K & N Air Filters

Stan_Lindholm · Post by **Stan_Lindholm** » Fri Oct 01, 2004 1:14 pm

The other day I got a mailing from Challenger Aviation advertising their air filter, which is now apparently approved for our airplanes.

Anyone had any experience with their filters? Any discernible difference in power? Any other comments good or bad?

n3410c · Post by **n3410c** » Fri Oct 01, 2004 1:55 pm

I just received one and installing it for my 170 now. I haven't had a chance to run it but will surely pass on the information when I do. I know others who have changed them out on 185's and think it is one of the better modifications they have done.

Post by **GAHorn** » Fri Oct 01, 2004 2:43 pm

Air filters are a compromise. Too efficient and they reduce manifold pressure with a constantly downward trend as they accumulate dirt....too inefficient and they don't trap much dirt.
The original Cessna filters were either paper (which became water-logged in rain and resulted in a loss of power when perhaps the pilot needed some climb/manuevering capability) and were serviced by reverse-compressed air or discarded/replaced,....or they were a "flocked" wire-screen which were to be serviced by washing in solvent and re-oiling with engine oil. Eventually the flocking would be deteriorated to the point it was largely just a wire-screen and had to be replaced. The service interval was normally 25 hours for both types.

The most popular alternative has been the Brackett filters which are synthetic foam blocks held in a dedicated metal frame and which exactly replaces the factory original filters. When the Brackett is sufficiently contaminated it is simply thrown away and a new one installed. They normally last about a year, and are not user-reserviced except for replacement. (Cost: about $8 for replacement filters.) Like all filters, they carry a disclaimer when used under extremely "dusty" conditions.

Aviation Consumer ran a test on airfilters a few years back. The K&N was regarded as well-made but less capable of catching dirt than the Brackett, and more easily clogged to the point of reducing engine power by similar amounts of dirt.

I've personally nearly lost complete power using a paper filter on a C-150 while in rain when it became water-logged on a pipeline patrol, and subsequently another pilot flying the same airplane with the same type paper filter did indeed have to set it down in a swamp when he encountered a rain squall. The airplane was a total loss but he got out OK.

I've got a Brackett on my airplane and change it at annual inspection. I like it, and have had no problems. (Just remember to wring it out of excess adherent (sticky stuff) when you first install it. They come overserviced with that stuff for long shelf life.)

N1478D · Post by **N1478D** » Fri Oct 01, 2004 3:05 pm

IMHO, a year is way too long to change out a Brackett filter. Guess if you only flew it 15 hours a year it might be ok. I try to change my air filter out each quarter, sooner if I get into a dusty condition. It's so cheap compared to the damage that can be done by allowing dirt in to your engine. The same with engine oil, I change it every 20 hours, or 90 days, which ever happens first. Oil is cheap, but it is a hassle to remove the cowling every 30 days in these good flying months.

Post by **GAHorn** » Fri Oct 01, 2004 3:41 pm

Their website did not state approval for the 170 series, so I called and talked to them. (937-667-0510) Here's what I found out:
Their latest filter is not the K&N paper unit,... it's a K&N "surgical gauze and wire" and is STC'd for the 170, all series. (Remember to have your A&P-IA submit the Form 337 and logbook entry.)
It is their PN CP1172 and costs $112, plus shipping. This does not include the necessary installation kit, which is PN CP3274 and costs another $19.85. The filter requires 100 hour/annual service as a minimum (more often under dusty condiitons) and the required service kit with necessary materials is an additional $10 plus shipping. The filter is expected to last 25 cleanings before it must be completely replaced.
The sales commentary included "It's just like not having a filter" (presumeably in reference to air flow) and "my husband says it gives 2 to 3 percent more horsepower" and "our customers says it saves them fuel".
The units may be ordered either directly or through aviation suppliers. It was repeatedly said that prices "may increase at any time".
Their website http://www.challengeraviation.com/ has some anecdotal testimonials.

As a comparison, the Brackett complete assembly is $38.25 including installation materials, and replacement elements are $6.50 from Aircraft Spruce.

Disregarding performance claims, the Challenger/K&N filter will become as cost effective as the Brackett in about 20 years/2000 hours if annual/100 hr replacements are followed.

Post by **GAHorn** » Fri Oct 01, 2004 6:15 pm

I have now rec'd an email from Challenger which also states that aircraft of low utilization must have their Challenger/K&N filters replaced every 5 years as a minimum.

Fri Oct 01, 2004 11:59 pm

Holy Smoke George your all over this filter thing. Only problem is you went ahead and pointed out that the economics of the filter may not be that good. Should have talked a few of the speed deprived straight wing A model drivers into buying and testing them for us dihedrally enhanced folks. Then spilled the beans on the economics afterwards

n4517c · Post by **n4517c** » Sat Oct 02, 2004 1:21 am

I installed the K and N filter and saw and increase in RPM at the same airspeed during climb out, as opposed to the brackett. The K and N filter did rub on my cowling after flight, but an examination of the removed brackett showed that it did as well. I called Challenger and told them of the situation and received no response. A slight trimming of the cowling will solve that situation. The construction of the K and N is first class. and as all car racing types know, they have a great track record. K and N claims about 30% more airflow through the filter. Time will tell.

R COLLINS · Post by **R COLLINS** » Sat Oct 02, 2004 2:40 am

The K&N was regarded as well-made but less capable of catching dirt than the Brackett, and more easily clogged to the point of reducing engine power by similar amounts of dirt.

This defies the law of physics. It would appear that a filter that became clogged more easily than another filter when subjected to the same amount of dirt is in fact catching more dirt. What am I missing here? Did the K&N filter only catch dirt in one layer in turn causing a barrier to air flow where as the Brackett filter caught dirt over the span of the filter in a way that still permitted a better air flow. George do you still have the article from Aviation Consumer to elaberate on these tests?
Randal

Post by **GAHorn** » Sat Oct 02, 2004 3:44 pm

I do not have the article any longer (regretfully) and was relying on memory. I agree, the manner in which I stated the test results is poorly worded. The test results (as I remember them) were that the K&N paper filter was overwhelmed by dirt sooner than the Brackett by similar amounts. I believe it was a capacity thing. The K&N paper media allowed higher airflow because it had larger spaces between it's fibers, and therefore allowed more dirt (small pieces) through to the engine, ...but the larger particles which were caught remained on the surface of the element and soon reduced airflow. The Brackett design theory was that dirt was captured throughout the depth of the foam media and was capable of holding more grams of dirt of all sizes. The Brackett did not flow as well as the K&N paper filter when both were new, but it did better after both had been subjected to dirt.
The new Challenger filter (K&N) approved for the 170 is not the same paper filter as previously tested. The new filter is a "surgical gauze and wire screen" filter.
As for testimonials, I get an increase in performance when I install a new Brackett as opposed to my old Brackett. Is it possible that performance claims do not take into account that the filter being replaced was worn out?
What does it say about a filter's capability if it alows greater airflow than a competing design (when both are new?) Is the competing design more restrictive because it better filters the air? Or is the new filter's design actually filtering the air less efficiently?
Any filter will reduce air flow or it isn't filtering, in my opinion. The best filter is the one which captures quantities/particle sizes of dirt which are largely responsible for potential engine damage without excessive reduction in air flow (and therefore allows less damaging particles to pass.) The filter must also have sufficient surface area to allow it to hold the amount of dirt that is expected to be captured between service periods. It's a compromise that competes with the "which oil brand is best" arguments I think.
If I were "king" of the filter forest I'd design a filter similar to the Brackett that could be washed, re-oiled and reused. It wouldn't require expensive "service kits" or special oil, and would be easily owner-serviced and therefore inexpensive. It would sell so cheaply that I'd make no money on it and would soon go out of business from threats of law suits, and everyone would have to scramble to find a more expensive replacement and bad mouth me.

Of course, aircraft typically operate on the ground only briefly and dirt isn't much of a problem above 2K feet AGL or so. Mooney even had a by-pass feature that allowed ram-recovery effect on some models. It gave about 1" increase in M.P. as I experienced it in cruise. There was no reduction requirement in TBO for by-passing the filter.
Since I already have the Brackett I'll keep on replacing it for $6.50 a pop and live with it. If you're someone who enjoys the "challenge" of extracting every last bit of performance regardless of initial cost, and if you fly 500 hours per year or more, then I'd think the Challenger might be a viable product despite it's 5-year life limitation. (Cleaning each 100 hours for the maximum 25 cleanings allowed, equals 2500 hours, divided by the 5-year limitation equals 500 hours per year necessary to obtain maximum benefit of the filter within it's restricitons, and adds $40 to the cost of cleaning materials.) If their claims are truthful then fuel savings might pay for itself.
Of course, if one were to start with a new engine, then it'd be overhauled at the 1800 hour TBO, and no one would likely start a new overhaul off with an old filter, so the old filter would go into the trash and the initial investment would have to start completely over again, and cost savings would go out the window. IMHO

jrenwick · Post by **jrenwick** » Sat Oct 02, 2004 4:54 pm

The Challenger web site says "From the drag strip to the air strip...." If you're racing, aren't you willing to rebuild your engine frequently if it gives you a winning edge? I'm not racing my airplane, I'm going for maximum engine life between overhauls. I'm willing to sacrifice some airflow to catch more dirt. YMMV

Best Regards,

John

n4517c · Post by **n4517c** » Sun Oct 03, 2004 12:18 am

One thing I'm learning about the people on this site is that they have different priorites, which is logical. I've never been focused on whether my engine went 1300 hours or 1500 or 1800 hours. Frankly, I've treated several engines in the same manner and some have done much better than others, for no reason that I've figured out. We built them up the same way.
The majority of my flying time has involved hauling fisherman in a floatplane from the sporting camp, we once owned, to remote small ponds for the day and returning them at night. All of the ponds were within 5 miles of the camp and all required a climb of 1500 feet at full power from the camps and a descent of 1500 feet at the other end of the flight. Doing this every day during the summer season 6 to 10 times in the morning and the same at night, I never lost a cylinder in my supercub during a 6 year period. However, I certainly cared about performance because that extra 50 feet over the trees feels good!
I've always flown simple airplanes and usually check only two things on takeoff, oil pressure and RPM. If you fly your plane daily, and know how RPM changes with weather, one glance says your OK. I've never seen Brackett filters decay in RPM over time, within the accuracy of the gage, in my type of flying. I now fly my 170B out of short gravel and grass strips. When I swithched to the K and N filter and saw more RPM on climb out and more clearance over the trees; that felt good! The Brackett filter did not give me a great margin when it was new, and then slowly decline, it never had the better performance to begin with.
By the way, many take off contests have been won by the guy that removed the Brackett filter for the race. Obviously these comments do not mean much if you live in the desert.

jrenwick · Post by **jrenwick** » Sun Oct 03, 2004 1:33 am

Well, that's a good point. An air cleaner that breathes better might be right for operating on skis in the winter, when the dust level is down anyway.

John

R COLLINS · Post by **R COLLINS** » Sun Oct 03, 2004 3:26 am

George,
I understand your points about the cost issue and what is best for the longevity of our engines but thats not apples to apples if you posted a report from the paper filter design consumer report. I would still like to see how this new filter design performs against the Brackett filter. My plane presently has the Brackett assembly that has to be changed at the next service interval due to AD. The cost issue will not be as big a factor since I'm going to have to buy a complete assembly any way.
Randal

Jr.CubBuilder · Post by **Jr.CubBuilder** » Tue Oct 05, 2004 6:52 pm

Here're a couple points I'll throw out. At full throttle with no filter installed a motor will only pull a set volume of air over time at any specific density altitude. A good filter should be of sufficient size to support the volume of air that the motor will draw at maximum power. Beyond that aditional area will enable the filter to hold more dirt.

I've never seen a K&N gauze type filter on a dirt bike, they are available, none of the riders I've met over the years will use one because they don't hold as much dirt before they begin to choke the motor. They also get water-logged, not as bad as a paper filter would but bad enough to choke the motor and ruin your ride. Look at just about any dirt bike air filter and it's an oil impregnated foam filter just like a brackett.

That second problem is what makes me hesitant to put a K&N on my plane, although more power would always be nice. How hard would it be to get a filter bypass STC'd? It would be nice to be able to get straight ram air once off the ground and at higher altitudes. Then again I like simplicity.