Sunday, September 30, 2007

Synchros and RPM

How does an RPM indicator work?

In a car it is simple.
You only need a flexible shaft to connect a RPM meter to the engine. Inside the meter is a rotating magnet and a aluminum disc on a shaft with a return spring. The magnet spins and induces currents in the disc. These interact with the magnet and the disc begins to move... and so does the pointer.

And in an aircraft?
Well, at least in the Super Connie it is exactly the same principle with one difference. It is not possible to use a flexible shaft since the engines are 10 or more meters away from the cockpit. So they made something clever; they mounted a small generator on the engine and a even smaller electric motor inside the instrument. If the generator turns with 500 rpm for example, then the instrument motor does exactly the same.
And the rest is like in your car.... your old car... without electronic displays.

Saturday, September 29, 2007

Fire in the garage!

A very hot car!

In fact a little bit too hot for my taste.... it almost burnt down today! Just at noon when I was heating up my lunch in the microwave, my phone rang and my brother (he's a fireman) told me to look for my car because there was a fire in the garage where I parked it.
When I arrived there, the road was already blocked with firetrucks and hoses and police cars, firemen (and women) running around and the wole area smelled like burning plastic. Smoke came out of all openings of the garage.
I tought "well, there is not much to do at the moment" and I waited there and looked what's happening. About one hour later, when the firemen cleared up their equipment and the police had finished investigating, I was allowed to enter the garage for a look.
What can I say... everything was completely black. Even the light from the few remaining lamps on the ceiling seemed to be black. In fact the lamps have also been blackened by the huge amount of smoke.
What I saw was that my car was still there, on it's wheels and it seemed to be more or less ok. In fact it suffered amazingly little damage despite the fact that the fire was on the parking field directly next to it.
It was not a car that burned but some stuff from the janitor who stored his tools and stuff down there. I don't know how the fire started, that's what the police will try to find out now.

It took almost an hour to wash all the dirt from my car. There have also been some drops of molten plastic on it's backside. It must have been really hot there.

Well... it seems my car needs a new painting as you can see on the pictures and I need a good meal and some rest now. That was an exciting day...!

Thursday, September 27, 2007

Old tech goes digital

Interfacing the interface....
To drive the landing gear indicator and the unlock warning lamp, some reed relais and optocouplers are necessary. The simkits interface is able to drive only LEDs but I need 24 Volts for most of the original parts.
But this one was easy. The indicator has three wires, one common, one for "up" and one for "down". You just have to connect the 24 Volts to one of them and the corresponding sign will show up. If there is no signal at all... it shows the well known stripes.
The lamp socket has also three terminals. A common, a signal and one for the "push to test". You can push the red cap and the light will go on to test the bulb inside.

That's the good side of this old technology, everything is built simple and reliable.

Tuesday, September 25, 2007

Cheating with servos

The first original instrument is modified and "computerized". The frontal view is unchanged...

The same thing from behind. Almost everything is gone and an RC-car like servo is installed instead.
In fact it is not so differnt from the original design. The Mangenyns are replaced by servos but they have almost the same function, only the signals to drive them are different.
And yes... only one of the two pointers has survived. I glued the right and left pointer together because it makes not much sense in a simulator to show each side independently. In the simulator, the wing flaps always work on both sides, defects are not possible :-)

Thursday, September 20, 2007

...and now also with illumination... :-)

Monday, September 17, 2007


Yeppee...! The packet from Simkits has finally arrived. Friday I looked into the UPS website to check the tracking number and guess what... it was already delivered. Nice, but where? A unknown person has signed for the delivery shortly after noon. Who could that be...? Maybe someone of my new neighbours? I checked the online phone book and found the name, it's in the next house. Unfortunately there is nobody at home.
Two hours later I see the car of my neighbours coming. I ran over to ask them if they got my packet and yes... there it is.

Isn't that a bit strange ? Hardware for $2000 delivered to the wrong address without notice to me. If I had no internet access, how would I ever know? Well, everything went fine at the end . Thanks god I have a good relationship with my neighbours.

Two days later all the pointers are pointing correctly, the illumination is illuminating and I'm feeling a bit like at christmas.

Sunday, September 02, 2007

Pinching my finger

The reverse-lock actuator.

I'm still waiting for the Simkits packet, it should arrive next week. In the meantime I built the drive for the reverse lock. This motor will be installed inside the throttle pedestal and unlocks the reverser levers when the airplane is on ground.
While testing it, I pinched my finger between the lever and the bracket... and the motor jammed. I first had to reverse the power supply to release my finger.  Ouch!