more cabin heat ?

[jatkins]

I found my C 170B lacking heat yesterday , the oat was about -9c @ 3500ft.
( I have winter covers on )

I was woundering if anyone has modified the heating system, to use the hot air
which is dumped out of the bottom of the carb airbox, and run a scat hose from the bottom of the carb air box and tie the hose into the main heater hose with a Y conector. I am thinking you would get twice as much hot air, all the time,
except when you selected carb heat, at which time the heat would be back to standard. I guess my concern is
if this would put too much heat ( hot air ) into the heat valve at the firewall.

I would plan on removing the 2nd hose from the carb air box, and removing the Y connector as soon as it warmed up
in the spring.

John

[Bruce Fenstermacher]

John,

We have had a big discussion on this in other threads as to how the heat and carb heats should be plumbed. I will try to find them and put a link here.

But I will cut right to the chase. I'm assuming your 52 has the stock 2" ducts running from the from the front of the baffle to each muffler shroud then one 2" goes to the carb heat box and the other goes to the stock 2" heat manifold located on the left firewall above the pilots feet. I have the same setup.
I've tried connecting both 2" ducts to the Y at the carb heat box and then a 2" to the firewall heat manifold and in my opinion it does nothing to increase the heat in the cabin though you would think it would.

The problem is though you might be doubling the intake, you are effectively choking it off with the 2" duct to the heat manifold and the heat manifold itself. Cessna increased heat in later models by going to a single 3" duct from the from baffle through the muffler shroud and into the cabin. Then once int he cabin the distributed the heat better. The 3" inch duct effectively improves the volume of air to the cabin by a third.

These are just a few threads I found on the subject. There is one I can't find which discusses the legal (correct) way to plumb the heat and carb heat but I can't find it.
http://www.cessna170.org/forums/viewtop ... f=5&t=1380
http://www.cessna170.org/forums/viewtop ... f=2&t=3945

[jrenwick]

...The 3" inch duct effectively improves the volume of air to the cabin by a third....

Just a nit, Bruce: the cross-section area of a circular tube is pi * R-squared, so a 3" tube would handle about 2-1/4 times what a 2" tube can. The volume of air could be more than doubled.

John

[Bruce Fenstermacher]

Yep John I think I made that mistake before. I'll try to remember for next time.

[blueldr]

jatkins,

Depending on the year model of your C-170B, you have a couple of choices. If it is a model with a cabin heat manifold across the inside rear of the firewall,
move the battery back into the baggage compartment and install another cabin heat valve on the firewall front side leading into the heat manifold.
If it is the older style such as on the '52 model, install a cabin heat manifold and procede as above.

[jatkins]

I have a 52 170B, and I have the heater manifold to the cabin side of the firewall.
So adding a second heat valve sounds like it would work but !
I have a javlin aux tank, and a Selkirk rear baggage extension, so if I put the battery
behind the baggage extension, it would be awfully far back. That is not even considering W&B issues ?

I think I may try the black double walled scat hose for my heater hose, I think it is called CEET hose.
Does anyone experience with CEET hose ? does it make any differance ???

John

[GAHorn]

Here's the Spruce description of CEET:

Aircraft Ducting "CEET" type ducting has two plies of neoprene-impregnated fiberglass, similar to CAT except wire between plies. Sold by the foot.

Features: Fabric liner on the inside diameter of the ducting allows the air to flow smoothly even in tight bends. Thus, CEET has less air friction loss than ducting which is unlined.

Applications: For use in hot or cold air applications and for conveying fumes at temperatures ranging from -65°F to +350°F. Not recommended for conveying liquids or highly abrasive materials, or for negative pressure applications.


For only pennies more, I prefer SCEET:

Aircraft Ducting "SCEET" type ducting has two plies of silicone rubber impregnated fiberglass similar to SCAT except wire between plies. Sold by the foot.

Features: Highly flexible and can be easily installed around obstructions and sharp bends. Has less friction loss than similar non-lined ducting.

Applications: Ideal for use in conducting extremely cold or hot air at temperatures ranging from -80°F to +550°F, and for conveying fumes. Not recommended for applications involving liquids or highly abrasive materials, or for negative pressure applications.

Here's a LINK to the products: http://www.aircraftspruce.com/menus/ep/ducting.html