Aviation Mythology and Misconceptions

[silverstrata]

.

I thought I would start a thread on the erronious ideas that some professional pilots have. See how it runs, it might be interesting.

I will start it off with the argument from someone on this forum that you can do an ADF approach without an ADF. In short, he had misread the FCTM for the Boeing 737. But he may be a trainer - who knows. My answer was as follows:


Sorry, but you cannot do an ADF approach without an operating NDB and ADF - period !

If you do not have a ground station and the appropriate cockpit instrument, you are doing an RNAV FMC approach, not an ADF approach. And we have no RNAV approach plates in our Euro-Jepps, and so I'm presuming that RNAV (FMC/GPS) approaches are not yet certified to any of the airfields we visit in Europe.

Your reference in the 737 FCTM is referring to whether "raw data" or "map display" is selected - not whether the ADF is working or not. In other words, you can use map display mode, if you have overlaid VOR or ADF pointers for cross-checking (which many systems can do) or you flip between raw data and map display to check that the map is in the right position.

Note the note at the bottom of this section: - "Compare VOR and ADF systems to detect possible map shifts". You cannot do a map cross-check, if the VOR or ADF is u/s or not fitted !!


The 1996 Croatia USAF CT-43 crash is what happens, when people use a (map-shifted) RNAV FMC approach, instead of the raw NDB/ADF.


Ditto the B-Med Airbus going into Addis Abeba. The FMC plot and terrain display were off by some 3 miles, leading to a go-around just 60 ft over the high terrain. Now while the VOR would give occasional signals of its unreliability (the VOR was the primary fault), the FMC gave no indication that it had a map-shift. This was the biggest complaint in the report, that the FMC knew it was getting bum VOR information, and therefore may have a map-shift, but did not bother to tell the pilots. And the pilots could not check for a map-shift, because they were comparing bum data with bum data.


The map-plot indicated that the crew were highly influenced by the map and terrain display (rather than the VOR raw data), which showed them passing nicely through the valley. However, the terrain display was likewise mapshifted, and they were 3 miles north of the true inbound. If they had been following an erroneous and displaced VOR radial, it would have eventually taken them to the VOR, whereas this flight paralleled the VOR inbound, which is what would happen if you followed an erroneous FMC position on the map display. Which is why we do no do FMC approaches, especially when we do not have GPS input.

And I am not even sure that GPS-RNAV is entirely a solution at present (as was recommended in the B-Med report). It works well with high accuracy and reliability, but Europe is still concerned that the US may degrade GPS signals or switch the system off during periods of international tension. This is the primary reason for Europe developing and launching the Galileo GPS system. When that is up and running, and there is full confidence that erroneous signals can be detected and warnings given, then Europe may proceed to RNAV approaches.

[Clandestino]

Just a couple of myths I can recall in 15 secs:

Modern pax transport aeroplanes are capable of reaching coffin corner.

Mach stall exists.

FMS computed position obviates the need for brain computed one.

More experienced pilot is safer and v.v.

"Handling the Big jets" is obsolete.

FBW changes the aerodynamic behaviour of the aeroplane.

FBW is part of the autopilot.

You can not handfly an FBW Airbus in normal law.

With EFIS there won't be partial panel flying anymore.

EFIS display is basically digital.

Speed and altitude tapes are difficult to read.

With FMS taking VOR, DME, GPS, ADC and IRS inputs, there won't be map shifts anymore.

Turboprops are easier to handle and operate than jets.

Since, IAW our Mammonist doctrine, money spent equals dedication, sorting out merely hopeful from truly dedicated is best done by overpricing CPL training, making prospective pilot pay for type rating and topping it off by selling time in RH seat during normal pax ops.

What we read in "Fate is the hunter" is not applicable to modern airline ops.

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

As for Dubrovnik and Addis Abeba, what I recall is a slightly (an I really mean slightly) at odds with what you posted, I'll check my references and get back on it later.

[Wizofoz]

I was involved in a "Spirited' discussion here a few year ago with a Military pilot who fervently believed the "Killer Down-Wind Turn" myth!!

[old,not bold]

And then there's the myth that a B747-400 with one engine inoperative is precisely as safe as one with all 4 running properly.


Edit:

'Ere we go again. If the Mods want to kill it I won't be offended. Doesn't alter the fact that it's a myth, though.

[Shiny side down]

A number of odd ones encountered in very recent years

Myths-
Reduced thrust takeoff is for fuel savings

Temperature of fuel has no effect on volume uploaded

VS is safer than VNAV. (statement: VNAV is dangerous. Do not use it, use VS instead)

QFE Meters is the same as QNH feet

A professional pilot is one who safely busts MDA and finds the airfield in fog
:D

[AtoBsafely]

Silver,

"Sorry, but you cannot do an ADF approach without an operating NDB and ADF - period ! "

There are jurisdictions where the overlay approach IS automatically authorized with an approved GPS-FMS navigation system.

Not an absolute rule.

[Clandestino]

I meant to post "Pilots don't understand difference between RNAV overlay and underlaying approach" but I'm having second thoughts. I'm not sure it's a myth anymore.

And then there's the myth that a B747-400 with one engine inoperative is precisely as safe as one with all 4 running properly.Never heard of this one. Methinks original myth was "It is under no circumstances safe to cross the pond on three out of four engines"

[misd-agin]

737NG approach speed has been increased due to fuselage length(-800 models).

Turning into the 'dead' engine is dangerous.


Forgot about the previously mentioned 'dangerous downwind turn'. :ugh:

[OutsideCAS]

"Wow, your a pilot - you must earn loads of cash"

Biggest non-pilot mis-conception ever there.

[barit1]

Passengers will never choose to fly transoceanic on less than four engines!

[rudderrudderrat]

Turning into the 'dead' engine is dangerous.
It was on 707s!

The published VMCA figures increased by 20kts with wings level and we only had one hydraulic system running the Rudder boost. If you lost that - the VMCA increased by about 60 kts.
(See accident report for B707 base training accident Prestwick Airport in 1977)

Edit should be "VMCA figures increases by about 40 kts wings level"

[Clandestino]

The published VMCA figures increased by 20kts with wings level I can't wait to see this one explained.

[rudderrudderrat]

Hi Clandestino,

Then wait no more. See Page 20 para 2.4

http://www.aaib.gov.uk/cms_resources.cfm?file=/6-1978%20G-APFK.pdf

[con-pilot]

All pilots are treated with a great deal of respect.

There is one for you, as someone else already posted the one about being paid a great deal of money. :p

Then there are the old jokes.

"I wish had as many affairs on the road as my wife thinks I do."

"I wish I made as much money as my wife spends."

"I wish I had as much time off as my neighbor thinks I do."

Feel free to add more. ;)

[Clandestino]

Thanks Rudderrudderrat! It makes perfect sense :ok:

So turning into dead engine actually is dangerous on the highly-swept-winged aeroplanes with indifferent rudder and 5° bank into live was not just drag reducing measure as I was taught but necessity to get a certain aeroplane certified with low enough Vmca.

EDIT: That would be another myth busted:

Creatively interpreting the certification criteria to effectively bypass them is Toulouse specialty.

[Sir George Cayley]

You can only land on grooved runways in the wet.:hmm:

SGC

[Old Smokey]

#1 Jet aircraft do not exceed Mcrit in normal operations.

#2 Long Range Cruise speed is the speed for minimum fuel burn.

#3 Best Rate of Climb speed provides the best sector fuel burn.

Regards,

Old Smokey

[frontlefthamster]

I'm astonished we've got this far down this thread without the biggest myth of all...

Safety is our first priority

(by the way, you don't need swept wings to make turns towards the inoperative engine hazardous, though I've only found it a significant problem on pretty ancient aircraft)

[fireflybob]

How about airline pilots are millionaires and all they do is sit there and push buttons all day because flying now is "automatic"?

[wilyflier]

Just you try the difference between a downwind turn and an into wind turn when you are near enough to the ground to detect it, i.e. on a hang glider.
Its no myth. Its all about energy states between aircraft and ground.

[DozyWannabe]

How about airline pilots are millionaires and all they do is sit there and push buttons all day because flying now is "automatic"?

I think the highlighted part of that myth is most dangerous when believed by those who are airline VPs because Daddy was a millionaire and bought them a Harvard or LSE MBA.

[hawk37]

One of my favourites:

If an aircraft is not moving (stopped on a taxiway for example), then its not producing any power.

[Trim Stab]

One of my favourites which is particularly prevalent in corporate aviation - the suit at interview glibly announces

"in our company, safety is our absolute priority"

- then they make a derisory daily freelance offer contingent on you first paying for your own type-rating, ditching training, fire-fighting certificate, hazardous cargo certificate, and annual recurrent, and be available 24/365 at one hour notice, and then add that if you don't accept the conditions, there are "plenty of others who will"....

[eckhard]

hawk 37

If an aircraft is not moving (stopped on a taxiway for example), then its not producing any power.

One definition of Power is that it is the 'rate of doing work'.

Work = Force x Distance

If the aircraft's engines do not apply their force (thrust) through a distance, then no work is being done. Ergo, no power is being produced.

(To be honest, I've never heard this 'myth' being expounded anyway, but then I should get out more...........)

[Checkboard]

Just you try the difference between a downwind turn and an into wind turn when you are near enough to the ground to detect it, i.e. on a hang glider.
Its no myth. Its all about energy states between aircraft and ground.

Sorry, wilyflier, in a steady wind there is absolutely no difference in aircraft performance - only a visual "illusion" of slip or skid/speed increase or decrease (and it is the illusion which increases the closer to the ground you get). The aircraft neither knows nor cares what the ground is doing until it is forced to interact with it. ;)
Never heard of this one. Methinks original myth was "It is under no circumstances safe to cross the pond on three out of four engines"
Love it :)

[RAT 5]

Youngsters who love flying (nowadays) think they'll satisfy this desire and become an airline pilot. (Better to get another job and become involved with an aerobatic/tourer.)

[galaxy flyer]

Eckhard

Assuming the generators and hydraulics are operational, there is power on a stopped jet. Small point :O

GF

[barit1]

Youngsters who love flying (nowadays) think they'll satisfy this desire and become an airline pilot. (Better to get another job and become involved with an aerobatic/tourer.)

Or an antique! :D

[Mechta]

Temperature of fuel has no effect on volume uploadedPlease explain what you mean.

Obviously the mass of fuel and hence the total calorific content of the fuel per unit volume will vary with temperature. Are you making assumptions about the fuel measurement, i.e. the bowser's flow measurement device also takes account of fuel density, or the aircraft's fuel quantity indicating system is making an adjustment for fuel density?

Apart from the actual expansion of the aircraft fuel tank with temperature, its volume will stay the same. The volume of fuel that can be put into it will stay the same if we assume no tank expansion, but the mass will depend on fuel density.

[hawk37]

Eckhard,

Heat energy, and kinetic energy (exhaust) come to mind.

Power plants use turbines to produce electrical power, however of course, like the stopped aircraft, the power plants are not moving.

I'm sure the quote/myth is really meant to mean "there is no power (ie energy) gained by the aircraft" (except possibly warmer brakes).

However I've seen it referred to as "the aircraft is producing no power", clearly incorrect.

Hawk

[BOAC]

Conveyor belt, anyone?:ugh:

[silverstrata]

Killer downwind turn.


This one came about because of slow-speed aircraft turning downwind shortly after takeoff, while simultaneously climbing through a stiff wind gradient. Obviously the climbing into a tailwind will decrease your airspeed, resulting in a possible stall (and the turn itself will further degrade your speed).

Likewise, another glider hazard is the 'clutching hand' effect of descending to land and transiting from a stiff headwind into a nil headwind area (over the top of trees, for instance, into the calm region in front of the trees). As soon as you lose your headwind, you lose your airspeed and drop rather rapidly (feels like a hand dragging you downwards).

But obviously if there is no wind gradient, the windspeed and direction is irellevant to your flight control.

.

[oxenos]

"Daddy was a millionaire and bought them a Harvard or LSE MBA. "

If my Daddy had offered me a Harvard or an LSE MBA I would definitely have chosen the Harvard.

[Shiny side down]

In hindsight, my comment was made too simply. I should have included, volume required.

Exactly this-
The volume of fuel that can be put into it will stay the same if we assume no tank expansion, but the mass will depend on fuel density.

We need fuel by mass, despite delivery by volume. I flew with a fella who had difficulty accepting density values. When I tried to explain to him, it went straight over his head. His 'assumption' generally being that there must be more fuel on board, despite what the gauges say, because the book says the tanks hold x lbs.

I hope that makes sense.

[Mechta]

oxenos :ok::ok::ok::ok:

(that's how I read it too!)

Shiny side down, Thanks for the clarification

[Lyman]

Thank God windspeed has nil to do with lift. Wind shear is a lie. Does it matter then, if it is the a/c or the airmass doin' the turn?

I think elapsed time has sumpin' to do with it?

[Pugilistic Animus]

the turbulence penetration speed protects you from everything :uhoh:

[wilyflier]

Sorry checkerboard
I doubt you have spent any time doing such manoeuvres in a low mass aircraft with a high wind speed and airspeed ratio, where it is obvious.
Its NO illusion
The visible effect is that you have to lose height as you turn downwind or your airspeed decays.
Even more noticeable is how suddenly you regain that airspeed and height as you turn back into wind
There is another factor involved which could explain it, but I'll leave that for you to find out from your gliding experience

Strata,
(I think you got your take-off wind gradient inverted)
Sorry, forget I said that, I misunderstood that you were climbing through gradient on take off, but actually you referred to wind gradient climbing down wind. In the cases I quote the aircraft were descending downwind, no engine power
Funnily enough I detected the biggest changes occur During the turn , not once youve settled straight downwind

[Mechta]

Wilyflier, You could be doing your downwind turn through some hilltop rotor, or getting your inboard wing into lower, slower moving air. The wing only 'sees' the air surrounding it. As you can see the ground directly beneath you from a hang glider, it is very difficult to avoid slowing the glider down as the ground rushes below at a rate of knots.

Sliverstrata is correct in saying that climbing into a tailwind can decrease your airspeed. It is the same effect as decending into a headwind,only the wind gradient is has the opposite direction as your height changes.

If you watch, from the ground, a free flight model aeroplane circling, as it drifts downwind, it will appear to slow down as it turns into wind and speed up as it turns down wind. If you were to observe the same model from above, for example, from a hot air balloon, it would appear to fly a perfect circle.

[willl05]

If you were to stand behind a running engine, you could test if really no work is produced.

[eckhard]

Hi galaxy flyer, hawk37, and willl05,

Assuming the generators and hydraulics are operational, there is power on a stopped jet. Small point

See my argument below.

Heat energy, and kinetic energy (exhaust) come to mind.

Power plants use turbines to produce electrical power, however of course, like the stopped aircraft, the power plants are not moving.

I'm sure the quote/myth is really meant to mean "there is no power (ie energy) gained by the aircraft" (except possibly warmer brakes).

However I've seen it referred to as "the aircraft is producing no power", clearly incorrect.
I don't think you can 'gain power' in a physical sense. You can gain energy and convert that energy into work. The rate of doing that work is a measure of the power.

If the myth had stated, 'there is no energy in a stationary aircraft' I would absolutely agree that it was nonsense. There is a massive amount of energy, just waiting to be converted into work and power!

If you were to stand behind a running engine, you could test if really no work is produced.
I would say that work is being done on the air, not on the aircraft, as it is the air that is being accelerated, not the aircraft.

An interesting set of responses. It all comes down to semantics I suppose.

I was concentrating purely on the performance aspects of the whole aircraft, i.e. Power available and Power required. As we know, for all aircraft, power required against speed follows the classic curve that is similar in shape to the total drag curve.

For a jet aircraft, power available against speed is an almost straight line starting at the origin and shooting up and to the right. The faster one goes, the more power is produced (which is one reason that jet aircraft can fly at high TAS).

However, at zero TAS, there is zero power available; that was my point.

Of course there is considerable thrust available, as evinced by the exhaust stream. There is also electrical and hydraulic energy available from the engines, accumulators and battery, but I don't see how this relates to the 'myth'. After all, a passenger in the cabin may switch on a torch/flashlight using the chemical energy in that device's battery, but that hardly matters when one is discussing the performance-related power produced by the aircraft.

The aircraft cannot be producing any performance-related power when stationary, as there is no power available, due to the zero TAS. As soon as you release the brakes, the thrust accelerates the aircraft and the power immediately increases, in direct proportion to the speed (assuming constant thrust).

I fully accept that that this is a narrow interpretation of the word 'power' but I thought that this was what the original 'myth' was addressing. Sorry if I got that wrong. Another issue is the casual interchange of the words 'power', 'energy' and 'thrust' in everyday speech. It doesn't cause any difficulties at all, until someone comes up with the statement in the myth! Then some more accurate definitions are required.

We really need someone with a better understanding of physics than mine to put this one to bed!

:) Eckhard

[BOAC]

However, at zero TAS, there is zero power available; that was my point. - oh this is getting good for all we Oozlum bird keepers.

What about a 10 kt headwind, then, Eck? perhaps you mean 'zero GS' (think conveyor belt?)

[stilton]

'The hotter they get the better Carbon Brakes will work'

[eckhard]

Hi BOAC

What about a 10 kt headwind, then, Eck? perhaps you mean 'zero GS' (think conveyor belt?)

No, I think I mean TAS. An aircraft flying at 100kts TAS into a 100kt headwind requires exactly the same power as an aircraft passing it in the opposite direction at 100kts TAS with a 100kt tailwind.

If an aircraft is parked with the engines shut down and the park brake set, is there any need for any 'power'? What about a 10kt tailwind? Does this require some sort of 'reverse power' to resist?

The fact that that aircraft remains stationary comes down to the friction between the tyres and the runway.

BTW, what's an Oozlum bird?

[BOAC]

BTW, what's an Oozlum bird? - Let me google that for you (http://lmgtfy.com/?q=Oozlum%20bird?)

[eckhard]

Hilarious!

I feel this discussion about power may go in ever widening circles until it disappears into the ether.

[wilyflier]

Mechta Silverstrata
Quite right about climbing/descending through appropriate wind gradient
Indeed add local patches of accelerated wind above and around any hill or ridge particularly in 'stable' conditions and turning analysis gets very difficult
(There are two relationships we try to isolate in discussion, Aircraft to Air , and Aircraft to Earth , which are however linked by Air to Earth)
.
I think Lyman hit on something when he said Time came into it.
During the Turn(not straight upwind or downwind)the aircraft has to be accelerated + or - with respect to the ground in order to maintain flying speed. This takes time ,and has to be paid for with engine power or gravity(potential energy= height]
If you take the extreme case of an instant turn (on the spot) you can arrive at a minus airspeed.....So??? (Dont ask, Ive been there done that )

Consider further the interesting situation you were watching from the balloon,
Perfect circle ? Constant G?? Constant angle of bank???....I dont think so

These effects most noticeable where windspeed is a large compared to aircraft airspeed

I wonder how a Jumbo fares doing a 180 downwind turn in a 200 mph wind .

[Capt Pit Bull]

somebody..... make.... the... sufferring... stop.....

[ihg]

:
Originally Posted by fireflybob http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/buttons/viewpost.gif (http://www.pprune.org/tech-log/467965-aviation-mythology-misconceptions-post6787080.html#post6787080)
How about airline pilots are millionaires and all they do is sit there and push buttons all day because flying now is "automatic"?.I think the highlighted part of that myth is most dangerous when believed by those who are airline VPs....

well, I think the even more dangerous part of this myth is , when "professional pilots" themselves start believing it.....and think of "most basic airmanship" as dispensable stuff of the past...

Regards,
Ihg

[911slf]

Typical flying speed is of the order of 20 kt. Landing into a 20kt wind you can if you get it right, just step out of the air. But flying at 40kt groundspeed downwind at 200 feet is truly scary - one reason I gave up.

If you leave it very late to turn upwind the wingtip closer to the ground sees more airspeed than the other wingtip (windshear - because the tailwind is less very close to the ground), which makes it hard or impossible to turn - because the wingtip closer to the ground is experiencing more lift, which is just what you don't want when trying to turn. You are then committed to a downwind landing. Generally only a problem if you turn below 50 ft agl. Not a problem for airline pilots I trust. :)

[Checkboard]

During the Turn(not straight upwind or downwind)the aircraft has to be accelerated + or - with respect to the ground in order to maintain flying speed.
Yes - but it also has to be accelerated (change of velocity) with respect to the air - exactly the same acceleration, just a different frame of reference.
This takes time ,and has to be paid for with engine power or gravity(potential energy= height]
Yes, higher induced drag in the turn to pay for the inclined lift vector which is accelerating the aircraft.
If you take the extreme case of an instant turn (on the spot) you can arrive at a minus airspeed.....So??? (Dont ask, Ive been there done that )
Exactly the same as an aircraft flying past in dead calm air, and suddenly "magically" swapping head for tail - it ends up zooming past tail first, with negative airspeed.

Consider further the interesting situation you were watching from the balloon,
Perfect circle ? Constant G?? Constant angle of bank???....I dont think so

Yes, perfect circle (given the same steady wind conditions for the balloon and the model) Yes, constant G. Yes, constant angle of bank.

[main_dog]

somebody..... make.... the... sufferring... stop.....


:):):):)

And yet, I too keep on reading on... must be a masochistic streak.

Please tell me more about those dangerous "downwind turns"...

[eckhard]

Hi wily flier

I wonder how a Jumbo fares doing a 180 downwind turn in a 200 mph wind .

Never done a 180 turn but maybe about 45 degrees with a 150kt wind from the front quarter which after the turn becomes a tailwind from the rear quarter.

What happens? Well, as you'd expect, the groundspeed changes fairly quickly during the turn as the headwind component changes to a tailwind component but the airspeed stays absolutely steady at around 300 kts indicated.

In a holding pattern, the highest wind speed I've seen is about 65 kts. Here of course, I've done 180 turns and the same applies. There is no change in the IAS (about 220 kts). In the case where the wind is aligned with the hold axis, the groundspeed varies between about 185 and 305. (TAS about 240 kts).

So to answer your question; 'Very well, thank you!'

Eckhard

[silverstrata]

>>Please tell me more about those dangerous "downwind turns".

As before, it is the wind gradient that is dangerous, rather than the turn. Its like taking off in calm conditions and climbing up into a 50kt tailwind. The instantaneous effect of the wind gradient on your airspeed can be catastrophic.

Likewise turning into wind onto final, in a long-wing glider, in a region with a strong wind gradient. The upper wing can have more airflow than the lower, resulting in a turning force greater than the ailerons can counter. And since landing on the wingtip is not the approved arrival technique, the landing becomes rather exciting. (The solution is more airspeed.)

All useful things that a modern ATPL will never learn or directly experience. But knowing the flight sensations of such manouvres may well prove vital if you are - well - plummeting down at 10,000 ft per min over the Atlantic in a large jet with your nose pitched 15 degrees up, and not understanding the situation.

.

.

[eckhard]

silverstrata

Very well put. I too have seen large airspeed changes when climbing/descending into wind shear in the 747. Wave activity can also produce large thrust and/or airspeed changes.

I guess we never see those effects that you describe close to the ground as our bank angle is necessarily small, no large changes of heading are made below about 1000ft (OK, except at JFK on the Canarsie and other circling approaches) and our approch speed is in the order of 160 kts.

[Wizofoz]

I KNEW mentioning down-wind turn would catch SOMEONE!!

Wily, have you got the message that turning in a constant wind has no different effect on the aircraft than turning in still air?

The aircraft has no idea what the velocity of the ait it is in is in relation to the ground.

Trust us!!

(P.s.- I have done just as you suggested- held in 150kts of wind. No change in airspeed up vs downwind- really!!)

[wilyflier]

wizifoz
No auto throttle or power changes at all, during the 1 minute of turn?
If yes, then its still an open question, neither of us can tell how much due to banked turn and how much due to the effect I am supporting
Well it happens with a hang glider , changes of bank and G as you go round too.
As I implied before, analysis is masked by the impact of various different packets of windspeed as you go round. It is not a problem of 'the ground looks a bit faster', its to do with the need to energise acceleration and momentum against inertia during the turn downwind, and then turning the excess speed back into height during the turn into wind.
Not discernible with big powerful aircraft. very discernible with lack of power and light aircraft
Different question once running straight downwind, then the normal wind gradient helps you flatten/stretch the glideslope,as you descend; trouble is its harder to roll into the turn back, and you may not have the height to do it
Please dont mind me , its surprising my strange concept has not killed me in the last 72 years
PS it occurs to me you might get a different view of what happens if you watch a helicopter or auto gyro and see how those wings go up and down on the way round!

[Brian Abraham]

it occurs to me you might get a different view of what happens if you watch a helicopter or auto gyro and see how those wings go up and down on the way roundAs a helo guy I'm afraid I don't follow what you're saying here wiley, the up and down part.

[wilyflier]

Brian,
Just that in some teeter helos and most autogyros the advancing blade tend to rise and the retreating blade drops, thus looks canted from front or rear,you probably cant see that from where you sit heh heh

[Capt Pit Bull]

Wily,

Just that in some teeter helos and most autogyros the advancing blade tend to rise and the retreating blade drops, thus looks canted from front or rear,you probably cant see that from where you sit heh heh

And would this be related to airspeed or ground speed?


Wiz,

I KNEW mentioning down-wind turn would catch SOMEONE!!

I am going to hire a team of ninjas to hunt you down. Either that or just commit ritual suicide myself.

pb

[Armchairflyer]

Maybe I miss the point, but AFAIR the "danger" of the down-wind turn materializes only when the pilot tries to maintain a certain track over ground during the turn, with the tailwind first making him faster (relative to the ground) and becoming a crosswind pushing him "outwards" (again, relative to the ground), which might tempt him to overbank and stall the airplane (and/or trying to compensate with rudder only and crossing his controls to avoid an "excessive" bank angle).

So AFAIK the danger of the down-wind turn does not lie in the turn itself (with airplane unaware of wind direction), but in the reaction it might provoke.

[Tourist]

Wily


It is your visual association with the ground that is subconsciously messing up your circuits.


The downwind turn thing is easily put to bed.

ASW helicopters spend a lot of time flying in circles at low level (200ft and below)

The proof that this is a perceived and pilot induced issue is that on many occasions I have been pinging away in total darkness/IMC, carrying out orbits/circuits at 100kts in 40kts of wind at 200ft and below.

No problem until the sun comes up, and then suddenly it all feels uncomfortable on the downwind turn. Your mind overides what the instruments are telling you because the visual system is so strong.
The fact that when all you can see are flight instruments everything feels exactly the same as a zero wind day and your powers are steady is difficult to reconcile with the visual skidding over the ground and groundspeed changes etc.

You fly relative to the air, not the ground.
The only time the ground speed is of any relevance is at the moment you touch it.


Incidentally, you are venturing into the silly with the rotorblade thing. retire gracefully with some credibility.

[framer]

The proof that this is a perceived and pilot induced issue is that on many occasions I have been pinging away in total darkness/IMC, carrying out orbits/circuits at 100kts in 40kts of wind at 200ft and below.


By Jingo's........what does AWS stand for and what situations require that? That would leave me tired for a week!

[main_dog]

I believe it's Anti Submarine Warfare, but as an ex-GA fixed-wing pilot don't quote me!

Anyway Tourist please don't inject pesky logic and rationality into it, I was just sitting down with a bowl of popcorn and beginning to enjoy myself...

[Shiny side down]

This thread seems to have become stuck in a groundhog day style loop.

Aviation Mythology and Misconception(s)- was it intended to become the singular?:rolleyes:

[Wizofoz]

its to do with the need to energise acceleration and momentum against inertia during the turn downwind, and then turning the excess speed back into height during the turn into wind.


In defining Inertia, and talking about speed, you are reffering to velocity in which frame of reference?

BTW, I have landed a Ram Air Parachute over 1000times and flown conventional Gligers extensivley. Does that count as a big enough appeal to authority?

As to my experience in holding in high winds, we are talking about holding at 240kts odd in 100kts of wind. If turning downwind had any appreciable effect I would have noticed.

Please outline how you think the fact that the air is moving in relation to the ground effects an aircraft that isn't TOUCHING the ground.

[oggers]

Hawk:

[myth] If an aircraft is not moving (stopped on a taxiway for example), then its not producing any power.

Yeah that one bugs me too.

Eck:

One definition of Power is that it is the 'rate of doing work'.

Work = Force x Distance

If the aircraft's engines do not apply their force (thrust) through a distance, then no work is being done. Ergo, no power is being produced.

Sorry Eck but the engines still do work because even though the aircraft is stationary the engine still blew a mass of air over a distance. Hence willl05's comment about standing behind a running engine to test the theory. Ultimately the 'work' is being 'wasted' in a futile attempt to turn terra firma and the atmosphere in opposite directions but work is still done and power is still produced.

It really just comes down to Newton's 3rd law about action and reaction.

[BerksFlyer]

Oggers is correct. Work is being done by the engine on the mass of air it is accelerating (ie. it is being subjected to a force). Work done by an aircraft engine is work done on the air it is accelerating, not the aircraft to which the engine is attached.

Power, Joules per second, is being produced by the engine - it is burning fuel of high energy content.

[Machinbird]

Another myth:
They are seriously considering extending the retirement age to 70 for airline pilots.

[stilton]

They'll need to to wind up this thread..

[silverstrata]

They are seriously considering extending the retirement age to 70 for airline pilots



Well, they will have to do something.

At present, they are going to steal my licence at 65, but not give me a pension until 67. Who is going to pay, for this enforced unemployment?

[silverstrata]

So AFAIK the danger of the down-wind turn does not lie in the turn itself (with airplane unaware of wind direction), but in the reaction it might provoke.




Grrr....

The danger in a downwind turn is provided by the windshear, not the pilot's perspective.

If you take off on a runway with 90o crosswind of 5 knots, your tail wind component is zero (and you are not yet a part of the moving airmass).

If you now turn downwind and climb to 500ft, into a screaming 40 knot tail wind, the aircraft does not have time to react to that sudden wind shear ( by accellerating), and loses nearly 40 knots of airspeed. And in a light aircraft, that can be fatal - both in terms of height loss or airspeed loss.

So yes, a downwind turn can be fatal - but the lurking spectre of doom is the windshear close to the ground, and not the turn itself.

Try doing some gliding, to find out what windshear can do to an airframe.


.

[Lancman]

If a hang glider is flying at 20 knots in a 20knot headwind it has zero kinetic energy but plenty of potential energy, I hope. If it turns downwind it needs to get some kinetic energy from somewhere, quickly.

An aircraft with it's engines running on the ground with the parking brake set may be doing some work but it's efficiency is zero.

HTH.

[barit1]

If a hang glider is flying at 20kt in zero wind, it has x kinetic energy. If it suddenly encounters a 20kt tailwind (windshear), it now needs 4x kinetic energy to maintain the same airspeed. Newton says it cannot change inertial velocity instantly, and so a quick dive to convert potential energy is in order.
:8

[cwatters]

I maintain both camps are correct depending of what you are flying and how you fly it...

No aircraft (that has mass) can change ground track instantly as that would imply instant acceleration.

So it seems obvious that a sudden yaw into wind differs from a sudden yaw downwind. In both cases the aircraft will continue on the original track for a few seconds until the aircraft responds to the new forces on it, the track changes and it either accelerates or decelerates to regain it's original air speed. During that time the airflow over the aircraft is different.

It's equally obvious that this effect dissapears if you make your turns co-ordinated and slow enough that the aircraft has plenty of time to accelerate or decelerate and maintain air speed.

Inertia is very real. Consider a glider decending through strong wind shear on approach. One camp will say the changing head wind doesn't matter because the aircraft will accelerate or decelerate to maintain a constant air speed. The other camp will tell you that due to inertia a glider can't accelerate fast enough to do that and can suffer a loss of airspeed. I'm in the latter camp.

[silverstrata]

If a hang glider is flying at 20 knots in a 20knot headwind it has zero kinetic energy but plenty of potential energy, I hope. If it turns downwind it needs to get some kinetic energy from somewhere, quickly



Not true.

An aircraft does not feel wind at all. Wind is totally irelevant to the aircraft, and the turn downwind makes no difference whatsoever.

The problem is the shear (change of wind). If the glider turns downwind while descending through a shear (20kt tail increasing to 40kt tail), now the glider has lost 20kt of airspeed, and will need to lose height to regain speed (trading potential for kinetic).

The above scenario can happen, but is unusual. The big problem for a glider is final approach into 40kt of wind, and then flying into the lee of a hill or trees, so that the wind suddenly reduces to 10kt. Now the glider has lost 30kt of airspeed, and needs to readjust by closing the airbrakes.

Just remember. Wind has no effect on aircraft flight, but a rapidly changing wind (shear) does.

.

[cwatters]

Now the glider has lost 30kt of airspeed, and needs to readjust by closing the airbrakes.

Airbrake controls the glide angle. Elevator controls speed. At least that's what I was taught.

You can try retracting the brake and stuffing the nose down but it will still take time and height to accelerate. While you trade height for speed you descend through even more wind shear. Might not be able to recover your speed fast enough. It's one reason why you carry extra speed on approach in windy weather.

[Lancman]

'tis true Silverstrata, Newton says so!

As the stationary mass of the glider is turned through 180 degrees it must be accelerated by 40 knots if it is to stay airborne. This requires an input of energy. So a gentle turn whilst trading height for speed is necessary. To believe that an aircraft is excused from the laws of motion can be dangerous.

[Tourist]

Lancman

Newton was a clever chap, but Einstein trumps him.

You are completely, utterly wrong when you say:

"If a hang glider is flying at 20 knots in a 20knot headwind it has zero kinetic energy but plenty of potential energy, I hope"

Kinetic energy is all relative to some frame of reference, hence Einsteins "relativity"

The relevent kinetic energy to an aircraft in flight is that between the aircraft and the air.
That is the only valid frame of referance.

This is easy to see if you consider the aircraft relevant to the earth, or to the sun or to the spiral arm of the galaxy.

The kinetic energy is all about the difference in velocities of the two objects. It is not a quantifiable absolute, rather it is quantifiable between two objects.
In a crash, yes, the energy between the ground and the aircraft becomes relevent suddenly.

You notice that all those that believe this downwind effect to be true are the ones with the highest reliance on the visual external cues. Visual clues which we know are very susceptible to errors in the aviation environment.

The same problem comes up when yacht racing in a river/tidal estuary near the shore. As long as you sail by the water not the shore, everything is fine.

Wings don't get confused by visual effects, and neither do instruments. Trust them.

"To believe that an aircraft is excused from the laws of motion can be dangerous. " is undeniably true, but not as dangerous as a lack of understanding of those basic laws of motion Lancman

[silverstrata]

.
Airbrake controls the glide angle. Elevator controls speed. At least that's what I was taught.



You have never been gliding, have you.

The airbrakes place the glider on an artificially steeper glideslope. So if you lose airspeed due to windshear, you can close the airbrakes and maintain the same speed (because the artificially steep glideslope will now allow the glider to accellerate).

If you had to lower the nose every time you lost airspeed in a glider, you would soon find yourself surrounded by sheep, and separated from the airfield by a barbed wire fence.


.

[Armchairflyer]

The danger in a downwind turn is provided by the windshear, not the pilot's perspective.I beg to differ insofar as a) windshear can get me in trouble on, e.g., a straight climbout or approach as well, and b) pilot perspective apparently does make a difference when turning close to the ground, as explained here (http://www.djaerotech.com/dj_askjd/dj_questions/downwind.html) for example. Admit though that I completely and wrongly ignored the windshear effect in my reply. Learned something new again.

(And will hopefully find the time for a gliding trial lesson just for fun and educational purposes next season.)

[Al Murdoch]

Well, reading this was 10 minutes I'm not getting back...

[Wizofoz]

'tis true Silverstrata, Newton says so!

As the stationary mass of the glider is turned through 180 degrees it must be accelerated by 40 knots if it is to stay airborne. This requires an input of energy. So a gentle turn whilst trading height for speed is necessary. To believe that an aircraft is excused


Newton formulated the concept of frames of reference. An objects momentum is dependent on it's velocity which is relative to the frame of reference.

The aerodynamics of an aircraft are dependent on it's velocity relative to the air around it. The most useful frame of reference, therefore, is one in which the wind velocity is zero.

The aircraft has no idea whether the air around it is moving relative to the ground.

Tell me: you are currently on a planet rotating at around 1000mph, orbiting the sun at around 6000mph, and orbiting the galactic centre at around 300 000mph.

What would you say your momentum was?

Answer? The correct answer is, "Relative to what?"

By the way, do the math-what is the difference in acceleration between a glider going from 20 knots north to 20 knots south, and one going from stationary to 40 knots south.

Hint:- this requires a correct understanding of the tem acceleration.

Moment in is not exclusivley relative to the Earths surface or anywhere else.

[Luc Lion]

@Lancman, barit1, cwaters

If a hang glider is flying at 20 knots in a 20knot headwind it has zero kinetic energy but plenty of potential energy, I hope. If it turns downwind it needs to get some kinetic energy from somewhere, quickly.
An aircraft with it's engines running on the ground with the parking brake set may be doing some work but it's efficiency is zero.
HTH.

Truly amazing in an aviation forum.
But a common misconception that is worth an explanation.

Since 1632 and what is called "Galilean relativity" (no need for Einstein here), it is known that the laws of physics are the same in all inertial frames.
This means that the measurements of interacting forces, accelerations, variations of speed, momentum changes remains unchanged when switching to another inertial frame
although measurements of distance, speed, kinetic energy are changing through frame switching.

Let's look at this glider flying 20 kt in a 20 knot headwind and turning 180° .
A turn always requires an acceleration ; this is the centripetal acceleration.
In the frame of reference of the air, the glider turn changes its speed from +20kt to -20kt.
The integral of the centripetal acceleration has completed a momentum change of -40kt (x the glider mass).
In the ground frame of reference, the glider turn changes its speed from 0kt to -40kt.
The centripetal acceleration has also completed a momentum change of -40kt.
So yes, measurements of accelerations, momentum changes and forces give the same results in the 2 frames.
And that's untrue for kinetic energy.

Kinetic energy alone is irrelevant ; it can vary from zero to infinity just by changing the frame of reference.
The actual meaning of the kinetic energy in a specific frame is that "it measures the work that the mobile object can do through interacting with a still object of the frame".
It also measures the work necessary to give it its speed through an interaction with a still object of the frame.
So kinetic energy is only relevant in the frame of reference of the objects that the mobile interacts with.

The common misconception here is generated by these facts:
1. the ground frame has a special meaning to humans since it is the frame of the objects our feet interact with.
2. the concept of inertia is objectively handled in physics through the measurement of mass, but is subjectively felt in all day life as the work required for increasing the speed of a mobile object.
3. the "inertial work" can only be measured in the frame of the interacting object, but humans tend to consider that it is an absolute value measurable in the ground frame of reference.

Back to turning into head wind/down wind.
In summary, one can state:
1. In itself, turning into head wind or down wind makes no difference ; the airplane only interact with the air and so it is the frame of reference of the air that matters.
2. Turning whilst crossing a windshear does make a difference ; turning into increasing relative wind increases the total energy of the plane (temporary increase of air speed or height gain),
and turning into decreasing relative wind decreases the total energy of the plane (temporary decrease of air speed or height loss).
A turn into decreasing relative wind is a potential hazard at low altitude.
3. Flying perfect circles with reference to the ground makes irregular circles in the air (with non-zero wind). The rate of turn is lower when flying headwind and higher when flying downwind.
Thus flying a ground pattern at low altitude and allowing very high rate of turn when turning downwind is also a hazard.

Luc

[oggers]

...that's downwind turns put to bed then.

Next week: from the team that brought you The Danger of a Downwind Turn: the Steep Turn as Performed Above a Tidal Stream.

[error_401]

Nicely put Luc Lion and for the non-believers try to read a bit of reports on glider and small aircraft accidents in Samedan Switzerland.

Nice place to go btw. but tricky with the winds involving narrow turns to downwind in the valley.

So, yes there are reported and causal accidents due to climbing turns into downwind not having enough speed. But then from eyewitness accounts some of the guys turned in 30 deg. bank turns to downwind at some 5 kts above stall speed ... :\

The one I just found (in German): www.bfu.admin.ch/common/pdf/1833.pdf

Plus a nice one from my (oh so easy flyable) turboprop times: Approaching LSZH we experienced a nice windshear taking away about 12 kts of IAS. Reported to tower which gave the information to the followin 737. The skipper obviously aware asked about type of aircraft reporting the windshear. Was given "ATR 72". He then reported 17 - 18 kts speed loss at some 2'000 feet AAE.

Shoud answer both:
1st - no not a myth but can kill you if lacking IAS!
2nd - yes inertia plays a vital role.

[Wizofoz]

error,

The "downwind turn myth" specifically refers to a turn in a constant wind.

Windshear is an entirely different (and very real!!) phenomena.

[pilot999]

look at dynamic slope soaring, blows away all these stupid myths about downwind turns etc, its all about constant changing of kinetic and potential energy and converting low level windshear/ gradient on the rear of the slopes into useful energy.


http://www.youtube.com/watch?v=rfoxjNg-eg0&feature=related

[Tourist]

pilot999

You video has nothing to do with downwind turns.

[pilot999]

its got every thing to do with downwind turns and change of energy state:ugh:. Go back to your flight sim or Hello magazine.

[Lonewolf_50]

Note the note at the bottom of this section: - "Compare VOR and ADF systems to detect possible map shifts". You cannot do a map cross-check, if the VOR or ADF is u/s or not fitted !!


The 1996 Croatia USAF CT-43 crash is what happens, when people use a (map-shifted) RNAV FMC approach, instead of the raw NDB/ADF.

Approach required two ADF's to shoot properly, and acft was not equipped with 2, and IIRC there was a certification issue as well. (Been a few years since I read that accident report).

If I can find it, I'll post a link to the public released USAF investigation.

[oggers]

Sorry pilot999 but I couldn't see what was going on in that video. The ad-hom against tourist didn't shed much light on things either?

[911slf]

Don't disagree with the general drift (:O) of your post but Newton suffices. While Einstein extends our knowledge we don't need him for flying aircraft.

NEWTON Inertial frame of reference - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Inertial_frame_of_reference)

Contains this The motion of a body can only be described relative to something else - other bodies, observers, or a set of space-time coordinates. These are called frames of reference. If the coordinates are chosen badly, the laws of motion may be more complex than necessary.

In air that is moving at constant velocity you have a good frame of reference for flying speed. It is a rubbish frame of reference for ground speed.

My hang gliding instructor used to say 'the ground is a dangerous place, stay away from it'. :)

[Wizofoz]

its got every thing to do with downwind turns and change of energy state. Go back to your flight sim or Hello magazine.


You understand that kinetic energy is a relative value that varies depending on frame of reference?

Dynamic Soaring is possible bymutilising the different velocities of two air masses.

It is not possible in a steady wind. The acceleration an aircraft goes through in a turn is identical whether or not it does so in a wind.

[Wizofoz]

Oggers,

Dynamic soaring involves using a vertical sheer layer. In the video, a model glider is utilizing the lea of a hill, with a strong wind blowing in the free stream.

You fly above the hill with the wind, then dive into the lee. This is a positive shear and so you gain airspeed. Before the speed bleds off, you turn and climb(with the models they half loop) The free wind is now a head-wind and you again have a positive shear and gain airspeed. Repeat ad-Infinitum. Truly impressive speeds (300mph+) have been achieved by model this way.

BUT you need two winds of different speeds. It IS irrelevant to the discussion of down-wind turns in constant winds.

[Tourist]

pilot999

"Go back to your flight sim or Hello magazine"

:rolleyes:

It is still irrelevant to downwind turns as wiz says.


911slf,
yes, but it helped to make the point that you should not mock others knowledge of physics unless your own is adequate. Which his is obviously not.

[de facto]

I KNEW mentioning down-wind turn would catch SOMEONE!!----->
'I am going to hire a team of ninjas to hunt you down. Either that or just commit ritual suicide myself.'

PRICELESS:E:ok:

[oggers]

You fly above the hill with the wind, then dive into the lee. This is a positive shear and so you gain airspeed. Before the speed bleds off, you turn and climb(with the models they half loop) The free wind is now a head-wind and you again have a positive shear and gain airspeed. Repeat ad-Infinitum

Thanks. I think I get it now. I imagine that the whooping helps too ;)

[Tourist]

It's how the albatross flies.

[angelorange]

Clandestino: "Just a couple of myths I can recall in 15 secs:

Modern pax transport aeroplanes are capable of reaching coffin corner.

Mach stall exists."

Did you mean that or the opposite?

[neville_nobody]

Know of someone who was in a heavy jet and had a hold slapped on them very quickly them in the cruise. As they turned downwind and still getting their act together they almost stalled the thing; had the shaker going off and lost a few thousand feet in the recovery. Thankfully noone was below. Obviously it is an extreme example high winds and high(ish) altitude but possible none the less.

[Wizofoz]

It still has nothing to do with turning downwind.

[Clandestino]

Did you mean that or the opposite?

Exactly that.

Modern turbofan powered transports have too high Mach No where mach effects have significant effect on stability and controllability (it is way above Macrit or Mmo) and too low power output at altitude to reach altitude where 1g stall and Mach buffet intersect. Valid when HTBJ was written. With higher bypass and improved aerodynamics, even more valid today. If you fly Airbus: altitude where Vls and Mmo meet is way below hypothetical coffin corner, which doesn't imply that it should be taken lightly.

Mach buffet is anything but stall. Depending on design one may experience pitch-down, pitch oscillation, trim reversal, roll reversal or many other unpleasant surprises but there's no rapid onset of drag and loss of lift that goes with pushing the aeroplane over AoAcrit.

When frames of reference are mentioned, here's another myth:

FBW Airbus in manual flight maintains 1G with stick neutral in pitch, therefore at higher FL, where gravity is weaker due to distance from the earth, it will pitch up to maintain 1G so constant nose down pressure is required to maintain level flight.

I am pretty certain that ensuing furious FCOM quotes and stories of "I've seen it" or "My friend has seen it!" will help me to somewhat explain origin and persistence of aviation myths.

[framer]

Know of someone who was in a heavy jet and had a hold slapped on them very quickly them in the cruise. As they turned downwind and still getting their act together they almost stalled the thing; had the shaker going off and lost a few thousand feet in the recovery.
I obviously wasn't there so I'm not saying it happened like this but it is worth thinking about..... Many many airline pilots think that the top of the lower amber band that provides them 40 degrees bank to stick shaker, implies that as long as they are above that speed, then they can safely bank 25 or 30 degrees into a hold, at altitude, and expect the aircraft to maintain it's height and airspeed and fly around the hold no problem. There is no such guarantee. I personally think that, or a windshear, or both, are the most likely culprits for your scenario.

[Tourist]

"where gravity is weaker due to distance from the earth"

I'd be very impressed with the sensitivity of the accelerometers which would notice the half a percent(ish) difference at 40000ft

[Pull what]

Its a four star hotel
The crew bus will be here in 5 minutes
The load controller has checked the holds
The FO will back you up
Creosote Keith is really a nice guy
Bishop is joining Lufthansa
BA want BMI pilots

[main_dog]

It's just a temporary paycut, while fuel prices are so high
You'll be doing your upgrade within a year or two at most
There's no money in freight
Age 65 retirement will decrease time to command
Captain we've finished, we're closing the holds
We put safety first

[Luc Lion]

Security checks are contributing to the improvement of aviation safety.

[main_dog]

Captain we're ready, the last passengers are just boarding now
Coordination in progress
A girl in every port
Ryanair, the high pay airline
A pilot shortage is looming
Any manufacturer promised new airliner delivery date
Civil aviation authorities are watching over the airlines
Safety is our priority

[oxenos]

The tug is on its way

[main_dog]

Chocks in position
There's a passenger missing, but with no checked baggage
The stairs are on the way
Our people are our most important asset
Are you refusing a duty?

[RAT 5]

Spanish 'Calm' regarding the wind and they don't want to change the rwy.

"we are a safety first conscious airline and nothing comes before that."

"the door to flight ops management is always open, and so are our ears."

'we operate a no-blame culture."