A Question About the RAF's Tucanos

[Richard E]

A few years ago the RAF's Tucano trainers started to acquire a small "bulge" in front of the cockpit canopy, this picture shows a good view of it. Does anyone know what it's for?

Thanks

Richard

Edited September 2, 2009 by Richard E

[smeds]

Could be a GPS dome !

smeds

[Richard E]

Could be a GPS dome !

smeds

That was my initital thought but it looks too large; on the Tornado and Harrier the GPS antenna is a small circular dome on the fuselage spine. I did wonder if it was simply an aerodynamic device to alter the way the air flows around the cockpit canopy.

Edited September 2, 2009 by Richard E

[Dave Fleming]

I suspect it is for the GPS antenna, but the 'bump' is a platform to mount it on and to hold the 'gubbins'. The Tucano doesn't really have any flat surfaces to hold such a thing

[smeds]

I'll ask the ex to find out. She works at Linton on Ouse.

smeds

[TonyT]

Almost looks the size of an ADF antenna, though that should normally be on the underside. I would say far to big for GPS, ours are much smaller.

[Vickers McFunbus]

TCAS I believe - it was being fitted from about the middle of 2006. Tucano studes aren't afforded the luxury of GPS yet IIRC!

[rod mcq]

TCAS I believe - it was being fitted from about the middle of 2006. Tucano studes aren't afforded the luxury of GPS yet IIRC!

Correct - according to the Tucano aircrew at Leuchars last Saturday the bulge is associated with the TCAS system.

[smeds]

Ditto, the ex confirms its to do with TCAS.

smeds

[Wez]

TCAS I believe - it was being fitted from about the middle of 2006. Tucano studes aren't afforded the luxury of GPS yet IIRC!

Doesn't TCAS require a GPS feed? I thought apart from having an individual IFF/SSR ident for an individual airframe it also used GPS to resolve that individual airframe's relative position?

I could be wrong, I haven't worked on any TCAS systems, but I thought it told both the Air Traffic System and other similarly equipped aircraft the proximity of their own "bubble" (for want of a better description) to another "bubble". To do this you'd need relative position which GPS would provide.

That GPS isn't provided to the crew for navigation is another matter entirely...

If there's anybody out there that knows how TCAS works I'd be grateful for a description.

Wez

[andym]

Doesn't TCAS require a GPS feed? I thought apart from having an individual IFF/SSR ident for an individual airframe it also used GPS to resolve that individual airframe's relative position?

I could be wrong, I haven't worked on any TCAS systems, but I thought it told both the Air Traffic System and other similarly equipped aircraft the proximity of their own "bubble" (for want of a better description) to another "bubble". To do this you'd need relative position which GPS would provide.

That GPS isn't provided to the crew for navigation is another matter entirely...

If there's anybody out there that knows how TCAS works I'd be grateful for a description.

Wez

A description here:

http://en.wikipedia.org/wiki/Traffic_Colli...voidance_System

just google TCAS there's a fair bit.

HTH

Andy

[TonyT]

Doesn't TCAS require a GPS feed? I thought apart from having an individual IFF/SSR ident for an individual airframe it also used GPS to resolve that individual airframe's relative position?

I could be wrong, I haven't worked on any TCAS systems, but I thought it told both the Air Traffic System and other similarly equipped aircraft the proximity of their own "bubble" (for want of a better description) to another "bubble". To do this you'd need relative position which GPS would provide.

That GPS isn't provided to the crew for navigation is another matter entirely...

If there's anybody out there that knows how TCAS works I'd be grateful for a description.

Wez

Surely it will work off the Transponder Ident Wez, especially as Mode S is nearly upon us. but Mode C would cover it as it gives position and alt, would it not? there was also trials with a system and I seem to remember seeing it marketed unless I have gone barmy in my old age and that worked on firing the strobes. Bugger me, reading that back it makes it appear I know what I am talking about

will help you out Wez.

http://www.bas.uk.net/data6.html

http://www.airsport-corp.com/modec.htm

http://www.skygeek.com/4138.html

Edited September 15, 2009 by TonyT

[Wez]

Surely it will work off the Transponder Ident Wez, especially as Mode S is nearly upon us. but Mode C would cover it as it gives position and alt, would it not? there was also trials with a system and I seem to remember seeing it marketed unless I have gone barmy in my old age and that worked on firing the strobes. Bugger me, reading that back it makes it appear I know what I am talking about

will help you out Wez.

http://www.bas.uk.net/data6.html

http://www.airsport-corp.com/modec.htm

http://www.skygeek.com/4138.html

Transponder Ident will give you the code of the aircraft responding to an interrogation - as you rightly say, with Mode S this is specific to the individual airframe. Mode C responses don't give position, in a traditional IFF/SSR system there is no navigational inputs for position to be resolved they are stand-alone systems - it only gives an ident (squawk) and altitude. The ground station resolves the squawks position as a relative bearing from the radar, the height encoding allows air traffic to see the reported altitude but as a lot of systems use a Gilham encoder embedded within an altimeter, all it takes is for that altimeter to be incorrectly set and the wrong height is reported.

After following your link to BAS and reading the description of TPAS, its limitations and the refinement given by Mode S and its "extended squitter" I realised where the confusion had crept into my cluttered head. I was researching TCAS and Mode S at the same time back in the day when it was all new and shiny obviously got the two muddled up - silly old fool!

Still, thanks for the links, it served as a useful reminder.

Wez

Edited September 15, 2009 by Wez

[TonyT]

Most smaller civilian stuff the altitude encoder is a totally separate box that simply senses pressure off the line, its plumbed in via a splitter and is set and checked bi annually, additionally Airtragic will soon tell you in the local area if it's giving out spurious readings, surely all the TCAS aircraft then requires is the equivalent of an ADF in the TCAS system to track the transponder signal direction and distance, the mode C giving its height which would then come back to my "it looks awfully like an ADF antenna". If the TCAS has an effective range of say 5 miles then Direction and height is all you need to take avoidance actions when something appears.

Mode S is we all believe is a con to produce a future buy to fly system, that allows charging to be levied for airbourne time, this is supposed to go in everything from Balloons to Gliders, neither of which have batteries on board. Will lead to people not turning it on.

You wanna see some of the junk we have in them these days, the 172 S etc can download from the satellite in real time weather maps and information and display it.

Edited September 15, 2009 by TonyT

[Richard E]

Thanks for the answers gentlemen, that's been very helpful.