Oxford1G

2nd Apr 2001, 20:05

If you had to fly a DME arc, ie at 15nm,through 90 degrees, does any one have a simple rule of thumb to calculate the distance flown?

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Oxford1G

2nd Apr 2001, 20:05

If you had to fly a DME arc, ie at 15nm,through 90 degrees, does any one have a simple rule of thumb to calculate the distance flown?

Bored Cheese

2nd Apr 2001, 20:21

Calculate the total circumference of the circle using pi. Divide as required. i.e in this case by 4. There's your answer. I realise that you already know this but quite honestly once you have done it a few times in the air it's fairly easy.

I think that your question is good because you are obviously thinking about the vertical profile of your approach routing. Your future Captains will appreciate flying with a colleague who doesn't have to level out for 12 miles during a DME ARC procedure because he was only thinking about the lateral plot.

I think that your question is good because you are obviously thinking about the vertical profile of your approach routing. Your future Captains will appreciate flying with a colleague who doesn't have to level out for 12 miles during a DME ARC procedure because he was only thinking about the lateral plot.

HugMonster

2nd Apr 2001, 20:22

The circumference of a circle is 2πr where r is the radius and π is 3.14159265358979323846264338327950288419716 (approximately). :)

Therefore, if you are going to fly through 20 degrees of arc on a 12 dme arc, you will fly (2π x 12 x 20)/360 = 4.2 nm approx.

The formula can be simplified to (radius x arc)/60.

In your example, the distance flown is 22.5 miles. Using a closer approximation for π, we get 23.561946 nm, but the first is probably good enough for government work! :)

Therefore, if you are going to fly through 20 degrees of arc on a 12 dme arc, you will fly (2π x 12 x 20)/360 = 4.2 nm approx.

The formula can be simplified to (radius x arc)/60.

In your example, the distance flown is 22.5 miles. Using a closer approximation for π, we get 23.561946 nm, but the first is probably good enough for government work! :)

Oxford1G

2nd Apr 2001, 22:16

Thanks very much.

Vmu

2nd Apr 2001, 23:07

Arc flying for dummies:

HugMonsters simplified formula can be simplified even more by memorizing two numbers; 6 and 3.

Flying a 10-mile arc you will cover a mile for each 6 radials.

Flying a 20-mile arc you will cover a mile for each 3 radials.

Example:

30 degrees to go on a 10-mile arc: 30/6=5nm to go.

30 degrees to go on a 20-mile arc: 30/3=10nm to go.

For other arc's you can interpolate using these two numbers

------------------

"Recovery was marginal..."

HugMonsters simplified formula can be simplified even more by memorizing two numbers; 6 and 3.

Flying a 10-mile arc you will cover a mile for each 6 radials.

Flying a 20-mile arc you will cover a mile for each 3 radials.

Example:

30 degrees to go on a 10-mile arc: 30/6=5nm to go.

30 degrees to go on a 20-mile arc: 30/3=10nm to go.

For other arc's you can interpolate using these two numbers

------------------

"Recovery was marginal..."

Oxford1G

3rd Apr 2001, 12:32

VMU, Thanks very much, just what i needed.

yowie

4th Apr 2001, 09:28

How about the good ol 1:60 rule.

As exampled earlier,12nm arc through 20deg=4 track miles(20/5=12).Try a 15nm arc through say 100deg (100/4=25nm).

Sorry guys,knw how to do it,cant explain myself very well,but it works really well and quick to work out in your head!!

As exampled earlier,12nm arc through 20deg=4 track miles(20/5=12).Try a 15nm arc through say 100deg (100/4=25nm).

Sorry guys,knw how to do it,cant explain myself very well,but it works really well and quick to work out in your head!!

najib

4th Apr 2001, 14:58

Just multiply the arc (radius) by 6 (2n=2*3.14), you will get circumfrence distance (that is distance for the entire circle if you were to fly the complete circle). Now if you are to fly 60 degrees: 60 degrees is 1/6 (16%) of a 360 degrees circle ( 60/360 ). So if u are flying 15 Nm. arc for 60 degrees total distance flown is 14 miles.

(DME ARC*6)* factor of 360 degrees (degrees to fly/360)

I hope it's not too complicated; a bit of arithmetic fluency really helps.

(DME ARC*6)* factor of 360 degrees (degrees to fly/360)

I hope it's not too complicated; a bit of arithmetic fluency really helps.

HugMonster

4th Apr 2001, 21:50

najib, arc is not the same as radius.

You've also very successfully managed to complicate a very simple calculation.

Why multiply the radius by 6, divide by 360 and multiply again by the arc angle?

You get the same result radius x arc / 60.

e.g. 10 dme arc (circle radius 10 miles) - 30 degrees of arc.

10x30=300

300/60=5

Easy, no?

You've also very successfully managed to complicate a very simple calculation.

Why multiply the radius by 6, divide by 360 and multiply again by the arc angle?

You get the same result radius x arc / 60.

e.g. 10 dme arc (circle radius 10 miles) - 30 degrees of arc.

10x30=300

300/60=5

Easy, no?

MasterGreen

5th Apr 2001, 03:36

Very Good HugMonster. 5 stars and a lollipop. Nice to see we got there in the end.

MG

MG

najib

6th Apr 2001, 10:11

Hey, I was attempting the query from a conceptual point of view. So if one forgets which number to divide by, then he/she can derive. Some people are good in remembering the formula and some are good in understanding the theory. Anyway, as long as oxfordg1 is happy, we are happy!

cromañon

6th Apr 2001, 20:07

check this one. It is simple and precise

if you fly a 60º arc yu are flying the arc distance hence a 90º arc you will be flying 1.5 times the arc.

what about a 30º arc?

got it?

if u dont let me know and with a few more examples i am sure u will get it.

se ya

if you fly a 60º arc yu are flying the arc distance hence a 90º arc you will be flying 1.5 times the arc.

what about a 30º arc?

got it?

if u dont let me know and with a few more examples i am sure u will get it.

se ya

COWPAT

7th Apr 2001, 17:57

Just use LNAV, VNAV and an Autopilot whilst having a cup of coffee!

Cmdr Data

7th Apr 2001, 21:44

1 in 60 rule, like others have said.

If you are on the 20 dme arc and have to fly 45 deg, 20 is 1/3rd of 60, so 1/3rd of 45 deg is 15. Hey presto: 15nm.

If you are on the 20 dme arc and have to fly 45 deg, 20 is 1/3rd of 60, so 1/3rd of 45 deg is 15. Hey presto: 15nm.

ITCZ

10th Apr 2001, 18:01

Arc discussed on Dunnunda Thumb Rules thread, inter alia. From that discussion... one in sixty works well.

On a sixty mile arc, you change bearing one degree per mile flown.

30DME arc, two degrees per mile,

20DME, three per mile

15DME, four per mile

12DME, five per mile

10DME, six per mile

9DME, seven per mile

8DME, eight per mile

7DME, nine per mile

6DME, ten per mile

Less than 5DME, write a complaint to the issuing agency, because it is too small.

Anything in between, interpolate because you will be bloody close.

Also note that if your RMI is marked in 5 degree increments, each mark on a 12DME arc represents a mile flown/to fly. If you are incorporating a descent profile like 3nm per 1000 feet to lose, that is 1000 feet per three divisions on a 12DME arc.

With numeric skills like that, you think my countrymen could do something about the aussie dollar. <sigh>.

[This message has been edited by ITCZ (edited 10 April 2001).]

On a sixty mile arc, you change bearing one degree per mile flown.

30DME arc, two degrees per mile,

20DME, three per mile

15DME, four per mile

12DME, five per mile

10DME, six per mile

9DME, seven per mile

8DME, eight per mile

7DME, nine per mile

6DME, ten per mile

Less than 5DME, write a complaint to the issuing agency, because it is too small.

Anything in between, interpolate because you will be bloody close.

Also note that if your RMI is marked in 5 degree increments, each mark on a 12DME arc represents a mile flown/to fly. If you are incorporating a descent profile like 3nm per 1000 feet to lose, that is 1000 feet per three divisions on a 12DME arc.

With numeric skills like that, you think my countrymen could do something about the aussie dollar. <sigh>.

[This message has been edited by ITCZ (edited 10 April 2001).]

BIK_116.80

16th Apr 2001, 03:21

HugMonster,

From memory, I am pleased to confirm that your approximation of pi is correct.

Again from memory, I can offer the next few decimal places, which are "9399".

Look it up and tell me I am wrong.

From memory, I am pleased to confirm that your approximation of pi is correct.

Again from memory, I can offer the next few decimal places, which are "9399".

Look it up and tell me I am wrong.