The Hobbit Hole III - Journey to the Cross-roads!

[HairOfTheDog]

Welcome to The Hobbit Hole!

Journey to the Cross-roads
The Two Towers Edition

Come on! Come in! -if you would like to have some seedcakes and a pint and relax a while. (If it is a special occasion, we still have a few bottles of the old wineyards left!)

Our first thread ( New Zealander builds Hobbit hole ) reached 4,100 posts, and we thought that was big. Our second thread (The New Hobbit Hole ) held us for over 48,000 posts, and we loved it dearly. We talked about moving to a new thread for the last 38,000 posts, but we are really slow to muster! Finally, the time has come. Tomorrow (at 12:01 am, to be precise!) The Two Towers comes out, and we start a new chapter.

[Sam Cree]

Happy Mother's Day, Suzi!

Thanks, Bear.

[Sam Cree]

Hi, Hair.

I am wondering about airplane pilots and speed and distance problems.

I suppose they must be aware of magnetic compass variation, and correcting and uncorrecting for it, along with air currents, or wind, or whatever they call it, and compensating for that too. Perhaps as well, airplane compasses suffer from magnetic deviation, as they do on boats?

I imagine pilots rely mostly on electronic stuff these days, but suppose they keep aboard the old fashioned devices as well?

Was wondering if they use the old "True Virgins Make Dull Company" memory rhyme.

[Lil'freeper]

re Flat Presidents.

We ducked in the VCenter for a pit stop and didn't stay long. I was hoping to find a flat Bubba for FFrodo to wave his sword at. But alas, no luck.

An anecdote that will appear in my final report: White House tours are canceled until further notice due to heightened security and even the visitors' center had a security check point. Frodo had to go through the x-ray machine- they wouldn't let him through the metal detector!

Must have been the sword. ;)

[HairOfTheDog]

Aviation uses Magnetic north for heading and navigation. It only matters that everyone uses the same reference direction, not that it is true, so True North is irrelevant really. The compass itself is a *bear* to nagivate by because the ball bounces and rolls with every movement, and there are some Magnetic Compass turning errors that happen in aircraft that are not apparent on ships just because of the speeds involved. Basically, the mag compass is accurate in straight and level flight, but useless once you start turning....

The magnetic compass on the plane is used to manually set a mechanical or gyro-driven Heading Indicator that is used to navigate by. It must be periodically reset during a flight, and fancier avionics have a 'slaved' Heading Indicator that maintains a constant accurate reading.

Heading Indicator with adjustment knob.

Mag compass...

[HairOfTheDog]

As for figuring for wind.... Yes, compensating for wind must be figured into both the heading and the estimated time for the flight... Here is another instrument that is used to navigate by.... Picture that your aircraft is the center dot on the instrument, and the line indicates the course line that would lead you in a particular selected course over the ground.

The instrument is showing that the airplane is to right of the desired course (but not too far off, because it is not off the scale) ... and heading parallel to the course. In this case, without other information, it looks like a corrective heading of 330 would be a good heading to intercept and get back on course.

[HairOfTheDog]

I can't wait for your report! Sounds interesting!

[HairOfTheDog]

Here is the little gadget, like a round slide rule, where wind direction and velocity, plane direction and velocity, are all dialed in to give the pilot the heading that will maintain the desired course over the ground, and the estimated time to get there...

Of course, there are electronic versions of this out now as fancy as palm-pilots but I wouldn't be surprised if a lot of pilots don't still use these.

[HairOfTheDog]

ooops Sam..... one more post to you above...

[Sam Cree]

Those little gadgets might be handy on a boat in sustained strong current conditions, such as crossing the Gulf Stream. I may look into getting one. Although it is no problem to figure the set, drift and their effect on your compass course ahead of time, or even as you go.

There is a similar one for boats, maybe not as good though. The "nautical slide rule."

The rationale for using true North, I think, is that meridians are all true north, so if one wishes to pay attention to lines of latitude and longitude (which I regard as fairly traditional) it then makes sense to base navigation on them. I note that aircraft do conform to this by measuring their speed in knots.

Well, I am pleased that we have opened up this can of worms, I want to say more, but have to run for the moment.

[HairOfTheDog]

The only difference between the nautical version and the aviation version would be the scale.

[ecurbh]

Fiddler on the Roof on TCM now!

[HairOfTheDog]

I think the rationale for not using True North in aviation is the added workload of rapidly changing variation when flying east to west at 200 knots.... the pilot would have little time for anything but refiguring True north every two minutes when moving. The compass gives a constant and reliable direction indication that doesn't rely on either a pilot's math skills or a breakable electric instrument to determine heading. Every pilot in the same airpsace coming in would have the same reading.

By the time more reliable electronics and slaved avionics came along, the traditions were set. Runways and navigation aids and charts were all built according to magnetic, so changing it would have only caused problems. I am not sure why nautical navigation was not set up the same way, since it is much older. Ramius?

IMO - True north is only important because we like the organization of it. It is an artificial creation. Magnetic north can't ever break.

[HairOfTheDog]

Fiddler on the Roof on TCM now!

Sam! - Watch it!

[HairOfTheDog]

Check this OUT!

www.whitehousekids.gov

Sean Astin video interview on volunteerism over on the right of the page and "Flat Stanley at the White House" in the headline.

Flat Stanley..... harumph! See Flat Frodo at the White House, post 32,777

[Wneighbor]

"Flat Stanley at the White House"

That's messed up.

I clicked on the Sean Astin video but nothing happened. Well, I got an empty web media box but nothing ever happened "in" it. white screen, that's all.

[HairOfTheDog]

Hmmm..... worked fine for me.... Maybe you didn't wait long enough for it to load? - It took a minute for me, even on cable.

[HairOfTheDog]

It is a RealPlayer format...

[Sam Cree]

Yeah, I think the nautical one only goes up to 60 knots!

It doesn't do current calculations either, most people do those right on the chart, or else on a plotting sheet.

[HairOfTheDog]

That is interesting, because really, the effect of current on a boat in water is most equivalent to the wind effect on an airplane.

A plane in flight travels with the air mass, and would not 'feel' wind other than it's own velocity.... Like a boat just drifting with the current. The effect of wind on the plane is only in affecting the desired path relative to the ground, like the effect of current on a boat.

The effect of wind on a boat would depend on the sail area of the boat and would be much harder to develop a rule about.

[Sam Cree]

"the added workload of rapidly changing variation when flying east to west at 200 knots..."

That makes sense. 'Course a straight line route accross the continent is going to have a constantly changing psc course but a constant true course.

"IMO - True north is only important because we like the organization of it. It is an artificial creation. Magnetic north can't ever break."

Can't argue with that. However, true north is the same anywhere in the world, magnetic north doesn't coincide much. And while magnetic north may not "break," it does change constantly, even in the same location. For instance, in Miami, it increases by average 9' westerly error every year.

I have been able to use charts based on data from 1820 successfully in the Bahamas, because it's a mercator, same as we use today, lat/lon.

Mariners have been using the Mercator Projection for hundreds of years, I guess, which is organized according to lat/lon. Yeah, lat/lon is an artificial construct, but a good one, aside from being the one everyone is used to. For instance, it probably lends itself to celestial nav much more easily than a system of constantly changing and complicated magnetic lines with parallels.

Not sure if I knew what I was getting into when I asked you that question. But it's interesting.

We don't have cable, so will have to rent Fiddler.