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Fast Taxi


FlyingMonkey

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Desser has what they call "Leak Guard" tubes now. They are thick and the equivalent of a Michelin Air Stop tube. They do cost more, but they are well worth the extra money. We have lots of thorns here in AZ and none of us at my field get flats from debris and we rarely even have to put air in the tires. I might put 1-2 psi in my tires every 6 months.

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Is there a way to check pressure without removing the wheelpants? I'm not sure I can see the stems with them on...

 

I have seen a tricycle TPMS system used on a CT. About the size of an modern electronic car key.

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1) Pandas are a protected species. Just sayin'.

 

2) Aftermarket TPMS systems are somewhat frowned upon in the motorcycling world. They have failure modes that can result in a sudden loss of all air pressure. Probably should have an LOA to add something like that to be strictly legal.

 

3) Extra fuel in the Sky Arrow would not help me much, since most of my trips are with Karen, and from our Page trip you know we had to leave a couple gallons out as it was. But these planes are touted for surveillance and pipeline patrol and the like. There's one in Knoxville that's used to gather air quality samples. For single pilot operations, extra fuel would certainly be nice.

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Dresser did not offer the 400X4 in 6 ply, only 8. According to a local long time tire retailer, there is no need to put extra pressure in an 8 ply tire over a 6 if the load rating is not a factor. So, I put 32# in the nose with the 8 ply. That is on the Italian wheel. Will do the same on the Matco wheel, I guess.

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You guys can use whatever pressure you want, but,

 

 

When I tested these the 8 plys and talking to Desser (Ken, 1 of 2 owners) at the same time we found that the lower pressures caused the front tire to turn on the Marc wheel very easily and pulled the stem on 3 different CT's. At 30 psi I saw a stem go sideways from a straight taxi then a 180 in 200 yds. I have seen the stem completely pulled over 6-8 times now. The Matco wheel does help. The Marc mains weren't as bad. Desser originally wanted 60 psi in all the 8 plys, but that was decided to be too much. We tested 45 psi and have not had any issues. You may get away with 35 in the front so long as you are the type to keep a close eye on the pressure and don't let it drop below 30 psi. The 8 plys do ride a little rougher because they have more air and they are an 8 ply which is stiffer by nature. The Marc wheels even on the mains do allow the tire to move on the wheel much easier than the Matco's The Matco wheels have not only more metal to rubber contact surface area, but the inside edge of the wheel is roughed up to help prevent the tire from moving. The 8 ply isn't a bad tire, but because it is an 8 ply it has some stiff sidewalls. I sent the first 2 sets back because 30 psi didn't make them round and filled out and we thought they had flat spots in the rubber. That was only because there wasn't enough pressure to fill them out and put enough pressure against the side of the metal wheel. FD does approve up to 35 psi, but do what you need to do to keep from being stuck on the runway. For the front wheel taxiing is the worst.

 

 

That's the unfortunate thing about that smaller 4.00x 4 tire is there isn't any real options. The main tires do have an option of a 4.00x6 6 ply and used with a "Leak Guard" tube you should be in good shape. In the small tires I would keep 35 in them anyway because too many let the pressure drop before they get checked often enough. It will also guarantee the tire won't turn on the wheel and really strand you.

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Where is the citation for Dresser to call for 60 psi? I looked on their site and couldn't find it. (I thought tire manufacturers tended to stay away from specing the pressure and left that to the equipment manufacturer?)

 

Why is the tire turning on the wheel for airplanes when it doesn't for cars, lawn mowers and farm tractors? From the discussion above, it didn't seem to be from spinning up on landing but from normal taxiing.

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The pressure came right from Ken (one of the owners) at Desser. That was their initial thoughts. After I tested the tire with some real field test they kind of revised that number and they were happy at 50 psi at the time. If they have changed I don't know. It was a fairly new tire for them back then. You can get away with less than 50, but I would never let my front go below 35 psi and we keep the mains at 45. FD's drop test was done at 35 psi. That is where they get that number and I beleive it was from higher than what was actually called for for the test.

It's a good, lots of rubber, but stiff tire. If your camber is out it will wear on the edge because of it's square profile. The problem hasn't been with the tire itself. It has more to do with the crappy Marc wheels and our cars and tractors don't just have one wheel up front and don't go from zero to 100+ mph in an instant either. If you want to see a similar affect drop your auto tires to 20 psi and go drive all day. Eventually you'll roll a tire. We usually don't have inner tubes for our cars either and our rubber bead to metal ratio is much higher. The Marc wheels don't have the tire to metal contact as others do and when we taxi and the pressure isn't sufficient to hold the tire against what metal there is then a turn on the sole front wheel cause a side stress which starts to turn the tire on the wheel. Here is a bad example, but an example never the less. We have all that weight and side force on that single tire so it moves, if you lowered the pressure far enough for the us light weight weak humans you can turn that tire too on the wheel. I do it all the time when mounting tires and want to rotate a heavy spot to another point on the wheel. Lower the pressure and I can turn the tire on the wheel. A heavy and side loaded aircraft doesn't need that low a pressure, but get it to a certain psi point and it will turn it too.

 

Almost all the tires I have seen had the stems pulled on taxi when there is weight and side load in a turn. I have seen and heard of a few happen on landing. Using the 8 ply doesn't bother me if it was on my plane (other than a stiff ride), but allowing the pressure to get too low would bother me greatly and I would check it a lot more often that I do now. I have had to fix three on the tarmac away from my airport with odd ball tools because of pulled stems.

 

There has been one other problem for a few with the 8 ply. FD didn't really allow enough space between tire and the front strut rod that protrudes down through the fork. I have seen another bunch shave some rubber from this contact because the 8 ply has a little more rubber. This is an FD goof in my opinion because they made the tolerance way too close. It doesn't happen to everyone, but you should take a look. It's easy to see. Sometimes it is so little as not to worry, but others shave a lot. pressure in the tire can play a part. FD told me I could grind the extra tubing sticking down, but don't go into the weld. This helped a few that had the rub issue.

 

No one else has done this testing, but I did tell Desser as we talked through this and I told FD. It isn't documented because I'm the only one who has ever done any research on this.

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I appreciate the discussion, but continue to maintain that Dresser should be publishing specs if they have a position on the issue.

I wonder if any of this has to do with typical operating temperatures? It gets warm in Iowa, but nothing like it does in AZ.

I'll double check my fork to be sure there is no interference. I hadn't noticed any so far, but it is easy to miss with the wheel fairing in the way. It might be an issue at higher pressures.

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The problem has been no matter what MFG (Rotax, FD, Desser, ect..) that there are to many factors and different applications and they can't test or even know that many exist. The example is Desser has never tested all the wheels that their tires may go on. Use a cheapo Marc front wheel and things change or are affected unbeknownst to Desser.

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Roger, come on. You said Ken from Dresser wanted 60 lbs, then you talked him into 50 lbs. That gives the appearance that Dresser does indeed have a position. I'm only asking for them to state it.

 

Otherwise, what we have is you explanation for why you like a tire pressure. And, you quibble on your own number by admitting that 35 will work. Sorry, that is not an industry standard criteria. You can hardly blame the CT community for asking for a little more than Roger's word, especially when you yourself refer to other sources.

 

I can put anything I want to into these tires, but SLSA should have a standard that we can all accept. Apparently we end up back with FD and 35 lbs.

 

 

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I don't know what to tell you, it's all I have and it's all they have. I'm just passing on what I saw, tested and discussed with people back then. If they have changed then I don't know anything about it. When you call them make sure to ask how pressure differential behaves on the Marc or Matco wheels. My guess is they will say they don't know. I can't make post documentation.

 

You could do all new testing and document this for Desser, FD and the CT group ?

You can experiment if you would like and get some new results. You will need to test more than one plane (at least 2) and use a Marc wheel and a Matco then change pressure and taxi each time. Not just straight, but with several turns. Then you can write it up and send it to Desser and FD and try to get them to post it.

You and I both know the document side will never happen. It hasn't for many years. I have been there and done that with most the Mfg's that involve our plane and you haven't seen them post one thing. They have made some of the changes, but you never knew why. Where do you think Matco's on all CT's came from after Jan. 2009?

 

I was sent 5 Sensenich props last year too because they didn't know how they performed against other props and on the same plane and they didn't have the resources to test them side by side at the same time. I don't know of any prop MFG to do that type of testing. I used 4 2006 CTSW's and all with different props. I wrote it up and you will never see them publish any of it. It is just myself, 2 guys at Sensenich and FD that know the results. That said I did put info out here about it in another post months ago.

 

What would happen to us as individual owners, the forum and the MFG if many of us quit testing and researching then posting our experiences on our results or the better ways to do things or discovering better parts for everyone to benefit from. It would end up being a dog eat dog atmosphere trying to get any info about our planes at all and it would be far bigger parts issue and more costly. I agree the MFG's should be more forthcoming in many things, but I can see there is no way any MFG can test for all applications, factors, variances and individual ways of doing things and we have become a too litigious society, so if they put too much in print then it is much harder to defend.

 

 

So all I can do as an individual is pass on my experiences, research, testing results, info from phone conversations from MFG's and schooling from those MFG's, other than that, that's all I got.

No documentation, not my job and you'll have to take that fight to them.

I follow or do all I have posted to my own plane or pass on special experiences from what I saw on another plane.

 

I do all this because I like and want to help, but it's just me and my lowly .budget. I can't control any of the big boys.

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As one data point, I have about 350 hours on my Marc Ignegno wheels and brakes.

 

The decal for the mains (5.00x5) calls for 29 psi, and that's what I've used. I have not had a tire rotate on the rim, at least not enough to cause problems.

 

On the basis of the higher pressure indicated on the new Sky Arrow, and Rogers's advice, I'm going to bump up to 35 psi. I have Desser Monster retreads, but I don't recall the ply.

 

My nosewheel is a 4.10x3.50/4. Not sure of the manufacturer, though the Equipment List shows it as a Cheng Shin (the wheel, not the tire). It calls for 21.8 psi, which I've also used. Probably bump that up to 25 psi. If that sounds small and light pressure, remember that mine's a pusher, so there's very little weight on the front tire.

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