Carburetor Heat during landing?

[Tumbleweed]

How many CTSW/CTLS owners use the Carburetor Heat during the landing phase, ie pulling it on when you put down the first flaps abeam the numbers in downwind?  The POH check list say to use it - but there is a theory by many CTSW drivers that the Rotax 100hp is not prone to carb icing. Your thoughts please. 

[ct9000]

It cannot do any harm why not use it for the peace of mind anyway. I am in the habit of using carb heat on the power reduction in prep for landing and remove it as you come over the fence. This practice is just automatic whatever plane I fly, except when not fitted of course.

[Anticept]

I have seen icing on the ground but not in flight.

Regardless these carbs are able to ice up, just that in CTs the cowling is so tight that things stay kind of warm.

That won't always be the case.

[Madhatter]

Part44.pdf

[GrassStripFlyBoy]

I don't use it, and have flown with three highly experienced FD type instructors who don't either.

I see no harm in using it.  Understand that the FD airbox is not a traditional "carb heat" ducting.  Speaking from SW perspective and I believe true for all types, there is no duct routed from the exhaust to the airbox, and the airbox still allows a massive amount of air by the diverter door when carb heat is pulled, this is likely why there is negligible RPM drop when pulled.  This is more of an "alternate warm air selector", than carb heat.

The only time I'd pull the knob is if engine was running rough and in potential icing conditions. 

[FlyingMonkey]

Theoretically you will lose a little engine power by having it ingest the warmer air.  But it’s probably not a noticeable difference.  I quit doing carb heat checks in my pre-takeoff checklist because there was literally zero RPM loss with carb heat, so it was a meaningless check that told me nothing.

I’d make sure carb heat was off when departing from a short field or one with a scary departure, but you could probably leave it on all the time with zero performance impact.  So use it if it makes you feel better, otherwise just pop it out at the first hint of engine roughness for any reason.

[Tumbleweed]

Thanks to all for your input.  The article posted by Madhatter is really interesting reading.  Stuff I had not read before about Rotax 912 and it's Bing Carburetor.

[Warmi]

Some manufacturers install what it is often called “full time carb heat” solution which basically just feeds some of the engine warm air to both carbs. I have it on my plane and no carb heat lever and all my POH says on the subject is something like “ if suspecting carb ice, just add more power”    

[FlyingMonkey]

16 hours ago, Warmi said:

Some manufacturers install what it is often called “full time carb heat” solution which basically just feeds some of the engine warm air to both carbs. I have it on my plane and no carb heat lever and all my POH says on the subject is something like “ if suspecting carb ice, just add more power”    

Many 912 installs just stick air filters on the backs of the carbs and give them warm under cowl air all the time.  The RV-12 is one example.

[FastEddieB]

3 hours ago, FlyingMonkey said:

Many 912 installs just stick air filters on the backs of the carbs and give them warm under cowl air all the time.  The RV-12 is one example.

Isn’t there some gain in efficiency with a properly designed airbox? I always thought there was.

 

This, from Google:

Since the 1990s, engine designers also sought to exploit the properties of oscillating gas to improve performance.

Many high-performance motorcycles have the airbox fed from funnels in the front of the bike, where increased pressure forces more air into the intake and thus improves power. Examples for this ram-air intakeconstruction are the SRAD models of the Suzuki GSX-R750, the Kawasaki Ninja ZX-6R or the BMW S1000RR.

Secondly, designers exploit a property of air cavities known as Helmholtz resonance. Flow through the airbox is optimal at its resonance frequency, which depends on airbox volume and the inlet area and length of the snorkel. The resonance is typically chosen to be at a medium speed where torque otherwise drops, caused by valve timing overlap.

[Roger Lee]

If you have K&N air filter right on the carbs then these run in carb heat all the time, but that also makes it run rich.

Cool outside air has always been preferable and forced air like a ram air vent can be even more beneficial. 

These ideas aren't new. I remember them from when I was a kid.

[Towner]

Early Mooneys had ram-air. To be used at higher altitudes and in clean air, you would open a small door on the cowling. This allowed air to bypass the filter and would give about 1" of additional manifold pressure. More efficient air intake through the filters was created for later models, but it was pretty cool for the older models. If your filter, which was stuck on the outside of the cowling, ever iced up, you could also use the ram air to get undisturbed air for hopefully long enough to get out of the icing conditions.

[Tip]

I have seen several CTLSs were the push pull wire bows and the carb heat stays on once it’s apply. It would be a good practice to reach in behind the balance tube to verify that the interlock setup is throwing both ways.

 

 

 

[CT_MATT]

I had that problem where the valve was stuck partially causing noticeable power loss at high RPM.  After I resolved the issue, I avoid using carb heat until the need arises.