Realistic weather related runway friction performance and runway material condition

[DmitriKozlowsky]

Runways are more difficult to stop on when wet and when iced over or snow covered.

Can't say for certain. I don't see any runway skidding issues when landing regardless of weather or runway condition.

Material condition of runway also effects performce of stopping aircraft. If those variables could be taken into account that would be interesting.

I am not an aviation professional, but I play one when I watch MayDay or Air Crash Investigation. Runway condition was a topic that was handled on few mishaps.

[=DROOPY=]

When it comes to runway friction measurements taken during a winter weather event, you are venturing into the proverbial abyss. 

Not sure how military airports conduct friction testing, but at all FAA certified FAR Part 139 airports, they are mandated to conduct friction testing during winter weather events, and convey that information to the airport ATCT, and through what we call SNOTAMS.

In my humble opinion, and considering that runway friction is one facet of my occupation, I would advise that if any runway friction related changes be made, that the changes be restricted to 'wet' runway conditions only.

A 'wet' runway, as far as simulating runway surface friction, would be much more of a 'known' set of conditions, vs simulating Ice/Snow/Slush/Sleet/Freezing Rain/Graupel and, as if that wasn't enough, the surface depth of those types of winter precipitation present on the runway surface. For proper measurements, those depths also have to be entered into the database for a proper measurement to be correlated. (!)

IRL, (where I am employed) if a runway measurement through friction testing is deemed unsafe, the runway is effectively closed to any and all air operations, and the runway surface treated and continually tested until it is deemed 'safe' for use. 

In those instances, friction measurements are taken continuously, during the time snow removal crews and equipment are working on the runway, and until the the amount of friction measured meets or exceeds what the (as far as US is concerned) FAA determines is required, with several variables at play, including the above, along with the consideration of the age of the runway, and what the runway itself is made of-Blacktop or Concrete. 

During warmer weather, when rain is the only thing to worry about, we issue what are called FICON NOTAMS for each active runway.

They usually follow a format similar to:

RWY 17L FICON 5/5/5 100% WET EFF 2408171812-2408181812

The 5/5/5 refers to Touchdown/Midpoint/Rollout sections of the runway respectively.

100% = Full length of Runway 

Wet= 1/4in or less of liquid surface moisture. 

2408171812= Year/Month/Day/GMT

Based on that, aircrews will adjust their braking action according to their aircraft landing weight and runway surface length available. My job is to just provide the information so they can plan accordingly.

Fun fact: Most, if not all concrete runways, are 'crowned' in the center, and have grooves cut from the centerline to the shoulder to allow for efficient drainage to prevent the aircraft from hydroplaning.

Edited August 18, 2024 by =DROOPY=

[MiG21bisFishbedL]

I've been wanting this for a while, mostly because I want an actual reason to deploy drag chutes on the Fishbed and Farmer. Overall, DCS models rolling friction in a pretty simplistic manner, it feels.

Edited August 17, 2024 by MiG21bisFishbedL

[DmitriKozlowsky]

On 8/17/2024 at 2:37 PM, MiG21bisFishbedL said:

I've been wanting this for a while, mostly because I want an actual reason to deploy drag chutes on the Fishbed and Farmer. Overall, DCS models rolling friction in a pretty simplistic manner, it feels.

 

Friction is constant in DCS, IMHO, based on my observation. There is no variation between runway, taxiway, or tarmac. Friction is higher on rough field and grass, but is consistent. So landing on wet grass is no different the on dry grass, or sand-corral in Mariannas. Which is OK, as DCS is about flight and combat not total ground to ground experience in aircraft handling. Its a reasonable compromise. However in extreme wet or snow conditions, ED should or could make stopping more difficult. Also I don't fee; brake fade in DCS. Overheated brakes should stop working or cause fires, but that malfunction is something I have not experienced in DCS in any fixed wing mod I own. Not for lack of trying. But DCS , in Hornet does simulate, stores separation collision, which is good touch.

[DmitriKozlowsky]

On 8/17/2024 at 2:37 PM, MiG21bisFishbedL said:

I've been wanting this for a while, mostly because I want an actual reason to deploy drag chutes on the Fishbed and Farmer. Overall, DCS models rolling friction in a pretty simplistic manner, it feels.

 

On Russian aircraft you should always use brake chutes. Russian aircraft, except transports and airliners, are designed to rely on chutes as primary speed arrest system on landing roll. Gear brakes are too weak. Thats a compromise on weight, cost, and complexity. IRL and in DCS, Mig-21 can roll off runway if chute is not deployed or released ,  by accident, upon inflation. I happen to agree with Russian design logic. Brake chute extraction is extremely reliable. Ground crew really has to go out of their way to tangle and mispack a chute. Even on American designs, B-47 in 1950's, flight crew could do it themselves, just by rolling up and stuffing chute back into housing, and hooking lanyard to release clamps. I am a terrible cross-wind lander. I use brake chute, in a prohibited fashion, to correct for pilot error, to stop crazy fishtailing. With one major rule, never to violate. DO NOT USE ON BOUNCE! Bounce, Go Around. Good ol'fashioned TOGA.

Take Off power, Gear up, Accelerate.  Your basic flight safety 101 taught in flight schools.

[MiG21bisFishbedL]

On 9/3/2024 at 11:35 AM, DmitriKozlowsky said:

On Russian aircraft you should always use brake chutes. Russian aircraft, except transports and airliners, are designed to rely on chutes as primary speed arrest system on landing roll. Gear brakes are too weak. Thats a compromise on weight, cost, and complexity. IRL and in DCS, Mig-21 can roll off runway if chute is not deployed or released ,  by accident, upon inflation. I happen to agree with Russian design logic. Brake chute extraction is extremely reliable. Ground crew really has to go out of their way to tangle and mispack a chute. Even on American designs, B-47 in 1950's, flight crew could do it themselves, just by rolling up and stuffing chute back into housing, and hooking lanyard to release clamps. I am a terrible cross-wind lander. I use brake chute, in a prohibited fashion, to correct for pilot error, to stop crazy fishtailing. With one major rule, never to violate. DO NOT USE ON BOUNCE! Bounce, Go Around. Good ol'fashioned TOGA.

Take Off power, Gear up, Accelerate.  Your basic flight safety 101 taught in flight schools.

Honestly, I can stop the Fishbed on almost any runway in DCS without the use of a chute. Even landing well overweight with too much fuel. The amount of friction you can produce does not feel accurate to operational accounts I have read. Is it LNS/Mag3's fault or ED's? I can't say. I'd just love to see it addressed. I usually save the chute for STOL operations when I'm popping it before touch down, as demo'd here:
 

So, being forced to rely on that chute is something I'd LOVE to see.

Also, if you're having issues with the Fishbed on landing in a nasty crosswind, the chute is a very good solution. Another would be land at a higher speed. 90% of any issue you have in the Fishbed can be addressed if you just perform whatever maneuver or phase of flight at a higher relative speed. As Have Doughnut indicates, it's a very honest aircraft. Also, play with flaps. Sure, you won't get BLC, but sometimes full-flaps can be detrimental in strong winds. It's not in the POH, but honestly? The only people who are going to jump on you for it are people who need to accept they're not getting that highly coveted AF Career, anyways.

Edited September 4, 2024 by MiG21bisFishbedL

[DmitriKozlowsky]

8 hours ago, MiG21bisFishbedL said:

Honestly, I can stop the Fishbed on almost any runway in DCS without the use of a chute. Even landing well overweight with too much fuel. The amount of friction you can produce does not feel accurate to operational accounts I have read. Is it LNS/Mag3's fault or ED's? I can't say. I'd just love to see it addressed. I usually save the chute for STOL operations when I'm popping it before touch down, as demo'd here:
 

So, being forced to rely on that chute is something I'd LOVE to see.

Also, if you're having issues with the Fishbed on landing in a nasty crosswind, the chute is a very good solution. Another would be land at a higher speed. 90% of any issue you have in the Fishbed can be addressed if you just perform whatever maneuver or phase of flight at a higher relative speed. As Have Doughnut indicates, it's a very honest aircraft. Also, play with flaps. Sure, you won't get BLC, but sometimes full-flaps can be detrimental in strong winds. It's not in the POH, but honestly? The only people who are going to jump on you for it are people who need to accept they're not getting that highly coveted AF Career, anyways.

 

THey are popping brake chutes before weight on wheels. That is dangerous, and in USAF is prohibited , in every type, AFAIK. FIshbed can land on grass, and on grass the friction is so high that chute is not needed. But those guys popping before touch down. Really bold and ballsy. Becouse it assumed that there will be no bounce.These appears to be at airshow, so the pilots are likely best of the best with honors, from the squadrons. In USAF, B-47 crews and their aircraft were lost becouse they popped before touchdown. A/C would stall too high and just fall , breaking gear, or bouncing and stalling within fuselage height.

[MiG21bisFishbedL]

On 9/4/2024 at 9:14 PM, DmitriKozlowsky said:

THey are popping brake chutes before weight on wheels. That is dangerous, and in USAF is prohibited , in every type, AFAIK. FIshbed can land on grass, and on grass the friction is so high that chute is not needed. But those guys popping before touch down. Really bold and ballsy. Becouse it assumed that there will be no bounce.These appears to be at airshow, so the pilots are likely best of the best with honors, from the squadrons. In USAF, B-47 crews and their aircraft were lost becouse they popped before touchdown. A/C would stall too high and just fall , breaking gear, or bouncing and stalling within fuselage height.

The popping the drag chute before landing, as I understand, was a STOL technique for the Fishbed. It's not that risky, but your ground crew will hate your guts since it mandates a thorough go-over of the airframe.

[DmitriKozlowsky]

2 hours ago, MiG21bisFishbedL said:

The popping the drag chute before landing, as I understand, was a STOL technique for the Fishbed. It's not that risky, but your ground crew will hate your guts since it mandates a thorough go-over of the airframe.

You can see the near-hard touch down. Almost expecting the gear to fold uncommanded. Bending main gear means that aiframe is probably bent at wing root. By bent, it may not be physically apparent to be bent, but certainly the airframe's life has just been shortened, or depot maintenance has been pushed up.

[MiG21bisFishbedL]

On 9/6/2024 at 2:41 AM, DmitriKozlowsky said:

You can see the near-hard touch down. Almost expecting the gear to fold uncommanded. Bending main gear means that aiframe is probably bent at wing root. By bent, it may not be physically apparent to be bent, but certainly the airframe's life has just been shortened, or depot maintenance has been pushed up.

Exactly, your ground crew is going to hate you for it!

[Lace]

I think the main reason Soviet/Russian designs featured brake chutes is nothing to do with their inability to engineer an effective wheel brake system, but due to the winter conditions in which they were expected to operate.  Same reason the RNoAF F-16s and F-35s have brake chutes, the Viggen has a thrust reverser, etc.  You are eliminating the reliance on tyre/runway friction to stop the aircraft in ice and snow.

It would be great if runway surface friction was accurately modelled, and varied due to weather conditions.

[DmitriKozlowsky]

8 hours ago, Lace said:

I think the main reason Soviet/Russian designs featured brake chutes is nothing to do with their inability to engineer an effective wheel brake system, but due to the winter conditions in which they were expected to operate.  Same reason the RNoAF F-16s and F-35s have brake chutes, the Viggen has a thrust reverser, etc.  You are eliminating the reliance on tyre/runway friction to stop the aircraft in ice and snow.

It would be great if runway surface friction was accurately modelled, and varied due to weather conditions.

WInter is part of it, but cost and complexity is primary reason. There have been infrequent incidents of Russian aircraft, especcially SU-34 and SU-24, running out of dry summer runway due to brake chute failiure. Wheel brakes are not enough to stop landed Russian tactical aircraft. They have to use chutes, then rely on brakes after chute release.This allows wheel brakes to be lighter and simpler. Russians figure that chance of chute fail is far lower then brake fade or brake fail. In this they are right. American F-15s and F-16s have run off the runway , with zero altitude, low speed, ejection, due to brake fail. Always risky. Not all runways have functional emergency trap wires. American major air bases have runways to handle largest B-52 and C-5M landing at max gross weight. So they are very long. Long enough that tactical aircraft can stop even with marginal brakes. But that is not case for all runways , where USAF F-15s and F-16s operate fromNorwegian F-16's have tail brake chutes for winter snow runway use. Finns use hook to stop on road runways and winter snow covered runways. 

[renhanxue]

10 hours ago, Lace said:

I think the main reason Soviet/Russian designs featured brake chutes is nothing to do with their inability to engineer an effective wheel brake system, but due to the winter conditions in which they were expected to operate.  Same reason the RNoAF F-16s and F-35s have brake chutes, the Viggen has a thrust reverser, etc.  You are eliminating the reliance on tyre/runway friction to stop the aircraft in ice and snow.

It would be great if runway surface friction was accurately modelled, and varied due to weather conditions.

Trivia: the flight manual for the real-life Viggen notes that using the thrust reverser on a snow-covered and/or icy runway may reduce the runway friction coefficient. I guess it's because you're blowing away all the gravel and other stuff that might otherwise add some friction.

There are probably many reasons why the Swedish air force chose a thrust reverser for the Viggen over a braking chute (like the Draken had). For one thing it was supposed to operate from 800x17 meter strips with very short turnaround times, and they probably didn't like the crosswind restrictions of a braking chute nor the time required to repack it. A carrier-style hook was probably an acceptable alternative (and one of the alternative aircraft considered was the F-4) but I guess they didn't like the infrastructure requirements. There were a lot of runways in the dispersed basing system, after all.

The Gripen can operate from the same 800x17 runways though without a thrust reverser, but it has both better wheel brakes and the ability to use the entire canard surface as a huge airbrake. It's also significantly lighter than the Viggen.

Edited September 10, 2024 by renhanxue

[Lace]

10 hours ago, DmitriKozlowsky said:

WInter is part of it, but cost and complexity is primary reason. There have been infrequent incidents of Russian aircraft, especcially SU-34 and SU-24, running out of dry summer runway due to brake chute failiure. Wheel brakes are not enough to stop landed Russian tactical aircraft. They have to use chutes, then rely on brakes after chute release.This allows wheel brakes to be lighter and simpler. Russians figure that chance of chute fail is far lower then brake fade or brake fail. In this they are right. American F-15s and F-16s have run off the runway , with zero altitude, low speed, ejection, due to brake fail. Always risky. Not all runways have functional emergency trap wires. American major air bases have runways to handle largest B-52 and C-5M landing at max gross weight. So they are very long. Long enough that tactical aircraft can stop even with marginal brakes. But that is not case for all runways , where USAF F-15s and F-16s operate fromNorwegian F-16's have tail brake chutes for winter snow runway use. Finns use hook to stop on road runways and winter snow covered runways. 

Or, do they fit smaller, lighter braking systems [i]because[/i] they have a brake 'chute due to winter stopping requirements, and the SOP is to deploy it on every landing? 

 

[bies]

B-47 regularly landed with drag chute deployed way before the touchdown due to B-47 slick low drag design, after that touchdown, another, bigger chute was released.

[MiG21bisFishbedL]

On 9/10/2024 at 4:54 PM, renhanxue said:

Trivia: the flight manual for the real-life Viggen notes that using the thrust reverser on a snow-covered and/or icy runway may reduce the runway friction coefficient. I guess it's because you're blowing away all the gravel and other stuff that might otherwise add some friction.

There are probably many reasons why the Swedish air force chose a thrust reverser for the Viggen over a braking chute (like the Draken had). For one thing it was supposed to operate from 800x17 meter strips with very short turnaround times, and they probably didn't like the crosswind restrictions of a braking chute nor the time required to repack it. A carrier-style hook was probably an acceptable alternative (and one of the alternative aircraft considered was the F-4) but I guess they didn't like the infrastructure requirements. There were a lot of runways in the dispersed basing system, after all.

The Gripen can operate from the same 800x17 runways though without a thrust reverser, but it has both better wheel brakes and the ability to use the entire canard surface as a huge airbrake. It's also significantly lighter than the Viggen.

 

That's some interesting stuff.

I imagine, in the end, using an arresting cable would require another course that some conscripts would have to go through and another set of specialty equipment that could potentially be destroyed by an aggressor or (more likely) broken by 19 year old dimwits despite the best efforts of the manufacturer to idiot proof it.

Thrust reverser makes sense.

Edited September 19, 2024 by MiG21bisFishbedL