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N82HB
01-01-2011, 06:48 PM
My airplane does not have carb heat. It has been that way for 350 hours, but that doesn't make it right. Should it have it? I would love some opinions...
Kelly

Dorsal
01-02-2011, 06:03 AM
I asked the same question while I was building and my research suggested carb heat was not necessary if your intake is drawing from inside the cowl. This is, of course, only what I found and chose to do and at 70 hours I have significantly less time on my plane than you do. I sometimes contemplate moving my air intake to the scoop (possibly a skosh more HP) in which case I would implement CH.

Av8r3400
01-02-2011, 09:17 AM
I took off the ducted carb heat system from my yellow plane. In doing so, I gained 200 static rpm from the loss of restrictions.

The anecdotal information that I have heard, and believe, is that the only planes which have ice issues are the ones with the ducted carb heat setup on them. This is due to the intake just behind the prop taking in the colder air. With the intakes by the firewall the air is preheated by the ambient temp inside the cowling lessening the likelihood of ice.

I have no scientific evidence to support this, but it does make logical sense.

The liquid heating type of carb ice prevention (http://www.ultralightnews.ca/bing/carbheater.html) does seem to be interesting, though.

Dorsal
01-02-2011, 09:47 AM
I took off the ducted carb heat system
Good to know, I can leave mine the way it is without the feeling there might be an extra fraction of a HP left on the table.

kitfox2009
01-02-2011, 03:36 PM
G`day Kelly
For Canadian homebuilts it is mandatory according to Transport Canada to have some approved form of carb heat regardless of where the carbs are located. In order to meet this requirement (and also for my own piece of mind) I installed the small hot water manifolds that mount between the intake and the carbs. I have no operating experience prior to installation so are not able to comment on power loss,etc. They are always "on" therefore I just do not worry about icing.These units are available from Bob at Light Engine Service (780-418-4164) or possibly directly from Sky-Drive in UK.Supposedly the carb throat body maintains enough heat to prevent ice build up without preheating the intake air resulting in a noticeable power loss.

Have fun

Don

KF5 Vixen C-FOXK
912UL

DesertFox4
01-02-2011, 05:13 PM
Kitfox2009- Good point. Required North of the border. I'd also go with the hot water manifold type if I felt the need. No issues with carb. ice yet with the intakes by the firewall. I do spend most my time in the desert so moisture usually isn't a problem. Unusual for dew points and temps to get within 10 degrees of each other.
I'll deffer to the guys that fly in moister climates for their experiences in this matter.

N82HB
01-02-2011, 06:11 PM
I just helped a friend bring a 912 powered Kitfox back from Iowa. It has the carb heat on it, but my first thoughts were the remove it. Weight, simplicity, and all those words kept creeping up on me.

I know mine works fine, but I wanted some more input.
Thanks so much,
Kelly

jtpitkin06
01-02-2011, 09:38 PM
I would like to offer up the following sobering facts on carburetor ice. The NTSB files are full of accidents caused by carburetor icing. Many of the reports have statements from the pilot such as:

I thought (brand name) engines don’t get carb ice.
I didn’t use carb heat because it’s a warm day.
It can’t be carb ice because it isn’t (raining, snowing, sleeting, freezing)
And my favorite...

I flew for hundreds of hours without it and never had a problem.





It's a safety feature. Use it.


OK... I'm climbing down off my soap box, now.


John Pitkin
Greenville, Texas

Andrew G
01-03-2011, 05:36 AM
You'd think fuel injection would have been advanced by Rotax years ago... as a standard feature. Why don't they?

Av8r3400
01-03-2011, 06:02 AM
One word answer: Liability.

Every time BRP approaches a manufacturer about fuel injection they all run away from "aircraft" usage due to liability. (This is per one of the people who is in the know at a Rotax service center.)

Dorsal
01-03-2011, 06:25 AM
While I support John's usually sage advice I would still like to know if anyone has ever experienced carb ice on a Rotax 9xx with the intake inside the cowl?

wannafly
01-03-2011, 09:34 AM
912s on my fox IV. no carb heat...no icing so far, knock on wood:D. 84 hours on it with the air intake against the firewall

sdemeyer
01-03-2011, 10:23 AM
Up here in the Pacific North Wet, rain and moisture are common every day experiences. It's relatively common to have temp/dew points within 3deg. I have flown in all types of conditions and have never had carb ice on my 912UL, that I know of. My neighbor on the other hand, gets carb ice frequently on his 172.

Tom Waid
01-03-2011, 02:50 PM
My neighbor on the other hand, gets carb ice frequently on his 172.

If your neighbor has an early 172 with an O-300 I feel his pain. The O-300 on my 172 is a great engine but it'll pick up carburetor ice on a Summer's day here in Florida.

jtpitkin06
01-03-2011, 09:56 PM
I think that’s a valid point that some engines and installations are more prone to ice than others. For example: The Continental O-200 and O-300 have a carb hung from free standing intake manifold with long runners. They have no effective ambient or conductive heating and they ice up like an igloo. The Lycoming O-235 and O-360 have the carb and manifold mounted on the bottom of the oil pan where it gets conductive heating and it is much less likely to get ice.

With that in mind, there is definitely something about the Rotax with the intakes inside the cowling. It gets some ambient heat and it appears less likely to ice up. Perhaps some of the resistance to icing is also due to higher RPM and higher manifold pressures on approach than a non-geared engine.

Another factor may be that the Kitfox pilot rarely uses long power off descents. The high drag airframe requires the pilot to “cruise” almost all the way to the airport. That’s quite different from some cleaner aircraft that can descend for ten minutes or more with the throttle closed.

Certainly, we can look to certified aircraft for guidance on good practices. FAR 23.1093 requires an intake air heating system. The regulation states it must provide a temperature rise of 90°F at 75% power. I have doubts the ambient temperature rise in a Kitfox cowling is enough to meet this requirement.

One problem I see is most pilots do not know when they have ice on approach. The power is reduced and the pilot typically makes sequential reductions in power, not increases, as one makes an arrival. Unless the pilot needs a large power increase, icing goes unnoticed. Once on the ground the power demands are small and the ice typically dissipates as the throttle is opened for taxi. The net result is, the pilot never realizes there is carb icing until a go around is necessary and full power is suddenly not available.

In any case, if you have carb heat on your aircraft now, I certainly wouldn’t take it off just to save 2 pounds. It’s cheap insurance and low maintenance.

As for injection, it’s not always immune to icing. Ellison states carb heat is mandatory with their injectors. I am installing an AeroInjector on my engine and it will also have pilot selectable “carb” heat.

Check gear down.
John Pitkin
Greenville, TX

49LOOPER
01-04-2011, 11:42 AM
I've got a Kitfox 4 with the Rotec R2800 Installed, but it uses the Bing 94 for a carb. When I was searching for a carb heat solution, I discovered the Jabiru engines use an easily installed, electrically heated system attached to the Bing carb throat forward of the slide. It has two possible setting. One can be used constantly to preclude carb ice with little to no performance decrease, and a increased setting for known icing conditions. I purchased it from the Jabiru dealer in Shelbyville, TN, but have not used it in flight yet (shortly I hope). It is easily installed, light, takes up hardly any space and really heats up quickly. I turned it on and touched it, and it works! Downside is it was $200.00. Kind of expensive if you've got two carbs. Dave Dean (49LOOPER)

Ken Birchard
01-05-2011, 02:39 PM
I put the Bing 64/32 electrodes that screw into the vacuum port on the carbs in my 912uls. Easy to install, hook to a switch on the panel and shouldn't affect HP. Look like they should work. Haven't tied them out yet...Ken:)

Bryan
01-05-2011, 07:36 PM
I will chime in here. I am not going to say which is the best but I will tell you that I visited with Lockwood Aviation at Oshkosh this past year about my 912engine quiting on me shortly after takeoff on my third touch and go. I was wondering about the possibility of carb ice and after talking with them they felt real strong about the 912's not needing carb heat. They told me that the only instance of a 912 icing that they were aware of was on their Aircam, and it was in perfect icing conditions. They told me that with a cowled engine and the carbs located directly above the exhaust, and heat rises, that there was no need to have the carb heat. We came to the conclusion that my problem was vapor lock. Just wanted to let you know what I was told. :cool:

jtpitkin06
01-05-2011, 11:23 PM
I'd like to hear from someone that has a carb temp gauge on their 912 engine.

JP

Monocock
01-06-2011, 06:21 AM
I looked into carb heat with my Mk 5 and 912s (smooth cowl) and was basically told that the heaters would make no difference whatsoever to the carb temp on the basis that they already operate in a hot and closely cowled environment. I stand to be corrected, but I took this advice as sound.

As I understand it, an engine that is mounted in an exposed location (ie back of a pusher ultralight type) is more at risk of carb icing.

Interesting topic though.

ALAN
01-06-2011, 11:41 AM
I have 750 hr on my Fox 912S and never had carb heat. I fly all winter in upstate NY and never had a prob. If you have it use it !!

HighWing
01-06-2011, 10:18 PM
John,

A suggestion for a homework assignment. When you are not busy flying or building, check the accident database for Kitfox accidents flying behind Rotax 912 series airplanes and see if you can come up with any carb ice issues in carb heat free airplanes. I have been monitering several Kitfox list/forums for over 15 years and the only occasion I remember is the Alaska group in the mid 90s that reported burps in their engines while cruising that they postulated was ingested ice, and that it was ice was just a guess. None of them had a carb heat system. The comments on this thread that the only reported instances of carb ice in a Kitfox with a 912 has been in airplanes with the carb heat induction system with forward air intake is spot on.

Then again if you really are a belt and suspenders guy, go for it, but you will be a member of a tiny minority of Kitfox owners.

jtpitkin06
01-09-2011, 10:26 PM
John,

A suggestion for a homework assignment. When you are not busy flying or building, check the accident database for Kitfox accidents flying behind Rotax 912 series airplanes and see if you can come up with any carb ice issues in carb heat free airplanes......

Thanks for the homework assignment.
I’d love to provide you with an accurate report of the number of carb icing incidents in Kitfoxes with Rotax 912 engines. But here’s the problem... When someone does have an icing problem and the engine quits, chances are they don’t get on the phone and call the FAA to report they had icing. If they landed on the airport dead stick (as is usually the case) they restart the engine and press on. Sometimes they check out the fuel system thinking it was contamination, alcohol from mogas, bad plugs, lead in the gas, or a dozen other suspected problems. But most refuse to believe it was ice. Even if ice is suspected, the pilot is not about to report it.That makes it hard to get accurate figures.


Am I a belt and suspenders kind of guy? I suppose so. Having carb heat is a pretty simple decision for me.


The FAA requires it on all carbureted engines for certified aircraft.
Canada requires it on all carbureted engines, certified or experimental


Now, Just because you or several others have flown without detecting carb ice doesn’t make me all warm and fuzzy. If I told you I’ve flown over 18,000 hours without an ignition failure, would you be willing to remove one of your ignition systems? Probably not.


There is a Canadian company that makes heaters for the Rotax 912 with Bing carburetors.It is noteworthy that this web page:
http://www.lightsportaircraft.ca/912rotax-parts/carb_heat.html
has a picture of an unheated carburetor installed on a Rotax 912 engine with ice forming in the throat. I’ll take that as pretty solid evidence that 912s can get ice under certain conditions. [It is not stated if this picture was from an engine with intakes inside the cowling] I do admit, however, it appears that a 912 with the Bing carburetors installed in a Kitfox with intakes under the cowing is resistant to icing. The point is, resistant does not mean it is immune.


For me, having carb heat is safer than not having it available. If I’m in the minority, I’m happy with that.


Now, I was just looking at some pictures of the factory built Kitfox SLSA. Is that a carb heat knob next to the throttle?
JP

Dorsal
01-10-2011, 06:19 AM
John,
Yes, I believe the LSA rules require Carbheat. Your reasoning seems solid to me, if I had it I would keep it however I am not terribly concerned flying without it. I think your ignition analogy is a good one, I have never had one fail and certainly would not take one out. Maybe someday I will put in one of those electric carb warmers.

RIVERFOX
04-14-2011, 08:00 PM
JP, give us a little more info on your switch to the AREOINJECTOR and what is needed for the conversion.

Dorsal
04-15-2011, 08:01 AM
I believe JP is talking about his Corvair conversion engine not a Rotax.

jtpitkin06
04-20-2011, 05:13 AM
Yes, I’m installing a Corvair engine and using a Aeroinjector for fuel delivery. This is not a Rotax conversion. Carburetor conversions can be difficult. I don’t recommend carburetor swaps unless you have a really big problem with getting your fuel mixture correct. To my knowledge, most Rotax engines run just fine with the Bing carbs. I mentioned the Aeroinjector as it is less prone to icing than almost any carburetor, and even so, I will install a heat source.

Yesterday morning I was reading the NTSB accident reports and there was another carb ice dual fatality accident. The student and instructor were doing simulated emergency landings. Interviews with other students reported the instructor never used carb heat during emergency landing practice because the RPM was “in the green”. The engine was a Lycoming O-235. I mention this report because I hear far too often that Lycoming engines don’t need carb heat even though the operating manual says to use it.

Certainly, if you have heat on an engine, use it. It’s free. If you don’t have heat on your engine, you may wish to do the following test:


Take you aircraft up about 2000 feet over the airport on a cool humid day and pull the throttle to idle. Spiral down for a power off landing. When you get on short final add power to go around. If you get full power, then your engine installation is ice resistant, but not ice proof. If you don’t get full power, then you probably need to install carb heat.


If you elect to do this test, please be prepared for a total power loss.


Be safe... JP

Av8r3400
04-20-2011, 06:48 AM
I have done just that on several occasions, JP. From as high as 5000 agl, power off decent to an aborted landing. I did this after the needle adjustments, to test it's placement. I have never experienced a "total power loss" in any of these tests. Ever.

Does anyone here know the physics of how a constant velocity carburetor works? Why it is less prone to icing? Why there aren't iced up motorcycles laying on the side of the road all the time?

Every one seems to love to bash the Rotax 9xx engines. (It's almost an Olympic sport around here.) Yet, they are still the best performing and maybe the safest engine to install in this design aircraft. C'mon guys.


If you doubt me. please find an example (NTSB report) of a KITFOX, with a 912 properly installed, that crashed due to carburetor icing. As has been said, nothing is ICE PROOF. However this setup is very ice resistant.

Dorsal
04-20-2011, 12:08 PM
I can't say if anyone is missing a point or not though I do expect that most on this board are familiar with the fundamentals of carb ice (never hurts to review it :)). I believe the question at hand is; does the specific installation of a Rotax in a Kitfox drawing air from behind the engine and inside the cowl provide enough pre-heat as to prevent our Bing carbs from icing. That would be difficult to answer definitively so the questions becomes has anyone with this setup experienced carb ice. Mostly what I read here are the experiences of others and the choices they have made which I value highly. In the end, of course, my choices are mine alone and I try not to assume anything :D

jtpitkin06
04-20-2011, 12:52 PM
I don’t think we are bashing Rotax engines on this thread, at all. This is experimental aviation and discussions on anything affecting safety is probably a good thing. I’m very happy to hear av8r3400’s installation provides an adequate level of protection for icing. As previously discussed, the combination of the intake inside the cowling and the Bing carburetors appears to be quite resistant to icing. That’s good.

The Rotax 912 has enjoyed a pretty good record of dependability. Even the two strokes have done quite well installed in the Kitfox over the years.

Because I am installing a Corvair engine, I’m in unknown territory. I must use extra caution as the engine and airframe combination is extremely limited. So if I tout installing carb heat, it is a rally for anyone installing anything other than the Rotax 912 in the factory configuration. Doing the power off descent test should be part of anyone’s initial flight testing.

I did take the suggestion of av8r3400 to look at crash reports. While looking through the NTSB files I did find one report of a Kitfox with a Rotax 582 that crashed due to carburetor ice. But none with a 912.

http://dms.ntsb.gov/aviation/AccidentReports/o0robt455jfawr3patqw2jjq/I04202011120000.pdf (http://dms.ntsb.gov/aviation/AccidentReports/o0robt455jfawr3patqw2jjq/I04202011120000.pdf)

(http://dms.ntsb.gov/aviation/AccidentReports/o0robt455jfawr3patqw2jjq/I04202011120000.pdf)
In addition, there are several reports of partial engine power loss due to unknown reasons in the 2 strokes, the 912’s and engines other than the Rotax. Many of them would indicate carb ice, but it can’t be proved.


What I did find alarming was the number of fuel system problems. From contamination to improper plumbing; one thing kept popping up… Fuel starvation due to plugging of the filters seems to be the number one cause of power loss in the Kitfox.



Please folks, check those fuel filters and increase the inspection frequency no matter what engine you have installed. Also inspect the tank screens for blockage.


There’s a lot of information to be gained by plowing through the NTSB files. The search function makes it pretty easy to look for just Kitfox or Rotax. I recommend it for anyone looking to improve their aircraft.



It’s unfortunate that others had to crash for us to get the information.


Enjoy the build and fly safe.


John Pitkin
Greenville, TX

chefwarthog
04-20-2011, 04:23 PM
Well I don't get it, we are in 2011 and Rotax it is still useing 1930's technology. The first warplane engine were build with carduretors fuel distibution in the first worldwar. My quad use injection, my pick-up, the cars, the skidoo and they don't ice up or stop working for nothing, the only thing that remain carb feeded it is my lawn mower, ah a get it, it got a kind of propeller underneath!

Carbs have to be sychronize, clean up, set up in the right way and it work well, but it is still 1930's technology, and Rotax sell that ''hot tech'' for a reasonable 24 000.00$. I think the engine monopoly on aviation from Rotax served them well but not us.

Apologize for that thread, but I stell don't get it.

Eric

brjohnso
11-19-2018, 03:18 PM
I don't know why anyone would remove a carb heat system. Carb ice happens. It happens on Kitfoxes, I happens with the 912, and it has killed people in Kitfoxes before. https://aviation-safety.net/wikibase/wiki.php?id=138373

Rotax also has a fuel circulation feature to prevent vapor lock, but for some reason, not everybody connects that up either.

brjohnso
11-19-2018, 03:27 PM
There is nothing special about the 912 or the Kitfox when it comes to carb ice. It is as vulnerable as anything else. Ice is uncommon but not rare, and it's also unpredictable. It can form as fast as a minute or two. https://aviation-safety.net/wikibase/wiki.php?id=138373

I had it happen to me once in a Cessna. It took less than a minute to form and my engine stalled during my takeoff roll.

jiott
11-19-2018, 07:55 PM
Sorry to totally disagree, but the Rotax Bing carb is different than other aircraft carbs in that it is a constant depression altitude compensating carb whose throat design is NOT as susceptible to icing. I will not try to describe the design reasons this is true because its been quite a while since I read up on it. Go do a search yourself and read about it. Also the position the carbs are mounted in the Kitfox tight cowl gives it an icing advantage compared to many other aircraft.

Mind you I am certainly not saying that the 912 in a Kitfox will never ice up, but I am disagreeing withe your blanket statement that "there is nothing special about the 912 or Kitfox when it comes to carb ice". There are probably thousands of us who have been flying 912 Kitfoxes without carb heat for hundreds of hours without a single icing incident.

jrevens
11-19-2018, 08:48 PM
... https://aviation-safety.net/wikibase/wiki.php?id=138373
...


Hi Bruce,
It seems as though you are presenting this link/accident as a sure example of Rotax carb ice, on this and another thread. While I suppose it's possible, to my knowledge that has never been proven one way or the other. If I'm wrong about that, someone please correct me. I was there at that Kitfox fly-in, along with others on this forum. I remember the airplane having some kind of problem during it's initial takeoff from Homedale, and returning to the field. The wonderful couple from California had that airplane really loaded-up, and I remember them taking things out and removing the seats, I assume to possibly check something on the fuel system. I don't know if anything was found or not. They put things back together and took off (uneventfully as far as I could see) to get fuel at Caldwell before heading home. So if this accident report is accurate they had a problem of some kind again during the first takeoff attempt from there, aborted, and then attempted yet another takeoff that ended in tragedy. It seems like it's very possible that the problem(s) was something other than carb ice - maybe a fuel pump, or who knows what. There are others here who surely have a lot more knowledge about this accident than I do, but unless you know something I don't, I think it's wrong to present this as a certain carb ice accident. There were a lot of Kitfoxes of all models and engine types there, even a Rotec radial, and as far as I know no one else was experiencing carb ice - I might be wrong. I certainly noticed none with my O-320 powered T-18 that day, and I have had carb ice with that engine before.

HighWing
11-19-2018, 09:56 PM
I posted a response on the old 2011 comment series on this thread. My feelings are exactly the same as they were then. I started my first Model IV in 1993. A year or two later a couple of guys were at the factory fly-in with info on the first Kitfox ever forum. It was of the email variety and I read every one - unlike today where things are topic related with some topics of little interest to me. In the early discussions, the consensus was just as it is today and the carb-heat box that came with my kit was never installed. A neighbor who was on the Alaska trip mentioned in my previous comment in this thread was the one who had the burps during a flight segment and with nearly 2500 hours has no carb-heat box on his Model IV to this day. He mentioned the experience in a hangar flying session last week. I don't remember everything, but in the 23 or 4 years I have been actively participating in the lists or forums, there have never been any comments from owner pilots about incidents that have suggested carb-icing issues in our airplanes that has even tempted me to rethink my original decision.

atosrider
11-20-2018, 10:53 PM
there were two occasions when I thought the engine was running rough because of carb ice, out of 600 hrs with a 912ULS in a Rans S6, with the water heated carb sockets .... both times it was flying into a wetter air mass, that forced a descent ... suddenly I wished I could divert more hot water into that system ... but in the model III with round cowl, there might not be room against the firewall ....
I find all this talk of pre-heated air under the cowling rather hard to believe, sure we are getting some engine cooling, but the air flow has to be very variable with changes in airspeed, angle of attack, and power setting ...
my project came with the 1992 air box, so I read with interest that it might cause as many problems as it is supposed to prevent ..
the norm for aircraft is having a carb heat system, and I dare say the norm for pilots is not knowing they had carb icing ...

Ronin
11-21-2018, 03:37 PM
This was my replies in a different thread;


I have experienced carb ice in two different 912s powered planes, A Europa XS and a Rans S-6.

This was the kit I had mounted in the Europa I flew

http://skydrive.co.uk/proddetail.asp?prod=CH-912-3

Left it on at all times and it didn't hurt performance in a measurable way.

Esser
11-21-2018, 04:56 PM
My buddy in his Model IV had suspected carb ice less than 4 weeks ago. I don't know why everyone is so averse to cross of a potential safety issue off a list.

jiott
11-21-2018, 10:41 PM
Those of us without carb heat and speaking for myself are certainly not averse to it at all. We are only disagreeing with the comments that imply we are idiots and that there is no difference between a 912 Kitfox and other Lyc/Cont aircraft that all require carb heat. Even though many of us have never found the need for it, I would be the last person to discourage someone from installing it if they feel a need for it. After all, it has no down side other than a little cost and complexity.

If I lived in Canada, especially the northern parts, I think I would install it. Correct me if I am wrong, but I believe it is required by the equivalent to the FAA to be on all aircraft in Canada and most European countries.

jrevens
11-21-2018, 11:01 PM
I had an issue with the statement earlier in this thread stating that carb ice - "...has killed people in Kitfoxes before. https://aviation-safety.net/wikibase/wiki.php?id=138373" Jumping to conclusions and using that link to imply something that is certainly not stated in that accident report didn't seem right. I'm not at all adverse to anyone using carb heat either... of course not. You're right Jim... it is required in Canada. I would not dare to question the necessity of a regulation imposed by bureaucrats, requiring compliance in all circumstances. No potential variance allowed. ;)



I'm just having a little fun here... no insults intended.

Ronin
11-22-2018, 07:18 AM
Those of us without carb heat and speaking for myself are certainly not averse to it at all. We are only disagreeing with the comments that imply we are idiots and that there is no difference between a 912 Kitfox and other Lyc/Cont aircraft that all require carb heat. Even though many of us have never found the need for it, I would be the last person to discourage someone from installing it if they feel a need for it. After all, it has no down side other than a little cost and complexity.

If I lived in Canada, especially the northern parts, I think I would install it. Correct me if I am wrong, but I believe it is required by the equivalent to the FAA to be on all aircraft in Canada and most European countries.

Sounds good but it can happen anywhere. In the Rans S-6 it was around 1,500 feet while crossing the Mississippi river somewhere in Arkansas in April. In the Europa it was at 10,500 over Jacksonville Florida in April. The Europa one I had to shut it down it started shaking so bad I thought it might come off the mount. Dead sticked it into St Augustine and pulled the cowl immediately after landing. The left carb was hot & dry but the right carb was cold to the touch and wet like condensation. I also found water in the airbox. Had no throttle loss or indication what was going on until the engine must have ingested a chunk of the ice, it sounded like we had hit a bird on the lower fuselage.

atosrider
11-22-2018, 08:06 AM
does anyone with a model III have the hot water extension sleeves installed on a 912? Those skydrive water jackets must put the carbs about an inch closer to the firewall, and I question if there is still enough room against the firewall for an air filter ...
the other carb heat system of using probes that are electric heaters received bad reviews a decade ago when I was choosing which way to go to add carb heat to the 912, on an imported experimental registered Rans S6 ... does anyone have experience with the heater probes

Hockeystud87
12-10-2018, 10:52 AM
I wan't to add to this to give another data point in case there is someone out there debating on heat or not.

I have concluded that flying last week I did experience carb icing. Engine showed all signs of it. Gradual increase in roughness, carb air temp sensor showing in the yellow. As I pulled heat engine increased in smoothness with an occasional large bump as a chunk of water/ice breaks off and enters the engine.

I also live in the Pacific Northwest. Humidity and rain is kind of our thing here. I think it's important to know where people are flying that do and don't have issues.

My setup

94 Model 4 Speedster
Round cowl
912 UL (stock)
Bing carbs
Carb heat/cool rammed air box (the box that sits on top your engine)

Weather and conditions

outside temp was 32F +/- 2F degrees
Low ceiling (thick overcast) ~2000+ of airport
High humidity
dew point and temp spread less than 10 degrees.
carb air temp sensor showing anywhere between -2C up to 8C

I will be installing the hot coolant carb heaters on my plane plus keeping my carb heater box. The way I look at it is I have no loss for adding the coolant heater except maybe a pound of weight and I get the additional increased safety of having the hot air if needed. Also get cool air provided to the engine.

I think the combination of the two makes my plane able to counteract even a larger amount if icing scenarios if they are to occur. Gives me more options and tools to tackle tasks in case of a Xcountry where I get in a pinch.

jiott
12-10-2018, 11:51 AM
Al, I am not surprised at all that you may have had carb icing with your airbox setup that brings in cold outside air; with that kind of installation you certainly need a carb heat option. But that doesn't mean that the common setup that most of us have (warm undercowl air with no airbox) is at all likely to experience carb icing in your same climate location. Certainly do what makes you feel comfortable, but you may be going overboard with belts and suspenders.

Hockeystud87
12-10-2018, 12:03 PM
I agree I think my data point shows more evidence that the carb box does create a increased icing situation. I just want to make sure that if someone is researching them selves they understand the differences in the two carb setups. I don't want anyone getting "tricked" into a false sense of security if they have a similar carb setup to mine or believing they have a un trusty motor with a different setup.

My setup may be a little over kill but I consider my self a happy paranoid pilot haha!

I had a engine out while solo, during my long cross country, with only 32 hours under my belt. So I might be a little more sensitive/paranoid about my motor than most. Whether that's good or bad IDK! :D

Slyfox
12-10-2018, 12:08 PM
Al, I am not surprised at all that you may have had carb icing with your airbox setup that brings in cold outside air; with that kind of installation you certainly need a carb heat option. But that doesn't mean that the common setup that most of us have (warm undercowl air with no airbox) is at all likely to experience carb icing in your same climate location. Certainly do what makes you feel comfortable, but you may be going overboard with belts and suspenders.

to add to the description of my setup like mentioned by others. I have an oil cooler right up front under the gear box, a good size one at that. plus I have the oil cooler thermostat. which insures the oil is 180+ so I'm sure my carb are in the warmest air in the back with ru2700 filters which is the smallest you can get for the bing carb. moving to the water system, I incorporate a heater off my radiator (redneck type with funnel off the back and scat tube into the cockpit) I also cover up most the radiator to insure 180+ on the water. so my engine doesn't run cool. might also add to warmer area for the carbs.

Hockeystud87
12-10-2018, 12:28 PM
I want to add that when I was using the carb heated air from the carb box I was not impressed with the rise in temperature I saw. I have a carb temp prob that sticks into the inlet air stream of the carb. The rise I saw was only maybe 15F. I can't confirm if this is 100% accurate and not being effected by the carb housing but at lest would have expected a larger rise over all. This was even after having the carb heat on for a few minutes. Not impressive =/.

DesertFox4
12-10-2018, 12:53 PM
When I purchased my first Kitfox (model 3/912 ul) back in 1998, it came with the carb heat box with a K&N cold ram air filter mounted atop the pilot’s side of the engine. My playground is the desert southwest. Our local Kitfox pilots with the same Rotax engines never encountered carb ice so I removed that from my engine. Also there was an incident reported where a nut and washer came loose inside a carb heat box and got down on top of one of the pistons and severly damaged the engine. That really was the icing on the cake, no pun intended, to remove that system.

Flash ahead to my model 4 with 912uls and no carb heat system-
While returning from a Priest Lake, Idaho flight with 4 other Kitfox’ all Rotax equipped, we had a fuel stop scheduled for an airport in central Idaho. The day was one with high humidity and overcast with very intermittent sprinkles on our windshields and outside temps in the 60’s. We made a fairly quick decent from altitude all the way down to landing. A couple of us, including myself, had a couple of short bursts of rough running engines in that long low powered decent.
Our combined conclusions, likely carb icing. I believe it was all of our’s first encounter with minor carb ice. None of us had a carb heat system installed.

So what do I think I understand about carb icing on carbureted Rotax equipped Kitfoxs?
1. Yes it can occure with the right conditions even on a Kitfox pulling warm air from the back of both the bump cowls and smooth cowls, however it is rare.
2. The standard carb heat system that was used on many early 912 equipped Kitfox aircraft with the cold air intake will induce carb icing much quicker and in less severe ice forming conditions than those engine installs pulling warmer air at the back of the cowls. Most reported incidents of carb ice come from owners flying with the carb heating system installed that have cold air intake locations.
3. The original carb heat diverter boxes could offcast small parts that could translocate into a running engine thereby ruining a pilot’s day very quickly.

Would I intall a carb heating system? Yes. If I flew in a high humidity level area frequently and ever encountered suspected carb ice even once.
Or if the governing body in charge said install one or stay on the ground.
What system would I install? Certainly not the cold air intake box.
I would install the engine coolant carb heating system mentioned previously in this and other threads. Or just go with the fuel injected engines and then no worries.

Slyfox
12-10-2018, 01:01 PM
so please explain why fuel injection doesn't have a problem. they still have a throttle body with a filter into the airstream. just curious. I have an io360 that doesn't have carb heat. but never thought much about it.

Esser
12-10-2018, 05:53 PM
No Venturi in a fuel injection setup

Slyfox
12-10-2018, 06:38 PM
but what really messes with my brain is this talk about moisture and possible ice in the air box.

DesertFox4
12-10-2018, 07:37 PM
Steve,
I’ve never heard or read that the old carb heat airbox itself would incur ice but that the cold air delivered by and through that carb box set up does allow carb ice to form inside the carbs more easily than yours and my system that draws intake air for our engines from the warmer part of the cowling.

Slyfox
12-10-2018, 08:28 PM
try #42 of this thread. that's where I got the info.