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Jan 16, 2019, 01:16 AM
"I will return" Federico
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Indoor Static Thrust Test - 95" Extra 330SC-E

To determine the minimum thrust I need (or would be happy with) for my 104" Extra 300 V2, I needed an accurate measurement of the thrust I have been getting out of my 95" Extra. The electric set up in that plane has been very good for most conditions in which I practiced and competed in 2018, flying scale aerobatics. While the thrust could have been improved with a different prop or bigger motor, that setup struck a good balance between weight, thrust and flying time. After more than 150 cycles on the batteries, I can still get a ten minute flight performing two Intermediate IMAC sequences (#IamIMAC), with time left over for extra maneuvers.

Once I knew what thrust I was currently getting and happy with, I could calculate a thrust to weight ratio, then work backwards from an expected all up weight on the 104" to calculate the minimum thrust I would need from an electric power system. Adding 2 lbs for the additional parasitic drag of the bulkier airframe should get me close to the same vertical performance I had with the 95".

After borrowing some climber's tubular webbing from a co-worker I finally had what I needed to stake the 95" Extra to the ground and run her up to full throttle. Unfortunately, the weather turned cold and more than half a foot of snow landed by Sunday morning, so I moved the test indoors. Here are the results:

95" Extra 330SC-E
Motrolfly DM5335 189Kv
Jeti Mezon 135 Opto ESC
Falcon 24x10 CFE
2x Glacier 6s 8000mAh (12s)
AUW: 20.6 lbs

Temperature: 68 F
Voltage at start: 50.1V
Max RPM: 6980 (ESC log)
Max Amps: 98.0A (ESC log); 99.3A on WOT #1; 100.0A on WOT #2 (Telemetry; spike to 113A at end of run)
Min. Voltage at end: 45.0 (ESC log); 46.0V (Telemetry)
Lowest cell Voltage pack A: 3.74
Lowest cell Voltage pack B: 3.79

Max static thrust (5 sec WOT): 31 lbs
Thrust-Weight ratio: 1.5:1

From this thrust to weight ratio I can now work backwards to get the minimum thrust I need from the 104" Extra at various weights. So, with an estimated AUW of 28.46 lbs with 4x Dinogy 65C 5000mAh packs (12s2p) I would need a minimum of 1.5 x 28.46 = 42.7 lbs. Add 2 lbs for the added drag of the 104" brings the total to 44.7 lbs.

Video of the test can be seen below. Unfortunately, the numbers on the Dr. Meter scale were not visible. I had a Mobius camera strapped to my eyeglasses, so not the best setup for recording. I was unable to get a thrust measurement from the first WOT, because the scale had locked up before I could advance the throttle. The black webbing was a safety line, just in case the plane broke free. If that failed, a shipping box provided a nice crash barrier. LOL.

95" Extra 330SC-E Static Thrust Test (2 min 18 sec)
Last edited by rclad; Feb 18, 2019 at 07:50 PM. Reason: Fixed video link. Revised total thrust based on second test (not shown).
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