A term that's missing in helicopters is Vx (best angle of climb speed). The reason it's missing is that if you can climb vertically in the hover, Vx is obviously zero. But in other cases, (like after an engine failure), Vx would be a) so variable that it would be a nightmare to caculate b) probably be below an airspeed that would indicate reliably So, the term Vtoss was developed - it's below Vy, and a repeatable airspeed and gives a better angle of climb than rate of climb, because for the time you want to use it, you're more interested in clearning the ground in a short distance than in a rate of climb. For what it's worth....
Shawn, you are (obviously) correct in describing the general origin and nature of Vtoss, but it is not correct to say it is less than Vy; it generally is but not always. (B212 clear area take off for example.)
212man: I stand corrected, but would ask two questions - a) why would you go to a speed higher than Vy? Doesn't seem to make sense. b) is this the same flight manual supplement that has the Vtoss defined as 25 knots plus the windspeed? If so, then you need to have a weather reporting station in order to be legal to use the procedure, as pilots can't determine the wind speed (legally that is). When I was at Transport Canada we tried to get that supplement changed, but to no avail.
Sikorsky uses Vbroc to define the speed needed to keep broccoli fresh. Vy is the speed for going to the YMCA.
Who knows which abbreviation to use? I love the different terms for turbine temp (T4, T4.5, T5, T6 T7, EGT TGT TIT ) and the terms for Gas producer speeds (N1, Ng,) and power turbine (N2, Nf, Np).
The increase in ground speed must be desirable for Bell, thus the adjustment. I might hazard a guess that the Vtoss needs are somewhere the angle of climb, ans well as rate. Could be the increase in speed toward Vy gets them an even better angle for the first segment gradient requirements.
I would imagine that they do not need a meteorologist to get the wind because the climb can be met at zero wind, so the procedure does not need accurate wind to be flown safely.
Above is just poking around at reasons, I really am as surprised as you. Say hi to folks at HAI for me.
I'm sure that 212man intended to say that Vtoss can tend to, but is limited at, Vy.
An increased Vtoss can be used to eliminate a mass limitation due to first segment performance - at the expense of increased Take-off Distance Required (clear area / runway operations). At the limit - i.e. Vtoss = Vy - the first segment and level acceleration are eliminated as the helicopter is in the second segment climb configuration when it achieves Vy.
It is more usual to provide tables with reducing Vtoss - to limit the take-off distance required; thus reducing the size of the required heliport and airspace (short field / restricted area).
More modern RFMs provide tables with variable: TDPs; drop downs; reject distances; Vtoss; and take-off distance required, thus profiles can be configured to meet the constraints of the take-off site. This can permit the pilot (on the ground) to tailor the profile and mass to the more limiting element of the take-off site.
The latest helicopters already permit these profiles to be flown accurately by the autopilot (once the TDP has been reached and if a Vtoss is used) thus minimising the distance required in the event of an engine failure.
Wind accountability can be used in the calculation of some elements of performance (and that is why regulations require it to be factored to 50%).
I remember the term Vbroc first from the good ole 58T in which it was easy to keep the broccoli fresh because the heater (that's the air-bleed one as fitted to our versions, not the old parafine-burning stove version ) was particularly ineffective and could only maintain the cabin about 2 degrees higher than outside on a cold winter's day. As for going to the YMCA - can't mention that any more since the Village People version of the song
I'm sure 212 man also meant to say that Vtoss may equal Vy on a helicopter where the power margin OEI is such that at higher weights it is necessary to acclerate to Vy to achieve Category A or Class 1 performance (depending whose rules you are operating to)
The French (= Eurocopter) like to define Vtoss (or should that be V2?) as the speed required to maintain a 100 feet per minute rate of climb, or better, OEI on the first segment after TDP, with the landing gear extendeded (in the case of a retractable u/c helicoptere) at 2 minute power (or maximum contingency power in some Flight Manuels) and maintain a gradient of climb of 3% or higher. Of course, this is further complicate by whether one is talking of JAA, CAA, FAA or ICAO definitions where all sorts of other terms like net rate of climb or gross rate of climb are there to confuse.
I'm not sure there is as much confusion as you have indicated - we live in an era of harmonised regulations and the certification basis for all western aircraft (and now probably the Eastern European) is FAR/JAR.
As far as CAA regulations are concerned, they are a feature of the past as EASA (using FAR/JAR 27/29) is now the certificating authority for Europe.
Even ICAO Annex 8 is in the process of being amended to recognise that fact.
Unfortunately, there is all too much confusion. Many pilots flying helicopters outside Europe, are flying in machines which were certified many years before FAR/JARs were even being thought about. It is entirely possible where I work, to pick up a DGAC flight manual published in the 1980s and yet the UK CAA manual for the same aircraft, published at the same time, uses different terms and conditions for its performance pages.
The regualtions may now being harmonised, but there's no chance that old Flight Manuals will ever be updated and they will still be full of terms and conditions that do not apply in the 21st century. You may have many pretty, new helicopteres in Europe, but out in the third world most of us fly helicopteres which, like their pilotews, are old, tired and no longer performing quite as they were when new (though, hopefully, all the problemes one has with new machinery have been recognised and sorted out)
If I may offer a consolation - operational regulations are retrospective (unlike certification); aircraft that have been certificated to Category A can meet the requirements that are specified. Those aircraft that have been certificated (by the UK CAA in BCARs or affilated regulations) as Category A (by default) meet the operational requirements.
Only if the operational regulations that you are using specify performance requirements (and some do not) do you have to manage this situation. On investigation, it may be clear that where the certification basis is not FAR/JAR compatible, there is a translation path on a once-and-for-all basis.
Such is the price of progress as a look into the complexity of AC 29-2C (guidance on certification) will reveal.