charles.harbert

Paul, I know from a purist engineering standpoint that the IVO twisted prop is
not your idea of something that you would want to put on your airplane. However,
it actually does work very effectively based upon actual application. We can
agree as to the basic theoretical assumptions, but it's difficult to disagree
with proven results. Before I bought my IVO prop, I must have talked to 20
people who actually flew with the IVO and had previously used fixed pitch, and
even M/T or Hoffman c/s props. Most of these were Velocity owners, but there
were also Lancairs, Glasairs, etc. Almost universally, they liked the prop and
saw significant performance improvement in both takeoff and top spd.

Velocity (factory) previously suggested that they use the IVO until the torque
reversal problems with the big 4 cyl a/c engines caused them to chg their
position (Franklin 6 - okay). The issue was continual retorquing of the blades
(maint issue) until they no longer lossened (break tape). Privately, they told
me that they would prefer to use an IVO if they could solve this problem.
Interestingly, there are many Velocity's with Lyco 360's still using the IVO
without problems for many hundred hours with 200 kt top speeds.

As for the speed limitations,IVO has several 200+ knot planes flying. The
Sandler Pirhana which is being sold to the Turkish Air Force is a 300 mph plane
using an IVO. I've personally talked to Lancair owners using IVO's on big 6 cyl
a/c engines who are flying at 250 mph. I've had my own plane up to 185 kts and I
wasn't even at full throttle. So to say that the plane using an IVO can't exceed
200 mph is just not true.

I've written previously on this issue because I think that it's important that
we report factually, and not just condemn something based upon a theoretical
analysis which may not have all the necessary information.

I really doubt those 200 Kts claims. I will believe it when I see one go
over 200 Kts in the Sun 100 race.

I will tell you a little interesting story about the IVO prop. Dave Atkins has
sanded and rounded the leading edges of the blades. Dave told me at S&F that was
worth
ten MPH. 

Dave entered his airplane with that IVO variable twist prop in the Sun 100 race. 

Later, just before the Sun 100 race started, Dave told me he did not expect to win
the 
rotary powered airplane prize as his airplane was only going about 180 MPH. Tracy
routinely 
goes 206 MPH with a thicker blade, fixed pitch wood prop. Granted, Tracy probably has
a bit more 
HP than Dave but not enough to make up the difference in top speeds.

BTW Dave was not able to compete as just before the race started his RV6 rudder pedal
broke.
This could have caused him to crash on landing if it had not broken while he was
taxing out to the start line. All you RV guys, beef up those rudder pedals. I am sure 
Van G  has a suggested fix by now. 

More on the variable twist IVO prop soon as I was able to study the one Tracy bought 
at Shady Bend just before this years S&F. It looks worse than I thought.
 
Paul Lamar
 
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