RV-4 Prop Recommendations

Scott Hersha · #1 08-06-2016, 08:21 AM

I bought a flying RV4 recently, and I'm looking for advice/recommendations on changing or modifying my prop. Here are the details:

>O-320 E2D was recently overhauled and has new Ly-Con flow balanced cylinders with 9:1 forged pistons, so it probably makes 165-170 HP.
>relatively new Catto 2-blade prop; 70" long, 72" pitch.

The airframe is pretty clean and has Sam James wheel pants, which are probably not as slippery as the Vans pressure recovery pants, but overall there is not a lot of drag reduction opportunity to try to get more speed.

The pitch is too low for this airplane, in my opinion. At wide open throttle I'm seeing RPMs of 2850-2910 at all altitudes up to 11,000'. At a cruise power setting of 2400, my MAP is from 26.5" at 2,000' to 21.0" at 8,000', and true airspeed is 142-147 knots. WOT at 8,000' results - 22.3" MAP, 2830 RPM, 173 K true on a hot day with density altitude of 9591'.

I've recorded a lot of data at different power settings, but at a normal cruise power settings, the throttle is more than half way to idle from full open, and I'm only seeing speeds in the 140K range, which I think is too low. I don't want to over speed my engine. I know some people do that all the time, but I would rather see 2700 at WOT.

So, my questions for those of you with experience is what would be a target prop pitch for an a average weight 165hp RV4 with a fixed pitch prop. The engine is capable of using a constant speed, but I'm not interested at this point in spending $10K and having to remove my engine to modify the firewall to make room for a governor. I would like to keep it light, simple, inexpensive. I talked to Craig Catto at Oshkosh, and he says he can re-pitch it, but how well does that work? I think he just adds material to the back side of the prop to make changes. I would like to possibly sell this one and buy a new Catto with the correct pitch, but what would that be? Is there a formula somewhere?

Advice is welcome, thanks.

AX-O · #2 08-06-2016, 08:36 AM

They have a formula and most of the time can tell you off memory. The data that you collected is exactly what they need.

I believe they do one repitching for free. If not, it will be minimal compared to buying a new prop (approx 3K for a 2 blade).

Repitching works. They change the airfoil shape therefore changing the "pitch".

Look at pics of the last plane Paulo designed. During flight test Craig had to repitch the prop in Brazil because the rpms were too low. He took some sand paper and reshaped the trailing edge of the prop. That brought the rpms up to where they wanted them. Small changes in airfoil change the "pitch".