothpicks in place with a drop of CA. Any further adjustments are made with the wheel collars.
My first sailplane back in 1971 did not have spoilers until after encountering the first killer thermal. I managed to get it out of the thermal and into sink in time to save it and didn’t fly it again until I had added spoilers. That first model used torque rods to actuate the spoilers from a servo in the fuselage. Since then, I have used servos in the wing or pull strings to actuate the spoilers from a fuselage mounted servo. Pull strings are easier and cheaper as well as being just as effective so that is what I use if possible.
The first LilAn had the spoilers in the outboard wing panels in order to keep the wake of the spoilers from impinging on the stab. This required spoiler servos in the outer wing panels and servo plugs in the wing joint. The limited space in the wing made spoiler linkage more difficult to install and adjust. Therefore, I decided to move the spoilers to the center panel and go back to pull strings to actuate the spoilers. This removes the servos from the outboard wing panels where the weight isn’t needed and use a single larger servo in the nose where the weight is needed. The original Lilan with outboard spoilers didn’t require elevator mixing. Moving the spoilers to the center wing panel did require elevator mixing but much less that my Ava’s one piece spoiler.
The drawing shows the spoiler installation I have been using since 1975. The spoiler must be located far enough aft of the spar shear web to clear the spoiler horn. For the LilAn, I followed Mike Drela’s advice and extended the top sheet further aft and placed the spoiler hinge line at the aft edge of the top sheeting. The distance from the spoiler hinge line to the actuating link attachment point (dimension A) should be slightly less than the distance from the center of the servo arm to the point at which the pull string or pushrod is attached to the servo arm. The angle between the actuating link and a line from the spoiler hinge to the actuating link attachment point should be 45 degrees when the spoiler is closed to insure that the spoiler can extend to 90 degrees when opened.
A simple jig fabricated from a scrap of wood and a short piece of 1/16 inch music assures that the horns on both spoilers are identical in length and angle relative to the hinge.
The hinge tape has enough spring to close the spoiler when the pull string slacks off and a magnet holds the spoiler closed. I swiped refrigerator magnets from the kids but lately I have been buying the smallest magnets for holding cabinet doors closed from Lowes. (Yes, kids could have magnets back then). I found a small oval magnet that is almost the right size except that I had to cut it in half to reduce the strength to insure smooth operation. The pull string should have no elasticity. In the early days, we used radio dial cords but radios haven’t used dial cord for many years so I now use 65 pound Stren fish line.
A polythene spoiler string guide tube is installed in the wing. I didn’t take a photo of the LilAn spoiler tube installation so used a photo from one of my older models
For three panel wings, the pull string guide tubes exit the bottom of the center wing panel inside the fuselage
¼ inch aluminum guide tubes carry the spoiler strings through the bulkhead ahead of the wing. The spoiler strings are hooked to 4-40 screws that clamp wheel collars to the spoiler servo pushrod. The rear of the spoiler servo pushrod slides through a guide hole in the aft bulkhead.
Tie a loop in one end of a 36 inch length of Stren fish line and push the other end through the wing polyethylene guide tubes. Fish the end of the string with the loops thought the aluminum guide tubes and bolt the wing on the fuselage. Hook the loops in the string over the wheel collar screws and pull tight. Extend the spoiler servo and clamp the spoiler fully open. Pull the spoiler string through the spoiler horn and insert a short piece of tooth pick to hold the string in place. Close the spoilers and adjust the wheel collars until both spoilers start to open at the same time. The spoiler strings should have a little slack when closed to avoid loading the servos when the spoilers are closed. After all adjustments are completed, lock the toothpicks in place with a drop of CA. Any further adjustments are made with the wheel collars.