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  #21  
Old 10-09-2018, 10:18 AM
ericv ericv is offline
 
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there are four "A" types who had responded to this thread. This link was for them and any other non-responders who are "A" types.
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  #22  
Old 10-09-2018, 10:52 AM
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JonJay JonJay is offline
 
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Quote:
Originally Posted by DanH View Post
...in particular if the jack and spare tube are needed for ballast anyway

Kidding aside, the numbers don't lie. At 1800 lbs and 8.1 ft per/sec with 90% on the mains, the dead minimum is 36 psi if the inside of the tread is not expected to mash against the bead. Even at 36, consider the tube abuse with the sidewalls folded double while rolling.

I realize shimmy is a serious issue for the round leg models, but it is best to be aware that tire pressure is not a random pick item. Everybody drops one in eventually, and there are also pavement edges to consider.
Which tires?
Zero issues at 30 psi all these years with tires or tubes. Original Air Hawks (replaced at 460 hrs with tread to spare) and now Desser Retreads (passing 770 hours and just now ready to rotate with at least half tread remaining).
So, that's my experience with my 6.
Sidewalls folded double? There is little visual difference in tire profile between even 25 psi and 50psi. However, I do trust your smarts and I know better than to argue with you so I won't. I am having a hard time understanding why I have never had an issue when it sounds like my tires should be eating tubes and I should have flats all the time.
Perhaps I am just lucky, in all the airplanes I have owned as I have never ran any of them above 35psi.
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  #23  
Old 10-09-2018, 11:50 AM
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DanH DanH is offline
 
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Quote:
Originally Posted by JonJay View Post
Sidewalls folded double? There is little visual difference in tire profile between even 25 psi and 50psi.
Folded at impact, given an 8.1 ft sec descent rate.
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  #24  
Old 10-09-2018, 12:23 PM
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JonJay JonJay is offline
 
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Quote:
Originally Posted by DanH View Post
Folded at impact, given an 8.1 ft sec descent rate.
I hope the gear and prop arenít folded too!
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  #25  
Old 10-09-2018, 08:47 PM
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Dan Langhout Dan Langhout is offline
 
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Default Inquiring minds . . . .

Quote:
Originally Posted by DanH View Post
.. . . . . At 1800 lbs and 8.1 ft per/sec with 90% on the mains, the dead minimum is 36 psi if the inside of the tread is not expected to mash against the bead.. . . . . .
Curious where this specific number comes from?
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  #26  
Old 10-09-2018, 10:22 PM
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DanH DanH is offline
 
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Quote:
Originally Posted by JonJay View Post
I hope the gear and prop arenít folded too!
Not at 8.1 ft/sec.

Quote:
Originally Posted by Dan Langhout View Post
Curious where this specific number comes from?
One of Neal Willford's excellent design spreadsheets. The whole series was available for download, but I just searched EAA.org without luck. They were published circa 2003.

I should review the inputs for precision before swearing on a bible. The particular file I picked from my hard drive was named RV-7, and dated 2005.
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  #27  
Old 10-10-2018, 06:53 AM
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Walt Walt is offline
 
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Quote:
Originally Posted by ericv View Post
there are four "A" types who had responded to this thread. This link was for them and any other non-responders who are "A" types.
I run 45-50 all around, and if your aiplane visits my shop that's what they go out with. Never had a flat or any shimmy issues.
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  #28  
Old 10-10-2018, 08:19 AM
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DanH DanH is offline
 
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Previously I said...

Quote:
I should review the inputs for precision before swearing on a bible. The particular file I picked from my hard drive was named RV-7, and dated 2005.
...so I poured a cup of coffee this AM, then dug out the spreadsheet, an RV-7 leg drawing, and the Michelin Tire Databook. After making a few corrections, we have:





BTW, the Michelin databook specifies 50 psi for a 6-ply 5.00 x 5. Lower pressure reduces the load rating.

I'm not trying to tell you lower pressures won't work. I am telling you tire pressure is an engineered value, not a random pick. The 36 psi value shown allows the tire to be mashed dead flat given a vertical velocity of 8.6 fps, about 500 fpm in pilot-speak. This is within the capability of the gear leg, although the margin is not huge.
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Last edited by DanH : 10-10-2018 at 08:25 AM.
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  #29  
Old 10-10-2018, 08:59 AM
Robert Anglin Robert Anglin is offline
 
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Default fill, check.

Dan has some very good data above and is always the place to start. I would only add that if you are new to tire care, there is an old habit you may wish to keep in mind. When you find that sweet spot that you like for you tires. Say 38 P.S.I.G., you may wish to think about rounding that up to 40 and add 3 P.S.I.G.
For most small aircraft tires the pressure will drift down a lot faster than a car tire. It is good to check them and not let them get to low as that is were they get the most damage, as in under pressure and not so much from bring a little high on the pressure. We always add 3-5 P.S.I.G. to our preferred setting and then inflate to that point. By the time most small aircraft tires set for a couple of week they will have drifted down to where you like them to be anyway. I know every tire and tube like to drift down at it own pace depending on what type and size it is. This is just an old trick we have found that keeps us from servicing tire more often than we have too and does not hurt the tires as well.
You will find that sweet spot that works for you and the type or brand of tire and tube you are using in do time. Change it around a few time till you like what you find. Yours, R.E.A. III # 80888
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  #30  
Old 10-10-2018, 11:22 AM
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JonJay JonJay is offline
 
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Thanks Dan for the thoughtful response and education. I am not too stubborn to make a change, even after hundreds of hours of doing something one way with no issues.
Perhaps all of the years of flying antiques has habits held over that where not based on anything concrete....
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