Notification 14-10-24

[N661DJ]

What am I missing?
I have the new style carb.heat air box on my RV8A and don't see what the issue is with the change to relocate the screen from the front of the baffle ramp to the inlet of the heater, down stream of the heat muff. Is the aim to increase the heat output to the carb? if so, will it not decrease the output to the cabin heater? Previous installs using the screen at the main air inlet have not been a safety
issue.
I have not flown the airplane yet, waiting DAR inspection, however, the new heat muff looks like it will be an improvement over the previous model. I would expect increased output in both the heater and carb heat.
Dick

[rvbuilder2002]

Window screen has quite a bit of resistance to airflow. Particularly accelerated flow.
Try a simple test by waving a framed screen for a window in the air... the resistance is very evident if you try and move it fast.
It is undesirable to have that flow resistance in the supply circuit for induction air (this would be the flow path for all induction air when carb. heat was turned on).
It was ok with previous installations because the air circuit that had teh screen was only sourcing air for the cabin heat.

So, adding the screen in the location specified (the cabin heat outlet of the heat muff) does three things.
- It removes an undesirable resistance to flow for the engine induction air while carb heat is on.
- It still protects the cabin heat circuit from insects, etc. from being able to get through.
- It adds a slight flow resistance on the cabin heat outlet of the muff to prevent the engine from sucking air backwards through the system (this would reduce the actual temp of the air being delivered to the engine when carb. heat was turned on).
It does not reduce the cabin heat performance. It actually helps it. By slightly slowing down the airflow through the heat muff... allowing a higher temp rise.

I have been flying the very first prototype of this exhaust system and heat muff for about 4 years on my personal airplane. I assure you the cabin heat and carb heat work very well...
If installed as prescribed.

[Squeak]

Ok I give up. Where?s a guy buy one of the EA EXH/MUFF 320/360-1 HT.MUFF? Only found this on Vans Parts List: EA EXH/MUFF 320/360-1 EXHAUST WITH HT.MUFF $1010.00. Hmmm not needing the exhaust just Heat Muff.

[rvbuilder2002]

Using this heat muff requires a specific exhaust system sold by Van's, that is built specifically to use this heat muff..
If you already have a system, this muff wont work with it.