1678

Item 1678

DESIGN: AeroVantage ~ PropRotor - Blade - Tip

Tip Speed:

Propeller:

It is recommended that "to produce maximum thrust at full power your tip speed should fall between .88 and .92 mach." This appears to be for a somewhat advanced 3-blade design.

Another propeller supplier says, "Thus, it is important to keep tip speeds below 75%-80% of Mach.

And another says. " We always set the reduction ratio around 760 fps (0.7 M) tip speed at maximum RPM. This should give you maximum thrust for take off and climb out, then when you throttle back you will still have good thrust for cruise speed."

Look into the reason(s) for the large descrepencies.

Rotor: Prouty's book shows main-rotor tip-speeds of 662-fps (0.61 M) to 780 fps (0.72 M). It must be noted that on the advancing blade during cruise the tip speed will be higher. Approximately, a150-knot forward speed will add 0.23 M to the foregoing. Note that the PropRotor, unlike the helicopter rotor, will be experiencing axial airflow during cruise. An early report on tiltrotors says for efficient cruise the RPM will be relatively lower that that for hover and this relatively is hard to read but it is 70% or 90% on the diagram. Perhaps they are considering the advancing tip-speed during the transition.

Notes:

Miscellaneous:

Last Revised: October 3, 2008