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Hartzell BA 72" or 74" performance

acroflyrgirl

Well Known Member
I called Hartzell to ask about performance differences between the BA 72 and the 74". They said the performance is minimal but that if you could swing the 74" that would give you more repairability room since it can be repaired down to 72"

I would like to know the hard performance numbers between the 72 and the 74. Anyone have hard data out here?

Thanks
 
If it was a fixed pitch prop you could tell more from an rpm change at full throttle, but because it is a constant speed prop, you probably won't see any difference in performance.
 
I don;t have any hard numbers for you, but I’ve been doing a lot of prop testing recently and I think I’d agree with Hartzell (because the data I am getting on their props is very close to what they said I would get, which means they know their performance). Interestingly enough, I weighed the same decision, and got the same answer from Hartzell (and Vans) over fifteen years ago when I made the same decision for my RV-8 prop. I bought the 74 so I’d have an inch on each blade to dress out if needed. Have never needed....
 
Good advice on the longer prop

I sent 5 constant speed props out for overhaul and two were rejected due to blade length. So, the 74” prop would be my choice if I was gonna keep the plane for a long period of time. The shorter prop looks cool though.
 
I’d go for max ground clearance

I called Hartzell to ask about performance differences between the BA 72 and the 74". They said the performance is minimal but that if you could swing the 74" that would give you more repairability room since it can be repaired down to 72"

I would like to know the hard performance numbers between the 72 and the 74. Anyone have hard data out here?

Thanks


Lots of anecdotal evidence on past VansAirforce threads that the 72 flies a bit faster and the 74 climbs a bit better....but the differences, if they exist at all, are obviously really minimal. However people often suggest that the 74 is a better decision because you get an extra inch on each blade to repair in the event of a prop strike. It’s the “more is better principle”. :D But if you really think it through you’re probably better off with the 72. The 74 gives you less prop ground clearance (and the ground clearance on RVs is not generous) so you’re more likely to have a prop strike with the 74.

And when you have a CS prop strike it will invariably result in an engine removal/tear down. That means it’s an insurance claim. Now even with an extra inch of blade up your sleeve the chances of the prop being repaired are probably quite small. But the question you need to ask yourself is whether you really want that damaged prop repaired....or replaced entirely by your insurance company. With a 74 inch prop you might find your insurance company wants to repair it to save a few dollars. But if you have a 72 inch prop you are guaranteed a brand new prop.

So my recommendation is go 72 if you plan on insuring the aircraft. More ground clearance means less chance of a prop strike in the first place and in the event that you do have a prop strike you are certain to get a new replacement prop. That will make you feel better and it will look better in your logbook too for prospective purchasers down the track.

The extra 1.5 knots of cruise speed will just be a bonus. :)
 
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