 |
Matronics Email Lists
Web Forum Interface to the Matronics Email Lists
|
| View previous topic :: View next topic |
| Author |
Message |
William Halverson
Joined: 27 Feb 2010
Posts: 88
|
 Posted: Tue May 18, 2010 9:05 pm Post subject: fuel feed |
 |
|
Would negative G maneuvers help open the
valve? Specifically an outside loop or turn?
William
At 08:59 AM 5/18/2010, Walter Lannon wrote:
[quote]
If there was zero turbulence and the turn was
perfectly co-coordinated throughout it may not work.
But in the real world it probably will.
If necessary I use a very brief "knife edge" - definitely not co-coordinated.
I have a problem with the fuel in vent lines
being the cause of unequal feed. If the lines
are properly routed in relation to the max. fuel
level in the tanks and are not blocked by some
other material the fuel in the line will flow to
wherever the pressure is lower. If the engine
is using fuel that flow will be back to the tank.
The comments I have heard so far lead me to
believe the Yak series fuel feed tank check
valves are exactly the same as the Nanchang and
are therefore the primary reason for unequal fuel flow.
The file and/or hacksaw cuts in the flapper used
by the PLAAF and others do not address the problem.
They simply destroy the intended function of the valve
Have at it guys!
Walt
---
| | - The Matronics Yak-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?Yak-List |
|
|
|
| Back to top |
|
 |
cd001633(at)mindspring.co
Guest
|
| Posted: Wed May 19, 2010 6:15 pm Post subject: fuel feed |
|
|
Hi Walt,
I may have missed something in reading your e-mail regarding the mod you did to the check valve - what was the mod? Was it roughing the flapper contacting surface? I heard in the past that doing so would preclude a "mechanical seal" of the very smooth mating surfaces.
Also, regarding the vent drain on the bottom of center section (CJ6) - indeed a mud dubbers (South FL) would fill the vent with grass and ruin the day. To make the vent drain less hospitable to these critters, about 1/2" above vent bottom I drilled 2 holes, perpendicular to each other and inserted 2 cotter pins - creating an "X" cross section. This has worked for me thus far...
Sam Sax
Miami
--
| | - The Matronics Yak-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?Yak-List |
|
|
|
| Back to top |
|
|
talew(at)bellsouth.net
Guest
|
| Posted: Wed May 19, 2010 6:44 pm Post subject: fuel feed |
|
|
Hi Sam
The mod you refer to was proposed to me by Joe House .
He suggested that by using rough sandpaper on the flapper valve the
chances of it sticking were minimized . I did that and also took Papy's
advise . After trimmed to level flight in cruise keep your feet off the
rudders . I have no problem keeping within 2 gal in 2 hrs . Formation
flight is a different challenge .
I am sure Walt will have some good advise .
Terry
.---
| | - The Matronics Yak-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?Yak-List |
|
|
|
| Back to top |
|
|
wlannon(at)persona.ca
Guest
|
| Posted: Thu May 20, 2010 3:22 pm Post subject: fuel feed |
|
|
Hi Sam;
Sorry for the delay. Got tied up with domestic duties.
Feed tank check valves: Their purpose is to maintain a constant supply of
fuel in the feed tank at all times and flight attitudes including
manouvering, turbulence, yaw, etc.
They should meet two operarational requirements;
First they should close securely enough to prevent return fuel flow to
either main tank. A very small amount of leakage may be acceptable but the
practice of file or hacksaw notching of the brass flapper or the valve body
face seriously degrades that function.
The flapper mating surface is not highly polished, some are fairly rough,
perhaps to eliminate the possibility of surface tension?
Second: They should open readily when fuel is drawn from the header tank.
Possibly both may be open at times with equal fuel in the tanks but I'm sure
one will close with the first yaw induced (ground turn) fuel movement.
Ideally they should alternately open and close with a small variation in
fuel quantity between the main tanks resulting in a close to equal quantity
in each tank throughout the flight. Flight loads on the fuel from
manouvering and turbulence will disrupt this ideal scenario but overall they
should remain fairly equal.
The original CJ valve design does not meet the latter part of this second
requirement. In fact it is the above disruptive fuel loads that keep them
working at all.
The reason for that is quite simple. The pressure on the opening side of
the flapper acts through a 1 cm hole in the valve body on an area of 0.785
cm/sq.(approx.)
The pressure on the closing side of the flapper is acting on
the entire flapper which is about 2 cm in diameter with an area of approx.
3.146 cm/sq.
If the fuel quantity in both tanks is equal the pressure on both sides of
the flapper is equal BUT the actual force applied to each side is no where
near. There is 4 times more closing force than opening due to the
difference in effective area.
If there was no such thing as yaw, turbulence, etc. a fuel imbalance of
approx. 50 liters would be necessary to open the valve. Assuming of course
that the vent system is 100 % serviceable.
My modification reworks the valve body seat (which is a flat surface larger
than the flapper) to a seating surface ring (approx. 0.5mm wide) around the
inlet hole.
This makes no change to the opening force but gives a drastic reduction in
the closing force because the fuel pressure from the opposing tank is now
acting on BOTH sides of the flapper thereby reducing the force differential
to near zero.
Zero would be perfect and would be obtainable with a line contact ring but
it is a hand filing operation and 0.5mm (0.020") is close enough.
Two other potential problems are eliminated by this mod. 1. I have seen (on
project CJ's) flapper valves virtually glued to the valve face. Had to soak
one in lacquer thinner to open. Probably due to residue from Chinese fuel.
2. Now you can polish the flapper and the body seat to zero leakage in the
closed position with no fear of "surface tension" sticking.
Have to add:------------ Somewhere along the way the Chinese have recognized
this problem and corrected it to some extent by replacing the flapper with
one that has a larger cut-out section in the seating side.
On the original flapper that cut-out was "as cast" simply to reduce the
valve weight and was smaller in dia. than the hole in the valve body.
The new flapper has a cut-out larger than the body hole which, by increasing
the effective area, increases the opening force. This is not as effective
as my mod. but will improve the operation.
I have some ideas re. applying my mod to this valve but would need to do a
prototype.
Walt.
---
| | - The Matronics Yak-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?Yak-List |
|
|
|
| Back to top |
|
|
|
|
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum
|
Powered by phpBB © 2001, 2005 phpBB Group
|
Get Email Distribution Too!
FAQ
Search
Memberlist
Usergroups
Register
Profile
Log in to check your private messages
Log in
