REFLECTOR: First flight - oil temps

[Scott Derrick]

Al,

Because the inlet is so short I think you are right that all or most of 
the opening within the boundary layer.

I think pursuing options A & B would be the most logical. Option A the 
easiest to try. Bring up the gear and see what happens..

I would then try option B. Its quick, cheap and easy to play with.. For 
option B you may need fairly large VG's and space them a couple inches 
apart. About 10 of them

If you decide to implement option C, be sure to extend the forward lip 
to get it out and below the boundary layer and extend the rear lip to 
compensate for the raised forward lip.

beautiful looking plane Al. Nice paint..

Scott
.

Al Gietzen wrote:
>
> Thanks everyone for the congratulatory messages, and for the support 
> that is always so helpful. No pics to post yet because my camera 
> battery went dead after the first three shots, so I’m awaiting for 
> shots from Bill who took hundreds (OK, only about 150) and will be 
> editing for a while J.
>
> The principal issue of the day was the higher than comfortable oil 
> temperature; most likely due to insufficient air flow through the 
> cooler. For anyone who would like to think aerodynamics for awhile and 
> give an opinion on the simplest and best approach to remedy; read on.
>
> Rotary engines eliminate about 1/3 of the waste heat via the oil, so 
> the cooler for a 265 hp engine is large. The core here is about 5 ¼” 
> wide, 22” long and 3 ¼” thick. It is located in the wing root behind 
> the spar with inlet underneath and exit on the top. Alan Shaw, who I 
> believe pioneered this approach, found the location worked very well. 
> When I discussed the installation with him years ago, he opined that a 
> scoop under the wing was probably not necessary because of a pressure 
> differential between bottom and top surfaces. Since then, my 
> investigations of pressure distributions, and similar installations 
> that aren’t working so well, make me wonder.
>
> Photo 1 is a view under the wing showing the OC air intake, wheel 
> well, and the big armpit scoop for the coolant radiator in the cowl. 
> The inlet opening is about 1 1/8” wide and 23” long. There really 
> isn’t a scoop, just an opening with an extended airfoil shaped lip 
> which extends about ½” into the free stream. The idea was to minimize 
> drag, and assume a more negative pressure at the exit would produce 
> the necessary flow. Photo 2 shows a front view where you see the wheel 
> well and the inlet – very little extension into the free stream. 
> Analysis suggests that the turbulent boundary layer on a smooth 
> surface at the inlet location could be about 5/8 – 3/4” in thick.
>
> The air exit fairing is shown in photo 3; and is shaped as it is to 
> maintain attached flow and cause minimal turbulence going aft. The 
> effective exit area is about 1.6 times the inlet area. The thickness 
> of the core suggests the need for pretty good pressure differential 
> for adequate flow.
>
> Here are some options:
>
> a) For the first flight the landing gear was never retracted. Since 
> the open wheel well forward of the inlet would likely cause 
> significant turbulence; try another flight with the gear retracted to 
> see if that improves the results.
>
> b) Place some VGs forward of the inlet to ‘energize’ the boundary 
> layer, and see if that helps.
>
> c) Extend the ‘lip’ of the inlet to form a proper ram scoop, possible 
> also with VGs forward to break up the boundary layer, and accept the 
> slight increase in drag.
>
> d) Do something at the exit ( local ‘expert’ suggests there may be 
> flow separation before the aft end of the fairing causing high 
> pressure behind the exit). Put VGs on the top of the exit fairing 
> and/or reduce exit area.
>
> e) None of the above.
>
> I suspect the normal aerodynamic pressure differential between the 
> inlet and outlet points is minimal; especially in level flight where 
> it could be near zero. Option c) seems the most sure-fire to me.
>
> Thanks for input.
>
> Al
>
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