[TECH] Max Operating TO Weight

[CS-Hover]

Hi

defining the MTOW for a given profile mission, considering that should be the more limiting weight of the 3 conditions
1 - TO procedure
2 - en-route performance
3 - Ldg procedure

i like to ask (need feedback), to someone that allready have done the calc, what, normally is the more critical condition.

i have done it, and for my numbers (TO and LDG at sea level, and the cruise at 2000 ft, only...) the more limiting condition, for any temperature, is allways the cruise enroute at MCP OEI - i have allready some feedback, telling me that for this cruising altitudes, the en-route portion isn't the limiting factor...

thanks in advance

[helmet fire]

This is machine dependant.

The BK117 for example is not cruise limited at MAUW OEI until about 6000 ft (and that is insufficient climb gradient, not drift down).
The Black Hawk on the other hand is cruise limited right to sea level, but you can always jettison fuel/external load/fuel jugs to make it a non limiting factor.

Also if the landing DA is significantly different from the T/O, then the higher one may be the limitation.

Also, define your limitation? Are you talking in terms of OEI? Airframe? Cat A? Helidecks? Passenger Charter? Drift down? Range? or what?

[CS-Hover]

Helmet, yes i understand that it depends of the machine/profile of mission, but i'm stilll trying to figure out, if i'm making the right calculations (read as: i'm learnig how to do it :ok: )

i'm assuming that TO and LDG distances are unlimited (use runways for now.. - no helidecks, vertical TO or similar - just make it as normal airplane :sad: )
i'm looking only, to find the maximum weight i can takeoff at the first place, that assures all the profile conditions...

so, i check, the weights for
- Cat A
- Cat B
- HOGE
- 2min Power (OEI)
- 30min Power (OEI)
- MCP (OEI)

and check what is the more limiting weight (and condition: if Cat A at TO/LDG using Cat A profiles, if Cat B to the same thing.. or HOGE etc...) for a given conditions of altitude (fixed) and plotted agains't diferrent temperatures - and allways give me the MCP as the more limiting condition ( gives me the less weight)

[Gomer Pylot]

In the GoM, the limit is max certificated gross weight. We just load up to max gross and head out (or in). The only model I'm aware of that won't cruise at MGW OEI is the BO105. We certainly aren't doing Cat A takeoffs or landings, but then you said you have unlimited runway available. There certainly are altitudes at which this doesn't apply, but at sea level we don't often need to consider altitude power restrictions.

Considering the places we operate from, an engine failure on takeoff will likely result in bent metal, but we're flying around a quarter million hours per year, down considerably from the past few decades where one company could fly that much, and AFAIK there have been zero accidents resulting from engine failure on takeoff. That isn't killing us, flying into the water/terrain/platforms with both engines operating is.

[Aser]

CS-Hover, you will NOT find a single answer without a complete scenario.

Gomer pylot:
Considering the places we operate from, an engine failure on takeoff will likely result in bent metal, but we're flying around a quarter million hours per year, down considerably from the past few decades where one company could fly that much, and AFAIK there have been zero accidents resulting from engine failure on takeoff. That isn't killing us, flying into the water/terrain/platforms with both engines operating is.

That's not the point, the oil company CAN pay for a Cat A operation and egpws etc.Just one dead is worth enough.But, this is another thread :=

regards

[Gomer Pylot]

The point is that the cost of one fatality is less than the cost of the extra flights required, at least to the oil companies. If a few people get killed, it's no great loss, as long as it doesn't cost too many dollars/pounds, and these costs have been calculated to a fine point by the company attorneys. It's strictly an economic decision, and the economics do vary by location.

[JimL]

CS-Hover,

The reason you haven’t had too many replies is that you have asked a question that needs to be qualified to be answered. However, I will add some views to give the thread a kick.

Because of your second post (and because it makes it more interesting), I will take the case of a twin that is operating in Performance Class 1 using Category A procedures.

Let me take the case you started off with - a runway with unlimited length for take-off and landing: most modern helicopters can take-off and land using the Clear Area (runway) Cat A procedure at the maximum certificated mass at Sea Level and in ISA conditions - well within limits; the cruise will not be limited at 2000ft (most helicopters would not see a decrease of cruise speed under those circumstances).

Now let’s make it more interesting by raising the temperature until the helicopter is taking off at MUAM for the Clear Area procedure. Because there are no rejected take-off or obstacle issues (your conditions), the first segment (100ft/min at Vtoss at 200ft) and acceleration segment (power to accelerate from Vtoss to Vy) pose no problems and the likely limitation will be the second segment climb performance (150ft/min at Vy at 1000ft above the take-off surface).

Having established that we can climb at 150ft/min at Vy at 1000ft, experience (many calculations) tells us that the cruise limit (50ft/min at Vy at cruise altitude) occurs at approximately 1000ft above the second segment climb limit. The second segment climb is planned at the 30 minute power (which in practical terms is usually the same as the MCP) - which results in the take-off and 2000ft cruise limits being reached at the same take-off/landing mass.

If we now change the take-off or landing conditions - i.e. we shorten the runway, or add obstacles, the take-off or landing mass will be limited but the cruise conditions (at 2000ft) will not.

The most limiting take-off mass will occur when the helicopter has to reject onto a helipad, or has to clear obstacles in the take-off distance required (TODRH) or in the take-off flight path (obstacles in the take-off flight path will require an increase in the climb gradient - i.e. less mass). The take-off mass will be highest for the Clear Area procedure, less for the “Restricted/Confined Area - Short Field” procedures, and least for the Helipad. As the take-off mass decreases so more power is available for the cruise (at the reduced cruise mass).

Jim