Speed, Performance & C-Rating

Jul 27, 2012 14 Comments by

In the November MAN Ultimate Electrics column, John Reid tests different C-rated battery packs to see how they affect the performance and speed of a pylon racer. In this video we will see the amp and volt draw for each pack along with the watts and rpm produced.  Then we head to the field for some high-speed passes and check out the speed by using a palm radar gun.  Our thanks to Thunder Power Batteries for providing us the battery packs to test and Hangar 9 for the Sundowner.

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About the author

West Coast senior editor About me: I’ve been involved with RC aircraft since high school and have flown just about everything. I started my RC career with scratch-building, but now like many pilots I rely on ARFs to get me in the air. My main focus is on pylon racing, aerobats, combat and scale warbirds.

14 Responses to “Speed, Performance & C-Rating”

  1. High Nitro says:

    I come away thinking you have a GREAT flying field…
    Regarding the batteries, the 45C seems to be the “best”, does it not? Did they puff on you?

    • John Reid says:

      The 45C did post the best overall speed. None of the batteries puffed and all our in great shape, ready for the next flight.

  2. Bruno says:

    So, how can the RPM on a 2700 25C cell be that much greater then the others?
    Sorry but I don’t think that 22.692RPM is an accurate reading, specially when your only changing the batteries (same motor kV)…

    • John Reid says:

      I would have to agree with you Bruno, I will be testing out the batteries again and posting them to my blog. If there are any inaccuracies in the readings they should show up on future testing.

    • Gord Seifert says:

      That really doesn’t make sense. You can hear that the first test was at a slightly lower rpm than the second, certainly not 1.5 times as high. I would suspect that the tach might be set for three blade props for the second two tests, but it obviously shows ’2b’ (I assume that means 2 blade) on the display for all three tests, so I just don’t understand. Faulty tach?

  3. D. Andreas says:

    I did not see the article, but consider this; using batteries with equal voltage and current rating.. As their C rating goes up the battery internal resistance goes down. The lower the internal battery resistance the more power and sustained voltage is applied to the motor. This then applies directly to motor RPM (Kv). All this assuming that the system is set up properly. Now for reality, not all batteries are created equal and this will show when pushing the limits of a power system. The typical sport flyer may never see a difference in various batteries.

  4. cajuncat51 says:

    I have a Cessna 128 55″ wingspan, 900kv motor, 50A ESC & 2200mAh battery. I changed the esc from 35a to 50a due to a burnout. I’ve been told to go my 2200mAh 25c 3c and upgrade to a 2400mAh 30c 4s battery . I’m coming back into rc and re-learning the new gizzmos and all about EPO foam. What is your input on this set-up ? And would the best set-up for this EPO plane ? Your advice will be greatly helpful for this ole’ Air Force Vet !

  5. Mark says:

    You know you could have saved yourselves a lot of effort and got far more valuable data by simply measuring individual cell internal resistance with one of the chargers or other devices that perform such measurements. Just a thought…

    • John Reid says:

      Well that is true Mark, but that would make for a boring video. :-) Data is always good to have and does give you an accurate reading, but this does not always lend itself to real-world results. Plus it is a lot more fun to do something like this.

      • Mark says:

        Agree that making a video is more fun than measuring voltage drop with reliable equipment but flying introduces many variables that are eliminated via lab testing. Would be curious to see your testing that showed that voltage drop testing was inconsistent with ‘real-world results’. I have been testing and using lipolys for ~6 years and have always had 100% correlation between measured test results and observed performance. Additionally, how do you think Thunder Power sorts their cells when matching and assembling into packs? ;)

  6. John M says:

    Thanks John, am upping my size in electrics to 26cc size 3Ders.
    Will think out batteries with help from your tests. I have found a big difference in brands of batteries, they are not all created equal!

  7. Keith B says:

    There is no accounting for flying variables like wind speeds , directions, humidity changes during the day of testing, barometric pressure changes, etc. which ALL have an effect on flying performance. Sorry, but all this “testing” ( fun flying) is bogus to me. I think it was just an excuse to make a video.

    (10 years test pilot USAF 1970 – 1980)

  8. Paul says:

    Nice testing but at the end you had no comparison chart to show the results side by side. to see the results I had to write down the numbers by hand.

    Also the slowest battery had the highest RPM???

  9. Jim Petro says:

    Very relevant report. A club member recently bought higher C batterys and has seen “eyeball” flight improvement. I have ordered higher C lipos for my new EDF.
    Twenty some years ago there was an ongoing debate about NiCad battery cell interconnection types. “Experts” produced workbench tests. MEC asked me to produce a ‘true’ test. I made batterys with the different interconnections and used a UC plane to speed test each on a calm perfect day. Each battery was cycled and flown until it repeated 3 close speed runs. We flew and charged for several hours…That’s a lot of spinning around!
    With requards to the test pilot, I am an Embry Riddle grad and started model airplanes when I was 6 (that’s 67 years ago). The testing was accurate and relevant to real world model flying conditions.
    There were 4 different battery constructions and the top 3 speeds varied by only a couple mphs from each other. The best was with the MEC PowerTube battery with the compression assembly (like a flashlight). My reasoning is that it was the only one that didn’t affect the cells with welding or soldering heat during assembly.
    An article was written and submitted to a top RC magazine; It got scathing previews from conventional battery makers (also advertisers) and ended my writing for that magazine.
    I accept your tests and look foreward to additional real flying.

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