1. Dec 27, 2005

### karim102

Hi:rofl: ,
I wanna know why does airplane used 400 Hz? and what device can contral the correct frequency for the airplane.

Thanks
I appreciate it

2. Dec 27, 2005

### itsjustme

What exactly do you mean? Do you by any chance mean the Squawk radar. If you are talking about the radio it uses it is 100MHz - 130MHz and you can alter it by changeing the frequency on the radio. Now if you are flying IFR you will come across an instrument called the Squawk radar, basicly the airspace controller tells you to set it on a certain number and thats all you do, that number then pops up on their radar screen, i dont know about the frequencies it is sent by but i know that you cant change it and even if you did it would not work anymore.

3. Dec 27, 2005

### Averagesupernova

I think the OP means the power system uses 400 Hz and not a specific instrument.

4. Dec 27, 2005

### Bystander

Transformer cores, rotors and stators in motors, and other inductors require less iron, weight saving, at 400 Hz than at 60 Hz.

5. Dec 28, 2005

### Averagesupernova

I was curious about the OPs question as well. I would have guessed that it is weight saving but I didn't post it because it was only a guess. Thanks Bystander.

6. Dec 28, 2005

### karim102

ya,
I understand but I wanna know, if it used to loss wieght in aircraft, So why they don't use genertor which give more 400Hz, exactly I don't understand why they put 400Hz.

7. Dec 28, 2005

### Averagesupernova

Then what would you suggest karim102? Obviously they had to settle on something. Realize it was a long time ago that the standard was set.

8. Dec 30, 2005

### phantom_photon

I think I can explain this, but somebody please correct me if I'm wrong.
Transformer losses increase with frequency (due to hysteresis, eddy currents, skin effect, etc.), so the 400Hz figure represents an optimal trade-off between efficiency and compactness. For an aircraft it is important to reduce size/weight of components but beyond a certain frequency the reduced efficiency (due to aforementioned losses) begins to outweigh the benefit of having compact components. Also, high frequency transformers are generally more expensive due to the various means of compensating for losses (thinner laminations, etc.).

9. Dec 30, 2005

### Averagesupernova

Transformer loss usually DECREASES with frequency. Obviously there was some kind of trade off. Not sure what that is though. Was hoping for an answer.

10. Dec 31, 2005

### phantom_photon

I beg to differ.
Recall that E = 4.44*f*n*A*B. For any given core material there will be a saturation threshold for B which should not be exceeded. So for a given voltage and number of turns, increasing the frequency allows for decreasing the cross-sectional area of the core without bringing the core into saturation. Wikipedia has this to say on the topic: