X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from outbound-mail.vgs.untd.com ([64.136.55.15] verified) by logan.com (CommuniGate Pro SMTP 5.3.7) with SMTP id 4341292 for flyrotary@lancaironline.net; Wed, 09 Jun 2010 07:25:33 -0400 Received-SPF: pass receiver=logan.com; client-ip=64.136.55.15; envelope-from=alwick@juno.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=juno.com; s=alpha; t=1276082696; bh=47DEQpj8HBSa+/TImW+5JCeuQeRkm5NMpJWZG3hSuFU=; l=0; h=Message-ID:From:To:Subject:Date:Content-Type; b=BO0yvSIrCok+JTcOQOJ2I4O3KBCXLWJBq3Ej+IL2BqrdVok4cizFUD+/U8kIfU7mf VFnJE27m1oalvY2Cgt0hSPZ2N7x8EyCmRRl5Z/wc7BWGhJz2gQ3lZhHuaW1xzxrp+a 7eaQlSn95ysG9IrBzJ89fOHG1Fv4TNSCELy3cxHQ= Received: from Penny (c-98-246-117-71.hsd1.or.comcast.net [98.246.117.71]) by smtpout02.vgs.untd.com with SMTP id AABGA88QQALGZXB2 for (sender ); Wed, 9 Jun 2010 04:23:58 -0700 (PDT) Message-ID: <41E48E3BC68B45FBB471B20301949B95@Penny> From: "Al Wick" To: "Rotary motors in aircraft" References: In-Reply-To: Subject: Re: [FlyRotary] Re: high/low pressure pumps question Date: Wed, 9 Jun 2010 04:24:00 -0700 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_03A4_01CB078B.95AF8DF0" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Windows Mail 6.0.6002.18197 X-MimeOLE: Produced By Microsoft MimeOLE V6.0.6002.18197 X-UNTD-BodySize: 17455 X-ContentStamp: 43:21:2482030255 X-MAIL-INFO:2a04f0f58d8df9dda470a1f091a479f9a5a01dd0d5fd35a924d16d85557d41d44105209df46584c4fd9051511019ad853001c9d9 X-UNTD-OriginStamp: L941HVjjYzDhN3itp//mkMJcmC/pvUWuqxFb7zgLcKqZ0PplJahnRA== X-UNTD-Peer-Info: 10.181.42.32|smtpout02.vgs.untd.com|smtpout02.vgs.untd.com|alwick@juno.com This is a multi-part message in MIME format. ------=_NextPart_000_03A4_01CB078B.95AF8DF0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Hello Todd. You describe multiple forced landings related to fuel. = Pretty clear you copied a fuel design that has a very low vapor safety = margin. If you measure fuel pressure at pump inlet and pump temp you can = predicted this failure. I really want to encourage any fact gathering = method. Ed often does an excellent job of calculating these types of = things. Greatly improves understanding. To actually measure how close = you are to failure, you'd have to put those numbers in a spreadsheet. = Add atmospheric pressure info from your instrument panel. Pick up one of = those Hodges fuel testers that measures vapor point of this particular = lot of fuel. Next you just have to apply a hair dryer to your pump and = voila, you have measured how safe your design is. All while sitting on = the ground. Use clear tubing and do this on your workbench and you can = see fuel turn to vapor.=20 I enjoy lurking, witnessing this group improve their conversions. I = noticed this method of returning fuel to pump inlet was being promoted. = No one was offering counterpoints. I'm fully aware this is a serious = life risk. Please question this particular design.=20
Hello Todd. You describe multiple = forced landings=20 related to fuel. Pretty clear you copied a fuel design that has a = very low=20 vapor safety margin. If you measure fuel pressure at pump inlet and pump = temp=20 you can predicted this failure. I really want to encourage any fact = gathering method. Ed often does an excellent job of calculating these = types of=20 things. Greatly improves understanding. To actually measure how close = you are to=20 failure, you'd have to put those numbers in a spreadsheet. Add = atmospheric=20 pressure info from your instrument panel. Pick up one of those Hodges = fuel=20 testers that measures vapor point of this particular lot of fuel. Next = you just=20 have to apply a hair dryer to your pump and voila, you have measured how = safe=20 your design is. All while sitting on the ground. Use clear tubing and do = this on=20 your workbench and you can see fuel turn to vapor.
 
I enjoy lurking, witnessing this group = improve=20 their conversions. I noticed this method of returning fuel to pump = inlet=20 was being promoted. No one was offering counterpoints. I'm fully aware = this is a=20 serious life risk. Please question this particular design.
 
<So as Ed has pointed out, while millions of cars return the = fuel to the=20 tank, millions don't.
 
This statement defies all logic. You are comparing apples to = oranges. All=20 auto fuel designs that utilize the pumps like ours return fuel = to=20 tank. They do this because it's essential for safety. Only fuel designs = that=20 have variable displacement pumps eliminate return to tank.
 
Apologize for my use of strong wording. = I was=20 thinking: "omg omg, people are going to die needlessly". My = bad.
 
-al wick
 
----- Original Message -----
From:=20 Todd = Bartrim=20
Sent: Tuesday, June 08, 2010 = 10:31=20 PM
Subject: [FlyRotary] Re: = high/low=20 pressure pumps question

Hi Al;
    Returning the fuel to the = fuel=20 line rather than the tank (thereby to the fuel suction), is I admit = not ideal.=20 Not by a long shot. However in some cases it may be a necessary evil = that can=20 (and so far has) been made to work. In most vehicles there is one = tank,=20 sometimes two so it is relatively simple to return fuel to the source = fuel=20 tank. Most airplanes also have 2 tanks and occasionally one, so = returning to=20 the source tank is again fairly simple and should be the first choice. = where=20 it becomes more complicated is when you have to manage 4 or even 6 = tanks. It's=20 difficult enough to come up with a simple, safe, light and affordable = for the=20 average home builder, way to manage selection of these 6 tanks, but to = return=20 the fuel to the source tank, would become a potential problem. Some = builders=20 simply return to a single tank which they draw down first then switch = back to=20 before it overflows, while others always drawn out of the same tank, = and=20 simply transfer fuel to that tank. Nothing wrong with that and it is = ideal for=20 many. Fortunately were not all the same, which is why were here on = this=20 list.

    My reason for 6 tanks is to increase = range for=20 either flights to remote areas with no fuel service or over long = stretches of=20 inhospitable terrain (like passing over my mother-in-law's). The plan = of=20 transferring fuel in my mind allows the distinct possibility of = pumping=20 precious fuel overboard whether it be from directly transferring fuel = or via a=20 fuel return to a tank that is not the source. There is also the = possibility of=20 failure of the transfer equipment, which would result in inaccessible = fuel on=20 board. Sure these are remote possibilities and could be lessened by = the=20 addition of various safety checks and devices all which add complexity = and/or=20 workload to the pilot. Not much but some. So I chose to try to = implement a=20 variation of a return-less system.

    Sure as = you've=20 said the failure frequency could be in the hundreds of hours, so in my = short=20 time it has been just fine, but still not proven. However what would = be the=20 incident frequency of lost or inaccessible fuel? More, less? I can't = say, but=20 I do know that if it happened there would be absolutely nothing I = could do=20 about it in flight, so I'd better hope that I didn't really need it. = With my=20 current system design, I have 2 facet pumps and 2 FI pumps that are = plumbed in=20 such a way that is fairly simple for fuel management, but also allows = full=20 redundancy in that any pump failure would not prevent me from being = accessing=20 fuel. The issue of vapour lock remains but the facet pumps 7psi of = pressure=20 has so far proven to be more than adequate for elimination of this = threat. So=20 if this were to happen at least I would have options to try to clear = the=20 vapour. Better to be able to do something than nothing.  Now with = that=20 said, I feel the chances of a vapour issue developing halfway through = a flight=20 are even more remote. This would be most likely to rear it's ugly head = during=20 the take-off you described after a long taxi and wait in the south = Texas sun.=20 Or in my case more likely while flying in mountain valleys when = working it a=20 little harder. Exactly the time I wouldn't want it to happen. That's = why the=20 facet boost pumps are always on at these = times.

    So=20 as Ed has pointed out, while millions of cars return the fuel to the = tank,=20 millions don't. But, I must add, most or all of them have a true = return-less=20 fuel system which we don't. Some of us are trying to copy that within = the=20 limitation placed upon us. Could we make it a true return-less system? = Sure we=20 could. At the low, low, price of a few more pounds and cost and = complexity per=20 tank. There is no free lunch here. Would I be willing to pay that = price, while=20 dead-sticking it down into a mountain valley. Of course I would, but = using=20 that logic would result in an ultimate safe plane, as it would never = get=20 finished. So here we are discussing ways to make it work without = returning=20 fuel to the tank. And I can say that it has worked well. I just can't = say that=20 it will always work well.
    I would never suggest = to=20 anyone that the way I did it is the best, but when asked about it, I'm = happy=20 to report my knowledge based on my experience along with any cautions = based on=20 that same experience. Then in the ensuing discussion I may learn = something.=20 Which seems to be the case here, as Charlie, who started this thread = with his=20 question has shown his idea based on what he's learnt from the = discussion and=20 it has his own subtle differences, with regards to regulator plumbing, = that=20 I'm surprised I overlooked and I think it has real promise. So much so = that=20 I'll consider a possible change to my current system.=20

    Other commitments these days usually = restrict me to=20 lurker status (that always sounds creepy), but the occasional = questions=20 directed at me usually don't go unnoticed and I enjoy the free = exchange of=20 ideas that happen on this list. I appreciate the words of caution, but = when=20 phrased as a command not to go against the grain, it loses it's = validity as it=20 is reminiscent of another place where free thinking is discouraged. = We're all=20 aware of the risks of venturing from the beaten path, which is why = we're here=20 to discuss, dissect and hopefully come up with a better=20 way.

    Al, I do value much of your advice even = if it=20 comes across as harsh, but I figured I'd explain my mindset which I = suspect is=20 shared by a few others here, which is to minimize and take calculated = risks,=20 but not reckless risks.

Todd
C-FSTB



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