RV-8 Tire Pressure

[PaulT]

I bought the larger AeroClassic 380x150-5 6 ply.
Should these run at the same pressure as the standard tire (tyre ), or lower, due to the considerably larger footprint?
Paul.

[DanH]

Originally Posted by ColoRv

Wow Dan, you're pretty sure your way is the only way aren't you?

Not at all. My way changes as I learn. I am pretty sure there is great value in studying the databooks and fundamental mechanics, and only then considering tribal knowledge.

Let's lighten up and have some fun. Are you running the standard 199-102 Cleveland wheel and brake kit on a -3 through -9? Most are, so consider this puzzle...

The technically correct maximum inflation pressure for the 199-102 kit is 31 psi per Cleveland drawing 50-76.

The maximum inflation pressure for a 199-156 kit is 50 psi, again per Cleveland 50-76.

The two kits use the exact same wheel halves, bearings, bolts, etc. The only difference between the kits is the brake disk....so why the difference in inflation pressure?

Originally Posted by PaulT

I bought the larger AeroClassic 380x150-5 6 ply.
Should these run at the same pressure as the standard tire (tyre ), or lower, due to the considerably larger footprint?

Paul, please look up the rated pressure and weight capacity in one of the databooks previously linked.

[wera710]

Lance, I've known more than a few 8 pilots running PSI down at 28. Nothing wrong with that other than that you will find youself having to add air more often. Handling is fine that low and on bumpy fields its not altogether a bad thing to have lower pressures. But as others have stated, your idle RPM is too high.

As far as having to use brakes...eh, in the grand scheme they are cheap enough, so don't be afraid to use em. I am sure some braniac has done a spread sheet on replacing brake pads every year or so versus the extra fuel used in a long taxi back to the hanger (proving that some folks take SPORT aviaton WAY too seriously, lol) but in the end, do what you gotta do to get the bird stopped where you want it. There is really no right answer on PSI. You have a usable range for a given aircraft weight and we are blessed with the ability to experiment within that range to see what works for what conditions. Too low a pressure and you turn your wheel pants into mud scoops. Too high and you make a brick out of every landing. Best advice, IGNORE all of our recommendations and find out what suits your individual RV the best for the kind of surfaces you use.

[Bartman]

anyone know what should be use in the 380x150 tires

[judoka5051]

That's kind of the direction I plan on heading. First I'll lower the idle, then play with the tire pressures. BTW, The idle is set there because I have the Rotec TBI and it acts up when it gets hot, and wants to starve the engine at idle. Changing to a carb tomorrow, so hopefully I can change idle to 600 or so.

Lance

[Walt]

All I have to say: Tubes+low pressure = Flat tire

[walkman]

Also, minimum aquaplane speed varies with the square root of tyre pressure, if you often land or taxi on hard surfaces with standing water.

[Sam Buchanan]

Originally Posted by Walt

All I have to say: Tubes+low pressure = Flat tire

I would be careful with blanket statements like that.

Over the past 15 years I have tried various tire pressures for my RV-6 with standard size tires. Low 20's, mid 20's, high 20's, mid 30's and higher. All are a compromise between rolling resistance, inhibiting shimmy and harsh landings. Trying various tire pressure is a valid way to tailor gear characteristics for a particular environment.

But in all this experimentation, I've never had a tire go flat (well, there was the time when I didn't tighten the valve core enough...). Flats do seem to be more prevalent according to anecdotal evidence on the nose tires, maybe due to the lighter weight construction of the tires and tubes (?).

[DanH]

Originally Posted by Sam Buchanan

Over the past 15 years I have tried various tire pressures for my RV-6 with standard size tires. Low 20's, mid 20's, high 20's, mid 30's and higher......Trying various tire pressure is a valid way to tailor gear characteristics for a particular environment.
But in all this experimentation, I've never had a tire go flat.....

That's because you're a good pilot. No leg pulling; the facts say so.

I just happen to have an RV-6 leg in my gear design files. I was using it as a comparison sample of a well proven tapered gear when I was doing one for a biplane. This is one of Neal Willford's spreadsheets.

Assume a 6.5" wheel diameter per the Michelin databook for a 500-5. Further assume the tire is smashed flat and pinching the tube at 1/4" additional radius (think two layers of rubber, sidewall and tread, sandwiched between rim and asphalt). Last, assume a 3.1G hit, equal to a vertical drop of about 14". The minimum tire pressure to meet this criteria is 38 psi.



At 25 psi the tire is pinched hard against the rim at about 2G, less in a one-wheel stab at the ground on a windy day, with a bit of side load.

No flats? You're good

[Sam Buchanan]

Originally Posted by DanH

No flats? You're good

Naw...just lucky, I guess. I can assure you my poor ol' RV-6 has seen its share of bounced landings......the bottom of the wheel pants can attest to that.....

I air the tires to 35 and pump them back up when they start looking a little "low" which is 26-28.

I'm not presenting an argument to prove or recommend any particular pressure-- just wanted to counter the statement that lower than rated pressure will guarantee a flat tire. My experience since 1999 has shown me otherwise.