912S Airbox

[carpat]

Could you guys indicate me if you are using the Airbox with your 912S? Is there enough room under the smooth cowl to install it?

Thanks,

Pat

[Dave S]

Hi Pat,

I am using the airbox on a smooth cowl series 7. also have the aux 40 amp alternator. See attached photo of both. The airbox comes with drip trays - although nothing has ever dripped into them. Everything fits under the cowl just fine. The airbox has some advantaged - the carbs are are absolutely not going to move since the airbox is clamped to the engine ring mount, the alternate air feature is good to have and can be routed to a heat muff for carb heat if a person wants to do that. Also - it is supposed to be good for 5 hp and over not having it.

Sincerely,

Dave s
KF 7 Trigear
912ULS Earp

[Dorsal]

Also using the airbox, connected the filter directly to the airbox, works well. There are some pictures of it in my album.

[War Eagle]

If my memory serves me right, the 912s airbox can only be installed on the Series 7 or later because that is when there was a design change made to the engine mounting which moved the engine forward several inches. This changed the CG and also provided the room to install the 912s airbox.

[Dave S]

John,

That is correct - certain versions of the Kitfox (earlier designs) placed the oil tank back-center of the engine, no room for the airbox on these. - If I recall the manifolds are also switched side to side on certain earlier kitfoxes and the carb inlets will no longer match up with the airbox outlet.

Sincerely,

Dave S

[hansedj]

That is correct our series 6 has no room for the airbox

[farmboy]

I just purchased a 6 with a 912, it has a aluminium racing air box. I do not know anything about these seems like most people have a air filter on each carb. What are the pros vs. cons are air boxes more likely to ice the carbs,affectfuel economy,performance? Should I leave it on or pull it. Thanks for the input!

[Dave S]

Farmboy,

Just curious....is the air box you have the Rotax design or is it of a different manufacturer/different design?

FYI...My comments earlier in this thread were in reference to the Rotax design and would not necessarily apply to a different design.

Sincerely,

Dave S

[farmboy]

Hi Dave, The manufacturer is aluminum racing it looks just like the Rotax box same design, it has two chamber doors on it I assume cold air and carb heat.

[Dave S]

If the airbox is essentially the same design as the Rotax, then it should have about the same characteristics.

1) It's presence is supposed to be good for 5 HP, allowing the engine to get to its rated 100 - check the Rotax specs for specifics on this. I have investigated a light sport aircraft call a "GOBOSH"....same engine, no airbox, POH rates the 100HP engine at 95hp, not 100. Supposedly the airbox does this by managing the airstream going into the carbs. It is also supposed to have an effect of optimizing efficiency to some degree.

2) On our 7, the airbox is connected via 2 1/2" scat tubing to the airfilter located in the NACA duct on the bottom of the cowl with the other opening covered with a screen under the cowl to serve as an alternate air source should the normal cold air pickup get plugged somehow (snowflakes plugging the filter for instance).

3) The airbox clamps up both carbs reducing the stress on the rubber seals to the intake runners and guarantees the carbs cannot pop out of their sockets.

If their is a negative, it is the few ounces of weight under the cowl and the fact that it takes up some space.

Mostly people do not put these in initially because of the cost; and, 912's historically do not seem to have any big issues with carb ice although I am sure it is possible to find the right circumstances to cause that if a person tries hard enough.

FWIW...on our 7, although the alternate under cowl air is probably a little warmer than the cold air intake, it is not enough to cause an RPM reduction like you get with carb heat when switched to alternate air. Never flown it without the airbox so I don't have any comparative performance data.



Sincerely,

Dave S

[Dorsal]

I also use the Rotax airbox and like the fact that it provides better support for the carbs. In my case I simply have the air filter clamped directly on the airbox with the carb-heat wired shut.

[farmboy]

Dorsal mine is wired shut also thanks for the info Boys.