Online Community of Zenith Builders and Flyers
NORMAL RADIATOR INSTALLATION
Normal radiator installation
Normal radiator installation hardware stud
CUSTOMER MODIFIED RADIATOR INSTALLATION
Typical size of Zenith angle used to secure radiator baffle
Builder attempt to increase aircraft performance by reducing cooling air intake by about 1/3 of needed opening as tested by Viking Aircraft Engines. Aft portion of radiator airflow is 1/4 of original system
Did some calculations on the reduced airflow,
Reduced air flow of 33% due to reduced opening size, then reduced air density in Colorado of almost 40% ( 12.25 kg/cu meter @SL vs 7.36 kg/ cu meter @ 5000 ft) resulting in a big decrease of air molecules flowing thru the radiator to cool the coolant.
Net air flow vs SL air flow with reduced opening size =.66(reduced opening) X (1-.40)(air density @5000ft)=.39 (61% less air molecules to cool the engine!!)
Then if you climb to 8000ft in Colorado (3000 ft AGL), cooling is reduced even further!
The 3” opening height is critical to maintaining air flow thru the radiator
Also, the height at the back of the radiator box should not taper down. There has to be enough room for the airflow to turn 90 degrees to pass thru the radiator. If there is a taper, it will choke the air flow thus reducing the air flow thru the radiator even further.
Moral to the story. Maintain a minimum of a 3” opening , no taper to the air box to achieve the required airflow thru the radiator (and required cooling)
The output of the engine also is reduced with altitude but not to the extent to cover up the above.
The installation of the radiator in the video liked on the Viking home page https://www.vikingaircraftengines.com/installation.html shows Garry Simmons installation and it has some clear narrowing from front to back. Not nearly what Colorado install picture has, but still narrowed. Is this example video wrong? Should we not be following it? I used that install video as the basis for my install, I did ensure I had at least a 3" opening, but given the use of the rubber attach points in the video, the aft end narrows. The other video that Alissa pointed me to for the Alaska 750 STOL also has a narrowing and additionally he fully enclosed the exit air with only an outlet in the rear, is that going to be problematic for him?
I am going do double check my measurements be it would be good to get some clarifications on weather we should be following the advice of these two examples.
With regards to our Alaska 750 STOL, we recently found that enclosing the underside of the radiator did prove to be a problem, and have recently addressed the problem. Since we still want to protect the radiator from debris that may be tossed up from the nose wheel, we have replaced the full cover with louvers. We're waiting to test.
Very nice. Looks like a good addition even if our louvers do work.
The important thing is: Don't make it smaller than standard for the first flight. I always make my first flights without a cowling. The engine does not need a cowling. The cowling is only there to increase airspeed and for looks. Tie everything down and fly without the cowling until all parameters are good. Then install the cowling and compart to the obtained parameters. Do the best you can to mimic the cooling that was available without the cowling, for the engine and gearbox. The slight tapering towards the rear is not detrimental
I. An personally attest to the programming change being the issue. Before his forst
flight I was contacted by the builder as I am in Colorado as well. Wanted to come by and take a look at my build (750 STOL Viking 110). When he was there he asked to hook up to the ECU and take a copy of the existing parameters. He had the right equipment to do so. I didn’t see an issue so I let him. After all this surfaced I of course was concerned that mine may have been corrupted by him. Did lots of testing on the ground and it ran as silky smooth, cool and just damn mesmerizing as the day I first started it. I will be starting another build in the next year or so (750 HD) and the ONLY correct choice to me is the Viking. I am very interested (Drooling) over the larger turbo versions!!! Thanks Jan! Absolutely GREAT product!!!