K & N Air Filters

[GAHorn]

George,
The cost issue will not be as big a factor since I'm going to have to buy a complete assembly any way.
Randal

The K&N set up costs $131 The Brackett set up costs $38. (Remember that shipping and A&P-IA sign-offs will cost additional for either.)

[GAHorn]

Update: The K & N now costs $205 initially, plus $23.85 conversion kit, plus $14.95 for "sealing grease" and $9.95 for a "gasket kit".
I'm still keeping my $8 Brackett. It's easier to throw away $8 each annual and be done with it than to deal with K & N servicing kits and instructions, and I'm convinced the Brackett protects my engine better. (The Brackett AD is not applicable to units mfr'd after '96.)

An excellent treatise on the Brackett is offered by them at:
http://www.brackettaerofilters.com/HOMEBLD.pdf

[Dave]

When I rebuilt my 170 in 88 I threw away the original cessna paper filter as it just fell apart and replaced it with the Brackett, the latest and greatest. Some "old boys" told me later that there is a definate and documented loss of airflow with the Brackett foam filter.
Mine was subject to the AD and always seemed to be coated with dirt and bugs just from being parked outside and it seemed like a pain to buy the elements year after year.
I switched to the K&N about 2 years ago. It was $126 and well worth it. There is an increase in static and takeoff RPM (very useful) and it does not attract the dirt at all like the Brackett. No installation kit was necessary, it fit right on with no changes. The Challenger cleaning (recharge) kit is available at the local hardware store for $13. It is very important to clean it exactly as the instructions say.
The first thing I noticed was that the increased airflow made the carb heat control start moving out and I had to increase the lever tension.
Also these same K&N filters, known as "inlet barrier filters" and marketed by "AFS" (aircraft filtration systems) are replacing most existing helicopter inlet filter systems including the Centrisep particle seperators.
They use the same recharge system except, of course, a much greater amount of fluid.
So far I'm very happy with the system. If I kept the plane in a hangar I probably would have stayed with the Brackett but thats not the case and the K&N is much better for my location.

[russfarris]

This is only my experience, but a few years ago I was considering getting the K & N filter.

As an experiment, I did a post-flight full throttle static run-up - using an electronic tach, I got 2,260 RPM, at 650 asl and 60 degrees F, as close to a standard day as I could get. I then completely removed the Brackett filter element, and performed another static run-up. Results? Exactly 2,260
RPM.

I decided to save my money, of course my airplane is lucky enough to live in a hangar, so I don't have the issues Dave had.

Dave, can you recall how much of an RPM increase you noticed switching to the K & N? Russ Farris

[Dave]

The RPM increase was about 3-5 rpm. Not a whole lot but enough to notice the difference. I had been starting to think I should have been getting quite a bit more until I watched another 170's tach on take off. There sure isn't any excess power with the standard prop-engine combination although they always seem to have no problem getting off the ground in most situations, hot/cold weather or higher altitude strips.
Maybe theres a luck factor involved!
Dave

[russfarris]

The RPM increase was about 3-5 rpm. Not a whole lot but enough to notice the difference. I had been starting to think I should have been getting quite a bit more until I watched another 170's tach on take off. There sure isn't any excess power with the standard prop-engine combination although they always seem to have no problem getting off the ground in most situations, hot/cold weather or higher altitude strips.
Maybe theres a luck factor involved!
Dave

Hi Dave, you must have a pretty fancy tach to register a 3 to 5 RPM increase! My electronic tach (designed for R/C model use) rounds off to 10, maybe you meant 30 to 50 RPM. I don't think even Bob Hoover would notice a 3 to 5 RPM increase on take-off!

170s are: 1. Classic airplanes 2. Beautiful to look at, and 3. Excellent handling. Over-powered they ain't! The limitations of a fixed-pitch prop are inherent; with a constant-speed prop the 2,700 RPM limit (or close to it) would be obtained during take-off. I've never flown a 170 with the O-360, but even a O-320 ( 150 hp) with a C-S prop would be quite an improvement.

Russ Farris

[Dave]

Hi Russ
I think your right, 30-50 rpm. I took some digital photos of the filter on the Bell 407 and will post them for interest once I figure out how to get them on here. It's almost identical but about 10x the size. It also has a motorized bypass door and pressure differential sensor. By the way the K&N recharge kits are on sale at Canadian Tire for just over $11.
Dave

[GAHorn]

It's pretty much a matter of physics that if you compare two clean filters of similar area (such as the Brackett and K&N) that the one with less restriction is a worse filter. The one with less restriction is not filtering air as well.
Other than fuel , your engine consumes mostly air. Dirty air can reduce your engine to a need for overhaul in very few hours. (As little as 75-150 hrs. according to some sources.)

The Brackett is designed to meet the hp output of the engine (and this can be verified by the static rpm test.) If your Brackett gets dirty...it's saving your engine. Replace it. ($8 bucks. Cheap.) If your airplane is stored outdoors, cover it up. Cardboard and tape will do it.

At any rate, there's simply no way one filter can trap smaller particles more effectively than another filter without also reducing air flow, unless a greater surface area is allowed. The surface area of our intakes is pretty much a fixed dimension, so it comes down to either a pleated filter or a foam filter. Would you believe a foam filter usually has greater surface area?

[russfarris]

Since the subject is air filters...nowhere in Part 43 covering owner preventative maintenance can I find where it is legal to change and sign off an air filter of any description by the owner/pilot!

Am I wrong on this, George? Russ Farris

[GAHorn]

FAR 43, Appdx A, (c)" Preventive Maintenance (23) Cleaning or replacing fuel and oil strainers or filter elements." does not appear to include air/induction filters.

However para. (30) (ii) does define/state preventive maintenance those items that were included in the STC approval process as "preventive maintenance". So the answer might lie in whether or not the air filter STC instructions/paperwork includes replacement/servicing as "preventive maintenance".

Re: the Bracket filters again,...one reason some folks feel the Brackett filter excessively reduces MP is failure to follow installation instructions which require the installer to "squeeze excess wettant" from the filter before installation. A simple way to do this is wrap it in a paper towel and squeeze the heck out of it, removing all excess wettant. That's the way it was intended to be installed...without all that extra goop it was packaged with.

[Bruce Fenstermacher]

FAR 43, Appdx A, (c)" Preventive Maintenance (23) Cleaning or replacing fuel and oil strainers or filter elements." does not appear to include air/induction filters.

George as with many things I think this can be read differently. Since it doesn't specifically say you can't replace "induction filter elements" I take it to mean we can replace the induction filter as that is part of the total fuel system of the aircraft.

When I look at these regulations that aren't specific I try to reason what the intent of the FAR was. I don't think because it is in black and white, that we will argue we are allowed to disassemble the fuel system in order to change the fuel strainer or filter nor will we argue that we are allowed to change the oil filter or dissassemble and clean the oil screens.

In other words the FARs are written to allow the pilot to do routine maintenance that if not done could result in power loss or engine failure. Changing an induction filter element is a simple proceedure and for the most part less complex than the changing a fuel or oil strainer or filter element.

I personally feel comfortable changing my filter under FAR 43, Appndx A.

The danger in my thinking is when people stretch the logic to unreasonable proportions. After all if we are allowed to change the fuel and oil strainers or filter elements both of which if completed incorrectly can cause power loss and perhaps a crash, then why can't we also remove and reinstall a wing. If done incorrectly the crash from the wing maintenance is still a crash the same as from a power loss.

And what is unreasonable? I think it's this much. => |_____|<=

[GAHorn]

I believe the regulation is very specific, and should be taken exactly "as read". (I don't agree with it,...but I believe it's very specific on this subject, that air filters are not included as preventive maintenance.)

Using the logic you suggest, Bruce (and I don't take issue with the relative complexity of the task...you and I agree on that....but just following the rules) ... changing tires and/or greasing wheel bearings on an aircraft equipped with Cleveland or McCauley brakes would include brake replacement as preventive mx, as it entails removing/replacing the brakes. But brake replacements are specifically NOT included as preventive maintenance.

Sorry... but I'm afraid I cannot agree that air filter replacement is included in the preventive mx addressed by FAR 43, appdx A. (Also the replacement of ELT batteries is NOT preventive mx either, according to the SAT FSDO. The rule allows aircraft MAIN battery replacement, however.)

[jrenwick]

FAR 43, Appdx A, (c)" Preventive Maintenance (23) Cleaning or replacing fuel and oil strainers or filter elements." does not appear to include air/induction filters.

George as with many things I think this can be read differently. Since it doesn't specifically say you can't replace "induction filter elements" I take it to mean we can replace the induction filter as that is part of the total fuel system of the aircraft....

Sorry, Bruce, you're stretching the meaning too far here. From AC 43-12a, final paragraph (emphasis is mine):

Items 6 and 23 (Part 43, Appendix A, paragraph (c)). These items permit the draining and reservicing of oil, and the removal, cleaning and reinstallation of oil screens, filters, and strainers in an aircraft oil system to be done as preventive maintenance, and are subject to the provisions of Sections 43.13(a) and (b).

"We don't have to make sense; we're the government."

The list of preventive maintenance items in part 43 Appendix A smells to me like the result of a negotiation between two opposing interests: mechanics, who might feel uncomfortable signing the log books of an aircraft that was worked on by anyone other than a licensed mechanic, and owners, who quite reasonably think they should be able to do simple, ordinary tasks on their own aircraft (and who are going to go ahead and do them anyway, ahem!). It's a compromise, and sensibleness usually loses out in these things.

Best Regards,

John

[jrenwick]

... (Also the replacement of ELT batteries is NOT preventive mx either, according to the SAT FSDO....

George, you should remind the FSDO of AC 91-44A, section 8(a) on battery replacement. It says a pilot can replace ELT batteries if removing and reinstalling the ELT is a simple installation. The forum already has a much more exhaustive thread on this, so I won't go into it.

Best Regards,

John

[GAHorn]

Yeah, I've been there with them, John. The problem arises when the ELT is located in a compartment aft of the baggage bulkhead requiring removal of that bulkhead (like most permanent installations), and also of the need to disassemble some models of ELT's to gain access to the battery compartment.
In general, unless the ELT is located within the cockpit/cabin of the aircraft, and unless no tools are required to gain access to the battery compartment, it's considered a complex operation.

...George, you should remind the FSDO of AC 91-44A, section 8(a) on battery replacement. It says a pilot can replace ELT batteries if removing and reinstalling the ELT is a simple installation. The forum already has a much more exhaustive thread on this, so I won't go into it. Best Regards, John

Re: AC 91.44A section 8(a) does NOT APPLY to Part 91 operators: This specifies that a FAR 135 operator may train his pilots to replace ELT batteries. Quote:"The replacement can be done by the pilot if the preventive maintenance limitations of Part 43.3(h) of the FAR, are complied with." (FAR 43.3(h) pertains only to FAR 135 (air taxi/commercial) operators.)

(And get this! If your ELT uses the DuraCells... just because the DuraCells you installed two years ago (2005) has expiration dates of 2010... doesn't mean you can wait until 2010 to replace them....they must still be replaced annually with fresh batteries, and IAW 91.207 (d) the ELT must still be tested and recertified annually. This according to SAT FSDO.)