Air-brake/Spoiler Setup
Schemmp-Hirth Type Air-brake/Spoiler
Air-brake and Spoilers tend to share a meaning in the model sailplane community. But in realty they are quite different. Air-brakes are what most model sailplanes are fitted with.
These Air-brakes extend up out of the wing vertically and create a large increase in drag as well as spoiling the lift generated by that area of the wing. The position of the Air-brakes determines their effectiveness and handling; ie. Does the glider pitch up or down when the brakes are extended.
Spoilers, on the other hand, were used on early gliders as they provided a simple means of spoiling the lift and increasing the drag by extending a hinged surface on the wing out into the airflow. This method is still used today on commercial airliners.
For the sake of sanity, and since I have been calling them Spoilers since I started flying sailplanes, we will refer to the thingy’s that come up out of the wind and then disappear into the wing, SPOILERS.
Spoilers constantly needing attention, we’ll discuss setting up the spoilers when you’re building the model, and how to maintain and repair these little monsters when they act up.
Moving Parts:
The first time I saw one of these spoilers, I was surprised how simple the design was, but yet how perfectly they seemed to work. And they do work very well.
When hooking up the servos in a new plane, begin with attaching a control linkage to the brass slide mechanism. Once connected, exercise the spoilers a couple of times to get everything working. Now its time to take the spoiler apart. Raise the spoiler up and carefully grab a hold of the top section, right above the pivot arms. The top section of the spoiler is “snapped” onto these pivot arms. With firm but gentle pressure, pull straight up on this piece. It will pop off. Just be careful, you have two of them to pop off. It’s a good idea to study the cover, see how one end is notched and the other is not? This NON notched end is fuselage end of the spoiler cover. Remember this when you reassemble them later.
Setting up the spoilers:
Assuming you have the servo already mounted in the wing and the servo arm odd at a 45 degree angle from center, with the throttle stick in the low or cut off position. Figure out the length of control linkage you need, don’t forget the clevis.
Once that linkage is soldered or threaded on, align the clevis with the hole in the servo are, but do NOT attach it. Placing the “PIN” of the clevis into the outside edge of the arm will hold it long enough to tell if you have a serious travel issue.
Advance the throttle lever toward the top, and watch as the spoiler climbs out of the wing. Be careful not to over extend the spoiler though. When at full throttle, if you have more spoiler to get out of the wing, you will need a longer servo arm. Sometimes you can not fit a long arm, due to the thickness of the wing, but that’s pretty rare.
If you need less travel, move the clevis “in”on the arm of the servo.
When you have the spoiler operating without binding, its time for final adjustment. With the wing laying on the bench, spoiler up, look down into the spoiler box linkage connection point. You will see a brass, flat “blade”. This is the actuator arm for the system. Bring the throttle to the full down or closed throttle position. You should not be able to push the control rod any further into the wing/spoiler box. Now hook the clevis to the appropriate servo arm hole.
SLOWLY, Advance the throttle; did you notice the pivot arms didn’t move up for the first 1/3 of the stick travel? That’s normal. There is a lock position that is essential for these spoilers. The “over lock” prevents the spoilers from getting sucked up out of the wing during high lift maneuvers. I’ve had this happen, so be careful, it makes for short flights.
Watch the spoiler rise out of the wing as you reduce the throttle, but don’t let it over extend. If you can get full throttle, and have the lower edge of the bottom “plate” even with or out of the top o the wing, you’re doing well, so lets bring it back down and watch the brass arm lock the spoiler down. Did you see it lock? If so, snap the top skin/plate back onto the pivot arms and check it for binding.
Repeat this procedure for the opposite wing, being careful to follow these instructions completely.
Final, Final adjustment.
Install the wings onto the fuselage. Standing in front of the plane, slowly extend the spoilers. They should “crack” the surface at the exact same time. If the servo arms were in the same position on both servos and you started with the linkage pushed in and locked tight, there should be no adjustment needed her, but this is the real word. You may need to make a slight end point adjustment. The key is slight. You do NOT want to mess with the over lock position. Now, extend the spoilers all the way up. With them fully extended, measure from the wing skin to the top of the spoiler cap, the measurements should be the same. If they are not, you can make another small end point adjustment here too. Check them ½ way down. They should be exact and it is important to make them exactly the same. If not the plane will yaw to one side a little when they are extended. The best way to get them exact is with the mechanical end of it first. Making sure the arms are in the same position as the 1st step. Also, you can bring the stick to ½ throttle and measure them there. This will give you an indication on what needs to be adjusted. Once you’re satisfied with the operation, you can install the servo well covers.
If you ever need to repair or maintain the spoilers, please refer to the SPOILER REPAIR AND MAINTENANCE VIDEO, or the written version HERE
