Flap retraction

[tommoutrie]

come on.. somebody clever must be able to prove that the way virtually every business jet departs is the way the people who build them intended. Somebody must be able to show that I'm talking rubbish. I mean, come on, we all must be doing it the right way...surely..

a thousand pounds

its my real name

I can't run away

make me look foolish and get some cash

[mutt]

You must remember that you are operating a relatively powerful corporate aircraft, when the regulations were written this wasn't the case, you are also assuming that the aircraft has a better climb gradient with a lower Flap setting, once again this isn't always the case.

Under FAR25, the aircraft has to be certified to meet all the required gradients with an engine out, this information is only applicable to us when we need to clear takeoff obstacles. How do you protect yourself for clearing the obstacles if an engine fails right after you have retracted the flaps?

Mutt

[Empty Cruise]

Most places, 95% perhaps, what OEI AA you chose has no consequence whatsoever. The remaining 5% it has a very clear and immediate impact, and buggering around with it can terminate you if you lose one donkey.

For that reason, I am sure we all agree that the OEI AA needs to be respected, full stop.

Now, let's say you have all donkeys burning - so you can retract your flaps at a lower altitude, right?

Consider losing your engine before you reach en-route climb speed, ie between V2+10-20 and Venr. You now have to continue acceleration or stay at whatever speed you're at, in neither case knowing where you are in respect to obstacle clearance. Or could re-deploy flaps and drop back to V2+10, but that somehow defies the purpose of the exercise...

You know that you're quite a bit above the OEI flightpath when you start retracting at eg 400 ft, but how much? Enough?? If you have a 1500 ft ADER acceleration height, you might make it up there and still be above the OEI path from 35ft at this stage - but what if it's 2000 ft? 3000?

Problem is that if you roll the flaps before you reach your obstacle clearance altitude and you lose a donkey immediately after, you have no scooby doo about where you are or will end up in relation to your OEI path.

OEMs only build the things and specify the minimum certified height they want you to retract the flaps. Consider CMF, ASE, INN, SFJ etc etc etc. - your AA is waaay above cert minimum in all these cases, so by respecting your performance needs, are you flying the aircraft contrary to how the OEM tells you how to fly it?? A careful look at the AFM will reveal correction tables for 2nd segment extended above 400/1500 ft respectively.

In other words - the OEM only builds and certifies your aircraft - you, your company and your authority must then come up with how you operate it. Suffices to say that if you roll flaps at 400 ft at either of the above mentioned places or their relatives, you clearly have had an imagination failure You don't need to put yourself in that (flapless) position, so why do it?

Deck angle limits need to be respected, but the old idea about the owner firing your sorry ass because you exceed 8-10 degrees? Had a very nervous owners wife out of INN on a CL30 telling me not fly out of there too steeply flew the usual profile reaching 18 deg ANU, she afterwards said it was the best takeoff ever... They don't often notice a deck angle - but they DO notice a shoddy (ie too fast) rotation rate...

Anyone here ever actually had a pax complain about deck angle?? Would be interested to run a poll...

[mutt]

And Empty Cruise wins the 1000 quid

Mutt

[tommoutrie]

Nope, still my money I'm afraid chaps.. For the sake of not typing too much lets stick with an aeroplane where the flaps can retract at V2+10.
2nd segment climb gradient is ALWAYS better at V2+10 clean than it is a V2 flapped which are the two conditions you have the climb gradients for. Therefore, when you are all engines operating and accelerating through V2+10 you MUST retract the flaps to ensure that in the event of the engine failing you remain above the required gradient. If you do what most operators do and remain with the take off flap set but accelerate above V2+10 and then the engine fails you have a draggy aircraft trying to climb with one engine out. If you had already got rid of the flap the aircraft would already be climbing as efficiently as possible.

Its a two way bet... im a grand up now..

[tommoutrie]

pick an aircraft, any aircraft, lets get the charts and I'll prove it to you

we've all been doing this wrong for so long that nobody wants to believe it!

tomorrow I'm going to prove the world is, in fact, flat

[tommoutrie]

and no, never had anyone mention deck angle. I took a photo out of the window of a 320 out of Heathrow recently sitting in the back on the way to paris and I've tried to measure it against the horizon and the deck angle is pretty close to 30 degrees. Another GA myth!

[Empty Cruise]

Tom,

Just a quick q - on your chosen aircraft where you may retract the flaps at V2+10 - what is your en-route (ie clean) climb speed? What is your manouvering speed clean?

I am not saying that no aircraft exist where you don't climb clean at V2+10, but for most of the serious kit out there, V2+10 (or whatever is specified) is a transient speed, not a speed you continue flying.

On my current aircraft the gap between flap retraction (V2+12) to Vfto is in the order of 20 kts, and on the 737 it was around 25 kts.

If you can explain how you get from V2+10 to Venr without busting your gradient OEI (or indeed, explain how climbing below your Venr clean improves the gradient OEI), I shall be most impressed - or a grand richer

[tommoutrie]

no problem. For the case where the aircraft is one that cleans up at V2+10 lets go for the CJ. The process in the CJ is if you take off with flap 15 and happen to have an engine failure you continue at V2 up to whatever platform height you are able (engines are limited to 10 mins for the later ones and 5 mins for the early ones at max thrust). If you make 1500 feet you fly level, accelerate to V2+10, clean up and climb away at that speed to your 10 minute engine limit where you reduce thrust to max continous, accelerate to Venr, and then continue the climb as necessary. In reality, most people just accelerate at the 1500 foot platform to Venr and climb away clean from there. If you look at the charts for a flap 15 take off and a flapless take off the 2nd segment climb gear up OEI is always better for the clean condition and it just so happens that the speed for the flapless condition is almost exactly the V2 +10 of the flapped take off. Which is why you are supposed to retract the flap passing V2+10 when you have all engines operating.

I'm currently on the Challenger and its exactly the same for that except that I don't have clean take off tables for it because you can't do it. However, if you plot the L/D of any commercial wing you will find the reason the flap up speed is what it is is that is where the L/D curves are closest. Venr is the enroute climb speed single engine and you use that once you've run out of max thrust time and have to go to max continuous.

Which aircraft are you on? I'll get the manuals and have a look at the actual pages for your type to make sure I'm not talking balls and if I am I will post over the cash

[tommoutrie]

does my challenger count as serious? cos its the same on that..

[Empty Cruise]

yep, Tom - the 300 is a decent piece of kit - same there, though, V2+10 (or whatever it was, haven't flown it for 3 years now) is below Venr - which raises the question why Bom in their wisdom have not chosen Venr=V2+10?

[tommoutrie]

The speed for flaps up (V2+20 on my 601) will still give you best angle. A better angle than V2 with flaps 20. The enroute climb speed, commonly called Venr, gives you best rate. Which is what you want once above your platform except in very unusual circumstances. Its also slightly easier to fly because you are going faster and the fin works better so you need less rudder and consequently there's less drag.

[tommoutrie]

Point is, most folk ignore all this and the initial climb out is at increasing speed - which is fine if you take the flap up but its definitely not if you leave the take off flap set. Its grossly incorrect to be doing 190 with flap 20 still selected in the challenger yet thats what my last companies SOP's called for. My old company are happy climbing the challenger with flaps 20 at V2+70 on the way up to 1500 feet. And its utter, utter rubbish! The flaps should go up at (maybe shortly after) V2+20 on a challenger on any take off. The theory is true for any pretty much any aircraft.

[tommoutrie]

Just been looking at the 737 and 777. All engines you climb at V2+15 to 25 and take the flaps on schedule which appears to be roughly V2+30. So again, you don't go through the flaps up speed without taking the flap up!

its all the same..

we've all been doing it wrong and contrary to popular belief it actually does matter!

[A Pandy]

For the sake of adding to the discussion, as I mentioned in a previous post when operating our Lear 45s we call for flaps at V2+25 as per the manual. However I have just finished a type course on the Gulfstream G650 and Flight Safety International teaches for flaps to be raised at 400agl. The Operating Manual as well as the Gulfstream checklist call for flaps to be raised at positive rate just after the gear. No mention of speed or altitude. Same call for flaps 10 and flaps 20 take-off.

[gaunty]

Gents enjoying the chat and great to see a good work out on why?.

The below may contribute to the debate as to where the 400-1500ft numbers derive.
I always go back to 1st principles when I can, and D.P Davies "Handling the Big Jets" is a great primer. The title is a bit confusing insofar as that it contains a very detailed discussion of the design tricks and trade offs the manufacturers make to get to their target specification.

FAR Part 25 has some very instructive reading for aircraft >5700kgs.

FAR. Part 25 as amended, was previously 25.77
§ 25.111 Takeoff path.

(a) The takeoff path extends from a standing start to a point in the takeoff at which the airplane is 1,500 feet above the takeoff surface, or at which the transition from the takeoff to the en route configuration is completed and VFTO is reached, whichever point is higher. In addition—
(1) The takeoff path must be based on the procedures prescribed in § 25.101(f);
(2) The airplane must be accelerated on the ground to V EF, at which point the critical engine must be made inoperative and remain inoperative for the rest of the takeoff; and
(3) After reaching V EF, the airplane must be accelerated to V 2 .
(b) During the acceleration to speed V 2 , the nose gear may be raised off the ground at a speed not less than V R. However, landing gear retraction may not be begun until the airplane is airborne.
(c) During the takeoff path determination in accordance with paragraphs (a) and (b) of this section—
(1) The slope of the airborne part of the takeoff path must be positive at each point;
(2) The airplane must reach V 2 before it is 35 feet above the takeoff surface and must continue at a speed as close as practical to, but not less than V 2 , until it is 400 feet above the takeoff surface;
(3) At each point along the takeoff path, starting at the point at which the airplane reaches 400 feet above the takeoff surface, the available gradient of climb may not be less than—
(i) 1.2 percent for two-engine airplanes;
(ii) 1.5 percent for three-engine airplanes; and
(iii) 1.7 percent for four-engine airplanes.
(4) The airplane configuration may not be changed, except for gear retraction and automatic propeller feathering, and no change in power or thrust that requires action by the pilot may be made until the airplane is 400 feet above the takeoff surface; and
(5) If § 25.105(a)(2) requires the takeoff path to be determined for flight in icing conditions, the airborne part of the takeoff must be based on the airplane drag:
(i) With the takeoff ice accretion defined in appendix C, from a height of 35 feet above the takeoff surface up to the point where the airplane is 400 feet above the takeoff surface; and
(ii) With the final takeoff ice accretion defined in appendix C, from the point where the airplane is 400 feet above the takeoff surface to the end of the takeoff path.
(d) The takeoff path must be determined by a continuous demonstrated takeoff or by synthesis from segments. If the takeoff path is determined by the segmental method—
(1) The segments must be clearly defined and must be related to the distinct changes in the configuration, power or thrust, and speed;
(2) The weight of the airplane, the configuration, and the power or thrust must be constant throughout each segment and must correspond to the most critical condition prevailing in the segment;
(3) The flight path must be based on the airplane's performance without ground effect; and
(4) The takeoff path data must be checked by continuous demonstrated takeoffs up to the point at which the airplane is out of ground effect and its speed is stabilized, to ensure that the path is conservative relative to the continous path.
The airplane is considered to be out of the ground effect when it reaches a height equal to its wing span.
(e) For airplanes equipped with standby power rocket engines, the takeoff path may be determined in accordance with section II of appendix E.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as amended by Amdt. 25-6, 30 FR 8468, July 2, 1965; Amdt. 25-42, 43 FR 2321, Jan. 16, 1978; Amdt. 25-54, 45 FR 60172, Sept. 11, 1980; Amdt. 25-72, 55 FR 29774, July 20, 1990; Amdt. 25-94, 63 FR 8848, Feb. 23, 1998; Amdt. 25-108, 67 FR 70826, Nov. 26, 2002; Amdt. 25-115, 69 FR 40527, July 2, 2004; Amdt. 25-121, 72 FR 44666; Aug. 8, 2007]

Part 25.101 thru to the end describe all the certification design requirements.

BTW I think I saw some mention of the CJ, these aircraft whilst jet are <5,700kg and therefore actually Part 23. There are a number of excellent design and cost reasons why these manufactrurers use the less strict Part 23 rules although provide Part 25 type take off perfromance.

enjoy.

BTW for very sound legal reasons, FSI teach exactly, the manufacturers FAA certified AFM, IMHO any operator that goes away from that document better have a very very good reason if it goes pear shaped, the lawyers will make mincemeat out of you. Too many COMs and procedures are based on folklore or the CPs personal prejudice. The AFM is the law, period.

Qantas thought they knew better than Boeing and came within an millimeter of a hulls loss with many lives. Fortunately very the close shave brought them to ther senses.

[Empty Cruise]

Tom,

Must have misunderstood your first post - thought you advocated flying fixed pitch and retracting when you reach V2+10 or wassever...

Now see you say - either that way or fly a fixed speed (V2+10-30) to AA, then accelerate and take flaps on schedule.

The latter makes a lot of sense in my book, the former not ;-)

As for Venr being a rate rather than a gradient speed - where does it say so??

[tommoutrie]

I dont know where it says it but I have L/D curves for it and although its slightly slow (but not very) its close to it.

Hello Gaunty - All the net take off flight path stuff refers to one engine inoperative operation and the thrust of my posting this in the first place is that I don't think training organisations like Flight Safety do, in fact, teach what is in the manufacturers books. I think they get so fixated on engine failures that they teach a normal take off incorrectly. I think operators don't really know or care what they put in their SOPS and because the CAA don't approve that bit (they only accept it) they don't care either.

However, I think it is actually important. Flown the way that everyone currently does it we make more noise and degrade the flight path and use more fuel. Not much more, granted, but some. And in a plane like a Challenger if you save a little bit near the ground and carry it to height it takes you a little bit further..

Also, nobody has actually said what their plan is should an engine fail when they are at 1000 feet, take off flap still set, V2 +50 ish. At V2+50, are you still on the required SID gradient? Who knows - your rate of climb is pretty good but your forward speed is much higher so you don't actually know. Then, if you don't have a plan as to what you are going to do, how can you be sure (or prove to the authorities in a theoretical way) that you will stay above the PDG?

My belief is that FSI and the ilk have simply missed whats going on here and confused the OEI situation and the all engines operating situation.

Am I convincing anyone or is this just rubbish?

[tommoutrie]

does anyone know anyone from FSI who could have a look at this?

[JonDyer]

Originally Posted by Empty Cruise

Must have misunderstood your first post - thought you advocated flying fixed pitch and retracting when you reach V2+10 or wassever...

So did I and I've read back through it all twice now.

Originally Posted by TomMoutrie

Also, nobody has actually said what their plan is should an engine fail when they are at 1000 feet, take off flap still set, V2 +50 ish. At V2+50, are you still on the required SID gradient?

Which required SID gradient? Are you talking noise abatement, obstacles in flight path / airspace, Step climbs or OEI gradient? Which?

Originally Posted by TomMoutrie

Am I convincing anyone or is this just rubbish?

Normally my default position with your ideas is no... but I must admit I am intrigued and I'm wondering if you are right.

What you are wrong about is Kak Klaxon's suggestion that you post a link to this thread in Tech Log. If you do that you may well get a definitive answer and you may win or lose your money.