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Thread: Carb Air Temp Gauges

  1. #1
    scubber's Avatar
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    Carb Air Temp Gauges

    Looking for experience with Carb Air Temp Gauges. Have a 0290D-2 in the cub. This particular engine sure seems to make ice. So far carb heat has kept it going, but would like to minimize the surprises. This engine doesn't give the normal slow drop in rpms, but just suddenly coughs and then the drop. Have even had it cough on climb out turning over 2,500 rpms. After the cough dropped from 2,525 to 2,200. Below wasn't pretty at the time. . .big eyes. Most times I'm able to detect a slight vibration in the rudder pedals, and then I keep pulling heat. So . .looking for experience with the gauges. And ice sensor v.s temp gauge. Big difference in price. Thanks. Larry C.

  2. #2
    skywagon8a's Avatar
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    Never used a carb temp gauge much at all. Whatever you settle upon remember that ice formation can happen from several degrees below 32 F to above 70 F. The amount of humidity in the air is a key factor. You need to understand the signals the engine is sending you. A manifold pressure gauge can be a help as well as the tachometer.
    N1PA

  3. #3

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    You might review a similar recent thread https://www.supercub.org/forum/showt...he-best-method The only reason to have a carb temp gauge is for metering partial carb heat in flight. I prefer carb heat to be on or off, I don't use partial, but my planes haven't been ice makers. You might consider an optical ice indicator. It detects the presence of ice. Then you can manage your carb heat to suit.

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    ... just a reminder ...Click image for larger version. 

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    scubber's Avatar
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    Thanks to all for your input and fast response. It is good to have reinforcements of some of the things I have been pondering about the issue. Seems as far as the "temp unit", the gauge would not be significant/use full . . unless temp & dew point is the 3-5 point spread. Much appreciated. Larry

  6. #6
    PerryB's Avatar
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    A good digital EGT is another good indicator. If it drops more than about 20° for no obvious reason, you're probably starting to develop ice.
    After Monday and Tuesday, even the calendar says WTF !
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    BC12D-4-85's Avatar
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    Decreasing manifold pressure and EGT's can indicate ice formation leading to throttle restriction.....providing the aircraft's pressure altitude, power settings, and ambient air parameters remain relatively constant. Climb, descend, change power settings, fly into a warmer or colder air mass for example changes things. I recall the carb temp gauge in the Beaver. It's yellow arc was to be avoided via carb heat. Never had another to observe just a manifold gauge in every carb'd plane since.

    Gary
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    mvivion's Avatar
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    As noted in the thread that Stewart referenced, I'm not a big fan of carb temperature gauges in general. I've used them in the Beaver, as noted by Gary, in fact, in that airplane in coastal areas (Kodiak), I ran constant partial carb heat to keep the temperature out of the icing range.

    That said, I had a carb temp gauge on an O-360, which ALWAYS shows in the caution range.....carb heat just wouldn't get it out of the "caution"range.....ie: useless.

    I flew a couple Cubs in Kodiak. Carb Ice Central. I simply applied full carb heat on a regular basis throughout the flight.

    Pay attention to what your engine is telling you, and develop a practice to prevent ice.

    MTV

    MTV
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  9. #9

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    Anyone use one of these? It makes more sense than carb temp.

    https://www.aircraftspruce.com/catal...icedetect2.php

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    PerryB's Avatar
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    One thing I haven't seen mentioned, with regard to carb heat, is leaning. Whenever I have to use heat, I lean to restore my EGT to around 1360, which is where mine typically cruises at sea level on an "average" day. This restores virtually all of the power loss (except that attributed to the lower density of the hot air), and keeps the plugs clean. I also use carb heat and leaning (to peak) during warmup. It puts a warm but correct mixture through the sump, speeding up oil temp. I warm up around 1200-1300 RPM for good oil sling.
    After Monday and Tuesday, even the calendar says WTF !
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    BC12D-4-85's Avatar
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    Here's another thought......how about keeping cold air from contacting the carb to begin with? Look at the cowling and note any potential route for cold ram air around the starter nose, oil cooler inlet, and carb heat box, etc. Cold air flowing and hitting the carb body (Lycoming or Continental) can't be of much help if carb body cooling from fuel vaporization is already an icing threat. However, how about ducting heated air to the carb venturi area externally? It might be a good try. Isn't that why Lycs with a heated oil sump-carb connection may have lower incidences of carb ice?

    Gary
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  12. #12
    PerryB's Avatar
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    Quote Originally Posted by BC12D-4-85 View Post
    Isn't that why Lycs with a heated oil sump-carb connection may have lower incidences of carb ice?

    Gary
    That has to be a significant factor. With regard to the first part of your post, keeping the lower cowl sealed against external air entry must help. I went on a campaign a couple years ago to seal mine like a frogs bottom. I used wide weatherstripping foam across the top sheet that the rear baffle felt compresses into, same around the oil cooler, and Gorilla taped the inside of the opening around the air filter housing. The only air in my lower cowl either comes through the cylinders or the oil cooler. It's probably about the coolest running O320 you'll ever encounter and I almost can't remember the last time I had an indication of ice development. I never connected the dots until reading your post, but there has to be something to it. For your heated blast tube idea, how about a piece of 2" SCAT attached to the dump hole on the bottom of the airbox. Loop it around to blow on the carb body and secure it to something with an adel clamp. You'd probably have a nearly ice-proof setup (assuming a Lyc with a tight cowl) and if not you still have carb heat as always.
    After Monday and Tuesday, even the calendar says WTF !
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    BC12D-4-85's Avatar
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    Now sometimes comes the inevitable discussion about raising the carb temp, typically via heated internal air but can be external as discussed, we can create the evil carb ice. That depends on the humidity and moisture content of the air mass inducted. The more the relative humidity at a given temp the greater the potential for ice precipitation on cool surfaces. No mystery. And usually no way to know easily when aviating.

    Cold air may have a high relative humidity, but when heated above freezing the relativity drops versus standard air at that temp. It dried out while cooling via fog/frost/freezing drizzle/snow or simply replacement with dryer air. I'd opt for Lyc's heated sump-carb interface plus whatever heat and block any additional cooling per PerryB's observations.

    Let's experiment.

    Gary
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  14. #14

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    YOU GUYS ARE KILLING ME!! I am just trying to drink some whine and view some posts and not ya got me drunk thinking!!! If ya warm the carb, is it like carb heat and air expands so now we loose power due to less O2??? Heating a carb is simple, front oil cooler with ducted scat tube to carb BAM!! Now you have a hot carb. If a hot carb was good someone would have done it. Now I understand how a carb works so we are back to post carb temp. Heated sump is good. How about all exhaust heat ducted over intake tubes in a continental? One of the members insulated #2 intake from cold and improved performance. I just want a simple downwind turn post!!!
    DENNY
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  15. #15
    BC12D-4-85's Avatar
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    Ask yourself how many planes partially depart - fly - land and end up without sufficient power for that flight ? I suggest some are carb ice evolved.

    Gary
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  16. #16

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    I agree !!! With the 0320 cub I do the usual taxi run up mags/carb heat check. Once I turn Crosswind I pull carb heat, so I only have a 90 degree turn if engine quits. I try to remember to pull carb heat before I reduce power. I use carb heat on downwind. Trying to leave it on until final but have old habits!! However, what range is COLD AIR HIGH RELATIVE HUMIDITY?? I might have tried to crash my cub with my wife in the back seat from this issue!! I was just trying to point out that heating a carb might not be a good thing. Still have whine so disregard if needed.
    DENNY
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  17. #17
    skywagon8a's Avatar
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    Quote Originally Posted by BC12D-4-85 View Post
    ..Isn't that why Lycs with a heated oil sump-carb connection may have lower incidences of carb ice?

    Gary
    Quote Originally Posted by PerryB View Post
    For your heated blast tube idea, how about a piece of 2" SCAT attached to the dump hole on the bottom of the airbox. Loop it around to blow on the carb body and secure it to something with an adel clamp. You'd probably have a nearly ice-proof setup (assuming a Lyc with a tight cowl) and if not you still have carb heat as always.
    You have accurately defined why Lycomings are less susceptible to carb ice than Continentals. Recall the VW Beetles with their 4 cylinder air cooled engine which had it's carb mounted above and separate from the engine. On certain days when the engine started running rough, when you opened the "trunk" you could see a carburetor completely covered with ice. The carb didn't have the advantage of engine heat to warm it's body. It made ice both inside and outside.
    Quote Originally Posted by DENNY View Post
    I try to remember to pull carb heat before I reduce power. I use carb heat on downwind. Trying to leave it on until final but have old habits!!
    DENNY
    In addition, pull the heat before you lower the nose, increasing your speed on the downwind if you have just taken off and remaining in the pattern. The higher speed will dilute the warm air reducing it's effectiveness.
    N1PA

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    I know it's not that relevant to discussion of an O-290 powered Super cub, but in my R44 helicopter flying we relied pretty heavily on a carb temp gauge and flew around almost all the time with at least partial carb heat on the Lycoming O-540. We alwsays used carb heat after engine start to warm the induction system, as directed by the Robinson RFM. At about 10F, the carb heat was no longer sufficient to keep the carb temp out of the yellow arc on the gauge, so we turned carb heat off. Robinson says that carb icing is unlikely in ambient temperatures under 25F.

    I use the same type of philosophy in the O-470 powered 182 (it also has a carb temp gauge that works pretty well). Sometimes, when it gets below 10F or so, you need carb heat to keep the magneto checks within tolerance during runup. Almost all the Alaska C-180/182 powerplant failures I reviewed in the NTSB database seemed to be carb ice related. I will use continuous carb heat to keep the temp out of the yellow arc on the gauge, until it gets so cold that carb heat won't do that anymore....I would like my next airplane to be fuel injected.
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  19. #19

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    Cold air induction is very popular with the injected Lycoming crowd. To increase power. Another advantage of FI.

    I paid to convert my 470 to 520. No way am I going to use partial carb heat and give back any of the power unnecessarily, and lucky me, my 180 doesn't make ice. It might (and has) on a low power descent on a high humidity day, but that's predictable for any carb'd engine. I know of other similar 180s that do make ice. The same is true among Cubs. Some make ice, some don't. I find it fascinating that after all these years the FAA hasn't tried to understand why similar airplanes make ice differently.

  20. #20
    hotrod180's Avatar
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    Quote Originally Posted by BC12D-4-85 View Post
    ..... Isn't that why Lycs with a heated oil sump-carb connection may have lower incidences of carb ice?
    I don't buy thius.
    The Continental C145/O300 has the carb bolted to the sump, just like the Lyc 320,
    and they are very prone to carb ice in some airplanes.
    Cessna Skywagon-- accept no substitute!

  21. #21
    BC12D-4-85's Avatar
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    Quote Originally Posted by hotrod180 View Post
    I don't buy thius.
    The Continental C145/O300 has the carb bolted to the sump, just like the Lyc 320,
    and they are very prone to carb ice in some airplanes.
    Good point there. I've never sat behind or looked at one uncowled so have no idea. There's a comment at the end of this article on icing that may pertain: https://www.boldmethod.com/learn-to-...happen-to-you/

    Also....does the carb on an O-300 run as warm as one on an O-320? Same for the oil sump metal to carb metal contact point? The commenter in the article above claims it's the physical design, but maybe a carb temp gauge would show differences between the Conti and Lyc setup. Don't know tho.

    Gary

  22. #22
    BC12D-4-85's Avatar
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    Then there's this FAA test classic from 1983 - http://www.tc.faa.gov/its/worldpac/techrpt/ct82110.pdf - They took an O-200A and ran it in a test cell with varying conditions of fuel and air while monitoring carb and engine temps plus ice formation. Auto fuel made ice at twice the rate of 100LL in this situation. It's a lengthy report but worth reading if carb icing is of interest. I read it years ago but forgot the details.

    Gary

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