X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Tue, 05 Jan 2010 11:51:28 -0500 Message-ID: X-Original-Return-Path: Received: from imr-db02.mx.aol.com ([205.188.91.96] verified) by logan.com (CommuniGate Pro SMTP 5.3.0) with ESMTP id 4065180 for lml@lancaironline.net; Tue, 05 Jan 2010 10:55:52 -0500 Received-SPF: pass receiver=logan.com; client-ip=205.188.91.96; envelope-from=Sky2high@aol.com Received: from imo-ma03.mx.aol.com (imo-ma03.mx.aol.com [64.12.78.138]) by imr-db02.mx.aol.com (8.14.1/8.14.1) with ESMTP id o05Ft0mg031881 for ; Tue, 5 Jan 2010 10:55:00 -0500 Received: from Sky2high@aol.com by imo-ma03.mx.aol.com (mail_out_v42.5.) id q.d4e.66ccb762 (14501) for ; Tue, 5 Jan 2010 10:54:59 -0500 (EST) From: Sky2high@aol.com X-Original-Message-ID: X-Original-Date: Tue, 5 Jan 2010 10:54:59 EST Subject: Re: [LML] Re: Fuel Planning - Capacitance probes X-Original-To: lml@lancaironline.net MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="-----------------------------1262706898" X-Mailer: AOL 9.5 sub 155 X-Spam-Flag:NO X-AOL-SENDER: Sky2high@aol.com -------------------------------1262706898 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Bob, Thanks for the informational response. Of course the water would either have to be mixed into the fuel or sitting in the sump. The common way to get water mixed into 100 LL is during fluid introduction into the tank such as when filling up. I monitor all fill ups but the tanks could be filled up with a water/fuel mix - at least its filled up. It would take a great deal of still water in the wing tanks before any part of the probe was submerged enough for it to register. This is possible in the always-full header tank, but the float provides backup information about actual liquid making the tank full or not full. The logic of the always-full header means that it was full of good fuel the last time it was used, thus avoiding sudden surprises on takeoff. Preflight sump checking should take care of the still water problem whether or not capacitance probes are used. Fiberglass tanks, unlike metal ones, resist the formation of condensation as a source of water. In my case (the one I keep defending) my aircraft is always hangared, thus it is unlikely that condensation could affect me at my home airport. The Lancair is so small that traveling often results in finding hangar space. However, it certainly has spent overnights parked under the stars, rain clouds and, uh, out in the cold. That certainly includes the brutal long-term parking conditions at Redmond, OSH or SunNFun. When I travel, the tanks are filled with whatever the FBO is using - the request is for 100 LL. Yes, the LML is important so that all may benefit from experience, both good and bad. The system I use, taken in the context it is used, is safe enough plus it eliminates other more common failure modes such as those we see across GA from the use of selector valves. The few fuel related Lancair crashes I have reviewed are most often the result of mistakes made by the pilot and in some cases the result of known low levels of fuel aboard. This discussion has been most illuminating but, unfortunately, has been focused on fuel monitoring systems and not the more frequent and deadly accident cause - flying too slow, too low. Scott Krueger Flying my slow build since last century (1996). PS Apparently, JP4 is unreliable as a fuel since it leaks out so readily ;<) In a message dated 1/5/2010 7:16:12 A.M. Central Standard Time, n103md@yahoo.com writes: > I have no idea how the capacitance probes you talk about work. > Here is how the VM Fuel system probes work: Scott: The probes that you describe are just the same as the ones that Gary described. Good for you in figuring out how to lower the output frequency to match between a smaller sensor and your VM system. In that system, capacitance is translated into a frequency so that it can be transmitted with little effect of electrical noise. The capacitance that is being measured is a tube dipped in the fuel with a concentric wire. That forms a cylindrical capacitor with a dielectric that is (ideally) either gasoline or air. The dielectric constants are: air 1.0 gasoline 2.0 So the capacitance of the probe doubles with it filled with gasoline instead of air. But some other liquids have much higher dielectric constants: ethanol 30 methanol 33 water 80 A probe that is 10% full of fuel and 1% full of water would read just about full. If the concentric tube sensor is fully immersed, then area is constant and the observed capacitance is a measure of the dielectric constant of the fluid. This is the basis for detecting additives in racing fuels, such as alcohol: http://www.foxvalleykart.com/fuel2.html That also means that a few percent of alcohol (ethanol or methanol) would cause the tank to read more full than it is --- while also reducing the fuel value of the liquid in the tank. In other words, there is a way to measure the composition of the fuel, as well as its level with a simple redesign of the sensor and the controlling electronics. > Oh well, you use your experience and I'll use mine. I think the point of having a mailing list like this is so that we can both benefit from both of our experiences. I'd like to think that I could learn from someone who landed an F-4 with 6 gallons of JP4 on board without having to try it myself. He turned back to base with maybe 20 seconds to spare when the tanks were still reading in the upper half, but the gauge readings were a little lower than expected and were "bouncing around more than normal". Think about the decision process, and how much room was actually left for thinking about whether there was really a problem. If Bill had waited another minute before turning around, his story would be different, and we might not have had the opportunity to learn from it. -bob -- For archives and unsub http://mail.lancaironline.net:81/lists/lml/List.html -------------------------------1262706898 Content-Type: text/html; charset="US-ASCII" Content-Transfer-Encoding: quoted-printable
Bob,
 
Thanks for the informational response.
 
Of course the water would either have to be mixed into the fuel or si= tting=20 in the sump.  The common way to get water mixed into 100 LL is d= uring=20 fluid introduction into the tank such as when filling up.  I monitor= all=20 fill ups but the tanks could be filled up with a water/fuel mix= - at=20 least its filled up. It would take a great deal of still water in the wing= tanks=20 before any part of the probe was submerged enough for it to register. = ; This=20 is possible in the always-full header tank, but the float provides ba= ckup=20 information about actual liquid making the tank full or not full.  Th= e=20 logic of the always-full header means that it was full of good fuel= the=20 last time it was used, thus avoiding sudden surprises on takeoff. =20 Preflight sump checking should take care of the still water problem= whether=20 or not capacitance probes are used. 
 
Fiberglass tanks, unlike metal ones, resist the formation of condensa= tion=20 as a source of water.  In my case (the one I keep defending) my aircr= aft is=20 always hangared, thus it is unlikely that condensation could affect me at= my=20 home airport.  The Lancair is so small that traveling often results= in=20 finding hangar space.  However, it certainly has spent overnights par= ked=20 under the stars, rain clouds and, uh, out in the cold.  That certainl= y=20 includes the brutal long-term parking conditions at Redmond, OSH= or=20 SunNFun. When I travel, the tanks are filled with whatever the FBO is= using=20 - the request is for 100 LL.
 
Yes, the LML is important so that all may benefit from experience, bo= th=20 good and bad.  The system I use, taken in the context it is used= , is=20 safe enough plus it eliminates other more common failure modes such as tho= se we=20 see across GA from the use of selector valves.  The few fue= l=20 related Lancair crashes I have reviewed are most often the result of mista= kes=20 made by the pilot and in some cases the result of known low levels of fuel= =20 aboard.
 
This discussion has been most illuminating but, unfortunately, h= as=20 been focused on fuel monitoring systems and not the more frequent and dead= ly=20 accident cause - flying too slow, too low.
 
Scott Krueger
Flying my slow build since last century (1996).
 
PS Apparently, JP4 is unreliable as a fuel since it leaks out so=20 readily ;<)    
 
In a message dated 1/5/2010 7:16:12 A.M. Central Standard Time,=20 n103md@yahoo.com writes:
> I=20 have no idea how the capacitance probes you talk about work.
> Her= e is=20 how the VM Fuel system probes work:

Scott:
The probes that you= =20 describe are just the same as the ones that Gary described.
Good for= you in=20 figuring out how to lower the output frequency to
match between a sma= ller=20 sensor
and your VM system. In that system, capacitance is translated= into=20 a
frequency so that it
can be transmitted with little effect of=20 electrical noise.

The capacitance that is being measured is a tub= e=20 dipped in the fuel
with a concentric wire.
That forms a cylindrica= l=20 capacitor with a dielectric that is (ideally)
either gasoline or=20 air.

The dielectric constants are:

air 1.0
gasoline=20 2.0

So the capacitance of the probe doubles with it filled with= =20 gasoline
instead of air.

But some other liquids have much high= er=20 dielectric constants:
ethanol 30
methanol 33
water  80
=
A=20 probe that is 10% full of fuel and 1% full of water would read just
a= bout=20 full.


If the concentric tube sensor is fully immersed, then= area is=20 constant
and the observed capacitance
is a measure of the dielectr= ic=20 constant of the fluid. This is the
basis for detecting additives in= =20 racing
fuels, such as alcohol:=20 http://www.foxvalleykart.com/fuel2.html
That also means that a few pe= rcent=20 of alcohol (ethanol or methanol)
would cause the tank to read more=20 full
than it is --- while also reducing the fuel value of the liquid= in the=20 tank.
In other words, there is a way to measure the composition of th= e=20 fuel,
as well as its level
with a simple redesign of the sensor an= d the=20 controlling electronics.

> Oh well, you use your experience an= d I'll=20 use mine.

I think the point of having a mailing list like this is= so=20 that we can both
benefit from both of our experiences. I'd like to th= ink=20 that I could
learn from someone
who landed an F-4 with 6 gallons= of JP4=20 on board without having to try
it myself.
He turned back to base= with=20 maybe 20 seconds to spare when the tanks were still
reading in the up= per=20 half, but the gauge readings were a little lower
than expected
and= were=20 "bouncing around more than normal".

Think about the decision proc= ess,=20 and how much room was actually left
for thinking
about whether the= re was=20 really a problem. If Bill had waited another
minute before
turning= =20 around, his story would be different, and we might not have
had the= =20 opportunity
to learn from it.

-bob

--
For archives= and=20 unsub=20 http://mail.lancaironline.net:81/lists/lml/List.html
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