oldfart
Elite Veteran
Location: Vancouver, Canada
| Centuryman,
You have discovered something with your 50 nitro that it takes some many years to discover/understand.
When I first started working on blade designs, part of the considerations were gearing. Just as running tires with larger diameters in a car, changes its' gear ratio, so does running larger or smaller blades.
In effect, a smaller blade, at HIGHER pitch, will absorb the same power as a larger blade at LESSER pitch (rotor speed set to be the same)...and visa-versa.
Or conversely, a longer blade at a LOWER rotor speed, will absorb the same power as a shorter blade at a HIGHER rotor speed.
I measured power requirements many years ago, using various blade prototypes on a rotor head driven by electric power (easier to measure watts compared to HP). It is also easier to measure drag of a particular blade configuration (airfoil, tip shape, rotor speed, pitch angle, length, relative lift generated etc.) using an electric motor with equipment to measure wattage, then it is using a nitro engine and trying to measure the relative horse power/torque.
As the rotor disc is the final stage of the power system, how it performs will be directly related to the gearing delivering the power to it. So the gear ratio of your nitro heli will also be an important part of the equation relating to pop and blade size.
Calculating for the same rotor speed (e.g. 2000 rpm), a smaller rotor disc at a higher pitch will be like running the same power at a lower gear. Like shifting with your car when you want to accelerate to pass o r merge. The acceleration needed to pass, is like the "pop" for maneuvering. As the power required to fly is provided by the motor, this is a way to go...as long as you can get the pitch ranges required.
As the extra mass of a longer blade and the moment arm it works through is different, this also plays a part. That is why there are ways to get a longer blade to also "pop" very well. But for this discussion, we are trying to keep all thing relatively equal - e.g. the same type/design shorter blade compared to the same type/design longer blade.
But where there is a BIG change, is when the power to turn the rotor and fly the heli must come from the inertial energy in the rotor disc, as in an auto. Here the longer blade will have a distinct advantage.
As you have discovered, electrics have instant power & torque and a lot of both, compared to their nitro brethren. So it is easy to go for longer blades even at high pitch settings in similar sized helis. Of course you have limits here also, as the harder you work them (the faster you draw the power out of the battery packs) the shorter the flights and the harder on other related components. |
, because my logo 14 + 600mm is in 6S (same motor, same contro, same blade, same ratio), because T600 is in 6S...
