Overheating

[Murray Parr]

[quote]Thanks for the comment Murray - the configuration of my cooling system (horizontal radiator at the lowest point) would suggest little chance of an "air bubble" anywhere. Couple this with about 6 run ups where temperatures reached almost to 120C - I would expect any entrapped air to have been forced to the highest point and then expelled. I have also checked the collection header every day before engine start - so far I have added about 200 ml to fill to the lip, suggesting that some air has been removed/quote]

My radiator is also at the lowest point in the system, however, the hose orientation has one hose high and the other diagnally across from that at the low point in the radiator but the radiator is not horizontal and there is definately a large area inside the radiator that traps air and no matter how hot or how much flow it has, the air can never escape that environment. Just a thought given how quickly yours is heating up

[Skippydiesel]

My radiator is also at the lowest point in the system, however, the hose orientation has one hose high and the other diagnally across from that at the low point in the radiator but the radiator is not horizontal and there is definately a large area inside the radiator that traps air and no matter how hot or how much flow it has, the air can never escape that environment. Just a thought given how quickly yours is heating up[/quote]

Persuasive argument - how would I go about diagnosing an air bubble in the radiator?

Then if I find that this is the case - how would I remove it, without making the modifications that you have mentioned ?

[Murray Parr]

As long as one of the hose connections on the radiator is at the highest point, the radiator shouldn't have any air in it. Also make sure none of the hoses have high spots in them. If your system has a hose connection on the radiator that isn't at the high point then you can get the air out by either tilting the plane or if that isn't possible you could try removing the radiator from its mounts and manouvre it around to get the air out that way. Once the air is removed it shouldn't get air back in it again until you empty it in the future. If you think your system is free of air then maybe look into wether your temp guages are accurate.

Another thing to look at is make sure you have enough exit air volume

[Skippydiesel]

"Another thing to look at is make sure you have enough exit air volume"

Murray - in a sort of way this is where I think the problem is - insufficient air getting into the cowling, leading to insufficient cooling air moving through the radiator. The focus at the moment is experimenting with temporary fixed cowl flap, to try & induce greater exit air flow.

[Skippydiesel]

"Another thing to look at is make sure you have enough exit air volume"

Murray - in a sort of way this is where I think the problem is - insufficient air getting into the cowling, leading to insufficient cooling air moving through the radiator. The focus at the moment is experimenting with temporary fixed cowl flap, to try & induce greater exit air flow.

Oh! On the possible air bubble in the radiator - today, I strongly pulsed (squeezed) both the in & out pipe,s to the radiator, with radiator cap off & on - no hint of air in system. Also carefully inspected installation to try & guess where air might be trapped. Cant envision any potential for trapped air.

[Skippydiesel]

I am going to place some digital thermometers I have, on the radiator inlet/outlet hose right where they enter/exit the raditor, to get a separate reading (estimate) on coolant temperature to compare with Dynon readings.
This wont happen until starter motor has been replaced - how long ????

[lakespookie]

I really think you need to examine your inlet vs outlet area and how you are routing the radiator air volume, I know rotaxs are not primarily air cooled but i suspect that a lower cowl entrance when the cowl is on is causing a high pressure at the exit and limiting your overall airflow unless you have that volume of inlet air segregated from the upper plenum inlet and exhaust air. If you are running with no cowls you are making it worse. Also with the extra inlet i would confirm your exit to entrance ratio is 3 to 1 at a minumum.

Just out of curiosity what is your Radiator size/area? i think the Current factory experiment with the 1 week wonder used split rads to add extra cooling volume and also to simplify some of the concerns with plenum exit pressurization but i could be wrong and i dont necessarily trust my goldfish brain.

[Skippydiesel]

I really think you need to examine your inlet vs outlet area and how you are routing the radiator air volume, I know rotaxs are not primarily air cooled but i suspect that a lower cowl entrance when the cowl is on is causing a high pressure at the exit and limiting your overall airflow unless you have that volume of inlet air segregated from the upper plenum inlet and exhaust air.
This is not a traditional front or even side mounted radiator (the largest Rotax supply) - its sort of belly mounted, in that it is located at the bottom of the firewall but designed to be incorporated into the cowling (https://webuildplanes.com/cliff-jarvis/). The concept is that of a pressurised/sealed cowlin, with all exit air going out via the radiator
If you are running with no cowls you are making it worse. .
The no cowl runs demonstrated that the cooling systems oil, coolant & fins, are all working - to the point where suboptimal operating temperatures were recorded
Also with the extra inlet i would confirm your exit to entrance ratio is 3 to 1 at a minumum
See above comment - we are trying to get away from this ratio (foolish?)
Just out of curiosity what is your Radiator size/area? i think the Current factory experiment with the 1 week wonder used split rads to add extra cooling volume and also to simplify some of the concerns with plenum exit pressurization but i could be wrong and i dont necessarily trust my goldfish brain.

I have seen split radiators on Europa aircraft - certainly worked but at considerable additional weight & complexity

We may end up with a pilot controlled cowl flap for ground ops & climb out, closing when reaching cruise altitude.

[lakespookie]

Cowl looks pretty but i suspect your prop Is not driving much air into the inlet based on the few pictures i could see and where the prop pitch starts. That does not help you much with ground running it really would help to see actual detailed pictures of your cooling layout and air flow even if its just a drawing. I looked through that link but i was not able to see the rad (I think maybe i saw it at the bottom)and obviously with the cowl on you cant really see the airflow pathway. If i remeber correctly and i dont trust my goldfish brain, the liquid cooling was something like 65 to 70% of the cooling on a rotax so directing airflow through the rad is critical. So having it bottom mounted is not the worst thing but you need to make sure your inlet air is being directed and forced through the rad not just near it.

This is one of those times where a picture or drawing showing the airflow pathway would do wonders. If you are just ramming air into the cowl with no direction then you are not going to have much cooling as air is not going to want to go through restrictions like a rad. I didnt see any baffling anywhere or some kind of plenum so i really have no way of adding any value with out a drawing or more pictures.

That being said that White is clean nice paint job.