Carb Ice Questions

[Onex107]

I don't think I've had any carb ice in 200 hours. Any rough engine I had during flight I attributed to the Injector mixture/needle set up. I have seen ice on the outside of the intake manifold, with the cowl off during a short test run. Probably a good reason to have the oil temp over 100 before takeoff with a warm intake manifold. My Aerovee is very rough at start and won't idle lower than 1200 rpm until the cylinders and oil temp get up. I suppose that could be ice. It's very difficult to prove "carb ice". By the time you look for it, it's gone. I think all certified aircraft pilots are familiar with it and expect it to happen, especially during reduced throttle and landing. Full carb heat before throttle reduction was second nature. If you wait too long to apply the carb heat, it doesn't work because the engine slows and is not sucking enough of the hot air. Only the fuel injected engines seemed to not have that problem.

[Sonerai13]

I have had three instanced when flying a Sonex that acted an awful lot like carb ice. Engine started losing RPM, and got a bit rougher. I responded by first opening the throttle all the way, as others have suggested, with little effect. I then closed the throttle all the way, and then moved it back to wide open. In all three cased, this solved the problem. Was it carb ice? I will never know. But it sure acted like it, and CLOSING the throttle fixed it. I surmise that, if it was carb ice, it may have been building up on the needle and slide, and opening and then closing the throttle cleaned both off. Just conjecture on my part, but I can't come up with any other reason for the event, or why closing the throttle may have fixed it.

Note too that there is a possibility of building up ice in the induction system after the carburetor. This is possible with all engines, not just slide-type injectors. I doubt this is happening in the AeroInjector engines, and if it was, moving the throttle in any direction wouldn't solve it I don't think.

Anyway, that's my story and I'm sticking to it. YMMV.

[Gordon]

The Carb Heat Discussion............

Just for the record........here in Canada you MUST have provision for carb heat (unless the engine is fuel injected) and the MUST have a gascolator in the fuel system and your MUST NOT have an inline fuel filter in the system to be in compliance. When you get your "final inspection" by the MD-RA (the Canadian version of DAR) you will need to be in compliance on those items or your won't get your C of A (certificate of airworthiness). The inspector can use his discretion on certain issues concerning your project but those ones are non-negotiable.

I guess they want to "protect us from ourselves"...........that's probably a good thing.

Gordon.......Onex........Hummel 2400

[berger]

Hello Joe and All,

For about two years, it appears to me that my engine is subject to what I call "unhappiness", especially when flying in mild OAT and mostly high humidity. Since the occurrence of carb icing seemed to be very rare using the standard Sonex set-up with an AeroCarb, I thought it was due to some other issue with the engine itself. I've been searching and investigating for all those months with no success in finding any apparent cause.

I've posted many e-mails on the Jabiru/CAMit forum about that and I've investigated so many things without finding something really wrong. Lately, I've removed #5 cylinder head and lapped the valves which where possibly slightly leaking, thinking I had found the culprit. Not at all... Two flights were done with a happy engine and the third, the unhappiness re-appeared. Prior to that, I replaced all the spark plugs and checked their internal electric resistance. Two had very high values whereas they should be close to one ohm.

This is how it usually goes. On the ground, nothing wrong. Engine starts quickly, run-up does not show anything wrong at all, ignition 0-10 rpm drop, sometimes.

Take-off and climbing are fine. #5 is the hottest cylinder and I have to climb at not more than 1000 ft/min if I want it to keep it below 145°C (290°F). This makes around 80 kts. At 5000 ft, level-off, tuning the mixture to have EGTs about 680-700 °C (1256-1292). Everything is fine... after a few minutes into the cruise flight, typically like on last flight, 17 minutes, a single burp comes. Then some EGT would up-drift and the engine would no longer run as smooth but with some unhappiness, losing perhaps 10 to 20 rpm, but not always. From that point, the unhappiness will usually stay for the remaining of the flight at most power settings above 2000 rpm. I must say, I rarely tried to apply full power under these conditions. Checked the ignitions, same as on the ground, good. This happened 4 times within the last 20 flights (around 20 hours), except that sometimes, the unhappiness comes without the initial burp. It seems to happen more when the OAT is mild and the air is humid (last week it was hazy and 12°C (54°F)). The stunning point is that this phenomenon only appeared after 8 years that I fly my Waiex. Never before. True enough, the engine had its top end overhaul at 125 hours, back in 2012-13 and since then it runs cooler. But why did it work fine from 2013 to 2016, without the "unhappiness" if this was due to carb icing... Puzzling.

Also, back in the fall of 2016, I checked the AeroCarb and noticed there was a slight notch in the metering orifice's side. I checked the same orifice two days ago and the side notches (both sides) seemed to have increased in size. It now looks like a round face with two ears. The metering needle is wobbling and thus laterally grinding into the Delrin orifice and I wonder if this would be the cause of the "unhappiness". To me it would be difficult to explain how, but perhaps the needle get trapped in the shallow notch, while reducing the setting from climbing WOT to cruise power, only on one edge which would twists the needle somehow and mis-distribute the fuel, or allowing the fuel to pour from the front round side of the needle, producing drifting EGTs and some slight roughness...
Has anybody else noted that the metering orifice geometry is affected by the needle?

This "unhappiness" of my engine appears every three to five flights, and after several engine mechanics told me my engine does not show signs of defaults, including those of Jabiru France, I'm interested to read that some other Sonex owners might have experienced some icing of their AeroCarb/Injectors. Actually, Art K told me about this thread on the Jabiru/CAMit forum.

Now, for those who like Joe experienced some presumable icing, what were the atmospheric conditions when this occurred, e.g. humidity and OAT?

As said, in my case, it is pretty much corresponding to the "serious" icing zone of the following website, except that it does not seem to happen below around 5°C (41°F).
http://www.ycem.com.au/b2/CarbIceV1.html

Thanks for any contribution.

Have Safe Fun!

[hickej]

I have never experienced anything that felt like carberator ice but I have had an ‘unhappy’ engine. What I’ve learned with the Jabiru and Aerocarb over the last 5 years and 620 hours is that each power setting and density altitude has a unique leaning scenario. After I solved my fuel vapor burps by getting rid of the gascolator, I would still sometimes experience rough engine running at cruise. I did double check my intake manifold couplers and ended up replacing them due to visible cracking. Any leaks there could cause roughness. Using the Dynon lean function I was able to see the exact rich-of-peak behavior and realized that leaning ‘by ear’ was leaving me with some cylinders close to max EGT allowing them to drift into lean-of-peak. I was surprised to find that my ‘go to’ cylinder for low altitude leaning temperature wasn’t always the first to peak at higher altitudes. Once I got into the habit of using the Dynon lean function each time I go into cruise I have not experienced any roughness. Like I said, each altitude, temperature, power setting can have very different leaning behavior. Worth a check.
-Jim
Waiex 3300 620 hours built 2013

[berger]

Hi Jim,

Thank you for your comments.

Just like you, I've also noticed that the power settings have to be closely followed by a mixture input and also that the engine is very sensitive to very shallow slopes. Descending to 50 ft/min will increase very slightly the RPM, perhaps 10, and it will follow some up-drift of some EGT(s), receiving more air due to the RPM increase. So either the RPM or the mixture has to be adjusted accordingly.

But what I notice and call "unhappiness" is different. When it comes, it will mostly stay until I've landed. This might be because I never tried to apply WOT and then idle settings when this phenomenon appears. Will go through this process the next time.

Thanks,

Sosthène

[berger]

Well, I forgot to mention that the Tech support at Sonex pointed me to the gascolator as a possible culprit for the troubles I have, instead of the AeroCarb: Vapor lock.

I will install a thermal insulation around the colator tomorrow, just in case.
Of course, I triple checked the induction hoses among many other points...

Thanks

[lgsievila]

I have a Bing carb on my Camit 2200 with electric carb heat. I have never had a noticeable issue with carb icing or an unhappy engine. I have 2 settings for carb heat, high/lo, and always use low setting on approach to landing. The only time I have ever had the engine run a little rough is if I lean too much with my Hacman mixture control. I also have a gascolator,electric fuel boost pump, red cube fuel flow sender, fuel pressure sender, and bypass with check valve that will let gas to the carb if all else fails. All are insulated. On takeoff at WOT my #3 cylinder EGT is hottest and at cruise #4 is hottest. Twisting the carb towards the hottest cylinder will change your EGT temps(lower). I flew 3600 miles last year from the West Coast to KOSH without a hiccup. Maybe a different carb would work better-just sayin.

[Kai]

Loren,

Your observations correspond exactly with our own findings.

I'm not saying that the Bing is an intense love affair, but as long as it can draw fresh air from outside the Sonex cowling, is properly set up and furnished with adequate carb heating and the HACman mixture control, it performs according to expectations.

Thanks
Kai

[berger]

Hi Kai and All,

Thanks for your suggestions to swap to the Bing.

Before doing so, I really need to be sure the "unhappiness" is really related to some AeroCarb needle icing. At the present time, I'm just trying to realize that this can be, despite the words of AeroVee that it should not. Also to be noted that in my country --Switzerland--, this would require a Major Modification process which might imply remaking the whole Test Flight program which took me at least two years the first time, without counting the number of stamps and taxes and paperwork to be done.

Right now, I return from the airport where I undertook some actions in order to inspect the heart of the AeroCarb. I removed the air filter, the metering needle and its carrier, inspected the orifice without the needle, with a bore-scope from the top of the carby.

The needle carrier has no sign of wearing of any sort. The needle had some sharp edges conditions explaining the scoring of the orifice's inside surface. Also, I checked the fuel flow coming through the orifice. There was plenty of fuel pouring from the orifice's hole. So, except for those scoring which do not look so bad all together, with no chips sticking out --I still have to unload the pictures to study some more in the office--, I do not think that the "unhappiness" lies in there. This confirmed pretty much my first rough analysis back in fall of 2016.

Still, the "unhappiness" cause seems to stuck hidden, unless I consider that there have been a minority of testimonies of owners/pilots who seemed to have experienced some similar symptoms to the "unhappiness" and some would attribute these symptoms to carburetor icing. On my side, I always trusted Sonex/AeroVee words telling the AeroCarb within a standard Sonex installation cannot ice, but fighting a ghost for two years now, I really badly need some cause for it to be cured and slowly, the fingers are pointing toward this possibility...

I was pretty keen to insulate the gascolator to rule out this as a culprit, but thinking twice, I did not make it this morning because if the cause of the issue really is carb ice, depriving the gascolator from some heat might push me in some dangerous corner. Also, when the new engine produced around 8 kW of additional heat inside the cowling, I did not have noticed any vapor lock, even on the ground taxiing back from a summer flight.

It remains that the "unhappiness" did not show at all from hour 1 to around hour 280, knowing that the engine was running much too tight for the first 125 hours, producing enough heat (carb heat) it makes no mystery. But why did the syndrome --perhaps carb/needle icing-- only appeared 155 hours after the top end overhaul, without any major modification?

Personally, I think it is more the needle which might ice under certain conditions because it is in direct contact with the vaporizing fuel and has only poor thermal connection with the hot engine block. I thought about inserting the needle carrier with some thermal grease (as for computers CPU) in order to have a better heat flow toward the tip of the needle dipping into the cold fuel.
Any thoughts about this improvement?

Thanks,

Sosthène