Hypothetical Question from my Instructor. HELP!

[Elfatness]

EDIT: My question has been answered. Thank you to everyone who gave me hints and advice and didn't just flat out give me the answer. In the end I did figure it out myself with alot of help from the hints I received on here, although to be honest I was quite confused about the whole thing for a while. At least I understand the concept now!

To everyone else that just seemed to want to hate on my instructor or hate on the question he asked, I think you guys really need to gain some sort of a life. You automatically took judgement to someone you don't even know. I have learnt that in the future not to post questions of this nature on PPRUNE.

I will however continue to observe and post the odd post on here however this will be the last time I ask a question of any nature.

Happy Flying everybody! Be positive! And thank you.

Elfatso

[windowshopper2010]

I won't answer it for you, but have a think about what effect w/v has on TAS and Track. I think your instructor has thrown in a good red herring for you.

[cac_sabre]

all crosswind vector for the aeroplane? probably totally wrong..

[b_sta]

Think about how to get the maximum difference in groundspeed between the plane vs the clouds.

[sisemen]

Push the nose to vertical (downwards) and hope you can pull out in time :E

[Capn Bloggs]

I won't answer it for you, but have a think about what effect w/v has on TAS and Track.
A good red herring's right! :E

[T28D]

Skim the tops VFR , Bloody dangerous and illegal, Instructor should know better even if it is Hypothetical

[Elfatness]

thanks for all your answers so far! I am currently doing a fair bit of brain racking :)

I'll get back to you guys as to how I go!

PS: Im a real freshy!! a whooping 32 hours in the logbook!! ;) So I really do appreciate you all giving me the time of day :)

[Elfatness]

I did already bring that up with him T28D... haha ;)

[framer]

Tell him a low centered over Kangaroo Island is bringing a water laden airmass down from the north causing the geo-stationary orographically lifted cloud layer, so therefore a southerly heading will achieve the desired effect.

[*Lancer*]

You're both in the same airmass = doesn't matter which direction you fly.

[Elfatness]

ok im still struggling to work it out :( I think im more stupid than even I realised!

[AerocatS2A]

The answer has been given at least once in this thread. Think about what airspeed means and what you travelling through.

[ForkTailedDrKiller]

Have a look at the rules for VFR flight!

Dr :8

[Aimpoint]

I have attempted to answer it twice and failed


I'm guessing these were "into the headwind" and "with the tailwind"? What other options are left? The answer is a few posts above.

Bloody dangerous and illegal

Dangerous, yes! Illegal? No. VMC (class G) below 3000ft means you simply need to be clear of cloud. I guess it depends how high the cloud tops were in the instructor's question...and that they are in non-controlled airspace and not a GAAP, I mean, Class D airspace.

To be honest though, the instructor is just pulling his own wang indulging in his self-importance by keeping the student guessing. Bloody three-bared rock star.

[VH-XXX]

In his defence he did say hypothetical.

Your intructor is just trying to trick you. It doesn't matter which direction in which you fly, it will be the same.

That being said, often the wind just above the clouds can vary significantly to under them, so in theory, it may actually matter which direction you are travelling in.... but you would have no way of knowing that until you got up there.

[Elfatness]

Just to clarify Aimpoint, he is a great instructor and a top bloke :)

And to everyone else, thank you for all you assistance :)

[Ascend Charlie]

If it takes a yard and a half of calico to weave an eskimo's underpants, how long will it take a double-breasted cockroach to tapdance through a barrel of treacle?

Your instructor is playing games with you.
It doesn't matter which way you fly, you are moving in the same parcel of air as the cloud.

[j3pipercub]

If it takes a yard and a half of calico to weave an eskimo's underpants, how long will it take a double-breasted cockroach to tapdance through a barrel of treacle?

Is it an African or European cockroach?

j3

[OZBUSDRIVER]

More pertinent, J3....laden or unladen!

[prospector]

Is it an African or European cockroach?

a double-breasted cockroach

One would first have to ascertain whether it is possible to have double breastfed cockroaches of either variety.

[mustangranch]

For such a question there is two answers.
1. If you fly at 2000 feet to ybdg from Melbourne there is a bloody big mountain called mount macedon in the road and terrain won't let you.
2. There is no direction that will make it feel faster. The clouds will move with the wind. I.e. if you track north your ground speed will be low however TRUE airspeed remains the same. If you track south, well good luck getting to Bendigo from Melbourne.

Stupid question requires stupid answer. But what he wants is for you to understand tas.

[Elfatness]

Mustang, I Should point out that I am based in Bendigo, so there was no actual flying to the destination as such :)

[A37575]

There are more intelligent questions your instructor can ask you rather than that sort of hypothetical stuff. How about you ask him the following questions which are more directly applicable to your 30 flying hours than which way clouds seem to go.

Please Mate (or Sir if you wish to be polite)
How do I know if the engine on my aircraft is delivering its certified power on take off? What is Minimum Static RPM for the aircraft I fly and where would I find that information. Ask him to show you - don't just take his word for it.
Secondly, Dude (Sir), what is it's relevance to my take off procedure and specifically how do I check it? And what are my actions if the actual RPM is above or below the published range of Minimum static RPM?

Your instructor should be able to tell you the correct answers to those questions since they relate directly to flight safety - YOUR flight safety:ok:

[OZBUSDRIVER]

Elfatso, your instructor is just getting you to think relative to your aeroplane. Unless you come under the effect of windshear or downdrafts or thermals all the air around you is moving relatively with you as if you are flying in still air. If you are like a particle of air if you are sitting in a gondola of a ballon. Even though you are moving over the ground you perceive you are in calm no wind conditions. You are part of the moving parcel of air. If you observe an Aeroplane flying around you his airspeed relative to you will always be the same. As if the Aeroplane is also flying calm no wind conditions.

What will get inside your head later on is what happens to your performance due to inertia as you change direction in an airstream like turning from a headwind to a tailwind. Very important if you are flying a very light aeroplane. :ok:

[AerocatS2A]

What will get inside your head later on is what happens to your performance due to inertia as you change direction in an airstream like turning from a headwind to a tailwind. Very important if you are flying a very light aeroplane.
I really hope you are joking here, otherwise, it's time to hand in your licence. :=

[framer]

Uh oh.....not the downwind turn debate.....

[Elfatness]

Guys I didn't post this thread so that everyone could have a dig at my instructor, I assure you I am learning as per the syllabus & he is a fantastic instructor, especially compared to some of the horror stories I've read on here with other instructors!
I love a good challenge to so I'm more than happy with these "hypothetical" questions.

Again I'd like to thank everyone for their time and assistance, I could have been quite easily ignored! (which is what I was expecting tbh)

Anyways, whats this "Downwind Turn Debate".... Or should I go thread searching?? Sounds interesting :)

[Wally Mk2]

I think the general consensus here is that it's a fruitless question & serves no purpose to learning to fly.Don't forget yr instructor is just that, he's there to instruct.No one is born with any knowledge at all in any field we all learn along the way so get this rocket scientist to learn you & explain his theory & what benefit it would have on yr flying lessons.
At the end of the day flying just above the clouds is just a visual experience ( & a bit of fun)& you wouldn't be able to tell the difference anyway regardless of which way you where driving the plane (it would appear fast anyway) as you have nothing to gauge or compare against at the time.
Enjoy the flying, leave the rocket science stuff to the wannabees!

Wmk2

[Capn Bloggs]

Wally, actually, it is a very good question for those that don't understand or don't know how aeroplanes interact with the airmass they are in, and said movement relative to the ground. Not only for the rocket scientists but also for those curious about their flying machine, as it seems Elfatness is. :ok:

[OZBUSDRIVER]

The dreaded downwind turn argument is a long term argument that upsets a lot of people for exactly the same reason as your original argument.

Without hijacking your thread. Heavy drivers understand what to do if encountering microburst conditions on approach to land. Heavies have(edit) lots of inertia. As the shear hits IAS changes...why is it so? Flying into the rapidly increasing airflow IAS increases...but the argument for relative airmass says there should be no change. ASI increases and aircraft starts to overshoot...pilot reduces power and lowers nose to regain approach path and then flies into the downburst, powers up and trys to arrest the sudden undershoot...so now the aircraft is nose up and under power trying to regain approach path and then aircraft flies into the strong tailwind of the microburst nose high and under full power and low energy...plenty of people have died until authorities finally believed the met guys that their aircraft can be brought down by an airmass. Me no heavy driver but it took a looong time before the authorities learnt to teach their drivers to go full power, nose up fifteen degrees and go round. More learned heavy drivers can give better description what SOP is for microburst detection on approach. MICROBURST is an airmass with a severe rapidly changing wind vector in both speed and direction.

Inertia and airmass in the extremis!

FOr the lightie driver the downwind turn is an optical illusion....happy:ok:
Your bum will tell you funny things but trust your horizon,attitude and power.

[AerocatS2A]

Happy Oz. :ok:

Your point is misstated a little though. The relative airmass argument ONLY works when the airmass is stable. If you are experiencing windshear or climbing/descending into a changing wind gradient, then yes, your IAS will change. But this is not a steady airmass. In the case of a downwind turn in a steady airmass the IAS will stay the same except for the slight decrease due to the loading that happens in any turn. Anything else that happens is due, as you say, to optical illusions, and at low level, the pilot trying to fly with reference to the ground.

[Checkboard]

I like this instructor's question, and that he is asking it of a 30 hour student :)

While I agree with the airmass bit, and that the answer the instructor was looking for was "it doesn't matter", if the clouds are cumuliform of sufficient depth they will have a ground speed associated with the lower layers they are sitting in, not the high layer you are flying in as you skim along the top ... ;)

[ad-astra]

The BEST lesson that this thread has given is that ask a simple well explained hypothetical question and every nutter with an axe to grind, a high horse to ride or soap box to climb will feel they are obliged to reply to the question with anything but an answer.
FFS it was just a Hypothetical question to make the kid think :ugh:

Elfatness enjoy the flying - it can be a great industry.

[sagan]

Good on your instructor for making you think and understand a concept. Unfortunately this is not the place to get help. This is the place for attacks and the vomit of the weak links of this industry. Pathetic. As Ad-astra says it can be a great industry. Just keep away from this rubbish.

[Elfatness]

It all makes perfect sense now, with the help of many of you! I must admit I was quite confused by the concept however now its as clear as mud ;)

And I love flying, I wish I had started sooner! At 28 I may be pushing it to make a decent career out of it considering Im a few years away from even gaining my CPL at my current rate of training, however I'm going to give it a red hot crack!

Cheers again for the input :)

[aerokitty]

Just to put this to bed I feel I should mention this was not a training question but a competition question for all local students. It's amazing how something fun gets turned into a cat fight (pun intended)

[Volumex]

Here's anothery:
Imagine a plane is sat on the beginning of a massive conveyor belt/travelator type arrangement, as wide and as long as a runway, and intends to take off. The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation.
There is no wind.
Can the plane take off?

Mythbusters answered it well.

[FGD135]

The correct answer to the original question has been given many times in this thread.

In my experience however, there are plenty of pilots, some "old and experienced" that would have answered this question INCORRECTLY.

In the case of a downwind turn in a steady airmass the IAS will stay the same ...

Only in theory does there exist such a thing as "steady air mass" AerocatS2A :E

The answer to the conveyor belt question is, NO - the aircraft cannot take off.

[Dexta]

Of course the aircraft can take off! The wheels will spin really fast but the aircraft will take off in essentially the same distance as if there was no conveyer belt (the wheels spinning fast may add a tiny bit of drag thus extending the ground roll by 1 to 2 feet).

[MakeItHappenCaptain]

Ah, but once the wheels (tyres) exceed their speed rating, you will be in trouble...:E

[FGD135]

Of course the aircraft can take off!

To take flight, the wings must generate lift. But the aircraft is stationary, relative to the air surrounding it - so there cannot be any lift generated.

Very straightforward when viewed in those terms.

[Volumex]

Mythbusters - Plane on a Conveyor Belt - YouTube

[Ex FSO GRIFFO]

Here's one back to the Instructor,

A boat has rope ladder hanging over the side.
Each rung of the ladder is 6 inches apart.
The incoming tide comes in at the rate of 1 foot per hour.
How long is it before the first three rungs are covered??

See yas.....:ok:

[ollie_a]

Wow I really hope the comments that an aircraft on a conveyor belt could not take off are tongue in cheek.

In case anybody is actually taken in:

Yes, the aircraft can take off.

Not up for typing the reasoning out word for word but a good explanation is here:

The Straight Dope: An airplane taxies in one direction on a moving conveyor belt going the opposite direction. Can the plane take off? (http://www.straightdope.com/columns/read/2638/an-airplane-taxies-in-one-direction-on-a-moving-conveyor-belt-going-the-opposite-direction-can-the-plane-take-off)

[AerocatS2A]

To take flight, the wings must generate lift. But the aircraft is stationary, relative to the air surrounding it - so there cannot be any lift generated.

Very straightforward when viewed in those terms.
Except those are the wrong terms. The conveyer belt doesn't have any mechanism by which it can prevent the aircraft from moving forward relative to the air. It can spin the wheels as fast as it likes but unless the wheels fail, the aircraft will still move forwards.

Edit: The answer to the conveyer belt question actually depends on how the question is worded. If the conveyer belt is defined as being capable of keeping the aircraft stationary (through magic or whatever) then the aeroplane won't fly. On the other hand, if all it does is attempt to match the wheel speed, ie, it is a real world conveyer belt that obeys the laws of physics, then it can't stop the aircraft from moving forwards.

As far as the theoretical stable airmass goes, a stable airmass for practical purposes is a very common occurrence. It only really needs to be felt as smooth air.

[Wally Mk2]

..geeez 'griffo' what drugs ya on there mate?:)

The boat displaces the same amount of water regardless how high/fast the tide rises:ok:
Good test: Place one rubber ducky in the bath tub in one inch of water so it floats with some of it's cute yellow butt exposed. Add water to tub & watch the ducky rise with same amount of butt exposed (sick buggers we are:E)....'till the bath overflows that is then all bets are off as mum will kick ya ass:E

'Aero' yr spot on there mate:ok: The wheels are the only thing that will not be normal in the T/off, they simply spin faster:ok:

Wmk2-)

[sisemen]

The question that was asked is:

Which direction should you fly to make the clouds seem like they are going the fastest past you?

I refer the honourable members to the answer previously given in post # 5

[neru1]

You have decided to go for a nice scenic fly at Bendigo, the cloud is scattered at 2000ft with a wind of 360M/15kts. You climb up above the clouds so you can skim the tops (remember hypothetical) and get that feeling of speed. Which direction should you fly to make the clouds seem like they are going the fastest past you?
All hypothetical questions are meant for checking your fundamental understanding of the concept. Hence I would respect the intention of the instructor for posing this problem. The comments (positive and negative) posed by all are justified in their place since the thread starter has not specified his level of pilot training at which the instructor has posed this problem. So assuming that a genuine answer is required i would like to make an attempt at answering the question form the scratch.
The problem is of understanding of wind effect and relative velocity. This can be answered in two ways. First, assume same AIR MASS so that only relative aspects remain or answer algebraically using the wind triangle.
Clouds drift at wind speed at same level. (I am assuming that clouds are not vertical and are at 2000 feet where the wind velocity is 360M/15kts. So flying above clouds means you are also experiencing same wind velocity. If TAS is assumed to be 200 knots (hypothetical) then ground speed of ac in direction 360 is 200-15 = 185 knots. Speed of clouds is 15 knots but in same direction. So as per vector speed calculation, the relative speed is 185 + 15 = 200 (opposite direction –ADD).
In reverse direction of 180 (ac heading) the GS is 200+15 = 215. Speed of cloud remains 15 but in same direction. So relative speed is 215-15 = 200 knots (same direction –SUBTRACT).
So in both cases along the direction of winds the relative speed is 200 knots.
Now let us take other directions. Extreme cases are perpendicular directions. i. E. 090 or 270.
Ignoring the effect of drift on ac (as TAS is not specified) the speed of ac will be 200 (=TAS no HW or TW) and speed of clouds remain 15 in perpendicular direction. So the resultant vector will be more than 185 and less than 200 (as hypotenuse is less than sum of two sides). This will be true for all other directions as well where the function of sin cos will reduce the relative speed.
Hence the answer is that the ac has to fly in line with the wind, along or opposite to get the maximum relative speed. Other directions the relative speed would be less.
Hope that I have answered the query correctly!!

[Ultralights]

The scariest part of that mythbusters episode was the UL pilot believed he wouldnt get off the ground..... :ugh:


I find it amazing something so simple, can be made so difficult.

ignoring windsheer/microbursts/turbulence etc, evey aircraft flies in Nil wind, calm conditions, Ground speed is irrelevent.
the only time an aircraft is NOT in a nil wind calm condition is when its attached to something that stops it moving with the air mass. such as the ground...

even if the wind is 090 at 100 kts, the clouds wills till pass under the wing at the aircraft IAS..

not so hard.:ok:

and on the "oh geez, not this ****e again" downwind turn, again, only thing that matters is the path over the ground determined by windspeed relative to the ground.. once the aircraft is airborne, see above.. nil wind condition.. but the airmass relative to the ground is what will determine if you end up in the trees or not..

[Ex FSO GRIFFO]

Hi Wall,....

Have ya ever seen me sign orf wif 'See Yas' before......???

I was expecting 'someone' to bite.......but....? 'QUE??'

See Ya :p :ok:

p.s. A VERY noice 'red'.... in answer to yr question...

[Wally Mk2]

.............yeah Griffo me old buddy same red you where drinking, called 'Que':ok:

'Ultra' have to agree there, the UL driver was surprised..............that's more amazing than anything else been said here!:E
At the end of the day as long as the numbers on the dial keep the machine airborne what does it matter?

Joke: Local Irish swimming pool has decided to be more community minded during a water shortage one long summer, they closed lanes 7 & 8:E..................still looking for my rubber ducky though:)


Wmk2

[Oktas8]

A very thorough post from Neru. From an instructor though I would hope for simplicity as well as thoroughness.


The aircraft flies at a particular TAS. Direction & wind are of course irrelevant for TAS.
The clouds fly at zero TAS. Ditto direction & wind.
Therefore direction & wind are irrelevant to the difference in speed between the two.

Now altitude however is quite relevant to TAS - so you should fly just above the layer at 10,000' rather than just above the layer at 3000' for that real feel of speed...

Hmm. Now about that downwind turn:

The aircraft accelerates (turns) as a function of angle of bank and TAS.
The wind vector has exactly the same effect on an aircraft at all times, in terms of direction and speed.
Therefore the wind cannot cause the aircraft to accelerate (turn), unless the wind itself changes.
Therefore all acceleration (turning) done by the aircraft, in a steady wind, is caused solely by a function of angle of bank & TAS.
This function of AoB & TAS doesn't have compass bearing in it, therefore one would not expect TAS to change in a turn, unless the wind itself changes.

Hope that works...

[Capn Bloggs]

A very thorough post from Neru.
But, as others have pointed out, wrong answer. Any relation to the ground of either clouds or aeroplane is irrelevant; the aeroplane flies only in the air immediately surrounding it. That airmass may be doing 5kts or 500kts (relative to the earth) in any direction. But as far as the aeroplane is concerned, it is merely pushing (or being pulled by the prop!) through that airmass at the IAS resulting from the thrust/drag balance.

Consider standing on the ground as a 500kt airmass passed overhead with Elfatness sitting in his C150 flying in said airmass. He may look like (depending on which way the cesspit in pointing) he's flying at 600kts! But, on his ASI, it reads 100KIAS, because it is reading the relative windspeed past the pitot head. Doesn't matter which way he's actually pointing travelling (as long at he doesn't turn too tight :}). It's the relative windspeed that determines the speed of the clouds whizzing by in that airmass. The speed, or direction, for that matter, over the ground, of the whole airmass, with C150 in it, is irrelevant.

Another example. Fill up one of those half seashell tubs with water. Now, build an island in the middle (not too big, you have to pick this thing up soon). Get a motorised boat and set it to motor around the island. Boat is observed passing island at a couple of knots. Boat speed relative to the ground the tub is on is also a couple of knots.

Now, pick up tub and walk around backyard. Tub is now doing 5 knots in various directions! But, relative to the island in the tub, the boat is still only doing a couple of knots. Even though the water mass is moving relative to the earth, the boat still only does a couple of knots relative to the island. Sama Sama a moving airmass with aeroplane in it.

:ok:

[Oktas8]

Should I have said "from an instructor, I would expect simplicity and a correct answer, as well as thoroughness?" I confess that neru's post was so long I didn't read all the way through to his incorrect answer. Oops.

I think, just maybe, you didn't read my post either... which is actually correct. But nice examples all the same. I learned quite a bit about these principles from considering aircraft ops from an aircraft carrier. Bit like your boat-in-a-portable-bathtub example.

[Ex FSO GRIFFO]

Re
"Now, pick up tub and walk around backyard. Tub is now doing 5 knots in various directions! "

You betcha...mostly vertically down...at 32ft/sec....

Unless said tub is also full of ice into which a few tinnies have been carefully placed....
:p

[Checkboard]

Ignoring the effect of drift on ac...
So the resultant vector will be more than 185 and less than 200 (as hypotenuse is less than sum of two sides).

I hope you see what you did, there. ie. Ignored the drift in one case, and then compared it to a case with drift ... :8