Received-SPF: pass
 receiver=logan.com; client-ip=204.127.217.102; envelope-from=ceengland@bellsouth.net
Message-ID: <46A18681.7050409@bellsouth.net>
Date: Fri, 20 Jul 2007 23:07:29 -0500
From: Charlie England <ceengland@bellsouth.net>
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.1.2) Gecko/20070222 SeaMonkey/1.1.1
MIME-Version: 1.0
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] First flight - Oil temp
References: <list-1311265@logan.com>
In-Reply-To: <list-1311265@logan.com>
Content-Type: text/plain; charset=windows-1252; format=flowed
Content-Transfer-Encoding: 8bit

replying to an old post from 8-6-07, because it had relevant pics

Hi Al,

I try (often unsuccessfully) to refrain from posting about stuff with 
which I have no hands-on experience. But I thought it over, & if you're 
listening to PL, I figured 'Why not?' :-)

Here are a few thoughts, from only from the things I've read & seen on 
fast planes.

In OCinlet1, you mentioned that the bottom 'lip' of the inlet is to the 
rear of the inlet top. I can't cite any references, but I think I've 
read that air will have a harder time being 'captured' by the inlet if 
it's configured that way. (Pressure/turbulence in the inlet effectively 
closes the inlet & the slipstream just sees the inlet as a bump, like 
your wheel cover.) That would imply trying option C, as you described in 
this email.

In the exit pic, it looks like the top edge leads the bottom edge. Any 
chance that this allows the higher energy air high on the sides to curl 
around the into the outlet, since the edges slope forward? Also, how 
sharp-edged is the exit duct end? If the exit lip is rounded at all, it 
will encourage the air to curl back into the inlet. How sharp edged is 
the wing trailing edge behind the exit? (Same issue: air curling up & 
forward on the wing.)

You mentioned possible flow separation on the top of the exit. What if 
it's just pressure recovery on that part of the wing? From the pics, it 
looks like both the inlet & outlet are placed far back toward the 
trailing edge. All the stuff I've read implies that the boundary layer 
gets very thick as you get closer to the rear of a structure, and also 
that pressure near the trailing edge of an airfoil is actually positive 
instead of negative. The standard cockpit air *inlet* on a Thorp T-18 is 
a 2x6 inch hole at the rear base of the canopy near where it meets the 
tailcone. Further evidence implying high pressure on top is the fact 
that there are several EZ type planes flying successfully with NACA 
cooling inlets in the *top* of the cowl.

Hope I'm not just adding to the confusion...

Charlie


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 my friend 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.
> 
>  
> 
> The custom cooler for this 265 hp engine is large.  The core here is 
> about 5 Ľ” wide, 22” long and 3 Ľ” thick. It is located in the wing root 
> of the Velocity, 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 ˝” 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
> 
>  
> 
> 
> ------------------------------------------------------------------------
> 
> 
> ------------------------------------------------------------------------
> 
> 
> ------------------------------------------------------------------------
> 
> 
> ------------------------------------------------------------------------
> 
> --
> Homepage:  http://www.flyrotary.com/
> Archive and UnSub:   http://mail.lancaironline.net/lists/flyrotary/