Fixing an unusual cabin heat mod

[brianm]

Somewhere back in the mists of time, 69V's intake system for the cabin and carb heat was modified in an odd way. The nose bowl was modified to run the scat tubes straight forward from the muffler shroud. I assume it was an attempt to get better cabin heat via ram air. Has anybody else seen this mod? I hate it because even with my long skinny arms reaching far enough to tighten the hose clamps is difficult. Putting the lower cowl on is effectively a two-man job. I might tolerate it if actually improved the cabin heat, but somehow I doubt that it does.

The horizontal baffles are new-ish and apparently custom made because they don't have the flanges. I'm planning on putting things back to stock this winter. Would anybody mind grabbing the measurements for the position of the flange on the baffle the next time they have their cowl off?

69V's nose bowl

Check out the patches. Whoever did the fabrication screwed it up the first time and put the flange for the left side at the height where the right one should have been and vice versa.

[gfeher]

Sometimes you wonder "what were they thinking?...". You're in luck Brian. I changed my baffles to new Airforms ones at last annual and I still have the old pieces. So I can easily measure it on the one I removed. I'll measure and take a picture or two of the removed baffle on my bench the next time I'm at my hangar. Might be a couple of days before I can get to my hangar though. We're getting a bunch of snow through tomorrow. The cabin heat scoop is at the inboard edge of the left cowl grill, but I don't think the exact location of it in that area is critical because I noticed that the location of the one on the new Airforms baffle was slightly different from my original. (Full disclosure: the stock cabin heat scoop on my plane is used for cooling my Sky-Tek alternator, not for cabin heat. But that doesn't matter. The scoop's location is the same.)

Edit: I should explain. My '52 B model and the '48 model both have the early plenum-style cooling baffles. The left front horizontal one in question on the '48 and the one on my '52 have essentially the same part number, 0550112-5 on the '48 vs 0550112 on the '52. I think the only difference is that the '52 version has a scoop on the top of the cabin heat opening where the '48 doesn't.

[sfarringer]

This cabin heater modification kit was a Cessna design. Look at Figure 34, Item 87 of the '48 IPC.
My airplane had it at one time, as you can see the remnant patches in the cowling.
Don't know if it was an improvement.

[GAHorn]

This cabin heater modification kit was a Cessna design. Look at Figure 34, Item 87 of the '48 IPC.
My airplane had it at one time, as you can see the remnant patches in the cowling.
Don't know if it was an improvement.

Correct! The Cabin Heat Conversion Kit, PN: 52-3-827 ... is a Cessna mod to delete the "periscope" to improve both cabin heat air-flow as well as cylinder cooling.

This is an excellent example of why it's important to have and consult the IPC on our airplanes. I'm always surprised at owners who contact me on issues and are actively engaged in actual maintenance in working on their airplanes without resource materials such as IPC, OM, and Service Manuals. (Not suggesting Brian is one of those... this discussion merely brought that issue to mind.)

FARs require that anyone performing maintenance or repairs have available the necessary information in manuals: 43.13 (a) - "(a) Each person performing maintenance, alteration, or preventive maintenance on an aircraft, engine, propeller, or appliance shall use the methods, techniques, and practices prescribed in the current manufacturer's maintenance manual or Instructions for Continued Airworthiness prepared by its manufacturer,..."

The current manual is the 100 Series, 1962 and Prior and other available information in the form of Service Bulletins, etc. Any and Every owner of a 170 should at least have the IPC, the Service Manual, and any applicable Service Bulletin and/or AD. Even tho' the IPC is not an "FAA approved" document, it is the mfr's publication and is therefore relevant.

[DaveF]

I thought it was a torpedo tube.

[johneeb]

I thought it was a torpedo tube.

Yes, and remember these airplanes are from the era when the Photon Ray Torpedo was the weapon of choice.

[brianm]

Thanks George. When I looked at the IPC I saw "Cabin Heater Conversion" and for some reason assumed it meant the gas heater. I still don't like it and will probably have it removed. It also doesn't show in the picture but the mod was duplicated on the right side for the carb heat. I don't see that in the IPC at all. I'm guessing somebody thought that if it was good for the cabin heat it would be good for the carb heat, too.

[hilltop170]

In fig.34 I see what all the parts are for except #90 ?

[GAHorn]

In fig.34 I see what all the parts are for except #90 ?

The early cabin heaters shared plenum with carb heat. Item #90 is a cap/plug to seal off that carb heat connection.

[Bruce Fenstermacher]

Air intake scoops didn't show up until about '51, definitely by '52. '49s and prior had no scoops, just the hole in the engine baffle.

[hilltop170]

I agree, Bruce. My ‘51 170A had the scoops.

[n2582d]

Brian,
A couple of thoughts about adding a flange to the forward baffles. Late 170B's and early 172's had union p/n 0450262 mounted to the bottom of the baffle. Here's a picture of p/n 0450262:

0450262

Apparently mechanics used the left baffle as a parts counter and screws, rivets, etc. ended up going down the ducting and eventually into the intake. Here's the Service Letter to correct the problem:

Click to Enlarge

If price is a consideration, instead of buying p/n 0450262, I'd recommend making your own from Aircraft Spruce flanges.

[3958v]

I had that mod on my plane. I removed it and replaced it with the original set up. and found no change in cabin heat. Its my experience that older 170s have very poor cabin heating. The only thing that seemed to help a LITTLE was replacing my mufflers with the Hanlon Wilson style exhaust. Bill K

[Bruce Fenstermacher]

If you going to put the duct back to the baffle, I'd look for '51-'52 with scoops or at least make scoops.

As Bill points out, I've found with almost 15 years of fooling around with '52 and prior heat systems, there is very little you can do to improve them. Cessna started to improve heat by removing the '2 scat for "3 through the entire system. That is 1/3 more volume of air. They also made the route to the cabin shorter and more direct with less twists.

I've run scoops, pancake mufflers, Hanlon-Wilson mufflers, both 2" scats joining in a Y at the carb for carb heat as it came from the factory if you run pancakes. I've run the same Y with Hanlon-Wilsons. The Y allows twice the volume to the carb box. In the Y is a one way flapper valve. When carb heat is on, the carb success as much air volume from both sides as it can take. What ever is left goes to the firewall heat manifold. The flapper hangs at rest theoretically blocking the carb heat box and all 4" of scat volume is jammed into 2" to the manifold.

If you have Hanlon-Wilson mufflers, the Y is suppose to be eliminated. The left muffler suppling the carb heat direct and the right muffler crossing over and supplying the firewall head manifold.

No matter what combo of the above I tried, heat never seemed to change except I felt warmer cause I wanted to after doing all the work.

What I always thought might work but never got a chance to do was change over to a quasi-'53170B system by using the '53 on right Hanlon-Wilson muffler and heat shroud system, and replacing the 2" scat with 3". Replacing all or at least the flange of the firewall heat valve to "3. This the volume of air, the muffler and the delivery to the cabin, would be most like the '53. The reason I never tried this and most other won't either is this.

1. You must have the correct right hand Hanlon-Wilosn muffler and if you have a '52 and earlier, why would you have the wrong muffler. (I had the wrong muffler so this hurdle wasn't stopping me.
2. You must have the 3" round funnel like intake for the front of the heat shroud. These are made of unobtainium. I never found one.
3. According to my research Cessna did use a 3" firewall mounted heat valve, which looked exactly like the 170 2" version and I believe interchangeable. I never came across one but didn't look hard cause I needed that funnel in #2.

Bottom line. Knowing what I know, I'd probably leave your heat mod alone cause it is a Cessna mod. And I like the odd originality of that. What are you going to do, put another patch over it?

[n3833v]

I found on my 48 the hose between the firewall and inside next baffle was broken and had little heat. It is a short jumper. I have the scoop on the front engine baffle.

John