watt_the?!

10-04-2005, 01:01 AM

Hi All,

This year we had an opportunity to havea go at doing the math for some competitors in the National Electric Flight Rally here in Australia and were amazed at how it went.

The new class had a limitation of lipo power of no greater than 100g, and a higher weight (cant remember what it was for nimhs).

AFAIK that was it.

We found that almost the entire field were using setups at 7.4V or low capacity 11.1V and 4.5 x4.1 props or so and going for 20-23k rpm.

upon crunching numbers we thought that the pitch speeds seemed very low, and we found that it was possible to make a 11.1V, 1570 3s pack at about 97grams weight, so amp draw could be as high as 20A on 12C for bursts.

We adopted a high rpm philosophy to maximise pitch speed and arrived at a 3 x 3.5 (we could only get a 3x3 prop though) at over 40k rpm.

This gave a huge advantage over the other setups and drew 20A static.

So the idea was to conserve the burst current draw by limiting it on the Tx and using only when necessary.

the first flight had our plane travelling with the pack for the entire race and then it dropped the throttle limiter to finish the race more than a lap in front (in the last 3 laps or so).

after several races we monitored battery temp and decided to use WOT for the entire last race. Needless to say it was a big win.

I am wondering if others use this approach (i.e. maximise pitch speed), as i just went over to the E-Hornet and noticed a mega 16154 and 5.5x4.5 prop setup at 21A and i thought that surely this isnt the fastest it can go.

Our plane covered the 260m round course in 8 seconds, which includes the turns- which is 117km/h, or 74mph average speed.

allowing for at least 1s turnarounds, the straights mustve been done in around 3 seconds- or close to 100mph.

frighteningly so, these speeds coincided beautifully with the math done.

i.e. 40,000 rpm at 3 inch pitch is approx 120mph.

whereas 21000rpm on a 4.5 inch prop is under 100mph.

is this an approach used globally?

tim

This year we had an opportunity to havea go at doing the math for some competitors in the National Electric Flight Rally here in Australia and were amazed at how it went.

The new class had a limitation of lipo power of no greater than 100g, and a higher weight (cant remember what it was for nimhs).

AFAIK that was it.

We found that almost the entire field were using setups at 7.4V or low capacity 11.1V and 4.5 x4.1 props or so and going for 20-23k rpm.

upon crunching numbers we thought that the pitch speeds seemed very low, and we found that it was possible to make a 11.1V, 1570 3s pack at about 97grams weight, so amp draw could be as high as 20A on 12C for bursts.

We adopted a high rpm philosophy to maximise pitch speed and arrived at a 3 x 3.5 (we could only get a 3x3 prop though) at over 40k rpm.

This gave a huge advantage over the other setups and drew 20A static.

So the idea was to conserve the burst current draw by limiting it on the Tx and using only when necessary.

the first flight had our plane travelling with the pack for the entire race and then it dropped the throttle limiter to finish the race more than a lap in front (in the last 3 laps or so).

after several races we monitored battery temp and decided to use WOT for the entire last race. Needless to say it was a big win.

I am wondering if others use this approach (i.e. maximise pitch speed), as i just went over to the E-Hornet and noticed a mega 16154 and 5.5x4.5 prop setup at 21A and i thought that surely this isnt the fastest it can go.

Our plane covered the 260m round course in 8 seconds, which includes the turns- which is 117km/h, or 74mph average speed.

allowing for at least 1s turnarounds, the straights mustve been done in around 3 seconds- or close to 100mph.

frighteningly so, these speeds coincided beautifully with the math done.

i.e. 40,000 rpm at 3 inch pitch is approx 120mph.

whereas 21000rpm on a 4.5 inch prop is under 100mph.

is this an approach used globally?

tim