Tale of two tires. New Tires for my RV-12!

I recently put on my third set of main tires at 632 hrs. I thought I would
try something new and changed from the Desser Aero Classic All Weather tire to the Desser Elite retreads. I do a lot of transition training and probably go through tires more than the average Joe! My first set of tires which came with the kit lasted 308 hrs. The second set lasted 324 hrs. On both sets of tires around 170 hours into each cycle I flipped them on their rims to have even wear on them. Also because I practice the technique of Softfield Takeoff and Landings I still have the orginal Nose wheel tire on the plane. Here are a few observations I made while mounting the new tires. Vans actually has the best price on their web store for the Aero Classic tire. Being a first time builder and not wanting to mess with a good design I stayed with the exact same tires for the second set of tires. On my third set of tires I decided it was time for a change and selected Desser Elite Retreads. The Elite tire, as a result of having more tread is definitely taller or bigger in diameter by approximately 1/2 to 3/4 inch. However it is about the same width as the Aero Classic. So you will have to trim the front and back of your wheel pans. I recommend at least 1/2 inch clearance front and 1/2 clearance in the back as seen in the pic below. The Elite should last a lot longer than the Aero Classic, I wouldn't be surprised if they lasted 100 hours longer than the Aero Classics. Your mileage may very! It cost about $20 more for the Elite. You can run up to 50PSI per there web site, but above the chart on this page http://www.desser.com/pressurechart.php there is a disclaimer that says, "Always consult with your owners manual for factory recommended pressures"! At this web site under the FAQs under the title, "What Tire Pressure Do You Recommend" they go into a little more detail about tire pressures for Vans Aircraft and in the end the POH pressure will be the best. http://www.vansaircrafttires.com/pages/Articles%7B47%7DFAQ.html At the higher PSI the tire becomes very hard. I would think that on a hard landing it would send quite a shock wave up your struts into your airframe. I will be running about 25 psi per tire to soften them up a bit until I get some experience with them. Weight, the retreads are only about a pound heavier than the Aero Classic. Balancing, one tire required 3/4 ounce and the other only 1/4 ounce to balance them on the Harbor Freight Aircraft balancer. Not bad! Since we don't change tires very often you can review the procedure on EAA video link below.
http://eaavideo.org/video.aspx?v=1967222618001
Here are a few pics of the tires and process and more pics in the next post!

Worn out tire, 324 hrs!


What a New Aero Classic All Weather looks Like!


What a New Desser Elite Retread Looks Like!

Send your old tires to Vlad. He'll get another 800-1000hrs out of them. I'm going to start sending him mine .

Tale of two tires. New Tires for my RV12! Part 2!

The Tube!

Trimining the Wheel Pan!



Tire Diameter!
Aero Classic. Inflated.


Elite, uninflated.

scard said:

Send your old tires to Vlad. He'll get another 800-1000hrs out of them. I'm going to start sending him mine .

Click to expand...

Thank you Scott and don't forget the tubes
Happy new year to 22C crew!

I would think that on a hard landing it would send quite a shock wave up your struts into your airframe. I will be running about 25 psi per tire to soften them up a bit until I get some experience with them.

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You may get more "shock" than you bargained for if you have a hard landing and the tire bottoms out or a you get a flat. Lowering tire pressure to get a "softer" ride is not a good trade off with aircraft tube tires. Personally I think 35 psi should be a minumum for most aircraft tube tires. When you get into the 25 psi range the sidewalls start to flex excessively and will cause the tube to fail (I would guess 98% of flats are caused by underinflation).

It may come as a surprise to a lot of people, but tire pressure and ply rating are a design aspect of the landing gear system.

The RV-12 is a light (structurally) airplane. The tire pressures specified are for a reason. If a tire pressure is used that doesn't get the full energy absorption expected by the designer, a major unplanned for load could get transferred through the landing gear legs to the fuselage
Example - because of low pressure the tire sidewall fully collapses under a high load which will cause a sudden spike in peak load through the landing gear. To high of a tire pressure can cause the same thing... the tire acts more like a sold wheel and transfers a majority of the load directly to the gear leg and fuselage.

In simple terms, the tires are meant to be a major part of the energy absorbing system during a less than normal landing. Staying within the recommended pressure range (when one has been published), is strongly recommended.
Because the RV-12 is a relatively light aircraft (comparably) the main tires are recommended to be 25-28 PSI.
If someone installs a tire that is a lot stiffer than the one originally supplied, those #'s may no longer apply)

The ELITE looks like it might be the wrong profile for RV (scuff) type landing gear.

This is the profile you would use on landing gear like the Warrior has.

Do let us know how it works out.

rvbuilder2002 said:

It may come as a surprise to a lot of people, but tire pressure and ply rating are a design aspect of the landing gear system.

The RV-12 is a light (structurally) airplane. The tire pressures specified are for a reason. If a tire pressure is used that doesn't get the full energy absorption expected by the designer, a major unplanned for load could get transferred through the landing gear legs to the fuselage
Example - because of low pressure the tire sidewall fully collapses under a high load which will cause a sudden spike in peak load through the landing gear. To high of a tire pressure can cause the same thing... the tire acts more like a sold wheel and transfers a majority of the load directly to the gear leg and fuselage.

In simple terms, the tires are meant to be a major part of the energy absorbing system during a less than normal landing. Staying within the recommended pressure range (when one has been published), is strongly recommended.
Because the RV-12 is a relatively light aircraft (comparably) the main tires are recommended to be 25-28 PSI.
If someone installs a tire that is a lot stiffer than the one originally supplied, those #'s may no longer apply)

Click to expand...

I stand corrected for the RV12, 25-28 it is!

The only problem I see with such low pressures is folks tend not to check pressures often enough, 25 psi now means 20 or less in 2 months.

Anyone know the difference between the Elite and the Monster Retread at Desser Tire?

I had a set of these from Desser in size 8.00 on my Cub. They also had a 50 lb air pressure rating. I ran them 15 to 18 psi as recommended by Piper for 10 years without a problem. What a tire!! And, you are right. They never looked low.

Tom

Walt,

Piper recommends 24 or 26 psi (would have to check my POH for which) for my Cherokee 180, so I never gave the RV-12 reassure a second thought. What was it that made you think that too low? I agree that in two months they'll be lower.

Rich

RFSchaller said:

Walt,

Piper recommends 24 or 26 psi (would have to check my POH for which) for my Cherokee 180, so I never gave the RV-12 reassure a second thought. What was it that made you think that too low? I agree that in two months they'll be lower.

Rich

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Well maybe just my experience, I can't think of a single flat I've seen/repaired that was caused by a puncture, its always some type of split in the tube which is "generally" caused by excessive flexing of the sidewall which can be attributed to low tire pressure. I have no objection to the manufacturers recommendation, but one must be diligent about maintaining specified pressures if you want to avoid problems (flats). If you get into that 15-20 range you are just begging for trouble.

On another note I wonder how many folks actually check their tire pressures every 30 days?

Why do they leak down so bad? My unfinished plane has never been out of the garage, and they lose air regularly, still have the stickers on them.

Walt said:

....If you get into that 15-20 range you are just begging for trouble......
On another note I wonder how many folks actually check their tire pressures every 30 days?

Click to expand...

With our little 5.00x5 tires 15-20lbs looks FLAT! You would have to be very inattentive to let them get that low. Looking at the tires is part of the pre-flight, and it's possible to get pretty good at sensing low pressure once we have learned the plane. I keep 26-35 lbs in the RV-6 and (knocking on wood....) haven't had a flat in 16 years. More than 35 on the RV-6's springy gear is more harsh than I can stand.

My experience with leak-stop tubes has been that air needs to be added about every two months to keep pressure within 2-3 lbs of target pressure.

DonFromTX said:

Why do they leak down so bad? My unfinished plane has never been out of the garage, and they lose air regularly, still have the stickers on them.

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Don, you are probably seeing leakage from the original, natural rubber kit tubes which are quite porous. The "leak-stop" tubes are made of some sort of synthetic rubber (like auto and motorsickle tubes) which maintains pressure much better. You will want those tubes once you start flying.

In addition to the already-mentioned leak-stop tubes, fill with Nitrogen instead of compressed air. It is alleged that the Nitrogen won't leak as much as plain air.

Don, you are probably seeing leakage from the original, natural rubber kit tubes which are quite porous. The "leak-stop" tubes are made of some sort of synthetic rubber (like auto and motorsickle tubes) which maintains pressure much better. You will want those tubes once you start flying.

Click to expand...

Are you referring to the LeakGuard tubes found at Aircraft Spruce or something else?

Thanks,
Tom

Leak guard, leak stop, also found a Desser Tire.

http://www.desser.com/products_airtubes.php

Leak guard style tubes have been standard in RV finish kits for quite a few years now.

rvbuilder2002 said:

Leak guard style tubes have been standard in RV finish kits for quite a few years now.

Click to expand...

Thanks, Scott, glad to know they are part of the kit.

Another common cause of slow leaks is a valve core that is either not tight enough or defective. I've had to replace a couple over the years.

I wonder if the tire spec for pressure is just the max they are rated for by the tire manufacturer as opposed to the recommended working pressure.

I had a bad stem valve on one tire that created a slow leak until I replaced the valve stem - saved some money and hassle there!

Maybe it's just me, but I find it tough to judge the tire pressure state by sight with the wheel pants installed.

Rich

RFSchaller said:

I wonder if the tire spec for pressure is just the max they are rated for by the tire manufacturer as opposed to the recommended working pressure.

I had a bad stem valve on one tire that created a slow leak until I replaced the valve stem - saved some money and hassle there!

Maybe it's just me, but I find it tough to judge the tire pressure state by sight with the wheel pants installed.

Rich

Click to expand...

The pressures specified for the RV-12 are based on actual static testing of the landing gear system (I already mentioned the tires and their air pressure are part of that system).

Has anyone put on Alaskan Bushwheel style tires yet?

Scott,

I understand. The comment was aimed at the difference between what the tire can physically take versus the aircraft mfg recommended pressure.

Rich

Maybe a crazy idea but, Those tire monitor idiot lights on newer cars could have an application in aircraft. I do not know how they work and what is required but there is obviously a bit of a problem with keeping our tires inflated properly. It would be great if those little sending units could actually monitor and display the pressure rather than just alarm when pressure goes below a certain set point.

Randall in Sedona

Technology is there

The technology to send the operator or pilot the exact tire pressure in each of the tires already exists. My Hyundai Sonata has this feature. Hope it never goes bad as I am told that replacement of these devices is costly!!!

Auto Zone has stem caps with pressure display, but as I recall it was a go-no go indicator for specific pressure. I didn't buy any because I was concerned they might introduce a leak, and with wheel pants I can't see them anyway. They might make sense for folks who don't have wheel pats.

On our trailer (the "other" RV) each tire stem has a screw on pressure monitor with a little replaceable coin-type battery in it. They transmit to a cigarette-lighter-plug-in device that shows 4 green LEDS and alarms if one goes low. The low alarm setting is in the on-tire device and cannot be changed. You do not get an actual readout of pressure. The set of 4 was about $50 on eBay, made in China.

Our Jeep Cherokee had inside-the-tire sensors with continuous analog pressure readout plus alarm. Our Ford truck has alarm but no continuous readout. These automotive inside-the-tire sensors have built-in batteries that (in many cases) cannot be replaced, requiring the more expensive replacement of the sensor ($50-$80 each) involving a tire demount-remount. They last 5-7 years and became mandatory about that many years ago, so lots of people are starting to get warnings and finding this out.

The trailer system we have could be easily adapted to a plane. It was sold in two versions, one with alarm set at (if I remember right) about 50psi and the other with it set at 25 psi (not user changeable.) The heads are not that heavy and don't project out very much but they might rub the inside of a wheel pant.

Check out this link.
http://www.tirepressuremonitor.com/pressurepro/10-wheel-monopole-monitor/
I have one of these types setups on my truck and fifth wheel trailer. The sensors mount on the valve stem and weigh 2/3 of an ounce. You set the tire pressure to what you want then install the sensor. It bases its warnings on percent high/low from this starting point. It reads out pressure on the display unit when you advance through the sensors that are installed and give audible warning if values fall out of the high/low range. It has saved me several times with my trailer tires. Sensors battery last 3 years or so then you can send unit in for refurb. Well worth the dollars if it saves on incident.

Hey John, Any idea why everyone is buying 6 ply tires? As light as we are, I would think that 4 ply would be a better choice.

Thanks...............Tom

Jetguy said:

The Tube!

Trimining the Wheel Pan!

Tire Diameter!
Aero Classic. Inflated.

[

Elite, uninflated.

Click to expand...

Hey John, Any idea why everyone is buying 6 ply tires? As light as we are, I would think that 4 ply would be a better choice.

Thanks...............Tom

Click to expand...

Not really sure about the 4 ply. The original tires are 6 ply so I stuck with that on these. I'm all about less maintenance so I didn't want to go to far from the original setup. I run wheel pans to and a flat tire on landing would ruin them. and then I'd have to fix it. If I had to guess the 4 ply may puncture more easily. Also there is a weight rating on aircraft tires so check that to. The retreads seem to be holding up very well. I'll have to check to see how many hours I have on them now. Probably over a hundred. Turned out that the hardness of the retreads wasn't a factor on landings. Can't really tell the difference between them and the originals. I run about 30 psi with no problems and check the pressures monthly.

John,

I don't know if a flat would ruin a wheel pant, but I suspect it might. I helped a guy with a tire that went flat in his hangar. We had to jack up the wing just to get to the wheel pant bottom screws to get it off.

The wheel pants look great, but from a practical stand point they don't seem to be worth the expense and maintenance complications. --- And yet mine are still in place. I guess it's like my bad comb over --- looks good to me!

Rich

Thanks John. Desser has both, and the 6 ply is only $5 more, but the 6 ply tires are on a short 7 day waiting period. I guess I will just wait for the 6 ply. My thoughts were that I could run just a bit more pressure, and still retain the cushion with the 4 ply tires. My guess is that the 4 ply would be a tad lighter as well. Appreciate your thoughts.........Tom

RFSchaller said:

I guess it's like my bad comb over --- looks good to me!

Rich

Click to expand...

I hear these are becoming fashionable?

Dave12 said:

I hear these are becoming fashionable?

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I didn't know Alec Baldwin flew a 12...

Just a little thinking here, pressure sensor, Bluetooth module, now to get it to talk to the dynon and garmin units..... fun project to work on on overnights......

Bob burns
Rv-4 n82rb

RV-12 Maintenance Manual on Tires

Jetguy said:

I recently put on my third set of main tires at 632 hrs. I thought I would
try something new and changed from the Desser Aero Classic All Weather tire to the Desser Elite retreads.

FWIW:

Page 5-8 of the maintenance manual (Rev 4) specifies "All three tires are 5.00 x 5 size, either 4-ply or 6-ply tube type aircraft tires are acceptable."

Click to expand...

My go-to reference for aircraft tires is the Michelin Aircraft Tire Databook. Most of what is found there will apply to other brands in the same sizes. I winnowed the little chart below for 5.00-5 main tires.

Note that inflation pressures may be adjusted downward in proportion to load. For example, a 5.00-5 4-ply has a 31 psi max pressure when unloaded. Max static load is 800 lbs per tire. If we assume 90% of the load is on the mains, an RV-12 at 1320 lbs would load each tire...

(1320 x 0.9) / 2 = 594 lbs

So:

(594 x 31) / 800 = 23 psi minimum pressure to achieve design spec, which is mostly a matter of how much the tire can compress before the rim and bead mash into the carcass. See the "bottoming load" values.

For an RV-12 at 1320 lbs, a 4 ply rating is more than enough. An 1800 lb airplane could maybe use the 4 ply rated tire, but it would be right at the maximum allowable load...

(1800 x 0.9) / 2 = 810 lbs

and thus would need a slight boost in tire pressure:

(810 x 31) / 800 = 31.3 psi

A 6 ply tire on an 1800 lb airplane can run an unloaded tire pressure as low as....

(810 x 50) / 1285 = 31.5 psi minimum pressure to achieve design spec

Note that minimum pressures for both 4 and 6 ply are (as a practical matter) the same, given the same load. That's not a coincidence; they're dimensionally the same. The difference is burst pressure (maximum strength, if you will), not operating pressure.

Remember two details. First, these are unloaded pressures. Add 4% for rated load.

Second, these are tire manufacturer's numbers. An airframe designer or wheel engineer may specify something different for reasons of their own, and as an EAB operator, you also have a say. For example, as Scott noted recently, a higher than specified tire pressure may increase airframe component load, given a maximum smash into the runway. A landing gear analysis says running tire pressure at max (for example, a 6-ply at 50 psi) does in fact increase component load, but the actual difference is not large. Me? I'll take the higher pressure and try not to crash into the runway with maximum gusto.