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Earnest nailed it. Ten years ago you really did need to at least attempt to "engineer" a solution. But now there is a pretty good variety of functioning flying examples in a variety of airframes. Pick the one that's similar to yours and copy it. I'm not an engineer, but I work with a bunch of them and I can tell you that there's no shame in copying somebody else's engineering if it works. Especially when the alternative is engineering something on paper that doesn't work as well as the system you probably should have copied.
Or you could analyze it to death for the rest of your life and never build and fly anything. I nearly fell into this trap. Instead I chose to try to build something that was "good enough" with the hope that it might just turn out to be "pretty dang good". I assumed it wouldn't be perfect out of the box but would only sacrifice "a few fpm in climb and a handful of kts at cruise". Leaves some room for tweaking after the fact to find those fpm and kts.
Mike Wills
RV-4 N144MW
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From: "George Lendich" <lendich@aanet.com.au>
Sent: Monday, January 25, 2010 4:10 PM
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Subject: [FlyRotary] Re: Wedge/Oblique Duct
Ernest,
You are most probably right, but I'm trying to think how the pros might do it on paper, before committing to a physical design.
How might a Aeronautical Engineers tackle a problem like this - there are most probably some simple formulas, perhaps.
George ( down under)
George Lendich wrote:
Ed,
I have been thinking about this, if I use A1V1=A2V2 to solve for the inlet opening size, how do I know if the speed of air through the duct is correct i.e. 10% for cruise and 30% for climb.
Also If I use the Cessna 171 speed of approx 100 K for cruise = 10 K through core, 70 knot climb and approx 20 K through core. Do I then use the climb speed to calculate inlet air openings and attach an adjustable louver exit OR I suppose I could do as Tracy does and calculate for cruise and attach a spray bar.
I'm still a little confused on the best approach.
George ( down under)
George, maybe the problem is that there isn't a "best approach". There's "not worth a cuss"; and there's "good enough". There might even be a "works pretty dang good". Everybody wants bragging rights to having landed the perfect solution on first flight, with the difference between perfect and "get it in the air" being a few fpm in climb and a handful of kts at cruise.
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