Lynn Allen wrote:
skydaddy61 wrote:
Forwarded to someone who knows someone....
Roger that and thanks, I thought I was going to have to ask the Boyz at Sears
I know of one in Boerne, Texas, Oberville, and he has seen the high temps.
Lynn
The reply from my source familar with both the Yak and CJ:
This one made it around the Yak-List a few weeks ago. The CJ doesn't run as hot as the Yak 52 in normal ops. Naturally, the two aircraft have different engines (285 hp Housai vs 360 hp Vedenev) and the CJ has a different oil cooler arrangement that yes, is inside the right wing.
[A friend] does a complete airshow routine in his 52 and typically has to limit the number of maneuvers due to ambient high temps that maybe present during the show. Of course, his throttle is buried during most of the act with alot of flow blocking lomchevaks.
I looked over his oil cooler and thought that maybe a longer exit pan (outlet duct) with a downward curved lip might induce a better draw to bring more than normal flow through the cooler. Look at any Citabria used in aerobatic competition and you'll see this mod'. Other than that possibly a larger or secondary cooler needs to be added. A friend with a Yak 50 experiences the same troubles with temps. As for the CJ, it is not a problem although I do not push the engine that hard to begin with. Hope that helps.
I wouldn't be shy to try some temporary sheet metal add-on or fiberglass mock ups to see what works best and then fabricate a permanent best fix. A lot of test flying but hey, what better excuse to go up for a jaunt.
Some possibly-relevant personal experience:
BITD I was an engineering co-op at Swearingen. They were testing the PT-6 on the Metro. Many flavors of cowling, fillets, and oil cooler ducting were tried. One iteration had oil cooler inlet ducts on both sides of the nacelle. We found that air flowed in the outboard oil cooler inlet duct and right out the inboard inlet duct due to the venturi between the nacelle and fuselage. No flow at all through the cooler itself.
They put a baffle in the inlet plenum chamber, but the low pressure between the fuselage and the nacelle was still lower than the exit duct. Air flowed down one side of the cooler and up the other side. Zero flow out the cooler exit doors.
THEN, we discovered that the NACA inlet ducts as installed had the wrong profile. The inlet lip was a smooth bullnose cross-section. But according to the NACA reports we dug up it needed to have a "speedbump" on the inside to induce low pressure...
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