Better Perf during rolling takeoff?

[Robini]

Wich aircrafts get better performance if using rolling TKF?
What i have heard the A330 get's better...not sure if thats true or not.
How is it with the A318/319/320/321? And the Boeings?
Is there another aircraft except the 330 thats get better perf?

[barit1]

The primary reasons for rolling takeoff have to do with engine life: Less risk of FOD or erosive particle ingestion, and longer warmup time leading to hot section preservation.

In most cases the takeoff performance difference is very small.

[Henry VIII]

On FCOM 3, TO section the only note says : take off roll is permitted.
No specs on FCTM.

FCTM says that thrust usually reaches the TO value around 60Kts, so performing a rolling TO the same TO thrust should be reached a bit earlier.

I guess the reason(s) for a rolling TO are explained by barit1, for buses and no.

[FE Hoppy]

Power against brakes will always give better perf than rolling. With rolling you are using TODA before you have take off thrust.

[AirRabbit]

The “trade-off” comes in the exchange of distance for kinetic energy. If you make a 90-degree turn to align with the runway before adding power, you get a bit more concrete in front of you, but you start with zero kinetic energy. If you turn the corner with some forward movement you keep a bit of kinetic energy but you sacrifice a bit of distance to keep it.

[mutt]

Does any manufacturer recommend one of the two methods? Or do they consider both of them to be the same if conducted in the proper manner?

Mutt

[doubleu-anker]

FE Hoppy


"Power against brakes will always give better perf than rolling. With rolling you are using TODA before you have take off thrust."

Not necessarily.

Take the extreme case of a high speed taxiway entry onto a runway. If this is the only entry to the t/o runway and you are doing 40 - 50 knots before you hit the centre line, in a nice gradual turn, are you going to stop the aircraft again, apply power etc., then release the brakes?

My argument is this. If the aircraft is moving then keep it moving and introduce the power for t/o, provided you have been cleared for take off of course.

[stilton]

Disagree with the power against brakes club, turn on as close to the end of the runway as you can get, but keep rolling, keep the momentum going and get the power up smartish.

Momentum is valuable, combine that with rapid thrust advance and you will always use less runway.

[FE Hoppy]

Here's a note from an EASA AFM near me:

NOTE: For rolling takeoffs, performance data is valid from the point
where takeoff thrust is achieved.

So unless your rolling take off is from a taxiway that allows you to acheive TO thrust at the threshold or at the point at the end of the alignment allowance considered in your calculation then beware! If the stopway doesn't get you the Judge may!!

[barit1]

They are being very conservative in that NOTE, probably because it's cheaper than actually doing the flight test, AND because pilot technique introduces some variation.

Think of it this way: On a rolling takeoff, at the point takeoff power is reached, you've already gained 30-40 kt. speed. On a static runup, the equivalent point is ZERO kt. Applying the above NOTE, actual performance will be BETTER than a static TO.

(PS: on the SE overpowered taildragger I'm used to flying, running up to TO power then releasing the brakes is a sure recipe for a groundloop - assuming you didn't dig the nose in first! :} )

[FE Hoppy]

I think the point is that in the time the engines are spooling up the acceleration rate is less than had they been at TO thrust from the start, so the ground roll to that point( the point where TO thrust is set and the two cases reach the same speed) MAY be longer or shorter depending on the entry speed for the rolling example. Unless you are prepared to give minimum threshold crossing speeds I'm not sure how you could realistically predict the initial ground roll distance up to the point where TO thrust is set and therefore calculate the remaining acceleration.

The Aft limit of the CG envelope can be limited by brake release tip up to ensure no probs with setting thrust but I agree this doesn't apply to a tail dragger.

[BelArgUSA]

If I have a takeoff at a weight where limited by runway...
I line up the airplane (full length, when through that argument a couple of days ago).
No inter-sex-ion for me.
Line up, set brakes, spool up engines, start roll, full thrust as soon as possible.
xxx
What for a rolling takeoff...?
Do you like to give sideload "Gs" to your cabin tail passengers...?
So to avoid that, takes you 1,000 ft of wasted runway to get to full thrust.
xxx
I know many of you fly 737 and 320s... A 10,000 ft long runway is plenty.
You certainly have enough for rolling takeoff and do 3 touch and goes...
But, my young friends, if the runway is 5,500 feet long, hold the brakes, then spool your engines.
xxx
Better performance with rolling takeoff...? What vocabulary is that...?
Do you have radial tyres for better cornering...?
:rolleyes:
Happy contrails

[N1 Vibes]

Ref the A330, RR Trent 700 powered, the system used for acceleration on T/O is called, Modified Engine Acceleration Schedule for Take Off (or MEASTO for short). This is what limits engine thrust to below take-off until the correct groundspeed is reached (which I think is the quoted 60 knots).

The reason the Trent 700 needs this, is because it had a tendency to surge if the throttles were applied judiciously before a good forward speed was reached.

Regards,

N1 Vibes

[barit1]

Thinks: "How on Earth can they run T#700 full bore on the bloody test bench, then?" :E

(unless, of course, the collossal concrete containment cubicle is on wheels... :E:E)

[Flight Detent]

My understanding of the Boeing B737NG takeoff technique is that it really doesn't make much difference if it's done efficiently, and in the rolling takeoff case, the delay in advancing the thrust from the initial setting is no longer than approximately 2 seconds!

Cheers...FD...:ok:

[stilton]

If you are trying to use the minimum runway why would you want to accelerate all that weight from a dead stop, when you can have full thrust and 10-20 knots already 'in the bag' at roughly the same point.

You don't need to make a Formula one turn onto the runway either and you certainly don't need '1000 feet' to line up.

The difference in runway used to line up is minimal (if you do it right) and most modern engines are at full chat in seconds.

It's a different matter when ATC 'forces' you into position and hold on a limiting runway.Then I would set full power before releasing the brakes (or start the roll when they cannot hold the aircraft any longer)

Whichever technique you decide to use choose one ! I have sat in the back on the runway as power is increased while the brakes are dragging with the aircraft in motion for hundreds of feet !

Not exactly sure what they were trying to do but that is definitely the worst of both worlds :ooh:

[Rotates Lowly]

Then I would set full power before releasing the brakes (or start the roll when they cannot hold the aircraft any longer)

Do that in a B737-300 and up? Poor passengers' necks...:eek:

[zeus_737]

Rolling takeoff... well asper FOBN ... understanding setting of takeoff thrust....
engine accelaration depends upon the rate of setting the thrust levers to the flex or toga detent... i.e if we ram it to toga... engine will still accelerate at the max persmisseble rate of the FADEC as oppose to slowly easing the engine up to takeoff thrust and not using the fadec control optimally...( ramming the thrust lever is not implied .. jus a matter or argument)so u can eat up runway even from a complete stop if ur not prompt enough to set the takeoff thrust...

so if u think that ur using up too much runway doing a rolling takeoff.. well i disagree... with the FBW.. NSW u can make a very smooth transition from a taxing turn to a rolling takeoff.. and about the g's
well ever felt the g's when u set TOGA thrust when taking off?

and about intersection takeoff... well to each his own.. but sometimes its better but most of the time its not.. :ok:

[Denti]

Rolling takeoffs are recommended in my company on 737s (classic and NG).

The relevant text from the FCOM:


A rolling takeoff procedure is recommended for setting takeoff thrust. It expedites takeoff and reduces risk of foreign object damage or engine surge/stall due to a tailwind or crosswind.
Rolling takeoffs are accomplished in two ways:
• If cleared for takeoff prior to or while entering the runway, maintain normal taxi speed. When the airplane is aligned with the runway centerline ensure the nose wheel steering wheel is released and the LHS applies takeoff thrust by advancing the thrust levers to just above idle (40%N1). Allow the engines to stabilize momentarily then promptly advance the thrust levers to takeoff thrust (autothrottle TO/GA). There is no need to stop the airplane prior to adding thrust.
• If holding in position on the runway, ensure the nose wheel steering wheel is released, release brakes and then apply takeoff thrust as described above.
Note: Brakes are not normally held with thrust above idle unless a static run-up is required in icing conditions.

[parabellum]

I've flown a number of Boeings and in each one Boeing have recommended the rolling take off if permissible, if you are runway limited then I would suggest it isn't permissible?

[misd-agin]

Simulator season. Five takeoffs and 5 aborts at V1+10.

Three takeoffs allowing autothrottles to advance the power resulted in all three a/c departing the runway about approx. 60 kts.

Two takeoffs manually advancing the power resulted in two aborts still on the pavement.

How quickly you get takeoff power matters. Most pilots doing rolling takeoffs are farther down the runway before takeoff power is set vs. a static takeoff.

[BelArgUSA]

Bless you my son...!
:ok:
Happy contrails

[Old Smokey]

I think that a point that seems to have been missed, and perhaps what the original poster was alluding to is confusion with the "Roll-On" Takeoff (not Rolling). That is, a Takeoff where the aircraft enters the runway at the nominal Takeoff commencement point already rolling with residual speed from the taxy.

For a 90 degree or 180 degree turn to line-up, this is obviously not practical or safe, but there are many Runway entry points such as Brisbane 19 and the new Singapore 20C where significant taxy speed can safely be maintained up to the SOT (Start of Takeoff) point where Takeoff Thrust / Power is then applied whilst still rolling.

I recall working on one Douglas jet aircraft where the AFM stated that the Maximum Achievable Takeoff Weights were (1) Roll-On Takeoff, (2) Standing Start, and (3) Rolling Takeoff in that descending order. The AFM went on to explain that a properly executed Roll-On Takeoff was one where the aircraft had a minimum speed of 10 knots at the normal SOT. In these circumstances Standing Start Takeoff limiting weights were permissible, whilst better than Standing Start actual performance could be expected.:ok:

Regards,

Old Smokey

[stilton]

757 / 67 'Rotates lowly' and while they are good performers it is not exactly Bugatti Veyron acceleration.

Certainly not whiplash inducing :E

[misd-agin]

stilton - "757 / 67 'Rotates lowly' and while they are good performers it is not exactly Bugatti Veyron acceleration.

Certainly not whiplash inducing http://static.pprune.org/images/smilies/evil.gif"



Hmm, 757 w/RR engines at Max Power is very impressive.
Especially if your weight is down around 180-190,000 lbs (85,000 Kg).(typical weight for a 2-3 hr flight).

Thrust to weight is almost down to .5, which is similar to fighter a/c 'dry' thrust to weight ratios.

[stilton]

True, but if I was that light it is very unlikely I would be using full thrust for take off.

A good example would be departing Bristol in a 757 at max weight (closer to 250,000 pounds) for an 8 hour flight back to NY.

[john_tullamarine]

horses for courses ..

(a) standing start is useful for reference as it is the most easily repeatable set of data .. but it shakes the stuffing out of the aircraft so should be used only when it is sensibly appropriate.

(b) if the aircraft is heavy and we don't dilly dally with the levers, the power is set in a few turns of the wheels - near enough to standing start

(c) if the aircraft is light (and low Hp/OAT), the aircraft will be some distance down the roll prior to achieving takeoff settings. If the runway is short/limiting, this is probably not a sensible strategy, if long and definitely not limiting, it is more useful for the aircraft maintenance than a standing start (I acknowledge BelArg's concerns but they are related more to the limiting runway situation, with which I concur)

(d) roll on from a highspeed exit or displaced threshold - refer OS' words.

(e) autothrottle .. on the Boeing many of us used to override the autothrottle, pushing the levers up manually and then let the auththrottle fine tune the setting. Seemed to work real fine.

[Chris Scott]

Quote from stilton:
Whichever technique you decide to use choose one ! I have sat in the back on the runway as power is increased while the brakes are dragging with the aircraft in motion for hundreds of feet !
Not exactly sure what they were trying to do but that is definitely the worst of both worlds.
[Unquote]

Amen to that. Not sure about hundreds of feet, but any are too many. It seems to be the norm now on B737s (CFM) with at least one British airline. Does it result from an SOP, to cover some engine issue or other?

[doubleu-anker]

misd-agin

"Simulator season. Five takeoffs and 5 aborts..........."

Interesting post.

If it is the 747 simulator, try this one. Full or as much power on the brakes, before you go skipping and get the sim instructor to fail an outboard engine and see if you keep it on the tarmac.:}

[Tee Emm]

On a related matter. The 737 Classic and NG FCTM states thrust levers should be opened to approx 40 percent N1 and a slight delay not more than two seconds to check equal power, before pressing TOGA for the autothrottle.

My estimation from observing hundreds of take off's in the simulator is that most pilots open up the thrust levers to well beyond half way up the quadrant (the old stand 'em up policy required of the JTD8D engines) and then as the N1 passes rapidly through 40 percent, they hit TOGA. Certainly the engines are never allowed to stabilise momentarily at 40 percent N1. It is almost as if they are attempting to "hurry up" the acceleration with rapid thrust lever movement. I can never understand what they are attempting to achieve because certainly their technique is not the Boeing way. Maybe they are just impatient or perhaps they cannot be bothered to read the FCTM?

Different story on the 737-200 series where the JT8D engine requires a specific EPR setting before the throttles are full advanced to take off EPR. That specific initial EPR setting for stabilisation is 1.6 EPR or close enough and that requires a throttle setting half way up the quadrant. Hence the term "Stand them up."

[misd-agin]

doubleu-anker - "misd-agin

"Simulator season. Five takeoffs and 5 aborts..........."

Interesting post.

If it is the 747 simulator, try this one. Full or as much power on the brakes, before you go skipping and get the sim instructor to fail an outboard engine and see if you keep it on the tarmac.http://static.pprune.org/images/smilies/badteeth.gif"

----------------------------------------------------------------------

I'm a fan of the skids marks at the brakes release point that swerve towards the side of the runway. :sad:

Tee emm is correct about folks pushing more and more throttle lever while the motors are lagging behind. If it's already lagging why do you think pushing the power lever forward will help? As doubleu-anker implies, good luck keeping it on the runway if you get a large power split.

The best skid mark to view that is Cancun (CUN) Rwy 12. Main gear skid marks come within feet of leaving the runway.

Another is MIA Rwy 08R. FO thought it was from someone turning onto the runway too fast but you can see where the nose tire skid marks start on the runway centerline stripe.

JFK 31L had a differential N1 skid mark, it faded over several months/years, so someone replaced it with a new one. :(

Never understood how the skids marks were produced until I saw it happen. Full left nose wheel while the a/c shudders and bounces to the right with smoke billowing from the nose tires! :eek::eek::eek: FO and I were speechless.

[aguadalte]

misd-agin

"Simulator season. Five takeoffs and 5 aborts..........."

Interesting post.

If it is the 747 simulator, try this one. Full or as much power on the brakes, before you go skipping and get the sim instructor to fail an outboard engine and see if you keep it on the tarmac

Just hope you don't try to abort in real life at V1 + 10 ...:confused:

doubleu-anker,

That's my favorite engine-failure training on the 340! Early recognition and quick action will save your day:ok:

Fly Safe, what ever bird you fly!

[Chris Scott]

Confusing that we've got rolling-T/O and full-length T/O discussion threads running in parallel, with so much potential overlap.

Tee Emm describes "standing up" the throttles on the JT8D (1.6 EPR), and we used to do precisely that on the JT3D-engined 707s (1.2 EPR, I think).

If we were joining the runway from a 90-degree angle, the PF would stand up the throttles (err: sorry captain, the thrust levvers) when we were about half way round the corner. They were then greedily grabbed by the F/E, and – after the airplane had accelerated round the corner – he would eventually announce something like "engines all stable". The PF would then call for "take-off" :rolleyes: power (not the only ambiguous call in those days).

I always feared we were vulnerable to an outboard failing to spool-up as we shot round the corner...

Quote from Tee Emm:
I can never understand what they are attempting to achieve because certainly their technique is not the Boeing way. Maybe they are just impatient...


Possibly. As humble SLF, what grates me most about the current technique on some CFM/B737s is when, having lined up and still rolling forward at idle thrust, the pilot applies the brakes and [U]simultaneously starts increasing the power for the procedure you describe.

[misd-agin]

"aquadalte - Just hope you don't try to abort in real life at V1 + 10 ...http://static.pprune.org/images/smilies/confused.gif'

*********************************************************

Sims = training and events you can't, or shouldn't, do in the a/c.

[Bruce Waddington]

misd-agin,

You write "Sims = training and events you can't, or shouldn't, do in the a/c. Yesterday 11:03

"Training" for rejected take-offs above V1 is trouble looking for a place to happen. It is called "negative training" and should be avoided at all costs.

Back to the thread now ... In the Lear 45XR that I now fly you must add 300 feet to the runway distance required if doing other than a brakes on take-off.

best regards,

Bruce Waddington

"fly the way you train and train the way you fly"

[misd-agin]

We'll classify aborting past V1 as "events you shouldn't do in the a/c".

Balanced field V1 abort stays on the runway.
V1+10 abort should go off at approx. 60 kts.

Guys don't necessarily believe that a 10 kt difference makes a 60 kts difference at the end of the pavement.

The training event isn't to practive V1 aborts after V1. It's to show the results of that incorrect decision.

I don't think that's negative training.

[411A]

Power against brakes will always give better perf than rolling. With rolling you are using TODA before you have take off thrust.

Not necessarily so...can be type specific.

B707-320B (advanced cowl) aircraft are a specific example, due to auxiliary inlet door design.
Maximum Achievable Takeoff Weights were (1) Roll-On Takeoff, (2) Standing Start, and (3) Rolling Takeoff in that descending order. The AFM went on to explain that a properly executed Roll-On Takeoff was one where the aircraft had a minimum speed of 10 knots at the normal SOT.

Spot on, and applies to the above referenced type.

[Chris Scott]

Following 411A's remarks, here's a slightly bigger chunk of his quote from Old Smokey (post #23):
...the "Roll-On" Takeoff (not Rolling). That is, a Takeoff where the aircraft enters the runway at the nominal Takeoff commencement point already rolling with residual speed from the taxy.
For a 90 degree or 180 degree turn to line-up, this is obviously not practical or safe...
...I recall working on one Douglas jet aircraft where the AFM stated that the Maximum Achievable Takeoff Weights were (1) Roll-On Takeoff, (2) Standing Start, and (3) Rolling Takeoff in that descending order. The AFM went on to explain that a properly executed Roll-On Takeoff was one where the aircraft had a minimum speed of 10 knots at the normal SOT.
[Unquote]

This "roll-on" technique is precisely what I try to describe in post #33 – the Boeing-recommended technique I was taught (like 411A?) for the JT3D-powered B707-320B/C.

Whether Old Smokey is right to say that the 90-degree-turn case is not practical or safe, I'm not sure. Achieving a minimum 10kt demands a slightly less-sharp alignment, so the turn is not completed until a little bit further along the runway centreline. The main issues are probably: (1) integrity of nosewheel steering; (2) strain on L/G (B707 legs are short); (3) possible asymmetry of spool-up leading to loss of control.

As for the 180-degreee-turn case: it depends on the situation, the comfortable radius of turn the aircraft can achieve, and pavement width. If the runway has a very short spur just downwind of the most-downwind entry point, the take-off run can sometimes be maximised by entering the runway and turning the long way round (270 degrees or more). This works very well at a steady speed. On completion, a large aeroplane will have overshot the centreline, of course, but can be gently nursed back as it accelerates.

If, however, the thrust levers have been "stood up" before the aircraft is pointing in a safe direction, it becomes a fairly demanding and vulnerable manoeuvre.

[Old Smokey]

Just playing it safe and conservative Chris Scott, I'd hate the thought (particularly in a large geometry aircraft) of someone doing a 90 or 180 degree line-up whilst attempting to maintain 10 knots throughout the manoeuvre.

I have no problem with your suggested "slightly less sharp alignment", I do it too, but I've seen a good many trainees shooting for a nice 30 degree flare onto the centre-line, thus using 100 to 200 metres of runway in the process. Not so bad for a JAR certified aircraft which considers line-up allowance, but for a large geometry FAR25 aircraft (which makes no consideration of line-up allowance), you're behind the 8 ball, even if you do it correctly.

Regards,

Old Smokey

[stilton]

I must be missing something, on the Aircraft I fly 75 / 67 unless you are doing 8-10 knots in a 90 degree turn at heavy weight you will slowly come to a stop.

Around 8 knots will take you smoothly round a 90 degree turn onto the runway with no great stress (providing you are smooth) so there you are, not having wasted any runway with 10 knots already 'in hand' you can advance the power a little before alignment enough to be equally spooled then straight to take off power once lined up.

Best of both worlds, useful momentum in hand with take off power set and no runway wasted :E