Carb Ice on Corvair Conversions

Discussion in 'Corvair' started by ekimneirbo, Sep 14, 2015.

Help Support HomeBuiltAirplanes Forum by donating:

  1. Sep 14, 2015 #1

    ekimneirbo

    ekimneirbo

    ekimneirbo

    Banned

    Joined:
    Oct 31, 2014
    Messages:
    1,009
    Likes Received:
    324
    Location:
    Deep South
    On another thread we have been discussing "carb ice" on certified aero engines. I was wondering if any of the Corvair
    conversions have had carb ice problems?
     
  2. Sep 14, 2015 #2

    Bill Clapp

    Bill Clapp

    Bill Clapp

    Well-Known Member

    Joined:
    Feb 17, 2015
    Messages:
    297
    Likes Received:
    290
    Location:
    Valdosta Ga
    I have been using the Aerocarb from SOnex for many years and have never had an incident of carb ice in over 2000 hours. I dont use any carb heat source. On my installations we just have a K&N filter on the carb and use cowl air. Since there is no throttle plate or venturi in a slide carb the opportunity for ice to accumulate is very minimal or none. I know of instances of carb ice with MA carbs.
     
  3. Sep 14, 2015 #3

    Daleandee

    Daleandee

    Daleandee

    Well-Known Member

    Joined:
    Sep 11, 2015
    Messages:
    875
    Likes Received:
    552
    Location:
    SC
    My 3.0 Corvair has a Marvel Schebler carb. In nearly 100 hours of flying I cannot recall any instance of carb ice but I do have carb heat and I use it religiously. I bought the MS carb from a man that removed it from a running Cessna 150. It has been flawless in operation from the first start excepting the fact that I had to reset the idle.

    Dale Williams
    N319WF @ 6J2
    Myunn - "daughter of Cleanex"
    120 HP - 3.0 Corvair
    Tail Wheel - Center Stick
    Signature Finish 2200 Paint Job
    98.3 hours / Status - Flying
    KITPLANES Newsline
    https://www.youtube.com/channel/UC49h6Qijc17_Ebfz0CbRFtg/videos
     
  4. Sep 14, 2015 #4

    djschwartz

    djschwartz

    djschwartz

    Well-Known Member

    Joined:
    Jun 22, 2008
    Messages:
    982
    Likes Received:
    94
    Location:
    Portland, Oregon
    If your carb or throttle body is mounted directly to the cylinder head as with the original ones in the car you are unlikely to have any icing problems as the carbs are heated by contact with the heads. If you plumb the engine for a remote mounted carb then you should have carb heat available through an air box similar to what aircraft use.
     
  5. Sep 15, 2015 #5

    mcrae0104

    mcrae0104

    mcrae0104

    Armchair Mafia Conspirator HBA Supporter

    Joined:
    Oct 27, 2009
    Messages:
    2,961
    Likes Received:
    1,955
    Location:
    BDU, BJC
    There is nothing special about Corvairs that makes them more or less susceptible to carb ice than any other aero or auto engine as far as I'm aware.

    Carb Ice: Don't let it happen to you. www.FlyCorvair.com
     
  6. Sep 15, 2015 #6

    ekimneirbo

    ekimneirbo

    ekimneirbo

    Banned

    Joined:
    Oct 31, 2014
    Messages:
    1,009
    Likes Received:
    324
    Location:
    Deep South
    One reason I was wondering about possible carb icing is because of the long intake tubes on some conversions and the exposure to colder air rather than the warmth generated by touching or being near the engine. Depending on the carb used,there doesn't seem to be any warming there either.The slide type carbs may not be problematic but the distant location would not seem to be the best choice. I'm not saying there is a problem, only asking if there might be one.
     
  7. Sep 15, 2015 #7

    Bill Clapp

    Bill Clapp

    Bill Clapp

    Well-Known Member

    Joined:
    Feb 17, 2015
    Messages:
    297
    Likes Received:
    290
    Location:
    Valdosta Ga
    The lowest temp on a carb would be just past the venturi (lowest drop in pressure) however the farther out down the tube you go the warmer the air becomes as it pick up heat from the engine compartment (unless you fly in northern MN in wither :)) The main issue is if you have a venturi (most slide carbs dont) to produce the sudden temp drop, and if you have an object past the carb for ice to accumulate on - such as a throttle plate. I use to fly my plane with a TORNADO venturi past the carb and never had carb ice with the Aerocarb. The Tornado spun the air/fuel for better disippation. Seemed to work fine. Almost all carb manufacterers recommend carb heat (mostly for insurance reasons) - but I guess it would be better to have it and not need it than.....
     
    don january and dcstrng like this.
  8. Sep 15, 2015 #8

    ekimneirbo

    ekimneirbo

    ekimneirbo

    Banned

    Joined:
    Oct 31, 2014
    Messages:
    1,009
    Likes Received:
    324
    Location:
    Deep South
    My basic thinking is about how to best design an intake system that "won't" ice rather than one that can be deiced when needed. I read the attachment that mcrae0104 provided above on WWs experience with icing. There was a comment that the heat system he uses is to be applied before icing begins, not after there is some buildup. I would like to build a Corvair with fuel injection. There are several reasons I'm thinking about that. One reason is I don't like the idea of a single intake tube that dumps both fuel and air into a "log". The intake tube isn't conducive to equal amounts of fuel or air to all the cylinders. There are long runs, sharp turns and short intake runners. The shape and size of the components vary, changing the flow patterns. I would like to build an injection with individual runner tubes to each cylinder. The longer tubes with gentle curves would provide better velocity (hypothetically) at the lower rpms....and better cylinder filling. Injectors at each cylinder should provide better atomization of fuel with less tendency for fuel pooling. Computer monitoring should provide a more accurate fuel/air ratio and better mileage. Icing would be virtually eliminated, but I want to know how it can be positively eliminated. There would be a throttle body involved and it would have throttle plates. It may/may not have a venturi where the throttle plates reside. I guess that a slide type of throttle body could be employed that would remove any venturi shape from the intake. Usually, any air intake has a rounded shape at its entrance to smooth air flow. I'm wondering if that might cause some venturi action even if there is no actual venturi at the entrance to the intake.
     
  9. Sep 15, 2015 #9

    TFF

    TFF

    TFF

    Well-Known Member

    Joined:
    Apr 28, 2010
    Messages:
    11,532
    Likes Received:
    3,229
    Location:
    Memphis, TN
    FI cant ice up. Throttle plates have no venturi effect. If physical ice gets in there like in an IFR condition you have alternate air source. Mechanical Icing like IFR is going to be impossible for you as you have already proven how conservative you are; you are not building a plane for known icing. Venturi effect carb icing only happens at the venturi when the atmosphere has lots of moisture. Carb icing is just like how the AC in your car and house work. Pressure drop. it is also how they puff up your Fruit Loops. Apples and oranges when talking icing of carbs and FI.
     
  10. Sep 15, 2015 #10

    Dan Thomas

    Dan Thomas

    Dan Thomas

    Well-Known Member

    Joined:
    Sep 18, 2008
    Messages:
    4,830
    Likes Received:
    2,046
    The pressure drop causes a temperature drop. But the fuel vaporizing in the carb causes a much larger temperature drop, which is why FI doesn't have much of an icing problem. Lycoming's FI has a venturi at the throttle body inlet to generate reference pressures relative to air density and velocity for the fuel controller's function.

    Throttle plates DO have a venturi effect when they're closed or nearly so. The air is sucked around the edge of the plate at great velocity, and if you remember Bernoulli, that means a pressure drop, and if you remember the Gas Laws, it also means a temperature drop.
     
    don january likes this.
  11. Sep 15, 2015 #11

    Bill Clapp

    Bill Clapp

    Bill Clapp

    Well-Known Member

    Joined:
    Feb 17, 2015
    Messages:
    297
    Likes Received:
    290
    Location:
    Valdosta Ga
    Why do you do what you want to do? A basic question to ask before diving headlong into designing a new intake and FI system for a corvair. Are you trying to eliminate the need for carb Heat? (Ive proved that I can do that with a simple 450.00 slide carb) What advantages will you have for the complexity and money involved? Is the engine actually going to be more efficient? More powerful? (I fly at 150mph on less than 5gal/hr - not bad) What is your goal!
    My dad always asked, "before you buy your first car - ask why you need it. Then buy one that accomodates those needs" I have a bunch of FI stuff here for trying that down the road. But first I will have my new Corvair heads made up that have bolt on intake manifolds that will accomodate the FI ports and runners. .... lots of work. Not enough reward at this time...I do have an IO-320 sitting here I can bolt on.....

    Just a thought.
     
    don january likes this.
  12. Sep 16, 2015 #12

    TFF

    TFF

    TFF

    Well-Known Member

    Joined:
    Apr 28, 2010
    Messages:
    11,532
    Likes Received:
    3,229
    Location:
    Memphis, TN
    Much smaller venturi effect on the RSA and it is dry; very low pressure drop. It is there to change the air pressure to measure it. It is also on the walls, being open, no restriction. Throttle plate very small amounts of vacuum at small angles. The carburetor only works if it has high vacuum at the venturi. High pressure drop to pull the fuel out of the bowl. If the impact tube iced up on a RSA the engine would go rich; if both impact and vacuum iced up it would probably not change mixture at all.
     
    don january likes this.
  13. Sep 16, 2015 #13

    Dan Thomas

    Dan Thomas

    Dan Thomas

    Well-Known Member

    Joined:
    Sep 18, 2008
    Messages:
    4,830
    Likes Received:
    2,046
    The airflow around the edge of the throttle plate is not at the same pressure as measured by the manifold pressure gauge. It's lower. At idle we see about 10"Hg MP. The air squeezing past the throttle plate will be much lower than that because of its velocity. As it gets past the plate it slows and the pressure rises to what we see on the MP gauge.

    It's only because no fuel is involved at that plate that ice doesn't make problems, and because any ice there is quickly removed when the throttle is opened and the pressures and temperatures rise, especially if the air isn't totally saturated.
     
  14. Sep 17, 2015 #14

    don january

    don january

    don january

    Well-Known Member

    Joined:
    Feb 11, 2015
    Messages:
    2,628
    Likes Received:
    1,042
    Location:
    Midwest
    Here is something new,I have a corvair conversion on my kr2 and I took a carb off an 1942 or maybe a bit older W45 farmall tractor and mounted it to the intake's and run a heat box and guess what, never any problem's, High low fast or slow. I have read that Harly Davison bike carb's will work, I think I'll stick with my carb heat and save up for the next best thing to come. I dont fly much in the North Dakota winter with my KR but plan on doing more this winter. My carb is mounted under the engine with a 2 into 1, joy's of homebuilt, switch and learn, dont crash and burn. Don wicks kr2.jpg
     
    dcstrng likes this.

Share This Page

arrow_white