Heater Vent Valve

tgmillso · #1 10-29-2017, 04:28 AM

Hi All,

I was vacantly staring at my firewall today waiting for the last of the required parts before I lift the engine in place when I realized that there was potentially a massive heat dump starting me right in the face.
With the heater vent valve closed, the air is simply ducted into the back of the engine bay, where you have temperature sensitive items such as a lithium battery, magnetos or electronic ignition, not to mention that on hot days all you are doing is heating the firewall, which is actually the last thing you want to be doing. What will probably make things worse is that I have an outlet duct/ramp planned to improve exist flow and ensure adequate engine cooling on hot days, but the downside of this will be that this air against the firewall will have minimal air circulation apart from the heater duct pumping a scorching hot blast into the area.
I'm thinking that a possible solution is riveting a 2" diameter stub to the outlet of the heater bypass, then ducting this air through a scat tube into the exit airflow before it leaves the cowling.
I continually read on this forum about equipment overheating at the back of the engine or mounted near the firewall. Ashley Miller's RV-10 has firewall insulation, but you will see in the uninsulated sections (engine mount bolts etc) the temperatures are still hitting 60 degrees (see pictures in the link below).
https://photos.google.com/share/AF1Q...V0MVZXcWVPandn
Am I way off the reservation here, or is this something that should be addressed whilst I have access and the possibility to do so?
Tom.

Mark Dickens · #2 10-29-2017, 06:15 AM

That's exactly what I did...I just routed the hot air to the exhaust exit area. I can't swear that it makes a difference, but it makes me feel better

tgmillso · #3 10-29-2017, 03:36 PM

Thanks Mark. I think I will give it a crack. I found the flanges on Aircraft Spruce for $7. They're only aluminum, however this doesn't really matter in this case. I'll give it a run with the exit duct on, then run it with the duct off and will report back with the temperature differentials. I payed way too much for this EarthX battery to be unnecessarily slow roasting it.
Tom.

Richard Connell · #4 10-29-2017, 04:14 PM

Quote:

Originally Posted by tgmillso

Thanks Mark. I think I will give it a crack. I found the flanges on Aircraft Spruce for $7. They're only aluminum, however this doesn't really matter in this case. I'll give it a run with the exit duct on, then run it with the duct off and will report back with the temperature differentials. I payed way too much for this EarthX battery to be unnecessarily slow roasting it.
Tom.

FWIW I?ve never had any issues with temperatures in the cowl in over 700hrs of all sorts of environmental conditions around the country. I became mildly paranoid about my PMAG when I installed if at 350h and put a RTD sensor on it linked to my EFIS.
It rarely goes over 110F in flight. However heat soaking on shutdown sees it rise rapidly. IMHO that?s going to be the main issue for your battery. In flight temps on the firewall (at least in the 7) are a non issue.
Also, the actual amount of heat transferring into the heater air from the heat muffs isn?t that great at cruise speeds either. A common RV complaint is not enough heat.

Cheers

Carl Froehlich · #5 10-29-2017, 04:20 PM

This is one of the big problems with the RV-10 cabin heat valves location. I used a piece of this between the valves and the firewall (holes cut out for the valves), leaving it long on the top so that it draped over the valves. This way the dumped air was directed away from the engine driven fuel pump and down toward the cowl exit. http://www.aircraftspruce.com/catalo...clickkey=55063

Also considering the heat muffs in an RV-10 are way more than needed, I put a 3/4? office on each baffle heat muff SCAT tube flange (a piece of aluminum cut to fit the edge of the flange, 3/4? hole drill in it, held in place with some aluminum tape on the edge, and the SCAT hose slid over the top).

This way on the hot day you are not stealing all that air from the top of the engine just to dump it as well as decrease the differential pressure for engine cooling air, and there is still more cabin heat than I?ll ever use.

Carl

tgmillso · #6 10-29-2017, 05:34 PM

Hi Richard. Thanks for your real world experience with this. There's nothing quite like having some solid data.
Carl, you bring up a good point about wasted cooling air running through this tubing. I had originally planned on blocking off the outlet to create dead air in the SCAT tubing, then I thought that doing so would cause adverse heat buildup in the vacinity of the muff and also mean that the heater vent could only be fully open or closed, as there would be no bypass to split the flow into. A cover on the inlet side would make more sense, but I just didn't want another Bowden cable or servo if I could get away from it.
My concern is that with this exit air ramp that I create a bunch of dead air in front of the firewall, and even Emag Air warn about this in their installation notes. I'd ditch the exit ramp, but I've been told by some experienced builders that if you want to be operating in the heat of summer here, then it's a worthwhile investment, not to mention the fact that I've already riveted the attachment flanges for it to the firewall. Perhaps I'll start with blast tubes onto the EarthX battery and the PMags and monitor the temperatures and see how things progress.

Tom.

Carl Froehlich · #7 10-29-2017, 05:56 PM

Quote:

Originally Posted by tgmillso

SNIP......
Perhaps I'll start with blast tubes onto the EarthX battery and the PMags and monitor the temperatures and see how things progress.

Tom.

A blast tube is required for each pMag.

I?m not a fan of mounting any battery on the engine side of the firewall as it is bad environment for what has become a critial flight component. For that matter a single battery IFR airplane exceeds my risk tolerance. So - you are on your own for that.

Carl

tgmillso · #8 10-29-2017, 08:58 PM

Fully appreciate your concern about the battery operating environment. I'm still thinking of rebuilding my battery holder so that it is an insulated vessel with blast tubing. This should also stop the heat soaking on the ramp, as the core temperature will be super low and it will take time for the engine bay heat to soak through after shutdown. Right now I just have 16 thou radiation shields on standoffs around the stock EarthX battery box.
Tom.

rvbuilder2002 · #9 10-29-2017, 09:50 PM

Waste heat muff air dumping into the engine compartment has be a standard part of light aircraft design for 60+ years.

The volume of hot air exiting the heat valve is small when compared to the amount of hot air being dumped through the cowl after passing through the cyl. fins.
It is critical that there always be airflow through the heat muff(s) to prevent the muff(s) and the exhaust system an that area from getting over heated.

In my opinion there is little to be gained (other than weight , cost, and build complexity) by adding a duct to out the heat valve bypass air overboard.

It is good practice to avoid that air dumping directly on heat sensitive items.

Carl Froehlich · #10 10-29-2017, 10:15 PM

Quote:

Originally Posted by rvbuilder2002

Waste heat muff air dumping into the engine compartment has be a standard part of light aircraft design for 60+ years. SNIP

Yep - you are correct. It is also reasonable to point out that wasted cooling air translates to needless engine cooling drag across the operating envelope. I am one of those ?get the most speed out of every drop of fuel? guys so I worry about such things.

Carl