Air flow to radiator

[Murray Parr]

Does anyone have some info on an appropriate cross sectional area for the opening to supply sufficient airflow to the radiator? Has anyone have a successful install that provides adequite cooling? I chose to mount mine horizontally to the engine mount upper and lower braces (rubber mounted) as there isn't much room anywhere else to locate it without increasing the cowl size.

Thanks in advance
Murray

[Kai]

There is a short video of something similar on Youtube.

Go to ‘Sonex in Sweden 2’. This Sonex A (#0513) also uses a sidemount radiator.

No tech data, but the thing has been flying for a while, so it presumably works.

Thanks
Kai
Sonex A #0525 DS SG
EP915ECI 120HP

[garyb]

Hi Murray

Check out my post viewtopic.php?f=60&t=2503
My Rotax powered Sonex has 160 hours on the clock now with no cooling issues, the CHT's generally run around 90 degrees C. My radiator opening is slightly bigger than the standard Sonex opening one side only, and I am thinking about reducing it down to the standard size. Check out some of my other posts for installation pictures.

Regards
Gary

[Murray Parr]

Thanks Kai, I was thinking of doing something similar to that one with the NACA duct coming from underneath the cowl. I found some specs I could use as a guide. Rotax states the radiator needs 0.75 cu.m/sec. of airflow (28.58 cu.ft/sec.)
If I make an opening of 5" x 9" that should give the required airflow at 54kts or 4" x 8" would require 76 kts to give enough airflow.
The prop blast is morre interesting, at 5200 rpm the airflow is almost double what is required for a 4" x 8" opening. I wonder if this would work out in the real world though, perhaps there are some others that can supply dimensions of the duct opening to the radiator and how the cooling system performs.

[Murray Parr]

Hi Gary,

Do you have dimensions of the opening height and width? How did you duct it from the opening to the radiator and does the duct reduce in size or have many restrictions along the way? I think what you have done is a much neater installation than having a NACA duct in the cowl as space is very limited in the cowl

[garyb]

Hi Gary,

Do you have dimensions of the opening height and width? How did you duct it from the opening to the radiator and does the duct reduce in size or have many restrictions along the way? I think what you have done is a much neater installation than having a NACA duct in the cowl as space is very limited in the cowl

Hi Murray

The opening is 7 by 3 inch which is only slightly larger than the standard Sonex opening then the duct gets larger up to the size of the radiator. There are no restrictions, and I will be reducing the opening down so the cowl looks like a standard air cooled Sonex.
Check out my Video https://www.youtube.com/watch?v=WQ1dQHzxcPE for temps.

Cheers

[BRS]

Gary,
Nice video. What do you use the 'rear view mirror' for? Looks like it is curved, wide angle?

-brs

[garyb]

Gary,
Nice video. What do you use the 'rear view mirror' for? Looks like it is curved, wide angle?

-brs

Thanks. Just use it on the ground for runups and taxying, its just a flat plexiglass mirror I have cut to fit the curve of the windshield bow.
Cheers

[Skippydiesel]

Hoping to be a Sonex owner very shortly.

Just an observation on Rotax 912 engine cooling.

I have been flying an ATEC Zephyr/Rotax 912 ULS for about 11 years.

Rotax stock, front mounted, coolant radiator is very effecting. The front location angled slightly down, must be receiving a high degree of ram air. Exit air is just into the cowling (no ducting).

The single Rotax oil cooler, is located low down on the firewall, fairly close to the cowl opening. It has no ducting. I assume it just gets a degree of the warm through flow/exit air, on its way out of the cowling. Like the radiator it seems to be very effective.

In winter, I partially close off the exit air, using a shaped & drilled piece of flat aluminium, I call it a fixed cowl flap. The size has been determined by trial/error. This reduces the air flow to both heat exchangers - so that my engine temperatures are within optimum operating ranges. The cowl flap is removed, when day time temperatures are consistently 25 degrees C or above.

My message is this - it seems to me that people overanalyse the Rotax cooling system. The oil cooler in particular does not usually require very special attention/ducting unless you anticipate a lot of long duration steep climbing/glider towing type work (grunt!). The coolant radiator will do it job with just a nice consistent air flow and may in fact require some restriction in cooler months so that the engine can operate efficiently.