Props, Props and more Props

Speaking of props...

A far says 7 inches for tricycle gear which is close to the props website which states 7.87 inches (20cm)

With my old 70 inch 2 blade prop that I'm replacing, I have 8 3/4 inches of clearance.

Worst case scenario, If my shock were to fail (-1.5") and my tire go flat (-3.5") that'll leave 3 3/4 inches of ground clearance.

That seems to low...

What are all of your ground clearances on your planes.

Thx!

I have a tricycle-geared RANS S-6 on 8:00x6 tires – the "tundra tire" offering from RANS.  These are considerably larger than the standard 5:00x6 tires, and make landing on unprepared surfaces much more comfortable.  I needed to purchase a new prop to replace my old 68" Warp Drive prop because of a chip / crack in the leading edge that was just beyond repairable limits.  (That prop did NOT have the protective leading edge installed, and I may have picked up a stone or even possibly hit a large insect in flight.)

I had been reading about other RANS owners who replaced their 68" props with 70" or even 72" props "for better performance," and was considering going with a longer prop myself.  But when I spoke to both Warp Drive (the type I currently had) and Sensenich (the prop I was considering purchasing), both companies recommended 68" props for my airplane / engine combination.  (My plane has the 912ULS, so 100 HP.)  I also talked to a recognized "guru" for RANS aircraft about it, and he said that he didn't believe the larger props would offer any better performance, and he was concerned that a longer prop would compromise ground clearance, potentially exposing the prop to greater damage from gravel pick-up, or even actual ground strike in the event of a flat tire on the nosewheel.

That got me thinking...  I looked at the plane from a side view, imagining what would happen if I had a flat on the nose-gear during  landing...  Those oversized tires mean that the resulting "pitch down" with a front flat would be exaggerated.  The nose would drop roughly 6 1/2 inches, and with the prop considerably forward of the nose wheel, it would lower the prop quite a bit.  

To confirm my impressions, I took a long straight board and set the back end even with the bottom of the back tires, then adjusted the angle of the board until it just touched the bottom of the nosewheel itself (the rim, not the tire).  With the 68" prop length, I still had adequate clearance to the ground.  But with an additional inch of radius, the ground clearance would have been pretty darn tight.  

I ordered and installed the 68" Sensenich ground-adjustable prop, and am quite comfortable with both the performance and the ground clearance.  Bonus points for the fact that the Sensenich prop looks WAY better than the old flat-tipped, skinny bladed Warp Drive prop.  

Thx James.

I'm looking at a 68 also.

Was the sensenich prop balanced right out if the box or did you have to add weights?

Does the sensenich props quick adjustments work for your plane?

I heard from one person that the pins didn't go fine enough and he had to do it by protractor defeating the purpose of adjustments.

68” is a good length. I tested 14 props years ago. I tested Long, short, 2 blade, three blade, flexible and stiff. I had four identical aircraft and was the only one setting pitch and could dictate take off settings. We took off together in pairs and then flew within 50’ - 100’ of each other. The only research project like it. RPM was certainly the deciding factor regardless of what the prop Mfg’s claimed. Back then they all performed pretty much the same. I didn’t have an EProp back then. Warp Drive suffered in climb. The Sensenich is fairly well balanced, but because you bolt on other things on the gearbox prop flange a prop setup should be dynamically balanced..

The Sensenich pins are okay to get you in the general ballpark, but hand adjustment is needed to make sure the blades are all equal pitch. That came right from Sensenich when I questioned the pin use and accuracy years ago.

As of a couple of years ago Sensenich came out with a new improved prop.

Thx Roger!

Any recommendations on ground clearance?

And did your close friend with the e-prop say his takeoffs we're the same or shorter?

I just got an email from JG at stolspeed who tested this prop against others and said it increased his takeoffs distance.