Bristol Britannia Record Flight

Maybe it wasn’t the radio altimeter they were using to determine absolute height.

I believe what this is alluding to is pressure pattern flying, to determine where the winds were.

On those old weather radars, was there not a return that was evident at the bottom of the screen caused by a side lobe pointing straight down toward the earth’s surface?

I seem to recall that if you slected a short range on the set, with the scanner tilt angle set to zero, you could relate the ring to the range scale and it became a crude measure of absolute height. By referring to it occasionally, marking it’s position with with say a chinagraph, and seeing if it showed a climb/descent you would be able to determine the change in atmospheric pressure in the area you were flying in, by comparing it with your 1013 standard setting.

Very crude, but effective, and usable above the 2500ft. limit of the rad. alt.

Of course I could be talking a load of tosh…….

Nevetheless, El Al, did do some pretty impressive flying with their Britannia fleet. I also believe they felt they were held back from getting it into service as BOAC had to be the first, and in corporation style, were dragging their feet.

Ndege.

Thanks guys, that appears to be a satisfactory set of explanations. Anyway Roy, as you have a link to G-ANCF on your reply, and this is a Brit thread, here is a photo of her at Paya Lebar, Singapore, taken if I remember correctly in 1970.

According to Wikipedia:

In civil aviation applications, radio altimeters generally only give readings up 2,500′ above ground level (AGL).

http://en.wikipedia.org/wiki/Radar_altimeter

This ties in with my experience as a radar fitter of 40 years standing (and sitting), where the range is limited by the pulse repetition frequency, and the power output, which for a radar pointing directly downwards and primarily used to aid landing is relatively low.

I’m still in the dark about height restrictions on Rad Alts.

I believe the problem is basically one of signal scatter. The higher you go, the wider the ‘beam’ and so there’s not enough to bounce back and give you a decent reading. Apparently a pulsed radar altimeter will work at high altitudes (satellites use them for terrain mapping) but these for some reason are not suitable (or required?) aboard aircraft.

Amazing how much trivia you collect along life’s journey!!

Roy.

We seem to have drifted way off course with this thread, perhaps it’s time to start a Historic Aviation Persons Forum!!!!!

The story was that the British POW’s who the Japanese used to extend the Kai Tak runway deliberately tried to sabotage the concrete mix. It worked after a fashion, the runways started to break up big time around 1968/69!!!

KeithMac 🙂

A bit like the story of one old codger saying to his old army pal “George, you remember them putting bromide in our tea when we was in the trenches to keep our urges down?” “Yea, I remember that” replies George. “Well, I think it’s beginning to work” 😀

Roger Smith.

Hi Ken, Well it’s a small world indeed. Both my daughters went to your old school, and used the Kai Tak pool! Sadly I saw the closure of KaiTak and the move to Sek Kong, now alas it’s all just memories.

The story was that the British POW’s who the Japanese used to extend the Kai Tak runway deliberately tried to sabotage the concrete mix. It worked after a fashion, the runways started to break up big time around 1968/69!!!

KeithMac 🙂

I asked about Lion Rock because I lived just below it in the late 70’s while stationed at Kai Tak.

KeithMac

I went to school just below it – St Georges forces school (my old man was in the Army – stationed variously at Gun Club, Sek Kong & Stanley.

We also went to RAF Kai Tak to use the swimming pool – our school didn’t have one!

All this in 1957-60 – when Kai Tak had Venoms.

And – on a Britannia note – I seem to remember a Brit landing heavily on the old Kai Tak runway – and bending a prop blade?

I also have a vague memory that the Capt was called Duffey ??

They used to fly directly over our flat……..

Mind you all this is 50 years ago – when I was 10-11 – so I may be talking complete rubbish – memory being totally unreliable 😮

I do remember playing down on the ‘new’ runway construction site – amongst the Caterpillar tractors and the huge dumper trucks as they delivered rocks to make the runway out to sea.

Ah! memories……………..:rolleyes:

Ken

Hi LionRock, Actually I’m sure I read the article to which you referred, however the significance escaped me at the time. I’m still in the dark about height restrictions on Rad Alts.

I asked about Lion Rock because I lived just below it in the late 70’s while stationed at Kai Tak.

KeithMac

Britannia Record Flight

Hi KeithMac

The article was inferring that by flying at a constant barometric altitude one is flying a long a line of constatnt pressure which in a temp rise would gain in altitude, however this altitude gain would only be recognised by the Rad Alt not by the baro Alt as it will remain constant.

If I knew how to post an attachment on here I would attach the article
concerned.

PS: Been to Hong Kong but that is the only connection

Hi Lion Rock, As I said I’m not an avionics expert, perhaps your right, the rad alt may have a limited altitude function. The problem with the Barometric type is that if you have set it at the normal pressure of 1013.2 mb and you are approaching an airfield to land, the altimeter tells you your altitude above sea level, not your actual height above the ground. A Rad Alt will. So perhaps the usefullness of the Rad Alt is limited to that sort of situation, take off landing and low level flight, therefore no need to have a huge range of operation.
I am also at a loss as to how a jetstream would change a Rad Alt reading, I’d like to know how bouncing a radio signal off the surface of the terrain underneath you is affected by entering a jetstream. I’m also a little baffled by the rise in temperature. According to Bernoulli’s theorem of streamlined flow the temperature should fall with a rise in flow velocity, which I thought would be the case in a jetstream – any phyisicists our there to explain this?

P.S. I’m intrugued by your “Lion Rock” tag – is there a Hong Kong connection?

Brittannia Record Flight

Thanks for the replies.

The Radar Altimeter in the last aircraft I flew -ATR 42 & 72 – only gave a read out below 2500ft anything above that did not give any indication irrespective of travelling over land or water which begs the question howdid the Britannia have that information at 25000ft!

The article was taken from the Presidential Address of the Royal Institute of Navigation in 1986, I understand the person giving the address was the Navigator of the Britannia on its record flight!

Where was the article?

The date of the flight was 18th/19th December 1957, and it is mentioned in the two most recent books on the Britannia, one by Charles Woodley and the other by Frank McKim. I mentioned it in an article I wrote recently, about the 50th anniversary of the first non-stop transatlantic service to be operated by a gas-turbine aircraft. This was BOAC Britannia G-AOVC, which left Heathrow for Idlewild on 19th December 1957, just a few hours after the El Al Brit had gone the other way. The anniversary did not get the news coverage I thought it deserved.

Andy A.

I’m not an avionics specialist but the difference between a barometric altimeter and a radar Altimeter is the fact that a barometric one shows actual altitude above sea level whereas a radar altimeter shows the height above whatever your flying. So if you were over a 10,000 ft mountain at a barometric altitude of 25,000 ft, your rad alt would read 15,000 ft!! So I think rad alts do work above 25,000 ft. Confusing or what!