Another Angle on Oil Temps?

[207WF]

Its hot air temp season again in SoCal, and a new idea has emerged about the persistently high oil temperatures that some of us -- but not all of us -- experience in the climb. Please chime in with the data for your bird. 1. Do you have the problem of high oil temps in the climb? 2. What is the gap between the top of your radiator and the top of the large hole in the front of the cowling?

 

We recently readjusted mine to close my gap a bit, and I want to believe that it lowered my oil temps in the climb, but some more data would help. I know that some CTs have a large gap there and others do not.

 

WF

[Rogerck]

I'm thinking about temporarily adding duct tape between the top of the oil cooler and the cowling bottom. Curious to see if this reduces climb out oil temp. If this works, perhaps a permanent rubber baffle could be added (we have on ELSA.) My concern is that the tape might block some otherwise required air flow. On the other hand, with oil and water cooling, the engine might not be sensitive to small changes in air flow.

 

Opinions?

 

Roger Kuhn

[Mike Koerner]

I'm sorry folks. I don't think closing the air gaps around the edges of the radiator is going to amount to much more than a hill of beans.

There's a ton of air available, even at 60 knots, to pour through the cowl opening. The radiator presents a huge restriction to the air flow so the air flow is spreading outward from the center of the radiator anyway. You essentially have 100% ram recovery and full stagnation pressure across the whole front surface air of the radiator, even with some air spilling around the edges. I suspect the leakage only affects the upstream air pressure in a very narrow band around the gap.

You might try working on the problem from the other end instead. Recognizing that the flow through the radiator is a function of the delta P across it, and that at any speed and altitude you have a fixed pressure on its upstream face, you might try to reduce the pressure on the downstream side by making it easier for the air to flow through, and out of, the engine compartment.

The lower edge of the rear of the cowl hangs down below the bottom of the rest of the fuselage. I think this step causes a pressure drop which draws air through the engine compartment. You might try increasing the size of the step or opening the gap up a bit as a way of increasing the flow through the radiator.

I would try this myself, but I don't really have a problem with high oil temperatures. I lower the nose if I'm climbing and otherwise back off the throttle a bit if I see the oil temperatures getting hot.

Mike Koerner

[Runtoeat]

Mike, you've made a good point. A lot of aricraft deal with oil cooling by using cowl flaps which provide enhanced airflow thru the engine compartment. I recalled a previous post where CT owner Waggles in Australia enhanced his CT's airflow by modifying his cowl in the area you mention:

My link

[S4Flier]

Airwolf came out with an oil chiller product last year that I was tempted to try: Oil Chiller. The basic premise is to create a heat sync similar to what you find on hot running computer CPUs which creates more surface area subject to air cooling. Although the intent was to wrap the device around the oil filter, they said that Rotax installs are putting it around the oil tank. Anecdotal results for Rotax were around 3-5 degrees cooler. YMMV.

 

I don't believe I can fit the chiller on my Sting but E-LSA CT's might be a different story.

[Runtoeat]

Dave, my friend uses the aluminum chiller on his Stinson oil filter and says it decreased oil temps about 7 F. He's got a big filter on the Stinson (Franklin engine?) so I don't know how much effect this might have on our small Rotax filter. The use of the cooler on the oil reservoir sounds like a better application and the evidence shows this does work per your post.

 

Roger, I'm not troubled by oil temps here in Michigan but I have the header wrap on my short list. This can't hurt and probably would lower the temps as you point out and looks cool too.

[mocfly]

Mike, you've made a good point. A lot of aricraft deal with oil cooling by using cowl flaps which provide enhanced airflow thru the engine compartment. I recalled a previous post where CT owner Waggles in Australia enhanced his CT's airflow by modifying his cowl in the area you mention:

My link

 

 

This modification did not work on the ctsw,it did work on the mc.

[Runtoeat]

Mocfly, I wasn't aware that this mod was tried on the CTSW. I see that the exit openings in the MC cowl have the rear edges lower than the front and thus would be scooping air so it seems logical that the mod works here. Still, I would think that the mod would provide greater scavenging and would move more air thru the engine compartment on the CTSW's than the modest opening of the factory cowl which should mean cooler temps. Perhaps the mod doesn't work here because the small air entrance in the front of the cowl is the limiting factor? Did you try this on a CTSW yourself or know who tried this?

[207WF]

None of you guys are measuring the gap or answering my question. Please measure the gap and chime in with your experience. I want data, not speculation here! WF

[mocfly]

I believe its is more related to the angle of the radiator relative to the opening, and the fact that FD has that piggy back configuration.

I am trying to figure out how to remotely measure the airflow behind the radiator. Once that is done i will ask FD what they use as a design figure.

[Adam]

Wayne, I'll measure my gap next time I'm at the airport. I flew to Flabob (breakfast), Big Bear (lunch) and Thermal (off the back side of Big Bear) this weekend. Coming out of Thermal (Palm Springs area for those not familiar with KTRM) was the first time I encountered climb temperature issues. 210 to 225 is good on my bird (green), once above 225 or so I start getting into the yellow. To combat this I was step climbing. Every thousand feet or so as I started to get into the yellow I'd level off for a few minutes. As I picked up airspeed the temp would come down. Once back to about 214 I'd go up another 1000. Still early in the season. I can see my new plane will be one of those that has this issue! In level cruise I am typically running 200 to 210. I heard you talking to So Cal coming through the Banning pass as I was headed into KTRM. Looks like you were playing out in the desert too!

[mocfly]

None of you guys are measuring the gap or answering my question. Please measure the gap and chime in with your experience. I want data, not speculation here! WF

 

 

Here is a picture of the gap of the cowling to the cooler and the cooler mount which doesn't look quite right. It looks to be about 1.0 to 1.25 total. Another interesting thing was the angle of the radiator assembly. I am adding that also. Maybe some of the guys who don't have high oil temps can measure the angle on their aircraft.

 

Flew from CHA to TAZ. 3.9 hours at the redline the whole way. I a really starting to dislike this aircraft. Pitch is good, CHT is good, oil pressure is good and the GD oil temp is driving me crazy.

 

I am ready to try anything at this point. Including a match.

[mocfly]

Roger,

I will make the adjustments this weekend and let you know what the outcome is. I am running 50/50 and based on what i see there are no obvious restrictions. I would assume that if there was a slight restriction an increase in pressure would follow?

 

What do you make of the radiator angle? I am having a german buddy of mine send a letter in German to the guys overseas about what the angle should be. I would be curious what they come back with.

Thanks again

Chris

[207WF]

Mocfly:

 

Thanks for the measurement and the photo of the radiator gap. Your gap is much greater at the top than mine. Mine used to be about 5/8" but I have it down to about 1/3" now and that has helped somewhat. I would like to raise the radiator a little further, as there is a lot of radiator coil hiding below the bottom of the hole in the cowl that is likely not being used to its full effect.

 

I wonder if the clamps on the side of the radiator can be turned 180 degrees to raise the radiator further. It looks like it might be necessary to replace one of the water hoses with a 90 degree banjo type to make that work. Any thoughts anyone?

 

WF

[mocfly]

WF,

After some calculations I believe a huge contributor is the angle of the radiator to the relative wind and the pressure/velocity in FPM thru both the coolers. I believe that a few degrees angle will make a huge difference and i am building a test rig to try some things. Since air has a lower heat capacity and density than liquid coolants, a fairly large volume flow rate (relative to the coolant's) must be blown through the radiator core to capture the heat. There is a fine line between increasing the angle to a point that creates excess drag and the condition that we/I have now. Not having any other data I can only assume that this is relevant.I would like to hear from those who do not have oil temp issues to measure that radiator angle and post it up.

I will post information as I get it.

Mocfly

[Ed Cesnalis]

I suspect that the angle means little. I can fly at 3 different flap settings and a variety of pitch attitudes and still no joy. The only thing that gets me into the green is climbing above 72 degrees F. Once I cross that altitude I am fine below it I'm in the yellow even in level cruise.

[ozairangel]

Dont forget to check the cleanliness off the heat dissapating surfaces, ie, the airflowthru the radiators which can become dirty with time, depending on your flying conditions, and if perhaps some oil got spilled when changing the filter, which can result in a nice insulating build up of dust etc.

[mocfly]

Oz,

Fd could have made cleaning easier if the didn't weld the oil and water cooler together. I have to wonder what goes thru the minds of the guys who design our planes.

Makes me want to scream. I am doing a couple of trials this weekend and will post results.

Maybe we can figure this out for all those that suffer from the dreaded oil temp phenomena.

Chris

[207WF]

Interesting angle on the angle, guys. How do you know the direction of the airflow in climb versus cruise in order to think about this? My radiator is tilted inward at the bottom edge, relative to the inlet hole in the front of the cowl. That is, the top edge of the radiator is closer to the cowl than is the bottom. My oil temp pattern is the oppposite of Roger's: hot in the climb then cooling in cruise. So, which direction do you think I would wish to change the tilt to experiment? WF

[mocfly]

I suspect that the angle means little. I can fly at 3 different flap settings and a variety of pitch attitudes and still no joy. The only thing that gets me into the green is climbing above 72 degrees F. Once I cross that altitude I am fine below it I'm in the yellow even in level cruise.

 

When you say pitch attitude do you know what the angle of the radiator is to the relative wind? What is the radiator angle when straight and level?

[207WF]

Roger:

 

I don't get it. Transitioning from climb to cruise should be "like" rotating the radiator back on the bottom, not forward on the bottom, from the perspective of the air flow angle, right? It seems that I should do the opposite of what you say since I am cooler in cruise. WF

[mocfly]

Starting do work on flow thru the radiator and was wondering if anyone had ever done a differential measurement of the cooler setup using a magnehelic gauge setup?

Cht's are in the green which is leading me to believe that the ram air ithru the upper cowl is flowing thru the cowl at the correct rate, leaving flow thru the lower section as a possible cause. Only way to measure the flow thru the color is differential pressure at the front and rear of the cooler and then a pressure measurement at the lower edge of the firewall. Any other suggestions or thoughts are always welcome.

I am trying post a couple of sketches For illustrative purposes.

Chris

[mocfly]

Roger,

I am trying to use more of a data driven approach to solve the problem and maybe help all the others that struggle with high oil temps at various times. I will be heading up to osh and talking to the guys at fd and rotax.

Interesting note is that this problem plagues the rv12 also. Needlesa to say i will be talking to the guys at van's also

Chris

[Jim Meade]

One of the things I'm going to do at OSH is take my tape measure and camera and carefully note the size and relative location of the air inlet on the CTLS. On the CTSW, the oil cooler is no where near centered on the air inlet. I don't know if that's an issue, but I will ask some questions of FD on it.

[mocfly]

This picture leads me to believe it may be a balance issue under the cowl.

Comments?