REFLECTOR: Vortex generators location for armpit cooling scoops

[Laurence Coen]

Andrew,

I have armpit scoops on my SR/RG that look just like yours.  When I mounted them I was concerned about the boundary layer and extended the scoops 3/4" out from the fuselage so the entire scoop is outside the boundary layer.  I also added an insert that looks like venturi that in theory should help with pressure recovery.  The fact that I don't have cylinder head cooling problems doesn't mean that it will work for you.  I am down draft cooling a 220 HP Franklin.  I have vortex generators ahead of my oil cooler inlet and that did lower my oil temp.  If you try vortex generators I would suggest that they be tall enough so they stick out of the boundary layer.

Larry Coen
N136LC


From: Andrew Ellzey 
Sent: Wednesday, August 14, 2013 3:50 PM
To: Velocity Aircraft Owners and Builders list 
Subject: REFLECTOR: Vortex generators location for armpit cooling scoops


I am still battling a high CHT at cruse on my # 5 cylinder on my updraft IO-540-E1A5, 300HP Lycoming engine. I can do full power climb outs in the pattern all day without any issue. From everything that I have read on this subject on the Reflector, this is common with the arm pit cooling.  The higher pitch angle in the pattern, and in a cruse climb, forces plenty of cooling air into the scoops, but the cooling ability drops off in level cruse fight attitudes. My question is, is there anyone left on the reflector that is using the armpit cooling, and do you have vortex generators in front of your armpit scoops to help the airflow boundary layer adhesion to this area forward of the armpit scoops? If you have vortex generators, what size, location, did you make them, buy them, can you send a photo, please.

I have swapped and calibrated my CHT probes, swapped the lowest CHT cylinder fuel injector with my #5 injector. Nothing helps, it seems to be tied with airflow into my scoops, or airflow inside my lower cowling. If the addition of vortex generators doesn’t  help, I will probably have to install some additional baffling to redirect more air to the aft two cylinders, #5, and #6. Cylinders 1, 2, 3, and 4 are getting plenty of air, in fact they are running cooler than I like at this time, but until I can get #5 CHT under control, I can’t lean my engine properly to know if I have adequate airflow for all cylinders or not. Installing my gear doors seemed to help.

Photo attached showing my armpit cooling scoops. The additional screws under the armpit scoops, attaches a mating internal scoop that directs the airflow to my aft lower cowling.  

Thanks again for your help,
-----------------------------------------
Andrew Ellzey
N151AJ 10 hours into Phase 1 testing


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