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R. Gross
Rocketboy Aircraft Products Inc.

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   Flight test 1   
   Flight Test 2                            
   Flight Test 3 - Flowing the Nozzles (you are here)                                                     
   Flight Test 4 - Instrument Calibration                  
  Flight Test 5 - Cruise Performance                                                          

This is the first of many fuel scans flown recently. The purpose of this is to collect data to allow the fuel injection nozzles to be adjusted to obtain a more even temperature peaking. This will allow the engine to run smoother and burn much less fuel, thereby extending the range.

The aircraft is flown to a typical cruise altitude and the engine is leaned out to approximately 100 deg rich of peak (ROP).
Then the fuel flow is noted on the left column. Scanning through the six cylinders and noting their EGTS is done for each fuel flow.
Then, the fuel flow is reduced by .2 GPH, and all six EGTS are noted again.
This process is repeated until the engine begins to run rough.

I filled out the form wrong placing all the egt's in order from left to right. Ignore the column titles. All numbers are EGT's.

Looking at this form, I can see that the number two cylinder peaked first at 12.1 GPH and the number four cylinder peaked last at 10.9 GPH for a spread of 1.2 GPH. After tuning the nozzles, I hope to see the spread at less than .5 GPH.
As of this date, the nozzles were modified and the following were installed.

#1 .029
#2 .029
#3 .028
#4 .028
#5 .028
#6 .0285

These sizes will cause cylinders 1,2 and 6 to peak later. The profile will be flown again, and if needed, the nozzles will be adjusted again. When finished, I'll be able to run the engine at 50 deg F lean of peak (LOP) and see lower temperatures and lower fuel consumption as well as have a smooth running engine.

The engine still only has 43 hours on it as of this writing. It was recommended that the final tuning not be done until the engine is fully broken in with at least 100 hours on it. Stay tuned!!

 

"You can't use runway behind you, altitude above you, or speed you never had"
- Rocketboy