Helicoptorial

Performance

Understanding performance enhances your helicopter operations. Thorough performance planning prior to your flight is still a must, however a good understanding of performance will reduce your planning time and help in situations that might have been unforeseen.

POWER AND AIRSPEED

Power and airspeed have a special relationship. As airspeed increases power requirements change. From the relatively high power demand at a hover, as you increase airspeed, power requirements decrease until a certain point, then increase again. (see chart below)

Add to that the understanding that power is affected by both altitude and air temperature and you have a basic understanding of their relationship.

If we add gross weight to the picture you can see how power requirements are affected.

USING THE CHARTS

These charts become very valuable when understanding how critical airspeeds are determined. Taking the low point in the power required curve you get your best rate of climb and maximum endurance airspeed. That's because this is the lowest power requirement for maintaining level flight. This also gives you the best fuel consumption.

Vh can also be determined with this chart. The intersection of the power required line with the power available line will give you Vh airspeed.

Maximum range airspeed is determined by drawing a straight line from the point of origin to the tangent intersection of the power required line. You can see how gross weight can affect max. range airspeed.

????

So...Big deal. Some flashy charts with some big words. What does it all mean?

Well first, we can go back and dissect why there's that dip in the power required line.

One word...Drag.

I'm not talking two cars racing or how you might dress on Saturday night. I'm talking about the combined drag on the aircraft. Lookyhere.. If we review our aerodynamics (Oh no, I said that word) we know that in helicopter operations there are three types of drag; induced, profile, and parasitic. Induced drag is the result of lift and steadily decreases as airspeed increases. Parasitic drag are things that hang from the fuselage (or even the fuselage itself) to slow the aircraft down. Parasitic drag rapidly increases as airspeed increases. Profile drag is a type of parasitic drag that results from the friction of the blade passing through the air. It gradually increases as airspeed increases. Putting them all together, we'll find that as airspeed increases, overall drag decreases then increases.

The power to overcome the drag on the aircraft is the power required. Things that the pilot has control over that might affect drag are: external loads, doors open operations, mirrors etc.

So, if you are conducting external load operations and an emergency occurs where power is desperately needed, releasing the load not only reduces weight it decreases drag!

Going back to our power available vs. power required, we know that if we decrease our altitude we increase our power available. So if you lose an engine..(if you have two)... adjust your speed and decrease your altitude to get the most out of the good engine.

You can probably think of more examples if you gave it a little thought. The point is that the reason for the development of these certain airspeeds that we learn is no mystery. The power vs. airspeed chart is essential to the development of these critical airspeeds. By understanding your aircraft's performance you become a more capable pilot.

Asta....Chuck

You can send your feedback and input to Chuck at chuckm@aero.com

Back *

Home