Besides the 25% to 35% premium in cost and the fact that you have to send the composite prop in for an inspection every 250 hours, what are the real advantages of a composite prop? Harmonics? Weight?
I spoke to Whirlwind about their 200RV and 151 series for use on the IO-360.
I'm not sure but that was quite a suprise to me! I can just imagine unbolting the prop, (TWO PERSON JOB FOR SURE!) shipping it in, waiting...waiting...getting it back, bolting it back on hoping that it's not damaged by the shipper (or the rookie builder!) during any of these steps!
I am yet to learn why I should spend the extra cash on a composit prop?!?
- Peter
PS - Did you check with MT on these 250 hour inpections?
The MT prop does not require frequent inspections. That said, I inspect my prop before every flight. A friend of mine has one on his Extra type machine for competition aerobatics. The MT prop is attractive because it is much lighter than the comparable Hartzell and has some built-in damping rather than acting like a tuning fork as does the Hartzell. There is still the "no-fly" zone, from 2250 to 2000RPM on all these CS props.
Anyway, an inspection every 250 hours is not too bad. Considering the average pilot is hard pressed to fly 125 hours a year, that would mean an inspection every two years of flying. Not a bad idea anyway.
Cheers, Pete
Peter Marshall
Newbie RV-8 builder.
You wanna draw, ....against the fastest rivet gun in the West??? LOL
The "no fly" zone that MUSTANG is referring to is a range of rpm that creates a harmonic load on the prop that will cause excess wear and fatigue on the blades. It will be different depending on the HP and ignition system of your engine but will be there with about anything you fly.
...it's truly not that hard to deal with. Just keep an eye on you RPM and optimize pitch to balance performance.
Those harmonic problems also are the reason you never want to use a cut down/modified aluminum propeller as some have done twenty or thirty years ago and crashed because of it. The composite props are easier on the engine (stress on the crank, mount, etc.) when doing aerobatics. That's why all the top aerobatic folks use them. Composites are also better for manufacturing different shapes for the blades. Discussing blade shape is almost (unless you are a propeller engineer) like arguing wing tip shapes-really which one do you prefer and do you get the performance desired? I sure you all know to take your prop maintenance seriously because to do otherwise can get you killed. Remember the old joke about the prop being there as a fan to keep the pilot cool-because when it quits turning you get to see the pilot sweat.
In fact, if you want to be scared in to maintaining your prop like a piece of fine china, watch the video that was taken with a high speed camera that shows how much they flex, bend and move during normal operation!!!
I saw this on the internet about a year ago but can't find it now... Has anyone else seen that video? It's UNREAL!!!
Yes, the no-fly zone sounds a bit restrictive, particularly if you are used to flying behind a smooth running 6 cylinder engine. I used to fly my C-180 TCM O-470 at 2000RPM and 20 inches for long range fuel consumption. Then I got a Pitts Special and tried the same kind of RPM with the O-360. Ouch! Even with a fixed pitch prop the O-360 did not want to run smoothly below 2300RPM. BTW, this was a highly balanced and blueprinted Lycoming. So, the restriction from Hartzell on the CS props is not so restrictive as you might think.
Cheers, Pete
Peter Marshall
Newbie RV-8 builder.
You wanna draw, ....against the fastest rivet gun in the West??? LOL
OK so here's a question. A C/S prop has a thrust bearing on each blade that absorbs the centrifugal force of each of the rotating blades. While cleaning up and preparing for sale part of my Dads estate I found sketches and several pages of the associated math for a C/S prop (he was a flight test engineer) that has no centrifugal loads on the hub. What do you all think should I pursue it?
- Peter
