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Why's and How's of a Coordinated Turn


Bearfoot

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WHY:

 

Ok, I know it is a stupid question, and is probably obvious to most. For those in the know or to whom it is obvious, could you explain WHY we want to make sure our turn is coordinated.

 

From Wikipedia:

Coordinated flight is usually preferred over uncoordinated flight for the following reasons: it is more comfortable for the occupants; it minimises the drag force on the aircraft; it causes fuel to be drawn equally from tanks in both wings; it minimises the risk of entering a spin

 

 

Obviously, this applies so much more to general aviation. Why is this important in military aviation, particularly fighters?

 

HOW:

 

I "step-on-the-ball" --- rudder input in the direction of the ball on the turn-and-slip indicator. At least, till I develop muscle memory enough to figure out how much rudder to use without feedback. I've seen photos of Tomcat's with a yaw string. We don't have that do we? Are we getting one? And would that be better than a turn and slip indicator?

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You learn to do it right, so in challenging situations like low visibility formation flight you don't collide. You can perform correct attack runs, landings, air refueling etc for strafing runs etc.

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Ok, thanks. In BFM on max rate or min radius turns, it is overwhelming trying to keep on eye on the other guy when he is not in your forward quarter (and tracking fast aft across the canopy!) AND another on speed and AoA. Was wondering if I should be worrying about the turn/slip reading as well. I'm thinking a full-featured HUD was one of those understated flying revolutions the D people really must have appreciated the most!

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Yes, you absolutely should be worrying about your slip. However, that doesn't necessarily mean looking at the indicator. Eventually, you should get a feel for how the nose moves during a bank, where the centerline of the aircraft is pointing out in the distance in front of you, and instinctively move your feet to counter oncoming slip.

 

The indicator is nice, but really all you need is your eye and looking at the terrain/clouds out front for a reference relative to where you know the nose is pointing.

 

e.g. if you know your nose is pointed at the mountain top, then as you roll you just watch the mountaintop for slip and move your feet to make sure it rotates exactly about that axis and no other.

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Yes, you absolutely should be worrying about your slip. However, that doesn't necessarily mean looking at the indicator. Eventually, you should get a feel for how the nose moves during a bank, where the centerline of the aircraft is pointing out in the distance in front of you, and instinctively move your feet to counter oncoming slip.

 

The indicator is nice, but really all you need is your eye and looking at the terrain/clouds out front for a reference relative to where you know the nose is pointing.

 

e.g. if you know your nose is pointed at the mountain top, then as you roll you just watch the mountaintop for slip and move your feet to make sure it rotates exactly about that axis and no other.

 

Thank you. It is going to take a while to build up this intuition!

 

I sometimes find that the turn-and-slip indicator shows that the opposite rudder from what I expect. In fact, without any formal (or practical real-world) aerodynamics training/experience, it is confusing to me that in the Tomcat on some turns the turn-and-slip ball slips to the opposite direction from the turn direction. E.g., when turning right the ball goes left thus seeming to indicate left/top rudder is needed or vice versa. Does not happen all the time --- many turns the rudder required is indeed in the direction of the bank. Have not figured out the pattern. Maybe speed or angle-of-bank or how far the nose is above/below the horizon?

 

This Tomcat is proving to be most challenging fixed-wing aircraft simulation I've ever flown!

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Here's my take on it:

 

In cruise, I don't think about it too much. When maneuvering I look at the turn coordination indicator which is not a problem because I have time. You don't need to use alot of rudder at high speed/low aoa.

 

In a fight, I am at high aoa most of the time so I don't really need to coordinate. I turn and burn with the rudders.

 

Slow/high AOA. This is the time to show your coordination skillz. Notice that when landing, and especially during CaseI an out of coordination turn will mess up your lift big time.

 

In the A10C, I found it easy to 'step on the ball' with the turn indicator but in the cat it confuses me because I get distracted by the rudder position line.

 

What I do now is this: when in AG or LDG mode, you get a FPI (flight path indicator). I use the small dot (the boresight?) in the hud to 'support' the fpi like balancing a ball on a plate and my turns are smooth and coordinated.

METEOP

 

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I find the "step on the ball" principle to be only valid when doing Cessna turns. Any time I'm not doing gentle turns I ignore the ball and just watch what the nose is doing, which is much easier to do in VR.

 

During aerobatics the ball doesn't make any sense; not just the Tomcat, but in the Tomcat and all the warbirds too. When doing an aileron roll, let's say to the left, the ball slams to the left for the first 90 degrees of the roll, and it slams to the right the second 90 degrees of the roll. However, if you actually step on the ball as it is indicating, you will be yawing all over the place during your roll. Another example is when snapping into a high bank angle. Going left again, the ball will slam to the left side even if I give max possible rudder deflection.

 

With the Tomcat in particular, the ball's movements are extremely delayed. I'll do a roll which looks nice and straight when looking over the nose, but the ball will be oscillating back and forth even after I've flown straight and level for a good 5 seconds, with the nose dead-straight and rock-solid.

 

It seems like the ball is really only useful when you are already established in a bank. Other than that, it's best to look over the nose and do it by feel.

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e.g. if you know your nose is pointed at the mountain top, then as you roll you just watch the mountaintop for slip and move your feet to make sure it rotates exactly about that axis and no other.

 

Ok, I tried this, and to be honest, I'm confused.

 

If my nose is pointing at a mountaintop and I bank to the left to initiate a turn, the mountaintop immediately moves away from the nose. So with the lineup lost between the nose and the mountaintop, how do I keep track of things. The axis of rotation is somewhere in the direction of the horizontal component of my lift vector (and perpendicular to it) ...

 

I know this must sound so stupid that it might seem like I am trolling ... but I'm not!

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I sometimes find that the turn-and-slip indicator shows that the opposite rudder from what I expect.

 

Yes. The Tomcat has both adverse and proverse yaw depending on your AoA. As a rule of thumb, at higher speeds it has proverse yaw and lower speeds adverse.

 

If my nose is pointing at a mountaintop and I bank to the left to initiate a turn, the mountaintop immediately moves away from the nose. So with the lineup lost between the nose and the mountaintop, how do I keep track of things. The axis of rotation is somewhere in the direction of the horizontal component of my lift vector (and perpendicular to it)

 

Yes, because you're not coordinated. It's easier to explain in video, as Jabbers does here (the explained theory is essentially correct, although his demonstration is backwards - he's trying to counter adverse yaw (left bank with left rudder) while experiencing proverse yaw, which is why he's totally uncoordinated the whole time if you watch his ball lol)

 

 

To explain what he should have been doing: at low AoA such as in his video, when you roll left, you put in a little right rudder. At high AoA (11+) such as when dogfighting, when you roll left, you put in a little left rudder (like a Cessna/warbird).

 

Something worth noting is that being perfectly coordinated 100% of the time is not necessary. It's a mark of good airmanship, sure, but you're not going to crash just because you've got a bit of a slip going on in a standard turn. When you're dogfighting, though, you should be worried about it a lot more. I find my feet moving all over the place in a dogfight. At really high AoA you're banking primarily with rudder, not aileron!


Edited by Jester2138
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Hello,

 

I am thinking the ball in the Tomcat is really sensitive. It is affected very much with even the slightest amount of rudder input. I have the crappy Thrustmaster rudder pedals so that may not help, but in real life flying, when doing high bank angle maneuvers you need quite a quick on the rudder to keep coordinated when entering the turn. The only time I got a sensitive ball was flying ultralight which had very few inertia on the yaw axis. I may be wrong but I guess an F14 would have quite heavy inertia on the yaw axis and far more stable ball as a consequence.

 

Pierre

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Yes. The Tomcat has both adverse and proverse yaw depending on your AoA. As a rule of thumb, at higher speeds it has proverse yaw and lower speeds adverse.

 

Yes, because you're not coordinated. It's easier to explain in video, as Jabbers does here (the explained theory is essentially correct, although his demonstration is backwards - he's trying to counter adverse yaw (left bank with left rudder) while experiencing proverse yaw, which is why he's totally uncoordinated the whole time if you watch his ball lol)

 

To explain what he should have been doing: at low AoA such as in his video, when you roll left, you put in a little right rudder. At high AoA (11+) such as when dogfighting, when you roll left, you put in a little left rudder (like a Cessna/warbird).

 

So it's proverse yaw at low AoA (requiring opposite rudder) and adverse yaw at high AoA (requiring rudder in same direction as turn)? I thought it was the other way around. And that may explain some of my confusion!

 

The other confusion I had with the fixed-mountaintop exercise: from the video it seems we use it to practice rolling/banking, but not actually turning. That is, your heading stays the same and that's how you have a static point of reference. I thought we were using the distant feature as a reference while actually turning, i.e. changing heading.

 

In another thread, Victory mentioned that rudder input is required only with lateral deflection of stick, then as this is relaxed and you pull back to turn, you remove the rudder input. This is with respect to the break turn on landing, but if it applies more generally then I can see the above exercise helping generally too. However, if you want to check/practice coordination throughout an actual turn (i.e., while your heading changes) --- which was what I was trying to do --- then I guess the turn-and-slip indicator is all you have?

 

 

Something worth noting is that being perfectly coordinated 100% of the time is not necessary. It's a mark of good airmanship, sure, but you're not going to crash just because you've got a bit of a slip going on in a standard turn. When you're dogfighting, though, you should be worried about it a lot more. I find my feet moving all over the place in a dogfight. At really high AoA you're banking primarily with rudder, not aileron!

 

When in dogfighting/BFM, I usually just "go with the flow", working all controls (stick, rudder, throttle) simultaneously without thinking about coordination etc. to just get pointed where I want to point. I do not actually come off too bad because of my previous (simulated) warbird experience. But just want to be sure I am doing things "correctly" by the numbers/book as well as "right" by the feel/intuition, if you know what I mean. So I would like to build up my airmanship skills.

 

The F-14 is the first DCS jet that I've tried to learn how to fly fully as my typical sim experience is otherwise 50% helos / 50% warbirds. The simulated warbird experience has help develop a lot of intuition with regards to rudder especially, but I find that it is only partially translating to the F-14. And, weirdly, I love that! It is presenting such a different and such an enjoyable challenge! It honestly is the most fun I've had learning to fly ....


Edited by Bearfoot
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Yes. The Tomcat has both adverse and proverse yaw depending on your AoA. As a rule of thumb, at higher speeds it has proverse yaw and lower speeds adverse.

 

 

 

Yes, because you're not coordinated. It's easier to explain in video, as Jabbers does here (the explained theory is essentially correct, although his demonstration is backwards - he's trying to counter adverse yaw (left bank with left rudder) while experiencing proverse yaw, which is why he's totally uncoordinated the whole time if you watch his ball lol)

 

 

To explain what he should have been doing: at low AoA such as in his video, when you roll left, you put in a little right rudder. At high AoA (11+) such as when dogfighting, when you roll left, you put in a little left rudder (like a Cessna/warbird).

 

Something worth noting is that being perfectly coordinated 100% of the time is not necessary. It's a mark of good airmanship, sure, but you're not going to crash just because you've got a bit of a slip going on in a standard turn. When you're dogfighting, though, you should be worried about it a lot more. I find my feet moving all over the place in a dogfight. At really high AoA you're banking primarily with rudder, not aileron!

Assuming what you say is correct (and I have no reason to think otherwise, in fact I agree and it's my experience as well) and the turn-and-slip indicator is modeled correctly in the HB F-14, then almost no-one of the more well known DCS-Youtubers is flying correctly, and coordinated using the t-s indicator. They just pretend they know it seems, talking about how one should use the rudder a lot while in fact I almost never see them fly coordinated, judged by the t-s indicator.

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There's a very big difference between knowing what adverse/proverse yaw are and being proficient at dealing with them. Considering the famous youtubers (e.g. Ralfi and Jabbers) tend to mostly fly the F18 (and F15 in the past) and they do not have formal training, I wouldn't be surprised if they were doing lots of things wrong

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I have still yet to find any video footage, real or DCS, of a centered slip ball during an entire aileron roll or when snapping into a high AoB. Until I see such a video, I'm going to stick by my experience (in DCS) of the slip ball being accurate only in gentle turns.

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Low aoa is adverse yaw, so when you stick left you rudder left also.

 

High aoa don't use the stick for roll! Use rudders only.

 

This way you don't need to think about reversing your rudder usage depending on aoa... These planes are designed to be as simple as possible (but not too simple) so you can concentrate on the kill.

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METEOP

 

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As a rule of thumb, at higher speeds it has proverse yaw and lower speeds adverse.

when you roll left, you put in a little right rudder. At high AoA (11+) such as when dogfighting, when you roll left, you put in a little left rudder (like a Cessna/warbird).

 

 

Low aoa is adverse yaw, so when you stick left you rudder left also.

 

Yikes. Which is it?

 

 

At really high AoA you're banking primarily with rudder, not aileron!

 

 

High aoa don't use the stick for roll! Use rudders only.

 

This way you don't need to think about reversing your rudder usage depending on aoa... These planes are designed to be as simple as possible (but not too simple) so you can concentrate on the kill.

 

Agreed! In fact, I find myself using rudder roll at low AoA / high-speeds as well. Whether "correct" or "incorrect", it feels right? Not so much in BFM but when practicing flying in "Star Wars canyon" runs (e.g., following rivers through valleys in the Caucasus).

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Yikes. Which is it?

 

Low AOA = proverse yaw, stick/rudder opposite. High AoA = adverse yaw, stick/rudder agree.

 

I find myself using rudder roll at low AoA / high-speeds as well. Whether "correct" or "incorrect", it feels right? Not so much in BFM but when practicing flying in "Star Wars canyon" runs (e.g., following rivers through valleys in the Caucasus).

 

It's especially important to use rudder correctly in BFM. Rudder roll is not necessary at low AoA and I'm not sure it would even work? Confused as to what you're talking about.

 

I have still yet to find any video footage, real or DCS, of a centered slip ball during an entire aileron roll or when snapping into a high AoB. Until I see such a video, I'm going to stick by my experience (in DCS) of the slip ball being accurate only in gentle turns.

 

You're never going to peg the ball perfectly and it's not necessary. But you should be generally coordinated. The ball seems accurate to me; you're probably just not coordinating correctly as described elsewhere in this thread.


Edited by Jester2138
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Low AOA = proverse yaw, stick/rudder opposite. High AoA = adverse yaw, stick/rudder agree.

 

Thanks.

 

 

It's especially important to use rudder correctly in BFM. Rudder roll is not necessary at low AoA and I'm not sure it would even work? Confused as to what you're talking about.

 

Sorry to mislead. Yes, I use rudder in BFM. Constantly. Arguably more than stabilator roll even. I just meant that I use rudder roll not just in high AoA BFM, but also other flight regimes.

 

As for working in low AoA regimes .... yes? It seems to? Shooting down a valley following a river at high speed, I find the slight roll/banks induced by just rudder input works fine.

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You're never going to peg the ball perfectly and it's not necessary. But you should be generally coordinated. The ball seems accurate to me; you're probably just not coordinating correctly as described elsewhere in this thread.

 

I've got the Spitfire well coordinated, so perhaps it's just the Tomcat. I've noticed its ball has a lot of inertia. Snap into a left 60-degree bank, even when kicking the rudder, the ball will still slam against the right from inertia. Settled into the bank, the ball then moves about halfway to the left, but if you were to follow that ball with your foot you would end up with too much left slip. I just keep my foot where it is and the ball slowly settles in the center. Same issue with rolls. If I watch the ball and do exactly as the ball says, my roll looks like shit. If I do like I do in the Spit, watching over the nose and ignoring the ball, I stay straight.

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Interesting notes on flying to Tomcat relevant to this discussion :

 

 

https://www.bobistheoilguy.com/forums/ubbthreads.php/topics/3882538/F-14_Questions_Answered_-_Ask_

What I may have said, I'll have to go back and re-read, is that above about 25 AOA, an experienced Tomcat driver would feed in rudder in the direction he wanted to go, and then put in opposite stick, cross-controlling the airplane. He would make use of the adverse yaw, and proverse roll, present at that AOA to maneuver the airplane...but it wasn't precise...and all you could do was point the airplane roughly, then unload it (again, big tails really helped), get the AOA under control and you could point with precision again.

 

In the -B/D models, you could (though there was some risk...Lord help you if you lost control of the jet because of this), select ATLS off (ATLS was the Asymmetric Thrust Limiting System - it would reduce an engine to min AB if the other engine did not have AB lit. This reduced the thrust asymmetry in the event of engine failure). With ATLS off, you could pull one engine out of AB, and the other engine would stay in AB, giving you quite a bit of yaw, without taking too much energy addition away. Use the yaw to point the airplane (particularly good in a very nose high, very low airspeed situation). Once the airplane started responding to the yaw, push that engine back into AB and fly again...at very low speed, you might need to pull the opposite engine out of AB to stop the yaw...this would not work in the -A...you would just induce a compressor stall, which would give you the thrust asymmetry...and a bit of an inflight emergency as well...not ideal...

 

DFCS helped with all of this. But we used to maneuver the airplane in a way the designers never anticipated...

 

That's what fighter pilots do...

 

https://fightersweep.com/6173/f-14-tomcat-tales-in-the-break-at-nas-key-west/

One of the first things we talked about during our brief for this flight was that I should always avoid “loaded rolls” with our analog flight control system. At slow speeds it could lead to adverse yaw where the nose of the jet opposes the direction of roll.

 

At higher speeds, the jet could be equally unpredictable, with proverse yaw (nose tracks in the direction of roll), roll coupling and in some extreme situations the aircraft could even depart controlled flight in violent fashio

 

The idea of not just using rudder to roll at high AoA, but also adding in stick in the opposite direction of the roll is supported here:

 

https://forums.eagle.ru/showpost.php?p=3285407&postcount=9

 

 

Under those parameters, especially at higher AOA, the F14A will roll opposite the stick (altitude doesn't matter, alpha does, which is G limited at high speeds). I used to put both hands on the stick to keep the stabs centered carefully so as to not induce opposite roll, and control roll with rudder. The aircraft rolled beautifully with rudder in moderate buffet and above. If you wanted to accelerate the roll rate, you could give it a little opposite stick to help the rudder roll.

 

Later the B and D got an upgrade to the SAS and DFCS to make this unnecessary. If Heatblur models this correctly, there will be a lot of confused/frustrated sim pilots. Air combat was flown in the A with Roll SAS off to eliminate adverse inputs that aggravated departure characteristics.

 

The point is that the Tomcat is a different sort of beast.


Edited by Bearfoot
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Low AOA = proverse yaw, stick/rudder opposite. High AoA = adverse yaw, stick/rudder agree.

 

 

This is not what my experience is telling me, nor what Natops, Victory205, Wikipedia et al. are explaining. Low or high aoa doesn't the slip occur in the opposite direction of the roll?

METEOP

 

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