Variable pitch prop design for electric

[Voidhawk9]

...due to the inadequate pitch near the blade roots forming an effective air dam at higher speeds.

If part of the prop isn't producing thrust, it is producing drag. I suspect this is the case for the inboard section of many props (not just IVOs) on many aircraft. I have toyed with the idea of a larger spinner to 'fair' more of the root of the prop to avoid this issue, but for most tractors this would also block cooling inlets, so would not be a simple mod.

 

[Dan Thomas]

The blade stations on a fixed-pitch prop are pitched to keep the entire blade at about the same angle of attack, with some changes depending on what the airframe manufacturer specifies. Some might want a little more pitch inboard for better cooling on the ground, for instance. The should be no part of the blade airfoil causing drag from negative AoA when the prop is pulling. The IVO, with its non-changing blade root, might have a negative AoA, or at least no AoA, in cruise.

The ideal prop, as I said earlier and Marc Zeitlin said, would have the roots changing pitch more than the tips to keep the whole thing at an ideal AOA. That would be difficult to do with the usual constant-speed prop technology. Maybe a long rod having a specific torsional flex that ran through the blade from the hub out to the tip, with the tip end fixed to the tip and the hub end fixed to the hub, and the root end of the flexible prop blade twisted via some mechanism, could get close to ideal. The hub would twist more than the tip.

Ideas are a lot easier to come up with than to implement.

 

[Voidhawk9]

The should be no part of the blade airfoil causing drag from negative AoA when the prop is pulling.

At it's design speed, true, if properly implemented. However towards the root, a lot of props are closer to squashed cylinders than proper airfoils.

 

[rv6ejguy]

I know lots of folks don't like the IVO design but for liquid cooled auto engines with rads in the cowl cheeks, the IVO blade profile at the root is far superior to most shank type C/S props in that location for ground cooling. Round sections don't generate any Delta, near round ones very little. My IVO at runup would generate 5-6 inches H2O in the cheeks when I was doing pressure testing.

Advantages and disadvantages to any design. Still good enough to pull my RV6A along at 182 KTAS if you wanted to burn a lot of fuel.

 

[BJC]

Advantages and disadvantages to any design. Still good enough to pull my RV6A along at 182 KTAS if you wanted to burn a lot of fuel.

And that is the bottom line.


BJC

 

[rv7charlie]

Wow Ross; that's a big number. As I know you know, one needs more than one number to make that number make sense. Care to share the rest?

;-)

 

[blane.c]

Didn't LoPresti modify the propeller root and with a strategically placed inlet in the cowl get a small amount of boost with the combination?

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