OK, so I planted the Eclipse this weekend......

Tue Apr 26 14:23:05 AKDT 2005

FWIW - mostly just my opinion -

Anyone who has seen one of Bill's planes knows they are meticulously set up
and cared for.  I seriously doubt Bill did anything to contribute to the
failure of the prop.   Nor do I believe there is anything inherently
deficient with the APC prop.

Most know that I have a good relationship with APC (not sponsored per se,
but they have always supported me with prop experiments and been 100%
responsive and interested in making a better product).  And I'd be willing
to bet I have more flights on the APC 15.75-13 3 blade (at 10, 11, or 12
pitch after re-pitching) than anyone else (one prop has at least 1,000
flights on it).  Which lead me to giving Fred Burgdorf at APC a call after
seeing Bill's email.

Way back when AT-6 racing was just starting, several existing APC props were
used in the new event, and several new APC props were developed for the
event (as APC has done for many modeling events).  One of the AT-6 guys had
a 2 blade prop break near the hub (might have been 2 props), but none of the
other AT-6 guys had the same problem.  APC re-tooled the mold and made the
prop stronger.  The same guy broke the new prop (same engine, same plane).
The hypothesis is that the particular engine, mount, airframe, RPM, (and
prop) etc. were a "bad" combination - a combination that resulted in a nasty
resonance that broke the prop - ergo, changing the prop itself did little to
alleviate the problem - changing anything else on the plane (to change the
resonance) would have been more likely to alleviate the problem.  APC did
post a warning on their website, and actually did terminate production of
large 2 blade props (relatively low demand at the time).  Currently, APC is
making large 2 blade props again, due to customer demand, and the website
does have a broader warning/info post under "safety concerns" which
discusses many of the factors that can stress a prop - most notably (to me)
that it is not possible to test every prop design on every possible
combination of airframe, engine mount, engine, RPM, maneuvering loads, etc.

After speaking with Fred today, I think APC (I assume Fred) and Bill may
have had a misunderstanding - the only 3 blade prop hub failure known to APC
is the one from Bill's plane.  There is also one reported (to APC) hub
failure of a 4 bladed prop (I believe the 15.5-12).  Outside of the above
particular AT-6, there are no other known hub (to APC) failures of 2 bladed
props.

This list has seen analogous discussions regarding servo life - some planes
beat up servos faster than others - it is not the fault of the servo.  While
some servos might be more resistant to being abused (by a particularly nasty
resonance), and a bigger, stronger, heavier servo might increase longevity,
it doesn't make the plane any less abusive to the servo.  Same thing with
props - different props have different resonances - and bad combinations can
exist with any prop made of any material.

In the case of Bill's Typhoon, the (unfortunately) needed rebuild might be
change enough to eliminate/reduce a problematic resonance - and it may not.
I know I wouldn't put the same prop back on to find out - but I wouldn't
hesitate to put that prop on any other airplane.

Regards,

Dave Lockhart
DaveL322 at comcast.net

----- Original Message -----
From: "Bill" <ahrensw at charter.net>
To: <discussion at nsrca.org>
Sent: Tuesday, April 26, 2005 9:32 AM
Subject: Re: Re: OK, so I planted the Eclipse this weekend......

> The APC prop was a 15.75 x 13 and was on a YS 160 on Hyde soft mount with
a nose ring.   I was not running engine at max rpm by no means although I
did not take a tack reading, I did have the needle about 2.5 to 2 ¾  turns
out with 30% nitro.   Talking with APC they indicated that had reported
failures of 3 bladed props.  APC recommended to keep tip speed down.
Failure accrued at the hub of prop.  Tonight when I return home  I plan on
sending some photo?s to Bob Pastorello, my camera is only 4 mega pixel with
limited macro.  We found 1 blade and it looks like once  this blade failed
it may of took out a 2nd.  We found engine with only 1 blade on hub.  Other
blade was never found or near engine impact zone.  Engine was about 400 feet
past where we found the first blade by a dirt road.  If I use a 3 blade prop
again, It will be a carbon fiber type only!!!!!!!! Ed White may be able to
add his observations. But I remember a buzz hearing lots of fiberglass
breaking and a second !
>  later seeing engine fall from plane. I am luck to have landed plane about
150 meters from me on its gear.
> >
> > From: "Charlie  Rock" <crock at kc.rr.com>
> > Date: 2005/04/26 Tue AM 08:04:34 CDT
> > To: <discussion at nsrca.org>
> > Subject: Re: OK, so I planted the Eclipse this weekend......
> >
> > Sorry to hear the rough landing of your long time trusted Typhoon..You
flew it very well..I too am curious as to what you think happened to the 3
bld? Charlie Rock
> >   ----- Original Message -----
> >   From: William Ahrens
> >   To: discussion at nsrca.org
> >   Sent: Monday, April 25, 2005 10:53 PM
> >   Subject: RE: OK, so I planted the Eclipse this weekend......
> >
> >
> >   I don't have as good as explanation as Jerry.  But there I last Sunday
pulling up to do a turnaround maneuver,  the full roll half reverse Cuban 8.
Just before rolling and applying power the engine departs the plane due to a
blade breaking off my APC 3 blade prop, it was a very bad sound of balsa and
fiberglass breaking occurring in seconds. The YS160 broke the beams of my
soft mount and pulled thru the nose of my trusty old Typhoon 2000.  Yes I
was experimenting with this prop and had about only about 5 hours of time on
it.  As I see the engine fall from plane I decided to try and fly the plane
back to the field.  Plane flipped up when the engine left,  I then realized
the plane had poor flying qualities.  (Now I now what a really tail heavy
plane feels like.)  , Needing control, I dove the plane to the ground to get
airspeed.  During dive I was not making much progress to the field, I was
not going to make the field due the wind at my back and the plane's poor
flying !
>  quality and would need to land in the farmers field.  It was like a
roller coaster ride down with plane, just trying to keep the plane from
flipping.  As I neared the ground I put the plane in a nose down attitude I
pulled full up and flared about 2/3 feet above ground.  Plane hits ground
nose first and the experiment is over.  Engine search took about 2 ½ hours
to find.  We actually found the blade that broke off before finding engine.
Vibration, cracked fuselage and both ailerons on wings!!,  Typhoon will need
a little work to fly again.
> >
> >   Bill A.
> >
> >
> >
> >
>
> --------------------------------------------------------------------------
----
> >
> >   From: discussion-request at nsrca.org
[mailto:discussion-request at nsrca.org] On Behalf Of bravo52
> >   Sent: Monday, April 25, 2005 9:52 PM
> >   To: discussion at nsrca.org
> >   Subject: OK, so I planted the Eclipse this weekend......
> >
> >
> >
> >   Yep, it is no more.  Man I loved that plane.  I loved the way it flew
like a bullet.  Because of the "new" radio's and the fact that it isn't my
primary plane, I programmed in some flaps.  Well, normally, when you deploy
flaps without mixing in a little down, the plane pitches up.  I was a couple
of mistakes high and my buddy said, "put down the flaps" and so I did.
Well, what happened next was probably the best looking crash I've seen in a
long time.  Two things happened.  First, the nose pitched up so fast ( I
think I was carrying too much speed) I think I sheered a control horn on the
right aileron.  Then came the tuck.  Oh yea, that baby tucked nose under and
rolled left.  I was on the flap switch faster than kiddies on candy but it
didn't help.  With full opposite aileron, I could barley roll level.
Unfortunately, I was about 60 degrees nose down and picking up speed.  One
of the qualities of the old Piorun Eclipse is little or no drag.  Any way,
by the time I got!
>   on the elevators and leveled out, it plane was about 3/4 of an inch off
the ground and accelerating!  Then things started slowing down.  I think
they call it temporal distortion.  In very slow motion, the plane was flying
ever so smoothly across the ground when parts just started departing the
aircraft.  The first to go was the prop blades.  I actually saw one fly
off...that is right before the left horizontal stab tip just touched the
ground.  Then it exploded in a cloud of foam.  Then, the left wing.  Pulled
the wing tube right out of the fuselage.  Now mind you, the fuselage is
still scooting along at Mach 3 shedding parts like crazy.  And even though
it seemed like minuets, this all happened in about 5 seconds!  All the
while, I'm thinking, "No problem, I got this.......".  In all, the fuselage
in primarily intact.  The left wing is good, the right wing lost the wing
tube and part of the wing root, allot of sheeting and some foam.  The left
horizontal stab has left the!
>   building.......... But......I think I can rebuild it!
> >
> >
> >
> >   Jerry L.
> >
> >
>
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