V Speed Question [Archive]

Courtman

30th Apr 2002, 20:12

Hiya!

As a fixed wing I'm not sure about this, but I'm being pestered by a colleague who's studying his dispatch licence and wants to know what vTOSS is?!

I think it may be linked to helicopter take-off safety speeds, but having never flown one I'm not sure. Can any of you rotorheads help my colleague out?!!

:rolleyes: :) :) :rolleyes:

The Nr Fairy

30th Apr 2002, 20:21

Vtoss is the speed at which you REALLY start enjoying yourself in helicopters.

And seriously, it's Take Off Safety Speed - the twin gurus out there will correct me if I get this wrong but it's the speed at which you can safely climb away after an engine failure, before that you're committed to landing back on.

And check out this Ray Prouty article (http://safecopter.arc.nasa.gov/Pages/Columns/RayProuty/pdf_files/CRITICAL_TAKEOFFS.pdf) for more info.

Courtman

30th Apr 2002, 21:56

Thanks for that one!! Another problem solved by PPRuNe....!

rotorque

1st May 2002, 08:33

Courtman,

Actually the vTOSS is the speed that allows controllability of the helicopter with regards to yaw control. Very similar to the blue line in your plank things.

The decision to land or fly away after an engine failure, in a helicopter, is refered to as the CDP or critical decision point. If an engine quits before this speed you do not have a choice - you will land. After this speed you may well be able to fly away with one engine out.

The speed that allows you to climb at the best rate is usually faster than your vTOSS. This speed is refered to as vYSE.

To put it in perspective, the CDP for a BK117 is around 40 kts (depending on conditions). The vTOSS is 50 kts and the vYSE is 65 kts. Each aircraft is different but these figures are relative to them all.

Hope this helps.