Neal Scherm wrote:

Hello all,
I am having a supercharged 13b motor built for my KIS Cruiser and need some
feed back on an electric prop. The lightest one I've been able to find is an
IVO
Does any one have any feedback on their Magnum line or suggestions as to an
alternative?

Thanks,
Neal
KIS Cruiser #4030

It may be light Neal but it won't work well over about 180 MPH. Bite the economic
bullet and go for a MT or Hoffman. Do you really need short takeoff distances?
If you can wait awhile I think some of my friends are building a electrical variable
pitch prop with carbon fiber blades at SZP. Our own project on this seems to have stalled.
See the ACRE NL web site below for drawings and suggestions.
I will try my turbo Kis Cruiser with a fixed pitch prop first.

Paul Lamar

Neal (& Paul),

I have a somewhat interesting data point on IVO's products.

Preface: I tried one on my Lyc 160 hp RV-4 about 5 years ago
& got very similar results to Tracey's with the 'brick wall
effect.'

Recently, due to hangar damage to my prop, I needed one in a
hurry. I jumped through the FAA hoops & borrowed my
neighbor's IVO which he purchased for a 160 hp 'low & slow'
a/c. I assume that it was the low pitch version, but did
have the knurled hub. This prop was 76" in diameter,
obviously much too large in diameter to leave on an RV.

I mounted the prop using the old spinner back plate, but no
spinner as IVO had recommended years ago. I cranked in
roughly the same pitch at the tip that I was seeing on my
old 68/73 wood prop. First flight, very unscientific test
conditions, yielded a top speed @ 2000' msl of around 170
kts (195mph) in relatively calm air both on my asi & loran.
Note that this is faster than this particular a/c has flown
in level flight since the original very efficient Warnke
72/72. It was turning 2500 rpm at full throttle. Takeoff
distance was not excessive, & climb rate was adequate. Later
adjustments to finer pitch yielded truly impressive takeoff
roll & climb rates. Originally, it took 5 1/2 turns to set
the tip pitch the same as my old prop. When I returned the
pitch setting to neutral to retighten the attach bolts, it
only took 4 turns to reach the no-load neutral point in the
adjustment range. I don't believe the adjustment screw moved
in less than 1 hr of operation.

The above tells me that the *concept* has merit, & could be
developed into a viable alternative as an in flight
adjustable prop. To say that the pitch does not adjust is
misleading. It obviously isn't ideal, but $10,000 isn't
either, & the big boys don't do perfect pitch change either,
since the twist should change with pitch. The less expensive
used constant speed props almost always have the same
problems with twist as the IVO since they were designed for
much slower planes than RV/Lancair class planes.

Now, the rest of the story. On my Lyc, I haven't been able
to keep the blades from moving & the blade attach bolts
tight during about 3 hrs of flying. The vibration level is
at least as bad as my wood prop was when it was badly out of
balance. In its current configuration, I would not consider
this prop a viable alternative on Lyc 4-cyl engines due to
blade movement & potential failure. It might be made viable
for Lyc's with further development. It might be viable now
for engines like the rotary, which don't have destructive
torque reversals.

I believe that IVO could probably design & make a viable
prop for fast a/c using a rotary by simply using something
like the Bates prop software, but he isn't highly motivated
due to the limited market of dozens vs. thousands of
airboats & ultralights.

Now, to the soapbox:  I don't believe any of us are well
served by melodrama in either endorsing or denouncing any
idea unconditionally. When these type questions come up, why
not lay out all the verified data (including all test
conditions), add opinion (indentified as opinion), & let the
questioner draw his own conclusions.

Charlie England
cengland@netdoor.com
flying Lyc RV-4

Usually I will say it is opinion if it is only my opinion. Nine times out of 
ten it is physics pure and simple or mechanical engineering if you wish.
Now having said that I am willing to listen to other engineering
analysis or physical analysis. I make mistakes or have gaps in my 
knowledge just like any other engineer or physicist.

BTW If I see something that does not make sense to me from an engineering
point of view I am going to tell you about it. I was just offered a job
in Detroit designing (engineering) cars for $85K a year but I turned it down
as I like being retired and doing what I am doing.

Paul Lamar
 
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