MCP table on a R22

[34']

Can anyone give me a simple explaination of what 'FULL THROTTLE' is actually telling us we can use when it comes to the Max Continious Power Table?

thanks

34'

[Camp Freddie]

I believe its telling you that anything to the right hand side of the "full throttle" line is theoretical. i.e. you cant do it because you have no power available, you are at "full throttle"

regards

CF

[Arm out the window]

All it's saying is that when you're low and cool, the engine can produce more power than the flight manual says we're allowed to use, so we have to artificially limit how much we let it make.
When you get in hotter and/or higher conditions, the engine can't make that much power even with the throttle butterfly fully open - the 'full throttle' area of the graph.

[34']

Thanks for the answers so far.

So in the 'Full Throttle' zone..I can fly or I can't? What power if any can I pull or does it mean the engine can't produce enough power to keep the RRPM constant if your in the "Full Throttle' zone. Am i understanding it correctly?

Full Throttle zone = Can't fly as RRPM can't be maintained even at carb full throttle

34'

[Hiro Protagonist]

Here's my attempt at a quick and dirty explanation...(I hope it's at least mostly right :E )

In order to take it easy on the engine and other components (ie. blades, power train), the R22 Beta II (like most helicopters) limits the horsepower the pilot is allowed to use.

When you increase drag on the rotors, (for instance by raising collective or applying more left pedal) the rotor rpm will decay, sensing this, the governor (or the pilot) will increase throttle to maintain a fixed rpm. When the throttle is opened more, the manifold pressure increases. (remember the thread on THAT subject a while ago?, maybe we should talk about carb ice too :E )

So, when we lift the lever, manifold pressure goes up. Now if we comply with the manifold pressure limit for the current conditions, an engine (In a R22 Beta II) in perfect condition should be producing 124 horsepower (or 131 for five minutes when you've added your .9 or whatever it is (it's been a while)). This is your limit. We can ignore the limitations and pull until the Nr starts to droop, and get away with it a time or too, but eventually the fact that you're pulling more than 121 hp out of the engine, and putting that through the drivetrain, and loading the rotor with that extra load might come back to bite us with damage to the aircraft.

As the air gets less dense, the normally aspirated engine in the robbie can't produce as much power, and above a certain density altitude the engine can't produce more than 124 horse power, and at that point you're allowed to pull it till Nr droops, because you're not exceeding the power limitation of the aircraft.

So...Yes you can fly there (but you might not be able to land there!) This often catches people by surprise when they take a robinson which they are used to flying at sea level, and go up high with it. At sea level, you get 124 horse power, but there's always more there if you need it which is a nice safety net. When you go up high the safety net disappears, and you'd better know you have hover power or a good exit strategy before you get on the backside of the power curve.

[Arm out the window]

You just have to think about what that chart's telling you.
In some atmospheric conditions, the engine can produce more grunt than it is 'allowed to' by the designers.
This is a common thing - depending on helicopter and engine type, there may be a limitation on the engine itself (eg don't pull more than a certain manifold pressure under certain conditions or damage may be done to the engine by internal pressures greater than it was designed for), or a stated maximum torque allowed to be applied to the drive train.

This chart says "In the 'non-full-throttle' zone, don't pull any more than this much MP or you may damage the engine. In the 'full-throttle' zone, your engine is producing as much power as it possibly can anyway, so you don't have that problem."

To clarify, looking at the R22 Beta 5 minute power chart (O-320-B2C), there are a bunch of different alt/temp combinations that would give you a MAP limit of 24 inches - eg Sea level & 0 C, 1500 ft & +10 C, 3000 ft & +20 C.
This tells you that if you're flying at any of these, don't pull more than 24 inches or you may hurt the engine. Note that for a given height, as it gets warmer, you're allowed more MAP.
However, following the 24 inches line across, when you get to about +25 C and 4200 ft, you reach the full throttle line. If you were flying under these conditions and raised the collective from some low power setting, you could expect the MAP to keep increasing and rotor rpm to be maintained until you got to 24 inches, where the throttle butterfly would be fully open. Raising the collective any more would cause the rotor rpm to droop, because the engine would already be giving you as much as it could.

I've cut a short story long there, but basically, to the left of the full throttle line, you have to physically stop yourself pulling more MAP than you're allowed. To the right of the line, you won't be able to reach the MAP indicated at the intersection of your temp and altitude - the engine won't do it. Yes, you can fly there, but the maximum collective you can pull will be limited by engine capability rather than your adherence to the limit MAP chart.

[robsrich]

Just a reminder that when you pull over the limit, it is not only the engine that could be damaged, (or not reach it’s TBO without power loss).

The drive chain and in particular the rotor systems have to work harder, and they also may suffer excessive metal or structure fatigue.

In part, the recent blade problems were probably caused by inadvertent over boosting; there was a belief that you can never hurt a Robbie, if it can fly then it is OK. Wrong!

The design life of this excellent machine built to FAR 27 standards is based on you not over boosting (exceeding graph limits) of the engine.

Be kind to your Robinson, know when too much is too much – metal does have memory.

Happy flying..