Radius of turn
Joined: Dec 2002
Aviation Qualifications: ATP+Mil
Posts: 3,984
Likes: 568
From: Where the Quaboag River flows, USA
Two USAF rules of thumb (we're not any better than a thumb):
Mach No. squared, i.e. M.80= turn radius of 6.4 nm
Groundspeed (in nm per minute)- 2 i.e. 360 Knot GS = 6 nm/min = 4 nm turn radius.
There are others for the mathematically inclined (not me), if you need more accuracy than that you are not flying, you are computing.
Mach No. squared, i.e. M.80= turn radius of 6.4 nm
Groundspeed (in nm per minute)- 2 i.e. 360 Knot GS = 6 nm/min = 4 nm turn radius.
There are others for the mathematically inclined (not me), if you need more accuracy than that you are not flying, you are computing.
Joined: Sep 2001
Posts: 143
Likes: 1
From: UK
In a Rate One turn situation:
Half a circle is performed in one minute.
Therefore: PixR= TAS/60 ; R being the radius of turn and TAS/60 the distance flown in the air during one minute if you expressed TAS in mph, kph, or kt.
R= TAS/(Pix60)
Pi being 3,1415... the product (Pix60) is fairly close to 200.
Therefore: R= TAS/200
If TAS is expressed in Kt the latter formula gives you the radius of turn in the air (for a rate one turn) in NM.
You can replace TAS by GS which gives an approximation of the raduis of turn on the ground (though in a turn for a given wind speed conditon, the Gs is not constant).
Application:
You are tracking inbound to a VOR/DME to take up a 5 Dme arc.
Your ground speed indicator reads 120 kt.
You can assume that the radius of turn is R=120/200=.6 NM
The latest distance reading at which you turn to position on the arc is 5.6 NM.
However I would suggest to give yourelf a bit more leeway and turn at 6 rather than 5.6 and then adjust the rate of turn accordingly.
Half a circle is performed in one minute.
Therefore: PixR= TAS/60 ; R being the radius of turn and TAS/60 the distance flown in the air during one minute if you expressed TAS in mph, kph, or kt.
R= TAS/(Pix60)
Pi being 3,1415... the product (Pix60) is fairly close to 200.
Therefore: R= TAS/200
If TAS is expressed in Kt the latter formula gives you the radius of turn in the air (for a rate one turn) in NM.
You can replace TAS by GS which gives an approximation of the raduis of turn on the ground (though in a turn for a given wind speed conditon, the Gs is not constant).
Application:
You are tracking inbound to a VOR/DME to take up a 5 Dme arc.
Your ground speed indicator reads 120 kt.
You can assume that the radius of turn is R=120/200=.6 NM
The latest distance reading at which you turn to position on the arc is 5.6 NM.
However I would suggest to give yourelf a bit more leeway and turn at 6 rather than 5.6 and then adjust the rate of turn accordingly.
