----- Original Message -----
From: "Mark Burton" <markb@ordern.com>
Subject: CS Prop Failure (a cautionary tale)
>
> Hi William,
>
> Please forward this email to the Europa mailing list for me.
>
> Here's a story that is relevant to everyone who has a constant speed
> prop fitted (irrespective of prop manufacture). Sorry it's so long but
> it's worth reading.
>
> Yesterday, I went flying in G-NEAT which is fitted with an Arplast
> PV50 electric VP prop and a Smart Avionics CS controller. Before
> starting, I manually adjusted the prop pitch to be fully fine to make
> engine starting as easy as possible. Start up, warm up, taxy, engine
> checks, everything's OK, let's go flying.
>
> Accelerate, liftoff, flying. At about 50' I realise that something's
> wrong, the revs are higher than normal and in no time at all we're off
> to red line city. For a brief moment I considered landing ahead on the
> rapidly shortening runway but with little wind and near gross weight
> that really wasn't a sensible option so I reduced the throttle and
> once I was satisfied that I could actually stay in the air without
> destroying the engine, I flew a very low and slow circuit and arrived
> back on the ground much relieved. Full marks to my passenger (another
> pilot) who kept quiet and let me concentrate on the flying.
>
> So what went wrong? No doubt you have guessed. The prop had stuck in
> the fully fine pitch position. Subsequent investigation found that a
> small wire in the PV50 hub had fractured where it was soldered to the
> diodes/switches. So black mark to Arplast for not providing any form
> of strain relief on the wire joint (pity their electrics are not as
> good as their blade aerodynamics).
>
> Another factor (and this one is my fault) is that the fine pitch limit
> of the propeller was set too fine because at climb speed the red line
> was being reached at less than full throttle. With a CS propeller you
> can get away with this because even though you can start the take off
> run with the propeller too fine for flight, the CS controller will
> coarsen the pitch as you accelerate and by the time you are flying the
> pitch will be OK.
>
> So the message here is that if you have a CS prop (of any type) you
> really should make sure that the mechanical fine pitch limit is set to
> such a position that if the prop remained fully fine you could still
> use full throttle at the normal climb speed. I believe this is
> actually a requirement (JAR/PFA?) but I wonder how many of us have
> made sure that we are compliant. I can see the sense in it
> now! Remember, no matter what prop you have fitted, it could fail at
> any time (bad wiring, brushes worn, motor shagged, controller toasted,
> finger trouble, ...)
>
> So today, I adjusted the position of the fine pitch limit switch on my
> PV50 to make it coarser. Flight testing showed that it could have been
> a little bit coarser still but the microswitch was at its limit of
> travel so it will have to do for now.
>
> One last thing, as you probably all know, I manufacture avionics and
> one of my products is a talking ASI (the SmartASS). I always use it
> for take off because it makes it very easy to maintain Vy while
> looking out the window. During my thrilling circuit yesterday, it
> helped greatly to have the airspeed called out every few seconds
> because it meant I could concentrate on flying the aircraft,
> navigating around the circuit and keeping the revs under control. My
> passenger was so impressed that after landing he immediately said he
> would buy one! That's great, but I'm not going to do any more demo
> flights like that again, even if it does guarantee a sale!
>
> Cheers,
>
> Mark
>
>
> --
> 09/12/2005
>
>
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