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Flying a circle around airfield.


bunraku

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Hi

 

 

I am trying to do a TACAN approach landing. In my example I am flying on course 000 towards Senaki using my TACAN. Senaki's runway is on a West to East orientation so I have set my Course to 090 on my HSI and bearing needle 1 is pointing at 000.

 

 

At around 15 miles away I turn left until this puts bearing needle 1 on 090. I then bank right and am supposed to fly a circle, always keeping the same distance and BN1 pointing at 090. And this is where I have the issues.

 

 

1) I am not sure exactly how to fly a circle manually. How severe the bank should be and am struggling to keep BN1 at 090. It always travels anticlockwise. Do I use the autopilot bankhold? And if so at what angle of bank and how to make sure it orbits the airfield?

 

 

2) And at what point to actually turn right towards the airfield?

 

 

Advice appreciate.

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Trying a circuit around the airfield should be better practice in my opinion.

 

I ve never tried doing an orbit with tacan but you can try doing something like this, align your aircraft with the runway and when you pass the end point of the runway start a 30 degree level turn until your heading changes 180 degrees, lower the bank angle to 15 degrees and keep it like that. This should more or less keep you in an orbit around the airfield.

 

Sent from my SM-G925F using Tapatalk

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It's probably unrealistic to try to fly an accurate Tacan arc by setting a constant bank angle. As well as holding quite a small angle, you would need to adjust it as you go round to allow for wind.

 

A better plan would be to fly a series of short legs, letting the tacan range go from, say, 16 nm, down to 14, and then back to 16, before turning 5 degrees in and repeating the process.

 

That, as I recall it, was how we flew tacan arcs 40-50 years ago!

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Morning,

 

If you visit http://wiki.hoggit.us/view/Airport_Charts_(incl._Freqs,_TACAN,_ILS) you can find a list of airports and the associated approach charts. These are also available in DC via your kneeboard.

 

You can also use this mod for higher quality charts on your kneeboard.

https://www.digitalcombatsimulator.com/en/files/2046353/

 

Unfortunately I am unable to acquire full IFR charts to pass to you.

 

TACAN approaches are typically flown from an initial fix which is found by flying a radial to a particular distance from the TACAN. You then fly towards the aerodrome, and depending on the weather either you then switch to a visual approach or a instrument approach, which due aircraft and DCS ATC limitations has to be an ILS.

 

The circle you are attempting to fly sound like a holding pattern, from which you depart from as you fly the leg that is pointing towards the aerodrome. The holding pattern is typically co-located with the initial fix and different formations of aircraft fly the hold at different heights to deconflict.

 

I hope this sheds some light.

 

Cheers,

 

Fend

 

EDIT:

These are the charts on your kneeboard

http://server.3rd-wing.net/public/Manuels%20DCS/DCS_VAD_Charts_A10C.pdf


Edited by fenderplayer946
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I am trying to do a TACAN approach landing. In my example I am flying on course 000 towards Senaki using my TACAN. Senaki's runway is on a West to East orientation so I have set my Course to 090 on my HSI and bearing needle 1 is pointing at 000.

 

Did you come up with this approach, or is there a chart or a guide that you're following?

 

From your description, while you're inbound Senaki heading 000, you're on Senaki's radial 180, and all is good (except that the approach is perpendicular to the runway, but the next step is going to take care of that).

 

At around 15 miles away I turn left until this puts bearing needle 1 on 090. I then bank right and am supposed to fly a circle, always keeping the same distance and BN1 pointing at 090. And this is where I have the issues.

 

Okay, this is called a DME arc (DME = Distance Measuring Equipment). In order to fly this arc at a specific distance from the TACAN, you obviously need to turn before reaching the desired distance. If you're following a chart, chances are it includes a so-called Lead DME, meaning that as soon as you reach that distance, begin a rate-one-turn in order to get on the arc.

 

In a simple example, the DME arc could be at 15nm, and lead DME would probably be something like 17nm.

 

Once again, all is good, the DME arc is supposed to get you aligned with the runway.

 

1) I am not sure exactly how to fly a circle manually. How severe the bank should be and am struggling to keep BN1 at 090. It always travels anticlockwise. Do I use the autopilot bankhold? And if so at what angle of bank and how to make sure it orbits the airfield?

 

Forget the bank angle. Your only job is to keep bearing pointer 1 at the 3 or 9 o'clock position, and check that the distance is within limits (say +- 1 nm from the arc you're trying to fly).

 

If bearing pointer 1 travels to the upper side of the HSI (getting closer to the 2 or 11 o'clock positions), turn a little less steep. If it travels to the lower side of the HSI (the 4 or 8 o'clock positions), turn a little steeper.

 

Just try to pin this bearing pointer to the 3 or 9 o'clock position and don't care about your bank angle.

 

2) And at what point to actually turn right towards the airfield?

 

Again, if you're following a chart, it should contain a lead radial.

 

So you're trying to get to heading 90 and get aligned with the runway. That means you want to be on Senaki's radial 270.

 

Since you're currently flying a DME arc, you will automatically intercept that radial at a 90 degree angle. That's bad. But if you start turning soon enough, you should end up well aligned on the radial, and with some 15nm to go, there's lots of time for small corrections and adjustments to go from "well aligned" to "perfectly aligned".

 

"Lead radial" means that as your HSI's 9 o'clock passes through this course, you should begin a rate-one-turn towards the runway (3 o'clock if the arc is flown CCW), and that should get you on a good final approach.

 

I hope this doesn't sound too cryptic, but AFAIK this is the terminology for what you're trying to achieve, and searching the web or this forum for these terms should give you a much clearer idea on how to do it.

 

But if you let us in on your source, we might be able to give some more precise pointers.

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Be thankful you have a bearing needle. DME arcs are much more difficult without them!

 

Getting on and off the arc it should be considered that turns have a radius. Intercepting the arc turn early in distance. Let's assume a 1 mile turn radius for ease of calculation. For a 15 DME arc, begin your turn at 16 DME. In the middle of the turn change the course knob from your previous inbound radial to the radial after the arc.

 

Depart the arc turn early in angle. When the bearing to station is 4-5° apart from your inbound course begin the turn inbound. That's about the time the two corners of the triangular arrows touch. A useful rule of thumb is that 1° is a 1:60 ratio of width to distance; so 1:15 is 4:60 or 4°. In the middle of the turn switch to referencing whatever method that will be used to track the inbound leg.

 

Maintaining the arc is a function of the angle between the wingtip pointing at the station and the bearing to the station. Call a bearing pointer exactly 3 o'clock as zero angle, closer to 2 o'clock toe in, and closer to 4 o'clock toe out. Flight with toe in will spiral in (decrease distance) and flight with toe out will spiral out (increase distance). Angle of toe in or toe out is controlled by bank.

 

Distance is controlled by toe. Toe is controlled by bank. There is a certain bank angle where the heading rate is equal to the bearing to station. It can be calculated but for illustration let's assume we only expect it roughly 10~20°. For bank more than this value toe is reduced (toe in) and less than this bank toe is increased (toe out).

 

Reasonable limits of DME should be +-1nm or 14-16nm for a 15nm DME arc. If our distance is 14nm or less it should be ensured that there is some toe out (bearing needle behind 3 o'clock) and if 16nm or more there is some toe in (bearing needle forward of 3 o'clock). How much is how fast you want to spiral out or in. Reasonably the toe should be no more than +-10° in most cases with +-5° being ideal.

 

The chain of thought goes something like this:

1. What is my distance? Is it too much, too little, or about right? If close, spiral out. If far, spiral in. If about right, maintain.

 

2. Is my toe in/out appropriate for my current distance? If spiral in, toe in desired. If spiral out, toe out desired. If maintain, zero toe.

 

3. Is my bank causing the toe to change correctly? More bank increases heading rate which produces toe in and vice versa.

 

Simply loop these 3 thoughts over and over until you're at the exit bearing. You can do the "polygon" arc with straight flight bouncing between your range limits or you can do a more continuous arc. Straight or insufficiently curved flight results in spiraling out so it is possible to only make inward turn corrections.

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It's probably unrealistic to try to fly an accurate Tacan arc by setting a constant bank angle. As well as holding quite a small angle, you would need to adjust it as you go round to allow for wind.

 

A better plan would be to fly a series of short legs, letting the tacan range go from, say, 16 nm, down to 14, and then back to 16, before turning 5 degrees in and repeating the process.

 

That, as I recall it, was how we flew tacan arcs 40-50 years ago!

^ this.. and still works 40-50 years later.

 

;)

 

Sent from my SM-N950U using Tapatalk

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