Propeller Ground Clearance

Hi All - I'm building a 9A and am wondering if it has enough ground clearance to safely use a 72" diameter propeller? What does Van's recommend for prop length?

Van's says that a 74" Hartzell blended airfoil CS propeller is good to go on the -A tricycle-gear models, so a 72" would of course have adequate ground clearance too.

Think about your intended primary runways though - if you may occasionally (or more than occasionally) operate on runways/taxiways with gravel or other small debris, the 72" will give you an extra inch of ground clearance to help avoid sucking some of that debris into the prop tips and nicking them. Aerodynamically speaking the 74" will be slightly more efficient.

Can you point me towards where Van's shows the recommended prop length for models? I've heard people talking about it and for all the searching I've done, I've never come across it.

The lengths I'm trying to choose between are 70" and 72". I'd like to go with 72" if it can be safely used. If it is true that Van's talks about using a 74" on an 'A' model then I should have no problem with the 72".

Straight from the horse's mouth...

This should help you out, assuming the link works...

http://vansaircraft.com/cgi-bin/cat...-430-387&browse=props&product=csprop-hartzell

FAR 23.925 Ground Clearance

We just had a similar discussion at our airport and also found the following.

Part 23 AIRWORTHINESS STANDARDS:
23.925
Propeller clearance.

Unless smaller clearances are substantiated, propeller clearances with the airplane at maximum weight, with the most adverse center of gravity, and with the propeller in the most adverse pitch position, may not be less than the following:
(a) Ground clearance. There must be a clearance of at least seven inches (for each airplane with nose wheel landing gear) or nine inches (for each airplane with tail wheel landing gear) between each propeller and the ground with the landing gear statically deflected and in the level, normal takeoff, or taxing attitude, whichever is most critical. In addition, for each airplane with conventional landing gear struts using fluid or mechanical means for absorbing landing shocks, there must be positive clearance between the propeller and the ground in the level takeoff attitude with the critical tire completely deflated and the corresponding landing gear strut bottomed. Positive clearance for airplanes using leaf spring struts is shown with a deflection corresponding to 1.5g.

Blended Airfoil not for 320s

Neal@F14 said:

Van's says that a 74" Hartzell blended airfoil CS propeller is good to go on both the -7A and -9A tricycle-gear models, so a 72" would of course have adequate ground clearance too.

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I don't think this is true. About a year ago when I was ready to order my prop for my IO-320, I called Van's to inquire whether the Hartzell 72" was the newer blended-airfoil or the old style. Ken Scott confirmed they only carry the old style and that he had inquired to Hartzell whether they had one and they said the blended airfoil was not available for 320s.. At Oshkosh, I talked to Hartzell at their booth and they were surprised and asked who's making kits for the 320. Talk about out of touch! So, I ordered the only Hartzell prop Van's offered which was the 72" 2-bladed, "Non" blended airfoil.

Things may have changed in the last year, but I believe if you have a a Hartzell 72" or 74" blended airtfoil on a RV9, there should be a 360 under the cowl.

kbehrent said:

I don't think this is true.

Things may have changed in the last year, but I believe if you have a a Hartzell 72" or 74" blended airtfoil on a RV9, there should be a 360 under the cowl.

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You're right. The 74" is only recommended for the 360 engines, and Van's doesn't recommend bigger than a 320 on the RV-9.

... but the -7A and -9A do have same fuselage/landing gear height, so if you decide to put a 360 on a -9A, theoretically you'll have the same prop clearance as similarly-equipped -7A.

Neal@F14 said:

... but the -7A and -9A do have same fuselage/landing gear height, so if you decide to put a 360 on a -9A, theoretically you'll have the same prop clearance as similarly-equipped -7A.

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Yes, the 7A/9A fuse/gear are the same. Haven't measured the clearance on my 9A, but I don't think I would be comfortable with a 74" even if it existed for the 320. Better to have a dragon tail for clearance for that size.

We've got the 74" on the RV-8 in my avatar. We also tested ground clearance by two guys lifting the tail up off the ground with the mains chocked and tilting the plane forward until the prop tip was about to touch with one of us up front to watch the prop. Although nobody (obviously) was sitting in the cockpit when we did this, the view out the windshield would be horrific if that ever happened while the plane was in motion. You'd be seeing a windshield full of pavement quite a bit before the prop ever touched and know pretty well in advance that you were in the process of having a very bad day.

Thanks for the discussion everyone! I'm planning on using a Whirlwind GA200L ground adjustable propeller and it's good to know that I shouldn't have any problems using the 72" version.