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270 Turning departure speed

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270 Turning departure speed

Old 6th Oct 2021, 17:40
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270 Turning departure speed

What is cheaper:

fly the 270 deg turn with V2+10 or

cleaunp in the turn and fly green dot?

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Old 6th Oct 2021, 20:56
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Is there a minimum altitude to start the turn?

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Old 6th Oct 2021, 21:17
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If there is no limit on altitude or turn radius, clean up in the turn.
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Old 7th Oct 2021, 10:47
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I expect that it is more efficient to increase speed and hence turn radius when you are pointing more or less in the direction you want to fly. Assuming the 270* turn roughly aligns you with required track to next way point, make it as slow/tight as possible. This should save time/fuel but probably not enough to matter.
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Old 7th Oct 2021, 12:20
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It depends on what you call cheaper? Minimum fuel or minimum total cost?

As an example min fuel for take off is TOGA thrust, minimum total cost is FLEX. Airbus say FLEX take off and acceleration ( as soon as possible) to the ECON climb speed is the most efficient departure. Getting creative will require an analysis by someone smarter than a pilot!
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Old 7th Oct 2021, 15:04
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mustafagander

Only looking at the fact that we're pointing the direction we want to go quicker (i.e., not burning fuel flying the wrong way), then yes. However, offsetting that is that by doing this, we're also spending more time with more drag (and in the lower less efficient altitudes). Which one wins? Probably none of us able to calculate.
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Old 7th Oct 2021, 19:47
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Rate one turn of 3 degrees per second will take the same time whether clean or flaps extended. Assuming you want minimise fuel burn then you would be better to clean up as soon as your procedures allow.
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Old 7th Oct 2021, 20:21
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Who flies rate one turns all the time?
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Old 7th Oct 2021, 22:21
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Do a 90deg turn the other way?

I’ll show myself out...
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Old 7th Oct 2021, 22:32
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Rt Hon Jim Hacker MP

Past 170 knots, the 25 degree bank limit causes the turn rate to be less than 3 deg/s
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Old 8th Oct 2021, 06:37
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If it is about fuel and not time, then flying the turn at green dot is by definition the minimum drag speed, if I recall...
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Old 8th Oct 2021, 08:28
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mustafagander

I think that’s probably the best answer. You’ll be climbing at not far off the same rate but reducing the distance = time = fuel for the entire flight.

Running the numbers at 220kts and 160kts with 25deg AoB, by the end of the turn you have saved ~4miles, which I would suspect far outweighs any extra drag from takeoff flap while you are in the turn. It’s what I normally do when, say, taking off south to go north or something like that. Also, as the actual rate of turn is ~40% quicker at the slower speed, you spend less time with the increased wing loading and drag from that. If you hold takeoff config as opposed to going to 250kts, it’s about 7nm saved.
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Old 8th Oct 2021, 09:55
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Making it complicated chaps and chapies..was at Farnborough when the Blackbird set the transatlantic speed record, started its turn overhead and passed over the Dutch coast before returning...simples.
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Old 8th Oct 2021, 10:14
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I did not fly them but I gather that in the Lightning if you do a turn after take off in reheat you run out of fuel before you get back to the airfield!
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Old 8th Oct 2021, 14:39
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PJ2

Doesn't matter how low the drag is, if you're flying away from your destination it won't help the fuel situation.
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Old 8th Oct 2021, 19:53
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But you're only flying away from the destination for the first (slowest) 2/3 of the turn)... Getting rid of drag and climbing into thinner air are the goals.

Another data point: In a heavy 747 Classic on a hot day, it didn't climb well at all at Flaps 20; you had to accelerate and get to Flaps 10 to make any progress at all. You took off at Flaps 20 because the runway wasn't long enough for a Flaps 10 takeoff. HOWEVER, the hard part was transitioning from Flaps 1 to clean; bank was further limited to 20 until at V2+100 KIAS (well over 250 KIAS). Hence, climbing at Flaps 1 until out of the turn was often the best case.
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Old 10th Oct 2021, 15:42
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Intruder: "But you're only flying away from the destination for the first (slowest) 2/3 of the turn)..."

That may be so, but any amount of flying-away that exists, has an effect that when considered, knocks the optimal clean up time (or speed to fly) away from what it would be if it wasn't considered (however little of a difference that may be)
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Old 10th Oct 2021, 18:49
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So V2 + 10 it’s is, always fly it like that, pointing in the right direction soon.
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Old 10th Oct 2021, 23:14
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Won't matter much because when you get to your destination you will get vectors anyway and your fuel savings will be gone.
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Old 17th Nov 2021, 01:05
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Question for a performance engineer wizard

The scenario is a 270 degree turning departure starting at 400 agl
  1. Immediate acceleration to clean maneuvering and retract flapslats
2. Constant speed turn at V2+10, then clean up approaching end of turn.

What results in overall Lower fuel burn ?
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