why does my HUD look off center?

Hi guys, i've noticed that my HUD sometimes looks like it's more towards the rides, it's hard to explain when i use the rudder it center it, does this have to do with crosswind ? is it another way to tell me that i need to turn towards that side because of the heading i'm supposed to go to? i noticed this also happens in flaming cliffs 2 on the F-15.

Thanks!

Yes, it's the wind.

Yes . It's a visualisation of the discrepancy between your calculated flight path (by given control input) and the real heading of your plane. This drift is caused by the moving air around you - commonly known as wind. :)

You're correct, it's due to crosswind (assuming you're flying coordinated). For coordinated flight, use the rudder to center the ball (rudder towards the ball - 'step on the ball') and let the pitch ladder in the HUD do its thing. No way to force it to center in the Hog, unlike e g in the Viper.

Same question here! thanks for the answers!!!

Hi guys, i've noticed that my HUD sometimes looks like it's more towards the rides, it's hard to explain when i use the rudder it center it, does this have to do with crosswind ? is it another way to tell me that i need to turn towards that side because of the heading i'm supposed to go to? i noticed this also happens in flaming cliffs 2 on the F-15.

 

Thanks!

Thanks for asking - was going to ask the same question myself! - All thanks for the response! You've helped me understand that little bit more.

Cheers all!:thumbup:

Yes, thanks for clarifying, I notice this in Falcon 4 Allied Force as well as ED sims.

Thanks guys, just another quick question, when this happens should i worry about using the rudder to center the pitch ladder or should i just let it center itself? it usually doesn't cause me to go off track by much but i'd like to know what the pilots usually do in that situation, thank you again for the help!

Use the rudder(s) to center the ball. Let the pitch ladder end up wherever it ends up. If you have a crosswind, it will be off from center when you are Doing It Right.

This, i e the ball in the glass tube, is what you need to worry about - forget the pitch ladder. Just step on the ball and keep it centered.

The one exception would be if you have an engine out, but I suggest saving that for later. :)

By what mechanism does the (real) A-10 determine the crosswind? Since it is within the moving airmass and moving with it, as long as the crosswind is steady, the aircraft should be unable to "know" that it is in a crosswind. Is there some sort of sensor pointing at the ground? That's the only way I can think of that the aircraft might be able to tell that there is a crosswind, barring gusts.

Edit: wait, I think PeterP answered this in the second post of the thread; that is, the flight computer predicts where your flight path would be without wind, using solely your control inputs (and perhaps indicated airspeed and/or altitude).

Use the rudder(s) to center the ball. Let the pitch ladder end up wherever it ends up. If you have a crosswind, it will be off from center when you are Doing It Right.

 

This, i e the ball in the glass tube, is what you need to worry about - forget the pitch ladder. Just step on the ball and keep it centered.

 

 

The one exception would be if you have an engine out, but I suggest saving that for later. :)

What is the ball?

What is the ball?

Is that a trick question? :D

In the above image, you can see an aircraft symbol banked right wing down.

Below that is a glass tube with white background and a black, ball shaped object. This tube with the ball is called the Slip Indicator. In the above image, the ball is offset to the right and the aircraft is slipping.

In order to fly coordinated, always "step on the ball", i.e. input rudder in the direction the ball is offset until the ball is centered. Also step on the ball during every turn, if it doesn't stay centered on its own (the A-10C's SAS should go a long way towards automating it, but not every aircraft has SAS, or it could fail).

In the above image, the pilot would need to input quite a bit of right rudder in order to fly coordinated.

Is there a way to use the ball or offset pitch ladder to help us know how much crab angle to use during a crosswind landing.. I am finding it very difficult to know how much rudder to put into a crosswind landing. Instead of just figuring it out using the known wind in knots and direction of wind, it would be much easier if we could use an instrument.

Thanks in advance.

Yes . It's a visualisation of the discrepancy between your calculated flight path (by given control input) and the real heading of your plane. This drift is caused by the moving air around you - commonly known as wind. :)

Which one is the calculated flight path and which one is the real heading. ie is the data block area the calculated flight path and the pitch ladder the real heading?

Is there a way to use the ball or offset pitch ladder to help us know how much crab angle to use during a crosswind landing.. I am finding it very difficult to know how much rudder to put into a crosswind landing. Instead of just figuring it out using the known wind in knots and direction of wind, it would be much easier if we could use an instrument.

 

Thanks in advance.

Recommended approach in crosswind is to simply point the airplane into the wind such that the airplane motion is along the desired path. There is no rudder input required beyond the normal turn coordination.

Upon touchdown the airplane may be rotated with pedal input to align the fuselage with the runway. This would be done without reference to the coordination instrument (the goal of the maneuver isn't a coordinated one anyway).

No, there isn't an instrument. Furthermore the ball is centered until the flare when you take out the crab angle.

Even knowing the exact crosswind component isn't a recipe for a fixed amount of rudder to apply to take out the crab angle. That's something you need experience and training for.

And if it's the wrong amount nothing bad happen, only a less than perfect touchdown.

So could you then say that the aircraft is slipping due to the wind and the pitch ladder in the HUD being offset is an indication of this. Therefore keeping the ball centered is stopping the slip. So keeping the ball centered will give you the correct amount of crab angle. I might be wrong, but Im just trying to work out a formula.

Slip is an aerodynamic condition of a non-zero beta angle. Crabbing is a no-slip condition. A heading into the wind to track along the extended runway centerline is just a crab.

The latereral inclinometer ball shows where the local acceleration is pointing, straight into the floor or left/right. The same knowledge can be found by dropping a ham sandwich and checking if it falls straight down to the floor or hits your left/right foot. When the airplane banks the balls wants to roll toward the part of the tube closest to the center of the Earth. A circular turning path throws the ball toward the outside end of the tube. A coordinated turn is one where these two tendencies balance such that the ball is centered between the lines. A weight on the end of a string would hang straight toward the floor of the cockpit.

The ball provides no useful information about crab angle as it is happily centered wings level with no heading change rate regardless of heading (and consequently ground track).

The simplest tool to use for a wind-corrected ground track is the total velocity vector (TVV) symbol on the HUD as it shows you the direction the airplane is moving. In airplanes without this tool (or TVV is off HUD) a trained pilot can judge the direction of motion by eye.

Calculating the heading to steer in a wind is a vector addition problem. Given a wind vector, true air speed, and desired course the heading to steer can be found. E.g.:

Wind 10 knots to the SE, desired track to N, TAS 100 knots.

Flight on heading 355.945° results in a 92.679 knot ground track of 360°.

In practice the calculation can be made much simpler by only considering the lateral wind component and 1° = 60:1.

E.g.: 10 knot crosswind at 45° (SE) is 70% component so 7 knot lateral. 100:7 is about 60:4. Adjust into the wind by 4° (356°) to track north.

Slip is an aerodynamic condition of a non-zero beta angle. Crabbing is a no-slip condition. A heading into the wind to track along the extended runway centerline is just a crab.

 

The latereral inclinometer ball shows where the local acceleration is pointing, straight into the floor or left/right. The same knowledge can be found by dropping a ham sandwich and checking if it falls straight down to the floor or hits your left/right foot. When the airplane banks the balls wants to roll toward the part of the tube closest to the center of the Earth. A circular turning path throws the ball toward the outside end of the tube. A coordinated turn is one where these two tendencies balance such that the ball is centered between the lines. A weight on the end of a string would hang straight toward the floor of the cockpit.

 

The ball provides no useful information about crab angle as it is happily centered wings level with no heading change rate regardless of heading (and consequently ground track).

 

The simplest tool to use for a wind-corrected ground track is the total velocity vector (TVV) symbol on the HUD as it shows you the direction the airplane is moving. In airplanes without this tool (or TVV is off HUD) a trained pilot can judge the direction of motion by eye.

 

Calculating the heading to steer in a wind is a vector addition problem. Given a wind vector, true air speed, and desired course the heading to steer can be found. E.g.:

 

Wind 10 knots to the SE, desired track to N, TAS 100 knots.

Flight on heading 355.945° results in a 92.679 knot ground track of 360°.

 

In practice the calculation can be made much simpler by only considering the lateral wind component and 1° = 60:1.

 

E.g.: 10 knot crosswind at 45° (SE) is 70% component so 7 knot lateral. 100:7 is about 60:4. Adjust into the wind by 4° (356°) to track north.

But on approach to a runway with cross wind I can keep the TVV on the runway using the ailerons and no rudder input.

Its all about asking the right question... So how then do you know how much rudder to give for a crosswind landing when you cant see the runway. example IFR, ILS approach.

If you can't see the runway you can't land, hence no rudder needed ;)

IF you are using the rudder to align your plane with the runway, you normally are doing that just before or during the flare, and at this point you have the runway in sight since quite some time, even in the worst conditions.

Ok this is finally answers my question! "just before flare" from the videos I saw they were crabbing a very long way out from touch down?

I dont think this is quite right. All the cross wind landing tutorials I have seen they say to rudder into the wind on approach to keep the aircraft aligned with the runway. Then just before flare you perform a slip to align the nose back into line with runway. So then this goes back to my question how do you perform a crab with ILS approach.

This doesn't make any sense.

If you apply e.g. right rudder to keep the nose aligned with the runway you have to add left aileron to maintain a bank angle to the left at the same time to keep the plane from drifting off the centerline.

This is a slip and you can fly the whole approach that way if you want.

 

If you want to simply maintain the runway track (with the nose offset for the crosswind correction) you have to adjust the heading accordingly and this is achieved by banking, not with the rudder.

A crabbed approach is coordinated and you don't need any rudder or aileron input.

 

With rudder application the plane only yaws and the heading changes, but the track doesn't change.

 

Do you have links for these strange crosswind landing tutorials?

No, the rudder isnt keeping the nose aligned with the runway. Its keeping the aircraft on a heading towards the runway, but the aircraft is askewed, crabbing. Applying rudder into the wind helps to stop the aircraft from being blown off course.

Ok thanks for clearing that up.

Skip to 5:03

All the crosswind tutorials say the same thing, rudder into wind

He says he's applying rudder to keep the nose at the correct angle. If you apply rudder you have to apply opposite aileron at the same time to avoid that the plane banks into the direction of the applied rudder, and that's a slip and not a crab!

Agreed, I find that video highly confusing. IMHO he's showing different types of slip approaches (didn't know there was more than one way to do it...), but doesn't show a proper crab approach at all.

For all I know, using rudder means inducing slip.

A crabbed approach doesn't/shouldn't use rudder and is flown coordinated, i.e. without slip, and only moments before touchdown the rudder is used to align the aircraft with the runway.

Ok thanks again

A good show of crosswind landings and decrabbing in real life. You can see that no one is flying with their nose pointing at the runway, they align with the runway just before touchdown or even after that (because of extreme conditions)