Ira,
Generally, when a prop is driven out of feather, it passes through a blade
position that is more condusive to starting prop/engine rotation. Mainly
because as there is no engine rotation, the relative airflow to the prop is
---From straight ahead. However, a stationary fixed pitch prop when presented
with this airflow from straight ahead is effectively stalled - a just a flat
plate. That is why the fixed prop is so draggy.
CS props generally go from fine pitch through coarse pitch to the feather
position.
regards,
MP
----- Original Message -----
From: "Ira Rampil" <rampil@anesthes.sunysb.edu>
Subject: Re: Flying (with an Airstart!)
> Hi Graham,
>
> That is an interesting observation. I must be missing
> some critical aspect of the physics involved in the difference between the
> two props and their hubs. In order to airstart an engine, the prop must
be
> taken out of feather in order for the relative wind to impart a rotational
> force. Is it a matter of degree of prop pitch? What am I missing?
>
> Ira
>
>
> On 3/20/02 4:15 PM, "Graham Singleton" <grasingleton@avnet.co.uk> wrote:
>
> >> Then John told me that several
> >> people had hypothesized that the Rotax would be difficult to air start,
so
> >> of course we just had to try it! After feathering and stopping the
prop at
> >> about 75 mph, we glided for a short while, with a ratio of about 15:1
> >> (short wings this trip), then took the prop out of feather and nosed
over a
> >> bit. At 110 mph the prop took a few quarter turn jumps. At 120 mph,
with a
> >> single half rotation, the engine caught immediately.
> >
> > Teh Rotax is not difficult to air start with a feathering prop, which is
> > not allowed in UK I believe.
> >
> > It is impossible to air start with a fixed pitch Warp Drive prop in a
Europa.
> >
> > Graham
>
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