Flight performance - rates of turn
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Flight performance - rates of turn
I'm trying to obtain realistic flight behaviour for an ATC training simulator, and I have a question or two on rates of turn, particularly at high level. Essentially, when is a rate-1 turn not applicable?
1) Are reduced rates of turn used, in normal navigation, above say, FL250 (and, briefly, why)?
2) In a holding pattern, are rate-1 turns always used, regardless of height - what about holding above FL200 (265kts) and above FL 340 (M0.83)?
Many thanks
GB
1) Are reduced rates of turn used, in normal navigation, above say, FL250 (and, briefly, why)?
2) In a holding pattern, are rate-1 turns always used, regardless of height - what about holding above FL200 (265kts) and above FL 340 (M0.83)?
Many thanks
GB
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A rate 1 turn is impossible to achieve at high TAS. Once you get above piston twin speeds, you cannot achieve a rate 1 turn as bank angles are normally limited to 25 degrees. As TAS goes up, a 25 degree bank angle starts giving you much slower rates of turn. 3 degrees/second turns are not achievable over about 160(?)kts or thereabouts. Taken to the extreme, Concorde could roll into a 25 degree bank and the turn would be enormous at 1200kts. The aeroplane still experiences the same 'g' forces, just the rate of turn becomes smaller with increasing speed.
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Many thanks Rainboe.
In the meantime I have located a formula which allows me to determine the rate of turn from TAS (assuming max bank angle 25 degrees). However, I am still puzzled about turn rates in holding pattterns.
If holding at 210kts, this gives a rate of turn of 2.4degs/sec. To complete a 180 degree turn, this would take 74 seconds (instead of the 1 minute turn). Therefore a standard (4 minute) hold, in still air, would require an extra 28 seconds to complete the turns because of the reduced turn rate (and increase the holding area). Does this mean that 4-minute holds are not achievable? Or, are the inbound/outbound leg times adjusted to compensate?
On another example, holding at 265kts above FL200, on a 1.5min leg, the turn rate is 1.9 degrees, or 94 seconds for 180 degrees, thus making the hold 6 minutes.
Sorry if this sounds daft, am I missing something
GB
In the meantime I have located a formula which allows me to determine the rate of turn from TAS (assuming max bank angle 25 degrees). However, I am still puzzled about turn rates in holding pattterns.
If holding at 210kts, this gives a rate of turn of 2.4degs/sec. To complete a 180 degree turn, this would take 74 seconds (instead of the 1 minute turn). Therefore a standard (4 minute) hold, in still air, would require an extra 28 seconds to complete the turns because of the reduced turn rate (and increase the holding area). Does this mean that 4-minute holds are not achievable? Or, are the inbound/outbound leg times adjusted to compensate?
On another example, holding at 265kts above FL200, on a 1.5min leg, the turn rate is 1.9 degrees, or 94 seconds for 180 degrees, thus making the hold 6 minutes.
Sorry if this sounds daft, am I missing something
GB
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For large aircraft holding, the 4 minute hold is dispensed with. Timing is adjusted for a one minute leg on the outbound sector, plus or minus an allowance for wind component, and allowing a drift compensation of double or treble drift. However it has all changed. I'm afraid nowadays one just programs the Hold page for the FMS with position, direction, and whether timing or distance is used for the hold, and one sits back and watches it execute a perfect entry and holding pattern. The old skills are gone!
Above twin piston size, 4 minute holds are not attempted. It was all Instrument Rating stuff of old!
Above twin piston size, 4 minute holds are not attempted. It was all Instrument Rating stuff of old!
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Surprised that nobody has mentioned it, but for the nominal 25 degree bank angle limit used, 180 Kt TAS is the limit speed for a Rate 1 turn.
That pretty much eliminates all jets, large or small from the Rate 1 possibility. If it is required, it must typically be done 'dirty' with Slat / Flap extended to reduce the minimum speed.
The reasons given in the first sentence are also why the 45 degree Procedure Turn falls apart above 180 Kt TAS, with inevitable overshoot of the inbound track. The 80 degree Procedure Turn is unaffected by this, and may be done at virtually any speed. (During Ground Radar calibration work at high altitude, I've seen some very neat asymptotic turns inbound from 80 degree Procedure Turns, even at speeds around 480 Kt TAS).
Regards,
Old Smokey
That pretty much eliminates all jets, large or small from the Rate 1 possibility. If it is required, it must typically be done 'dirty' with Slat / Flap extended to reduce the minimum speed.
The reasons given in the first sentence are also why the 45 degree Procedure Turn falls apart above 180 Kt TAS, with inevitable overshoot of the inbound track. The 80 degree Procedure Turn is unaffected by this, and may be done at virtually any speed. (During Ground Radar calibration work at high altitude, I've seen some very neat asymptotic turns inbound from 80 degree Procedure Turns, even at speeds around 480 Kt TAS).
Regards,
Old Smokey
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Old Smokey
Thanks for the update. I confess to being embarrassed by my ignorance. 
In a former life, I trained as an ATCO, back in the late 60's, and we were (then) taught 4' holding patterns, based on rate-1 turns. It seems, though, that even then, amid the Viscounts, Vanguards, BA11, Tridents and B707s flying at the time, that this was never possible (why the hell did they teach us that?).
In my little puddle jumper, I fly rate-1 turns (as taught religiously by an airline pilot), but at no time has anyone, then or now, ever indicated that rate-1 is not achievable by anything but the most modest of aircraft.
I'd always thought that ILS IAC were based on rate-1 turns, with the faster aircraft being a 'wider' pattern due to increased speed only (not reduced rate of turn).
Thank you (all) for putting me straight.
GB
In a former life, I trained as an ATCO, back in the late 60's, and we were (then) taught 4' holding patterns, based on rate-1 turns. It seems, though, that even then, amid the Viscounts, Vanguards, BA11, Tridents and B707s flying at the time, that this was never possible (why the hell did they teach us that?).
In my little puddle jumper, I fly rate-1 turns (as taught religiously by an airline pilot), but at no time has anyone, then or now, ever indicated that rate-1 is not achievable by anything but the most modest of aircraft.
I'd always thought that ILS IAC were based on rate-1 turns, with the faster aircraft being a 'wider' pattern due to increased speed only (not reduced rate of turn).
Thank you (all) for putting me straight.
GB
