Airbox to Carb Duct

Hi Sean,

"Does Rotax have a recommended Airbox to Carburettor flexible duct?"

Not as far as I know. The IPC shows P/N 860985 between the Rotax airbox and the carbs, but I wouldn't call it a flexible duct as such, more a short rubber tube.

"Is the duct ID 51mm / 2 1/64"?"

Either 51 mm or 2 in (50.8 mm) ducting will fit.

"What have you used (SCAT, SCEET, or something else)?"

My aircraft's manufacturer specified 2 inch SCAT hose in their manual (780 mm of it on each carby!) and it works well enough, but be aware that Thermoid does not specify a vacuum rating for SCAT/SCEET ducting and in fact specifically states that it shouldn't be used for negative pressure applications. There are alternatives available which do specify a vacuum rating - and interestingly the SCEET lookalike is rated to a higher vacuum than the SCAT lookalike.

I see multiple ways Mfg's have ducted their air filters boxes. They use Sceet and Scat. I usually see 2.5" to 3" hose. You don't want too small a tubing because you want full and free intake air flow and you don't want any restrictions.

SCAT and SCEET are both silicone and suitable for use forward of the firewall.  SCAT is single wall, and SCEET is double wall (lined). The liner in SCEET gives it a bit better airflow, but there is a concern that when used for induction air, the liner could come loose and block the airflow or be sucked into the engine. This is why most often you see SCAT used for induction air applications, when a molded tube is not available. 

Hi Roger,

"I usually see 2.5" to 3" hose. "

Are you referring to length or ID ? Perhaps you are referring to the fresh air inlet - I am after the airbox to carburettor details.

My 912 ULS has a 2" flange as does my airbox.😈

Hi Sean,

Just use your 2" tubing and that should be fine. Like I said I see both Scat and Sceet tubing and it just depends on the Mfg or owner. I have never seen any issues with either at my shop.

I see this multiple ways. From the airbox to the carb I see maybe 2" up to 3" like in a Flight Design. Flight Design added a 3" adapter to the carb and their airbox has a 3" outlet.  No air shortage there. Others I see use whatever the airbox outlet is up to the carb. Then I see K&N air filters right on the end of  each carb. I don't like this because of all the hot air the carb gets vs outside cooler air that may come in from a NACA vent  or a 2.5" from a separate air filter box to the Rotax aluminum airbox.