MONTY THE ANSWER MAN
ARCHIVE
TIRES
THE CARE AND FEEDING
OF TIRES AND TUBES...(110500)
By Steve Wilson <SteveWlson@aol.com>
Tube type tires, which are original equipment on our Swifts, slowly leak
air. It's normal! It is a fact of life you need to get used to! Aircraft
tires are one of the most important components which are routinely ignored
until they "look" too low. If you allow that condition be your
signal to check the air pressure, you're late! Your tires are probably
not broken, but they are overdue for your attention.
The failure mechanisms of
an aircraft tire are complex. Let's just say that the tire's worst enemies
are heat and over-stress caused by under-inflation. The hysteretic energy
resulting from the rapid elastic stress-cycling of a rotating tire can
generate enough heat to literally burn the tire. Remember seeing the smoke
coming from the under-inflated semi-truck tire? The rolling resistance
of a tire significantly influences the length of the takeoff roll. While
the rolling resistance is not directly proportional to inflation pressure,
it can increase as much as 50% for an under-inflation condition of 15%.
The inflation pressure recommended
by the manufacturer is a compromise which weighs three fundamental targeted
design performances of aircraft ground handling characteristics, dynamic
spring rate, and service life. There may be other performance characteristics
that are functions of inflation pressure, i.e., footprint shape and area,
bead seating force, etc., but I believe the above three are more easily
recognized by most of us. As the tire loses air pressure, its performance
changes are gradual and subtle. You might not sense the degradation of
handling performance of your airplane during takeoffs and landings until
it's too late. Sure it's a bother to check the tire pressure regularly,
say monthly or whenever the ambient temperature changes significantly.
The alternative is not very attractive either. The dynamic spring rate
will come into play, big time, if you over-inflate in order to avoid having
to check the pressure as frequently.
You say, you know all this
stuff already... Then just heed this reminder: "Your tires won't
let you down, if you don't let them down!" -- Steve Wilson
SMALL TIRES AND STALL
STRIP...(120200)
Subj: Small tires, stall strip
From: Dick MacInnes <rmacinnes@juno.com>
In one of the October updates from Arbeau you mentioned an STC that included
a machined stall strip as well as the small wheels, etc. I bought the
tires and tubes from Swift Parts some time ago and they sent me a copy
of Charlie Cummings 1986 337 on his N96CC along with his print. Also a
letter from Charlie Nelson to Jack Nagel dated 15 Sept 1993 authorizing
him to use this info. Also in the letter to Nagel Mr Nelson stated that
"it is our intention to have the installation of the 15X600X6 tires..."
added to our type certificate data as Item #201, and #603. My questions
are 1. Is there an STC or are we referring to the same data, and 2. did
Swift ever add the mods to the Type Certificate data. I'm not quite up
to going back to work on the bird yet but am trying to gather data, money!
and misc parts, like a more or less usable cowl (Have a Swift Tech) Appreciate
your work and insight Dick MacInnes N80923 rmacinnes@juno.com
Dick, What I was referring
to was the same thing you have. It is not a full STC but to my knowledge
the FAA has not turned anyone down on the use of it. I have typed up a
337 and sent it in for prior approval without any problem. I don't think
Swift has been successful in getting that data included in the aircraft
spec. Many Swifters are using the 15:6:00x6 tires now. I had them on one
Swift I had about 12 years ago and didn't like them. It was like landing
with the tires full of concrete. Maybe if your landings are better than
mine it would be OK! -- Jim
NEW TIRES REQUIRE RETRACTION TEST...(OCT 02)
Editor says... Here's a good one. Many thanks to Bill Tiley for sharing
it with us.
From: Bill Tiley <Yakflyer@aol.com>
Subject: Fitted Gear Well Mods
AARRRRGGGGGHHHHH!! During the last annual inspection, the IA said "your
tires are okay, but worn... you might want to replace them". I said
"Yeah, I'll do that later". We completed the annual, including
the retraction test and emergency crank-down, etc. A few weeks went by
and I decided to change the tires... replacing them with the new diamond
pattern tires I purchased from Swift Parts in Athens. No, I did not do
another retraction test. Wrong decision! On the 10th landing, the gear
failed to extend. Following procedures, I tried the emergency extension.
No luck. I then went into a shallow dive and pulled up to about 4.5 to
5 G's. The gear came down and locked. Funny thing about those diamond
tread tires (Specialty Tires of America), they are nearly 5/16 greater
in diameter than the standard 600 X 6. My fitted gear mod was accomplished
some time ago by using the standard 600 X 6. Damage was restricted to
the "enclosure mod", bending it outward, and popping some rivets.
I learned a lesson: Do a retraction test after replacing the tires! Bill
Tiley
BIGGER IS BETTER??? (SEPT 03)
From: PhillipLaBerge@peoplepc.com
Subject: Re: data plate
Jim,
What's your opinion about the savings in drag/lift or whatever with going
to 5" wheels instead of 6 inch wheels. I am operating off grass that
is not the smoothest in the world and am considering switching back to
6" wheels. Not sure it would make much of a difference at all in
the performance since my Swift is slow anyway.....big tailwheel, slots
in the wings, metal cowling off a C-310 with too much cooling drag, etc.
etc. Sincerely, Phillip
Phillip
The smaller wheels & tires do help speed "a little", especially
if the opening is closed up around them. Every little bit helps but if
you put the 6:00x6 tires and wheels back on I doubt if you would see much
loss. Be sure you check clearances on jacks afterward! I don't like the
small tires, it's like landing with the tires full of concrete. I think
they are harder on the airplane. I think they need about 50 psi. -- Jim
BIGGER IS BETTER??? PART DEUX... (SEPT 03)
From: PhillipLaBerge@peoplepc.com
Subject: Re: data plate
Jim,
The wheel wells are closed up around the smaller tires at this moment
but I think I agree with you about the hard feeling. The Swift that went
to France had the big tires at first and then the switch was made to smaller
wheels and tires when it left my place and headed towards Europe. I don't
remember how much air the bigger tires needed but I assume you could get
by with the old Piper formula of one pound for every hundred pounds of
gross weight. That was published in the Piper Stinson manuals and also
in the L4J manual that the Army Air Corps had with each Piper Cub they
used during the war. So.......twenty pounds or so should do it with a
1970# gross weight Swift. Add a few pounds for the wife and you'd be around
25lbs or so. Does that sound right? Sincerely, Phillip
25 pounds or so is Ok for the standard 6:00 x 6's but the low profile
15x600x6 tires need about 50 psi. -- Jim
TIRE TALES... (SEPT 03)
Subj: Tires
From: Dick Aaron <richard.aaron@us.army.mil>
Jim,
I saw your comments about the 5.00 size tires and pressures in the last
newsletter. I'm getting close to needing new tires (6:00's) and was wondering
what you recommend between McCreary's Air Trac, Air Hawk 4 or 6 ply. The
Aircraft Spruce catalog shows the 6 plys to be 0.2 lbs heavier and for
the Air Tracs to need 42 psi vs 29 psi for the Air Hawks. Regards, Dick
Dick
Get the lightest tires you can for a Swift. A pound or so might not be
much in the overall weight of a Swift, but the load on the hydraulic actuator
when you figure the moment is impressive. The lightest tires are usually
the cheapest. Get light, cheap tires and if you have to replace them every
few years, so what? I remember comparing cheap McCreary's to some deluxe
6 ply Goodyears once and the weigh difference was several pounds. -- Jim
TIRE PRESSURE... (FEB 04)
Subj: Low Profile Tire Pressure
From: Mike Foushee <mike.j.foushee@Cummins.com>
The original Swift manual calls for a tire pressure of 20 PSI as I recall.
My recently acquired Swift (N711E) has "low profile" tires (15
- 6.00 x 6). A logbook entry for an annual inspection done several years
before I purchased the plane indicated that they "aired" the
tires to 50 PSI which seems excessive to me. The tires LOOK properly inflated
at about 30 PSI. Is there an official tire pressure level for the low
profile tires on a Swift? Thanks for any information you can give me.
Mike Foushee N711E
Mike
I had the 15:6:00x6 tires on one Swift I had and I believe I used 45 psi.
I would use the lowest pressure possible. The tires absorb a lot from
a hard landing. I have previously heard of excess premature wear when
using lower tire pressures in the little tires. -- Jim
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