van's carb heat

[RV7ator]

When I installed carb heat on a FAB-equipped 7, I used the beer can Van's sells for the pick-off, knowing full well that sucking air across only 2" of exhaust isn't going to warm all that air all that much. No high math involved here; it doesn't pass the smell test. Yet I persisted. What I did do different was NOT use the Van's Carb Heat Connector because it is perched up on Z-brackets above the FAB hot air opening. This leaves a huge gap that will allow unheated air into the engine. I installed a spun aluminum 2" pick-off that Spruce sells to achieve a no-leak path from beer can (the plane's, not mine) to the intake (the plane's, not mine). It, incidently is rugged compared to the Van's offering. I removed the Z-brackets from the Van's connector to use it as the cabin air pick-off. The wimpy tack welds snapped within 20 hours; I remember others have posted similar failures. It's a piece of **** no matter the application.

I think I'll have a beer.

John Siebold

[Build9A]

John: Sounds like you came up with a good modification. Do you have any info on how much temp increase you get? thanks, jack

[dmeloche]

garnt,
got any pictures of your setup? i like the sound of it!

doug

[jthocker]

To All
I too was having trouble getting any rpm drop with Van's small muff. I started flying last July and had my time flown off in Sept. I had all the bugs worked out except for the carb heat problem. Winter was around the corner and I wanted to fly IFR but the carb heat kept nawing at me. First I sealed up the flange that Van supplies with the muff, no help. So I purchased a stainless muff from Wicks and installed it on the front crossover tube above the carb heat door. I did not route air to the muff, I just let it draw air from inside the cowl. This helped alot. Since I'm starting my annual(condition) inspection I decided to get some good baseline numbers after 1 year and 100 hrs. Usually when I do a runup I check for a drop with carb heat but never really look to see how much I get. After reading the replies about the carb heat I decided to wait a while and take note. So with the engine warmed up (325cht), 30 deg.C OAT, RPM at 1800 (Digital EIS), full carb heat, after 30 seconds RPM was down to 1740, carb heat full off Rpm recovered to 1800. Maybe I'll get a carb temp probe or the Grand Rapids EIS but for now I'm much happier with the full muff.
Jon

[dmeloche]

I finally bought and installed the wicks stainless steel muff. It is part number EC100-020. It clamps to the crossover tube and just fits between the 2 pipes. I did a runup and got a 60 rpm drop with this. much better than the vans setup. If you're concerned about the vans muff try this. I tried uploading a picture of the setup but gave up after a number of error messages. hope you can visualize it.

regards
doug

[jonbakerok]

These discussions about carb ice always strike me like ghost stories around a campfire. I'm not trying to diminish the threat, but carb ice has been a problem since the Wright Brothers days. Why can't we ever get any REAL information? Has no one ever studied it scientifically?

Think of what's been said so far:

1. Carb ice can happen anytime the humidity is above 50% the temperature is below 30 degrees celsius. 30 degrees celsius is 86 in real degrees! If that's all it takes then carburated flight in Houston would be impossible more than 9 months out of the year!

2. Carb ice can happen anytime the humidity is above 50% and the carb temp guage is between -10 and +10 degrees celsius. Has anyone ever seen water freeze at 50 degrees farenheight?

These numbers are so broad they're useless. It's like saying carb ice can happen on on Wednesdays.

Common sense tells me that there must be some other reason that once in a few hundred thousand flights someone's carburator freezes up. What are the other factors? What about air density? Should we be especially alert when the air pressure is significantly below 29.92? How much below? Are there other factors? Has anyone really gone down with carb ice on a clear humid June day in Atlanta buzzing around at 3000 feet? Or is the typical scenario a guy loafing along at half power at 10000 feet in the clouds in January? And how come the other few hundred guys doing the same thing that day didn't get carb ice? Was it the clouds, the air density, the sub-freezing weather? Or could it have been a dirty airfilter?

Sorry to be so bitchy, but when the topic turns to safety, I get really tired of the same old wives tales and a warning to "be careful". You'd think that with a subject as technical as aviation, we'd occasionally get some real science.

[jclark]

Jon,


You probably already know this but a few comments ...

The temperature that REALLY matters is the temperature inside the carb. The low pressure (higher velocity?) inside causes the temp to drop quite a bit inside.

I installed a carb ice detector on my Piper some years ago (light gets blocked by ice buildup) and I was AMAZED!!! At startup you set the initial threshold for the system (no ice) and even on taxi out there would be **some** buildup.

There were indications so often of **some** buildup that I now don't bother to turn it on. The point here is that there is more ice in there (on hot days with some humidity even) than you might think.

I only recall a couple of times where I felt performance was beginning to be affected by card ice. Once throttled back to fly with some friends who were in a 172 and the outside was VERY humid (and cool). The other on base over some water on a hot day. On the flying along case, I added carb heat and full power (told my friends I would wait for them at next stop) and on base I just added carb heat I think (in Piper handbook, you add it only if indicated) and landed no problem.

James

Originally Posted by jonbakerok

These discussions about carb ice always strike me like ghost stories around a campfire. I'm not trying to diminish the threat, but carb ice has been a problem since the Wright Brothers days. Why can't we ever get any REAL information? Has no one ever studied it scientifically?

Think of what's been said so far:

1. Carb ice can happen anytime the humidity is above 50% the temperature is below 30 degrees celsius. 30 degrees celsius is 86 in real degrees! If that's all it takes then carburated flight in Houston would be impossible more than 9 months out of the year!

2. Carb ice can happen anytime the humidity is above 50% and the carb temp guage is between -10 and +10 degrees celsius. Has anyone ever seen water freeze at 50 degrees farenheight?

These numbers are so broad they're useless. It's like saying carb ice can happen on on Wednesdays.

Common sense tells me that there must be some other reason that once in a few hundred thousand flights someone's carburator freezes up. What are the other factors? What about air density? Should we be especially alert when the air pressure is significantly below 29.92? How much below? Are there other factors? Has anyone really gone down with carb ice on a clear humid June day in Atlanta buzzing around at 3000 feet? Or is the typical scenario a guy loafing along at half power at 10000 feet in the clouds in January? And how come the other few hundred guys doing the same thing that day didn't get carb ice? Was it the clouds, the air density, the sub-freezing weather? Or could it have been a dirty airfilter?

Sorry to be so bitchy, but when the topic turns to safety, I get really tired of the same old wives tales and a warning to "be careful". You'd think that with a subject as technical as aviation, we'd occasionally get some real science.

[rv6ejguy]

There is a substantial drop in temperature through the venturi of the carb plus just downstream of the fuel nozzle, the temperature can drop even further due to the vaporization of the fuel. Best to fit a carb temp sensor and gauge to find out what is happening.

I've seen statements here that RV Lycoming engine installations rarely suffer carb icing. The fact that a Lycoming is installed in an RV has nothing to do with anything. If the temperature in the venturi is below freezing and there is enough humidity, you may form carb ice. I've had it at +23C one day and -18C another day, neither of which days were very humid.

Regs require an adequate system to prevent carb ice. Van's supplied 90 degree pipe muff will not. What will you do if you get carb ice? Good chance you are going down if you can't get out of the conditions. I think many unexplained power loss accidents are caused by carb ice. Accident investigators find nothing an hour after the crash as the ice melts from the latent engine heat. Traces gone.

I just don't understand people's reluctance to fit a proper system. It's not rocket science and it is important.

[osxuser]

As to Lycomings being less prone to carb ice, I don't know. In my relatively meager 370Hr's flight time, I've encountered carb ice 4 times. Twice it was one the ground while still in RUNUP. Once was in a 172 and once was in our o-360 powered 177. This is in Los Angeles and both of the ground incidences were with the temperatures between 60 and 80 degrees, and the relative humidity high. The time in the 172, I had to leave carb heat on or it would just keep coming back. I think that much of the time when a pilot encounters carb ice they don't even know it.

I know a flight instructor who encountered some severe carb ice in a 152, and didn't understand why when he pushed the carb heat off after it cleared up, it came back within a minute. So his solution was to dramaically lean the mixture to get smooth combustion. He really didn't think he had carb ice, he thought something else was wrong. I think the best was to avoid the whole issue is fuel injection, but lacking that option, I want to see at least 100rpm drop at runup if I'm gonna take off. The 177 had a pretty weak heat system coming off the muffler. But we installed a pickup off the #3 riser to fix that problem.

[n468ac]

The FAR's say you need a 90deg rise with carb heat ... it doesn't talk about rpm drop.