What's the ideal propeller ground clearance?

kicktireslightfires

kicktireslightfires

Pre-takeoff checklist
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kicktireslightfires
This question comes as I look at buying a new prop and decide which diameter to get. The prop manufacturer suggests that 7.87-8.66 inches is the ideal ground clearance from prop tip to the ground. And the prop manufacturer also says that you want as large of a prop diameter as possible, which still maintaining that level of ground clearance. Right now, I have 15.3 inches of ground clearance from prop tip to ground, which would suggest I could easily increase my prop diameter size by 5 or 6 inches. Curious to get other people's feedback on this. Also curious about potentially increased noise from increasing the prop diameter, since the outside edge of the prop blades will be spinning faster the longer they are, right?
 
kicktireslightfires said:
Curious to get other people's feedback on this.
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FYI: If this is a certified aircraft you are limited to what props (by part number) you can install on the aircraft/engine. Use of any other props outside of those specific P/Ns requires additional approvals.
 
Bell206 said:
FYI: If this is a certified aircraft you are limited to what props (by part number) you can install on the aircraft/engine. Use of any other props outside of those specific P/Ns requires additional approvals.
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That's fantastic. Thank you very much. It's not a certified aircraft.
 
Prop clearance is determined with nose strut flat and tire flat, so worst case. On a tail dragger in level position with a flat main.

My Cub is state of the art STOL and has an 80” prop. My Skywagon has an 86” prop. My old 172 had a field approval to run an 80” seaplane prop on tires but required a rubber collar to limit nose strut compression. Things to think about.
 
Clearance isn't usually the limiting factor I don't think. Proper pitch combined with length for the engine's power, and keeping the tip speed below the speed of sound are far more important. Well, at least after assuring it doesn't hit the ground.

Unless the pitch is much lower, a longer prop is going to lug your engine a lot more, but again, it's the combo that matters. Unless you're a "pointless" risk taker, you want to use a prop that meets the recommendations of the propeller or engine manufacturer regardless of homebuilt or certified.
 
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With a fully compressed nose strut and flat nose tire I only have about 5 inches. Would like more clearance as it would allow running a number of hydraulic constant speed props rather than the electric MT I have now. Ideal? More than I have currently would be ideal.
 
I don't have an answer but I would think that factors such as nose wheel or tail wheel, pavement, grass, or gravel bars/cow pastures would have a big impact on how much clearance you might want.
 
Only half of the additional diameter will reduce your ground clearance, assuming the same landing gear sag all around. So you can actually go 14 inches bigger diameter (7 inches longer blades/radius) and meet those minimums. But ask around to find out if there is actually a performance improvement for others with your type of plane and the props you are looking at. I like as much ground clearance as I can get without losing performance, because it's a lot less expensive to never have rocks taking chunks out of the blades.
 
kicktireslightfires said:
This question comes as I look at buying a new prop and decide which diameter to get. The prop manufacturer suggests that 7.87-8.66 inches is the ideal ground clearance from prop tip to the ground. And the prop manufacturer also says that you want as large of a prop diameter as possible, which still maintaining that level of ground clearance. Right now, I have 15.3 inches of ground clearance from prop tip to ground, which would suggest I could easily increase my prop diameter size by 5 or 6 inches. Curious to get other people's feedback on this. Also curious about potentially increased noise from increasing the prop diameter, since the outside edge of the prop blades will be spinning faster the longer they are, right?
Click to expand...
What manufacturer? Fixed or constant speed? My Cub has a Whirl Wind constant speed. Great prop but WW stopped making CS STOL props and focused on the RV crowd.
 
I had a flat nose strut a few months ago, I still had 3.5 inches or so. With a flat nose tire on top of it, possibly questionable with any dip in the pavement. I rolled it into my annual, seal needed to be replaced.
 
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