Tailwheel Lifespan

[Ryan Smith]

N2256D has been going through tailwheels lately. I'm not sure how many hours/landings were on the one that let go when I was flying, but the airplane has less than 20 hours (and presumably about 70 landings) since the tube and tire were replaced, and the new wheel blew yesterday with a student. All of the landings since I last flew the airplane were on pavement, but 70 landings seems to be an awfully low number. The mains look virtually brand new, even though they're probably a year old with several hundred landings on them.

I can say with relative confidence that the main spring has never been serviced since we've owned the airplane, to include the last six years that we haven't. The airplane has probably flown 1,000 hours since 1986 (guessing, I can't tell what the hours are on the tach from the pictures when my grandfather first bought the airplane). It has averaged 10-12 hours per month since it's been back in North Carolina, and 95% of that time has been for tailwheel training. I know George has stated in the past that the recommended service cycle for the main spring is every 500 hours. I will try to get a picture tomorrow, but sitting on the ground, the tailwheel trails (from the perspective of the king pin) about 2-3 degrees versus angling forward the same amount. Would the main spring be a contributing factor to the tailwheel blowing a tire so often? It's gotten worse in the past two months.

I'm not sure that technique doesn't have something to do with it as well. The main instructor for the airplane insists on students applying full back pressure on the yoke during takeoff before transitioning to a tail-high attitude. After a while, I can imagine that this would have some effect, even though the tail is never loaded in the sense that the airplane only flies with two people plus fuel. I've actually always just let the elevator rise into position from prop wash when I advance power on takeoff so I can have a little better feel for when the tail begins to "fly", whereupon I transition into a tail-high attitude. I somewhat understand Dave's methodology behind instructing his students to do that, but I can't help but think that is somehow contributing. Also, because of the interest I have in the airplane, I've watched more than a few of them during their training, and surprisingly, most of the guys are pretty good. There are quite a few professional pilots that are getting their tailwheel endorsement, so they're not slamming the airplane on the ground on landings.

Any input is greatly appreciated. The IA that maintains the airplane doesn't feel that the main spring is the issue and doesn't want to replace it if it's not going to improve the situation. He's been the IA on the airplane the entire time it's been in North Carolina, but my father would do owner-assisted annuals versus the current owner pulling the airplane into the shop and writing a check. That said, he's familiar to an extent with the airplane and 170s, but not enough that I believe he's making the correct judgement call in the situation.

[GAHorn]

By reading your post it becomes evident the problem is NOT the tailwheel assembly.... it's tires and tubes you're going through...correct?
If so, I should mention that the most common reason for early failure of tubes/tires is UNder-inflation. When the tire has less than 34 psi the sidewalls flex disproportionately and fail at a low number of cycles/landings. This also creates excessive friction between the tube and tire. The tube fails due to abrasion and the tire fails due to heat and broken sidewall fabric.
It is better to OVER inflate slightly than under-inflate. I doubt very much the instructor's technique is the problem.

(Be certain to confirm your tire pressure gauge is accurate, and avoid cheap tubes/tires. I personally prefer McCreary tires (Specialty Tire) and butyl rubber tubes. I usually get them from Desser Tire. They last years and years. The last made it 8 years and approx. 400 landings.)

[Ryan Smith]

By reading your post it becomes evident the problem is NOT the tailwheel assembly.... it's tires and tubes you're going through...correct?
If so, I should mention that the most common reason for early failure of tubes/tires is UNder-inflation. When the tire has less than 34 psi the sidewalls flex disproportionately and fail at a low number of cycles/landings. This also creates excessive friction between the tube and tire. The tube fails due to abrasion and the tire fails due to heat and broken sidewall fabric.
It is better to OVER inflate slightly than under-inflate. I doubt very much the instructor's technique is the problem.

(Be certain to confirm your tire pressure gauge is accurate, and avoid cheap tubes/tires. I personally prefer McCreary tires (Specialty Tire) and butyl rubber tubes. I usually get them from Desser Tire. They last years and years. The last made it 8 years and approx. 400 landings.)

I'll check the pressure tomorrow and see. I'm not sure what tire/tubes have been bought, but I can find out as well. Thanks for the quick reply, George!

[c170b53]

On my way home home from St. Louis I landed at Livingston Mo. For some cheaper gas. On the roll out, I got that old not so nice feeling from the tail. Yep another flat tailwheel. I saw an open hangar and decided to put my cap in hand and ask to borrow a jack. Turned out it was a small repair shop. I had a spare inner tube with me, so initially I was just going to do a replacement and patch the leaker for a spare. The shop lent me a jack but were keen to sell me an inner tube. My tailwheel had a small flat spot, so I went for a tire- tube package which made the shop happy. On removing my inner tube I counted 4 patches. Humm, guess I lost count.
I'm recounting this adventure ( ) to mention two things. 1) Sometimes I let my tailwheel drop below 45 lbs and find filling it up a pain. Solution, get a 1 inch schreader extension. 2) the new tailwheel tire inside sidewall was much rougher than my old tailwheel which was the original fitted to my Scott T/W assy. Likely it wear a hole into the inner tube faster than my old wheel, so I got another patch kit ready

[Bruce Fenstermacher]

Ryan as for the main spring one thing I can tell you is you just never know when that thing is going to snap. I have seen one bent so far that the king pin angle was at least 30°. I told the owner I wouldn't move the aircraft till it was replace. He said it's been that way for months and he thought now that I told him he would just do a wheel landing when he got home. It didn't snap best I know.

On the other hand my perfectly good looking spring snapped while the plane was tied down.

George's 500 hr recommendation is conservative based on cost verses repair. It should be adjusted for higher than normal landings per flight hour. I'd say 250 to 300 landings. It is just to cheap to replace the spring rather that repair damage after one lets loose. Unless of course your as good as I am and time it to snap while the plane is tied down.

[daedaluscan]

Should I change the whole set, or just the mainspring?

[bagarre]

The tailwheel is only held on by the main spring so most folks only replace that one.
I've never heard the other one's breaking.

Another way to increase tailwheel life and reduce tailspring loads is to do wheel landings

[170C]

I went through a period of having more tail wheel flats than I felt I should. Maybe my problem was under inflation? One thing I have noticed is that I order a new tube whenever I replace the tail wheel tire and it seems the tubes are made in vrs overseas countries. I can't say that they are inferior, but I would rather they were made in the USA. I purchase from Desser for tires and tubes.

[ghostflyer]

Well I have read everything that every body has advised and what is said is good ,but holding on the control column pull back on take off. no way. that's a loaded pressure on that poor little wheel. I even trim for the tail to come off ASAP so the aircraft lifts off in flat attitude and quickly gathers speed and then the climb angle is attained. There is a little forward pressure on the control column at this point in time BUT with a sudden engine out on takeoff the nose of the aircraft has to be lowered quickly so a stall is not induced so this trim setting helps.
I takeoff/land from all types of surfaces ,beaches, rough dirt roads and bush areas and pavements . My tailwheel tire has lasted at least 300 landings and has a few to go . However all my landings are wheeled on and the tail wheel is the last on . However after saying this I will bet next flight a stick or rock will mash it. When replacing a tire I always replace the tube also as they wear also. Tail wheel shimmy will induced wear on to the tire also so that area has to be servicable also .

[minton]

Sounds to me that the origin of the tire and tube could be an issue. Last time I was shopping for one they offered me a "Made in China" set. I declined.

[Dward]

A few years ago I installed a new tire and tube only to find the tube leaked like a sieve when inflated. I pulled the tube out while saying several choice things about imported tubes. When I got the tube out I found that when you stretched it you could see one section that looked like it had been used for a pin cushion. I then said more choice things about imported tubes until I remembered that my sister-in-law had visited with her toy poodle. I had left the new tire and tube on the floor in the family room where I opened the package. I’m just glad the little guy didn’t like the hard rubber tire.

[Joe Moilanen]

I usually do three-pointers, aft yoke on takeoff, and have never had a flat in the 26 years that I've owned it (better knock on wood). I always keep it inflated to 40+ lbs. When I change the tire and tube (for wear) I always put talcum powder inside the tire, maybe it is helps the abrasion between tire and tube.

Joe

[iowa]

finally blew my tire
it was badly worn
i must have a scott TW
the tire is a 2.80/2.50
is this pretty standard on all 170's?
thanks
dave

ps
yes, i know, it's been a long time since i've posted
been flying my 1942 fort sill L4!!!

[edbooth]

If you want some real entertainment, volunteer to judge spot landings sometime.... The punishment those tail wheels are subjected to....it's a wonder they last as long as they do.

[robrien]

I added an image of my tailwheel - worn fairly evenly across the top. My IA says there is a lot of life left in this - I'm curious what your thoughts are?