400Hz 3-phase power

I work in the avionics industry. Just how are you going to show all the environmental compliance test requirements. The commercial world uses RTCA DO-160() as the bible. There are many test requirements that must be shown for airworthiness. The big ones are that it does not upset other equipments, and is not a fire hazard. Even if the equipment is non-essential to safe flight and landing, it can not upset equipments that are essential or critical to SFL. Radiated and conducted RF emissions are the expensive test lab tests. Even for experimental test flights, the safety of flight paperwork must show that the equipment will not cause safety problems. ignator

Excellent. I learned my "something new every day" early today. Thanks. I'd wondered why they used that frequency in airplanes.

-- Fear not those who argue but those who dodge. -- Marie Ebner von Eschenbach

Probably good for the old-fashioned mechanical gyros too.. which had to have motors that ran at high RPM. Of course modern strap-down nav systems tend to use fiber-optic or ring laser gyros.

I wonder why 400Hz though, rather than 360 or something that's an integer multiple of 60Hz.. perhaps it originated in the UK where it would be an integer multiple of their 50Hz? I see an online claim that WWII-era German aircraft used 500Hz.

Here's the MIL spec for aircraft power from '59:

Yeah, no kidding. It also allows smaller, but higher speed induction motors. You won't believe how small a 1 Hp 22,000 RPM 400 Hz motor is, you can just about hold it between two fingers, and easily in the palm of your hand. Power transformers are also way smaller, if you haven't seen the difference, you won't believe it.

Jon

So, feed threephase motor 1 from the VFD, feed two of the phase wires to motor 2, which is shaft-coupled to motor 1. The third phase wire on motor 2 is a sinewave output at 400 Hz. This is kinda like a rotary converter, except it's the AC waveform smoothing you're really after.

Here's the current spec, 704F.

Kevin Gallimore

Usually, the newbies' next question concerns that box of dirt in the tail section for all the equipments' earth ground leads. ;-)

Cheers! Rich

Nobody knows, but at least 2,150,000 people think they have an answer:

Three MONGO PA amps (think stadium or rock concert) and a 3-phase oscillator? ;-)

Cheers! Rich

"Line Reactors" for 3-phase are surprisingly available and affordable.

That said. I can't see why making 400hz to run a generator to provide DC is sensible. What voltage DC at what current?

Thanks.

Best regards, Spehro Pefhany

Best regards, Spehro Pefhany

Transformers and AC electric motors (plus things like synchros, servos and resolvers) are a lot smaller and lighter (much less iron needed at that higher frequency) -- real benefits in aircraft. Included in the motors are the gryo motors as part of a navigation system, and the syncros or resolvers to transmit the information to the panel instruments.

Enjoy, DoN.

Hmm ... I've just thought of something. I have a couple of ancient aircraft instruments (a gyrocompass and an artificial horizon) which each use a gyro powered by 115V 400 Hz three phase. Fine, those should work well with a VFD powering them.

But also included are devices to adjust for proper axis on the gyros -- during spin up and more slowly once in the air. These consist of torque motors on each axis in the gymbals, which are fed current to bring that axis into alignment (vertical on the artificial horizon, and horizontal on the gyrocompass). Each of these are fed through a clip-in device which has what I suspect to be saline solution in the bottom of a shallow dome (curved down in the center), and feed that to four contacts at 90 degree intervals. I'm not sure how well that will balance with the synthesized sine waves output from the VFD.

And -- FWIW -- I can use only one of these instruments at a time, because the stator (these are inverted rotor motors) in one is burned out, and it takes me about a half an hour or so to swap it from one to the other. :-)

Hmm ... perhaps time to try rewinding the stator? I didn't even think of it back in the early 1960s when I first got these. :-)

Enjoy, DoN.

Enjoy, DoN.

Note the 787 is a bit different.

Electric start.

Perhaps not surprisingly, the A380 requires double the GPU capacity of a 747.

You can get MUCH better results if you learn to use advanced search options and better keywords (such as 'history'). Also, if you search books as well as the web-- but I don't see anything remotely authoritative yet.