alternate carb heat

Ray Toews wrote...
Has anyone ever tried using cowling air under the engine as heated air
for carb heat.

Serveral RV-builders including me have tried something similar.
Van's sells a mini heat muff that doesn't do mucgh but serve as
a mount for scat tube, so in essence we're drawing undercowl
air into the airbox when carb heat is selected. Sam Buchanan
has a picture on his website:

http://home.hiwaay.net/~sbuc/journal/engine4.html

about 1/2 way down the page. I did the same thing on an
RV-4 and I get a barely perceptible RPM rise when I select
carb heat, which tells me it's not helping much.

Your call.

Dave 'hot air specialist' Hyde

"Dave Hyde" wrote in message
...
Ray Toews wrote...
Has anyone ever tried using cowling air under the engine as heated air
for carb heat.

Serveral RV-builders including me have tried something similar.
Van's sells a mini heat muff that doesn't do mucgh but serve as
a mount for scat tube, so in essence we're drawing undercowl
air into the airbox when carb heat is selected. Sam Buchanan
has a picture on his website:

http://home.hiwaay.net/~sbuc/journal/engine4.html

about 1/2 way down the page. I did the same thing on an
RV-4 and I get a barely perceptible RPM rise when I select
carb heat, which tells me it's not helping much.

Your call.

Dave 'hot air specialist' Hyde


You get an RPM increase??? Sumpthin' is way, way wrong with that... ;-)

With the exact same setup, I get a barely perceptible RPM decrease...

KB

Kyle Boatright wrote...

You get an RPM increase??? Sumpthin' is way, way wrong with that... ;-)

Argh. Something's wrong alright, but not
with the airplane.

Dave 'fatfinger' Hyde

Sorry Dave
In this case I don't think it's the fingers that are 'fat'. ;-)
John


Dave Hyde wrote:

Kyle Boatright wrote...

You get an RPM increase??? Sumpthin' is way, way wrong with that... ;-)

Argh. Something's wrong alright, but not
with the airplane.

Dave 'fatfinger' Hyde

Kyle Boatright wrote:

"Dave Hyde" wrote in message
...

Ray Toews wrote...

Has anyone ever tried using cowling air under the engine as heated air
for carb heat.

Serveral RV-builders including me have tried something similar.
Van's sells a mini heat muff that doesn't do mucgh but serve as
a mount for scat tube, so in essence we're drawing undercowl
air into the airbox when carb heat is selected. Sam Buchanan
has a picture on his website:

http://home.hiwaay.net/~sbuc/journal/engine4.html

about 1/2 way down the page. I did the same thing on an
RV-4 and I get a barely perceptible RPM rise when I select
carb heat, which tells me it's not helping much.

Your call.

Dave 'hot air specialist' Hyde



You get an RPM increase??? Sumpthin' is way, way wrong with that... ;-)

With the exact same setup, I get a barely perceptible RPM decrease...

I thought the same at first, but he may be referring to turning on the
carb heat after he's already accumulated enough carb ice to noticeably
decrease his RPM. In that case, applying the carb heat should increase
the RPM as the ice is removed.

Matt

Matt Whiting wrote...

...but he may be referring to turning on the carb heat
after he's already accumulated enough carb ice to noticeably
decrease his RPM.

Yeah, that's it. g No, I'm afraid UltraJohn was right.
I haven't seen anything remotely resembling carb ice,
and from what I've heard it's not very common in RVs.
I get a very slight RPM *drop* with carb heat, presumably
to a slight temperature *rise* from switching to undercowl
air.

Dave 'cold throat' Hyde

"My wallet's fat and so is my head" - Greenday, 'Walking Contradiction