Archive for January, 2006

this week’s progress

I’ve had a reasonably productive week on the pit. I pulled out the left console, stripped it of its panels and gave it a lick of “skank grey”. Taking advantage of the console being out, I pulled out the ACES too and bored some holes with a holesaw so that I could access the woofer volume and speaker connections on the subwoofer under my seat. I hope to test it with the woofer tonight.
On the gear panel, I finished the lettering, painted the support strut and re-wired the mis-connected inputs to take the rapid-fire inputs 15 and 16 on device 1 into account. After a test last night all switches on that panel are working perfectly. Unfortunately I only have 2 ethernet couplers so until I get a few more from my supplier on, I can only have 2 of the 4 switch sets working. I’ll probably go with the gear/flap and the autopilot switch sets as they’re the most useful. All I lose is tailwheel/hook (not used in AF) and stores config/park brake (used maybe once or twice per sortie). By the way, if you’re wondering how I keep track of my wiring, here’s how (34k file).
This evening I’ll vacuum, de-spider and reassemble in time for our sorties in AF. This weekend I hope to get the eject handle and strobe light switches going, and possibly rig up seat arm and idle release switches.
Photos soon.

parlez-vouz PIC?

Well, I had quite an interesting night with my PIC tonight. I ran through a basic PIC tutorial which was ideal as it used a PIC16F628, and I had a PIC16F628A handy to program with my Velleman K8048.
The problem occurred shortly after I flashed the chip with the hex code the first time. Whilst still in programming mode, the program started running! Every time from then on that I tried to program the chip, it was unable to obtain the device ID and failed.
I fixed it with a combination of 2 techniques. Firstly, I discovered there is in fact an error in the code (possibly due to my use of the 628A instead of the 628) and I needed to change the line config 0x3D18 to config 0x3D38, as the original command apparently disables the reset pin making it impossible for the chip to hold in programming mode (or something).
Once this was done I managed to get it into the chip by first loading it in with the 16F84A settings and then, after it fails, with the proper settings. Bingo. The program loaded, I could erase the memory and load my empty template program.
Thanks to the online links that allowed me to get to bed before midnight (I can’t sleep with unsolved problems).

airspeed indicator musings

As you all know, my pit is designed to be largely compatible with many different types of aircraft, from helos to GA bugsmashers to fast jets. One interesting factor is the different speeds that these aircraft operate at, which, to a lesser man (or one with more time, money and patience) would result in the construction of at least 3 separate ASI’s.
However, I thought that even for fast jets, the main area of the altimeter used is from Vs to Vle – stall speed to max landing gear extended speed – as over that you’re using a HUD or autopilot mostly anyway. Even in the Viper, this tops out at 300 knots. So, I figured, why not use 2/3 of the gauge to display say the first 250 knots, and the remaining 1/3 to display, say, another 350 knots? This would require a polynomial function of airspeed against needle rotation.
So, assuming I’d be using a 400-step stepper motor for the needle (I know air-core movement would be cheaper but constructing one seems a little fiddly for now) I’d use, say, 3/4 of a revolution to indicate the range 0-600 KIAS, which gives me 300 steps (normally fixed-wing ASI’s start at 40 KIAS, but helo ones go from 0). So, after much mucking around with quadratics and second-order polynomial equations, and not a little nightmarish reliving of year 11 maths, and some sensational help from scatter and bigtonka from the VAAF, and some mucking around in Excel, I came up with an equation:
STEP = -0.0009Vē + 1.013V – 0.3443 where STEP is the stepper motor step number from 0-300 and V is the airspeed in knots from the sim data out.
This gives me 100 steps to go from 0-110 KIAS (averaging about 1 step per knot, better resolution at low speed), another 100 steps from 110-250 KIAS and 100 from 250 to 600 knots (from about 2 knots per step at the low end to about 10 knots per step at the high end). Super!
Only problem now is getting the PIC to do floating point math and figuring out how to do it (as I’ve never programmed a PIC before). Details. Check the graph. Bow to the might of scatter’s formidable mathematical l33tness, and my m4d Excel skillz.
{{popup AirspeedStepGraph.png AirspeedStepGraph 958×424}}Airspeed-Step Graph

building simulated aircraft instrumentation

My new favourite book – Building Simulated Aircraft Instrumentation by Mike Powell. The missus very kindly (with a bit of prompting) bought it for me for christmas, and what a book it is. Imagine building something as complex as an attitude indicator or three-hand altimeter FROM SCRATCH using nothing but cheap off-the-shelf electronics components and sheet aluminium. Well, with this book you can. I’m not exaggerating, this is the greatest book I’ve ever owned. I read it on the bus. I read it at work. It makes me scheme and plan and want to cover my pit in dials and gauges.
I think my first project will be an airspeed indicator – possibly with exponential markings so that it will be useful for GA and high-performance jets. It’s in the pipeline, after a few other things that I want to knock over first like a collective mod for my spare X45. Of course, Mike has another book in the pipeline for general pitbuilding (including a collective), but it’s a ways off.
Buy this book. It’s absolutely riveting, and utterly unique.

holiday flying

I had a grand plan – I would fly all over QLD and NSW on my laptop whilst I was away on holidays. It started well – Redcliffe to Bundaberg in a C172, and then the next day Bundy to Toowoomba in a Marchetti SF.260. Holidays got in the way then, and lots of early mornings on the beach and in the garden (pulling out over half a ton of palm fronds) meant no more flying. Still, you can enjoy the description and photos of the first two legs in the attached file.
Holiday Flying in FS2004 (2252k .zip file)
In other news, I may do any of the following things to the pit in the next few weeks:
- build the right console
- fix the gear panel
- build a collective mod for my X45
Watch and see…

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