# When the autopilot is used to make a 360, do all planes complete the turn in the same amount of time?

I’m currently in the process of making a mathematical function that calculates the time from the next waypoint that you need to begin a turn, in order to line up on the cross track of the next leg, because I’m fed up of being slightly late (or forgetting completely) and overshooting the turns completely. I plan on making an advanced auto-nav system with the Connect API once my GCSEs are out of the way.

I have the basis of the function, but I need some hard values to plug in: do all planes make a 360 in the same amount of time? I have heard of the ‘two-minute-turn’ but I’m just wondering if it is a standard system that is added to ALL planes or not.

I suppose I could set up a straight flight plan and go through every single plane making a 360, but that would take too long.

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It depends on weight and speed and the size of the aircraft. Try making a 360 in a 747 like you would with a spit, you’ll see the difference

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He means as in autopilot and the spit has no AP

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Yeah, this only applies to planes with auto-pilot.

If the bank angle is the same (because of the autopilot) then the speed shouldn’t matter right? A plane going quicker should in theory still make a 360 in the same amount of time, it would just be a really big turn circle compared to a much smaller plane. And this project I’m doing also cannot apply to planes without an AP.

The rate of turn is not related to the weight but to the bank angle, which is marked on the turn indicator on real planes. The turn radius is related to the speed: at higher speed the turn radius increases. You are actually looking at the turn radius when trying to intercept a radial.
Try at different speeds and to get the right feeling.

Happy landings
:)

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Yeah, thank-you I know it’s the turn radius that is needed - I’ve done all the maths, I just need constants. The bank angle for all planes is the same if you do it with autopilot right, so I’m asking whether they all make the 360 in the same time period.

Currently, I can calculate the turn radius using the speed and the information that all planes make the turn in the same amount of time (or not). Say you have a 747 travelling at 240 kts. The time taken to complete one 360 will always be the same, right? Say, as an EXAMPLE it takes all 747’s exactly 2 minutes to complete a 360. If travelling at 240 kts, that means that the circumference of that circle the plane makes can be worked out. Convert kts to MPH, 276 mph, and then we say that travelling at that speed, if the plane travels a distance of 276 miles in one hour, then we just find out how far it travels in 2 minutes (in this case, and this example, it would be 276 * 0.03, which is 9.2 nautical miles) so our 747 circles around for 9.2 nautical miles.

Then we can use circle theorem to work out the radius from that circumference, and then use trigonometry to work out when a precalculated distance (of a perpendicular line against the current leg, from the plane to where it intersects a midpoint line between the angle between the waypoints) matches our radius, and then… WE BEGIN THE TURN!

This all relies on that 2 minutes (or whatever it actually is) being the same across all planes). :)

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No, no I’m not after the same turn size, I’m not bothered if a 747 can’t do a 360 at the end of the runway and land again, I’m wondering whether it will take a 747 the same length of time to make an exact 360 as a small plane (if the small plane circles the airport, or the big plane circles the coastline).

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i can’t be bothered to read everything you said but i believe not. i think the A320 family does 3 degrees per second on auto pilot not emulated well in IF but yes other aircraft also turn slower i believe the A380 has slower turn speeds.
People should note: this isn’t about distance and curve size its about turn speed lots of people don’t seem to understand flight physics of course i understand why you wouldn’t if you haven’t done any theory but avoid answering questions you don’t know the answer to.

Planes bank angle increase to meet the 3 degree per second turn int eh A320 case. The angle also changes based on other factors. Since we are talking about autopilot

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I just got shut down! :P Thanks very much for the response though. I’ll just begin testing individual planes I guess then. It does make sense, and I have learned now that the two-minute-turn does not apply to all aircraft. If I’ve learned something, I’m happy! Which questions was I answering that I didn’t know the answer to btw, sorry for doing so. I was trying to explain a bit of maths in one of em…

yeh your maths was wrong planes don’t turn purely by speed (hat is only there to prevent the plane from stalling effectively) they turn by ailerons and bank angle

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… urm, yah, I wasn’t suggesting the pilot adds thrust to turn right, for example, or decreases it to turn left. I know it’s the bank angle! I will do some checking now. The maths (and speed) is just used to calculate distances - not to work out what turns the plane.

Also take wind into account. I wrote an algorithm to fly holding patterns and before I added track correction it was very interesting.

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That sounds good! And yeah, I forgot about the wind, I just presumed that you wouldn’t ever add a 360 to a flight plan, and the turn would be quick enough to be accurate without factoring in wind. I’m not planning on getting on the track, to a meter accuracy or anything, it’s mainly to avoid overshooting turns :) How does the algorithm work (if you’re prepared to share it :P)?

well maybe you should have said that

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