MrMel
Elite Veteran
Location: Lidingo, Sweden
| Taken from H.F., Logo section, which will give you a hint.
| Quote |
| Something to think about regarding the power put into a machine at the rpms some of you guys use. To increase rpms the input power increases exponentially, not linearly. For instance,.. say I fly at 2000 rpms and you fly at 2200 rpms. Many will think that's only a 10% increase, so it should take 10% more power. Many of us know this to not be true, but I've never known the "real relationship". A very smart friend of mine who is an engineering type, explained the power relationships and it's rather eye-opening. To make the above change actually requires 33% more power (1.33 times the original imput power). The formula works like this,... you divide the new rpm by the old rpm, CUBE the difference, and multiply times the imput power. I threw together a little spreadsheet to demonstrate, using my logo 10 setup (the one that will fly old/smooth style 3D for 9+ minutes but not the radical stuff you guys do these days). At 2000 rpms, I average 525 watts, or 28 amps on a 5S 4500 pack. The spreadsheet shows that going up to 2100 would mean 1.16 times the current input power ((2100/2000,.. which is 1.05) to the third power), which is 1.16. Going to 2200 takes 1.33 times the input, etc, etc. Flight times go down relative to current, so going from 2000 to 2100 takes me down from 9.5 to 8.2 minutes. Going to the "normal" (at least these days) 2500 rpms, would roughly half my flight time to 4.9 minutes. It can be said that the increased revs will require less pitch, which is true, but load difference from the tiny pitch change is miniscule compared to the load increase of rpms so it's virtually irrelevant.
current watts, rpm, new rpm, multiplier, new watts, cells (*3.7), capacity(mah), current, new current, flight time, new flight time
525 2000 2100 1.16 608 5 4500 28 33 9.5 8.2
525 2000 2200 1.33 699 5 4500 28 38 9.5 7.1
525 2000 2300 1.52 798 5 4500 28 43 9.5 6.3
525 2000 2400 1.73 907 5 4500 28 49 9.5 5.5
525 2000 2500 1.95 1025 5 4500 28 55 9.5 4.9
525 2000 2600 2.20 1153 5 4500 28 62 9.5 4.3
525 2000 2700 2.46 1292 5 4500 28 70 9.5 3.9
525 2000 2800 2.74 1441 5 4500 28 78 9.5 3.5
525 2000 2900 3.05 1601 5 4500 28 87 9.5 3.1
525 2000 3000 3.38 1772 5 4500 28 96 9.5 2.8
Here are the important fields, a little more readable
rpm, new, multiplier, flight time, new flight time
2000 2100 1.16 9.5 8.2
2000 2200 1.33 9.5 7.1
2000 2300 1.52 9.5 6.3
2000 2400 1.73 9.5 5.5
2000 2500 1.95 9.5 4.9
2000 2600 2.20 9.5 4.3
2000 2700 2.46 9.5 3.9
2000 2800 2.74 9.5 3.5
2000 2900 3.05 9.5 3.1
2000 3000 3.38 9.5 2.8
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, It like a big regulator.
