fbpx

 

Hi All, 

My new Sonex/Rotax 912 ULS is undergoing static engine cooling testing. When I get it right we can contemplate taxi & flight testing. Its not right yet.

A 15 minute engine run at 16C ambient, will deliver oil tempt 100C, Cylinder Head temps 115C, Cowling temp 45C.Thermocouples taped to the outside of the in/out tanks of the radiator will see 70C (on both).

The problem seems to be lack of air movement through the cowling & out the aft mounted radiator.

The cowling "nostrils" have an open area slightly more than the radiator area BUT are close to the spinner, in the interest of presenting a small frontal aspect. This puts the openings in the least effective arc pf the prop blades,

I have a dedicated front opening for the under engine oil cooler - I plan to enlarge this.

I have mounted a small fan on the radiator - resulting in a slowing in the rate of the temperature rise but having little impact on the decision to shut down due to high temp..

I am about to test a cowl flap vent fixed to the trailing edge of the cowling air exit (behind the radiator) mounted at about 30 degrees to try and induce a low pressure (suction) area to encourage air flow.

I have no doubt that any forward movement will improve matters but if this set up cant keep the temps within the "green" at 16C ambient what might be the time to shut down in our summers, which often get to 45C ?(not that I would be flying)

The relative temperatures of the Cylinder Head (115C) & Radiator (70c) concerns me - could I have defective coolant pump? (This is a new engine 3+hrs but has already had a dud starter motor)

  • Re: Coolant System

    by » one year ago


    Try starting it with the radiator cap off to check the circulation. You probably won’t get enough cooling airflow till it sees 80kts.


  • Re: Coolant System

    by » one year ago


    Static ground run temps can be very different from in flight temps. Air flow is very different too. I wouldn’t base all my numbers on just a static run.


    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell


  • Re: Coolant System

    by » one year ago


    Thanks Sam - I didn't realise you could see fluid movement in the coolant top tank. Have you actually tried this or are you speculating?

     

    As for the 80 knots - I have no doubt the system will work as hoped when the aircraft gets airborne however the classic time for overheating is during ground opps.


  • Re: Coolant System

    by » one year ago


    Roger Lee wrote:

    Static ground run temps can be very different from in flight temps. Air flow is very different too. I wouldn’t base all my numbers on just a static run.

    This I understand Roger - see my response  to Sam above. My concern is the time of year/ambient temperture.

    We are just entering spring - day ambient will not be this low (14-16C) for another 9 months. 

    In just a few weeks ,even a dawn start will likely have temps in the20 - 25C range and days in the 30 plus. Christmas - Feb  40-45C from about 11:00 - 16:00. 

    With a current start taxi of time of just 15 minutes before over temp approaching - my concern is I may only have 5 minutes or less in summer time.


  • Re: Coolant System

    by » one year ago


    Yes I have. You can see if the pump is circulating just be very careful of the spinning propeller.


    Thank you said by: Sean Griffin

You do not have permissions to reply to this topic.