-6 on the RA on the ADI

[crvm 0]

Just settling an older topic that was brought to my attention today. FYI, the -6 shows on the ADI when the nose of the aircraft is in contact with the ground. Best Wishes,Randy J. Smithcrvm@iwon.com" A little learning is a dangerous thing"

[Guest]

Hi RandyIs that because the sensor is situated forward of the main gear and corrected for the landing pitch angle?Just curious

[crvm 0]

I would guess the sensor is somewhere ON the nose gear and activates by compression of the gear upon T/D. Best Wishes,Randy J. Smithcrvm@iwon.com" A little learning is a dangerous thing"

[crvm 0]

''''

[Guest]

Hmmm... I don't really get itWhy would it need to be activated to show -6? I guess that is feet above the ground ;-) And why when the nosewheel is compressed? Maybe this is already discussed in the related topic. If so please excuse me! :-)Cheers

[teropa 4]

Hi,The RA is designed (calibrated) to show "0" when the aircraft touches down in the correct landing attitude. Now, assuming (and as I recall this really is the case) that the RA sensor is located in the nose gear, it would naturally show somewhat LESS once the nose itself touches down. In the landing phase the pilot really needs to know when the MAINS touch down, rather than the nose gear. If the pilot would expect the nose to come down first, then he/she needed some serious training :D.Thus, as the sensor is in the front, it shows less than zero, once it's on the ground.As simple as that.rgds,Tero

[Guest]

HiTero, thank you! You confirmed what I thought at first!Randy, I thought you meant some kind of switch activating the RA to show -6 when nosewheel compressed. TGIF :-beerchug

[Guest HPSOV]

Each radio altimiter has 2 sensors, one to send the pulse and one to recieve it. The sensors are located under the fuselage about 5 metres behind the nose gear. In the flare attitude (5 degrees nose up), the radio altimiter is calibrated to read 0 as the main gear contact the runway with full strut extension. As the struts compress, and the nose is lowered the sensors drop 6 feet from this flare position, hence the reading of -6 on the ground.This is a picture of one of the sensors for the left radio altimiter.http://www.users.on.net/roope/KIF_0628.JPG

[Guest Ian_Riddell]

"The sensors are located under the fuselage about 5 metres behind the nose gear."How soon they forget, eh, HP? :-hah.Here's a drawing of a similar setup (on a 747-400) which I posted a few months ago (showing how the RA system is calibrated).http://members.ozemail.com.au/~b744er/RadAlt2.gif"Each radio altimiter has 2 sensors, one to send the pulse and one to recieve it. "For the technophiles: Actually, it's a continuous wave, rather than a pulse (unlike ATC and DME) ;-) A weird, frequency modulated frequency modulated 4.3GHz signal.Cheers.Ian.P.S. BTW, what a dodgy antenna sealing job!.... Looks like one of mine :-hah The brown sealant is carcinogenic, so we have to use clumsy rubber gloves to handle it... hence the mess. Sometimes a sealant with a too long curing time is applied by mistake... turning the bottom of the fuselage into a brown streaked mess when the aircraft builds up speed :-( It's important for the metal base of the antenna to be properly electrically bonded to the fuselage or you will get erratic height readings. The sealant prevents water getting inbetween the antenna and the aircraft skin and helps with aerodynamic smoothing.

[Guest Ian_Riddell]

Here's a shot showing the location of the Rad Alt antennae... i.e the 6 small flat plate antenna closest to us.http://members.ozemail.com.au/~b744er/767/RadAltAntennae.jpgCheers.Ian.

[Guest]

When sealing antenna's I find it best to tape off the antenna and the airframe just leaving a narrow gap for the sealant, then appling the sealant after that just run the rounded end of a tounge depresser around the antenna which gives a nice looking smooth form, remove the tape. I then place some soft soap on my finger and run it around the antenna. It looks great.

[Guest Ian_Riddell]

Grrreat in theory, jeh1... :-) It's the tape removal that gets me every time...especially on VHF antennae, where the sealant-contaminated tape falls against the blade...or wraps around your arm. Liquid soap is a godsend... as long as the paper cup you have it in doesn't blow way on windy days :-hahGlad to hear there's a fellow sufferer out there (antenna sealing is a pet hate of mine).Cheers.Ian.P.S. I get plenty of practice sealing my leaky shower, but it still doesn't help.