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# Mallard Down in Perth

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# Mallard Down in Perth

4th Feb 2017, 05:20

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Originally Posted by compressor stall
Quote:
Neither does gravity, for that matter - if a feather were as aerodynamic as a bomb, they would both fall at the same speed.
So you have two bomb shaped objects of identical shape. One is made of graphene and filled with feather fibres (ie really light) the other normal alloys and explody-bits in the middle.

Both are dropped from a B1. Which hits the ground first?
I apologise for oversimplifying.

Ballistic Coefficient is the ratio of sectional density to coefficient (aerodynamic) form. It's effectively a combination of streamlining and inertia, which are both used to overcome the forces of wind resistance (friction). The reason a feather and a bowling ball both fall at the same rate in a vacuum is because gravity is a constant in relation to the earth's mass (9.8ms/s) acting on all atoms (regardless of mass): https://web.stanford.edu/dept/news/p...ity990825.html

Once wind resistance (friction) enters the fray, then something is needed to overcome that resistance for an object to continually accelerate at 9.8ms/s - an equal force to the opposing wind resistance.

A body in motion will not alter its course unless acted upon by an external force.

The body in motion has kinetic energy - 1/2 mass x velocity squared. Therefore, a proportional force is needed to slow its acceleration from 9.8 ms/s. That force increases as the kinetic energy of the object increases. However, the forces of wind resistance (friction) increase with air density (more atoms per equal volume = great frictional force) and the surface area of the moving object they are acting on. The square-cube law dictates that volume - and all other things being equal, mass - increases faster than surface area. So if two moving objects have the same density and form (both spherical, for example), the larger object will have more kinetic energy in relation to wind resistance. The same equation can be applied to two moving objects of the same form but different densities (mass/volume).

That answers your question as to why greater density of equal form can overcome the frictional forces of wind resistance when accelerated by the same force (gravity).

My question is, if two objects - regardless of size and mass - are moving within a constant air mass, and are not subject to wind resistance or any other physical force within that air mass, what force will cause those objects to alter their velocity?
4th Feb 2017, 05:46

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Did anyone else here go out to the low flying area on a windy day and conduct "Constant radius turns about a fixed point on the ground" training as part of their CPL?

Apart from the obvious real life applications it was also a good way to train people to not kill themselves in the "air/ground interface".

You know, teach them not to be fooled into thinking their ground speed was actually their airspeed and other such strong illusions.
4th Feb 2017, 08:53

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As usual, this has gone totally away from the very sad event that claimed 2 lives. If I was to take note of half the crap that is being spruiked on this thread I'd stop flying now and hand in my licence. One thing's for sure.... so many faceless experts, not all, and at least one admitted he wasn't a pilot, wonder how many others there are?
4th Feb 2017, 09:03

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Originally Posted by FlexibleResponse
Inertial mass is earth/time dependent for frame of reference.
It's true that inertial mass can be framed in terms of the earth's rotational axis - I concede your point. However, both the aircraft and its supporting air mass are subject to the same forces (coriolis, centrifugal, gravitational), and are therefore in the same inertial frame of reference to the earth. To all intents, the supporting air mass is the frame of reference for the aircraft.

That aside, if I read correctly, what you are saying is that, as soon as an aircraft changes direction, there is a change in inertial frames of reference between the aircraft and its supporting air mass. If so, then that inertial change must be measurable in relation to the air mass, and therefore show up as a change in airspeed.

I do not doubt there is such a change.

But in terms of the measurable difference between the two frames of reference of the aircraft and air mass, is it enough to stall a wing?

We are talking about an aircraft flying at circuit speed at 1000', and not the Space Shuttle, after all.
4th Feb 2017, 09:18

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OK, megan posted this in another thread. IMO, it appears to be exactly what happened on Australia Day.

In defence of this thread, if we can't learn from others' mistakes, we're destined to make the same.
4th Feb 2017, 09:27

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Did anyone else here go out to the low flying area on a windy day and conduct "Constant radius turns about a fixed point on the ground" training as part of their CPL?
Nope I cant recall doing that though my Oz CPL would have been back in the 80's. But did some glider thermalling at 200-300 feet sometimes in wind. Was only grounded once when allegedly below tree top height but I was a teenager back then. And the many glider cable break training flights were good practice for low level tight turns with wind to consider.
4th Feb 2017, 09:40

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Chris I would imagine glider flying would give you an intimate knowledge of exactly what is actually going on.

That you or others have not come across this in the training phase certainly clears up some misconceptions I had.

Another exercise was to handrail along a line feature at low level (maybe a bit lower than 200ft this time) and become proficient at overcoming the lag in controls and inertia of the aircraft. Becomes quite apparent when you come to a bend in said line feature and try to follow it. Need to act a fair way ahead of time to make that bend.
4th Feb 2017, 10:20
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flywatcher; I suggest that you think very carefully about the main thrust re ExFSO Groffo's post.

hold off bank in a gliding turn and you will surely crash and burn." I believe it related to the fact that the Austers, Tigers and Chipmunks all had Gypsy engines turning back to front from modern engines.
What he was alluding to was the your proposition that the aforementioned engines rotating in the reverse to modern engines may have some significance.

The proposition is false! The direction of rotation of the engine has no significance! Or, as Griffo puts it; BS!

Griffo; I really wonder how many posters on this thread really are Pilots, let alone have CPL's!

And for reference; The old saying amongst WWII RAAF Pilot trainees went;
I saw him crash, I saw him burn! He held off bank in a Gliding turn!

Related to me many times by my late Father; 39814 Baum; Ronald Wilhelm, Warrant Officer 1, 461 Sqn RAAF. 1st Solo in DH 82 AN 624 August 9th 1943 at No 1 EFTS Parafield South Australia.

Last edited by Pinky the pilot; 4th Feb 2017 at 10:30.
4th Feb 2017, 11:00

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Never had a cpl, sorry, not even a ppl, but I used to have a glider pilot's license.
We were never taught to fly circles around a fixed point in strong wind, except we tried it, to show us that that wasn't the way to do it.
We were taught to fly constant bank and speed, and didn't feel the "downwind turn syndrome" no matter the speed or bank angle, which was just what the practice was all about, even though the wind was enough to "park" the K13, about 63 km/h. yes, we flew metric, it is close to 35 kts.
We didn't use winch start but a trusty Super Cub for launching.
4th Feb 2017, 14:04

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Originally Posted by currawong
Did anyone else here go out to the low flying area on a windy day and conduct "Constant radius turns about a fixed point on the ground" training as part of their CPL?

Apart from the obvious real life applications it was also a good way to train people to not kill themselves in the "air/ground interface".

You know, teach them not to be fooled into thinking their ground speed was actually their airspeed and other such strong illusions.
Yes, it was part of my training syllabus for either the NZ PPL or CPL (can't remember which). It was also part of the check ride. This was in the early 1990s.

We followed line features and flew constant radius turns at 200' as well as setting up for precautionary landings. All good fun and educational.
4th Feb 2017, 14:21

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Originally Posted by P51D
As usual, this has gone totally away from the very sad event that claimed 2 lives. If I was to take note of half the crap that is being spruiked on this thread I'd stop flying now and hand in my licence. One thing's for sure.... so many faceless experts, not all, and at least one admitted he wasn't a pilot, wonder how many others there are?
Ironically, P51D, you have not stated which side of the argument you support and you would probably find that both sides are reading your post, nodding sagely, and saying to themselves "yes, yes, quite right!"

All I would say is that those who believe that a turn from headwind to tailwind in a steady airmass (i.e., no gusts/turbulence/shear) will cause a loss of airspeed should be preparing their Nobel Prize acceptance speech because their assertion, based on only the best anecdotal "data" of course, invalidates all of the hard work that physicists have been doing for the last hundred years! Einstein would have been very interested to learn that one of his two main postulates on which he formulated the special theory of relativity, that the laws of physics are identical in all inertial frames of reference (i.e., that there is no preferred frame of reference), has been proved wrong by some half literate "pilots" on the internet.
4th Feb 2017, 16:31

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No-one is saying the laws of physics change from one frame of reference to another. But there are forces that act on an inertial mass in relation to its position in reference to the earth (and other gravitational fields), so that when an aircraft changes direction in a constant air mass, the two inertial masses (air mass and aircraft) initially diverge in terms of reference. The sum of the difference can be calculated, but makes no appreciable difference to the air speed of an aircraft close to the earth's surface. That is my understanding.
4th Feb 2017, 20:27

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Virtually There -
But there are forces that act on an inertial mass in relation to its position in reference to the earth (and other gravitational fields), so that when an aircraft changes direction in a constant air mass, the two inertial masses (air mass and aircraft) initially diverge in terms of reference. The
There is not such thing as an INERTIAL MASS. There is just MASS. Good ole Newton came up the relationship - F (Force) = M (mass) x A (acceleration).

(Einstein refined it for relativistic speeds to include a correction factor based on the speed of light)

You can chuck the Inertial term out the window, its bulls.t

Lift is the Force that keeps the wings aloft, and the same thing that generates the turn.

Lift (Force) is generated by the air moving over the wings. FULL STOP. In a steady state air mass, the aircraft wings do not know if that airmass is doing 0 knots or 200 kts relative to the ground.

You can do 360 deg orbits all day, clockwise and anti clockwise in a steady state jet stream and you will never see one iota of IAS difference when turning.

Its not that hard.
4th Feb 2017, 22:20

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What he was alluding to was the your proposition that the aforementioned engines rotating in the reverse to modern engines may have some significance.
The proposition is false! The direction of rotation of the engine has no significance! Or, as Griffo puts it; BS!

Pinky, if you take off in a tail dragger with American engine, right rudder. If you take off in a early aircraft with Gipsy engine, left rudder. The fin is offset in opposite direction. In all over paddocks, circuits were left hand. Think about it before you call BS

Griffo; I really wonder how many posters on this thread really are Pilots, let alone have CPL's!
If you are implying I don't have a CPL I can assure you I have, with about 20,000 hr attached to it, some thousands at or below 200ft low speed small radius turns over fishing nets so I have a vague understanding of the effects of wind at low level.

Related to me many times by my late Father; 39814 Baum; Ronald Wilhelm, Warrant Officer 1, 461 Sqn RAAF. 1st Solo in DH 82 AN 624 August 9th 1943 at No 1 EFTS Parafield South Australia.

Related to me by my late father, first solo 1938, Cirrus Moth, Mascot, before my first landplane solo, Tiger Moth VH-AZP, Bairnsdale 1958

Last edited by flywatcher; 5th Feb 2017 at 05:37. Reason: just learned how to do quotes
4th Feb 2017, 23:44

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Well I did not know that there was a requirement to have a minimum ppl but preferred Cpl to comment!

This high standing opinion of many pilots is what kills so many.

The amount of times over my +30 years in aviation I have been asked by very high time and including ATPL pilot , what does this do or how does this work on a basic system is amazing. Many tech logs/MR,s entries cleared with "tested no fault found" should also include "Pilot trained to use it properly".

It is simple, this Mallard stalled. There is no evidence of any external or mechanical factor that assisted in the stall. There are whiteness and video footage in abundance - The ATSB should not need a year to do this report.

P.S. sorry to all the PPL, CPL & ATPL holders that do know others in the industry also know how aircraft work and fly.

Condolences to those poor kids.
5th Feb 2017, 01:39

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As Clare Prop said "Looking at the size of the display box, how did anyone think a 5700 MTOW kg aeroplane could fit into that area? "

The pilot also appeared to obey the 600 meter rule for 'built up' areas, with his downwind track being well out over the water and further reducing his available space.
Questione: Would a PPL ever be trained to do a right hand tear drop timed circling approach, to enable a tighter radius by turning into wind, away from the obstructions in the CDB and away from the low sun ? Would the air display organiser want to see a plan including that, for what was probably one of the few low level displays (a landing) of the day ?
5th Feb 2017, 01:40

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I posted the following back at #147. Flying helicopters in the offshore world it was not uncommon to have 60 knots of wind when taking off from a platform. Climb speed in our particular aircraft was 75 knots and the turn to downwind while holding climb speed was visually spectacular if not seen previously. Ground speed went from 15 knots into wind to 135 knots downwind, all the while maintaining 75 knots IAS. The point is, the aircraft doesn't care what the wind is, and if you are flying by reference to instruments you would have no idea what the strength of the wind is, or indeed, if there is any wind, save for the fact that you already have 60 knots airspeed prior to commencement of the take off.

It was said that in sports mode you could make the turn at 60° of bank for a really spectacular visual illusion. The airspeed didn't move, and the ball remained centred. How can all this be? Where were all these inertial effects? Why didn't we crash and burn?
5th Feb 2017, 05:05

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Originally Posted by Capn Rex Havoc
Virtually There -
But there are forces that act on an inertial mass in relation to its position in reference to the earth (and other gravitational fields), so that when an aircraft changes direction in a constant air mass, the two inertial masses (air mass and aircraft) initially diverge in terms of reference. The
There is not such thing as an INERTIAL MASS. There is just MASS. Good ole Newton came up the relationship - F (Force) = M (mass) x A (acceleration).

(Einstein refined it for relativistic speeds to include a correction factor based on the speed of light)

You can chuck the Inertial term out the window, its bulls.t

Lift is the Force that keeps the wings aloft, and the same thing that generates the turn.

Lift (Force) is generated by the air moving over the wings. FULL STOP. In a steady state air mass, the aircraft wings do not know if that airmass is doing 0 knots or 200 kts relative to the ground.

You can do 360 deg orbits all day, clockwise and anti clockwise in a steady state jet stream and you will never see one iota of IAS difference when turning.

Its not that hard.
I'm not sure how to even answer that. If you don't understand the difference between a non-inertial (accelerating) mass and an inertial (moving or stationary, depending on frame of reference) mass, then it is likely me who will be in trying to explain.

But here's the tip (if you don't know how to use Google - that's a good start): lift opposes gravity - gravity is a (relatively weak) force that acts on all mass and varies with the formula

Fg = M1M2m/R2

Where gravitational force is the sum of Mass 1 multiplied by Mass 2 multiplied by the gravitational constant (m = 6.67 x 10 to the minus-eleventh) divided by distance squared.

Note the "distance squared" part - any time Mass 1 and 2 diverge, the gravitational forces between them change exponentially.

Secondly, kinetic energy is relative to where it is being measured. That is to say, it is relative to the frame of reference.

If the frame of reference is Planet Earth - which is circling the sun at 30km/s, in a solar system travelling at 230km/s, in a galaxy moving at 5833km/s in a universe that may or may not be moving (we think it spins, hence why it is flat) - and you are flying along in your little 172 at 110kt (51m/s), what is your kinetic energy?

EK = 1/2m V2

How do you measure the velocity in the above equation without a frame of reference?

BTW, if you'd actually read my posts, you'd realise that I completely agree with everyone else that there is absolutely no discernible difference in airspeed (induced drag aside) when turning in any direction in a constant airmass . . . but that doesn't mean there is no difference.

My argument with FlexibleResponse is that inertial frames of reference have no real bearing on air speed turning upwind, downwind or cross wind - the velocity change is so miniscule as to be insignificant
5th Feb 2017, 06:03

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Virtually there - I think we are virtually there on agreeing. Thank you, for clarifying your position.

BTW, if you'd actually read my posts, you'd realise that I completely agree with everyone else that there is absolutely no discernible difference in airspeed (induced drag aside) when turning in any direction in a constant airmass
This is the key point in this thread discussion.

"Masses have inertia", that is a better way to say it, then talk about "inertial masses". "Inertial frames of reference" is the best way of saying it.

. . but that doesn't mean there is no difference.
Yes you are right. But the differences you are referring to are the ones due to relativity, and the relativistic adjustments aren't going to be the cause of a stall in a Mallard.

ps (I have a BSc in physics)
5th Feb 2017, 07:28

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Originally Posted by Capn Rex Havoc
ps (I have a BSc in physics)
That's OK, I have a CPL That means I know more about physics than Newton. Apparently. After all, he never flew