I agree with Bulent about bottom scoop needing to hang down more (think P-51) and  Bob White & Richard (refine the exit "profile").  Make your underwing inlet hang down 4-5 inches, at least.

Bulent, how far below your fuselage is the lower edge of your inlet (lower face of bottom of inlet, i.e., inside face, not lower outside contour)  I looks like top inner face of your inlet is 3 inches below fuselage and another 7 inches down to the lower inner face.

If RTV adhesive works, that would be fine.  If more strength was needed (later on at higher speeds) could anyone recommend a glue for  "temporary scoops" that might be stronger but soften for removal/modification with hair dryer heat, e.g., 130 degrees, just below the 140 deg or whatever that the fiberglass structure of the wing would be affected?

David Carter
----- Original Message -----
From: Joe Hull
To: Rotary motors in aircraft
Sent: Sunday, August 06, 2006 9:11 PM
Subject: [FlyRotary] First flight - Oil temp

It was bugging me that I couldn’t remember the reference to the reverse scoop – so here’s the link – it was Dick Rutan:

http://www.ez.org/cp47-p11.htm



Essentially put the reverse scoop on the top of the wing all the way ahead of the oil cooler for best cooling.



Joe Hull

Cozy Mk-IV N31CZ (65 hrs - Rotary 13B NA)

Redmond (Seattle), Washington



From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Joe Hull
Sent: Sunday, August 06, 2006 8:01 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: ***SPAM*** [FlyRotary] First flight - Oil temp



Al,

I’m not an aerodynamicist and don’t pretend to be one…with that said…I think your heading down the right path with either a larger bottom scoop or VG’s.  The bottom opening is definitely in the boundary layer that far back past the strake. The real trick is determining where the VG’s go – that’s more trial and error than science I think.



Also, I think it was Dick Rutan and/or Mike Melville who reported greatly improved oil cooling (the original Long-EZ’s had oil cooler in the wing root) by putting a reverse scoop about half way back from where you have yours – i.e. about half the distance of the oil cooler. I think Dick actually reported putting the reverse scoop just ahead of the oil cooler. I guess the pressure drop is not immediately behind the scoop as one would expect but rather a few inches beyond it.



Any who, the sure fire solution is obviously to drop the bottom scoop down and catch some of the free stream. You might be able to experiment without messing up your fiberglass and paint too much by creating a larger scoop that you can “glue on” with RTV or something that extends the existing scoop forward and down another inch or so. Once you find the optimum opening size and distance from the wing bottom – then do the real fiberglass work and open up and drop the existing scoop. Yes, you’d have to try to account for the fact that you would be forcing air through the original size opening – but if you get it to cool with a larger scoop and the original openings just think how well it will work when you open up the original holes!



Sorry for the ramble. Hope that gives you some ideas.



Joe Hull

Cozy Mk-IV N31CZ (65 hrs - Rotary 13B NA)

Redmond (Seattle), Washington



From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Al Gietzen
Sent: Sunday, August 06, 2006 6:45 PM
To: Rotary motors in aircraft
Subject: ***SPAM*** [FlyRotary] First flight - Oil temp



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 ¼” wide, 22” long and 3 ¼” 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 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