Props, Props and more Props

Hey Roger, thank you for the very valuable information!

I'm finshing up a STOL CH750 with a 912ULS and will mainly be operating out of grass and dirt strips. I live on an airpark in CO with a field elevation of 7000' and in the summer it's common to see 10k+ DA. I'm also considering a zipper big bore kit, but not sure if I will install it before I fly or see how she does first.

Based on what I've been reading it seems one the new breed of lighter/longer hollow core props would be better for me considering my mission and field elevations. That said, do you have any experience with durability between the Whirlwind, Senenich or others? Also, can you make a recommendation on dimater of either or both for my application? In my research Whirlwind is recommending a 75' 3 blade at about 11 lbs and 4350 MOI, and Sensenich is recommending a 72" 3 blade at 10 lbs and 3600 MOI.

Thanks again for all your contributions!

Bill

When I did my research project many years ago all prop Mfg's said theirs was the best. :) 

I would not use a Warp drive because it suffered in climb compared to all the others and the length you want would be too long. Sensenich just came out with a new prop about a year ago.and said it out performs their old one. If it were me I would go with the 3 blade 72". Sound like you want a better climb prop over a cruise prop setting. Since you will be flying at higher elevations and grass / dirt strips i would set the pitch a bit flatter so at your AVERAGE cruise altitude you could get 5700-5800. This should get you a good climb on the high DA days and shorter fields or something with obstacles. 

The Whirlwind would be okay too, but I lean a little more toward the Sensenich due to all their help, customer service and customization when needed. 

Go back to SI-11-91 on prop mass inertia.  You can kill the gearbox if you exceed the mass inertia tolerance.  This Service Intruction is being reworked in light of the new 915 type gearboxes which can tolerate a bit more mass inertia.  The weight of a blade is not what is important it has more to do with the length and where that weight is placed.  leading edge tape or inserts in a blade can dramatically shift the mass and that is what kills your gearbox.  

Don’t understand?  OK try this...take a nice hammer, just one from your toolbox, anyone as long as it is a regular length.  Now grab the hammer by the head, not the handle.  Pick a clear area and rotate it in a big circle with your shoulder vertical to the ground like a prop spins on your aircraft.  Now repeat the test with the same hammer, it has the exact same weight and length, but this time hold the handle and spin it again.   Bingo, you will feel it right away, that is what the effect of prop mass inertia is. 

Some of the newer composite props on the market today are still withing the inertia requirements. Props like Warp Drive that are over 68" and or with their nickle edge inserts are not. The Sensenich 72" new style composite prop is okay.

No matter what prop you pick once installed get it dynamically balanced. There are more components mounted to the prop flange than just the prop itself. 

Some of the newer composite props on the market today are still within the inertia requirements. Props like Warp Drive that are over 68" and or with their nickel edge inserts are not. The Sensenich 72" new style composite prop is okay.

No matter what prop you pick once installed get it dynamically balanced. There are more components mounted to the prop flange than just the prop itself.