Wind Power B/C

[maxxxxx]

Does anyone know to even approach solving this? I might just not be familiar with the equation:

The power generated by a turbine is 18,000 Watts. If the wind speed, which is initially 30 m/s decreases by 25%, what must the lift force be in order to generate the same amount of power?

Answer (Click to Show Hidden Text)

800 N

Edit: Looks like the link I tried isn't working, try this viewtopic.php?f=226&t=9285&start=195#p307423

[Alex-RCHS]

The question you quoted in your first post has been answered on an earlier page, but I think we decided it was a badly worded question.

Apologies for the double post, but could use another opinion on this one as well:

A 36% efficient coal power plant burns 8.5 million kilograms of coal in a day. (Assume the heat of combustion of coal is 31 MJ/kg) How many watts of power is produced per day?

Answer (Click to Show Hidden Text)

I got 95 TW
Answer key says 1.1 GW

You calculated the joules produced per day, but you need to divide it by the number of seconds in a day to find the power produced.

[wzhang5460]

What would be considered to be a "great score" for blades in millivolts for Division C, given that a good score would get you placing in the top 10 in nats? I know things have changed since last year, but I kind of want to get a better estimate of how I (belatedly) did last year and what to improve upon this year. Thanks in advance!

Edit: How does the width of a blade affect performance in general in your experiences?

Every competition will have different scores in terms of voltage due to differences in motors/fans/resistance. As long as you do relatively well compared to others, you should be fine. Specific to last years nats, I think 1st place got 650 mV on high power and 450 mV on low power (check old forums).

Do you happen to know what the resistance was?

[daydreamer0023]

What would be considered to be a "great score" for blades in millivolts for Division C, given that a good score would get you placing in the top 10 in nats? I know things have changed since last year, but I kind of want to get a better estimate of how I (belatedly) did last year and what to improve upon this year. Thanks in advance!

Edit: How does the width of a blade affect performance in general in your experiences?

Every competition will have different scores in terms of voltage due to differences in motors/fans/resistance. As long as you do relatively well compared to others, you should be fine. Specific to last years nats, I think 1st place got 650 mV on high power and 450 mV on low power (check old forums).

Do you happen to know what the resistance was?

It's changed since last year (since now the resistance can be much more), but I suppose it was at 7.5ish ohms because our blade performed better at Nats than at my home setup.

[wzhang5460]

Every competition will have different scores in terms of voltage due to differences in motors/fans/resistance. As long as you do relatively well compared to others, you should be fine. Specific to last years nats, I think 1st place got 650 mV on high power and 450 mV on low power (check old forums).

Do you happen to know what the resistance was?

It's changed since last year (since now the resistance can be much more), but I suppose it was at 7.5ish ohms because our blade performed better at Nats than at my home setup.

Oh I see. Our turbine got about 300 mV at States but i don't know what the resistance was.

[wzhang5460]

Do you happen to know what the resistance was?

It's changed since last year (since now the resistance can be much more), but I suppose it was at 7.5ish ohms because our blade performed better at Nats than at my home setup.

Oh I see. Our turbine got about 300 mV at States but i don't know what the resistance was.

I'm guessing 10 ohms?

[Alex-RCHS]

Knowing the resistance is nice but there are other factors at play as well. The motor itself has an internal resistance, and not every fan is the same.

[daydreamer0023]

Knowing the resistance is nice but there are other factors at play as well. The motor itself has an internal resistance, and not every fan is the same.

Based off of that, if you want a slightly more accurate comparison, you might want to grab a tachometer and try finding the rpm of your blade - that could give you a sort of guesstimate of performance.

[Ionizer]

Knowing the resistance is nice but there are other factors at play as well. The motor itself has an internal resistance, and not every fan is the same.

Based off of that, if you want a slightly more accurate comparison, you might want to grab a tachometer and try finding the rpm of your blade - that could give you a sort of guesstimate of performance.

I don't think this will help either. Different fans will still have different strengths. Different motors will have different frictions. Also rpm should depend on resistance as well. Electrical resistance adds a physical component that makes the motor harder to turn.

[chozillla]

This is a question from an invitational and I still do not understand all parts of question 1. Can someone explain the answers for me? In return I will send you the full invitational test
Here's a link to the question: https://docs.google.com/document/d/17Ye ... sp=sharing
See you all in a few days in Ohio
Thanks