question on cross wind landing?

[fitness88]

I've done reading on crabbing/de-crabbing and side slipping. Flying a self made mission with a steady cross wind I start crabbing when I'm on final, 10-15 miles out. I 'weather vane' the nose into the wind but I'm always using ailerons to try and keep the angle into the wind.

I find I drift too far left of centre line or too far right but in the videos it seems like a smooth drift once you get the correct angle into the wind.

Side slipping instead of crabbing is easier for me.

 

Any one like to share their techniques?

 

Thank you.

[effte]

In the real world, the FM states to "Hold the crab through touchdown". Not uncommon among fighters. Delta wings and swept wings aren't ideally suited for slipping, and there's always the issue of clearance for underwing stores.

 

The landing gears are built to take it.

 

Expect to be adjusting your crab continuously as you approach. It's really a non-issue, and something you won't even pay much attention to after a while. Just look where you are going and keep the aircraft travelling down the extended centerline. I suspect you are focusing too much on where the nose is, and lose track of what you should be looking at - your track towards the runway.

Edited October 31, 2014 by effte

[fitness88]

Thank you both for that good info. Good tip about coming in faster with a greater cross wind. Also quite correct about me focusing too much on the nose and losing the runway centre line as a result.

[effte]

Good tip about coming in faster with a greater cross wind.

 

Ah, missed that bit. No, you don't. The F-15C -1 FM says to use normal on-speed AoA, but that AoA variations are more critical with a crosswind.

 

 

In other aircraft, you may add to the approach speed for headwinds and gusts, but not for crosswinds per se.

 

For adding to the approach speed (Vref) due to wind, there's a Great Wind Additive Debate within aviation that has been going on for 40 years now, but the majority vote (which I consider fair advice) seems to be for adding half of the headwind and all of the gust factor to your approach speed, up to a sanity threshold. That's also the side the major manufacturers seem to be taking.

 

If the wind is 12012G20KT and you are landing runway 12 (wind out of 120 degrees, 12 knots gusting to 20 knots, 120 degrees runway heading), the headwind is 12 knots and the gust factor is the difference betweeen the steady wind and the gusts, or 20-12=8 knots.

 

You add 12/2+8 knots or 14 knots to your normal approach speed.

 

Had the wind been out of 210 degrees - direct crosswind - you only add the gust factor or 8 knots.

 

The headwind additive is to be prepared for the fact that the wind will drop off as you descend on short final, and the gust factor is so you won't end up slow if a gust catches you. The sanity factor advised for the big iron is 20 knots, so that's the maximum you ever add.

 

The trick is then to let the additives trickle off as you are on short final (another hot debate issue, stabilized approach vs approach speed changes). If you leave them on the ASI, you're going to float and land very long indeed. But let it bleed off too soon, and you're setting yourself up to get in trouble as the headwind drops off on the final few hundred feet of the descent - especially if you're hit by an unfortunate gust of wind at the same time.

 

What you can (and often should) do if the crosswind is approaching what you and your aircraft are comfortable with is to reduce the flap setting. This will mean a higher approach speed, but use the book number for that flap setting and the wind additive.

 

 

The spam can community (Cessnas, Cherokees and the like) tend to go with half the gust factor as the additives become proportinally larger with the slower approach speeds. Then again, they tend to stay on the ground a lot sooner as the winds pick up.

 

 

Bonus info: Not all crosswinds are the same. The saying goes: 'Learn to love left crosswind'. In the northern hemisphere, the wind tends to turn to the right in the gusts, so a left crosswind will have gusts which are more head-on, while right crosswind will become more crosswind in the gusts. I am fairly sure that's outside of what DCS models though. :)

 

Cheers,

/Fred

[fitness88]

Ah, missed that bit. No, you don't. The F-15C -1 FM says to use normal on-speed AoA, but that AoA variations are more critical with a crosswind.

 

 

In other aircraft, you may add to the approach speed for headwinds and gusts, but not for crosswinds per se.

 

For adding to the approach speed (Vref) due to wind, there's a Great Wind Additive Debate within aviation that has been going on for 40 years now, but the majority vote (which I consider fair advice) seems to be for adding half of the headwind and all of the gust factor to your approach speed, up to a sanity threshold. That's also the side the major manufacturers seem to be taking.

 

If the wind is 12012G20KT and you are landing runway 12 (wind out of 120 degrees, 12 knots gusting to 20 knots, 120 degrees runway heading), the headwind is 12 knots and the gust factor is the difference betweeen the steady wind and the gusts, or 20-12=8 knots.

 

You add 12/2+8 knots or 14 knots to your normal approach speed.

 

Had the wind been out of 210 degrees - direct crosswind - you only add the gust factor or 8 knots.

 

The headwind additive is to be prepared for the fact that the wind will drop off as you descend on short final, and the gust factor is so you won't end up slow if a gust catches you. The sanity factor advised for the big iron is 20 knots, so that's the maximum you ever add.

 

The trick is then to let the additives trickle off as you are on short final (another hot debate issue, stabilized approach vs approach speed changes). If you leave them on the ASI, you're going to float and land very long indeed. But let it bleed off too soon, and you're setting yourself up to get in trouble as the headwind drops off on the final few hundred feet of the descent - especially if you're hit by an unfortunate gust of wind at the same time.

 

What you can (and often should) do if the crosswind is approaching what you and your aircraft are comfortable with is to reduce the flap setting. This will mean a higher approach speed, but use the book number for that flap setting and the wind additive.

 

 

The spam can community (Cessnas, Cherokees and the like) tend to go with half the gust factor as the additives become proportinally larger with the slower approach speeds. Then again, they tend to stay on the ground a lot sooner as the winds pick up.

 

 

Bonus info: Not all crosswinds are the same. The saying goes: 'Learn to love left crosswind'. In the northern hemisphere, the wind tends to turn to the right in the gusts, so a left crosswind will have gusts which are more head-on, while right crosswind will become more crosswind in the gusts. I am fairly sure that's outside of what DCS models though. :)

 

Cheers,

/Fred

 

Thanks...time to break out the slide ruler:smartass:

[effte]

Nah, in the F-15 you get out easy. Just fly that AoA indexer and be happy. :)

[fitness88]

From practicing on the F-15c I see all you need to do is have the velocity vector pointing to the touch down spot on centre line and forget about where the nose is pointing, until you de-crab.

 

Also, has anyone noticed that disengaging the nose wheel steering [LAlt-Q] only works well after 50-70 knots? I understand below that speed you are going too slow for the rudders to steer but in addition if [LAlt-Q] is pressed before that speed the nose wheel turns erratically steering you uncontrollably and continues even after you attain 70+knots.

Edited November 1, 2014 by fitness88

[bkthunder]

Guys don't forget the F-15 AFM has a bugged Yaw CAS that's always trying to point your nose into the wind. Until they fix that, either switch off the Yaw channel or don't fly with wind.

It's still a beta (and god know for how long...)

[104th_Maverick]

Also, has anyone noticed that disengaging the nose wheel steering [LAlt-Q] only works well after 50-70 knots?

 

I dont touch Lalt+Q at all.... at any time!

 

After I land I use the rudder to steer until below 20kts (nose wheel will move with rudder on the ground) then when ever I want to make any turns I press and hold S for Nose Gear Maneuvering when under 20kts. When I've made the turn I simply release S.

 

This works perfectly well for vacating the runway and also taxiing to and from it.

[TAW_Blaze]

NWS disengage is misleading. I think there was another thread where it was stated this mode is for when the plane is being towed around.

[fitness88]

NWS disengage is misleading. I think there was another thread where it was stated this mode is for when the plane is being towed around.

 

I read that thread as well but it doesn't make sense. In real world jets you have a nose wheel disengage capability above approx. 70 which then only allows the rudder to steer.

I will do more research on this.

[TAW_Blaze]

I read that thread as well but it doesn't make sense. In real world jets you have a nose wheel disengage capability above approx. 70 which then only allows the rudder to steer.

I will do more research on this.

 

It does make sense. I think NWS is disabled by default so you can only steer with the rudder and if you hold the button then it enables it.

[fitness88]

It does make sense. I think NWS is disabled by default so you can only steer with the rudder and if you hold the button then it enables it.

 

The problem is when the NWS is disabled the NW itself is supposed to default centre and fixed to allow only rudder steering but under newly discovered conditions it doesn't. Instead it flip flops wildly.

Now with some testing I have noticed the NSW steering when disengaged above 60-70 will then force the NW centre and fixed but if disengaged below 60 the NW will track erratically.

 

Confirmed, after another test the NW when disengaged under 70 will rotate freely and without any control, perhaps by design to allow for better towing.

When engaged over 70 it snaps forward and centered and allows for only rudder steering, which is what you should have to control the plane.

Edited November 4, 2014 by fitness88

[fitness88]

Well, that would be nice if it worked in every situation.. Take batumi for instance with only 1 runway... If you have a strong enough and the right cross wind the TVV will be off the hud and unable to be used.

With effte's post about using the AOA. Yes you're correct. I still increase my speed in cross wind landings regardless, for me it makes it a bit easier to land.

 

Yes that just happened to me... is it a bug or real world.

[GGTharos]

The problem is when the NWS is disabled the NW itself is supposed to default centre and fixed to allow only rudder steering but under newly discovered conditions it doesn't. Instead it flip flops wildly.

 

Where does it say that? L-ALT-Q is a feature used for towing the aircraft, it is not used by the pilot normally, period.

Edited November 6, 2014 by GGTharos

[fitness88]

Where does it say that? L-ALT-Q is a feature used for towing the aircraft, it is not used by the pilot normally, period.

 

Not from the manual but from various websites dedicated to the F-15. Also it is commonly used on commercial aircraft as well.

Where did you see it say L-ALT-Q is for towing?

 

The last several flights I finally have great high speed runway control when T/O or Landing using L-ALT-Q. Under 70 it freewheels out of control, over 70 it snaps fixed and straight allowing for great control. As a result I assumed it has the dual function of both towing from what you wrote and rudder steering based on my experience.

Edited November 6, 2014 by fitness88

[GGTharos]

What is done on other aircraft is irrelevant.

 

In the F-15, the system disengages the nose-wheel steering automatically when the front gear strut is extended, and engages it when the strut is compressed. No action by the pilot is required.

 

Not from the manual but from various websites dedicated to the F-15. Also it is commonly used on commercial aircraft as well.

Where did you see it say L-ALT-Q is for towing?

[fitness88]

What is done on other aircraft is irrelevant.

 

In the F-15, the system disengages the nose-wheel steering automatically when the front gear strut is extended, and engages it when the strut is compressed. No action by the pilot is required.

 

Where are you reading this?

 

On approach when the gear is extended there will be no movement of the NSW until once the plane lands and the nose comes down...this I understand.

For me, at the moment it engages with the NSW down, steering the plane is easier to control with only rudder activity, until under around 70, then the NSW works better.

[GGTharos]

I read it in the F-15 pilot's manual, the -1.

 

Also, generally speaking you're supposed to be aerobraking until 90kts anyway, so the nosewheel shouldn't be on the ground before that. Then only time you would do this is if you're performing a minimum-ground-roll, in which case you need to land in a very specific way, get the nose down, and hit the brakes right away.

 

In normal operation, keep the nose at 13deg to 15deg pitch (less than 13, ineffective aerobraking, more than 15, tailstrike) until 80-90kts, then lower to the ground.

Edited November 6, 2014 by GGTharos

[fitness88]

I read it in the F-15 pilot's manual, the -1.

 

Also, generally speaking you're supposed to be aerobraking until 90kts anyway, so the nosewheel shouldn't be on the ground before that. Then only time you would do this is if you're performing a minimum-ground-roll, in which case you need to land in a very specific way, get the nose down, and hit the brakes right away.

 

In normal operation, keep the nose at 13deg to 15deg pitch (less than 13, ineffective aerobraking, more than 15, tailstrike) until 80-90kts, then lower to the ground.

 

Thanks for the information GGTharos.

What I said also applies to taking off, once speeds get over 60 especially with a crosswind, keeping the nose centre line is made easier with only rudder steering and having the NSW locked straight/forward. I've watched the NSW behavior from outside the plane and it does in fact free turn under 60-70 and locks straight/forward over 60-70...why do you suppose it does that if not to allow for 100% rudder steering?

[GGTharos]

I think the behavior that isn't modeled (I could be wrong) is for the nosewheel to unlock when the strut is not compressed and vice versa.

[fitness88]

I think the behavior that isn't modeled (I could be wrong) is for the nosewheel to unlock when the strut is not compressed and vice versa.

 

I've been looking around the net for additional info, will let you know when I find some. In the mean time...it works well for me.

 

Thanks again.