PDA

View Full Version : Bing compensation hose



HansLab
12-31-2011, 06:20 AM
All,

There is a little hose for adjustment of pressure within the Bing carburettors.
From Jabiru (wich also uses Bing) I learned that this compensation hose should be carefully atached to the airbox - thus having the same air(pressure) as the carburettor.
Now I see all kinds of KitFox / Rotax combinations - with the hose just hanging down the Bing...
Shouldn't it be apropriate to atach this compensation to the KF airbox, let's say underside? in that position it would povide the same air (pressure) to the carb's and would not be bothered by over-pressure (as I guess it would by installing it to the backside of the box)

What do YOU think?

And of course a very safe, healthy, flyable NewYear to you and yours.

Dave S
12-31-2011, 09:06 AM
Hi Hans,

Happy new year to you also.

You will see installation variations primarily because a lot, I am guessing the majority, of rotax installations do not utilize the airbox. The earlier series KF with the 912 could not use the airbox because of the combination with the engine mount and oil tank location. Many people do not use the airbox anyway because the engine works just fine with the intake air going directly into the carb through the carb mounted filters. Then there is the cost and a little added weight. I am not familiar with bing carbs on Jabiru engines. There are light sport aircraft sold in the US that do not have the airbox with their rotax engines and I am guessing they have dangling compensation hoses also.

Ultimately the aircraft builder has responsibility for working out his/her combination of engine/airframe, etc.

The compensation hoses, if not connected to an intake plenum (Airbox) need to be open to a volume of air which has the same static pressure as the carb air intake. That is likely what what is happening if the compensation hoses are dangling near the air intake off the carb but not in the airstream going into the carb - air under the back of the cowl should be about all the same static pressure provided the compensation hoses are not aligned with an airflow which pressurizes or reduces pressure on the opening to the compensation hoses.

If a person has the airbox - the compensation hoses have to be hooked up to the airbox to assure balance as the static pressure within the airbox is not likely to be identical to under cowl static pressure.

There are probably two gold standards out there - 1) studying the engine manufacturer's installation guide (Rotax or Jabiru Installation Guided); and, 2) observations and experience (which is why we are called "experimental").

The compensation hoses are really not very different from what we had on cars in the old carbureted days:cool: - although they just had a hole drilled in the top of the carb or a vent behind the airfilter - basically what the "compensation" does is keep the fuel level in the float bowl even by equalizing the static pressure on top of the fuel in the float bowl with the static pressure on intake end of the carb.

Cheers,

Dave S
KF7 Trigear
912ULS (with airbox) Warp
St Paul, MN, USA

kitfox2009
12-31-2011, 03:24 PM
I believe we have had this discussion here before, but if you go to the Rotax-Owners blog or forum it is being thoroughly discussed right now. I have mine routed to the rear of the air filters. Replaced the hoses with longer ones and drilled snug fit holes in the black plastic/rubber ends of the filters. The hoses project about 1/2" inside the filters. Been running that way now for over 80 hours. Seems to work well.
Cheers
Don