Anti-skid proper behaviour?

[Bond 42]

Anti-skid proper behaviour?

 

Rubbish. Lock up means 0 wheel rotation. Optimum braking is often achieved with a certain amount of wheel slip, around the 10% mark (i.e. wheels rotating 10% less than ground speed). So no, leaving rubber behind does NOT mean a lockup occured.

 

 

 

I know what lockup means, and I know what antiskid does. Except in DCS you see full line skids... As to give the illusion it’s a full on lockup. And I’m not saying it’s an actual lockup. If you land with antiskid off vs on, you can tell it’s working.

Edited February 28, 2019 by Bond 42

[Brun]

Seriously?

I'm guessing here cos I'm at work, but...

 

Since our DCS Hornet doesn't have the physical in-flight idle lock, it's easy to move the throttle to an 'unrealistic' position before touchdown. It might therefore be the case that when weight-on-wheels occurs, DCS doesn't register the fact that the throttle is already in the 'ground idle' position.

 

Might be something worth testing.

[mvsgas]

I have towed aircraft in a straight line and left tire marks on the ground (granted they where white hangar floor so it does not take much to scuff them). I have marshal in aircraft into their spot and aircraft left tire marks on the taxiway. To me if the tire is not smoking is not locking up.

Edited February 28, 2019 by mvsgas

[raelias]

I'm guessing here cos I'm at work, but...

 

Since our DCS Hornet doesn't have the physical in-flight idle lock, it's easy to move the throttle to an 'unrealistic' position before touchdown. It might therefore be the case that when weight-on-wheels occurs, DCS doesn't register the fact that the throttle is already in the 'ground idle' position.

 

Might be something worth testing.

 

This is actually intresting, I didn't realize that if I idle before we have WoW it might go to flight idle, I'll do some testing that and get back to you on the throttle bahaviour

[Bond 42]

Anti-skid proper behaviour?

 

Anti skid decreases braking performance.

 

 

 

Every plane I have flown in real life takes a huge penalty for antiskid off/inop. Sometimes double the landing distance due to no antiskid.

[Flamin_Squirrel]

Every plane I have flown in real life takes a huge penalty for antiskid off/inop. Sometimes double the landing distance due to no antiskid.

 

No, inop anti-skid does not increase landing distance, it increases the landing distance you have to allow for. It doesn't mysteriously alter grip levels. If you're a real pilot you should understand the difference.

[raelias]

No, inop anti-skid does not increase landing distance, it increases the landing distance you have to allow for. It doesn't mysteriously alter grip levels. If you're a real pilot you should understand the difference.

 

If you are you should probably know that there is no way a human can apply maximum manual brakes and do as good of a job as the anti-skid to prevent wheels lock-up, especially in wet runways, so i can 100% assure you the anti-skid inop will most def increase landing distance

[Bond 42]

If you are you should probably know that there is no way a human can apply maximum manual brakes and do as good of a job as the anti-skid to prevent wheels lock-up, especially in wet runways, so i can 100% assure you the anti-skid inop will most def increase landing distance

 

 

 

Exactly, thank you for explaining this to him... This is why I tend not to reply to anything on these forums. A lot of know it all’s, who don’t know it all.

Edited February 28, 2019 by Bond 42

[Flamin_Squirrel]

If you are you should probably know that there is no way a human can apply maximum manual brakes and do as good of a job as the anti-skid to prevent wheels lock-up, especially in wet runways, so i can 100% assure you the anti-skid inop will most def increase landing distance

 

Exactly, a human can't get close to the maximum grip available while preventing lockup, hence you have to be cautious and apply less braking than the available grip will allow. Anti-skid doesn't actually change the physics involved.

[Flamin_Squirrel]

Exactly, thank you for explaining this to him... This is why I tend not to reply to anything on these forums. A lot of no it all’s, who don’t know it all.

 

Laughable, coming from someone who thinks skidmarks = lockup.

[Bond 42]

Exactly, a human can't get close to the maximum grip available while preventing lockup, hence you have to be cautious and apply less braking than the available grip will allow. Anti-skid doesn't actually change the physics involved.

 

 

 

Lol cautious... okay. Of course the physics aren’t changed. But that doesn’t change the fact that antiskid off will increase landing distance. That’s real life. Not sure if you’re a real pilot or not, but you should know that if that’s the case.

[raelias]

Exactly, a human can't get close to the maximum grip available while preventing lockup, hence you have to be cautious and apply less braking than the available grip will allow. Anti-skid doesn't actually change the physics involved.

 

Of course but let's get back on topic, the skid marks shown on the hornet when you apply full brakes with anti-skid on is clearly a lockup, either the effect is wrong, or the antiskid is no modeled correctly, thats my point on this thread and I'm trying to figure out which one is it. So lets stop comparing the size of our things and focus on the topic

[Bond 42]

Of course but let's get back on topic, the skid marks shown on the hornet when you apply full brakes with anti-skid on is clearly a lockup, either the effect is wrong, or the antiskid is no modeled correctly, thats my point on this thread and I'm trying to figure out which one is it. So lets stop comparing the size of our things and focus on the topic

 

 

 

Back on topic- Yeah, I’ve noticed this. I have tried it with antiskid off and you can tell the difference. So it’s modeled somewhat but maybe not correct as you stated. Or maybe it’s just a graphic thing in dcs? Not sure.

[Bond 42]

Anti-skid proper behaviour?

 

Why do you feel insulted if someone want to discuss with you? If you do not want to discuss, you can write blog.

 

Anyway,

 

Have you ever watched some elite automobile racing sport? Guess what, most of them doesn't have any kind of anti-skid by regulation, and most drivers somehow manage to consistently apply maximum efficient braking every few seconds.

 

For given conditions, there is only one optimal braking profile which does involve xy% of skid. Anti skid system will try to keep your vehicle in that zone using modulation of brake pressure. Because it's modulating system, it will never be on best theoretical profile, thus you will have loss of brake performance. Of course, fully modulating control system will generate less loss than some simple on/off control system, but there is no system with no loss.

 

Now, I do appreciate that systems we have installed offer commodity of "foolproof" usage at cost of little bit longer stopping distance.

 

I do not have problem with DCS F-18 anti skid. I press W and it keeps directional control just fine.

 

 

 

But Nikola...

 

This is just wrong... a high performance car weighs a small fraction of an aircraft. In an aircraft you use way longer stopping distance for with no antiskid. Antiskid ON will give you the shortest distance. These are facts. There are performance charts that easily show this.

I get theoretical theory... but it doesn’t compute on aircraft.

 

And I don’t think OP was saying he has a problem with the antiskid and directional control... he was questioning why the skid marks when brakes are applied with antiskid on.

Edited February 28, 2019 by Bond 42

[Bond 42]

Performance charts have factored in braking performance of average human. (or system performance in case of auto-brake application).

 

You can try in your car "threshold braking" technique. Even with ABS ON it will give you better braking distance than with just slamming it.

 

Anyway, we can agree to disagree. :) :thumbup:

 

And you are right about OP question. My bad. I've seen skid marks behind a braking aircraft with no perceivable slip, so I think the effect in game is realistic but a little bit overdone. Imo, marks should not be that tick.

 

 

 

Of course factored human performance.. but they also factor in actual aircraft performance. There’s not much to agree/disagree on lol.

 

Here’s a quick example.. not an F-18 but it doesn’t matter. You’ll see it nearly doubles the landing distance. And that’s because if you do mash on the brakes. The tires will pop.. brakes overheat. Etc.

 

 

 

And again, back on subject... you may be right. Overdone might be a good word for it lol.

[raelias]

Why do you feel insulted if someone want to discuss with you? If you do not want to discuss, you can write blog.

 

 

I did not feel insulted at all, no idea why you implied that, the line you quoted i simply stated facts, anti-skid grately improves landing distance there is no argue that, it's not a matter of opinion, it's crazy to compare a race car driver to an aircraft pilot, there is so much that varies on the tire performance on any given landing while you brake, the lift on your wings as you slowdown, the angle of attack as your nose bounce slightly on the nose wheel spring, the conditions of the runway itself, not to mention you can't compare a professional who brakes hundres of times per hour and is trained to make sure to get it perfect everytime to a pilot ta brakes once every flight, not to mention the brake pedals are completly different.

 

Anyways this is all irrelevant to the point: antiskid improves perofrmance, thats a given. The question at hand is if it's performance is modeled correctly on the hornet or not, nothing more

[Manuel_108]

But Nikola...

 

This is just wrong... a high performance car weighs a small fraction of an aircraft. In an aircraft you use way longer stopping distance for with no antiskid. Antiskid ON will give you the shortest distance. These are facts. There are performance charts that easily show this.

I get theoretical theory... but it doesn’t compute on aircraft.

 

And I don’t think OP was saying he has a problem with the antiskid and directional control... he was questioning why the skid marks when brakes are applied with antiskid on.

 

Very true. You also have to factor in how much heavier airplanes are, you also have to take into consideration that, consequently, you have way less of an idea of what the wheels are doing at any given moment.

 

Putting it simply: It is impossible to have the same braking distance with A/Skid turned OFF.

Your braking technique doesn't matter, you can't do it as well, the feedback is simply not there.

With A/Skid ON, it will simply give you the maximum available braking power.

 

Source: Asked someone who is a senior examiner and flight instructor for various aircraft types at Lufthansa.

Edited February 28, 2019 by Manuel_108

[Bond 42]

Mashing on brakes is improper braking technique. It will undoubtedly destroy tyre, wheel, and braking components. However, braking performance with anti-skid inop chart doesn't factor in improper braking technique. The number is not higher "because if you do mash on the brakes. The tires will pop.. brakes overheat. Etc.", but because proposed braking technique is more conservative. (In fact it's completely opposite from "threshold braking" technique that offers maximum braking performance).

 

Btw, I enjoy discussion so far. :)

 

 

 

Well then you should come teach that to every professional pilot I know...Lol

That chart does not give those numbers based on bad brake technique. In fact, it gives those numbers based on a 400psi push of the brakes, out of a possible 3000psi system. Anything higher than that will pop tires, etc.

And I know this specially because I used to be an instructor in said aircraft. None of this is my theory. It’s just fact.

 

I enjoy a good discussion and yes it’s off topic... I just want people to understand how this actually works.. it’s obvious a few do not.

[raelias]

Mashing on brakes is improper braking technique. It will undoubtedly destroy tyre, wheel, and braking components. However, braking performance with anti-skid inop chart doesn't factor in improper braking technique. The number is not higher "because if you do mash on the brakes. The tires will pop.. brakes overheat. Etc.", but because proposed braking technique is more conservative. (In fact it's completely opposite from "threshold braking" technique that offers maximum braking performance).

 

Btw, I enjoy discussion so far. :)

 

I see your point, but I still find it very hard to belive that some would be able to maintain perfect braking manuelly better then an eletronic device in the aircraft, there is just too many things varying, even the predal pressure itself is hard to maintain the same as the aircraft shakes on the runway.

 

Im not sure about the hornet, but I can tell you what I fly, quoting the manual "The antiskid system provides maximum braking efficiency by maintaining the wheels at the limit of an impending skid."

 

The way it works is that gear tachometers send info to the system, if the wheel speed is below i belive 87% of the aircraft reference speed it sends a release order to the brakes as to maintain maximum brake performance, threshold braking as you mentioned, it does this calculation many times per second, based on that I dont belive a human could do better with not antiskid whatsoever

[raelias]

Actual testings

 

Alright so I just did some "scientific" testings: 2 approaches one with askid on and one off, same config same touch down spot (roughly) same speed both on speed AoA, no flare and maximum brakes on pedal and idle thrust as soons as touch down.

 

First the skid marks: Pic 1 and 2 shows skid on and off respectivelly, you can observe the skid marks looks the same.

 

Second the braking distance, I stopped roughly at the same spot on both configs, a little shorter

by .14nm with antiskid off which is courious considering full brake pedals and the skid marks at least looked the same, probably just touched down slightly earlier, I also was slight lighter from the new pattern (Pic 3 skid on, 4 skid off, pics 5 and 6 map with ruller for on and off respectivelly)

 

This data leads me to belive that the anti-skid switch on the hornet currently does absolutelly nothing at all, it's just a functionless switch at the current early access state Feel free to cary tests yourselves and let me know if you find otherwise

 

On a related noted, someone mentioned about the flight and ground idle, I observed the if you put your throttles to idle before you have weight on wheels it will indeed go to flight idle and stay that way thoughout the landing roll unless you move the throttles afterwards, I didnt not know it did that, very intresting (both tests were made on idle after WoW)

Edited February 28, 2019 by raelias

[Bond 42]

Alright so I just did some "scientific" testings: 2 approaches one with askid on and one off, same config same touch down spot (roughly) same speed both on speed AoA, no flare and maximum brakes on pedal and idle thrust as soons as touch down.

 

 

 

First the skid marks: Pic 1 and 2 shows skid on and off respectivelly, you can observe the skid marks looks the same.

 

 

 

Second the braking distance, I stopped roughly at the same spot on both configs, a little shorter

 

by .14nm with antiskid off which is courious considering full brake pedals and the skid marks at least looked the same, probably just touched down slightly earlier, I also was slight lighter from the new pattern (Pic 3 skid on, 4 skid off, pics 5 and 6 map with ruller for on and off respectivelly)

 

 

 

This data leads me to belive that the anti-skid switch on the hornet currently does absolutelly nothing at all. Feel free to cary tests yourselves and let me know if you find otherwise

 

 

 

On a related noted, someone mentioned about the flight and ground idle, I observed the if you put your throttles to idle before you have weight on wheels it will indeed go to flight idle and stay that way thoughout the landing roll unless you move the throttles afterwards, I didnt not know it did that, very intresting (both tests were made on idle after WoW)

 

 

 

Nice! I’ll test it sometime myself. Thanks

[Flamin_Squirrel]

Of course factored human performance.. but they also factor in actual aircraft performance. There’s not much to agree/disagree on lol.

 

Here’s a quick example.. not an F-18 but it doesn’t matter. You’ll see it nearly doubles the landing distance. And that’s because if you do mash on the brakes. The tires will pop.. brakes overheat. Etc.

 

And again, back on subject... you may be right. Overdone might be a good word for it lol.

 

You need to understand that many charts, including that one, incorporate the performance of both aircraft and pilot. Example: referencing V1 to reject a takeoff. The calculated V1 for rejecting a takeoff is actually slightly less than it otherwise could be, because it allows for 2 seconds for the pilot to make the decision to stop.

 

Stopping distance charts are no different. The reason the distances for no anti-skid are so much longer are because you can't safely access the aircraft's performance (you can't brake hard because you can't tell if you've locked up or not), so enormous safety margins are added in. It is NOT because you have less grip.

Edited February 28, 2019 by Flamin_Squirrel

[Davee]

I haven't tried comparing heavy vs light, but I often take most of the runway trying to bring the 18 to a halt.

 

I remember reading the 18 has better brakes than the 16, so I don't think I'll be able to stop the 16 before running out of runway unless I correct whatever I'm doing wrong.

 

 

+1

 

 

Always wondered if this is final or WIP.

[Bond 42]

Anti-skid proper behaviour?

 

You need to understand that many charts, including that one, incorporate the performance of both aircraft and pilot. Example: referencing V1 to reject a takeoff speed. The calculated V1 for rejecting a takeoff is actually slightly less than it otherwise could be, because it allows for 2 seconds for the pilot to make the decision to stop.

 

Stopping distance charts are no different. The reason the distances for no anti-skid are so much longer are because you can't safely access the aircraft's performance (you can't brake hard because you can't tell if you've locked up or not), so enormous safety margins are added in. It is NOT because you have less grip.

 

 

It’s not a grip thing my friend. When did I say less grip? And of course performance charts have human factors built in.

 

With the chart I posted, It’s an overheated brake thing, tire popping issue. You cannot apply the pressure you normally would with antiskid on. It’s simple. So simple. And the rest of the planes I’m typed in were the same way.

Edited February 28, 2019 by Bond 42

[Davee]

Hey fellas,

 

Not sure if this is correct or not but you may want to check to see if your engines go to ground idle. I’ve noticed multiple times that they don’t after landing and hinders your braking efforts. To check I always quickly come up off idle then back to make sure the engines are spoiled back.

 

 

Sent from my iPhone using Tapatalk Pro

 

 

+1