DIY Fly-by-wire

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DesignAndConquer

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Unread post14 Nov 2005, 04:23

I was helping my friend set up a joystick for a flight sim the other day and it got me to thinking. If modern fighters use stick position or force to dictate how much control surface actuation to command, isnt that the same basic idea behind a joystick for home computers (via potentiometers IIRC)?
And if that is correct, then it should be fairly easy to integrate a very basic fly by wire system for homebuilt aircraft. Granted a Long-Eze or RV-8 dont need the same level of envelope protection as a fighter but it would be an interesting proof of concept.

Any thoughts? Fire away!



Chris W.
Go fast. Make noise.
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Guysmiley

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Unread post14 Nov 2005, 17:01

The part you didn't mention is the actuators. You'll need some way of determining stick position and then have a control system (either digital or analog electronic) that drives the control surfaces via electric actuators.

I know you said proof of concept, but there are a few reasons I can think of as to why I wouldn't try this:

1. Weight. You'd be adding a lot more weight than a traditional pushrod system for a light aircraft. And light aircraft don't have a lot of excess capacity for more weight. You'd be reducing useful payload and fuel capacity.

2. Complexity. You're adding a lot of parts that can go wrong, and if you have a computer or electrical failure you'd better have a manual backup, but then see #1.

3. Power. You're going to need enough power to drive your electric actuators, and what happens if you lose engine power? See #2.

I know you're thinking about a concept, but these are the reasons I can think of off the top of my head why it hasn't been done, and isn't "fairly easy" to do. YMMV
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south

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Unread post13 Dec 2005, 01:20

Depends if your aircraft is stable or not.

If its unstable, you need to run it through a whole bunch of computers to determine the appropriate outputs to the sensors. Which is the real reason why FBW came about.

A decent elec engineer or mechatronics engineer should be able to whip one up for you though.
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VMF-214

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Unread post13 Dec 2005, 14:03

I'm a system engineer, I'm specialist in control system, I developed SCADAS (telecontrol system) for industry process.

From my knowledge I have two advices for you,

First, a control system in early steps is a thing that use to fail, so you need a manual backup system, a fail-safe control system is possible but not easy, you'll need to find the help of at least two experienced engineers (one for the electonic side, and another for the software) is very difficult that a single man have the full knowledge.

Second, buy a good parachute.

P.D.:About the actuators, you must to use std autopilot actuators, are the best and more dependable, and light, avoid as possible to develop special hardware, f.e. a MS Sidewinder joystic has the same or better quality than the A320's joystics. A digital control system is more complex than an analog, but safer and precise, also let's you do some tricks as to configure the ailerons as flaperons.

Good Luck... (You'll need it)
BAH BAH ...
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DesignAndConquer

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Unread post07 Mar 2006, 06:46

Thanks for the replies. It was just musings on our part if we ever got rich and were able to build whatever we wanted. I never knew it was so complex to integrate a flight control system.
A retail joystick the same quality as a commercial airliners? You're kidding! Do they use the same basic input system to measure requested deflection?

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