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Adverse Yaw?


Czechnology

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I've been consuming a good deal of audio books related to the Phantom in preparation for the (hopefully still on schedule for this year) release. I know about adverse yaw as a concept, and if you don't go give it a quick Google.

Essentially, I've heard through these audiobooks that atleast the early phantoms had some REALLY aggressive adverse yaw at slow speeds. Like a hard swerve in the opposite direction following by an uncontrolled snap roll that can transition to a full on tumble.

Was this corrected for the version of the phantom we're getting, or will this be something we have got contend with?

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There were a video posted around here a few days back with the Collins Foundation Phantom pilot explaining a few things. Adverse yaw at low speeds was one of them and how you should use rudder instead of ailerons to roll and everything, but what they have is a hard wing D model. I believe, from some readings here either, the slatted wing probably were less prone to that nasty effect, but I'm not sure either if the two versions we're getting from E are both slatted or maybe the early one is really early still boasting a hard wing. If we get a hard wing version it's obvious we should get the effect in all it's glory, but if they both are slatted maybe only a bit of it, though I wouldn't know how much of it.

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14 hours ago, Czechnology said:

Was this corrected for the version of the phantom we're getting, or will this be something we have got contend with?

It's no big deal. F-14 Tomcat A-B has it also (D had Electronics onboard to correct a problem). The reason of these phenomena is a lack of the airflow (or rather detached airflow) over upper part of the airfoil on High AoA. I assume that it's well known how it works. Adding a slats changed characteristics, but didn't solve a problem. To solve a problem one need Fly-by wire.

F-4E biggest difference was while landing and take -off: The C & D model had the non-slotted stabs. On take off the normal procedure was to hold full back stick and go full burner. When the plane rotated, you eased off the back stick after lift off when you reached the climb attitude. On landing you usually hit full back stick just at touchdown. For in-flight maneuvering there was plenty of elevator authority, but on and near the ground, you were limited.

The Air Force E model had the slotted stab with more downward lift. You could make a normal burner take off and pull back stick at take off speed. You could also land the plane normally with a flare.

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Low speeds, roll with rudder.

Or as one instructor would sing - “when it buffets, use yer boots!”.

The ailerons on the F-4 work as - to bank left, right aileron DOWN, left spoiler UP. The spoiler can exhibit some drag (it is a spoiler!) more than aileron deflection.
At very low airspeeds and high AoA, the spoiler can ‘drag’ the nose around akin to a rudder (stall/spin entry for the unwary VERY easy here). But in this regime rudder will ROLL the aircraft.

Takes a little bit of getting used to, but as long as YOU are ahead of the aircraft, and anticipate its idiosyncrasies, you can make her dance pretty well.


Edited by G.J.S

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On 6/4/2022 at 10:04 AM, Czechnology said:

I've been consuming a good deal of audio books related to the Phantom in preparation for the (hopefully still on schedule for this year) release. 

Can you recommend some of these audiobooks? 

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Found an old Airforce Film that mentions and talks about it. These seem to be the non Agile Eagle variants of the phantom their talking about, but  I'd imagine it's relevant. Essentially breaks it down as if you have a high AoA - they say that as you start to approach 14-15 units of AoA you need to use more rudder, and once you get up to 15 units you have to stop using the stick and swap entirely to rudder, or you'll suffer adverse yaw and likely enter a flat spin. 
They also make the particular note of "Recovery from a flat spin is impossible". Don't even mention ways to try and get out of it, just that it will push you out of your seat some, but not enough to keep you from ejecting.

EDIT:
They actually MENTION the E Model phantom. Don't know if all Es had the Agile Eagle upgrade, but they made no distinction between the E and other models, so I imagine the comments in the video and made above about using rudder during high AoA maneuvers will hold true, and we'll just have to wait until we can get our greasy flight simmer hands on it to see how brutal or forgiving the forces are.


Edited by Czechnology
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The adverse yaw affects were a function of AoA, not speed. The slatted F-4E and F-4F models virtually eliminated the violent departure hazzard and was in fact the primary reason slats were added. The gain in max AoA and maneuverability was just icing on the cake. After years of flying hard wing F-4s in PC flight sims, I have a habit of using rudder rather than ailerons to roll almost every aircraft I fly while pulling back on the stick. It turns out it makes sense aerodynamically even if the aircraft doesn't have severe adverse yaw affects and using rudder and stick together can get the best possible result. Modern fly-by-wire systems (even as far back as the F-15's CAS) tend to take care of the rudder for you, but I still have a habit of using rudder quite a bit, always watching the slip indicator and gently pushing rudder to keep the ball centered. 

[sIGPIC][/sIGPIC]

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I think the Hornet also benefits a lot from using the rudders to turn at low speed. It's possible with the Viper, but I heard on the other sim forum that USAF Viper jocks are scared silly of touching the pedals (and were astonished by a Navy background guy who did just that in the sim). 🙂 High AoA fighting is tricky, and that's one time when rudder can do a lot of good in a modern FBW jet. 

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On 6/4/2022 at 9:49 PM, G.J.S said:

The ailerons on the F-4 work as - to bank left, right aileron DOWN, left spoiler UP. The spoiler can exhibit some drag (it is a spoiler!) more than aileron deflection.

Actually, in this case, the right down aileron has more drag than the left up spoiler, THUS yawing the aircraft to the right. Among other things, that positions the left wing more perpendicular to the airstream, while the right wing is in opposite situation ... THUS there's more lift on the left wing, causing the airplane to roll right, opposite the intended direction.

Gene K

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59 minutes ago, Gene K said:

Actually, in this case, the right down aileron has more drag than the left up spoiler, THUS yawing the aircraft to the right. Among other things, that positions the left wing more perpendicular to the airstream, while the right wing is in opposite situation ... THUS there's more lift on the left wing, causing the airplane to roll right, opposite the intended direction.

Gene K

Really??? I’m intrigued . . . :wassat:

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With two ailerons I think that would be true, but a spoiler is a spoiler, and it can be hard to beat for making drag. Particularly since on the Phanom, the spoilers are pretty damn big. Ailerons are big, too, but they probably deflect less.


Edited by Dragon1-1
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1 hour ago, Dragon1-1 said:

With two ailerons I think that would be true, but a spoiler is a spoiler, and it can be hard to beat for making drag. Particularly since on the Phanom, the spoilers are pretty damn big. Ailerons are big, too, but they probably deflect less.

Aileron up-deflection does pretty much the same thing. The spoiler exhibits less of aeroelastic twist onto the wing, which makes it preferable.

At higher AoA the down-aileron will lead to flow-separation and increased drag, hence the adverse yaw and the need to roll with rudder.

Aileron an spoiler projected areas are quite similar at low AoA and will change with increased AoA.

Also check 2:50 for a comparison of their projected area size. With the AoA going up, the spoiler will lose effectivity due to the local airflow characteristics.

 

 

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3 hours ago, Lt_Jaeger said:

You should go back to your flying school. 🤣

 

Just kidding, of course. 

 😉 Was told that pretty much every time I converted onto a new type 🤣

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