Cabin Heat Conversion

How to keep the Cessna 170 flying and airworthy.

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hilltop170
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Joined: Sat May 06, 2006 6:05 pm

Re: Cabin Heat Conversion

Post by hilltop170 »

Gary-
I have flown my 1958 C-180A with the firewall guillotine valve (behind the heater valve) both open and closed (with the heat off) on the same flight long enough for the CHTs to stabilize. I did not see any change in CHT with a 6-probe EGT/CHT.

With the firewall guillotine valve open (the normal position), the same amount of cool air is taken from above/upstream of the engine whether the heat is on or off.
Last edited by hilltop170 on Thu Dec 19, 2019 7:03 am, edited 1 time in total.
Richard Pulley
2014-2016 TIC170A Past President
1951 170A, N1715D, s/n 20158, O-300D
Owned from 1973 to 1984.
Bought again in 2006 after 22 years.
It's not for sale!
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n2582d
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Re: Cabin Heat Conversion

Post by n2582d »

Richard, That's interesting. As I see it the only way to effectively "shut off" the fresh air is to have the guillotine closed and the cabin air/cabin heat butterfly valve in the cold air position. Good to know it doesn't make any difference in CHT's to have the guillotine open with the cabin heat valve off.

The fresh air valve I pictured in my previous post is mounted on 1966 and later 180's. With this fresh air valve Cessna uses a different firewall valve--one that just goes to the exhaust muff.
Last edited by n2582d on Sat Feb 05, 2022 7:28 pm, edited 1 time in total.
Gary
hilltop170
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Re: Cabin Heat Conversion

Post by hilltop170 »

Gary-
The guillotine valve shuts off ALL air to the cabin no matter how the heater control valve is set. With the guillotine valve open, you either get cold air from above/upstream of the engine or heat or a combination of the two.

Fresh air and cabin air changes are both good things, I can't imagine not wanting air circulation in the cabin especially since temp can be modulated for comfort with the heater control valve. Except of course if smoke or fire is coming thru the heater/vent system.

I looked at a buddy's late model 180 yesterday and concur the right side boot cowl air vent/flapper valve scat tube does go the the heater header. On my old 1973 A185F, someone had disconnected the hose from the flapper valve and capped the header port. The hose was open-ended to the cabin for an additional fresh air vent to the cabin. I liked having a separate source of fresh air.
Last edited by hilltop170 on Thu Dec 19, 2019 7:05 am, edited 1 time in total.
Richard Pulley
2014-2016 TIC170A Past President
1951 170A, N1715D, s/n 20158, O-300D
Owned from 1973 to 1984.
Bought again in 2006 after 22 years.
It's not for sale!
User avatar
n2582d
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Joined: Mon Apr 29, 2002 4:58 am

Re: Cabin Heat Conversion

Post by n2582d »

I wasn’t clear in my last post. My thinking was about limiting the amount of cooling air “bypassing” the cylinders through the 3” fresh air duct. With the guillotine closed and hot air selected fresh air is ducted overboard and the hot air from the muff has nowhere to go. (The owners manual warns against configuring the valves this way because the ducting from the muff might get too hot. Not sure if that is really an issue with modern SCAT ducting which can withstand +550°F vs. original CAT ducting which can handle +350°F). With the gullotine closed and fresh cold air selected there is no flow of fresh air from the rear baffle duct. Theoretically more air flows by the cylinders in this configuration. In this position hot air is ducted overboard at the firewall valve.
Gary
hilltop170
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Re: Cabin Heat Conversion

Post by hilltop170 »

I agree with everything you just said. Are you having CHT problems?
Richard Pulley
2014-2016 TIC170A Past President
1951 170A, N1715D, s/n 20158, O-300D
Owned from 1973 to 1984.
Bought again in 2006 after 22 years.
It's not for sale!
User avatar
n2582d
Posts: 2808
Joined: Mon Apr 29, 2002 4:58 am

Re: Cabin Heat Conversion

Post by n2582d »

No CHT problems. Just in the planning stage on my baffling. Don’t want to cut a bunch of 3” holes in my new AirForms baffling and then decide I should have gone with the boot cowl vent setup instead. So far I’ve collected the later style right muffler with the associated funnel and heat muff, the later style firewall mixer valve, and fabricated the manifold for the backside of the new Del-Air stainless firewall. Still need to find or make a spring for the gullotine slide and find or make some front vertical baffles as discussed here.
Gary
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gobrien
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Re: Cabin Heat Conversion

Post by gobrien »

hilltop170 wrote:Dave-
I had a C-180 heater system installed on my 1951 170A with the Hanlon-Wilson mufflers. It is pretty much the same as the -B model heater I think. The heater valve was put on the left side where the old one was. New side panels with heat ducts had to be fabricated. It came out very nice and works great but was unable to fit in a defroster outlet due to lack of space.
Hey Richard,

I am fabricating the '53+ heat system for my 1948 ragwing and have rookie questions:

1. Do you recall what thickness of Al sheet you used for the panels and ducts?
2. Did you use 2024 T3 for a particular reason? I'm thinking 6061 T6 would have adequate strength and the improved corrosion resistance is quite useful in our damp climate (Ireland).

Thanks,

Gareth
1948 170 Project (N4180V) now EI-AEN SN:18513 - Dublin, Ireland
https://www.taildragger.eu/
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GAHorn
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Re: Cabin Heat Conversion

Post by GAHorn »

Gareth, for ease-of-shaping you could use SO (soft anneal) sheet for this non-structural purpose (instead of T3 or T6)... just a consideration.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
hilltop170
Posts: 3481
Joined: Sat May 06, 2006 6:05 pm

Re: Cabin Heat Conversion

Post by hilltop170 »

gobrien wrote:
Hey Richard,

I am fabricating the '53+ heat system for my 1948 ragwing and have rookie questions:

1. Do you recall what thickness of Al sheet you used for the panels and ducts?
2. Did you use 2024 T3 for a particular reason? I'm thinking 6061 T6 would have adequate strength and the improved corrosion resistance is quite useful in our damp climate (Ireland).

Thanks,

Gareth
Gareth-
Memory says .032 for the side panels, definitely not .020. .040 would not be too thick, just heavier. Cessna used flimsy plastic on the later planes with that heater system. The duct on the firewall came out of an early C-180 so whatever Cessna used, I would guess .032. I would not add ANY holes in the duct pointing up under the panel, you want all the heat aiming down and aft.

Don’t know much about grades of sheet aluminum, I would not use hardened sheet due to cracking potential in the bends, some of them 90°. Corrosion resistance is good.

Also, 3” ducts will flow more volume but the inlet side to the heat muffs behind the cowl intakes are 2”. Where we placed the C-180 heater valve on the firewall would have interfered with the motor mount with 3” so we reduced to 2” all around.
Richard Pulley
2014-2016 TIC170A Past President
1951 170A, N1715D, s/n 20158, O-300D
Owned from 1973 to 1984.
Bought again in 2006 after 22 years.
It's not for sale!
User avatar
gobrien
Posts: 113
Joined: Sun May 19, 2019 11:36 am

Re: Cabin Heat Conversion

Post by gobrien »

Thanks Richard,

That helps, especially knowing the 2" supplied adequate heat. I'm planning to leave the original 2" valve in place and feed the existing scat into the new ducting. I've deleted all the suction equipment so hoping that will leave enough space for a demister. Given 2C is a LARGE temperature-dewpoint spread around here for 6 months of the year, I'll need it!

Gareth.
1948 170 Project (N4180V) now EI-AEN SN:18513 - Dublin, Ireland
https://www.taildragger.eu/
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