Viking sold 4 engines this week.  They are identical to the engine sold to the above pictured aircraft. Viking has 15 OEM sales of the Viking 130 and over 120 individual sales to builders across the world.  The 130 engine has been flawless (other than minor updates) since it's introduction 4 years ago.  Several customers and Viking prototype engines have been flying with ECU software much older than the above aircraft.  
This month, the location in Sport Aviation magazine, reserved to brag about builder completions, was hijacked in order to rant about a personal dissatisfaction against Viking Aircraft Engines.  
The events that led to the above off airport landing were:
  • Customer took delivery of the engine
  • Engine + fuel and electrical system was installed by builder
  • Customer complained about the engine not starting / running properly
  • Viking offered to pay for return shipment to troubleshoot.  (If it turned out to be a fault of Viking)
  • The engine arrived and started / ran perfect 
  • Viking continued to inform customer that something was clearly wrong with the installation of either the fuel or electrical system to the engine.
  • Customer believed he knew better and continued to say the issues were caused by him living in Colorado at higher elevation than Florida.  
  • Viking disputed this since the engine ECU compensates for all parameters such as density altitude and temperature.  

  • Viking did a high altitude test to further show that the alleged issues were not related to altitude
  • Customer bought ECU tuning equipment, changed vital parameters such as fuel and ignition timing.  This had already been set through a careful dyno session using sophisticated equipment and skilled personnel.  
Statement from engine tuner:
  • "The engines are all calibrated on an engine dynamometer at steady state. The main fueling map is up to 32 x32 breakpoints of manifold pressure and engine speed. This means that every running point from 800-7000rpm and 200-100mBar MAP can be visited, with a resolution of 250rpm and 50mBar. Each point is held for several minutes against the brake and the air-fuel ratio is set to the optimum value, the ignition timing and variable cam timing are also optimized at the same time. Exhaust gas temperatures are monitored as well as the exhaust gas lambda and detonation using external knock sensing to ensure that the engine is running correctly in every condition. In use, environmental corrections are made for engine and charge temperature and closed loop knock control is used to protect against detonation from varying fuel quality." 

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Normal radiator installation

Normal radiator installation hardware stud


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 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.


Here's an alternative way to prevent nose wheel debris from being thrown up - it not only would protect the radiator, it keeps the entire belly clean:

Trucker girl sticker is optional!  ;>)




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!!!


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