Can some of you more “experienced”
folks tell me..does the prop windmill after the engine quits, or does it stop
rotating?
Bill B
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Lehanover@aol.com
Sent: Sunday, August 22, 2010
11:29 AM
To: Rotary
motors in aircraft
Subject: [FlyRotary] Re: Prop
orientation with TDC
In a message dated 8/22/2010 10:28:20
A.M. Eastern Standard Time, blake.lewis@gmail.com writes:
On Sat, Aug 21, 2010 at 7:34 AM, Jeff
Whaley <jwhaley@datacast.com> wrote:
> What is the Rotaries best prop orientation at the prop flange relative to
TDC?
> The Lycomings are typically entering the compression stroke at 11-10
o'clock and 5-4 o'clock.
> The 13B goes through 3 compression strokes per e-shaft revolution - does
this predicate a 3-bladed prop is the ideal match?
> Jeff
The orientation idea comes from the older
4 cylinder airplane engines that had to be hand started. So the position of the
blade made a difference in that the person starting the engine needed a good
body position to start out. It was also a good idea, because in the event of an
engine stoppage, that very same position had the prop near horizontal, and that
kept a blade from digging in on landing.
In the rotary powered craft, the engine
will be at TDC twice per crank shaft rotation (for a two rotor) so, 2 times the
reduction ratio tells you how many times it gets to TDC per propeller
revolution. 3 times for a 3 rotor, and 4 times for a 4 rotor.
A 2 rotor with a 2.78:1 reduction unit
will see TDC 2 X 2.78 = 5.56 or about every 65 degrees of prop rotation.
This suggests that hand propping might be
more difficult because of the mechanical disadvantage of the reduction unit,
and should the engine fire, the length of time available to remove your hand
might be very short, should the very next rotor face fire as well.