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John Bolding
Joined: 23 May 2006
Posts: 281
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 Posted: Tue Nov 06, 2007 11:37 am Post subject: Fuel selector location? |
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My appologies to the group for continuing this thread but as has been
pointed out, many accidents arise from improper understanding,design and
management of fuel systems.
Paul,
IF you agree that it is possible to empty two low wing tanks equally by the
use of one pump in the "both" position as you seem to support by your
kitchen test then WHY do you say it won't work several sentences later??
My RV3 has run thru MANY thousand gallons of fuel in that condition(single
pump drawing from both tanks) while emptying the tanks at the same rate . I
DO concede that mine is not a very common case however, generally one or the
other will feed more fuel.
Someone pointed out that once you unport one of the tanks then all bets are
off as you possibly/probably (you choose) introduce a bubble into the line
and that changes the equation and that is absolutly true.
My Cessna 180 fed almost twice as much fuel from one tank as the other
while in the "both" position and that is a gravity system. ?? I have also
known other low wing operators that could NOT run in the "both" position as
one wing or the other would empty completely without drawing ANY fuel from
the other wing.
Sorting this out is what the initial engine runs and 40 hr test period is
for. (Among other things)
Fuel delivery, lack of same really, has killed a lot of homebuilders. The
early Glasair's had a bunch of problems with unporting 'till it was figured
out what was causing it. The Lancairs (and my Glasair) did NOT as they
continually pumped from the wing tanks to a header tank which overflowed
back to a wing tank. The header tank then gravity fed the carb.
John
| Quote: |
Hi John,
I stand corrected.
Your message got me to do an experiment in my kitchen. I took two
identical glasses and put 2 ounces of water in one and 6 ounces in the
other one. I then took a big suck on two identical straws. Measuring the
remaining water in the glasses I discovered there was one ounce taken out
of each one. So, as you suggested the water was not taken from the lower
level "Tank" but taken equally from both tanks.
You will notice this is not the same as the behavior of two gravity fed
tanks which will tend to equalize their levels. I started with 6 and 2
ounces and ended with 5 and 1. In a high wing model I would have ended
with 3 and 3.
So, I was wrong, but the "Both" solution still doesn't work for low wing
planes.
Paul
XL fuselage
do not archive
At 06:03 AM 11/6/2007, you wrote:
>Paul, Maybe I need to learn something here, WHY would the pump draw fuel
>from the tank with the lowest pressure (emptiest)??
>
>That has not been my experience (2000 hrs in an RV3) , my tanks empty
>equally with one pump sucking on both tanks at the same time.
> LOW&SLO John Bolding
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zodierocket(at)hsfx.ca
Guest
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| Posted: Tue Nov 06, 2007 12:12 pm Post subject: Fuel selector location? |
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Gents, I have added this before and it is in the archives. In Canada
your homebuilt low wing will not be allowed to pass it's final
inspection if it has a both selector installed. It is simply not
allowed.
SO if the whole Transport Canada is going to rule that it is not a good
idea then maybe it has merit to not install a both selector in a low
wing aircraft. I understand the principals of this requirement and some
have been discussed. Our registration process is more stringent then the
United States, which is why this issue never come up.
In short if a whole government body decides that their may be safety
issues, derived from past experiences then why would we wish to discuss
this?
Mark Townsend
Can-Zac Aviation Ltd.
president(at)can-zacaviation.com
www.can-zacaviation.com
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purplemoon99(at)bellsouth
Guest
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| Posted: Tue Nov 06, 2007 4:45 pm Post subject: Fuel selector location? |
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O.K. the best of both worlds be buy a fuel selector that has Left and Right.
Take the money that you saved by not buying the Left,Both, Right
selector,buy a egg timer set it every 30 min. when you change tanks...and
you're good to go.. Joe N101HD
---
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psm(at)ATT.NET
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| Posted: Wed Nov 07, 2007 3:39 am Post subject: Fuel selector location? |
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Hi Steve,
My memory of my early flying years is not terribly clear -- it was
around 35 years ago. I rented as many different makes and models as
I could find. I also did the high performance and complex
transitions, so that made a fairly large number of different planes.
As I recall the transition between high and low wing planes was not
at all difficult. Along with the fuel tank switching, the low wing
planes provided a gymnastic experience to enter and exit the cockpit
over the wing. I don't recall either of those being an issue for a young man.
The parts that I remember as being a problem had to do with the
complexities of the individual engines. I remember the Arrow had a
couple of "Orange" zones on the RPM where you couldn't leave the
engine running for any length of time. If you did the vibration was
likely to shake the engine right off the plane. Also, the fuel
injected engines were very finicky to start. They didn't have the
automatic start sequencers that cars with fuel injection always
include, so the pilot had to do a dance of different boost pump,
throttle, and starter functions to get them to start. Once they were
started the engines ran really nicely and didn't need any carb. heat
since they didn't have carburetors.
I also remember that each family of planes flew very differently from
any other design. I found I liked the crisp handling of Cessnas -
both the light and heavier models. Of course the heavier ones fly
completely differently from the light ones. I guess if I didn't have
medical certificate issues now I would probably buy a C-182RG. They
are really sweet planes if you don't mind heavy controls. They will
carry anything you can stuff into them at an honest 160 KTAS. They
also have no problem operating at difficult airports where many
planes must dodge golfers on takeoff. And yes, you can use the
"Both" fuel setting and have doors at ground level on both sides for
entry and exit. The only down side in today's environment is the 15
gallons per hour fuel burn.
Paul
XL fuselage
do not archive
At 05:43 AM 11/6/2007, you wrote:
| Quote: | Paul
I guess my early training was just to get me used to procedures for
"furture" flying.
When I switched to Cessna it seemed soooo easy to transition to less
complex designs.
SW
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Tim Juhl
Joined: 21 Mar 2006
Posts: 488
Location: "Thumb" of Michigan
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| Posted: Thu Nov 08, 2007 4:38 pm Post subject: Re: Fuel selector location? |
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I owned a 1975 C182 for a number of years. It had 40 gallon tanks in each wing and would not draw evenly on "both." To get it to fly hands off I had to install an aftermarket aileron trim and manage my fuel by drawing from the heavy wing. I found it to be a non-issue (even for a longtime Cessna Pilot.) I bought a digital kitchen timer (velcroed to the instrument panel) that had a countdown mode. When it reached Zero the display blinked (I couldn't hear the beep) and would easily get your attention during your instrument scan.
In my opinion, simple solutions that do not require that you re-engineer something are usually the best.
Tim
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Zodiac XL - Jabiru 3300A
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psm(at)ATT.NET
Guest
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| Posted: Thu Nov 08, 2007 6:25 pm Post subject: Fuel selector location? |
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Hi John,
I agree with you. I think this is just the sort of discussion that
is really valuable on this sort of discussion medium. For those who
are tired of it, I suggest they stop reading this thread.
The reason I said the both tank selector still doesn't work for low
wing planes was meant as a complete analysis of the feature as
compared with high wing planes.
In high wing planes, all the available fuel will get to the engine
eventually with a both setting. This is simply not true for low wing
planes. Even though a both arrangement can be made to work, as you
have proved, it still must become a "One or the other tank" system as
the fuel is burned up. This being the case, it seems like a more
round wheel to just have a "One tank or the other" all the time
rather than waiting until one tank becomes empty and the engine stops
before forcing the pilot to choose a good tank.
Paul
XL fuselage
At 11:34 AM 11/6/2007, you wrote:
| Quote: | Zenith-List message posted by: "John Bolding" <jnbolding1(at)teleshare.net>
My appologies to the group for continuing this thread but as has
been pointed out, many accidents arise from improper
understanding,design and management of fuel systems.
Paul,
IF you agree that it is possible to empty two low wing tanks equally
by the use of one pump in the "both" position as you seem to support
by your kitchen test then WHY do you say it won't work several
sentences later??
My RV3 has run thru MANY thousand gallons of fuel in that
condition(single pump drawing from both tanks) while emptying the
tanks at the same rate . I DO concede that mine is not a very common
case however, generally one or the other will feed more fuel.
Someone pointed out that once you unport one of the tanks then all
bets are off as you possibly/probably (you choose) introduce a
bubble into the line and that changes the equation and that is absolutly true.
My Cessna 180 fed almost twice as much fuel from one tank as the
other while in the "both" position and that is a gravity system.
?? I have also known other low wing operators that could NOT run
in the "both" position as one wing or the other would empty
completely without drawing ANY fuel from the other wing.
Sorting this out is what the initial engine runs and 40 hr test
period is for. (Among other things)
Fuel delivery, lack of same really, has killed a lot of
homebuilders. The early Glasair's had a bunch of problems with
unporting 'till it was figured out what was causing it. The
Lancairs (and my Glasair) did NOT as they continually pumped from
the wing tanks to a header tank which overflowed back to a wing
tank. The header tank then gravity fed the carb.
John
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