The International Cessna^® 170 Association

Hello. I have a cabin heater in a 170A that is letting in warm air when closed and in the course of diagnosing it, I found that it is a second unit, installed on the airplane-right side of the firewall. On the airplane-left side is the factory unit well documented in the manual and parts manual, but the only other unit documented that I've found is a Stewart-Warner gasoline model. Mine is definitely not that. It is labeled Sorensen, and I can't seem to find any reference to in in the forums, internet search, or my 337's. I could be overlooking a log entry. Before I do too much with it, I'd love to know more about it. It seems like a very simple unit, but the mystery is bothering me. Any insight would be much appreciated. Thank you!

Jason

Sorensen Sprayers, Inc, Box 344, Airport Rd, Worthington, MN holds an STC for installation of a 90 gallon sprayer system on helicopters. That’s all I could find.

If it’s not documented in your records, you will have to find a basis of approval or remove it to stay legal.
Do you have a pic of the installation? Is it exhaust/heat-exchanger powered..?? Or is it gasoline..? Other?
Or is the only difference the heat-contol-valve? (If the latter, this might be a simple minor alteration needing only a log entry, but you should repair it so you can shut it off completely.... What if you had a carbon monoxide leak into the cabin? Or fire? How would you deal with that?)

Thanks for the fast reply, George. I buttoned up the engine so no more photos right this moment. It is a very simple system, pull knob in the cockpit that throws a metal door open to accept heated air from the shroud around the airplane-right-side muffler. And after scouring the logbooks, I did find an entry from back in 1954 documenting the installation. Although it was dubbed a "Chinook Heater System Model AC." Mind you, reading these old entries are not easy, so here's the clip.

OK, then it sound as if you’re good-to-go ....(as soon as you repair the inoperative shut-off problem.).

Hey, this could be very cool for others who might want to install a "Chinook" heater system. If you happen to have a 337 for the install in '54, that would be approved data.

I know there is no 337 on file with the FAA, but I’ll dig through the paperwork again. It wouldn’t be the only one that doesn’t show to be on file that I need to re-submit. It’s a new-to-me airplane and still trying to catch up with everything. Thanks for the suggestion.

You’ll find the Chinook heater listed as optional equipment in the TCDS. So no 337 should be required. Once the pandemic is over I would think you should be able to get Bulletin AC-2 from the FAA in OKC.

Gary thanks so much. Of all the docs I went through, I completely overlooked this one. Thanks for the help!

Jason

Jason,
Glad to help solve the mystery. What’s on the cabin side of that valve? Does it have any ducting as depicted in fig. 50 of the C-170A IPC? Also, is there a tee to split the hot air from the right muff to both heater valves?

Here’s the weather in Huron, SD on December 3, 1954, when that was installed. One can see why they needed it!

Hi, Gary. Yeah I bet they were looking for as much heat as they could get. The cabin side of this simply dumps the air into the cabin near the feet of the front seat passenger. There is no ducting, and actually I'm not seeing any Figure 50 in the 170A IPC. Goes from Figure 49 into the section marked Optional Equipment, then on to Figure 51, which depicts what I have on the pilot side of the airplane. There isn't anything that splits the hot air. Each side has it's own source of hot air from around its respective muff. And in the cabin I have two "cabin heat" pulls. One for the left (Figure 51) and one for the right.

jastu23 wrote:Hi, Gary. Yeah I bet they were looking for as much heat as they could get. The cabin side of this simply dumps the air into the cabin near the feet of the front seat passenger. There is no ducting, and actually I'm not seeing any Figure 50 in the 170A IPC. Goes from Figure 49 into the section marked Optional Equipment, then on to Figure 51, which depicts what I have on the pilot side of the airplane. There isn't anything that splits the hot air. Each side has it's own source of hot air from around its respective muff. And in the cabin I have two "cabin heat" pulls. One for the left (Figure 51) and one for the right.

My copy of the 170A parts catalog also skips figure 50 and goes from page 91 to 93. Weird.

Jason,
Then your carb heat must be tee'd (is that a word?) to one of those. On the C-170B it comes from the left muff.

It's my copy of the C-170A which is out of date. Yours probably has this page:Here's Fig. 50:

Thanks for sharing that, Gary. I'll have to snag some photos next time I have it opened up and share. I definitely have no ducting in the cabin to share the heat as your drawing shows.

Fig 50, best I can tell, is the Cessna aux heat system. It is installed in N7A.

In the early heat duct systems there is/was a T. Actually a small t. The duct from the left and the right muff came into each t arm and the tail was attached to the carb heat. So with carb heat on bot sides feed the carb. The center top feed went to the heat valve on the fire wall. It would have been a simple matter of running one duct directly to the fire wall the other to a modified t. with one arm blocked off, in order to get 2 feeds for two valves.