Best fuel economy

[A_J]

hi, i am new to this community, i joined just today. would really appreciate if i get the answer to my doubt with proofs/reasons. So here i go with the question:
You take off from place A (departure R/W 27) for place B, A to B jeppesen track is 090. U take off with normal flap 5 setting, and u r given a SID, which has the very first waypoint in the runway heading only defined by safety altitude (lets say "4000'AMSL or above", elevation A=1000'), and then turn left/right to establish on course 090 to your destination. Now under the same given circumstances of winds, temperature, QNH, R/W length, T/O thrust, Climb Thrust, T/O weight, i mean everything remaining same, one pilot decides to accelerate on schedule (as per SOP) and then climb 4000' Baro to start the turn for track 090, other pilot decides to maintain take off flaps ( i.e. flap 5), and flap 5 speed till he reaches 4000' Baro to start the turn oncourse to avoid unwanted acceleration segment of T/O path before the turn (which will lead him away from his destination). Considering all other parameters remaining same, which case shall give comparatively less fuel burn and min time to reach destination.
Please excuse me, the fuel burn i m talking here is to the precision of unit decimal place (theoritically).
Thanks.

[rudderrudderrat]

Hi,

Since I am pointing away from my destination initially (270 degs), I would perform a NADP 1 (maintain TO Flaps & Climb V2 +10 to 3,000 ft agl before accelerating).

At 4,000 ft (3,000 agl & my conditional way point), I'd commence the turn and accelerate towards clean speed + 10 until I was pointing towards my first way point on track (within 30 degs), then accelerate normally.

[Slasher]

Altitude limit before turn - If your pointing away from the direction you want then keep flaps V2+10 etc till youve turned and are within 30 deg of the general direction of your final outbound track then accelerate to enroute. Its was known as a "Low Close In Turn" in the pilot (pre Airbus) era.

Distance limit - clean up asap (without banging the hills) and acelerate to Best Angle + 10kt. Then acelerate to enroute within 30 deg as above.

PS: I didnt know we were a "community" - just a bunch of drivers who happen to argue a lot at the same place?

[Standard CM1]

Hi,
The point of discussion /argument here is not noise abatement but fuel burn during departure.As long as your final track to destination is more than 70 degrees offset from your departure track you should execute a close-in-turn i.e maintain take-off configuration until within 30 degrees of your final track. Having said that, obstacle clearance is first priority and in this case cleaning up asap will guarantee optimum clearance (climb at best L/D speed)-min.clean speed.

Cheers:)

[ant1]

Slasher & Standard CM1:

IMC and you have high terrain on both sides of the track (don't have to fly over) and the turn starts at a given DME distance from airport located VOR.

Do yo keep T/O flaps in order to minimize turn radius and remain a little bit further away from terrain or just say hey, SID was designed for the specified speed restriction (> Fup speed) so there should be no problem cleaning the A/C ?

[khalilkarim]

Hi,

I can't understand the reason behind keeping flaps till 30 deg within the final course.

What I would do is, after t/o retract flaps at safe altitude(400' if no obstacles)
and climb to my initial altitude, while following the SID, at v2+10 at a higher rate of climb due to the elimination of drag caused by flaps.

[Slasher]

Ant1 and khalilwhatever the original question was on fuel economy, not speed eficiency.

For even more fuel savings do the TO using TOGA power till 400ft.

A good read of "Handling The Big Jets" and AC Kermode's "Aeronautics of Flight" will answer all the questions you guys have and will have later.

[Wizofoz]

What I would do is, after t/o retract flaps at safe altitude(400' if no obstacles)
and climb to my initial altitude, while following the SID, at v2+10 at a higher rate of climb due to the elimination of drag caused by flaps.

That would get kinda noisy as, if you tried to maintain V2+10 with flaps retracted, you'd stall, crash and die!!!

Perhaps you meant Vcl?

The problem with your logic is that, in order to accelerate, you have to REDUCE your rate of climb. this may make the total elapsed time to reach the 4000' increase, as the better ROC from being clean may not make up for the reduction in rate due to acceleration. At some point there would be a "Break even" but it would likely be much higher.

[khalilkarim]

Are you worried about noise from the engines or noise from the crash?
because if you're worried about the crash,don't be.


my logic says if i retract flaps i will have to pitch up more to maintain my safe speed thus the rate of climb will increase because your a/c will accelerate. (you don't have drag from your flaps anymore).
of course you can do that if you have no obstacles and no noise abatement procedures to worry about (since for noise abatement i have to reduce my t/o thrust) which is the case in this scenario since no one mentioned it from the beginning.

and by doing this you would be saving fuel Mr slacher..

[Wizofoz]

kalilarum,

I suggest you have a bit of a read of your manuals.

V2 is safe speed In the takeoff configuration. If you maitained V2 or even V2+10 while retracting flap, you would, in almost any modern Jet, stall.

Minimum safe speed clean is Vcl. As an example, on the 777 I fly, a typical V2 for Flap 15 at a moderate weight would be around 165kts. Vcl at the same weight would be around 230kts. Try retracting the flaps while maintaining 175kts and a smoking hole would ensue.

Do you actually fly a transport aircraft that does not require acceleration in order to retract flaps?

Actually, reading your post again, I can only assume you don't actually fly, as, I'm sorry, it displays a distinct lack of technical knowledge.

Did you know, for instance, that noise abatement procedures call for one to MAINTAIN t/o thrust longer, not REDUCE thrust earlier, as you suggest?

[khalilkarim]

wizofoz,

thanks for the information about the 777.
did it happen that you flew a private jet during your career?
for example the Hawker 800 if you retract flaps the nose will go up so does speed
from there i talked about my technique.
as for the noise abatement, in the hawker I have to add power in order to attain climb thrust.

[rudderrudderrat]

@ khalilkarim

if I'm climbing at v2+10 and I retract flaps maintaining the speed how would i crash??

There must be a language problem here. We understand you can maintain V2+10 with take off flaps - but please explain how you can maintain this speed with Flaps 0 (zero). If you can - why don't you take off with 0 flaps?

[khalilkarim]

the main reason behind putting flaps at take off is to reduce take off run,at least for the airplane I fly.

[ant1]

Slasher, yup little digression, sorry. The fuel economy plot appeared stalled so I felt tempted. :oh:

[Wizofoz]

khalikarum,

This is what is proving confusing to us mear airline pilots.

Flap reduces take-off run by reducing stall speed, and therefore lift-off speed.

If you can safley fly you aircraft flaps up at V2, with the appropriate margin over stall, there would seem to be no advantage in using flaps for take-off.

So, just for clarity, are you saying that maintaining V2 still gives you 1.2Vs flaps up?

You also still make no sense wrt noise abatement. Both NADP and the old ICAO A and B procedures call for maintaining T/O thrust to 1000-1500 ft, at which time you can "Reduce" to climb thrust. Yes, with sufficient Flex thrust CLB may actually be more than TO on some types.

But at no time are you called upon to reduce TO thrust early, which is what your first reference to NAP implied.

[411A]

Considering all other parameters remaining same, which case shall give comparatively less fuel burn and min time to reach destination.


For the airplane that I fly (L1011)....

other pilot decides to maintain take off flaps ( i.e. flap 5), and flap 5 speed till he reaches 4000' Baro to start the turn oncourse to avoid unwanted acceleration segment of T/O path before the turn (which will lead him away from his destination)

...with the proviso that the takeoff flap setting (14) is reduced to four (with an approprite speed increased to V2+20 minimum), and climb thrust is selected once flaps 4 is achieved.

In this way, the fuel consumption is reduced, slightly.

[khalilkarim]

the main difference between flaps15 and 0 is take off run specially at near MTOW weights.
thats why if we're light and on good runways we take off flaps 0 and climb faster.
I wasn't aware about the big jet's performance before that's why i said that.

As for the noise abatement, yes you are right.
for information,on the hawker on t/o we add few %N1 to the t/o thrust to obtain climb thrust specially when flying in moderate to hot weather.

so back to the subject,are you saying that take off flaps should be kept until on final course?

[Wizofoz]

khalikarim,

You are still not really answering the question.

Say you do a flap 15 take-off. You will calculate a V1, Vr and V2.

At what speed after takeoff is it safe for you to retract your flaps, and what is the minimum speed you can fly and manoeuvre with flaps retracted?

As to the OP, I think it will vary depending on type, but On Guards answer, accelerate to flaps up manouevre speed (Vcl), retract flaps on schedule and maintain Vcl until near the outbound course is probably a very good technique in most circumstances.

Just to confirm, you are a licensed pilot who flys a Hawker 800 professtionally?