John's Build

[jrevens]

I'm hoping to get some feedback from the group... I'm trying to decide which mod. of air filters to use on my 912uls - I'm not using an airbox. I'm leaning towards the smaller (R-1060) filters shown on the left in the picture. I believe that these are the filters used on the 912uls powered Kitfoxes first, but then there is the larger RU-1400 (shown on the right) that Kitfox recommends now. Obviously, more surface area is good, but I like the looks & less crowded area with the smaller ones. How have the R-1060's worked out for those of you who use them? Has anyone switched over to the larger ones and noticed any difference in performance?

[Av8r3400]

I wish I could use the 1060s! IMO, I think they'll be fine for you, John.

I'm forced to use a 6" diameter x 2" wide flat ones because of the lack of room from the carbs to the firewall.

[DesertFox4]

John, the R-1060 smaller cone shaped ones work well. Desertfox1 has them on his 912 uls and I can attest it performs great and they do fit nice as you indicated. Haven't flown the other size yet so no help there. Sorry.

If you do decide on the smaller ones your Rotax will get along with them just fine. I have on occassions looked at them installed and thought to myself that they do appear to be somewhat proportionally small for a 100 hp engine. Yet they do work so there you go.

[gregsgt]

What about an RU2700?

That's what someone recommended for mine.

http://www.knfilters.com/mobile/mPro...x?prod=RU-2700

[Av8r3400]

Greg, I've considered those for my plane. At 2" tall they would fit between the carb and firewall, and give me more clearance for the throttle and enrichener cables…

I believe they would actually flow enough CFM to work just fine for an 80 or even 100 hp engine. K&N elements flow incredibly well for their size.

(Mine are the RA-0450)

[gregsgt]

I've got the RA-0450 on mine now and due to the size and mass of them they have to be safety wired and I have interference problems with the choke and throttle cables. I also think it would help to reduce to reduce leverage on the carb boots from the shaking of the carbs if I went with something smaller. I'm going to change over to the RU2700 filters.

[Dave S]

Jrevens,

I don't see where a person would have any trouble with the smaller K & N filter.....the hallmark of the brand is extremely low restriction to airflow.

I think you are correct that generally speaking, more surface area is better; although, making sure the filters are always clean should prevent any restriction issues even with a smaller filter. Our airplanes don't seem to gunk up filters anywhere near as much as cars do.

Also consider since there are two filters if you are not using the airbox, each filter only has to feed two cylinders - essentially half the airflow for each filter.

Rotax tech info indicates the Airbox, which most people do not use, is good for a 5 HP performance difference. To put it another way, a 912ULS is rated at 100 HP with the airbox and 95 hp without it. (The Rotax powered GOBOSH LSAs on our field were rated at 95HP without an airbox). Performance may be more related to the airbox than the filters.

In the end, making sure there is room to change out to the larger filters if a person wants to experiment with both might be a good idea.

Sincerely,

[jiott]

I agree that keeping the filters clean is the biggest concern here. A fresh clean filter even smaller than the R-1060 will probably work fine. If I were operating regularly in off-airport, dusty, dirt strips with buddies who like to roost you with their prop wash, then I would go with one of the larger filters to avoid cleaning it so often.

[Dick B in KY]

I use the R-1060's on my 912 ULS and have had no problems. Gives me clearance on cables, wires and motor mount. Have two sets and switch them out at inspection time after cleaning and re-oiling.

Dick B

[jrevens]

Thanks everyone... I like the R-1060's, & decided to use them. The surface area of one of these filters is actually greater than what I have for filtration on my 160 hp Lycoming, so I have no doubt that it is plenty adequate for 1/2 of a 912uls.

As an aside, I believe that the extra horsepower with an airbox is based on 2 issues - first, you can feed the engine fresh air, unheated by the engine compartment. Secondly, you can get some ram-air effect with an external air inlet or scoop. The same basic thing could be accomplished with a filtered flexible duct going to each carburetor separately, & then you would have to incorporate carb heat into the system. The Rotax airbox does all of that nicely, plus providing balanced air pressure to both carbs. I decided to forego the airbox because I just like the simplicity & lack of clutter with the simpler setup, & having "carb heat" all the time with a little reduction in power doesn't bother me in this instance.