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Thread: Cessna 170/140 winter block off kit question

  1. #1
    Richgj3's Avatar
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    Cessna 170/140 winter block off kit question

    For you cold weather guys.

    On my 1952 170B the cowl opening block offs cover about half the opening on the inboard side of the opening. This results in covering the air inlet for cabin heat as it is behind that one. On the other side, the inlet for the carb heat is outboard of the plate and works normally.

    With the plate installed that covers the cabin heat inlet, there is no cabin heat. (No surprise). So logic says cut an opening in the plate the same size as the inlet. But that doesn’t work, verified by guys in the 170 association and also a guy with a 140 trying the same thing. The 170 forum is does not have a lot of members, so I thought I’d try here.

    I have to assume there is something going on with turbulence around there or a low pressure there that is interfering with the ram air going into the inlet. There is no way to reposition the inlet on that side to be unobstructed by the plate.

    The first picture shows the opening without the plate. The inlet is hard to see but it is a vertical oval close to the case.

    I wonder if anyone here has solved this issue.

    Rich
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  2. #2
    BC12D-4-85's Avatar
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    Not on a Cessna but with my Citabria 7GCBC I tried two mods....one was installing a 2" flanged SCAT adapter in similar front winter baffles. Then running a short tubing to another adapter mounted (screwed to temporarily) forward on the existing heater inlet. The second was to drill 2" holes in the cowl below the cooling air inlets and reposition the intake heating air sources. Cosmetically the latter changes things but worked the best.

    Gary
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  3. #3
    BC12D-4-85's Avatar
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    If there's not much room from adapter to existing duct opening the flanged duct adapters can be cut down to fit. All that's needed for the hose to grab is the width of the hose clamps, providing the SCAT hose can make the offset bend required.

    Gary
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  4. #4
    Richgj3's Avatar
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    Thanks. Not sure I can’t make the bend, but in any case I’m not sure that changes anything. I’m afraid the issue is there is no pressure there with the block plate in place. I like your second solution except as you say, not the best cosmetic solution. By the time I figure this out, it will be warmer!

    Rich

  5. #5
    SuperCub MD's Avatar
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    Hard to tell from a picture, but it looks like the intake scoop is to far inboard for the early cowl, which you have. That cowl should have the pressure baffles installed over the cylinders, the scoop should be in front of the cylinder head. This would be on S/N 20267-25372. Later B models used a different cowl and baffles with the scoop inboard. Maybe you have some miss matched parts. Check your s/n, maybe some pics with the cowl door open.

    The original winter kit covered the inboard cylinder openings, installed with spring hooks, and also had a plate to covered the center cowl vent.
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  6. #6
    Richgj3's Avatar
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    Mine falls in that range and the scoop on the passenger side is in front of the head, but on the pilot side the scoop is inboard as there is no room for it in front of the head on that side as that cylinder is farther forward than the other side. 52 models do have the earlier cowl with the shrouds over the cylinders. I think 53 models started with pressure cowl.

    In any case, I will check the service manual to see if there is a discrepancy in the configuration. Can’t see much with the cowl open because everything is under the nose bowl but I will take some better pictures from the front. It may be a couple of days from now as wife and I will be getting our second Covid shot tomorrow

    Rich

  7. #7
    BC12D-4-85's Avatar
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    https://support.cessna.com/docs/cust...es/P108-12.pdf

    Starting with Fig. 49 which setup do you have that's the closest?

    Gary

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    Richgj3's Avatar
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    Gary
    That link didn’t work for me. I’m on an iPad. Maybe that’s it. I’ll try to find it.
    Rich.

  9. #9
    BC12D-4-85's Avatar
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    No expert here but it looks to me like the left baffle air source feeds the carb heat and the right the cockpit heater.

    Gary

  10. #10
    mvivion's Avatar
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    Cessna never could figure out a decent way to “manage” air flow over cylinders AND provide cabin heat.

    Take the block off plates off, leave them in your hangar/garage, cover the oil cooler with duct tape and go fly.

    Lots of these things have been flown way colder than you’ll see that way with no harm done.

    My experience with Cessna “winter kits” is they’re useless except for covering the oil cooler.

    MTV
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  11. #11
    Richgj3's Avatar
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    Mike

    No oil cooler on C145/O-300
    On a 30 degree day I see oil temps of 130 without the plates and 175 with them. I’m not hung up on that. I’ve owned and flown a lot of antique airplanes where I never cared about oil temps. Maybe I’m reading too many forums.

    Gary

    My set up has the right side (passenger side) muffler providing carb heat. It’s inlet is outboard on the right opening and not covered by the plate. The cabin heat is supplied by the left (pilot side) muffler. It’s inlet is on the inboard of the left cowl opening. And is covered by the plate. This is consistent with other 52 model year C170B airplanes I have seen. There is more to this than the covering of the inlet because even when a hole is cut to allow air to get to the scoop, it doesn’t work. Other 170 and 140 owners report the same. I intend to try it myself but I’m not holding out much hope.

    Rich

  12. #12
    BC12D-4-85's Avatar
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    Rich the figures 49-50 I see show otherwise - left carb; right cabin. Not arguing just looking at available figures in the link. Why not hook it up to feed the right muffler that flows better to the cabin or match what Cessna shows?

    Gary

  13. #13
    Richgj3's Avatar
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    Gary

    I wish I could see that drawing. It sounds like it’s mirror image. The firewall fitting for the cabin heat is on the left side. The carb heat inlet to the heat box is on the right side of the box. The battery is on the right (passenger) side of the firewall. If your drawing shows it on the other side, that’s for a later model 170.

    When I say left and right it’s as viewed from behind the engine.

    Thanks for your interest and effort in helping with this.

    Rich.

  14. #14
    BC12D-4-85's Avatar
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    I tried to post pics above but no luck. I did look up the C-170A Parts Manual and it shows what you describe, not what's in the C-170B Parts Manual for S/N 20267-25372. I'm corrected. The mufflers for the C-170B are round...the C-170A not.

    Gary

    Edit:

    C-170 P/M: https://mrwebman.com/aviation/cessna...0_pm_pre59.pdf
    C-170A P/M: https://mrwebman.com/aviation/cessna...ls/170a_pm.pdf
    C-170B P/M: https://support.cessna.com/docs/cust...es/P108-12.pdf
    Last edited by BC12D-4-85; 02-11-2021 at 10:57 PM. Reason: Manuals for review
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    This is on a 1954 170B. Not a great picture but you can see where I cut the plate and then made an air scoop to direct the air through the heater intake. This works good, after the plane picks up speed. Plenty of cabin heat down to 0, at 20 probably only open it half.
    Flat Country Pilot
    Farm Field PVT
    54 C170B
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  16. #16
    nanook's Avatar
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    Do you realize the 170 with no oil cooler, has an air blast tube pointed at the oil temp probe? That would be the first thing I would block off. Then read what your oil temp. really is. I would be very cautious about blocking airflow over air cooled cylinders. In the past in Alaska, we would block the center vent holes on the nose cowl but not the cylinder openings. That applies to the 140 also. You can also put a cover over the 140’s oil tank, to keep the temp up. I certainly would not block off my cabin or carb heat cold air intakes...
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  17. #17
    hotrod180's Avatar
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    Quote Originally Posted by nanook View Post
    .... we would block the center vent holes on the nose cowl but not the cylinder openings.....
    That's the one that lets air blow in onto the oil sump. Cover it up in cold wx, might help a little.
    Cessna Skywagon-- accept no substitute!
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  18. #18
    Richgj3's Avatar
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    Good suggestions about the blast tubes. I knew they are there but forgot to consider them in the equation.

    Thanks

    Rich

  19. #19
    Richgj3's Avatar
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    Gary

    I think the confusion comes is that the 52 170B was the first year and has a lot of 170A artifacts. The Engine install is one, the panel with the piano key switches is another. The major change on the 52 B model is the wing and flaps, being exactly like the 172 of today. The 170B POH (owners book) that claims to be for all B models is focused on the later models. I have not been able to find a hard copy of the strictly 1952 book, but I know it exists.

    In any case, you all have given me good advice and I will try the simple things first. I do have the cover plate that covers the hole in the cowl that blows directly on the crank case.

    Just to close out the thread, I’ll take more pictures of the front where the intakes are for info

    Rich
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  20. #20
    BC12D-4-85's Avatar
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    Another option might be to put an air intake adapter (or another in addition to the original) in that sump cover plate and feed the heater muff. I did that on a PA-11 with a similar opening and it helped the cockpit airflow and heat. I realize there's a factory trough installed behind it to channel cooling air to the sump, but maybe that can be modified some for winter? After 75 years of living with winter plus 56 in alaska I like heat when flying.

    Gary

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