The Electrical System
This section is seriously frowned upon by Sequoia Aircraft Corp. as Alfred considers this a modification and he doesn't want other people being an alternative source of information. Therefor, please view this information in the spirit it is displayed. I make no warranties etc. and don't wish this to come back to me via Sequoia, but I enjoy this stuff so feel free to contact me.
The Sequoia electrical kit has provided builders with a reliable electrical system since its conception. From what I've seen of it (Not the sales hype) it looks quite extensive and is sufficient for an IFR aircraft.
The problems I have with it are four fold:
1) The $NZ is lousy against the $US.
2) I have a different plan for the instrument panel and so won't need most of the standard electrical system.
3) I have a built in hate for vacuum systems and therefor won't be having one.
4) Some parts of the design seem either over complex, outdated or not particularly sensible.. I'm not sure which.
The solution to all these problems is to use my electronics background to design my own system. I decided to contact Bob Nucolls for some ideas and I wasn't disappointed. Bob was very helpful and has some great ideas based on solid experience. (As said by someone else - don't put a wire in your aeroplane before reading Bob's work)
Since I am NOT putting a vacuum system in my aeroplane I considered using a completely split, dual battery system (two smaller batteries joined in parallel when starting) with a smaller alternator in the vac pump drive. I designed this system (based on Bob's work) then decided it was an overkill, it would perhaps make sense in a hard IFR machine but was basically more weight than I needed in a VFR aeroplane and therefor more to go wrong. Now I have a cut-down version of something similar that can be expanded as required and its all documented via AutoCAD. To size the wires I used a great spread sheet that I got from Kitplanes Magazine.
As far as the parts go, I have used locally obtainable parts that cost considerably less. The quality is still good but they are easy to buy from either Auto-Electrical stores or electronic shops (Dick Smith,Mouser,RS Components etc.). Some parts may need describing as follows.
|The Main contactors. These are truck parts and readily obtainable locally. Make sure you get the correct voltage as a lot of trucks use 24V. Also starter relays aren't continuously rated so get the correct wiring.|
|MOV. This stands for Metal Oxide Varistor. They sell in electronic stores for about 6 bucks each. I prefer these to diodes to catch voltage spikes especially since that is what they are designed to do !! Put these on all inductive loads to protect the controlling switch. ie contactors, motors etc.|
|Circuit breaker switches. I used these to save weight for some circuits. Not easy to find locally but Wicks has plenty of them.|
|Undercarriage relays. I couldn't see a point in using large heavy contactors for this. The max current is 15A (as per the CB) and aren't continuos loads, so I decided to use car horn relays. These are rated at 35A, are light and cheap. They also have mounting sockets available.|
|How about using lit switches instead of straight lamps for annunciators? You can wire the switch with one side to Gnd and the other to the (GND Activated) input side of the lamp. This way.. If the indicator doesn't come on for some reason, just push it to check the lamp hasn't blown !! OK.. it's a'la 737 and Boeing thought of it first, but it is a great system. (They are a bit more expensive and some have fairly dim bulbs)|
There are a lot of other ideas I've got for all this stuff. I'll add them to the site if there is anyone interested.
For instance. By using alternative component placement, I believe I can reduce weight by reducing the cable runs but still allowing maximum cable thickness for each circuit. One of the big ones was to move the start solenoid to the firewall. By doing this, it allowed me to pick the main bus power feed from just behind the firewall (rather than back at frame 6) and use the same conductor for the alternator to feed the battery. This way, the only double up is the short length from the firewall to the alternator. This has the added benefit of giving the alternator a larger conductor for the battery feed and so lower losses (It seems silly to carry around 8-10 feet of 2 gauge wire doing nothing - that stuff is heavy!!). Remember, the alternator can run at full rating just after engine start so for a 60A alternator the cable returning to the battery would be at least 4 gauge, 2 gauge is better for starting. 10 feet of that stuff is quite heavy. My way saves all but about 2.5 feet of it.
Why waste weight on either mechanical or electrical flap indicators? A paint stripe on the flap when at 15 degrees does fine, is light weight and won't fail !
Another idea that I feel I must explain is the gear circuit. This all came about after discussing problems that some completed Falco's have. What I am referring to is the addition of a latching relay in the gear actuator circuit. What this does is to prevent the gear motor from actuating when you don't want it to. The problem was that when 'G' was pulled, the noseleg would move slightly off the up stop. This in turn would start the motor again. Of course there are 2 problems now. 1) the gear is actually up already so it doesn't really need to go up any more and 2) the gear is apparently a lot heavier than normal (due to the now higher 'G' load). The upshot of all this is that the CB trips due to high current from the motor straining. A lot of guys pull the gear CB before doing any aeros. My solution cost $6. By adding the latching relay, this tells the gear circuit that once the gear is up not to try and wind it up again. This is ONLY in the UP circuit so gear down is not affected. The circuit is reset by selecting gear down (for however short a time) so if you want to try again, just select down momentarily, then back up.
Anyways, here are my schematics as I get them ready.
WARNING: THESE ARE NOT SEQUOIA ELECTRICAL DIAGRAMS AND ARE IN NO WAY INTENDED AS AN ALTERNATIVE TO THE SEQUOIA ELECTRICAL KIT AND IS IN NO WAY ASSOCIATED WITH SEQUOIA AIRCRAFT CO.
(Please note that I haven't indicated the correct wiresizes yet on * files)
- My Base System*
- Fuel Level
- Nav Lights
- Strobe Lights
- Pitot Heat (If I bother)* (I didn't bother!)
- Landing Light
- Gear Lights
- Gear Actuator
- Fuel Boost
- Instrument & Cockpit Lights/Dimmers* - I didn't use these in the end.. I got some from a Tomahawk wreck
- Flap Actuator
- Electric Gyros
- Ground Power*
You need Acrobat to view them.
For great quality parts check out Mouser Electronics.
|18th April 2001
Spent the day making a printed circuit board for the gear annunciators, air switch and my latching relay trick for the undercarriage retraction improvement.
This is the bubble tank I use to make PCB's with.
|The copper side of the completed board.
Not the most complicated in the world but it makes life a lot simpler.
I used QuickCAD for the layout then exposed some photosensitive copper clad board through a laser printer output on tracing paper. Gave a nice result.
|The top of the board. I went for the
low tech approach (relays). The way I figure it, for a lot less effort the relays will
last a hell of a long time anyhow. The black thing is a pressure switch to sense airspeed.
Actually the black thing was the wrong type - I now have a white thing !! I intend to
re-make this board at a later stage anyhow with a few more functions etc.
Note: The black rectangle is the latching relay... small eh?
Further to all this. I just purchased my Alternator from Vans Aircraft (Yup- home of the RV.) I recommend looking around his site. Lots of gear at hard to beat prices. The Alternator is a light weight 60A model and comes with a built in regulator (a'la your car !!). It doesn't make sense to me to have a voltage regulator so far away from anything (as Sequoia has it) because if you get any voltage drop across the Alternator/Regulator lines (and you will ALWAYS have a little bit) it can't regulate as well. It makes sense to have it near the bus or battery. The built in regulator is not the best option actually. While the theory is great, there aren't any "aircraft style" regulators available built in to alternators so until there is, the best option is the external regulator (I like B&C the best) but installed close to the bus... say the firewall. In order to use the Vans alternator it needs a modification. Check out my alternator page to see how to do it and a little more on internal regulators.
Giovanni's Falco has the standard Falco set-up but Syd put Aluminium main cables in to save weight. The voltage regulation is TERRIBLE !! (For what its worth - If you are considering aluminium cables.. DON'T DO IT !! - they are lighter but the connections are very un-reliable and will eventually build up a resistance and a consequential voltage drop. Piper tried it once - they re-called them all as a fire risk !!)