Curvature of horizon?

[ACW599]

Apologies if this isn't quite the right forum to ask this question, but I suspect military aviators may be best placed to come up with an answer.

I've recently been re-reading 'Night Fighter' by C F Rawnsley and Robert Wright, which to my mind is a classic of aviation literature. In one of the chapters Rawnsley describes a high-altitude test flight in a Mosquito XV, and seems to imply that from 43,000ft he could see the curvature of the earth ("It was the first time that I had seen for myself that it really did curve, and that the earth was round").

The highest I've ever been was 47,000ft in a Hunter (on a gin-clear day over South Wales) and whatever flight levels 747s and the like habitually attain. However, on no occasion have I been aware of seeing curvature of the horizon, and a bit of mathematics suggests it's unlikely. Any FJ folks who've been there care to comment?

John

[artyhug]

You mean the earth isn't flat? Damn I knew that Copernicus bloke was on to something...........

Might explain why my studes are always failing the Nav phase though...........;)

[Raymond Ginardon]

Been to the high fifties a couple of times (most certainly a 'guest appearance' rather than sustained), in the nanosecond that I looked away from the engine instruments, I did not notice the curvature of the earth. Been to 48 a lot, a more determined search did not reveal any sign of curvature. I think a lot of the 'curved earth' perception comes from photos - I take loads of photos and (because the lens is wide angle?) the earth appears curved - makes for a nice photo, but it's not what I saw with my Mk1 eyeball.

Ray

[bluetail]

once got up FL37.5 in the old Nimrod mighty war platform, (on an air test mind you so not much gas) which is a long way up for the old girl.

Not a chance of seeing the curve that low, but I,ve also been down at 200ft in one which is definately a bit low for comfort

[safetypee]

The curvature is just discernable when ‘above FL 550’ (Lightning days), the effect is clearer as the daytime sky darkens at altitude.
Modern jet pilots can deduce curvature due to the HUD horizon indicating the local geographic level, which is not aligned with the observed horizon, this is depressed due to the curvature of the earth.

[Vage Rot]

Not visible at FL 450 - the highest Ive been to.

[akula]

Hello Bluetail,
Have recently voyaged to FL410 in the Mighty Hunter, it may as well have been Mars for the venerable warbird....

ALWAYS assume NEVER check
ps. no curvature visible

[Pontius Navigator]

Done 410 in a Mark 1 Nimrod. Things got very quiet.

Reckon you can see the curvature at sea level on certain days too.

[BOAC]

I'm with safetypee

[rivetjoint]

A friend who regularly does 70k+ says you can see the curvature but it never goes dark just a deep blue.

[Mr C Hinecap]

Yup - it can be seen at sea level sometimes. It seems to be more to do with the width of your field of view. I've only seen it when I had an unbroken view left to right that was all sea, calm and wider than my field of vision. On board ship & certain coastal places.

[Yeller_Gait]

this photo was taken at FL350 earlier this year, over Greenland at about 3am.

http://uk.msnusers.com/4n0q7i3tstdoujmbnenv40ii63/Documents/P5290058.JPG

It just about shows the curvature of the earth.

[kippermate]

Been to F420 before, but we were in a horrendous CB, very bumpy, and I was too scared to look outside!

:yuk:

kipper

[adrian mole]

During a ride in Concorde (G-BOAC) on hot weather trials in the Far East (circa 1975) I attained FL650 several times. Rivet, the earth is round and the sky was very dark purple going on black. I even took some photos...

[Kolibear]

I had a quick trip round the Bay (of Biscay) in Concorde a few years back and you could see curvature, the sky was dark and the windows were pleasantly warm.

[rivetjoint]

adrian mole, probably the David Clark visor effect then!

[Navaleye]

I saw on a Concorde trip. I think it was about 55k ft to JFK.

[BEagle]

Went a fair bit above FL 500 in the Vulcan many years ago. But the view out of the windows was so limited, 'twas hard to tell whether or not the horizon was curved. Besides, we were turning hard at the time to pi$$ off the Phantoms which were failing dismally to get into missile launch parameters....:E

[buoy15]

Managed FL415 in the middle 70's returning from a direct NavEx to Bear Island (to eat the rations) at about 2000 in July, and the curvature was noticeable when looking north. Not much else though:zzz:

Aussie quote

"You've only got too much fuel on board when your on fire!!"

[Nick Figaretto]

Best way to see the curvarure of the earth, is with your eye's pupil just slightly above sea level when you're bathing in the sea on a perfect, calm day.

[West Coast]

FL510 and flat as Kansas. Newspaper was blocking the way however.

[NVG_CAT3_retd]

Been to FL 000.5 but the trees got in the way.

[ScienceDoc]

Or try to look above a long wall running along the seaside. You will definitely see the curvature then.

[JessTheDog]

Try a round-the-world cruise. You'll end up where you started, so it must be round! ;)

On a serious note, I think our ancestors worked out the Earth's curvature before it was circumnavigated - perhaps by the shadow of the Earth cast on the Moon. Any thoughts???

[D-IFF_ident]

Try here:

http://mintaka.sdsu.edu/GF/explain/atmos_refr/dip.html

Makes perfect sense to me....

Turns out that I am 1.5 meters tall, I have 6.4 eyes and Vr is 106Kts. A square 3/6.4 x 106 is about 0.00068 times the spped of light and Adrian is 0.039°.

Hey, if that's what the Eng gets then who am I to argue.

[Beeayeate]

Curvature of the horizon is an optical illusion caused by the fact that the Mk 1 eyeball is itself spherical. Therefore it stands to reason that you will see any sufficiently long straight edge as a curve. I mean, all the maps I've ever seen have straight edges so the horizon must be straight . . . innit!

:rolleyes: :ok: :ok:

[BEagle]

E pur si muove!

.

[Beeayeate]

You've got a mauve cat? :confused: :rolleyes:

[BEagle]

No purple pussy - it's what Galileo is alleged to have muttered sutto voce when forced to agree that the Sun rotated around the Earth and renounce his theory that it was the Earth which rotated around the Sun!

"It does move, all the same!"

A motto I've often though of adopting when faced with senior idiots who won't accept clear facts, prferring to stick with their established dogma!

[Beeayeate]

Aha! Mr Galilei of Florence - who didn't get an apology for 359 years!

Without established dogma we'd all have to make it up as we went along. Wouldn't that be fun? :rolleyes: :ok:

[Pontius Navigator]

I think I might be able to get a photo of the earth curve. How would I get it on the forum?

[Beeayeate]

PN, check your PMs.


:ok:

[MobiusTrip]

FL 650 (and geometric hight ++) pan as a flatcake.

Perhaps it's a perception thing? Some people are saying they can see it at sea level others are in the flat brigade all the way up?

I have some pictures that 'show' the curvature of the earth (the SOP bolt the camera to the glareshield 'over the shoulder' jobs), one was taken at 370 - It certainly didn't look curved at the time though.

"Fascanating.........."

MT

[ACW599]

Very many thanks to all those who replied; it's been extremely interesting. Sounds as though the consensus is that there's no consensus!

John

[JessTheDog]

It appears you have to be very high indeed to see the whole of the UK!

From BBC news website

British engineers are preparing to push the limits of aeroplane technology.

Boxed and set: Zephyr sits in its packing case ready for despatch
Zephyr 3, a solar-powered propeller-driven vehicle, is set to fly to 132,000 feet (40 kilometres) in the next few months.

Only experimental rocket planes and the space shuttle will have gone higher.

It will rise into the stratosphere to take pictures of a giant helium balloon that will attempt to break the world altitude record for a manned envelope.

But Zephyr - built by QinetiQ, a commercial offshoot of the UK's Ministry of Defence - is more than just a flying camera gantry. The prototype vehicle, and others like it, may soon lead to a cheap alternative to space satellites.

Squadrons of these high-flying solar planes could be stationed permanently in the sky, for use in environmental monitoring or to supply immediate mobile phone coverage in remote areas, perhaps in a disaster zone.

The military, too, believes such platforms will have applications above the battlefield.

Zephyr's chief designer, Chris Kelleher, told BBC News Online: "You can communicate over long distances; at the altitude we are going to, you can see the whole UK, so you can see a very long way.

"You are operating in the sort of region that currently relies on low-Earth orbit satellites but these make perhaps two passes in a 24-hour period, one of which is in the dark.

"These aircraft, if we meet the night-storage of power issues, would operate continuously and indefinitely over a city or battle theatre."

The US space agency (Nasa) has developed a solar-powered plane, Helios, which has already gone to 96,000 feet (29 km). But Zephyr's smaller size will allow it to go higher still.

The British vehicle has a 12-metre wingspan and weighs little more than 12 kilograms. Its Mylar skin covers a carbon composite frame; the solar cells on the top of the wing provide 1 kW of power to five motors.

The model plane motors have been adapted for use at high altitude
Its intended operating altitude has presented engineers with unique problems.

Zephyr will have to cope with extremes of temperature. Sun-facing surfaces will get very hot; shaded regions of the airframe will experience cooling down to about minus 50 Celsius.

A special "space grease" is needed to protect motor bearings. Consideration has also been given to the performance of batteries and electronics to ensure they continue to perform efficiently throughout the flight.

Zephyr is actually quite fragile; it has to be picked up in several places at once or it will snap.

For the ballooning record attempt, Zephyr will be tethered to the envelope's gondola on a 450-metre line. The tether will attach to the end of the wing.

At launch, the plane will be raised on a special beam with its wing in a vertical position. For the first 30,000 feet (9 km), Zephyr will be a passenger under the gondola.

Then its motors will be opened up by one of the balloon's pilots, Colin Prescot, and the vehicle will slowly circle and raise itself into a position to take pictures of the giant balloon.

A high-resolution camera will feed images direct to Earth; a broadband video camera will send moving pictures via microwave link, first to the gondola and then down to Earth.

"Zephyr is stunning - very ambitious," said Prescot, who will control the plane through most of the balloon journey.

"I have a control box with large buttons to direct the trim and yaw of Zephyr by radio link. The buttons have to be big because my fingers inside the space suit I'll be wearing will be very podgy.

"I have a video screen in front of me to keep track of it and I will be able to see it out of the corner of my visor."


At the peak altitude, Zephyr should be making three circuits every two minutes, travelling at a speed of 70 metres per second (155 mph).

Even if Zephyr reaches the intended altitude it will not actually set any official records. The rules for its particular class of aircraft demand vehicles take off from the ground.


All testing points to an attempt on the balloon record in the next three months
"This flight is about validating the assumptions we have made about operating unmanned aerial vehicles (UAV) at high altitude," Paul Brooks, the QinetiQ manager in charge of the Zephyr project, said.

"For future applications, we don't think you'll need to go so high but we're going there because it will be very demanding and will prove the concept."

Colin Prescot and co-pilot Andy Elson plan to make their balloon journey some time in the next three months. As tall as the Empire State Building, their manned envelope will be the biggest ever flown.

The balloon will be launched from a ship off southwest England and will travel out into the Atlantic, taking perhaps 11 hours to get up and down.

British Airways has agreed to move the flight path of high-flying supersonic Concorde further to the south to take it away from the balloon.

[emitex]

Sorry to be picky;

"British Airways has agreed to move the flight path of high-flying supersonic Concorde further to the south to take it away from the balloon.

So Zeyphr's a bit behind schedule, eh?

[JessTheDog]

Excellent spot!!!

Sorry to be picky;

"British Airways has agreed to move the flight path of high-flying supersonic Concorde further to the south to take it away from the balloon.

So Zeyphr's a bit behind schedule, eh?

It was a QinetiQ project, after all!!!:E :E :E

[Pontius Navigator]

Had a look at my polar photo, unfortunately what the camera saw did not accord with my memory. It was a cheap camera anyway and shot through a small cabin window didn't get much horizon in.

[ehwatezedoing]

You guys doesn't know where to look!!!! :p


Spotted nice topless "curvatures" once at FL001....along a beach....

Sooooo, not high & fast but low & slow:ok: