912is Sport Cold Air Intake

[rocketman2tm]

Here is some data that this group might be interested in.

I have always figured that the location of the air intake on the 912is is not in an ideal location in a cowled airplane. Putting the intake behind two air cooled cylinders definitely heats the air up some, but I wanted to get some data to know how much. My dad and I installed two thermocouples on the plane; one on the outside of the plane at the wing root and the other right in front of the air filter. I figured if the temperatures were 30 degrees above ambient, it might be worth putting in a cold air intake. They were over 70.

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Granted, this was only during climb out but that is when full power is needed. Cruise resulted in much lower temperatures. Doing a density altitude calculation my engine is performing as though it is almost a mile higher than the rest of the airplane. At this point it seemed like it was worth pursuing a cold air intake.

I installed the naca side duct that Kitfox sells. I originally installed this with skeet tubing and immediately knew this is not the long term solution.

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So I decided to make my own ducting. I 3D printed some parts out of PVA and tacked them together with super glue. Instead of doing fancy measurements, it was much easier to just trim the parts to length and then figure out the angle while holding the part up to the airplane.

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Once the PVA part was complete, I fiberglassed over it. Once the fiberglass was cured I threw the part in a bucket of water for a couple days. PVA is water soluble so after a few days I was left with just the fiberglass part. Below is a picture of the finished installation. Not Mike Patey worthy, but I'm happy how it turned out.

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So the moment of truth - What are the results? Without touching the prop and flying on days that are similar temperature and density altitude I am finding that my RPM is about 250 to 300 RPM more than what it was without the cold air intake. My climb out RPM is back in the yellow.

[avidflyer]

I wonder how much this will make you likely to have carb icing issues. Not saying it will, just wondering. It does look nice though for sure. JImChuk

[jiott]

Isn't the 912is fuel injected? No carbs.

[Eric Page]

Very good intel, John. I'm putting a 912iS in my plane, so this will be something to look at when I'm working on the cowling. Thanks for that post!

[avidflyer]

Isn't the 912is fuel injected? No carbs.


Opps, I should have read the title better. How do I delete my post??? :-()

[efwd]

Greatly appreciated John. I have been considering doing this. I find that I just like to fly the thing these days and although I have things I would like to do, it means grounding it for mods. Where is your Air Filter now?

[rocketman2tm]

I know the feeling Eddie. The air filter is inside the side NACA duct. I also mounted the MAAP sensor (don't remember the exact abbreviation off the top of my head) in there with it. That way the ECU knows the engine is breathing cooler air as well.

[Dusterpilot]

Do you have an air filter?

[rocketman2tm]

Yes, the stock rotax 912is sport air filter is located in the side NACA intake. I believe the 915 has the filter located in the side NACA as well.

[Danilo]

What kind of climb performance are you seeing with your 912iS? about to pull the trigger on this engine but I read recently that if you are close to gross weight climb performance is about 300pfm...if that.

[rocketman2tm]

I'm not sure that I've ever seen it quite that low. 500 fpm is probably the lowest I've seen it at gross on a hot day. Keep in mind though that there are not a lot of mountains in southeast Wisconsin where I fly.

On a cold day when I'm by myself, I've seen well over 1600 fpm.

[Danilo]

Thanks! This is what I was hoping to hear!

[Eric Page]

Alex (@alexM) and I flew a 912iS powered Kitfox recently in the western Rockies of Colorado. I don't recall exact numbers, but performance was perfectly acceptable climbing out of Montrose with OAT in the mid-40s. We got the plane up to 12,300' MSL before it ran out of steam. This was with two grown men, nearly full fuel and ~30lbs of baggage. The plane has a 3-blade fixed prop; not sure of brand.

[Danilo]

Thanks Eric! I was just a bit concerned as I'm about ready to pull the trigger on the motor for my kf7 and I saw a video from 7Kilofox on youtube where he mentions his STI not being a very good climber when at gross (he mentions something like 300FPM...) He's at sea level but I can see the humidity and temps in Florida where he's at be an issue.
My Model 7 has the standard wing but similar bushgear landing gear setup as his.

[Eric Page]

The airplane we were flying has Shock Monster gear, 29" tires and no wing strut fairings, so pretty much as draggy as a Kitfox gets.

Keep in mind that 7kilofox also flies a Cessna 210, so his standards for airplane performance may be somewhat skewed.

[Danilo]

Excellent! I'm also on shock monsters and 29's with no fairings yet. This makes me feel much better and confident about the 912iS

[Jcard]

Did the lift strut fairings, covered the gear legs with leading and trailing edges, fairings on the shockmonster shocks.
Went from 90 to 105 cruise, less map and 7 gallons per hour to 6

[Danilo]

What engine are you running that was burning 7gph? got any pics of the fairings for the shockmonster?

[Jcard]

Couple pictures. rotax 912ULS with aftermarket fuel injection and turbo.

[Danilo]

Wow, those shockmonster fairings are beautiful! What wing do you have?

[tracstarr]

I'm curious if the intake box has holes in the bottom to release the increased air pressure (if there were none) from constantly having the rammed in there from the naca duct. If there is increased pressure wouldn't that be akin to flying with higher air density than the altitude you are at and possibly improving performance?

[Geek]

Nope. No holes in the bottom of the Kitfox intake duct.

G

[rv9ralph]

constantly having the rammed in there from the naca duct.

NACA ducts are not ram air. Ramp type inlets are intended to draw air without disturbing the boundary layer. In other words, if more air is entering the NACA duct than needed, the remaining air will flow past without slowing down.

[tracstarr]

NACA ducts are not ram air. Ramp type inlets are intended to draw air without disturbing the boundary layer. In other words, if more air is entering the NACA duct than needed, the remaining air will flow past without slowing down.

Interesting. I obviously didn't know that.

[tracstarr]

Finished up my intake today. I was going to order from Kitfox directly but it was 8 week plus wait. Instead I just went at it myself. Attached a few pictures of the install. I ground tested it today with good results. With an outside air temp of around 32C today I would normally have intake temps reaching 56C and not be able to fly or get them to come down on the ground. Today I was happy to find I was getting a max reading of 40C. Even after 20 min of doing full run up and a few full power aborted take-offs that was the max. Now, I'm not fully happy with the sensor location. I put it in the same spot as Kitfox suggests... back of the intake box. It's reading the temp at the filter. After shut down and pulling the cowling I found the tube leading from the filter to the intake was very hot from the radiant heat so likely the temps were higher as they entered. I'm thinking of testing with the sensor installed closer in the tube. I'll have to make a bracket for this. The other option might be to make a heat shield as well?

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