Cabin Heat, Water Cooled Engines - Which Way is Best and Why?

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by wsimpso1, Feb 18, 2019.

  1. Feb 18, 2019 #1

    wsimpso1

    wsimpso1

    wsimpso1

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    OK, there are some mighty tempting water cooled (auto conversions) engines out there. If one of us were to use one of them, we also have options for cabin- and windshield-heat. Which one is best and why? Options appear to be:

    Exhaust muff and mixer box forward of the firewall. NEVER liked this scheme, seems like an open invitation to CO poisoning. That being said, I do have 2100 hours with such things, and when done well, it just works;

    Automotive heater core plumbed with glycol-water in the cabin like we run in 17 million new cars built every year. I can run a sexy looking NACA inlet into the box, run a control valve on the plumbing, butterfly valves on the cabin and windshield ducts, and a scupper from the box out the belly in case it leaks. Yes, I have room for it;

    Oil cooler plumbed with engine oil in the cabin. Ditto on placement and operation;

    Automotive heater core forward of the firewall, with air plumbed through the firewall like we do with exhaust pipe muffs;

    Oil cooler plumbed with engine oil forward of the firewall, air plumbed through the firewall.

    If you have other options, we should talk about them too.

    I do anticipate taking my bird into the teens where the air gets really COLD. Anybody know if the core needs to be bigger than is standard in cars.

    So, what are the risks and rewards, losses and gains, etcetra? Those of you who have done so, how did it work out? Any pitfalls, fatal flaws, areas that require special efforts or attention?

    Billski
     
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  2. Feb 18, 2019 #2

    Richard Schubert

    Richard Schubert

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    The key to good cabin heat on unconventional installations seems to be recirculating cabin air through the heating element, not bringing outside air in to heat.

    Velocity uses a nose oil cooler for heat. Some use heated motorcycle suits :>)
     
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  3. Feb 18, 2019 #3

    TFF

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    I would go with a car like set up that had valves on both inlet and outlet in the engine compartment to shut off, and when off, the valves divert the flow of the core to still flow the circuit, just without the core.
     
  4. Feb 18, 2019 #4

    BJC

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    Related comment, based on a single typical heat muff source of heated air. Performed well at 6 F on the ground, where defog was important, and for extended duration at 12 to 22 F above 10,500 feet.

    A single push-pull control operates thusly: full forward dumps hot air into the cowling air exit; pull for increasing heat, continue pulling for full eat, then heat/defrost, pull full out for defrost only. Uses a rotary inlet and exit valve arrangement.

    You will want the ability to adequately defrost / defog; more important than cabin heat.


    BJC
     
  5. Feb 18, 2019 #5

    Pops

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    On my 1968 VW Bug with a V-8 engine, I used a heater from a fork-truck. Just one box with everything contained, heater core, blower motor, etc. Metal box about 8"x8" x 6". Don't remember the fork truck brand. The steel box could be replaced with one made from aluminum to save weight.
     
  6. Feb 18, 2019 #6

    Himat

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    Do not many modern cars have a heater core where the cooling medium flow all the time?
    Temperature control is then by air mixing. The hot and cold air mix is adjusted to get the required temperature, excess hot air is dumped. I do think there is advantages to cooling system layout with this scheme and there are no valves that can stick
     
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  7. Feb 18, 2019 #7

    rv6ejguy

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    I had a large brass auto core inside the cabin initially for about 10 years, worked well but never really liked glycol in the cockpit. 6 years ago, I did a complete overhaul and weigh savings program. Removed that core from inside and built an air duct system from an 8 X 8 X 1.75 aluminum heater core mounted FWF. Air source is a 3 inch ram tube mounted below the spinner. Ducts are twin 2 inch SCAT hoses coming off the back of the core to a box with hinged door on the firewall.

    Can control the amount of flow there to the cabin. Seems to work equally well and I can use that core to dump heat overboard in the summer for extra cooling. Water flows continuously through the core.
     
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  8. Feb 18, 2019 #8

    Monty

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    Why reinvent the wheel??

    This should keep you busy for a while:

    https://www.summitracing.com/search/part-type/heaters?ibanner=SREPD1

    I've used the vintage air units in car builds before. The nice thing about them is you can install it in the cabin and use the coolant servo to control how much heat is delivered. The fan control and defrost balance would allow for de-fog/heat modulation. I would install it to recirculate the cabin air, with a separate vent control that admits outside air.


    Monty
     
  9. Feb 18, 2019 #9

    Monty

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    The glycol in the cockpit is the biggest argument against using the automotive stuff. I think the chance of failure for a properly installed and maintained system is fairly low, but definitely not zero...and a big leak at 16Kft could definitely ruin your day.

    Monty
     
  10. Feb 18, 2019 #10

    Vigilant1

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    Just to be a contrarian: The use of an exhaust heat muff is going to be much simpler, lighter, and probably more effective than a heater using the liquid coolant. The temp difference is key to the heat transfer rate between two fluids, and the exhaust pipe is a >lot< hotter than the liquid coolant or oil. So, less surface area required, and potentially higher cabin heater/defrost air temps. Every liquid cooling connection, hose, and device (esp a heater core) is a potential leak point, which is not a minor thing when coolant is critical to continued engine ops. Also, heat from an exhaust muff will be available much sooner than from either the coolant or the oil.

    I'd strongly consider using a "regular" heat muff despite the temptations/options presented by liquid cooling. Electronic CO detectors are cheap and reliable.
     
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  11. Feb 18, 2019 #11

    Vigilant1

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    That sounds good compared to a separate heater core-- no additional fan needed, no additional liquid cooling connections or parts (complexity, weight, leaks), use of fresh outside air improves cabin air quality. Have you got a wag on the amount of heat delivered (toasty in your cabin even in the Alberta winter?) an the approx temp out of the vents?
     
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  12. Feb 18, 2019 #12

    mcrae0104

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    I agree with you generally about the weight of the two systems, but the temp difference is only one of several things that affect the system. The specific heat of air and water and the mass flow rate of the two systems are very different.
     
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  13. Feb 18, 2019 #13

    wsimpso1

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    Recirc also requires a fan be fit behind the panel. More volume. Do you know anyone who has done that? Please get them to post on here or connect me to them so I can chat with them.

    Ideally I need to know fan size (CFM) and core size (dimensions) and the OAT where the gadget is no longer adequate.

    Do you know at what OAT the Velocity setup becomes inadequate?

    Billski
     
  14. Feb 18, 2019 #14

    wsimpso1

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    Why the divert valve instead of the throttle valve?
     
  15. Feb 18, 2019 #15

    wsimpso1

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    Good to know. Can you share the OAT where that single heat muff becames inadequate. Today we have a beautiful day but it is -26C at 15000 ft.

    Sounds like it could be interesting to design. Defog is part of my scheme.

    Billski
     
  16. Feb 18, 2019 #16

    wsimpso1

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    I have been looking at the commercially available units for hot rods. I would probably build a fiberglass box... Billski
     
  17. Feb 18, 2019 #17

    wsimpso1

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    Some do, some still either throttle or divert hot coolant around the core. Valves are all available for such things, driven by a pull cable, vacuum, or electrics...

    Billski
     
  18. Feb 18, 2019 #18

    wsimpso1

    wsimpso1

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    How well did both systems work? Adequate down to what OAT?

    Billski
     
  19. Feb 18, 2019 #19

    wsimpso1

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    So, how well do they work? Do you know what OAT temp they cease to be adequate? Empirical results are valued.. I am beginning to think I will have to work out my own estimates of how much air and how much heat I will need...

    Billski
     
  20. Feb 18, 2019 #20

    rv6ejguy

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    I've flown at -15C and it roasts me out at that temp with the air valve fully open. My RV leaks a lot of air out through the corrugated baggage bay cover and the canopy skirt. In some of my other testing, the core can raise the exit air temp to 94% of the coolant temp at typical cruise airflows. I'd guess by the time the air gets to the vents, it's still at least 60C at 80C coolant temps. Burns your hand after 10 seconds.
     
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