Not for roll control. At least no current gliders that I've seen, and only one older design that I can't remember the name of.
Not for roll control. At least no current gliders that I've seen, and only one older design that I can't remember the name of.
"either push the top or bottom spoiler open - that way you would still have control feel."
You are thinking that the front hinged surface will provide some feel, but the issue is that a spoiler typically has a "dead" area until it extends up out of the boundary layer, 1/2" or more depending on the flight condition. while in the boundary layer it has little effect and no feedback to the stick. So your stick has the feeling of nothingness for a likely a couple of inches in the middle of its throw. If you read Ed Kolano's articles on stability he comments that pilots do not do well with this type of slop. It tends to result in overcontrolling as the stick is moved, nothing happens, nothing happens, then more than expected happens. And the stick is them moved the other way to stop the excess response from the initial stick motion.
Sailplanes have dive brakes so that they can temporarily increase their drag. They have plenty of lift so you hardly ever see flaps as flaps create lift and drag. I think the SGS 1-34 has flaps but my observation of one was that they are typically deployed to 90 degrees for the landing.
The MU-2 is an interesting study. If you lose or shut down an engine, you must NOT attempt to bank into the good engine using the conventional technique of turning the yoke. That raises spoilers at a time that you need all the lift you can get. The roll trim control partially extends the flaps on one side to create lift and that is the appropriate tool for banking the airplane into the good engine for one engine flight. I believe that there were some accidents that involved pilots regressing to the traditional but wrong technique with the MU-2. If you are not familiar with flying twins, with one engine shut down you fly banked about 5 degrees towards the good engine for best performance.
Best of luck,
Wes
N78PS
I must be thinking of something else (or something old I read once)
I'm still pretty far off from worrying about that anyway. Too many other things to do, some of which might make me some money.
Speaking from my experience flying a Starflight Ultralight (think Quicksilver but different and I think better construction). The spoilers on the Starflight give reasonable roll control but consider that I always remain upright. I am not at all sure that spoilers would work inverted and suggest that before you try anything of that nature that you build a RC model to test out the idea. Now the Starflight flys like an early Cub or Aeronca but I am 99% sure the reason they used spoilers in the design is that they create very little twisting force on the wing letting the structure be lighter.Originally Posted by dougbush
Peterson Javelin. I heard the spoilers were almost useless on initial roll (from a guy that found one real cheap).
http://en.wikipedia.org/wiki/Peterson_J-4_Javelin
I've read the comments and it seems as though the use of spoilers on GA aircraft is mostly on STOL types where they are more effective at lower speeds than ailerons. Small ailerons at higher speeds create less adverse yaw and larger ones at lower speeds create more adverse yaw. It is also true that small initial deployment of spoilers tend to get lost in the boundry layers. Chordal positioning of spoilers is important as well. Too far to the front and they will have a gross effect on lift with small deflections and perhaps be too effective. So, they are often seen just ahead of the ailerons in application. The L2M Taylorcraft of WWII when civil registered had to have them disconnected and wired closed. I do not know if they were connected to the aileron controls for roll authority. Always remember that aero forces vary as the square of the speed and linearly with all other parameters. When used on gliders for glidepath control, They are better than flaps because they do not change pitching moment. Gliders with flaps often use them in slightly raised position to reduce drag and pitching moment at high speeds. When they are used in concert on a glider, you can often balance their effects to get glidepath control with little or no pitching moment changes making for a similar effect of varying throttle on a power approach. - Just some comments from an old Heli Aerodynamicist.
To answer your original question, ailerons and roll spoilers both have pros and cons. For ailerons they are simple to operate, they are effective with any movement, and they are easier to design the control system. But they create more drag due to a constant gap in the airfoil, more induced drag due to increased lift toward the wing tip on the down aileron, poorer stall/spin characteristics and adverse yaw. These cons can be designed around with some attention to detail (gap seals, wing twist/taper and differential ailerons). For spoilers the control forces are low (also somewhat design dependent), they are very effective and have less drag, stall characteristics are typically better and there's no adverse yaw. But the control forces can be too light (requiring control feel springs) and they lose lift (by definition). For a lower and slower airplane ailerons make more sense. For a faster and higher airplane (ones that Mach matters), roll spoilers or a combination make more sense (because ailerons can become less effective (or reverse) depending on wing structural stiffness and twist. Roll spoilers are not speed brakes that extend up on both wings at the same time OR extend from the both the top and bottom of the wing simultaneously (less pitching moment).
What, we're not going to talk about wing warping?
If you can't decide on ailerons or spoilers, just go with neither and design a machine with 2 axis control, lol.
Not trying to hijack the thread, just want to clear up the T'craft L2 spoiler question. Yes, they built L2s at the house of T'craft. They also built TG-6 three seat glider trainers (adopted from the L2) under the same roof. The gliders had mid span spoilers common to all gliders. No connection to ailerons. Post war, every one wanted a plane, not so much a glider. Some were converted to L2s, some just donated their wings to a project. PPLs never got instuctions in the use of spoilers. So lots of pranging going on. A club L2 at my field was one of the pranged. I almost bought a different L2 once. It also had its spoilers disabled. A pity, it sure could have used them.
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