Important notice
Please remember that people from all over the world read and post on this forum, and that every country has its own rules, regulations and standards. This forum is based in the USA and so much of the information posted here is for the benefit of people who operate aircraft in the experimental/exhibition or experimental/racing categories. Advice given on this forum may be region specific. A person from Europe, for example, may make suggestions perfectly appropriate for a U.S reader, although not acceptable in his home country!

Please take this into account and carefully consult the authorities, standards and approved documentation where you fly.
Fournier Forums Upload picture | User Cp  |  Register  |  Members  |  Search  |  Help
    |- Fournier Aircraft > Maintenance Post New Topic   Post A Reply
carb ice printer friendly version
next newest post | next oldest post
Author Messages
gburris
Private

Gender: Male
Location: 4al3
Registered: Feb 2015
Status: Offline
Posts: 4

Click here to see the profile for gburris Send email to gburris Send private message to gburris Find more posts by gburris Edit or delete this message Reply w/Quote
Posted Thursday, May 7, 2015 @ 00:24 AM  

What is the best way to avoid carb ice on a long cross country flight ? What can you do if it happens ?
John Olsson
Sergeant

Gender: Male
Location: South Africa
Registered: Dec 2010
Status: Offline
Posts: 36

Click here to see the profile for John Olsson Send email to John Olsson Send private message to John Olsson Find more posts by John Olsson Edit or delete this message Reply w/Quote
Posted Thursday, May 7, 2015 @ 06:52 AM  

CARBURETOR ICING is caused by a temperature drop inside the carburetor, which can happen even in conditions where other forms of icing will not occur.

The causes of this temperature drop are twofold:

1. Fuel icing-the evaporation of fuel inside the carburetor. Liquid fuel changes to fuel vapor and mixes with the induction air causing a large temperature drop. If the temperature inside the carburetor falls below 0°C, water vapor in the atmosphere condenses into ice, usually on the walls of the carburetor passage adjacent to the fuel jet, and on the throttle valve. Generally, fuel icing is responsible for around 70% of the temperature drop in the carburetor.

2. Throttle icing the temperature loss caused by the acceleration of air and consequent pressure drop around the throttle valve. This effect may again take the temperature below 0°C and water vapor in the inlet air will condense into ice on the throttle valve.

Two criteria govern the likelihood of carburetor icing conditions: the AIR TEMPERATURE and the RELATIVE HUMIDITY.

The ambient air temperature is important, but not because the tempera­ture needs to be below 0°C, or even close to freezing.

This temperature drop in the carburetor can be up to 30°C, so carburetor icing can (and does) occur in hot ambient conditions.

It is no wonder carburetor icing is sometimes referred to as refrigeration icing. Carburetor icing is consid­ered a possibility within the temperature range of -10°C to +30°C.


The relative humidity (a measure of the water content of the atmosphere) is a major factor.

The greater the water content in the atmosphere (the higher the relative humidity), the greater the risk of carburetor icing.

That said, the relative humidity (RH) does not have to be 100% (i.e., visible water droplets-clouds, rain) for carburetor icing to occur. Carburetor icing is considered a possibility at relative humidity values as low as 30%. Herein lies the real danger of carburetor icing, that is can occur in such a wide range of conditions. Obviously the pilot must be alert to the possibil­ity of carburetor icing at just about all times. Flight in or near clouds or in other visible moisture (i.e., rain) might be an obvious cause of carburetor icing, but visible moisture does not need to be present for carburetor icing to occur.


In this aircraft, fitted with a fixed pitch propeller, the symptoms of carbure­tor icing are straightforward. A loss of RPM will be the first symptom, although this is often first noticed as a loss of altitude. As the icing becomes more serious, engine rough running may occur.
Apart from the normal check of carburetor heat during power checks, it may be necessary to use the carburetor heat on the ground if carburetor icing is suspected. Safety considerations apart, the use of carburetor heat on the ground should be kept to a minimum, because the hot air inlet is unfiltered, and sand or dust can enter the engine, increasing engine wear.

Very few operators recommend the use of anything other than FULL carburetor heat. A normal carburetor icing check will involve leaving the carburetor heat on (hot) for 5 to 10 seconds, although the pilot may wish to vary this, dependent on the conditions. The use of carburetor heat does increase fuel consumption, and this may be a factor to consider if the aircraft is being flown towards the limit of its range/endurance in possible carburetor icing conditions.

With carburetor icing present, the use of carburetor heat may lead to a large drop in RPM, with rough running. The instinctive reaction is to put the carburetor heat back to cold (off), and quickly. This is, however, the wrong action. Chances are this rough running is a good thing, and the carburetor heat should be left on (hot) until the rough running clears and the RPM rises. In this instance, the use of carburetor heat has melted a large amount of accumulated ice and the melted ice is passing through the engine causing temporary rough running.


--------------------
RF4D flying in the Afican Sky!

Collin
General

Gender: Male
Location: McMinnville. Oregon
Registered: Oct 2006
Status: Offline
Posts: 711

Click here to see the profile for Collin Visit http://www.cfiamerica.com Send email to Collin Send private message to Collin Find more posts by Collin Edit or delete this message Reply w/Quote
Posted Thursday, May 7, 2015 @ 12:54 PM  

Hi,

I have had carb ice with my RF4 3 times. Running at full throttle or high power settings makes more heat in the heads and cylinders then the carb is getting warmer air.

Also have a look at this page.

http://sbeaver.com/cgi-bin/fournier/cutecast.pl?session=a9T09XxDhPEVgf4Ne5SoRGKmHS&forum=17&thread=417

gburris
Private

Gender: Male
Location: 4al3
Registered: Feb 2015
Status: Offline
Posts: 4

Click here to see the profile for gburris Send email to gburris Send private message to gburris Find more posts by gburris Edit or delete this message Reply w/Quote
Posted Thursday, May 7, 2015 @ 06:11 PM  

Thank you, for the reply's The real question is what do you do when you encounter carb icing at altitude in a RF4 ? Having own a C-182 for 14 yrs I'm familiar with carb ice and have used the carb heat to cure the problem.The RF4 if I understand the design correctly,, depends on tight baffles to route warm air into the lower half of the engine and carburetor to avoid the icing problem. I purchased # 4066 and I'm about to fly it 500 nm home along the Gulf Coast ,USA.That will take me ? 5 to 7 hrs depending on winds etc.East Texas,Louisiana,Mississippi,South Alabama in May with lots of humidity.Yes I know its a glider and altitude is my friend "Severe Clear" would be great.Any suggestions would be appreciated ,,thanks
Bob Grimstead
Captain

Gender: Male
Location: Perth, Western Australia or West Sussex, England
Registered: Dec 2006
Status: Offline
Posts: 2027

Click here to see the profile for Bob Grimstead Visit http://www.redhawksduo.co.uk Send email to Bob Grimstead Send private message to Bob Grimstead Find more posts by Bob Grimstead Edit or delete this message Reply w/Quote
Posted Saturday, May 9, 2015 @ 05:21 PM  

If you experience carburettor icing, open the throttle wide and raise the nose to slow down to 60 knots or 70 miles an hour.
That will maximise the under the Cowling temperatures so that the heat will clear the ice.
The simple act of opening the throttle and maybe pumping it a couple of times will break most of the ice off the butterfly where it forms.
That's all you can do -- and it works.

Of course your best insurance is to make sure that all the baffles are working properly in the first place and there is no leakage out of the top of the Cowling where it fits over the fuel tank top decking.

In my experience, whatever the power setting, the carburettor inlet temperature is about 25°C or 50 degrees Fahrenheit higher than ambient.

Yours Bob

--------------------
Flying and displaying Fournier RF4Ds VH-HDO and G-AWGN, building replica RF6B G-RFGB and custodian of RF6B prototype F-BPXV

gburris
Private

Gender: Male
Location: 4al3
Registered: Feb 2015
Status: Offline
Posts: 4

Click here to see the profile for gburris Send email to gburris Send private message to gburris Find more posts by gburris Edit or delete this message Reply w/Quote
Posted Sunday, May 10, 2015 @ 04:50 PM  

Bob,Thank you !!! I understand the concept.I have also notice the the gap above the fuel tank you mentioned and plan on sealing it temporally with duck tape to bring it home,, or do you have another suggestion ? This is a great forum and very impressed with the knowledge of the membership.Any and all suggestions would be greatly appreciated. #4066 has seen very little flight time maybe 10 hrs in 4 years.I had an A&P who knew the former owner and had worked on the AC sign off on the annual.We spent a day and a half going over the RF4.The extension of the main gear seen a little awkward/rough and at times locking the gear on retraction was difficult.I have coupled a pair of scissors jacks together and plan on raising the AC from the skids under the wing and work the gear again before I start for home.Lifting from the skids to work the gear is okay??? many thanks again Greg
Post New Topic   Post A Reply Jump to:
Contact Us | cfiamerica.com | Privacy Policy All times are GMT -4 Hours.
Welcome to The Fournier Forum, Guest!  
Login
Username :
Password :
In order to fully utilize the abilities of this board, you are required to register as a member. Registration is free, and allows you to do lots of things including turning on or off certain features of this board. Register now!
Forum Rules & Description
Who Can Read The Forum? Any registered user or guest
Who Can Post New Topics? Any registered user
Who Can Post Replies? Any registered user
Who Can Edit Posts? Any original author
Tips for maintaining Fournier Motor gliders
Currently Active Users: 87
There are currently 0 members and 87 guests on the boards. | Most users ever online was 822 on 08-01-2020 10:15 PM
Search This Forum
Search Keywords: Search From:
Powered by CuteCast v2.0 BETA 2
Copyright © 2001-2003 ArtsCore Studios