Outside, lights are winking everywhere. ’Tis the season. No, not those lights. Tire pressure warning lights. My van reminded me the other morning that it’s time to top off the summer air with winter air. I’m embarrassed to admit I’ve come to rely on that light to check air pressure the same way I’ve come to rely on cheaters to read a menu. As the temperature falls nationwide, it’s a good time to remember tire pressures fall with it, with or without an idiot light to signal the season.
While I’ve got you here, let me carry that thought to its extreme, as I’m wont to do when both words and caffeine are flowing. I cut my teeth (and my fingers) in the Sonex community. Like many lightweight aircraft, the Sonex airframes get by admirably with low-cost, lightweight Azusa aluminum wheels. In my decades of exposure to them I’ve never seen one break. In 500 hours’ flying with them on my personal airplane I had only two flat tires. Both were found at the hangar, after taxiing back from a flight. I attribute both to underinflation and I attribute the underinflation to laziness, seasonal temperature changes, and complacency. In each instance the inner tubes were found to be torn on the sidewall. Nothing inside the tire was found that could be blamed. I suspect an underinflated tire slipped on the wheel on landing and tore the tube. Each time the opposite tire had less than 30 psi, which is 20 psi less than I liked to run.
No matter what wheel and tire combination you have, underinflated tires promote wear and increase the risk of having a flat tire. Underinflation also increases rolling resistance, which can impact steering and, critically, increased takeoff roll, which makes the trees at the end of the runway loom large in your windshield. If you want to look at the bright side, underinflation decreases the landing roll, but I’ll accept a normal landing roll to avoid a very short, potentially expensive one if a tire goes flat on landing. There are also personal, physical benefits to keeping your tires inflated. If you’ve ever ignored tire pressure for a while you undoubtedly noticed how much easier your airplane was to ground handle by hand after reinflating them. Internalize that effort, commit it to memory, and commit yourself to checking tire pressure regularly. Don’t wait for a light to come on. It may be the light of an emergency vehicle.
I can appreciate the point being made here, but we are not talking cars. In airplanes, we accept and follow manufacturers limitations and directions. Sometimes we allow that “E/AB” moniker go to our heads and make decisions that we are probably not qualified to make.
If the manufacturer has made a mistake or is “CYA”ing their position on a part, let them know. But for this publication to post an article that supports ignoring the manufacturer’s instructions is irresponsible.
John,
The Sonex plans specifically call for 50 PSI. That is based on much experience. The wheel manufacturer casts 30 PSI into the wheel and that may work well for go karts, which is the market the wheels were originally developed for. What’s interesting is if you google “Azusa Wheels” the top hits are all aviation suppliers, such as Wicks, so clearly these wheels have been adopted by homebuilders.
Other OEM users of these wheels may have different pressure recommendations based the tire size they use and the gross weight of their aircraft (or go kart).
I stand by my 500-hours of flight time with these wheels on my Sonex and my experience inflating them to 50 PSI versus 30 PSI.
Sonex Wheel and Brake Installation: https://www.sonexaircraft.com/documents/instruction_sheets/wheel_brake_install.pdf
I agree that now is a good time to check pressure with cooler temps but many manufacturers recommend low pressure. The recommended main tire pressure by Cessna for my C140 is 16psi. I would guess many high wing short field taildragers are similar.
Having been an Aeronca owner for many years, they use a 6.00-6, I believe. That size is used on many other machines and carry 25 + lbs with them. New Aeronca owners tend to just initially inflate them on the Knockers and Chiefs to that and wonder why their plane is almost uncontrollable , pouncing like a basketball when landing. I would explain to them anything over 15 lbs would cause that. And ideally, assuming they checked pressure frequently, keeping them at 11 lbs was perfect. 11 lbs made them an easy and controlled lander. The higher pressures made the owners want to sell. But much lower landing speeds reduced the tendency to rotate on the rims.
I attended a “rust remover” seminar some years ago and this very subject came up hosted by a senior maintenance engineer from a regional airline. It so happened that while he was employed that a major tire manufacturer approached his airline with an offer of free aircraft tires for Dash 8’s and BAE 146 commuter jets in response of garnering service life and performance of these new tires which if my memory serves me correctly were of radial construction (I think also using tubes). Long and short of this exercise was that the new tires imposed significantly higher side loads on the rims resulting in a lot of cracked and unfit for continued use wheels. Higher tire pressures exponentially increase wheel stress. Caveat Emptor.