PPRuNe Forums

PPRuNe Forums (https://www.pprune.org/)
-   Tech Log (https://www.pprune.org/tech-log-15/)
-   -   I can't believe what I am reading! (https://www.pprune.org/tech-log/10014-i-cant-believe-what-i-am-reading.html)

KIFIS 13th Aug 2000 10:22

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



Tinstaafl 13th Aug 2000 14:59

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.

Puritan 14th Aug 2000 00:32

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 !"

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

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

ORAC 14th Aug 2000 01:40

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.

Tinstaafl 14th Aug 2000 02:46

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.

KIFIS 14th Aug 2000 11:22

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

Tor 14th Aug 2000 13:06


Posted by KIFIS
Iím pleased we all agree that speed it is.


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).]

compressor stall 14th Aug 2000 13:20

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?



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

HPSOV 14th Aug 2000 13:48

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.

KIFIS 14th Aug 2000 14:31



I rest my case.

KIFIS


Tor 14th Aug 2000 16:29

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).]

JJflyer 14th Aug 2000 22:23

Fly low and slow ...

JJ

Luftwaffle 15th Aug 2000 01:48

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

David Osborne 16th Aug 2000 11:41

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.



KIFIS 16th Aug 2000 12:37

GOSH:

I thought speed was the thing that keeps you alive.

KIFIS

FatEric 16th Aug 2000 17:04

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.

Tor 16th Aug 2000 17:23


Posted by: David Osborne
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.



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 :).



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



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).]

HugMonster 16th Aug 2000 18:01

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).]

Tinstaafl 17th Aug 2000 00:51

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).]

compressor stall 17th Aug 2000 18:02

David,

RTFQ :)

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


All times are GMT. The time now is 05:21.


Copyright © 2021 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.