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Toggle switch for small aircraft charging system in case of failure

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richard.cs:

--- Quote from: ITman496 on April 17, 2020, 10:28:36 pm ---I've never done a spice model before but I'd certainly love to try.  When I get those measurements I'll do my best!

--- End quote ---

Attached is a spice model I made a while back for a small bicycle hub dynamo, based on published measurements. It has the constant-current characteristic discussed, but at much lower output power. In this model I got fancy and used a modulator block to simulate the voltage and frequency change with road speed, but you can also put it in as an equation and have something like voltage=rpm*const1*sin(const2*rpm*time), from memory I started using the modulator because the simulation ran faster.

In this model there are some sources on the left performing simple calculations with V1 as a speed input, and then A1 turns it into a speed dependent voltage and frequency which represents the open circuit voltage. E3 just allows this to float and not be 0V referenced which is useful when it's used in a more complex simulation. L1 represents the inductance of the stator, and R2 the resistance. R1 represents the iron loss in the dynamo but doesn't affect the result very much. That's it for the stuff in the dotted box modelling the dynamo.

Outside the box is a resistor which is switched between 0.1 Ohms, 1 Ohms and 10 Ohms. The waveform plot shows the current in that resistor. Between 0 and 1 second the model has the bike moving at 5 mph, then at 10, then at 20 mph. The cyan line is current into 10 Ohms, red into 1 ohm and blue into 0.1 ohms. Of particular note is that 1) as the bike speed and therefore dynamo rpm varies 4:1 the current only varies 1.3:1, and 2) as the load varies 100:1, the current varies only 1.6:1 at low speed and 1.2:1 at high speed (where L1 dominates much more over R2).

Obviously this is not what you've got, but this type of model can be modified to suit your particular dynamo. There are two constants to tweak that set frequency(rpm) and voltage(rpm), and then put your measured resistance and inductance into R2 and L1. You then have a model that's a reasonable approximation and you can then connect things to the outputs like rectifiers, batteries, short circuits and see what kind of behaviour to expect.



ITman496:
Wow, that is fancy.  Is spice free?  I've never actually used it before.  I have an LCR meter, a decent handheld one, and a scope, so I'll be able to get the measurements pretty easily when I do get the engine running (Hopefully in a few days)

When you were looking into aircraft, did you have any particular model in mind?  I've seen a few minimaxes flying around in england, though I believe they are called the 88 instead of 1100.  I saw a picture of an english spec one on another forum that looked pretty sweet!

richard.cs:
There are lots of implementations of SPICE, some free, some not. That one is LTspice which is free to use and very powerful, but has a slightly odd user interface.

Aircraft-wise it's been years since I looked at it properly, but at the time I thought it would be cool to make a modern version of one of the early aircraft, which after all were very much man-in-a-shed technology. Something like a Blériot XI or Fokker Eindecker perhaps. Not in any way a historically accurate replica, but more using it as an inspiration for the basic airframe and then tweaking it to use a more modern construction and engine.

Did you ever see the scrapheap challenge / junkyard wars "flight of the century" special? There's a very poor quality rip on youtube:

When I looked into it it basically seemed that for the UK there are not really any simplified rules for small aircraft, either for construction or flying them,* and it looked to be a massive regulatory pain-in-the-arse (I do remember finding French rules interesting, under 250 kg is/was basically a free-for-all). Combined with leaving university and switching from "lots of time, no money" to "money for project, no time" it just got dropped. Ten years ago or so there was almost no-one building them in the UK, or at least not people who put stuff online. Perhaps that's changed now and I should revisit it, find some forums and see how other people are doing it and especially how they're dealing with the regulatory side.

Of course then there's the problem of finding space in a suburban house...

*It was a long time ago so memory is a bit fuzzy here. I would be pleased to be proved wrong.

edit: the forum seems to insist on embedding a youtube preview when I put a link in, and I can't seem to get rid of it even if I remove the URL tags. It doesn't appear in the preview of my post though. Unless that's my browser doing it?

ITman496:
I have no idea how it works in the UK, but I would certainly check into it!  There are certainly small aircraft flying around, people seemed to have found a way.

I know mine was designed to be built in about a 1 bay garage.  2 would be better, but you can make the dream work in a single bay.

I used to be ADDICTED to junkyard wars.  That show inspired a lot of what I learned and became today!

The usa ultralight class of aircraft (less then 255lbs) is also a free-for-all, including no license or anything needed.  I wish it was 250kg!!!  I'd have about twice the horsepower and twice the engine strokes.  But alas.

richard.cs:

--- Quote from: ITman496 on April 18, 2020, 06:32:31 pm ---I know mine was designed to be built in about a 1 bay garage.  2 would be better, but you can make the dream work in a single bay.

--- End quote ---

It surely doesn't fit in a single garage once complete? Unless the wings are removable?


--- Quote ---
The usa ultralight class of aircraft (less then 255lbs) is also a free-for-all, including no license or anything needed.  I wish it was 250kg!!!  I'd have about twice the horsepower and twice the engine strokes.  But alas.

--- End quote ---

It looks like I would need a private pilots license to fly something like what you've built in the UK, unless it can be made <70kg in which case it falls into a catagory meant for self propelled hang gliders. This wasn't possible until 2017 when this catagory had to take off on foot but now they seem to be allowing slightly more conventional aircraft within the mass and stall speed limits.

Construction wise it looks like it's a submit plans before beginning kind of job with multiple inspections throughout the build.

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