Some kind of autopilot?

[BigDuke6ixx]

I have 10,000 hours which is why I was trying to help but obviously did a shit job at helping.

 

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You explained everything perfectly it's just there are a couple of ppl in here with a totally ingrained flaw in their understanding of basic aerodynamics. They think that in flight the wind pushes continually harder against the big tail than the small nose. Until let go of that, they won't properly understand. And if they won't take your word for it, then they have real issues.

 

I'd give them my credentials, but they'd probably throw them back in my face.

Edited June 27, 2017 by BigDuke6ixx

[mvsgas]

So, now that we all shown how much we all know and how smart we all are, does anyone know what happen the the original post?

FatSlapper,

Did you figure what was causing the problem? I'm just curious now.

[BigDuke6ixx]

So, now that we all shown how much we all know and how smart we all are, does anyone know what happen the the original post?

FatSlapper,

Did you figure what was causing the problem? I'm just curious now.

 

It was user error. Good luck getting anyone to admit fault around here.

[mvsgas]

Who is "fault" and why are we admitting him/her? Is he/she sick? :smartass:

[Donnerblase]

Ok I will chime in a little. On the ground all Aircraft weather vane into wind during the Take-off roll and you use rudder to compensate as you roll down the Runway after you apply Thrust, due to the side force on the Rudder. As you rotate the Aircraft and the nosewheel comes off the ground it will naturally turn into wind if you dont compensate. If you are in a large Aircraft we hold the nose straight using rudder due to the time it takes for the Aircraft to lift off and will end up slightly cross controlled. Once Airborne we balance the Aircraft and fly away either flying a track or a heading. When Airborne the Aircraft flys straight unless you are out of balance. Unless you fly through a shear where the Aircraft sees a change in the wind, then the Aircraft basically doesnt care what wind it fly, there is no weathervaneing in as you call it. If you fly a track then the Aircraft nose will be heading into wind but there is no Aircraft movement into the wind that is just your Autopilot flying the Track. Now if you are dropping a dumb bomb off an Aircraft with no CCIP and the Wind is from Rt to Left over the Target then you need to fly your backside over the Target.

Your nose will be pointing into the wind slightly to maintain the Aircraft track over the Target. Again tho you are the one flying the track once off the ground the Aircraft doesnt know or care about any wind force as it is normally constant.

 

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OK, so I went back and did my research on the matter, as it kept gnawing on me, and of course you are right. While I was right in the description of the effect and what causes it, I had the wrong assumption that a sideslip angle was present whilst in the air. However, as you move through the air, no sideslip angle is present, if there are no gusts or pilot input, as from the point of view of the airplane, the whole medium around it moves, so only the relative movement of the aircraft to the medium counts. I don't quite know how I could forget about that, but I think I got it mixed up with the whole dynamic mode stuff during my thinking process (stuff like spiral modes where you have a sideslip induced fin force). That, and undercoffeinated Mondays... :doh:

 

Once the Aircraft is Airborne the Wind doesnt apply any force unless there is a shear layer or turbulence as the Aircraft is already miving within the Air. The only forces are Thrust Drag and Lift and weight plus the adjustments you make with the controls. Wind per se has no effect what at all on the Aircraft aerodynamically.

You are just moving with you speed in the air plus the speed of the Air. An Airliner in a 150 knot jetstream has zero affect vs an Airliner in still air handling wise. Forces only change when the wind velocity itself changes.

 

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This got me thinking and let me pull out the books on the matter. Thanks for that. :thumbup:

 

Coming back to my earlier question if this weathervaning-effect of airborne aircraft exists in DCS, I tried it out. :smartass:

 

For starters, I set the wind to come from 360 at 20 kts. That should be plenty wind to prove the theory. I took off from Nellis, with the obvious weathervaning tendency that I believe is completely undisputed. Once airborne, I flew straight north (into the wind) until established at 10,000 ft. I then flew a 90 degree right hand turn and headed east for a while. Without ever trimming, I had to keep the stick pushed forward (dang it, holding that Warthog for 20 minutes at a time is a pain I'm here to tell ya ;)), but other than that, I couldn't find any weathervaning tendency at all. Next I flew a 180 and headed west - again, no weathervaining tendency noticeable. Like, none at all.

 

Clearly, there wasn't enough wind! :smartass:

 

I then repeated the test with a wind of 60 kts. Again, I couldn't discern even the slightest bit of a weathervaning tendency. At a perfectly perpendicular 60 kts crosswind, I guess this effect should have somehow manifested itself.

 

So, either DCS fails to model a fundamental aerodynamic effect, or an aircraft once airborne will not weathervane into the wind (assuming steady winds, of course).

 

For fun and profit, I saved a track (1.75 MB, DCS 2.1, Nevada Terrain, circa 15 minutes). :)

 

Of course I'd love to test this in a real aircraft, but lacking all the required certificates, and the training, and the aircraft, I guess the LBA (German FAA) wouldn't be too happy about it. :D

 

Your observations are correct as always ;) Mondays appear to do strange things with thought processes...

[shagrat]

Coming back to my earlier question if this weathervaning-effect of airborne aircraft exists in DCS, I tried it out. :smartass:

 

For starters, I set the wind to come from 360 at 20 kts. That should be plenty wind to prove the theory. I took off from Nellis, with the obvious weathervaning tendency that I believe is completely undisputed. Once airborne, I flew straight north (into the wind) until established at 10,000 ft. I then flew a 90 degree right hand turn and headed east for a while. Without ever trimming, I had to keep the stick pushed forward (dang it, holding that Warthog for 20 minutes at a time is a pain I'm here to tell ya ;)), but other than that, I couldn't find any weathervaning tendency at all. Next I flew a 180 and headed west - again, no weathervaining tendency noticeable. Like, none at all.

 

Clearly, there wasn't enough wind! :smartass:

 

I then repeated the test with a wind of 60 kts. Again, I couldn't discern even the slightest bit of a weathervaning tendency. At a perfectly perpendicular 60 kts crosswind, I guess this effect should have somehow manifested itself.

 

So, either DCS fails to model a fundamental aerodynamic effect, or an aircraft once airborne will not weathervane into the wind (assuming steady winds, of course).

 

For fun and profit, I saved a track (1.75 MB, DCS 2.1, Nevada Terrain, circa 15 minutes). :)

 

Of course I'd love to test this in a real aircraft, but lacking all the required certificates, and the training, and the aircraft, I guess the LBA (German FAA) wouldn't be too happy about it. :D

Hmm, interesting... When I made a copy of the instant action take off mission, with the only change being the loadout removed, I had a different result.

On take off roll I used the rudder/nosewheel to keep the A-10C centered. After lift off I kept the aileron axis centered and the rudder neutral.

 

The plane started drifting sideways, as expected from the crosswind and still slightly turning its nose to the left, towards the wind direction... like the NASA guys explained. :dunno:

 

I did not trim the aircraft, and was in a slight nose up for ascend, so stick was pretty much neutral. Full throttle. Rudder centered.

[shagrat]

No when you fly the approach most people fly balanced with the nose crabbed into wind. There are 2 crosswind landing techniques. One favored by military pilots is to kick the nose straight in the flare and the aircraft lands straight when you kick it straight you have to use into wind aileron to keep the wings level. The second technique is to push the nose straight as you start to flare and lower the into wind wing to land with the upwind wheels first. I used the first method in the military and the second method on the B777 as it is much slower to respond

 

Yes, that is why you crab or sideslip (put a wing down into the wind) and usually trim the plane, so it counters the effects of the wind and keep its course.

 

If you don't the wind applies force to the rudder and should turn it around the CoG until it roughly reaches the WCA.

 

If it doesn't there must be a counterforce (usually rudder pedal) applied to counter the wind pressing against the tail rudder.

 

A force acting against an asymmetric bodysurface creates an asymmetric reaction defined by the mass (inertia) of the body. If the asymmetrics don't add up to zero in the center of mass the object will start spinning until a counteraction occurs.

 

In this case the counteraction will be the wind blowing onto the other side of the fuselage and tail rudder.

 

I think the problem here is you only think about the direction of movement relative to the wind. I solely talk about, what the planes nose should do.

[Donnerblase]

Yes, that is why you crab or sideslip (put a wing down into the wind) and usually trim the plane, so it counters the effects of the wind and keep its course.

 

If you don't the wind applies force to the rudder and should turn it around the CoG until it roughly reaches the WCA.

 

If it doesn't there must be a counterforce (usually rudder pedal) applied to counter the wind pressing against the tail rudder.

 

A force acting against an asymmetric bodysurface creates an asymmetric reaction defined by the mass (inertia) of the body. If the asymmetrics don't add up to zero in the center of mass the object will start spinning until a counteraction occurs.

 

In this case the counteraction will be the wind blowing onto the other side of the fuselage and tail rudder.

 

I think the problem here is you only think about the direction of movement relative to the wind. I solely talk about, what the planes nose should do.

 

Well for the airplane in flight, the only thing that really matters is the movement of the airframe relative to the medium surrounding it. So if you are in the air just going straight from your own point of view, you get taken with the air around you. Just like when you are on a boat crossing on a big river (without any changes in velocity of the flow), you paddle straight towards the other shore, but get dragged along with the flow. Now if you want to "land" on the shore with zero relative velocity to it, you have to counteract the flow velocity of the river, "crab" so to speak.

 

It is all a matter of point of view, basically.

[shagrat]

Well for the airplane in flight, the only thing that really matters is the movement of the airframe relative to the medium surrounding it. So if you are in the air just going straight from your own point of view, you get taken with the air around you. Just like when you are on a boat crossing on a big river (without any changes in velocity of the flow), you paddle straight towards the other shore, but get dragged along with the flow. Now if you want to "land" on the shore with zero relative velocity to it, you have to counteract the flow velocity of the river, "crab" so to speak.

 

It is all a matter of point of view, basically.

For the original poster it was important to understand why the plane still moves when he isn't giving control inputs or other then what he expected.

So we pointed out the asymmetrical loadout (drag and weight) and the crosswind, as the likely root cause.

 

Then someone said "there is no weathervaning in the air" what means as soon as you are airborne the wind is no longer acting on your fuselage and tail rudder... That's how the fight started.

 

I am only talking about the plane trying to put the nose into the wind if you don't apply ailerons or rudder as a counterforce.

[BigDuke6ixx]

Yes, that is why you crab or sideslip (put a wing down into the wind) and usually trim the plane, so it counters the effects of the wind and keep its course.

 

If you don't the wind applies force to the rudder and should turn it around the CoG until it roughly reaches the WCA.

 

If it doesn't there must be a counterforce (usually rudder pedal) applied to counter the wind pressing against the tail rudder.

 

A force acting against an asymmetric bodysurface creates an asymmetric reaction defined by the mass (inertia) of the body. If the asymmetrics don't add up to zero in the center of mass the object will start spinning until a counteraction occurs.

 

In this case the counteraction will be the wind blowing onto the other side of the fuselage and tail rudder.

 

I think the problem here is you only think about the direction of movement relative to the wind. I solely talk about, what the planes nose should do.

 

Sorry, but you still don't seem to have grasped the fact that the crosswind isn't having an aerodynamic affect which points the nose more into wind. There is no weathervane effect once airborne and the affects of gusts are only momentary. I think the rocket data is still confusing you, while in reality it's of no relevance.

 

A crosswind only affects landing, take off and navigation, it does nothing to influence the relative wind, which is the air flowing from the nose to the tail, what we measure as airspeed. Nor is the crosswind exerting a continuous asymmetric force upon the airframe when airborne.

Edited June 27, 2017 by BigDuke6ixx

[David OC]

I think I know what you're both trying to say in you're own way.

 

This may help:)

 

If a small airplane flies overhead in a strong crosswind, you can sometimes see that the plane is not moving in the direction in which it is pointed, as illustrated in. The plane is moving straight ahead relative to the air, but the movement of the air mass relative to the ground carries it sideways.

 

 

 

https://voer.edu.vn/c/addition-of-velocities/0e60bfc6/ff62f920#import-auto-id1851600

 

 

All this weathervane stuff is a load of weathercock and bull. Once you're airborne, there's no such thing as weathervaning or weathercocking! Once you're airborne, the wind cannot create any moment (roll, pitch, yaw) on the aircraft (excepting turbulence and wind-shear complications)

 

The aircraft will point wherever you choose it, relative to the airmass.

 

The only reason a weathervane/cock works is because it's fixed to the ground (which the aircraft isn't, except for the takeoff and landing roll - don't forget your ailerons ).

 

edited to say that if you think the aircraft has weathervaned into the wind on final approach or climb out, it's because you have done it with the controls.

 

http://www.pprune.org/flying-instructors-examiners/235170-weathervane-into-wind-landing.html

 

 

http://code7700.com/crosswind_landing.htm

http://code7700.com/windshear.htm

 

 

I would say that the wind would have more of an "affect" on smaller lighter aircraft size, say a 172 compared to a 737, because of the size and weight of the aircraft, so the wind is much more noticeable on pushing you and/or trying to change your direction (I would not call it weathervaning, once airborne) around in the 172.

 

.

Edited June 27, 2017 by David OC

[BigDuke6ixx]

I think I know what you're both trying to say in you're own way.

 

This may help:)

 

If a small airplane flies overhead in a strong crosswind, you can sometimes see that the plane is not moving in the direction in which it is pointed, as illustrated in. The plane is moving straight ahead relative to the air, but the movement of the air mass relative to the ground carries it sideways.

 

 

 

https://voer.edu.vn/c/addition-of-velocities/0e60bfc6/ff62f920#import-auto-id1851600

 

 

 

http://code7700.com/crosswind_landing.htm

http://code7700.com/windshear.htm

 

 

I would say that the wind would have more of an "affect" on smaller lighter aircraft size, say a 172 compared to a 737, because of the size and weight of the aircraft, so the wind is much more noticeable on pushing you and/or trying to change your direction (I would not call it weathervaning, once airborne) around in the 172.

 

.

 

A 20kt crosswind pushes any plane sideways at 20kts regardless of mass.

[David OC]

Do you think the wind would have more of an affect on a very slow 172 taking off, compared to a heavy fast 737 taking off then? Aircraft speed plays apart here, as does the wind speed.

 

Have you been in a small plane before?

 

 

EDIT

I do agree with you BigDuke6ixx, this thread started about some kind of autopilot engaged, so it is relative here to the Op's post.

 

instant action takeoff from Vegas flight

This below puts it very well, right?

 

"If a small airplane flies overhead in a strong crosswind, you can sometimes see that the plane is not moving in the direction in which it is pointed, as illustrated in. The plane is moving straight ahead relative to the air, but the movement of the air mass relative to the ground carries it sideways. "

 

https://voer.edu.vn/c/addition-of-velocities/0e60bfc6/ff62f920#import-auto-id1851600

 

 

The only thing I see getting confused here is the term "weathervaning" and not using the words "crabbing into the wind" and "drift angle"

 

"weathervaning" can only happen on the ground, "crabbing" or "drift angle" happens in the air.

 

 

"Note: the wind correction angle is the angular difference between the required track and the heading, intended to ensure that the track made good will equate with the required track. Note that the terms 'crab angle' and 'drift angle' are very often used instead of 'wind correction angle'. But the latter term is more precise; crab angle and drift angle do have slightly different meanings or associations. Drift angle is measured in flight, and is the angle between the heading and the track made good. Crab angle is the preferred term when associated with crosswind landing."

 

The effect of wind

https://www.recreationalflying.com/tutorials/navigation/wind.html

 

.

Edited June 27, 2017 by David OC

[BigDuke6ixx]

Do you think the wind would have more of an affect on a very slow 172 taking off, compared to a heavy fast 737 taking off then?

 

Have you been in a small plane before?

 

 

 

.

 

We are not talking about the what happens during takeoff, we are talking about how a crosswind affects a plane in flight. Was my last statement about the 20kt crosswind correct or not?

 

There isn't any confusion regarding crabbing and weathervaning, it's just that some people are insisting that a crosswind blows harder against the tail than the nose, thus causing a continuous rotation that the pilot must counter with control input. Some people have admitted their error, while some haven't.

Edited June 27, 2017 by BigDuke6ixx

[shagrat]

Do you think the wind would have more of an affect on a very slow 172 taking off, compared to a heavy fast 737 taking off then? Aircraft speed plays apart here, as does the wind speed.

 

Have you been in a small plane before?

 

 

EDIT

I do agree with you BigDuke6ixx, this thread started about some kind of autopilot engaged, so it is relative here to the Op's post.This below puts it very well, right?

 

"If a small airplane flies overhead in a strong crosswind, you can sometimes see that the plane is not moving in the direction in which it is pointed, as illustrated in. The plane is moving straight ahead relative to the air, but the movement of the air mass relative to the ground carries it sideways. "

 

https://voer.edu.vn/c/addition-of-velocities/0e60bfc6/ff62f920#import-auto-id1851600

 

 

The only thing I see getting confused here is the term "weathervaning" and not using the words "crabbing into the wind" and "drift angle"

 

"weathervaning" can only happen on the ground, "crabbing" or "drift angle" happens in the air.

 

 

"Note: the wind correction angle is the angular difference between the required track and the heading, intended to ensure that the track made good will equate with the required track. Note that the terms 'crab angle' and 'drift angle' are very often used instead of 'wind correction angle'. But the latter term is more precise; crab angle and drift angle do have slightly different meanings or associations. Drift angle is measured in flight, and is the angle between the heading and the track made good. Crab angle is the preferred term when associated with crosswind landing."

 

The effect of wind

https://www.recreationalflying.com/tutorials/navigation/wind.html

 

.

 

That is because I wasn't talking about the crabbing and the drift effect, as this is what happens, when you deliberately use the control surfaces to keep the plane flying the intended course by applying WCA.

 

I will try to draw an illustration to help clear up the confusion.

 

I appreciate what you guys are trying to explain, but we talk about different things, I guess.

[shagrat]

First my skills with mouse drawing images is substandard, I hope you can figure it out anyway.

 

First let's have a look at the airplane from a roughly 45° angle and assume that is the direction the wind is blowing towards the plane.

As the shape of the aircraft presented to the windforces is asymmetrical.

Now lets count the red dots, representing the wind force pressing against fuselage and tail/rudder and split them at the CoG.

 

 

We notice that a ratio of 14 to 21 (2:3) is splitting the windforce acting on the fuselage. So the planes inertia will resist the wind and apply a reaction in the opposite direction.

 

As the Center of Gravity (CoG, or the center point of mass) acts as a pivot point the reacting force is also split by a ratio of 2:3 so 1/5th of the overall force pushes the tail to the downwind side, which should push the nose into the wind. (Keep in mind we do NOT apply rudder, or aileron, or trim, or asymmetrical thrust to counter this!).

 

 

Now we come to the part where I am not hundred percent sure about the exact amount the nose turns into the wind, my best guess is: it doesn't turn completely into the wind, but just until the asymmetry of the resisting surface is equalized (1:1 ratio in our case 12.5 to 12.5 dots etc.)?

 

Still if the aircraft turns we alter the thrust vector and we should be altering our course slightly without ever touching the controls. That is why the original poster likely felt like "some autopilot" messes with the controls, or why it could feel like it, if you are used to 0 kts wind conditions in DCS.

 

 

At least this is how it SHOULD be, if the wind and forces on the fuselage are simulated correctly. For me it seems ok, when I neutralize the control the aircraft has a tendency to turn into the wind, as long as I do not apply any corrective control inputs. :dunno:

[Yurgon]

At least this is how it SHOULD be, if the wind and forces on the fuselage are simulated correctly. For me it seems ok, when I neutralize the control the aircraft has a tendency to turn into the wind, as long as I do not apply any corrective control inputs. :dunno:

 

So you say it is definitely modeled? You know the old saying: Track or it didn't happen. ;)

[shagrat]

This is what the control inputs should roughly look like to fly that course...

 

If you keep the aileron and rudder neutral, what happens?

 

[WindyTX]

Ok for the last time your diagram works on the ground cos the Aircraft is on the ground so the wind blows over it. Once Airborne it flys through the air balanced no one fly crossed controls ( there is an exception but lets keep it simple).

 

The boat crossing the river is a great analogy the boat drives straight through the water but moves at an angle cos the river water is moving.

 

I promise this is my last attempt to explain.

Edited June 27, 2017 by WindyTX
Doh

[BigDuke6ixx]

First my skills with mouse drawing images is substandard, I hope you can figure it out anyway.

 

First let's have a look at the airplane from a roughly 45° angle and assume that is the direction the wind is blowing towards the plane.

As the shape of the aircraft presented to the windforces is asymmetrical.

Now lets count the red dots, representing the wind force pressing against fuselage and tail/rudder and split them at the CoG.

 

 

We notice that a ratio of 14 to 21 (2:3) is splitting the windforce acting on the fuselage. So the planes inertia will resist the wind and apply a reaction in the opposite direction.

 

As the Center of Gravity (CoG, or the center point of mass) acts as a pivot point the reacting force is also split by a ratio of 2:3 so 1/5th of the overall force pushes the tail to the downwind side, which should push the nose into the wind. (Keep in mind we do NOT apply rudder, or aileron, or trim, or asymmetrical thrust to counter this!).

 

 

Now we come to the part where I am not hundred percent sure about the exact amount the nose turns into the wind, my best guess is: it doesn't turn completely into the wind, but just until the asymmetry of the resisting surface is equalized (1:1 ratio in our case 12.5 to 12.5 dots etc.)?

 

Still if the aircraft turns we alter the thrust vector and we should be altering our course slightly without ever touching the controls. That is why the original poster likely felt like "some autopilot" messes with the controls, or why it could feel like it, if you are used to 0 kts wind conditions in DCS.

 

 

At least this is how it SHOULD be, if the wind and forces on the fuselage are simulated correctly. For me it seems ok, when I neutralize the control the aircraft has a tendency to turn into the wind, as long as I do not apply any corrective control inputs. :dunno:

 

Sorry, but this is all completely wrong. There is no 'pivot point' around which the plane is rotated by a crosswind in flight.

[BigDuke6ixx]

So you say it is definitely modeled? You know the old saying: Track or it didn't happen. ;)

 

 

Someone did a track a few pages back proving that this nonsense doesn't happen. This guy has been told by several real pilots that he is mistaken in his observations and subsequent theorising. He simply doesn't know what he is talking about.

 

A little knowledge is a dangerous thing.

Edited June 27, 2017 by BigDuke6ixx

[kylekatarn720]

Sorry, but this is all completely wrong. There is no 'pivot point' around which the plane is rotated by a crosswind in flight.

 

cog will act as a pivot point if there is a difference of force on both sides

[WindyTX]

Thats the point once Airborne there isnt a difference unless you the pilot make one using the controls. Definitely the last post here.

 

Sent from my SM-G955U using Tapatalk

[Yurgon]

Someone did a track a few pages back [...]

 

That would have been me. ;)

 

My point being that if weathervaning exists, it should be very simple for the proponents to show it, instead of keeping on going in circles. Let's hope shagrat or someone else comes up with a track or a video showing exactly what they mean. After arguing for 100 posts, they should be able to show it within 10 minutes, and I'd really like to see this effect that I wasn't able to produce in insanely strong crosswinds. :thumbup:

[Flagrum]

The engines push the aircraft forward, the crosswind pushes it sideways. The result is a diagonal flight path over the ground. If we ignore the engines and the forward thrust, we would see the aircraft move with the speed of the wind in the direction of the wind - no matter the attitude of the aircraft. It moves with the air mass - think of hot air balloons.

 

Now the dreaded weathervane effectl ... the above is true during regular flight. But in order to move with the wind, the aircraft has to be accellerated in that direction first. During take off, there is no lateral movement - due to the wheels on the ground (+ nosewheel steering, if you insist). The moment the wheels come free off the ground, the cross wind begins to accellerate the aircraft sideways. And during this period, the cross wind affects different parts of the aircraft differently - due to wind resistance/drag of the fuselage and due to inertia of the aircraft.

 

And this is where some wheatervane effect should be observable!

 

20 kts crosswind, the aircraft unsticks. 20 kts wind act now on a big tail fin and on a small nose. The aircraft resists to move due to it's inertia, but the wind forces on the tail are greater than the forces on the nose. What will the airframe do now?