Posts about: "Radio Altimeter" [Posts: 6 Page: 1 of 1]¶

Hi canuck, I must admit to being rather jealous that you flew on Concorde! Your questions are particularly interesting as they arise from personal experience. Then to discover that M2dude was involved in overcoming the problem and explains it all so clearly is a delight.
Landing Concorde must have been "quite interesting". When ever I see videos of it; I always wonder how high up the eyeline of the pilots are compared to other airlines and especially when compared to the eyeline of a 747 pilot?(when the main wheels touch) I guess this must change the view of the runway when crossing the threshold. If so was special training required to overcome this as I would have thought that it would initially be tempting(though ill advised) to cross the threshold at too low an altitude? I know that the FE would call out the radio altimeter heights on landing but it must at first be difficult to disbelive the evidence of your own eyes.
I think am right to assume there were no spoilers so on landing did the act of bring the nose down spoil the lift or is that the reason why the non flying pilot pushed the yolk forward once she was down?
Thanks
Nick

ChristiaanJ
During AUTOLAND a flare manoeuvre was instigated by the Pitch Computer at 50' radio, where a fairly simple flare law was invoked. I seem to remember that the law , which used a combination of radio rate (from the RadAlt) and vertical acceleration (from the INS) gave you a commanded height rate of 10'/second at 50', exponentially reducing to 1.7'/second at point of main wheel touch down.
The autoland on Concorde was both extremely accurate and reliable, and an awful lot of guys said they hated using it 'because it can land the aircraft better than I can'; their words NOT mine. (Personally I never bought that one, the guys were just modest as far as I was concerned ). This in my opinion is an absolute testament to the AFCS designers; ChristiaanJ and his colleagues at SFENA and GEC Marconi.
To give the complete final approach story; as the aircraft tracked the glideslope in LAND mode, the autopilot G/S deviation, like most aircraft, was geared as an inverse function of radio altitude, and at 75' radio this deviation was flushed down the loo altogether, leaving the A/P to hold radio rate for just a few feet. At 50' the flare was instigated, and at around 35' DECRAB was commanded, where the yaw channel would use a rudder input alone to 'kick off drift' and align the aircraft with the runway centreline. (Concorde did not employ a fwd slip manoeuvre in crosswind conditions, being a slender delta). The 'final' command was at 15' radio, when the autothrottle smartly retarded the throttles. (The Pitch Computer flare law of course continuing to control decent rate all the way down). On touchdown the autopilot would be manually disengaged and the nose gently (usually ) lowered to the ground. (Concorde was only designed and certified as a CAT 3A system, so there was no automatic rollout guidance. However there was a runway guidance symbol on the ADI, which used a combination of Localiser deviation and lateral acceleration, to give you runway rollout track).
Now the flare law was tested every autoland, at G/S capture, and failure of this test resulted in the loss of LAND 3 status on the landing display panel. The most common defect of all with the Concorde autoland was in fact failure of the flare test, when at G/S capture, the previously illuminated LAND 3 indication would drop all of it's own to LAND 2. A simple changeover of autopilot paddle switches would nail the offending Pitch Computer, which would then be replaced before the next trip.

Dude

Sorry - missed the second half of your question.

We didn't have any trouble flying procedures drawn at 185kts. If necessary you could fly and manoeuvre at 190kts IAS, it was just very thirsty and noisy like that. We wouldn't manage 10miles out at 210kts on a SID, but I didn't ever encounter a SID like that. In the case of terrain-constrained ops (which may cause the above) we would have to come up with some usable aternative.

The 'tightest' destination I recall was Sondrestrom (as it was still called then). Although noone in their right mind would land a heavy on RW28 (as it was) we had to demonstrate it in the sim. It really wasn't an issue in terms of turn radius, the trouble was the radalt ramping caused by terrain combined with our higher speed. It was just possible to avoid the dreaded GPWS.

Of course when you took the real thing there we just landed staright in on 10.

I am not in any position to offer an answer t o your question XV105, but may I offer a 'speculation'? I would hazard that the projection you highlight might be a Radio Altimeter aperture? It looks like a casting or even a forging and far too fancy for a drain. It seems to me the surface in which the aperture is 'machined', would be pretty much horizontal in the landing configuration and thus offer accurate height of the centre of gravity perhaps? Given that the cockpit would be many feet above that, it makes sense.

Errr..... I'll get me coat.

looking at the Concorde instrument panel lately brings up a couple more questions:

Why is the radar altimeter positioned where the altimeter is normally placed ?
Did the designers decide it was more important for the radalt to have a more
prominent position in the pilots scan for a particular reason ?

While on the subject of radar altimeters Concorde has a fairly unique VSI, at least
for civil aircraft, it's vertical strip presentation is a clever way of saving space in
a compact, crowded panel.

But in the era that Concorde was designed a popular option on other jet transports was a vertical strip radar altimeter.

The radalt, after all is an instrument that is only used very briefly at the final stages of the approach and landing and is
situated accordingly, easily seen but not part of the classic 'T' airspeed, attitude, altimeter, HSI, of primary instrumentation

But in Concorde it literally has the most 'prime location'

For some reason I wasn't consulted on cockpit design despite going to school
with John Cochrane's son but surely a more conventional design would have had:

Altimeter, top right , VSI bottom right in their usual place and a vertical strip radalt
taking the place of the vertical strip VSI.

Curious as to the design choices, anyone with further insight ?

I'll always bow out to the pros did the actual design and flying - but this book quote may be one insight.

The Concorde , Christopher Orlebar, 2017, p. 55

From the point of view of the most critical phase of human piloting, the radio altimeter was far more important in the scan than the baro altimeter. Baro altitude was generally a problem for the automated part of the envelope, or the FE, while the guys up front needed only spare it a glance (most of the time) only twice a minute or so (or less often?)