X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Wed, 25 May 2011 13:44:38 -0400 Message-ID: X-Original-Return-Path: Received: from elasmtp-dupuy.atl.sa.earthlink.net ([209.86.89.62] verified) by logan.com (CommuniGate Pro SMTP 5.4c3j) with ESMTP id 4994084 for lml@lancaironline.net; Wed, 25 May 2011 10:02:53 -0400 Received-SPF: none receiver=logan.com; client-ip=209.86.89.62; envelope-from=colyncase@earthlink.net DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=dk20050327; d=earthlink.net; b=EhUPdM05VFoa7nwy4GjaLQr2ClB+EmapRXsmgpv/cMCOjtLamtYLD6d33F0+blY1; h=Received:From:Mime-Version:Content-Type:Subject:Date:In-Reply-To:To:References:Message-Id:X-Mailer:X-ELNK-Trace:X-Originating-IP; Received: from [216.57.118.194] (helo=[192.168.1.100]) by elasmtp-dupuy.atl.sa.earthlink.net with esmtpa (Exim 4.67) (envelope-from ) id 1QPEfB-0002jN-GP for lml@lancaironline.net; Wed, 25 May 2011 10:02:17 -0400 From: Colyn Case Mime-Version: 1.0 (Apple Message framework v1082) Content-Type: multipart/alternative; boundary=Apple-Mail-25--540060872 Subject: Re: [LML] Fuel restriction or air, Fuel Vent Check Valves X-Original-Date: Wed, 25 May 2011 10:02:17 -0400 In-Reply-To: X-Original-To: "Lancair Mailing List" References: X-Original-Message-Id: <89ECF867-F11C-423D-B0A2-14E7C8A8A19A@earthlink.net> X-Mailer: Apple Mail (2.1082) X-ELNK-Trace: 63d5d3452847f8b1d6dd28457998182d7e972de0d01da940ac53d1bb4f8f6c6148c112c33c6b40b2350badd9bab72f9c350badd9bab72f9c350badd9bab72f9c X-Originating-IP: 216.57.118.194 --Apple-Mail-25--540060872 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=windows-1252 Thanks Bill for pointing out my error. On a IVP each tank represents roughly 90 square feet of surface area. 90 * 144 * 1 =3D 12,960 lbs. On May 24, 2011, at 1:23 PM, Bill Hannahan wrote: >=20 >=20 > Regarding this;=20 >=20 > { the Andair check valves (at least the model I got) are marked 1psi = required to push air out the valve. > So each wing would have about 50 square feet top and bottom or about = 100 lbs. total force trying to blow the wing apart.} >=20 >=20 > There are 144 square inches in one square foot. 1 psi is equivalent to = 144 pounds per square foot. The 320/360 with extended fuel tanks has = about 15 square feet of wing tank, so about 2,200 pounds of force on = each skin at 1 psi. > =20 > =20 > Regarding this; > =20 > { The ES has tiny NACA scoops in the wingtips like the IV with the = thought that they would slightly pressurize the fuel tanks to help the = fuel feed to the engine. Sort of makes sense to me. I have no idea if = it works at all.} > =20 > The pressure produced by a NACA scoop is not proportional to its size. = A poorly designed or poorly located scoop may produce no pressure gain = at all. A well designed NACA scoop located near the front of a body, = that is, where the shape is still expanding, such that you can see the = inlet standing directly in front of it, may well produce full dynamic = pressure at zero flow, like a pitot tube. > =20 > Out of curiosity, I have looked at many fuel vents at fly-ins. There = is great variation in type and location. Some are located such that I = would expect them to produce near full dynamic pressure. > =20 > Dynamic pressure increases with the square of velocity. At 200 knots = CAS it is 27 inches of water, about 1 psi. 300 knots equals 62 inches of = water, 2.2 psi, 317 pounds per square foot trying to blow the skins off = the wing. > =20 > http://www.iflyez.com/manometer.shtml > =20 > Regarding this; > =20 > {Having a check valve or float valve in the vent line is common in = certified aircraft so I disagree that vent lines must be free flowing in = both directions. The twin cessnas use a float system to block the vent = when fuel is present. This has led to problems with unanticipated = blockage of the vent line leading to ADs like this one:} > =20 > I think the AD makes a good case for free flowing vent lines. > =20 > Imagine you have a vent with a float valve. You have an early morning = departure from Phoenix and top the tanks the night before. Something = comes up that delays the trip one day and your plane sits on the ramp = where temperatures skyrocket during the day. The fuel expands, the float = valve closes, and the wing is structurally damaged by expanding fuel. = The damage may be indicated by a big fuel stain on the ramp, then again = it may not be indicated until you take off. > =20 > I am somewhat suspect of multiple vents to one tank. I met a builder = with a BD4. He had doubts about the wing tip vents, so he had drilled = numerous holes in his inboard mounted fuel caps. I pointed out that with = gasoline, the fuel vapor concentration is usually above the combustion = limit, but with the fuel cap in a low pressure region, and the tip vent = getting ram air, there would be a continuous flow of fresh air through = his tank that could make it combustible. A static spark near the vent = could set it off. He thought that was interesting. > =20 > A check valve in the cap allowing air in, not out is probably OK as = long as the main vent is not in a negative pressure region, but it might = allow water in while sitting on the ramp. > =20 > I=92m a big fan of the Keep It Simple principle regarding fuel vents. = I only top off a few times a year for long trips and regard the = possibility of a little spillage taxiing out as a small price to pay. > =20 > =20 > Regards, > Bill Hannahan >=20 > wfhannahan@yahoo.com >=20 --Apple-Mail-25--540060872 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=windows-1252


Regarding this;

{ the Andair check valves (at least the model I got) are marked 1psi = required to push air out the valve.

So each wing would = have about 50 square feet top and bottom or about 100 lbs. total force trying to blow the wing apart.}


There are 144 square inches in one square foot. 1 psi is equivalent to = 144 pounds per square foot. The 320/360 with extended fuel tanks has about = 15 square feet of wing tank, so about 2,200 pounds of force on each skin at = 1 psi.

 

 

Regarding = this;

 

{ The ES has tiny NACA scoops in the wingtips like = the IV with the thought that they would slightly pressurize the fuel tanks to = help the fuel feed to the engine.  Sort of makes sense to me.  I have no idea if it works at all.}

 

The pressure produced by a NACA scoop is not = proportional to its size. A poorly designed or poorly located scoop may produce no = pressure gain at all. A well designed NACA scoop located near the front of a = body, that is, where the shape is still expanding, such that you can see the inlet = standing directly in front of it, may well produce full dynamic pressure at zero = flow, like a pitot tube.

 

Out of curiosity, I have looked at many fuel vents = at fly-ins. There is great variation in type and location. Some are located = such that I would expect them to produce near full dynamic = pressure.

 

Dynamic pressure increases with the square of = velocity. At 200 knots CAS it is 27 inches of water, about 1 psi. 300 knots equals 62 = inches of water, 2.2 psi, 317 pounds per square foot trying to blow the skins = off the wing.

 

http://www.iflyez.com/manom= eter.shtml

 

Regarding this;

 

{Having = a check valve or float valve in the vent line is common in certified aircraft so I disagree that vent lines must be free = flowing in both directions.  The twin cessnas use a float system to block the vent when fuel is present. This has led to = problems with unanticipated blockage of the vent line leading to ADs like this = one:}

 

I think the AD makes a good case for free flowing = vent lines.

 

Imagine you have a vent with a float valve. You have = an early morning departure from = Phoenix and top the tanks the night before. Something comes up that delays the = trip one day and your plane sits on the ramp where temperatures skyrocket during = the day. The fuel expands, the float valve closes, and the wing is structurally = damaged by expanding fuel. The damage may be indicated by a big fuel stain on = the ramp, then again it may not be indicated until you take off.

 

I am = somewhat suspect of multiple vents to one tank. I met a builder with a BD4. He had doubts about the wing tip vents, so he had = drilled numerous holes in his inboard mounted fuel caps. I pointed out that with gasoline, the fuel vapor concentration is usually above the combustion = limit, but with the fuel cap in a low pressure region, and the tip vent getting = ram air, there would be a continuous flow of fresh air through his tank that = could make it combustible. A static spark near the vent could set it off. He = thought that was interesting.

 

A check valve in the cap allowing air in, not out is = probably OK as long as the main vent is not in a negative pressure region, but it = might allow water in while sitting on the ramp.

 

I=92m a = big fan of the Keep It Simple principle regarding fuel vents. I only top off a few times a year for long trips and regard = the possibility of a little spillage taxiing out as a small price to = pay.

 

 

Regards,
Bill Hannahan


= --Apple-Mail-25--540060872--