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<< Lancair Builders' Mail List >>
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<<I doubt that you would take a file to such highly stressed components as
your crankshaft or a connecting rod. The propeller is probably more highly
stressed than either and just as (or more) intolerant of inept repair.
Particularly when one considers that often, the most egregious damage
sustained by props in service usually occurs in the most highly stressed
regions (the outer 10 - 12 inches is just closer to the gravel).
One of the things that can happen, without specific training in prop
maintenance, is to grind away enough metal to exceed allowable limits and
make the prop unserviceable and unsafe, even though the repair looks really
neat and smooth.
Bottom line - have it done by the best prop shop you can find.>>
In theory all of the above may be true, but with aluminum propellers it has
been standard practice for many years to use a file on them. My own
methodology is to:
1. Count the strokes of the file and keep them reasonably uniform. Then
take the same number of strokes from the other blade. This gives you half a
chance at keeping the balance reasonably good.
2. Always stroke the file span-wise, not across the chord. This keeps the
scratches running in the direction of the stress.
3. Make sure that you file away all of the nick. going almost all the way
to the bottom, leaving a line or mark remaining, is not much better than not
filing it at all. Running the file spanways will automatically smooth out
the nick, preventing stress concentrations.
4. After I file the blade I use sandpaper to finish smoothing it, ending in
150 or finer grit. If I feel ambitious I use rubbing compound to polish out
the scratches, but that is probably only for looks as the blade will start
eroding right away anyway.
5. Keep the overall profile (airfoil) as close to the same as before. I
have seen professionals ignore this.
6. Finally, don't file out a notch that is too deep - that calls for a
professional refinishing. How big is too big? Not sure, but 1/8 inch is
awfully deep.
I see lots of people (most, I think) that apparently think there is no
debris on paved surfaces as they never have the elevators in the up position
when taxiing or doing a runup. We just finished the annual on ours and had
to do some full throttle runups with fresh paint on the prop. After maybe a
minute total of full power on what we thought was a perfectly clean
surface - and with the wheel full back all the time - there were nicks in
the paint, indicating the presence of dust. Way back when I was taught to
fly out of a gravel strip and if the owner ever saw anyone running without
the wheel full back or applying full power before 20 mph on takeoff they
were severely reprimanded. On the second time was banished from the
airport. Sort of stuck with me.
Gary Casey
ES project, C177RG
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Please send your photos and drawings to marvkaye@olsusa.com.
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