Charlie wrote:  Don't be seduced by the *potential* advantage of a controllable prop. It's already obvious that the cruise/top speed numbers are much worse.
 
 
In the "Performance Testing / Handling" section; Ross actually flew side by side with a 180 hp RV-6A w/ hartzel and reported the following:   "VSIs were very similar through 8000 feet. We both arrived at 9000 feet at about the same time. Assuming optimal technique and equal aircraft weights, it would appear that the Lycoming/ Hartzell combination is slightly superior in climb rate to the Subaru/ IVO combo below 6000 feet. At 6000 to 8000, they would be very equal. Above 9000, the turbocharged engine has an advantage".
 

"We leveled out at 9000 feet to do the speed runs. Again, Les selected full throttle and played with the prop pitch a bit to get the highest IAS and GPS ground speed. I selected 33-34 inches and 4600 rpm. As speed built up, we called out our IAS and GPS speeds. These were virtually identical, give or take a knot or two. I would normally use no more than 30 inches for cruise so even with fairings on my aircraft, I would concede that Les' aircraft would be 1-3 knots faster at 9000 feet. We were both truing around 170 knots. GPS readings were within 1-2 knots in most cases".

"We both did a cruise climb to 12,000 feet. Above 10,000 feet, the turbo Subaru could slowly pull away from the Lycoming in the climb. Leveling out at 12,000, I used 30 inches 4600 rpm. Again, speeds were very close. with fairings and equal weight, I would give a 1-3 knot advantage up here to the Subaru turbo. Fuel flows with both engines leaned out appeared to be similar. The Lycoming maybe having a slight advantage here".

 

So in a side by side comparison the IVO didn't seem to perform all that poorly.  As in anything there are some unknowns of course such as the health of the 180 hp Lycoming he is flying against;  but on the other hand if you look at pictures of Ross's 6A it has to be one of the draggiest around with all those ducts and scoops sticking out!   Since my IVO came with the engine as a package deal, I will initially use it and will post results to the list on how it performed (or not).  I also have a neighbor with a 9A w/160 hp Sensenich so I also plan on doing some side by side comparisons in the future as well.  If worst comes to worst I can always place an order for a three blade Cato and e-bay the IVO... :)

dl