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Date: Sun, 09 May 2010 16:56:00 -0400
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From: "Robert Pastusek" <rpastusek@htii.com>
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Subject: RE: [LML] Desser Tires Air Pressure
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Lorn,

The most common cause of failure like this is under-inflation...and this is
relative to the loading, landing forces, speed, and other things. I used to
think that less pressure made for better shock absorption and therefore less
stress on the gear, but this is not necessarily so. Take a careful look at
the tube. If the hole appears as a very small slit, it's likely caused by
the tube being pinched between the runway and wheel rim on touchdown. If it
looks more like a "rubbed" hole, it's friction between the tire and tube.
Increased pressure will help both situations. I run my IV-P with 60 PSI in
the mains and 45 in the nose. The Goodyear Flight Custom III mains have more
than 250 landings on them, and look to be good for that many more. The nose
tire came in the original kit (1999) and has more than 500 landings on it. I
replaced the original Flight Custom II mains last year at about 300
landings, including some braking/stopping distance tests during initial
flights, and they are still serviceable. In my opinion, it is possible to
over-inflate tires, but the much more common tendency is to under-inflate.

I'd be interested in what others think...

Bob


-----Original Message-----
From: Lancair Mailing List [mailto:lml@lancaironline.net] On Behalf Of Lorn
H Olsen
Sent: Friday, May 07, 2010 8:48 PM
To: lml@lancaironline.net
Subject: [LML] Desser Tires Air Pressure

I just landed at St Simons Island (KSSI) and had a flat. This landing and
the prior landing were smooth although this one was a little fast. They have
just cut grooves in the KSSI runway giving great traction but also spinning
the tires instantly up to 90.

The right tire still had 44 lbs psi of nitrogen. I assume that the left
(before the flat) had the same pressure. Neither of the tires looked low
prior to the flight.

The flat was the same type that I have had in the past. The inside of the
tube right in the middle there is a very small leak. I am bringing the tire
home and will have it examined under a microscope to see if we can see what
caused the problem.

I got the tires and tubes directly from Desser. They are about 1 year and
have about 120 landings.

Remember that my calculation show that my empty weight has approximately 400
lbs on the mains and nose. When at 1,900 lbs gross, there is about 320 lbs
on the nose and 790 lbs on the mains. The Desser tires are rated for 500 lbs
at 70 psi.

I am thinking that the tube is slipping/rubbing against the tire at
pressures below 40 psi causing the small holes in the side of the
inner-tube. I use talc on the tube. This time I also used talc on the tire
to seat it on the tube. The tire seated very easily but I am not sure
whether this will cause slipping in the future.

Can anyone help me with a recommendation as to the tire pressures that they
are keeping in both the mains and the Nose.

--
Lorn H. 'Feathers' Olsen, MAA, ASMEL, ASES, Comm, Inst
DynaComm, Corp., 248-345-0500, mailto:lorn@dynacomm.us
LNC2, FB90/92, O-320-D1F, 1,700 hrs, N31161, Y47, SE Michigan


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