Recently flew a two-blade Raptor about 10 hours on the front of my RV-8. This is the late model carbon prop specifically designed as a much lighter alternative to the 7497 aluminum BA. That's not to say the 7497 was copied in carbon. It's a clean sheet design to optimize properties, with a lot of subtle differences, including the hub structure.
I'd say Hartzell engineering nailed it. A very nice prop all around. Seems to pull harder at low speed, like during runway acceleration or when pulled into an upline. No notable change in top speed or cruise. The Big Deal, at least with me, is the low mass moment of inertia, as it drives a pleasant change to handling properties, in particular given an RV-8 with an angle valve 360 or 390.
A typical F7497 aluminum blended airfoil is roughly 59 lbs, while the equivalent Raptor is about 38 lbs. That's 21 lbs lighter overall, or ~35%. However, the weight loss is in the blades, not the hub. The MMoI is approx. 0.57 slug*ft2 for the composite vs ~1.93 slug*ft2 for the aluminum....70% less. That's huge in terms of effect, and it shows up in multiple ways. For example, start right at the beginning, just seconds into the takeoff roll...push the stick to raise the tail to longeron level. With the aluminum prop, you'll need a rudder input to keep it straight while the airframe rotates in pitch; gyroscopic precession drives the nose 90 degrees to the pitch change, in the direction of rotation. With the carbon prop, the same pitch rate results in very little rudder requirement, a reduction proportional to the reduced MMoI. The effect (or more more precisely, the lack of effect) extends to all maneuvers with high pitch or yaw rates.
Another design driver; unlike the previous paddle carbon prop, the blade chord does not require a shaft extension or extended hub to clear the cowl intakes at full coarse pitch. It's a bolt-on with standard RV cowls.
Given the short term test, I did not do a dynamic balance. Still, perceived vibration was less than with the 7497, in particular within the classic range from 2100 to 2350.
I liked it a lot.
I'd say Hartzell engineering nailed it. A very nice prop all around. Seems to pull harder at low speed, like during runway acceleration or when pulled into an upline. No notable change in top speed or cruise. The Big Deal, at least with me, is the low mass moment of inertia, as it drives a pleasant change to handling properties, in particular given an RV-8 with an angle valve 360 or 390.
A typical F7497 aluminum blended airfoil is roughly 59 lbs, while the equivalent Raptor is about 38 lbs. That's 21 lbs lighter overall, or ~35%. However, the weight loss is in the blades, not the hub. The MMoI is approx. 0.57 slug*ft2 for the composite vs ~1.93 slug*ft2 for the aluminum....70% less. That's huge in terms of effect, and it shows up in multiple ways. For example, start right at the beginning, just seconds into the takeoff roll...push the stick to raise the tail to longeron level. With the aluminum prop, you'll need a rudder input to keep it straight while the airframe rotates in pitch; gyroscopic precession drives the nose 90 degrees to the pitch change, in the direction of rotation. With the carbon prop, the same pitch rate results in very little rudder requirement, a reduction proportional to the reduced MMoI. The effect (or more more precisely, the lack of effect) extends to all maneuvers with high pitch or yaw rates.
Another design driver; unlike the previous paddle carbon prop, the blade chord does not require a shaft extension or extended hub to clear the cowl intakes at full coarse pitch. It's a bolt-on with standard RV cowls.
Given the short term test, I did not do a dynamic balance. Still, perceived vibration was less than with the 7497, in particular within the classic range from 2100 to 2350.
I liked it a lot.
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