Maximum prop diameter

I?m helping a budding that is still flying off his 40 hours in his RV-14A. He is using a custom composite prop. The prop leading edge is starting to bubble so the prop manufacture is going to replace it. The current prop is 24? in diameter. The question is can a 26? diameter prop be safely used instead of the 24"?

Old rule of thumb.

I think the old rule is with the aircraft setting on the ground at full weight, take a ruler and get the distance from the ground to the center of the prop mount flange, subtract 9 inches, and then double that. You can google up propeller guide lines by Toni Bengalis. Some of those old guides are on the web for you. Hope this helps, Yours, R.E.A. III #80888

Rv 14 prop

Rv 14 with a 24" prop. I'm missing something. Help me.

Carl Froehlich said:

I?m helping a budding that is still flying off his 40 hours in his RV-14A. He is using a custom composite prop. The prop leading edge is starting to bubble so the prop manufacture is going to replace it. The current prop is 24? in diameter. The question is can a 26? diameter prop be safely used instead of the 24"?

Click to expand...

Sorry- that should say 74" to 76" prop.

Carl

I was thinking 74" was max and 72" recommended, based on this thread:

http://www.vansairforce.com/community/showthread.php?p=1101124

I personally will lean toward a smaller diameter - performance differences are small and the smaller prop is less likely to pick up chips and dings. If the composite prop has a nickel leading edge, less of an issue.

I've flown a short-gear RV-4 with a 76" dia prop, once. Wasn't a lot of fun, and I made sure I kept the tailwheel low whenever I was anywhere near the ground. I flew the same plane with a 72" dia prop for years.

Robert's 9" rule is a common rule of thumb. If the -14A has a substantial nose gear (the 10's?) and you'd have at least 8" & operate off pavement, then youcould probably get away with the bigger prop. After all, it's only an inch less clearance than the 74".

Charlie

Some follow up - need a data feed.

There must be something I don't understand. On this specific RV-14A and custom (Italian) 74" prop, I have the following measurements:
- Prop tip to tip measures 74.75"
- Prop tip to ground clearance measures 11.75"

On my RV-10, the prop to ground clearance is right at 8" (using standard Hartzell BA prop from Van's). I would consider this the minimum ground clearance for any RV.

The only thing i can think is going on is that a Hartzell 74" prop is actually bigger than 74".

I would appreciate one of you RV-14A guys flying with a Hartzell prop to measure the prop tip to tip lenght and tip to ground clearance.

This issue is this prop has some bubbling on the leading edge and the manufacturer has offered to replace it, including installation, for no charge and has offered to make the new prop 76" instead of 74".

Thanks,
Carl

I don't understand what you don't understand.

Prop diameter is prop diameter. The Italian prop might actually be metric, and their 74" number was the closest 'standard' American size for them to quote.

Ground clearance is only tangentially (pardon the pun) related. It will change with tire inflation pressures, loading, brand of tire, diameter of tire, etc etc, and especially if you're comparing different models of a/c. So all you can do is measure from hub center to ground *on that plane*, subtract 8 or 9 inches, and double the result to get the dia that's safe on that plane. Don't forget that different prop weights will change ground clearance a bit, at least on trikes.

If the current prop is actually 74.5" and you've got almost 12" of clearance, *I* certainly wouldn't worry about going to 76", but that's me. I'd actually prefer the larger diameter, for improved climb performance (higher mass flow at low speeds), and it shouldn't hurt cruise much, if at all.

Charlie

My confusion is around why Van's calls for a max prop diameter of 74" when this gives almost 12" of ground clearance - on a nose wheel plane. I'm thinking the plane would benefit from a larger diameter prop.

I exchanged email with Van's and they were clear on the 72" or 74" prop spec.

Carl

Carl, remember the RV-10 is 80" I think, not 74". I did go with the longer 74" prop on the RV-14 because even though it gives less clearance than the 72", it's still more than the RV-10 has. And I'm very happy with the prop performance and way it is. I don't know that going even larger is a great idea, but I certainly don't see any reason why on the A model, the 74" isn't a good way to go.
Tim