Quote:
Originally Posted by WVOtoGO
Sorry, but:
Like hell it wont !!
There’s a good reason why the best all around propellers are neither aluminum or titanium, but wood/composite.
Stiff/ridged is a bad thing. Just ask Piper and their Malibu issues with cracked supercharger housings. It was all caused by vibration issues from stiff aluminum propellers. To go to an even stiffer titanium propeller…. Ouch.
Aluminum and Titanium both support harmonic vibration. This is why so many propeller driven aircraft have propeller RPM restrictions (And I don’t mean the max, or red-line.). Many (if not most) failures of gyro instruments, motor mounts, engine cowlings, radio systems…. can all be traced back to the propeller and the vibrations it can not absorb and thus sends back through the engine.
Aluminum and Titanium would both exhibit typical tip fatigue failure issues. Where the aluminum props often show erosion in this respect, I might think (you're more into this than I) that the titanium may crack. “Propeller” and “Crack” are two words we don’t like to hear used together.
As far as the gyroscopic issues. Light and short are everything. The lighter and shorter the blades are, the fewer precession issues have to be dealt with, including their affects on the motor. I don’t think aluminum nor titanium are light enough to be made as short as a composite blade with the same available thrust. This is why all the serious aerobatic aircraft run MT (or some other make) composite blade propellers. And trust me, “cost” is no issue there.
- Shelby
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Yep, you could be right about harmonic vibrations. But, "stiffness" may be desirable or it may not be desirable depending on the frequency of the vibration and the operating frequency.
Traditionally, the stiffer the component, the higher the first order vibration frequency. If this can be well above the operating speed, the stiffer material wins.
It might be the situation, due to the shape of the propeller, that the operating range is between the first and second critical frequencies............and titanium might shift this point to an undesirable location.
In summary, titanium by itself is not an automatic reject for a propeller. It would depend on the harmonics of the material, if present, and the operating speed with respect to those harmonics.