Mailing List flyrotary@lancaironline.net Message #20274
From: Jack Ford <jackoford@theofficenet.com>
Subject: Re: [FlyRotary] Re: Fw: Rx-8 Rotors useable in 91 13B?
Date: Thu, 14 Apr 2005 19:02:20 -0700
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Section modulus for a rectangular cross-section (strength in bending) bh^2/6; Moment of inertia (stiffness) bh^3/12, (Taken around the neutral axis) so strength in bending is proportional to the depth squared, stiffness to the depth cubed.
The two values are related and one can be easily calculated from the other. s=I/c.

Jack Ford

----- Original Message ----- From: "Ernest Christley" <echristley@nc.rr.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Thursday, April 14, 2005 6:36 PM
Subject: [FlyRotary] Re: Fw: Rx-8 Rotors useable in 91 13B?


Ed Anderson wrote:

Thanks, George
 Appreciate the information on the seal grove.  Perhaps we'll just skinny down one  of Tracy's seals as on their web site they are reported 800% stronger than stock, then just stick them in the RX-8 rotor slot.  I mean even if milling the seals to fit reduces there strength to 200% of stock that should still be fine.  Must discuss with Tracy when he returns from Sun & Fun
 Ed


I'm going completely off the top of my head here, and stand a good chance of being wrong, thereby, BUT...

The seals (as they cross the exhaust opening) become a cantilevered beam, with a fulcrum or support point at the edge of the exhaust opening. Doesn't a beams bending strength increase as the 4th power of the distance between the sides?  I do know that if you split a beam in half, you'll have much less than half the strength.

The other issue would be that stronger doesn't necessarily equate to stiffer.

-- This is by far the hardest lesson about freedom. It goes against
instinct, and morality, to just sit back and watch people make
mistakes. We want to help them, which means control them and their
decisions, but in doing so we actually hurt them (and ourselves)."


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