Executive summary: the 74RV is faster than the Hartzell blended airfoil on my -7. Empty c.g. shifted aft one inch.
Original build used a Hartzell, as did my four prior -7s. Most bang for the buck, and since we travel heavy, assures the most forward empty c.g. This newest -7 has an IO-375 with 9.6:1 compression and vibrations felt harsher than prior lower compression engines. That was enough excuse to try a composite prop. Open oil hatch, pour in money.
I chose Whirl Wind Aviation's 74RV since it targets engines >200hp (I'm guessing mine is 220 from mods to ASP's basic 375), it's a bit heavier than the 200RV, and Hartzell and MT composites are too spendy.
I performed a few crude speed tests prior/post retrofit. At first I was disappointed. Same density altitudes and fuel flows, H and WW were identical full power TAS. Then I noticed that the WW was achieving the same numbers at 2640 rpm, not the 2700 the H turned. I suspect WWA set a mechanical fine pitch (high rpm) stop, so even if the governor is willing to do 2700, the prop isn't. At 2300, WW is about 2% faster, "about" because I'm familiar with H cruise performance, but collected no lower rpm comparison points prior to retrofit. The speed increase trend is obvious.
Empty weight dropped 25 pounds, the c.g. moved aft one inch.
The whole rpm regime is smoother, not a lot, but noticeable. The harshness is gone. The whole assembly has not been dynamically balanced, but the H installation needed only one short bolt to achieve tiny acceleration numbers, so I don't think much will be gained in rebalancing.
A few observations. Being a retrofit, I was mindful of the cowl/spinner gap. I did not use the .062 washer over the Hartzell bushing per Van's to position the aft H spinner bulkhead. WWA's gap dimension seems to expect the washer, so I asked them (and they did) shave the spinner trailing edge to achieve the same installed gap. Pay attention if you're retrofitting.
The cowl front face does not require modification from as molded to use the Van's bulkhead. I had to cut away the cowl front flange, leaving an 11 inch diameter hole to clear the WWA bulkhead.
The price difference H to WWA may not be worth the performance difference to you, but looks alone might sell you.
John Siebold
Original build used a Hartzell, as did my four prior -7s. Most bang for the buck, and since we travel heavy, assures the most forward empty c.g. This newest -7 has an IO-375 with 9.6:1 compression and vibrations felt harsher than prior lower compression engines. That was enough excuse to try a composite prop. Open oil hatch, pour in money.
I chose Whirl Wind Aviation's 74RV since it targets engines >200hp (I'm guessing mine is 220 from mods to ASP's basic 375), it's a bit heavier than the 200RV, and Hartzell and MT composites are too spendy.
I performed a few crude speed tests prior/post retrofit. At first I was disappointed. Same density altitudes and fuel flows, H and WW were identical full power TAS. Then I noticed that the WW was achieving the same numbers at 2640 rpm, not the 2700 the H turned. I suspect WWA set a mechanical fine pitch (high rpm) stop, so even if the governor is willing to do 2700, the prop isn't. At 2300, WW is about 2% faster, "about" because I'm familiar with H cruise performance, but collected no lower rpm comparison points prior to retrofit. The speed increase trend is obvious.
Empty weight dropped 25 pounds, the c.g. moved aft one inch.
The whole rpm regime is smoother, not a lot, but noticeable. The harshness is gone. The whole assembly has not been dynamically balanced, but the H installation needed only one short bolt to achieve tiny acceleration numbers, so I don't think much will be gained in rebalancing.
A few observations. Being a retrofit, I was mindful of the cowl/spinner gap. I did not use the .062 washer over the Hartzell bushing per Van's to position the aft H spinner bulkhead. WWA's gap dimension seems to expect the washer, so I asked them (and they did) shave the spinner trailing edge to achieve the same installed gap. Pay attention if you're retrofitting.
The cowl front face does not require modification from as molded to use the Van's bulkhead. I had to cut away the cowl front flange, leaving an 11 inch diameter hole to clear the WWA bulkhead.
The price difference H to WWA may not be worth the performance difference to you, but looks alone might sell you.
John Siebold
