Reference Ralph’s post below,

 

I think you can fill the “cups” of your machined firewall grommets with silicone very satisfactorily. Use the high temperature red stuff with a thin nozzle and work it well around the wires inside the grommet “cup.” I used this technique in several places in my IV-P with all the wires running through a single larger hole in the middle. You might also consider making you grommets with a “cup” on both sides, and filling both sides with silicone. This is not needed for sealing, but it will help with strain relief of the wires. If you don’t provide some strain relief, the wires will break fairly quickly where they pass out of your drilled holes.

 

Consider also how you’ll repair/replace failed sensors over time—you will have to do this—and how you’ll disconnect your sensors when you need to pull the engine…also a certain thing over time. It’s possible to disconnect each sensor and leave it wired to the firewall, but this will be a real pain. Based on good advice from Brent Reagan many years ago, I cut my connectors to the absolute minimum, but this is one case where a good quality multi-pin connector may be warranted?

 

In my opinion,  the 500 degree fire resistant materials should be adequate. I’m pretty sure you’ll lose the cowling well before the internal temperature gets to 500 degrees, and local internal “hot spots” at/above 500 degrees that damage your wiring will cause lots more trouble than losing the sensors.

 

For TSIO-550 powered aircraft, I consider the turbo oil feed and return lines an area worthy of significant attention. A leak/burn/break on any of these lines will cause instant fire when the oil hits the hot turbos. As the air/fire is being exhausted through the bottom cowling, the first you are likely to know about such a fire is when the floorboards start smoking… I installed a “standard” temperature sensor in the cowling exhaust flow path on each side. They read about 130-140 degrees during normal flight, and are alarmed at 200 degrees, with the intent that I’ll recognize this as a fire and secure the engine before it burns through the floorboards…

 

I would strongly recommend you replace the aluminum hard pipe to your wheel brake cylinders with good quality flex hose. The brake cylinders move a good bit during use, to include some significant vibration during certain braking situations. This will quickly fatigue the aluminum line and cause it to fail. You’ve probably already figured out that without other steering/braking, the MLG brakes are critical to safe operation of your airplane. Lose one brake in flight and a successful landing (defined as “the airplane is useable again”) is in question. If you really want hard line here, use stainless steel, and include one complete 360 loop to absorb the vibration and movement.

 

The wiring recommendations are just that; changing the brake line is a foot-stomper. No offense intended!

Bob

 

 

Dear subscribers,

 

I got tiered of looking at how all the wires run through my bulkheads (picture 186). There were even some gaps and I questioned that this would seal very well.

 

Since I was too cheap to buy the 300$ sealed bulkhead connectors I decided to make my own (picture 202, 203). I made a sleeve out of aluminum counted the wires and drilled a hole for each wire/cable with the right size. I was planning to fill the back side of my bushing with approx ¼’’ of flox to make the plug air tight. I was planning to make the flox really thin that it would flow in nicely and would seal good around my wires. I am concerned now that the flox might not be flexible enough once it is cured. Are you aware of any sealer that I could use that is really thin in the beginning and that would flow in nicely?

 

I also found a lot of wires to the engine monitoring system (picture 200) being extended in the engine compartment. Is this an area of concern? I was thinking of buying new sensors with longer cables and run them to the computer box in one piece.

 

What is proper for heat protection for the cables in the engine compartment. I found products that last to 500 degrees F. Some silicone/fiberglass combinations run up to 700 degrees. Can I go with the 500 degree products?

 

I do not have any documentation on my engine monitoring system and I don’t find anything on the internet. Can anyone give me a file/ copies for the wires installation sketches and set up instructions?

 

I got also done with my brakes now (picture 195). I used aluminum hard pipe since it is a very similar application which is used in our Cessna. I also used plasma nitride for rust protection on the rotors and drilled them to get more surface.

 

Ralf Bronnenmeier