The International Cessna^® 170 Association

Yesterday's online aviation newsletter (didn't want to name them or give them unwarranted promotion because of their sorry video-feed and editorials) ... offered a Boeing video showing the 747-8 performing certification rejected takeoff/braking tests with brakes deliberately worn beyond limits.
Essentially they removed all the brake lining material and performed a rejected takeoff using maximum-effort braking without thrust-reverse and proudly (justifiably) announced the airplane did better than expected. The brakes overheated to the point of becoming incandescent... the fusible-plugs in the wheels did their job and deflated the tires after overheating (to prevent tire-explosions).

Anyway... it caused me to remember way back in my youthful exuberance to rent a C-175 which belonged to an A&P mechanic (which should have been a warning-sign) and it did fine taxying out (not much use of brakes) but when we landed..... the brake pressure was firm... felt just fine.... but there was NO STOPPING going on! I made an comment <expletive deleted> and the guy in the right seat joined me on the brakes and we all but pushed those brake-pedals thru the firewall.... but NO STOPPING occured!
It gave the impression the airplane had actually increased it's speed!
A last minute kick of the rudder steered us away from the ditch on the right side, and re-directed our headlong course towards the trees at the far end rapidly approaching...and the fat woman in the back seat assisted as I pulled full-aft on the yoke and dragged the tail tie-down ring in the dirt as the belly of the airplane presented itself to a pile of rocks which had been cleared off the runway years earlier, but left at the far-left corner of the field.
Just as the nose-tire touched the pile of boulders the airplane dragged to a stop with the only damage being to put a crack in the fiberglass nosegear fairing.
When I called the mechanic/owner of the airplane he remarked to me "Yeah, I've been meaning to replace the brake pads on that thing...they're probably bare metal by now...I just haven't got around to it."

My point is that just because Boeings might stop with worn out brakes...I can tell you from experience that Cessnas do not...in fact.... they accelerate!

That was back in 1970 and ever since, whenever I've rented or borrowed someone elses airplane....I get down on my knees and actually inspect the brake linings. Clevelands should have at least 1/10th inch of lining visible, or they are not serviceable.
Rapco (brand) brake linings have a "wear indicator" groove mfr'd into their ends, so that a pre-flight inspection of the brake lining is simplified. When the groove is no longer visible...it's time for replacement.

Just out of curiousity, how long was the runway you were landing on and how fast were you when you touched down?

The primary items I check/inspect during the preflight of a tail dragger are the tail wheel tire pressure, tail wheel leave springs and chains, and the brakes. A lesson I learned the hard way. Shortly after purchasing my Champ I flew it, with a group of friends in J-3s, to the San Juan Islands. Every other landing in the Champ resulted in a ground loop - slow, harmless ground loops but embarrassing non-the-less. I figured the cause of the ground loops was me. After returning home and doing some reading, I lifted the tail and took a good look at the tail wheel leaf spring. I discovered the leaf spring was loose in the shackle allowing the spring to twist 45 degrees one way and the other. I had an A&P conduct an annual on the Champ before I purchased it - he missed the tail wheel spring.

gahorn wrote:Anyway... it caused me to remember way back in my youthful exuberance to rent a C-175 which belonged to an A&P mechanic (which should have been a warning-sign)

HEY! I resemble that statement, and am offended!

Fearless Tower wrote:Just out of curiousity, how long was the runway you were landing on and how fast were you when you touched down?

I really am reluctant to attempt this ... because #1- It refelects poorly upon my judgement at the time (judgement results from experience/bad experience teaches judgement), and #2 it involves a now-defunct airport.
It was a small, turf airstrip with a hangar at the south end at the base of a hill... and the runway sloped upward to the north. I had to approach over the hill in a steep/slow/full-flap approach. I recall seeing a man standing on the threshold (I could barely see him over the nose as we made the plummet over-the-hill, clearing the hangar-roof) with his hands out to his sides...palms downward... pumping his hands as if to say "Get it DOWN...Get it DOWN!". I was a 21 year old CFI and was very current/competent with short/soft field landings, and felt things were well in-hand at that point. The grass runway was 1800 feet long with a 100' hill at it's south end (but which allowed approach over/down it's slope to the hangar at the so. end.) The West (right side) was a huge arroyo filled with cedar trees...the East (left side) was upsloped with trees, the North end was 20' cedar trees, and the N/W corner had the 6' tall pile of rocks the size of watermellons at the rwy corner. It was my second landing there... as my friend and I had arrived from Houston earlier to pick up his skinny/tiny little man (110-pounds soaking-wet ) of an uncle...who, as he approached the airplane for the short observation-flight asked if "his wife could also come along?"
'SURE!", I replied, imagining she must be like him. He went back to his car and when he returned it was with the Barnum & Bailey FAT BEARDED WOMAN, Aunt Bertha! ... but I was too timid to revoke my permission in front of this huge whale for fear of hurting my friend and his uncles feelings, not to mention she looked like she could squash me if I pzzzd her off.
The takeoff, short runway, uphill, over the trees, gusty conditions, second takeoff ever made by me in a C-175 was with tree limbs brushing the undersides of the wings and stall warning screaming. I felt like throwing up.
We flew out over some property they wanted to look at (deer lease) and then returned to the brake-failure landing that felt like landing on grease. As my only choices were to destroy the airplane into the arroyo or the trees straight-ahead...or possibly save the aft-end of it by steering it into the rocks...I kicked hard left-rudder and steered toward the pile, and pulled the yoke full-aft to try to minimize the "hit" on the nosegear/prop. We ended up with the tail tiedown ring sitting in the dirt and the airplane's tricycle gear sitting as if it had touched-down against small-hillside of the 6-foot pile of rocks.
Bertha had unknowingly contributed to the braking effort by assisting in burying the tie down ring dragging in the dirt.

Now comes the part where I excersize bad judgement: (little joke, that)
....
After we got it off the rocks and removed the cracked nosewheel fairing...and despite the fact we realized the airplane had absolutely no brake linings, ... I still took off with my friend and flew it back to Houston Hobby airport in order to return it to it's A & P owner (a fellow appropriately named Sam Shadow.)

Knowing there was little, if any, braking action available I landed as slowly as I felt comfortable, seeing as how Rwy 35 had 5,000 feet (back in 1970's) I felt OK about it.... But when we touched down exactly on the numbers about 60 mph.... the dang thing did its "land on grease" acceleration-thing again and we almost rolled thru the crossing rwy 12R at the FAR END (back then it was known as 13) and I had to take that runway-in-opposite-direction sorta like a high-speed exit... cutting the mixture to bring the airplane to a stop because the brakes simply refused to hold the airplane even against an idling engine once the airplane was in-motion.
I know it sounds like exaggeration, but that's a truthful description of how poor those missing brake-linings performed. Once the airplane was rolling...it simply would not stop without lining on the brake-pads.

Since that experience...I have refused to operate several airplanes with very minor brake issues.... which other pilots have accepted. I simply will NOT fly ANY airplane with even the slightest symptom of brake problems.

Brad Brady wrote:

gahorn wrote:Anyway... it caused me to remember way back in my youthful exuberance to rent a C-175 which belonged to an A&P mechanic (which should have been a warning-sign)

HEY! I resemble that statement, and am offended!

I have a brother-in-law who is a former electrician and now an electrical engineer. His house circuits are full of open-wiring and unfinished projects.
I have a friend who is a plumber. His wife cannot get him to repair the plumbing in their house.
We all know a certain retired TWA Airline mechanic who lives on the TX/LA border near a large lake, on an airstrip, who owns about 5 airplanes or portions thereof.... none in which would I put any member of my family (although I wouldn't mind if an ex-wife rode in them....if he could get the congealed auto-gas out of them and get them started.)
His better-half has an airplane that is airworthy last time I saw it, but I don't think she lets him work on it.
I know a preacher's kid who has sampled every type of sin known to God-or-man.
I'm the son of a math-teacher and count on my fingers.
The point I was trying to make was that sometimes "familiarity breeds contempt" for aircraft mechanics. I've known many who would ground another person's airplane because it didn't have installed genuine General Electric BRAND landing lamps... but whose own airplanes are not worthy of being on an airport much less a hangar and had Wagner Tung-Sols from the tractor store that were wired with automotive wiring and vinyl tape (and electrically-supplied with a lawn-tractor battery, clamped to worn-out battery cables with a set of Vise-Grips.)

Not all mechanics are that way. I know Jim McIntosh has only serviced his tires with genuine nitrogen. (The nitrogen service cart belongs to Air Canada.)

I religiously service my tires with genuine all natural 79% nitrogen.

As a favor, I one time serviced a low nose strut on a C-170 for a guy at our airport. He told me that it regularly lost air. I told him it would be OK now that I had inflated it with a mix of 78% nitrogen. For some unknown reason, the leak apparently healed itself. The owner regularly told his friends about my "fix" for leaking struts.

blueldr wrote:As a favor, I one time serviced a low nose strut on a C-170 for a guy at our airport. He told me that it regularly lost air. I told him it would be OK now that I had inflated it with a mix of 78% nitrogen. For some unknown reason, the leak apparently healed itself. The owner regularly told his friends about my "fix" for leaking struts.

Best repair for a nose strut on a 170 is to remove it!

jrenwick wrote:

blueldr wrote:As a favor, I one time serviced a low nose strut on a C-170 for a guy at our airport. He told me that it regularly lost air. I told him it would be OK now that I had inflated it with a mix of 78% nitrogen. For some unknown reason, the leak apparently healed itself. The owner regularly told his friends about my "fix" for leaking struts.

Best repair for a nose strut on a 170 is to remove it!

isn't that a 171?

I just wish I could afford to hire a proof reader. It sure as hell looked a lot like a C-170 but it did have a nose wheel.

I recently began a personal investigational-study on nitrogen in tires. The local auto dealers are getting all hyped up about selling it to dummies. The Jeep dealer I bought from has a poster in the waiting room which always is an attention-getter... which offers to drain and refill your tires w/100% nitrogen which claims to extend tire life, improve gas mileage, and make you sexy all for only $100.

I caught a housewife about to order that service when I asked her if she'd studied science in high-school. When she replied "YES"...I asked if she remembered how much of the atmosphere is made up of nitrogen, how much oxygen, and how much carbon-dioxide and other gases. She looked puzzled, so I reminded her that in round-numbers, 80% of the atmosphere was nitrogen and the oxygen made up most of the other 20% with a few other gases thrown in.
I then pointed out that...if the poster was correct in stating that nitrogen in tires benefit us because it has larger molecules and did not leak out as rapidly as the other gases and therefore keeps tires properly inflated better than other gases.... I asked her if the tire was already fillled with 80% nitrogen and it becomes deflated due to the other gases leaking out... and if we re-fill it with more 80% nitrogen mix... "Isn't the concentration of nitrogen automatically and quite naturally increased without paying someone $100?"

You should have seen and heard the scolding that woman gave the poor service-writer when he returned with his work-order to be signed by her!
I almost felt sorry for him.

As my investigation into this matter continued, I inquired of a college student in our church who is in the UT Civil Engineering College. Here's his response:

Okay, I think I may have found a way to determine all of the answers for your questions, you are right to be skeptical about the pure nitrogen refills. If the nitrogen remains in the tire while all other gases escape over time, after 4-5 refills you should have a 95% nitrogen tire

assuming nitrogen and the smaller gases to behave ideally, and temperature to remain the same...

psi (low 5%) = psi (full) - psi (full) * (.05)

for a tire filled at 40 psi, 38 psi would 5% low.

Now for the nitrogen levels

N= 78% - nitrogen level in refill
n= number of refills, refills needed after 5% leak
N(n) = % level of nitrogen after n refills
N(n - 1) = % level of nitrogen before n refills

N(n) = ((N(n - 1) / 0.95) + N*(0.05)) / 1.05

at first, N(n - 1) = 78% for a first- time filled tire

(78/0.95 + 78*0.05)/1.05 = 81.9

After one refill the tire is 81.9% filled with nitrogen, using this value for N(n-1) repeat the step again.

(81.9/0.95 + 78*0.05)/1.05 = 85.8

89.76 - 3 refills
93.7 - 4 refills
97.65 - 5 refills

It should take only between 4-5 refills to reach 95%. This is all assuming that the amount of gases that leak are not affected by the increase in nitrogen. This is a good rough estimate but probably not incredibly accurate.


Hope this helps!

someone should jump on that marketing bandwagon and make little nitrogen spray nozzles to bathe the OUTSIDE of each tire since that half of the tire area wouldn't otherwise be protected from the evils of oxidation etc. then you can sell N2 fillups for the tank in the car at gas stations, the possibilities are endless.

watch, this will someday come about and I'll kick myself for not doing it first. why, I'd be rich! just like the darn pet rocks...

Anybody ever watch 'em try to get 100% nitrogen in a tubeless?

I haven't watched the procedure, but they claim to fill the tire from a 100% nitrogen source, then deflate it and refill it, and claim that is whithin their definition of 100%.

"There's a fool born every minute." - P.T. Barnum, of Barnum & Bailey Circus.

gahorn wrote:..."There's a fool born every minute." - P.T. Barnum, of Barnum & Bailey Circus.

From the Wikipedia entry for "Cardiff Giant":

As the newspapers reported Barnum's version of the story, David Hannum was quoted as saying, "There's a sucker born every minute" in reference to spectators paying to see Barnum's giant. Over time, the quotation has been misattributed to Barnum himself.

I learned this last weekend as the result of doing a crossword puzzle.