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Kolb-List Digest: 15 Msgs - 05/07/18

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PostPosted: Tue May 08, 2018 4:47 am    Post subject: Kolb-List Digest: 15 Msgs - 05/07/18 Reply with quote

You could keep the down box and raise the engine to whatever height might be
I think flipping the box would put the prop higher than needed - forget how
You can get a wider chord prop to Absorb more power in a smaller dia. The
prop mfg could say what would work with the 3.47 box.
Just some thought based on fuzzy recollections.
________________________________ Message 6
Time: 03:23:13 PM PST US
From: Bill Berle <victorbravo(at)>
Subject: High Thrust Line Question
Kolbers, I ran into a significant problem on my Firestar, and it may cause
me to not be able to finish the project. I hope this is not as much of a
problem as I fear.

When I bought my HKS engine I did not know to ask whether it had one type
gearbox or another. It has the 3.47 to 1 box, which will spin a large
propeller very slowly.

After reading some ot the Kolb List stories about high thrust lines and
putting the Kolb over on its nose, I realized I wanted to keep the thrust
line as low as possible for best performance and handling. However, with the
gearbox rotated to the "down" position, it limited the propeller diameter to
64 inches with a one inch tailboom clearance. With the 3.47 gearbox I have,
a three blade propeller with 62-64 inch diameter is not enough... the engine
will overspeed before I get the full amount of thrust.

Someone suggested using a four or five blade propeller, but that would
prevent the wings from folding back.

I contacted the engine distributor to ask if I could switch the gears around
to make my gearbox a 2.58 to 1 ratio,a nd you cannot do that without
changing the gearbox itself.

So I asked how much it would cost to buy a new gearbox, andit is way too
high for me to consider doing right now. Maybe when I win the lottery.

Someone else suggested that I turn the gearbox around facing "up", which
would allow a much larger propeller. My first reaction was "Oh goodness no,
that will raise the thrust line too high, and it will cause the airplane to
nose over on takeoff, I'll run out of elevator control, etc. etc...."

But then I realized that was an assumption rather than a known fact. Before
I gave up on the project, perhaps I can move the gearbox upwards and not
have problems...
but how far?

So I would like to ask the experienced Kolbers: JUST EXACTLY HOW HIGH can
the thrust line be on a Kolb Firestar 2 before it creates
safety/handling/nose-over problems? Can the center of the propeller be 34
inches above the tailboom...36
inches...38 inches...40 inches????
Bill Berle - safety & performance upgrade for light aircraft - winning proposals for non-profit and for-profit

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