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Date: Wed, 12 Nov 2008 22:55:26 -0600
From: Charlie England <ceengland@bellsouth.net>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] IVO vs. Hartzell fly off...
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DLOMHEIM@aol.com wrote:
> 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
>

Shucks, if you effectively have zero money in it, there's no real reason 
to not use it, at least for initial testing. Just leave the spinner off 
& use the 'witness tapes'. I doubt there will be any problems since the 
rotary doesn't have torque reversal issues, but why gamble.

Not too sure about the numbers in the comparison test above, & how that 
can match up with the numbers in his test chart. A normally aspirated, 
properly leaned 180 horse engine at 75% power burns around 10 gal per 
hour. That would be full throttle at 7500-8000 feet (going 197 mph). 
Hard to believe that it could still be burning 9.3 at a 50% higher 
altitude, as long as it's properly leaned.

Charlie