REFLECTOR: VG Line-up Question

[John Dibble via Reflector]

Is it counter productive to have the VG height and length greater than 
what the calculations call for?

John

On 10/1/2014 11:21 PM, Bob Jackson via Reflector wrote:
>
> Thanks for the response, David -- and of course I don't mind you 
> posting my offline question and your response!
>
> It will be a few months before I've got my plane back up and flying 
> again to try any more experiments myself with the inlet VGs and 
> cooling.  It's also been an area of experimentation for me over the 
> past three or four years, but less focused on inlet VG's -- which 
> based on your results is looking like at least some misplaced energy.
>
> When I do my own experiments, I plan to also test the idea that the 
> top of the windshield is really the proper point to consider as the 
> front of the fuselage airfoil, rather than the aircraft nose -- due to 
> the discontinuity presented by the much steeper slope of the 
> windshield.  The windshield 'break' is about 6' ahead of the NACAs 
> (rather than 11' from the nose).  Working the 6' length through the 
> Reynolds number equation you provided results in an approximate 
> boundary layer depth at the NACAs of ~1.3" (rather than ~2.2").
>
> Velocity_GearUp_PlanView.jpg
>
> And using the alternative 1.3" boundary layer thickness and the design 
> rules you included in your write-up produces the following new layout 
> dimensions:
>
> ·1.2" VG height
>
> ·3" VG length
>
> ·3.25" counter rotating VG spacing
>
> ·13" VG pair spacing
>
> Given these new numbers, my first try would be with three sets of 1.2" 
> x 3" counter rotating VG pairs, in a line about 20" in front of the 
> NACA inlets, which should place the outer pairs just outside of the 
> centerlines of the NACAs.  I would compare that with two sets (instead 
> of three) with each set exactly centered on the NACA inlets, or with 
> your suggested layout if I didn't get the big CHT lowering we're all 
> looking for!  I'm not sure I have the patience and time to construct 
> and conduct the full (really cool!) manometer experiment that you did!
>
> Thanks for your contribution to improved engine cooling!
>
> Bob Jackson
>
> N2XF XL/RG/XC
>
>



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