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How to calcualte the radius of turn required to clear obstacle

Asked by: 4013 views
Aerodynamics, Airspace, Commercial Pilot, Instrument Rating, Private Pilot, Student Pilot

You are a sightseeing pilot and you are flying in the middle of two mountains. The height of both mountains is 2000 ft ABOVE your current altitude. Your IAS is 150 kts with 20 kts tail wind, what is the minimum distance from the left or the right mountain that you must have in order to make a U-Turn (your position exactly in the middle) with 4 nm clearance of the mountain’s edge? I solved it but I want to check if I am correct. The website below is helpful. http://www.flightlearnings.com/2009/08/26/radius-of-turn/

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4 Answers



  1. MaggotCFII on Nov 11, 2013

    Try this link:

    http://www.csgnetwork.com/aircraftturninfocalc.html

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  2. Brian on Nov 12, 2013

    Depends on the bank angle. The formula to determine this is velocity squared divided by 11.26 tan (bank angle) where velocity is in knots and bank angle is in degrees. The resultant radius this formula gives you will be in feet.

    Source: AFNA p178 — http://www.faa.gov/regulations_policies/handbooks_manuals/aviation/media/00-80T-80.pdf

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  3. Bob Watson on Nov 13, 2013

    If in doubt, slow down. Reducing your speed a little bit makes a big difference in turn radius.

    Also, IIRC, you want to turn into the wind and not away from it (i.e. start from the downwind side of the canyon) in that situation. Turning into the wind will shrink the radius of the turn whereas turning with the wind will increase it. If you’re already in a tight spot, you don’t want to see the mountains get any closer than they already are.

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  4. Clark Hall on Mar 01, 2014

    This can be a dicey situation. As was suggested start on the down wind side of the canyon and hug the canyon wall before starting the turn but watch for the down draft on the upwind side of the canyon. I suggest you go out in a big flat area with section lines so you have something to reference and do some turns to see how much room it takes. It is harder to look across a canyon and know the distance. Look at the ground as you do the practice turns over flat ground to get a feel for distance. This practice should be done at 500 feet or so if you are not used to flying that low. And work your way down.

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