Today's Message Index:
----------------------
1. 09:28 AM - Re: Re: fuel flow for CH701 (Les Goldner)
2. 09:46 AM - 2018 List of Contributors (Matt Dralle)
Message 1
| INDEX | Back to Main INDEX |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: fuel flow for CH701 |
Thank you for your article about preventing fuel starvation.
I have had 3 Z701's, 2 with Rotax 912UL's and have never experienced fuel
starvation, even after running long distances where one tank emptied.
It's interesting that both planes used fuel very differently. My first always
eat about 20% more fuel from my right tanks (I had a 40-gal system) and my
current plane (20-gal system) uses almost identical amounts of fuel from both
sides. I think you explained this difference in was due to air pressure.
-----Original Message-----
From: owner-zenith701801-list-server@matronics.com
[mailto:owner-zenith701801-list-server@matronics.com] On Behalf Of kissell
Sent: Friday, August 17, 2018 2:39 PM
Subject: Zenith701801-List: Re: fuel flow for CH701
--> <kissellr@ameritech.net>
I recently received a phone call from someone at the NTSB regarding the Zenith
fuel system. I have not yet followed through with the query but it did cause me
to re-examine the Zenith fuel problem which I wrote about more than ten years
ago.
In an article I found regarding a crash from fuel failure in a CH-750
https://generalaviationnews.com/2016/04/29/bad-fuel-system-design-contributes-to
-accident/, I analyzed what was in the article and present here my analysis of
how fuel starvation can occur under very special conditions. In the original
article (http://forums.matronics.com/viewtopic.php?t=48650I ; I mentioned how a
difference in pressure, developed by the slip stream above the vented fuel caps
can impact fuel flow. I did discuss the case when the fuel tanks are full and
the possibly of fuel venting in flight but did not discuss what happens when
fuel runs low in one tank.
The crash article explains that there was about 6 gallon of fuel left in one
tank and the the other was empty. The puzzle was how can the engine starve for
fuel when there is six gallons of fuel in one tank.
Using the dimensions of the Zenith 701 tank (10 gallon) each, six gallons would
require about 3.25 inch of depth in the tank. The tank has a floor area of about
427.4 square inch and there is 231 cubic inch in a gallon of fuel so 6 gallon
has 1386 cubic inch of volume. Divided by the tank floor area results in
1386/427.4= 3.2428 inch of required depth in the tank for the 6 gallons.
So now the question becomes how much pressure difference between the two tanks
does it take to support 3.25 inch of fuel height. Each cubic inch of fuel weighs
0.0272728 pound, ( see previous article using 6.3 pounds per gallon), so 3.25
times 0.0272728 = 0.0884 pound. Since this was all done relative to square
inches the pressure difference is thus about 0.09 psi.
This indicates that if the fuel caps and air flow combination created a pressure
difference of 0.09 psi between the two tanks, the fuel in the tank with the
lower pressure would settle at abut 3.25 inch higher than the fuel level in the
other tank and would maintain this level difference throughout the flight,
providing the conditions did not change. Eventually the tank with the higher
pressure (lower level) would run out of fuel before the other tank and the tank
with fuel (lower pressure) would still have about 6 gallons of fuel that would
not be usable because the pressure difference would be supporting (lifting) the
fuel as before. The tank fuel lines tied together would likely fill with air
being pulled from the empty tank towards the one with fuel.
The aircraft fuel pump would not be able to draw fuel since the line has only
air in it. It can be seen that very little pressure difference is required to
result in a substantial volume of fuel trapped and unusable. This "head" or
difference in fuel level is proportional to the difference in tank pressure. As
this shows it is very important to that the pressure on the top side of each
tank are kept the same if all of the fuel is to be usable. In the article I
wrote ten years ago I solved this problem on my aircraft by adding snorkel tubes
to my fuel caps which created about +0.1 psi of tank pressure (measure value)
during flight. The exact pressure is not that important, but both of them being
the same is. Another recommendation was to add a vent tube to connect the top of
each tank together to equalize the pressure. This is not easy on the Zenith
designs and in my case I had already built the aircraft. The snorkel vents,
described in the earlier article have been in use o!
n my aircraft for 10 years and have solved my fuel level so far. I hope this
helps you builders make good fuel systems in particular on Zenith aircraft. I
have found my aircraft,N701UB to be a joy to fly and very reliable. The crash
article was perhaps a little harsh towards the design, I think it's pretty good
and thank Zenith for it. But there are always room for improvement..
regards Bob Kissell, Dayton, Ohio N701UB 400+ CH701 flight hours and climbing..
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=482504#482504
Message 2
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | 2018 List of Contributors |
Dear Listers,
The 2018 Matronics Email List and Forum Fund Raiser officially ended a couple of
weeks ago and it's time that I published this year's List of Contributors.
It is the people on this list that directly make these Email Lists and Forums
possible! Their generous Contributions keep the servers and Internet connection
up and running!
You can still show your support this year and pick up a great gift at the same
time. The Contribution Web Site is fast, easy, and secure:
http://www.matronics.com/contribution
Or, by dropping a personal check in the mail to:
Matt Dralle / Matronics
581 Jeannie Way
Livermore CA 94550
And finally, I'm proud to present The 2018 Fund Raiser List of Contributors:
http://www.matronics.com/loc
Thank you again to everyone that made a Contribution this year!!
Matt Dralle
Matronics Email List & Forum Administrator
Other Matronics Email List Services
These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.
-- Please support this service by making your Contribution today! --
|