I can't believe what I am reading!
 

I can’t believe what I am reading !

There is a thread running on Tech Log that involves a discussion about the merits of speed versus height. I can’t believe what I am reading.
It appears some pilots seem to think that if the situation is critical then clawing for height is the way to go. This is not so. Speed is the thing that keeps the aeroplane flying not height. Shave the roofs of buildings and go through the tops of trees but keep her flying until you feel safe.
Before I became an airline pilot I was a crop duster. Ask any crop duster how he keeps his heavily laden aircraft in the air. He will tell you SPEED. Height does not come into it.

KIFIS

Kifis,

I suspect you have misread the arguments put forward.

In the height over speed debate, the point at which height is preferable to speed is once Vx, Vy, Vxse or Vyse (as appropriate) has been attained - and not before.

If I'm correct in my interpretation of your post then, yes I agree with you, as long as the speed is lower than Vx, Vy, Vxse or Vyse. But once that IAS is reached any further increase in speed reduces the efficiency of the conversion of fuel into performance.

As in,

Q). You wanna know the three most important things in flying an aircraft ?

A). Airspeed, AiRsPeEd, and AIRSPEED !

(outside, of course, of the three most useless things, i.e. fuel in the bowser, runway behind you, and airspace above you)

Also..........

Q). Define V2 ?

A). (I.e the technical version as given by the novice pilot - nb. I've used FAA terminology as it was more readily available - still applies imho)..........

(a) The critical engine inoperative and its propeller in the position it
rapidly and automatically assumes;
(b) The remaining engine(s) at takeoff power;
(c) The landing gear extended, except that if the landing gear can be
retracted in not more than seven seconds, the test may be conducted with the
gear retracted;
(d) The wing flaps in the takeoff position(s):
(e) The wings level; and
(f) A climb speed equal to that achieved at 50 feet in the demonstration of
Sec. 23.53.

..........below which you lose directional control of the aircraft.......blah blah blah........

A). (The 'real' pilots version is....) "The speed below which you will crash !"

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So, whilst bullsh_t might baffle brains, airmanship wins every time !

Not so simple. Go back to the Eastern crash many years ago. The engine tore lose and damaged the wing. They took the figures, converted speed to height, and everyone died.

A, very conservative, opinion is do not allow speed to reduce below what you have, if it keeps the aircraft flying (unless terrain says otherwise). Keep speed, then height. Fly the aircraft. When you have the room to make mistakes experiment.

I think I must beg to differ. If I'm in a light twin ie no performance guarantees on one engine, then I will reduce IAS to Vxse or Vyse. Unless of course OTHER information dictates otherwise eg stall symptoms at faster speeds, obvious degradation of performance (measured in terms of climb ability or handling complications).

After achieving this speed & dealing with the problem to hand and with time to assess current conditions THEN I'll reconsider whether this speed is necessary. But until addtional information is available I'll consider that climb performance is critical and use Vxse or Vyse.

Of course there are always exceptions to any generality eg in level flight above MEA etc in which case it come down to situational awareness about what item is currently the most critical, next most critical etc.

However the original thread specifically referred to an after T/off situation. Once you have achieved Vx, Vy, Vxse or Vyse as appropriate, then any additional speed results in a net LOSS in total energy available to you to use after an engine fails at any given point after take off.

Thank you all for your thoughtful and interesting replies to the speed height question. I’m pleased we all agree that speed it is. I must expand my original statements and say that if the aeroplane is fully under control and you feel safe ( by that I mean you actually now know your own name ) then by all means start climbing. I categorize what we are talking about by mentally putting it into two stages. First a determination to get the speed and second some thought about when to climb. It’s just possible one can’t remember those “ V “ numbers and if so a little extra speed only means a little change in the applied rudder pressure. Sounds easy but of course it is not.

I fly for pleasure only these days and I prefer singles. Less to think about.

KIFIS

I think you've misunderstood either the original thread or the replies on this one.

The original thread was about: "do you prefer to maintain a higher than BROC-speed OR to use that energi that will be used for this acceleration to gain height" (In the T/O).

I guess we'll all agree that *speed-controll* is essential if suffering an enginefailure in a light piston twin. If you maintain S/E BROC-speed and your functioning engine runs at MCP you'll get the most climb (or the least decend :)) possible.

Therefore the answer is (for my part): No - I dont want the extra speed, I want the extra height. I want to accelerate to blueline speed and the climb untill safe altitude has been reached without further acceleration.

[This message has been edited by Tor (edited 14 August 2000).]

KFIS,

Tomorrow you wake up with psychic abilities. You know that you will have an engine failure in your pawnee[?} precisely 30 seconds after take off. For some inexplicable reason you take off.

do you:

(1) keep it at 50 feet at a high speed until the 30 second mark, or:
(2) keep it in a best rate of climb until the 30 second mark, thence adopt the best glide speed.

The arguement can equally be applied to a twin - substitute the best glide with the Vyse.

that is a simple way to look at it, and was really what the discussion was originally about.

regards

cs

PS - Tor - do you climb at blue line speed if you have 2 engines? Surely you climb at Multi engine Best rate...that gives max height in min time...unless your a/c they are one and the same?



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Those who restrain desire do so because theirs is weak enough to be restrained.
William Blake

I reckon that in that circumstance youd definately take the height over the speed.
In that 30secs in a Pawnee youd get say 500ft (wild guess?) which would give you enough height to pick the best place to put back down. In addition you would be in a glide descent which would allow you to judge when you will hit the ground much better than if you were trying to judge when you would run out of speed.

I rest my case.

KIFIS

compressor stall

Yes that would of course be multi BROC-speed assuming normal operation. You guessed right, I'm currently flying PA34 and yes BROC and S/E BROC are both 105mph.

Anyway I completely agree with you - I'd go for no. 2 option (who wouldn't). I think KIFIS (perhaps) missed the point and thought that some were saying that height was more important than any airspeed at all.

Tor

[This message has been edited by Tor (edited 14 August 2000).]

Fly low and slow ...

JJ

... and be sure to slow down for sharp turns. :)

I can't believe what I'm reading either.

Please tell me that these postings are NOT by real airline pilots.

Every schoolboy knows that a conventional aeroplane achieves height by virtue of its forward horizontal motion creating lift.

Also every schoolboy knows that acceleration is not speed, it is the rate of increase in velocity.

GOSH:

I thought speed was the thing that keeps you alive.

KIFIS

Simple really
A320 FCOM - Windshear drill is to pull back on the funstick as far as it will go. Speed can decay to below vls but no probs. Book says nothing about maintaining speed.

Actually then every schoolboy is wrong. Lift only counters the weight of the A/C. What makes it go up or down is either excess thrust or a deficit of thrust respectivly. Thats basic aerodynamics - I guess thats too much to ask a schoolboy to know anyway :).



Yes but if the A/C is standing still on the RWY, don't you have to accelerate to achieve a certain speed?

That is exactly what this is about - do you want to keep accelerating or start climbing. You only have a certain amoungth of energy so how do you want to use it?

Tor



[This message has been edited by Tor (edited 16 August 2000).]

Actually, Mr. Osborne, acceleration is rate of change of velocity. A small difference, perhaps, but a significant one.

Speed is a one-parameter variable. Velocity has two parameters - speed and direction, since it is a vector. In this way, an object circling a point (e.g. conker on a string) is maintaining a constant speed but, since its direction of travel is constantly changing, it is accelerating towards the fulcrum at all times.

Next, when an aircraft departs the runway, its horizontal acceleration is decreasing, but its speed is still increasing. Part of the upwards motion is trading horizontal kinetic energy for upward, part is lift action from aerodynamic surfaces.

But enough of this rubbish. The point most people have made is that after problems on lift-off, you get the aircraft to the speed at which it is aerodynamically most efficient. This could be considered to be two different speeds, however. If you have objects to clear, you would aim for best angle of climb, until clear of the objects. Once that is achieved, trim forward for best rate of climb. In a simple piston twin, this is blue line speed. Any speed in excess of these figures is simply wasted, and possibly disastrously so. First and foremost in your mind should be to get the aircraft away from the ground.

Put simply:- Nobody ever collided with the sky.

[This message has been edited by HugMonster (edited 16 August 2000).]

I might add:

Given an angle of attack indicator & appropriately calibrated data, who cares about speed/velocity?

After all, it's the angle of attack of the wing that is of paramount importance and all these speeds are just ways of trying to describe an appropriate AoA under a given set of conditions - typically 1 g.

It's easy to demonstrate unstalled flight at less than the 1g stall speed, which is the one quoted in the manual. Some of course also quote a speed for a given Angle of BANK, but even that is still based on an Angle of Attack.

[This message has been edited by Tinstaafl (edited 16 August 2000).]

David,

RTFQ :)

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Those who restrain desire do so because theirs is weak enough to be restrained.
William Blake

I think that what you want, altitude or airspeed may depend on what aircraft you are flying. I have no experience on light twins, but more time than I care to think about on *big iron*.

Seeing as how a forced landing in a field is not an option on heavies, once I've cleared the obstacles, give me SPEED every time. If I've lost one engine, I may soon lose another. In that case my minimum control speed is 210 kts. If I'm at Vx to get away from the ground, I'm well below that. Also, there may be some damage that the *book* doesn't cover. As previously mentioned, if the American DC-10 (not Eastern) had kept the speed, they would probably still be here.

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[This message has been edited by quid (edited 18 August 2000).]

Quid - In a light twin you don't want to be at Vx either (since you woudn't care about the angle). You would be at Vy as you would like to get away as fast as possible. When you have reached safe altitude you would accelerate to what ever might be convinient eg. cruise climb.

Having flown a DC-10 simulator, I was taught that you would like to be at V2 - V2+15 if you lose an engine (around 175 kts if I remember correctly a MTOM) untill clear of obstacles and then accelerate to BROC-speed or 250.

If you lose an engine on the ground roll after V1 wouldn't you climb at V2. If you accelerate to 210 kts you can't be sure you clear the obstacles - no?

Tor ;)

[This message has been edited by Tor (edited 18 August 2000).]

Tor-

If I lose one at V1, I'd certainly climb at V2 to 1000' AGL, then transition (flaps zero) and climb to 1500' AGL. Our obstacle clearance data assumes I will do that. If VMC (or at a familiar location) where obstacles are not a factor, I'd tend to be on the fast side of V2, just in case. <g>

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Quid - so you do admit you prefer height over speed (or atleast your SOP does) :)

Tor

[This message has been edited by Tor (edited 18 August 2000).]

Tor-

Altitude over speed? No, I didn't say that.

First, there can only be one SOP (and I help write them at my carrier, so I've got to follow them). <g> The SOP has to cover the worst case scenario to clear obstacles in the t/o flight path. We choose to fly at V2 to 1000' prior to transition to clear obstacles. We could have chosen to transition at 400', the FAA minimum.

Now, if I didn't have to follow an SOP, when I lost one, ONCE I'M CLEAR OF OBSTACLES, I'd accelerate and get it clean ASAP.

BTW, V2 is significantly slower than Vx in the t/o configuration.




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quid -

The thread that the original post refers to was about what to do imediately after T/O (ei. before obstacles has been cleared).

I agree once you have cleared obstacles there is no point in flying slow. I'am only flying light twins so slow is of course relative :). My only experience with Big Irons is from a JAA MCC course (European for CRM. It included 21hrs on a DC-10-30 sim - great fun :))


Tor

Differences in operating & performance techniques are significant I think.

Jet types aren't necessarily anywhere near Vx or Vy when they're at V2. They can be some way behind the drag curve. In this case a speed increase can improve performance.

Light A/c though are usually at or near max performance speeds very shortly after take-off.

Sorry if I'm late.

KIFIS, are you refering about this threat !?
http://www.pprune.org/ubb/NonCGI/For...ML/001111.html

Anyway, funny to see that the guy who gave me the check on type was also a former crop duster...No need for height here, only speed.

Now, speaking about light twin just after T/O . No single crop dusting, no heavy jet with big amount of thrust, no... whatever.
JUST LIGHT TWIN NEAR MAX GROOS WEIGHT AFTER T/O.

If, in case of an engine failure you lose more rapidly speed than height . Well, it's obvious, I will keep my blue line and look for this height.

All I want is seeing the "danger zone" as short as possible.

This is in reply to ORAC's message of 13 Aug.

I believe he was referring to the American Airlines DC-10 accident at ORD in 1979 or so.

The pitch bar on the HSI normally commands
V2+10kts. With the loss of an engine, The pitch bar commands V2. The Captain followed
the commands as he was trained to do, and the left wing stalled, since the slats had retracted with the loss of hydraulics resulting in the crash. Subsequent simulator studies proved that if V2+10 had
been maintained, the aircraft would have been flyable!

Unbelievably, the procedure remained that the Flight Directer MUST be on for T/O, with
the expectation, that if a similar event were to occur, one was expected to ignore the pitch bar command and fly "through" the
bar! Talk about being a "slave" to the automatics!

EBD

OH DEAR!
Cx. the quote below chaps.

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[quote]Watch well lest the ground riseth up and smiteth thee.[quote]

Follow the flight-director at your peril - maybe on the ILS it's great but on take-off it (sometimes) can command daft pitch angles - as it does too with a windshear case - thus try and fly those pitches angles and watch your airspeed pointer !

(all imho, of course)

flight directors on takeoff have to be "looked through" in many situations..while V2+15 is the optimum climb speed for most swept-wing aircraft while still in the take-off config...if i lost an engine at V1 i would climb at V2...if i had already accelerated to V2+15..then maintain that speed unless collision with an obstacle is iminent...the dc-10 crew proved a an old adage "ifit ain't broke don't fix it" to be true the airplane was climbing, and had no obstacle..but ingrained procedures instead of old-fashioned airmanship prevailed, and the and aircraft control was lost...the crew had no way of knowing the configuration of their wing..in the few short seconds they had to make the decision that we have had years to second guess...i personally would climb at a slightly higher speed than V2 if a violent engine "event" had occurred, and the aircraft was climbing at an acceptable rate...

That's the point!

eng fail btwn v1 and v2 -> maintain v2
eng fail btwn v2 and v2+15 -> maintain gained speed
eng fail btwn v2+15 and higher speed -> convert excess speed to hight and maintain v2+15,
because this speed equals about vx (for JET a/c).
That's what improved climb is all about.
Big difference between PROP & JET?
PROP vx is much closer to vs than in JET aircraft.

So acceleration may make sense, i.e. if the lim fac is a far out obstcl. and your in a JET. On the other hand, acceleration (during night in IMC) in a close in obstcl. situation will screw your day.

RGDS
ADUBI

KIFIS--- Height or Speed... wouldnt it really depend on what stage of the flight you are.. in a b737 if i lost both engines at cruise id maintain height till i got down to my best L/D speed ( pretty much the same if i lost one engine only ) before i started to descend.... basically converting EXCESS speed into height.

At toff ud follow your toff segments to meet obstacle clearance climb gradients( a min req of 2.4% on b737 in the second segment.... where ud probably be maintaining toff flaps, toff thrust, gear up, and speed of v2 to v2 + 20). the third segment ud be cleaning up ... and the height would basically depend on the obsatcles in your toff path and being able to clean up and set MCT on your operating engine within the toff thrust time limit of your engine.

so u pretty much got it... u need the speed but only so much ( best L/D ).... after which anymore is only a DRAG.