BaronVonVaderham Posted November 23, 2023 Share Posted November 23, 2023 Hey guys, I’m trying to understand the difference between anti skid and locked wheel protection. soo far what I find online is that they are the exact same thing. In both cases the system determines wheel speed, and in both cases, if one wheel is off, the system dumps brake pressure for that wheel. soo if both are the sage, why are they separate functions in an aircraft? Link to comment Share on other sites More sharing options...
ARM505 Posted November 23, 2023 Share Posted November 23, 2023 Is there any specific aircraft/manual you're referring to? But it's actually a very good question. My (probably wrong) answer is that in (for example) a 737, antiskid uses IRU data, compares it to wheelspeed sensor values, and maintain/releases brake pressure to maintain wheel speed at a certain reference speed in relation to ground speed (best guess, as the 737 FCOM isn't wonderfully explanatory in this regard if I remember correctly). The 777 manual is even less illustrative, saying only "When a wheel speed sensor detects a skid, the associated antiskid valve reduces brake pressure until skidding stops.", and that "Locked wheel protection is provided using a comparison with other wheel speeds". Apparently, pilots are on a 'need to know' basis in this regard, and they just don't need to know *shrugs* So: locked wheel protection on the other hand, compares one individual wheel speed to another specific wheel - then releasing brake pressure when the reference wheel is (for example) 50% slower than the other (basically three inputs: reference wheel speed, threshold, like the 50% in my example, and 'low' value, ie speed below which the protection will be inhibited) Link to comment Share on other sites More sharing options...
BaronVonVaderham Posted November 24, 2023 Author Share Posted November 24, 2023 Soo that’s the information I found as well. And talking to various brake system engineer, they say the same. As a system engineer I conclude that the two are not different. The functions that anti skid and locked wheel protection are trying to address at the same: protect against loss of lateral control on the ground, minimise braking distance, minimise wear and tear on tyres, protect against tyre burst. And the implementation depends on the overall aircraft design, where wheel speed, air speed, and/or inertia data may be used to control brake pressure for each wheel. And the algorithms for managing brake pressure may differ for different ground speed envelopes. Link to comment Share on other sites More sharing options...
AKarhu Posted November 24, 2023 Share Posted November 24, 2023 It is mainly a nomenclature thing, but as some Boeings were mentioned, one can think that antiskid is the system and locked wheel protection is a function of it. Basically, on 737 the "skid control" function of the antiskid system monitors wheel's deceleration whereas "locked wheel protection" of the same system compares the wheel speeds in pairs (inboard and outboard wheels, that is) and releases the brake pressure from the slower wheel. Link to comment Share on other sites More sharing options...
Jeb Posted December 6, 2023 Share Posted December 6, 2023 When a skid is detected the antiskid Valve dumps pressure to that brake, then it is applied over and over untill the skid is no longer detected... pressure is around 700psi to the brake, and goes to zero psi during activation. The transduce is in milivolts to the ASCU (antiskid control unit) which determines what action is called upon. Some ASCU look at skid, and locked wheels units. The transducer is mounted in the axle and is a little generator that is spun with the cap on the center of the wheel covering the axle nut.. since the transducer is bolted in the axle and only the center rotates with the cap it is how the skid is detected, most have to have at least a WOW signal (weight on wheel) and wheel speed >16 to 25kts. At least Boeing, airbus and a bunch of others I work on have. I9-9900k, 32MB, RTX2070S, 2560x1440 165hz monitor, track IR, Grass Monkey wireless Puck, Virpil T50-CM3, Winwing Superlibra stick with Hornet and Viper grip, Winwing Orion2 with Hornet, and F15E grip, Winwing PTO, home made 2060 mounts, Virpill ACE interceptor pedals Link to comment Share on other sites More sharing options...
BaronVonVaderham Posted January 7 Author Share Posted January 7 On 11/24/2023 at 8:37 AM, AKarhu said: It is mainly a nomenclature thing, but as some Boeings were mentioned, one can think that antiskid is the system and locked wheel protection is a function of it. Basically, on 737 the "skid control" function of the antiskid system monitors wheel's deceleration whereas "locked wheel protection" of the same system compares the wheel speeds in pairs (inboard and outboard wheels, that is) and releases the brake pressure from the slower wheel. This makes sense to me. Though they could give it a better name. in fact, if I understood correctly, the main function is the same, but how it’s executed is by different algorithms. Link to comment Share on other sites More sharing options...
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