Wheel breaks F18

[SmilingBandit]

18 hours ago, Rainmaker said:

If you are trying to compare heavy/passenger jets to fighters in terms of stopping power, you are far off the mark. Smaller brake stacks, a lot less of them, only two main tires...there’s not even a slight comparison there.  Fighters aren’t made to use up the brakes, they are very prone to generating a ton of heat, etc, etc and that’s with light landing weights. Anti-skid systems meter the brake pressure, so in a lot of cases, you get less pressure than you would with the system turned off. The system is designed around control, not max stopping power. 

You’re not kidding.  I recently gave a tour of my jet to some F-35 mechanics and they were astonished at how large our brakes were in relation.  Everything in aviation is a trade off, so why you would haul extra heavy brakes along when you operate from runways a couple miles long seems a poor choice.

[Rainmaker]

2 hours ago, SmilingBandit said:

You’re not kidding.  I recently gave a tour of my jet to some F-35 mechanics and they were astonished at how large our brakes were in relation.  Everything in aviation is a trade off, so why you would haul extra heavy brakes along when you operate from runways a couple miles long seems a poor choice.

What’s your airplane?  Just curious. Come from a maintenance background myself. 

[t1mb0b]

On 4/9/2021 at 10:53 AM, Dragon1-1 said:

It's counterintuitive, but the F-15 has a similar landing run to C-5 Galaxy (both just over 1km), despite the latter being much heavier. This is down to differences in design, such as thrust reversers and spoilers on the C-5, which most fighters lack. Generally, fighters land fast and don't want to get slow even in landing configuration. As such, they need to keep the nose up during the rollout (or use a braking parachute, like the Russians do). Also, DCS doesn't simulate that, but IRL you don't want to use the brakes at too high speed, because they'll overheat and become useless. They're pretty much used after you're almost stopped. 

 

If you can't stop in a short distance from taxi speed, you're rolling too fast. Larger planes have bigger gear, with more wheels, which generally improves braking performance. The Hornet only has a single wheel on each main gear, so it doesn't have much to brake with in first place.

 

 

OMG, yes and why don't apples taste like pears, and while i'm at it, OP, it's 'brakes'. If you don't apply your brakes your hornet breaks.

Edited April 10, 2021 by t1mb0b
correction

[Stearmandriver]

On 4/9/2021 at 6:05 PM, nighthawk2174 said:

I have the NFM-200 performance manual for the F18C not quite for our lot but I doubt that the braking distances would be any different.   For Full Flaps landing at 8.1° AOA at 32Klbs you should see an approach speed of just a hair under 135 knots.  For a no flare, standard atmosphere,  -4° glide slope landing there is a ground roll (full wheel brakes) of ~4500ft with a 700ft safety margin.  In DCS I am getting as stopping distance in the 4400-4600 ft region.  

This is the same data (standard atmosphere, 32k) I was using, but using the instructions on page 11 - 259, I get a ground roll of 3,000ft.  Adding a little headwind drops it to around 2,500ft.  Can I ask how you arrived at your ground roll of 4500ft?  I get something closer to that if I don't make the density ratio correction in table 1 on page 11 - 261, but a 32k standard atmosphere ground roll seems to come out at exactly 3,000ft for me... and that seems reasonable.  Am I calculating something incorrectly though?  That's always likely lol...

 

Edited April 11, 2021 by Stearmandriver

[Cpt Cuckoo]

On 4/9/2021 at 3:49 PM, Furiz said:

First check Anti Skid, it should be off on the carrier and on on the runway,

second have you advanced the throttle and pulled it back once you have weight on wheels?

when you land you have to throttle up and then down again to put the engines on idle, cause they will stay at 70% if you don't do that you'll have enough thrust for to slide off the runway.

Actually, I'm not talking about the break effects when landing as much as I am about just moving about on the carrier's deck at slow speeds such as when lining up for the catapult. Or even taxiing to the runway.  After the last update, on stable where I fly anyway, I sometimes tend to overshoot the catapult hookup because the breaks just have no grab in them at all, anymore. I never had that problem before, and it's quite irritating. Perhaps its in my HOTAS on the button I assigned for breaks. I changed HOTAS  a few months ago.

[TimRobertsen]

47 minutes ago, Cpt Cuckoo said:

Actually, I'm not talking about the break effects when landing as much as I am about just moving about on the carrier's deck at slow speeds such as when lining up for the catapult. Or even taxiing to the runway.  After the last update, on stable where I fly anyway, I sometimes tend to overshoot the catapult hookup because the breaks just have no grab in them at all, anymore. I never had that problem before, and it's quite irritating. Perhaps its in my HOTAS on the button I assigned for breaks. I changed HOTAS  a few months ago.

Hmm, sounds like something is buggy with the controls, maybe an axis is interfering.

Have you tried applying parkbrake? It should give you max brake-input regardless of control-setup. Have the input-indicator on ("Enter", I believe), apply full wheelbrake (with button/axis) and see if you brake-indication matches your parkbrake-indication.

 

I've found that sometimes, after updates, there's something wierd about the wheelbrakes if I it mapped to a button: they are stuck mid-position. I have usually found this out when I've started a mission mid-air, and then done a carrierlanding: the plane does a wheelie after it comes to a stop and is pulled back by the arresting wire.

[Cpt Cuckoo]

3 hours ago, TimRobertsen said:

Hmm, sounds like something is buggy with the controls, maybe an axis is interfering.

Have you tried applying parkbrake? It should give you max brake-input regardless of control-setup. Have the input-indicator on ("Enter", I believe), apply full wheelbrake (with button/axis) and see if you brake-indication matches your parkbrake-indication.

 

I've found that sometimes, after updates, there's something wierd about the wheelbrakes if I it mapped to a button: they are stuck mid-position. I have usually found this out when I've started a mission mid-air, and then done a carrierlanding: the plane does a wheelie after it comes to a stop and is pulled back by the arresting wire.

I'll check that out. Sounds like it could be the problem. I get the wheelie more than I should too.  I mapped the break to a new controller recently too.

[nighthawk2174]

  

On 4/10/2021 at 9:53 PM, Stearmandriver said:

This is the same data (standard atmosphere, 32k) I was using, but using the instructions on page 11 - 259, I get a ground roll of 3,000ft.  Adding a little headwind drops it to around 2,500ft.  Can I ask how you arrived at your ground roll of 4500ft?  I get something closer to that if I don't make the density ratio correction in table 1 on page 11 - 261, but a 32k standard atmosphere ground roll seems to come out at exactly 3,000ft for me... and that seems reasonable.  Am I calculating something incorrectly though?  That's always likely lol...

 

 

 

Just a normal landing as per the manual for 32k lbs, 15C, 29.92 for the pressure, no wind, no airbrake, no control surface deflection, full braking, anti-skid on.

Edited April 12, 2021 by nighthawk2174

[Thump]

On 4/10/2021 at 2:36 PM, t1mb0b said:

 

OMG, yes and why don't apples taste like pears, and while i'm at it, OP, it's 'brakes'. If you don't apply your brakes your hornet breaks.

 

 

 

[Munkwolf]

On 4/10/2021 at 3:36 PM, t1mb0b said:

 

If you don't apply your brakes your hornet breaks.

 

 

Between DCS and iRacing, I've honestly been surprised and depressed by the number of people that conflate the spelling.

[oldcrusty]

1 hour ago, nighthawk2174 said:

  

 

Just a normal landing as per the manual for 32k lbs, 15C, 29.92 for the pressure, no wind, no airbrake, no control surface deflection, full braking, anti-skid on.

 

 

OK, repeated the test with no speedbrake on a runway at sea level, standard day. Stopped at 4100 feet. I'd say I can live with it.

[Skysurfer]

If you really want to stop as short as possible, use full airbrake after touchdown and full aft elevator as practical for additional aerobraking. The one issue I see with the Hornet's brakes currently is the anti-skid. Full brake application still causes wheel lock-up and black skidmarks are visible on the runway. 

[Rainmaker]

19 minutes ago, Skysurfer said:

If you really want to stop as short as possible, use full airbrake after touchdown and full aft elevator as practical for additional aerobraking. The one issue I see with the Hornet's brakes currently is the anti-skid. Full brake application still causes wheel lock-up and black skidmarks are visible on the runway. 

at what speed?

[Skysurfer]

14 minutes ago, Rainmaker said:

at what speed?

 

Basically any speed. Below 100kts for sure.

[Rainmaker]

46 minutes ago, Skysurfer said:

 

Basically any speed. Below 100kts for sure.

Anti-skid effectiveness is reduced as you get slower. Depending on the system/aircraft, anti-skid is disabled all together anywhere between 15-50kts. 

[Skysurfer]

9 minutes ago, Rainmaker said:

Anti-skid effectiveness is reduced as you get slower. Depending on the system/aircraft, anti-skid is disabled all together anywhere between 15-50kts. 

 

Sure, it is disabled below 15kts on the Tomcat, for example. But I'm talking about the 100-80kts groundspeed band even. Would have to test it specifically for all speeds, however. 

[AKULA_OPTIMUS]

1 hour ago, Skysurfer said:

If you really want to stop as short as possible, use full airbrake after touchdown and full aft elevator as practical for additional aerobraking. The one issue I see with the Hornet's brakes currently is the anti-skid. Full brake application still causes wheel lock-up and black skidmarks are visible on the runway. 

That´s completely true, when you land on the Hornet, all you leave behind is black skidmarks literaly every single time you apply the brakes. Any speed below 120knots aprox, in every configuration, all the times. 

It is also true that from the cockpit you dont even notice, but from exterior views, its kinda anoying.

[Stearmandriver]

Ok, let's work this problem together... because I'm still getting a 3,000ft ground roll.  Check my work here, guys:

 

CONDITIONS:

32,000lbs

Standard Atmosphere

No wind

Full anti-skid braking

 

A1-F18AC-NFM-200 (Entitled "NATOPS FLIGHT MANUAL PERFORMANCE CHARTS NAVY MODEL F/A-18A/B/C/D", so I'm guessing it's the correct data) offers these instructions on using the provided tables to calculate a ground roll:  "Enter the chart with the prevailing density ratio and project horizontally right to intersect the appropriate gross weight curve.  From this point, project vertically down to the wind baseline. Parallel the nearest guideline down to the effective headwind or tailwind. From this point project vertically down to read flap setting (half or full). Then project horizontally to read the landing ground roll for dry or wet runway."

 

Pretty straightforward.  They even offer this sample graphic showing what we're about to do:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

With that in mind, here's my workflow:

1.  Enter the density ratio chart at 1.0 (standard atmosphere). Translate horizontally to the 32k lbs curve.  

2. Translate vertically down to the top of the Wind chart. 

3.  No wind, so translate vertically down through the wind chart to the Flaps chart.

4.  Translate vertically down to the Full Flaps line.

5.  Translate horizontally right into the Ground Roll chart.

6.  Translate horizontally right until intersecting the Dry Runway line.

7.  Translate vertically down to read the ground roll.

 

Here's the chart, red tracing showing the problem worked:

 

I arrive at almost exactly 3,000ft.  This is comparable to other jets of similar weight.

 

For more reference, this manual also includes a sample problem using similar conditions to ours.  They use a slightly lower density ratio, but 10kts of effective headwind.  Their solution is a full flap, dry runway ground roll of 2,700ft.

 

 

Now, I've never been able to stop the DCS Hornet any shorter than about 5,500ft.  Some of this is definitely attributable to my being unaware that the throttles had to be jiggled to attain ground idle after touchdown.  But I don't think that trick would get me down to 3,000ft, and it sounds like Nighthawk's test confirms that.

 

Have I gone wrong somewhere?

[Tholozor]

One thing to consider is that the NFM-200 is for the original GE-400 engines, our Hornet is equipped with the enhanced GE-402 engines, and we would need the NFM-210 charts for ground roll to really check it against the Lot 20. That said, I don't know how much of a difference the ground roll chart actually is between the two (if there even are any differences), as the -210 is practically impossible to get a hold of.

[Stearmandriver]

True, but unless for some reason ground idle thrust was significantly higher, I can't see a reason for engines within the same family to affect ground roll very much.  I'd expect greater impact to things like climb perf. 

 

Regardless, since we're all using the -200 charts here, the question still remains: how was the figure posted earlier of 4,500ft arrived at? 

 

 

[oldcrusty]

I tested this in DCS in various conditions.

On a dry concrete runway, standard day at sea level I get consistently 4070' ground roll.  Using only brakes with antiskid. No pull on the stick. Speaking of horizontal stabs... I'm not sure if Hornets FCS works similar to Super's but I think the stabs should have some NU deflection till the jet slows to 70?  Would have to ask or dig the info out somewhere.

On the same runway, setting the pressure to 31.10 decreased the roll by around 50'

The wet runway, 15C deg. and 28.35,  the roll was 4920'

I also tried a runway located at 5746' elev.  Standard day, dry concrete.  The roll was 4560'   So... The results are roughly halfway between what 'nighthawk' came up with and Stermandriver's graph. 

 

[Swift.]

19 minutes ago, Gripes323 said:

I tested this in DCS in various conditions.

On a dry concrete runway, standard day at sea level I get consistently 4070' ground roll.  Using only brakes with antiskid. No pull on the stick. Speaking of horizontal stabs... I'm not sure if Hornets FCS works similar to Super's but I think the stabs should have some NU deflection till the jet slows to 70?  Would have to ask or dig the info out somewhere.

On the same runway, setting the pressure to 31.10 decreased the roll by around 50'

The wet runway, 15C deg. and 28.35,  the roll was 4920'

I also tried a runway located at 5746' elev.  Standard day, dry concrete.  The roll was 4560'   So... The results are roughly halfway between what 'nighthawk' came up with and Stermandriver's graph. 

 

The technique is to pull back fully on the stick when below 100kcas, apply full brakes until the antiskid cuts off at something like 50kcas iirc, and speedbrake of course, bearing in mind its affect on directional controllability. I would test with this technique as this is the maximum deceleration that I'm sure the graphs are drawn from.

 

As for the 4500ft number, that looks awfully like the number for a wet runway in the given 32k GW example.

[oldcrusty]

24 minutes ago, Swiftwin9s said:

The technique is to pull back fully on the stick when below 100kcas, apply full brakes until the antiskid cuts off at something like 50kcas iirc, and speedbrake of course, bearing in mind its affect on directional controllability. I would test with this technique as this is the maximum deceleration that I'm sure the graphs are drawn from.

 

As for the 4500ft number, that looks awfully like the number for a wet runway in the given 32k GW example.

 

All tests I've done were w/ 32k gw.  The speedbrake directional control problem (if any happen) are not simulated yet.  For all my recent tests the speedbrake was not used. It cuts down around 350 ~ 400' of ground roll.

 

Now, here's the weird stuff...  At Haifa,  I'm able to stop in 3400' every time using only wheelbrakes w/ antiskid.  The runway surface looks the same as any other concrete runway (asphalt?)  The only visual difference I can see is the rubber laid on the surface from the tires, lol. I don't think DCS goes that deep into friction and types of runways.

[Skysurfer]

12 minutes ago, Gripes323 said:

 

All tests I've done were w/ 32k gw.  The speedbrake directional control problem (if any happen) are not simulated yet.  For all my recent tests the speedbrake was not used. It cuts down around 350 ~ 400' of ground roll.

 

Now, here's the weird stuff...  At Haifa,  I'm able to stop in 3400' every time using only wheelbrakes w/ antiskid.  The runway surface looks the same as any other concrete runway (asphalt?)  The only visual difference I can see is the rubber laid on the surface from the tires, lol. I don't think DCS goes that deep into friction and types of runways.

 

What about runway slope? Different runways across different maps "could" have a different friction value. (just an assumption of course).

[Stearmandriver]

9 minutes ago, Skysurfer said:

 

What about runway slope? Different runways across different maps "could" have a different friction value. (just an assumption of course).

Good thought; I was just wondering about map differences too.  Runways in PG are definitely harder to kill than Caucuses... but man, you'd expect ground friction values to be global?  Dunno.