Why Does an Airplane Use 400 Hz?

[karim102]

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

Thanks
I appreciate it

 

[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 that's all you do, that number then pops up on their radar screen, i don't know about the frequencies it is sent by but i know that you can't change it and even if you did it would not work anymore.

 

[Averagesupernova]

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

 

[Bystander]

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

 

[Averagesupernova]

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

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.

 

[karim102]

ya,
I understand but I want to 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.

 

[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.

 

[phantom_photon]

I understand but I want to 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.

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.).

 

[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.

 

[phantom_photon]

Transformer loss usually DECREASES with frequency

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:

The universal transformer emf equation indicates that at higher frequency, the core flux density will be lower for a given voltage. This implies that a core can have a smaller cross-sectional area and thus be physically more compact without reaching saturation. It is for this reason that the aircraft manufacturers and the military use 400 hertz supplies. They are less concerned with efficiency, which is lower at higher frequencies (mostly due to increased hysteresis losses), but are more concerned with saving weight.