flyrotary@lancaironline.net Mailing List Archive

The long skinny cooler does not have a great number of tubes. Cutting the tube count in half will more than double the drag and reduce oil pressure. Doing the double pass trick is actually quite easy.

Pressurize the cooler with compressed air while doing the groove and drilling the hole. Cut the threads off of the fitting and radius the hole in the fitting to look like a trumpet bell. Wire brush (stainless) the anodize off of the fitting before welding. Wrap the plenum with a wet towel up about 1" from the fins. Check that the stock bung is also radiused inside the plenum. If not, make that one the "In" port. Make your new radiused fitting the out port.

More than 1/3 of the waste heat must be removed through the oil cooler. That is some stock in trade saying so often heard on many sites. I would suggest that it should be closer to half of the heat must be removed through the oil cooler. The smaller number might be accurate for a street car at freeway speeds. Or, about 2,200 RPM. Now comes the racer or aircraft builder to ask for a nice steady 5,500 or 9,600 or more RPM. The stock cooler (or similar) mounted between the gear legs, in the prop blast might not be enough.

Let me point out again, Racing synthetics absorb heat more readily than conventional oils. Synthetic racing oils give up heat more readily than conventional oils. I would use Red Line 40 or 50 weight synthetic. So, your cooler (in effect) gets bigger. Overheated conventional oils turn into black snot.

Synthetic racing oils remain lubricants at stupid high temperatures.

Rotaries love turbocharging. Large area cold combustion chamber holds off detonation well into high boost. For very high boost lower compression rotors are available. Adding boost (intake air volume)

is the same as making the engines displacement bigger. So, more air and more fuel gives you more power than the stock engine. One feature that does not change with boost pressure is the combustion chamber volume. So, as boost goes up, so does the (effective) compression ratio. Higher compression means higher rotor heat, and higher oil temps. The racer had 132 rows of Setrab coolers and on scalding hot days oil temperature was still a problem. Just my opinion. I could be completely wrong.

Lynn E. Hanover

In a message dated 9/30/2018 3:56:32 AM Eastern Standard Time, flyrotary@lancaironline.net writes:

Hey Rotorheads;

This summer I bought the Fluidyne DB30618 but it is only a single pass. I recently inquired about them with Summit Racing and they say they will provide a 2-pass as a custom order. The stock oil cooler is a 2-pass but much more restrictive. The single pass added a longer hose with a 180 swept fitting to make it work.

I'm seeing higher temps than I'd like to despite my improved duct work. Actually inlet duct was improved, but outlet duct is new as I didn't have one before and I do wonder if the outlet duct is restrictive but I'm limited with space and old nose gear mount being in the way (as much as I'd like to remove the nose wheel mount it is integral to the engine mount, so I'm stuck with it), so I wonder if it would be better to remove the exit duct completely and just leave the oil cooler exit air un-ducted?

But to the main question for tonight, I'm thinking about converting my cooler to a 2-pass. I have been experiencing higher oil temps than expected at around 110C and considering the OAT has dropped considerably, I would like to reduce these somewhat. I suspect that the flow is not going through the entire cooler evenly with a majority of flow channeling through only a few of the tubes as it is not really any different than the temps it used to see with the Mazda cooler. The larger size and more efficient design should produce better cooling if oil was flowing evenly through all tubes and spending a longer time in the cooler.

So I'm thinking it should be simple enough to convert to a 2-pass cooler which should ensure a better distribution of flow through all the tubes. But is it really so simple?? See pic at

https://photos.app.goo.gl/TrU99jXjftz4X8h37

It would seem a simple matter to zip-cut a slot where the red line is, slide in a baffle plate and weld it up, re-sealing the end tank, drill a hole and weld in the new AN10 fitting and at the other end, zip off the old AN12 fitting and weld it up. This would also simplify plumbing, as the oil in line would be shorter and go straight in with no 180 bend.

But the thing is I can only weld on 3 sides of the baffle plate that I would install. I can ensure that it is tightly seated against the tube end plate between the tube but it wouldn't be a sealed junction. Do it right and an insignificant amount of oil may bypass there and not go through the tubes. Do it wrong and it could be a significant amount with a drastic reduction in cooling.

Obviously I've already removed the cooler and brought it home with the intent to do this mod, but now I'm second guessing myself. I've considered that if Summit Racing is modifying these as a custom order then they likely are doing just what I plan to do. Otherwise it would have to be done during manufacture by Fluidyne.

It seems simple, but I lost sleep last night considering all the various issues. Still didn't do it today, so I figured I'd pose the question to the group and go hunting with my kid tomorrow while I wait for the opinions to arrive.

On another topic, during a take-off roll the other day, the diaphragm in my old stock wastegate actuator blew. I didn't catch it with the throttle until I hit 16.5 psi of boost. No damage but I gotta say that's a fun way to get off the ground in a hurry! I usually limit myself to 6 psi of boost as that was the spring pressure. I do have an electronic controller (TurboSmart) which allows me to have higher pressures above the spring pressure, but that is intended for high altitude and mountain flying.

I've ordered a new adjustable piston type of actuator that comes with a selection of 6 springs. I intend to use the 3 psi spring as I usually use the boost very conservatively and the TurboSmart controller can give me more if I need it for short mountain strips.

Anyways, I look forward to your opinions on the oil cooler.

Todd Bartrim ....... 20.6 hours on new RV9 version 2.0..... I had to cash in beer cans for gas money....

C-FSTB

RV9 13Bturbo