What are the advantages and disadvantages of spoilers vs. ailerons for roll control?
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What are the advantages and disadvantages of spoilers vs. ailerons for roll control?
While there are probably many, #1 advantage would have to be eliminating undesirable yaw caused by ailerons.Quote:
Originally Posted by dougbush
I have been seriously considering spoilers for my design because if properly executed they will have less drag (no aileron gap). I'm still trying to figure out how to add trim back in without adding drag.
You can always use both. Smaller size/range of travel ailerons augmented with spoilers. Get the best (and worst) of both worlds. [Who says this design stuff is supposed to be easy anyway?]Quote:
Originally Posted by Mike Switzer
Some thoughts...
The big disadvantage to spoilers is the total lack of control feel that pilots expect. For light aircraft that use spoilers such as the Helio, you will see that there are still small ailerons to contribute to control and to feedback to the pilot. The aileron allows more precise control inputs.
Normally the yoke or stick force varies with speed and deflection of the control surface. Spoilers do not provide this force feedback.
More complex airplanes employ artificial feedback so that the stick forces match the desired and conventional relationship between pitch, roll, and yaw.
In addition, getting spoiler extension to result in the expected linear response to pilot control input through a mechanical linkage is a tricky bit of design. Spoilers operate through the wing's boundary layer which changes in depth with speed and angle of attack. Can require multiple test and modify iterations of multiple parts. A mechanical linkage that is not aided by a flight data computer can likely only be set up to operate well in a specified set of conditions.
Ailerons add lift to one wing and reduce lift and add drag to another. Off the cuff, I think that allows the overall lift of the wing to be higher than if a spoiler is only applied to one wing to cause the roll by killing lift on that wing without creating lift elsewhere.
If you have both spoilers and ailerons you buy two sets of linkages, which means moire build time, more weight, more test time, more maintenance.
Looking around the GA fleet, I will hazard a guess that if spoilers delivered superior performance across the entire flight envelope, they would be much more common than they are.
Best of luck,
Wes
N78PS
For the smart guys in the crowd, for a given span which configuration will produce the greatest roll rate or is it a wash?
Some decades ago, I was sharing a room in a Navy hospital with a room mate who was a USAF Col. He had a little experience with the P-61 Black Widow. It had smallish ailerons linked to roll spoilers. The spoilers came into play after a certain amount of roll input. He told me that although the P-61 was as big as some bombers, it rolled like a fighter. It could do a decent job against many single engine fighters.
Two of my fellow pilots where I use to work flew Mitsubishi MU-2s. They said that it had high wing loading so it that it could go fast. They had to design full span flaps so that it had reasonably slow landing characteristics. So that meant spoilers for roll. I was told that it seemed to roll about the outboard wing tip rather than the longitudinal axis. If you can imagine something like that. They both liked the plane.
Both of these airplanes likely provided a good living for engineers and test pilots as they tweeked the designs.
Bob
Not a smart guy so I'll say ailerons, hands down.Quote:
Originally Posted by Auburntsts
I was thinking of an arrangement with spoilers on both the top & bottom of the wing springloaded enough to hold them shut, operated by a rotating shaft with arms that would either push the top or bottom spoiler open - that way you would still have control feel. If you use the right kind of hinges there shouldn't be anything exposed to mess up the wing profile.
Aren't there several of the more popular gliders that use spoilers?
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.Quote:
Originally Posted by dougbush
Peterson Javelin. I heard the spoilers were almost useless on initial roll (from a guy that found one real cheap).Quote:
Originally Posted by Matt Gonitzke
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.
If you'd like to discuss wing warping, it's coming back! actually, everyone would like to do it again as it is much more efficient (if it could be done and still hold fuel, landing gear, flap systems, increased wing loadings, ...). The only drawback would be potentially poor stall characteristics.Quote:
Originally Posted by FlyingRon
Good discussion,
The B52 is spoilers only..limited to 45 degrees of bank I believe. Most airliners have both. T38 was aileron only with a 720deg/sec roll rate. The F4 had both. The C&D and hard wing E had serious adverse yaw issues at high AOA...the down aileron would just increase drag and pull the jet out of control.
At low AOA the aileron rules in roll, high AOA, the spoiler works better. (or rudder in the F4's case). An AOA or flap lever derived lockout for ailerons? The DC10 and 767 have a second aileron that works at lower speeds. Flap position or airspeed is used lock/unlock the extra aileron in those if I remember correctly.
Not an aero engineer but I did teach high school Physics 20 years ago.
Jake