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What's the nose and main wheels required tire pressure?
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rv10flyer

Joined: 25 Aug 2009
Posts: 364

Posted: Tue Apr 23, 2013 3:30 am Post subject: Re: What's the nose and main wheels required tire pressure?

If moisture is present it contributes to a greater change in pressure simply because at lower temperatures water condenses to become a liquid. The liquid form of water occupies very little volume and contributes only a negligible pressure to the tire. But at higher temperatures, such as those in a running tire, water evaporates inside the tire and becomes a gas which increases pressure in the tire.

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Wayne G.

rv10flyer

Joined: 25 Aug 2009
Posts: 364

Posted: Tue Apr 23, 2013 3:32 am Post subject: Re: What's the nose and main wheels required tire pressure?

1% Water Vapor and Other Gases – Escapes up to 250 times faster than Nitrogen



21% Oxygen – Escapes 3-4 times faster than Nitrogen



78% Nitrogen – The largest molecule in 

air, dry, non-flammable.

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Wayne G.

Bob Turner

Joined: 03 Jan 2009
Posts: 885
Location: Castro Valley, CA

Posted: Tue Apr 23, 2013 1:30 pm Post subject: Re: What's the nose and main wheels required tire pressure?

Wayne,



I believe what you are quoting are not "escape rates" but rather the diffusion coefficients of O2 and N2 thru rubber, in units of "number of molecules per thickness per area per partial pressure difference".



To get the diffusion rate you need to multiply these numbers by the difference in partial pressures (inside to outside). For a typical plane tire (filled to 45 psig, or 60 psi absolute) the difference in partial pressures are 36 psi for N2, 9 psi for O2; so in fact the rate of loss (assuming the diffusion coefficient for O2 is 4 times higher) is the same for both. Now, because there is less oxygen, a given number loss results in a larger fractional loss, so this will result in a net loss of total pressure which is faster than pure N2, and can be seen in carefully controlled laboratory experiments, but it is nowhere near 4 times faster. Furthermore, as has been pointed out, after one or two re-fills of air the tire has become enriched with N2 and depleted of O2, and is essentially similar to the original all N2 tire, which will have O2 leaking in from the outside until it has 3 psi (absolute) of O2 inside.

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Bob Turner
RV-10 QB

johngoodman

Joined: 18 Sep 2006
Posts: 530
Location: GA

Posted: Wed Apr 24, 2013 5:22 am Post subject: Re: What's the nose and main wheels required tire pressure?

I can't resist jumping into this one. I have 106 landings on the original Van's tires. I have only filled them once - when I built them. They still have 42 in the mains and 40 in the nose. I don't have wheel pants (hate 'em). Here is a photo. Notice no uneven wear.

John

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jfrjr(at)roadrunner.com
Guest

Posted: Wed Apr 24, 2013 11:51 am Post subject: What's the nose and main wheels required tire pressure?

John Goodman:  I understand you don't like wheel pants but in my 10 they make a huge difference in airspeed.  I took mine off before flying from KLVK to KSNS for painting.  After reaching cruise altitude (8.5K) I noted a 12K drop from my usual IAS after double checking all my settings.  I also had removed the main gear fairings but not the nose wheel. After the paint job and with the fairings and pants back on the IAS were back to the former "normals". In fact I may have gained a knot or two (? clear coat?).  Jay Rowe N333GR



Sent from my iPhone



On Apr 24, 2013, at 6:22 AM, "johngoodman" <johngoodman(at)earthlink.net> wrote:



 	  Quote: 	
		   

 

 I can't resist jumping into this one. I have 106 landings on the original Van's tires. I have only filled them once - when I built them. They still have 42 in the mains and 40 in the nose. I don't have wheel pants (hate 'em). Here is a photo. Notice no uneven wear.

 John

 

 --------

 #40572 Phase One complete and flying.

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=399274#399274

 

 

 

 

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johngoodman

Joined: 18 Sep 2006
Posts: 530
Location: GA

Posted: Wed Apr 24, 2013 12:27 pm Post subject: Re: What's the nose and main wheels required tire pressure?

 	  jfrjr(at)roadrunner.com wrote: 	
		  John Goodman:  I understand you don't like wheel pants but in my 10 they make a huge difference in airspeed.  I took mine off before flying from KLVK to KSNS for painting.  After reaching cruise altitude (8.5K) I noted a 12K drop from my usual IAS after double checking all my settings.  I also had removed the main gear fairings but not the nose wheel. After the paint job and with the fairings and pants back on the IAS were back to the former "normals". In fact I may have gained a knot or two (? clear coat?).  Jay Rowe N333GR

	




Did you remove the wheel pant brackets? Probably not. I have all the fairings, but no pants. My hubcaps probably give me a knot, as well. I'm guessing that the lack of pants costs me 5 knots, max. The ability to pre-flight the wheel every time is worth it - form follows function.

John

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Bob Turner

Joined: 03 Jan 2009
Posts: 885
Location: Castro Valley, CA

Posted: Wed Apr 24, 2013 2:47 pm Post subject: Re: What's the nose and main wheels required tire pressure?

I think you're both right. Like Jay, I noticed something like a 12 knot gain between fairings and no fairings. But I also noticed, as Vans has said, that most of the gain was due to the gear leg fairings, not the wheel pants.

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Bob Turner
RV-10 QB

rv10flyer

Joined: 25 Aug 2009
Posts: 364

Posted: Wed Apr 24, 2013 4:13 pm Post subject: Re: What's the nose and main wheels required tire pressure?

I can believe 5 kts like Bob. A round tube has 9 times the drag of a airfoil shape. 



John, you started out with 42 psi and one year later ended with 42 psi? You have some super rubber there! Or maybe every time you fly with your tires exposed, the 160 kt air molecules are keeping the pressure maintained.



I do love the looks and speed of my pants. Exposed tires/brakes were really nice for rentals. On mine, my preflight consist of ensuring they are not flat and that I have good brake pressure.

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Wayne G.

Tim Olson

Joined: 25 Jan 2007
Posts: 2881

Posted: Wed Apr 24, 2013 4:33 pm Post subject: What's the nose and main wheels required tire pressure?

I really wouldn't be hard to get rid of the ugly exposed wheels by putting the fairings on, but install a Camlok or similar latch right over the brakes if you really wanted the speed, efficiency, AND ability to do a full preflight of the wheels often.  There is middle ground.

Tim



On Apr 24, 2013, at 7:13 PM, "rv10flyer" <wayne.gillispie(at)gmail.com> wrote:



 	  Quote: 	
		   

 

 I can believe 5 kts like Bob. A round tube has 9 times the drag of a airfoil shape. 

 

 John, you started out with 42 psi and one year later ended with 42 psi? You have some super rubber there! Or maybe every time you fly with your tires exposed, the 160 kt air molecules are keeping the pressure maintained.

 

 I do love the looks and speed of my pants. Exposed tires/brakes were really nice for rentals. On mine, my preflight consist of ensuring they are not flat and that I have good brake pressure.

 

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 Wayne G.

 SB 12/01/2009-12/01/2011

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johngoodman

Joined: 18 Sep 2006
Posts: 530
Location: GA

Posted: Thu Apr 25, 2013 4:25 am Post subject: Re: What's the nose and main wheels required tire pressure?

Actually, I don't think the wheels are ugly. I guess it's just my background. I learned to fly in the Navy and on every airplane I ever flew, you could see the tires. Now that I'm long retired from the Navy and Northwest Airlines, I have finally seen airplanes with pants. I just plain don't like the looks of them. The RV-10 looks like it has watermelons where the tires should be.



I understand the drag thing, but it was pretty obvious that you are only loosing a couple of knots per wheel. I cleaned up the wheels as much as I could and added hubcaps to the mains - painted to look like the wheel of an AF-18. I actually experimented with a small airfoil directly behind the tire but never had the guts to test them. I was concerned about vibration and harmonics.



I'm happy with the results. Besides, think of all the money I saved by not having painted watermelons...(g)

John

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Mike Whisky

Joined: 05 Jun 2006
Posts: 336
Location: Switzerland

Posted: Thu Apr 25, 2013 7:33 am Post subject: Re: What's the nose and main wheels required tire pressure?

I just love this forum thanks to all who answered my question and I will start as per plans and see how things develop from there. 

Mike

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RV-10 builder (flying)
#511

rv10flyer(at)live.com
Guest

Posted: Thu Apr 25, 2013 8:16 am Post subject: What's the nose and main wheels required tire pressure?

just make sure the gap around the wheelpants and wheels are wide enough, 

lower psi than you initially put in will cause the tire sides to bulge and 

rub against the wheel pants, especially on landings. 1"gap all around is a 

good start.



--

rv10flyer

Joined: 25 Aug 2009
Posts: 364

Posted: Thu Apr 25, 2013 10:06 am Post subject: Re: What's the nose and main wheels required tire pressure?

I left 3/4" all the way around. I have had 42 plus or minus 5 psi in the mains with many full load/firm landings and no evidence of rubbing the red paint as of last week.

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Wayne G.

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