Dan why are you measuring Van's cowl inlet at the back or exit. The total area is measured at the tangent of the radius. Yes?
Sure. Problem is, how do you get all survey respondents to use the same measurement points, given tangents are not well defined? So, asking them to use the flat at the back of the inlet offers consistency. I can add back the additional area on my own, if necessary. Rarely is, because comparisons require only apples to apples.
Dan, Mr. Richard VanGrunsven is a degreed engineer.
Indeed he is. Are you trying to say there is only one conclusion, understood only by the degreed?
Rules of thumb for inlet to exit ratios have been known for a long time.
Believed for a long time, recently discounted. I've attached a scan below, from Dan Raymer's 2012 work, available here:
https://www.amazon.com/Simplified-A...45711451&sprefix=daniel+raymer,aps,155&sr=8-5
Read the attached a few times. There is a lot to consider in those three little paragraphs.
BTW, Raymer's "
Conceptual Design" is a reference standard well worth having:
https://www.amazon.com/Aircraft-Des...45711655&sprefix=daniel+raymer,aps,155&sr=8-3
As I've previously written here, inlet-to-exit ratios are all but useless in reality. Given good detail design, both low and high Vi/Vo inlets can be made to work well, meaning very different exit/inlet ratios.
On my RV-4 I made aerodynamic plugs I taped into the cowl inlet near the prop hub, reducing inlet area while meaning change in temperatures. Almost impossible to measure improved airspeed, but I am 100% sure it was good for "micro knots" ha ha.
Nothing in CR3405 suggests inlet plugs would be of value. The above result was entirely predictable. The primary goal for an inlet is maximum conversion of available dynamic pressure to increased upper plenum static. Exit size governs mass flow and velocity.
Here's an email written to a friend circa 2008, maybe 2009. I didn't arrive the current cowl configuration via the million monkeys approach.
https://www.danhorton.net/VAF/Cowl Inlet Dimensions/Cooling notes3.txt
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