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wise(at)txc.net.au
Guest

Posted: Sun May 16, 2010 6:22 pm Post subject: feul feed

G'Day All,

  

 I and a friend each run a Yak18T.

 We  suffer the same problem with both  aircraft, re even fuel feed.

 Flying in turbulence seems to help the problem, but  still air is bad news.

  

 The left tank will feed untill almost empty leaving  plenty of fuel in the right tank and on my mates 18, the low fuel warning light  on the left tank lit up and was fortunate enough to be close to a small country  strip where he landed in a hurry.

  

 He has teed  both vents into one. This has not  helped.

  

 I moved the left tank vent and re located the vent  to about 3/4 of a inch next to the right tank vent thinking that it may be the  vortex from the prop that is allowing the right tank to feed. Or rather stopping  the left tank to feed.

 I have changed the angle of the vent pipe facing  the airflow to try and perhaps get more air into the vent to assist the left  tank to feed more.

 This has only marginally helped.

  

 I landed on Saturday with the left tank low fuel  warning light coming on on finals.

 The right tank had 65 - 70 litres fuel remaining  and about 12 in the left when dipped.

  

 We have removed and carefully checked the check  valves. No problem there.

  

 Any suggestions would be greatly  appreciated.

  

 Thanks and cheers,

 Chris.

  

  

 Chris Wise

GT Propellers  Australia

__________________________________________________________

Tel.       +61 415 195 095            Fax.   +61 8 8326 7268

 

Email     chris(at)gtpropellersaustralia.com.au (chris(at)gtpropellersaustralia.com.au)  

Website   www.gtpropellersaustralia.com.au

 

The  information transmitted in and with this email is intended only for the person  or entity to which it is addressed and may contain confidential and/or  privileged material. Any review, retransmission, dissemination or other use of,  or taking of any action in reliance upon this information, by persons or  entities other than the intended recipients is prohibited. If you received this  transmission in error, please contact the sender and delete this e-mail and  associated material from all computers and/or systems. The intended recipient of  this e-mail may only use, reproduce, disclose or distribute the information  contained in this e-mail and any attached files, with the permission of the  sender.



   [quote][b]

wlannon(at)persona.ca
Guest

Posted: Sun May 16, 2010 8:35 pm Post subject: feul feed

Hi Chris;

  

 The Nanchang exhibits the same fuel feed  problem.  Typically the RH tank is late and I know of at least one forced  landing with a full RH and empty LH.  Believe this was in South Africa  about 6 or 7 years ago.

  

 The CJ6 has a single point vent system which I  don't believe is the problem.  However the effective length of the vent  line and the fuel feed line are both longer for the RH tank. Theoretically that  could induce a lag in the RH feed time but I don't belive it is  signifigant.  Any blockage of the vent by insect nests etc. will definitaly  cause a big problem.

  

 Other than the bugs that leaves the feed tank check  valves as the only remaining source.  SPEAKING FOR THE CJ6 ONLY (since  I have no knowledge of the check valves in any of the Yak models) I  believe I have solved that problem with a modification to the check valve  which, IMHO, was very poorly designed.

  

 If you have the opportunity to take  photos of one of your check valves and email to me I will try to determine  if the mod is applicable.

  

 Walt 

  

 [quote]   ---

wise(at)txc.net.au
Guest

Posted: Sun May 16, 2010 10:20 pm Post subject: feul feed

G'Day Walt,

  

 We carry a piece of plastic tubing that fits over  the vent pipes and we use this to check the vents by blowing into the  pipe.

 Every now and then we blow compressed air thru the  vent.

 At no time have we ever found a blocked air  vent.

 My mate also fitted new fuel cap seals. Did not  solve the problem.

  

 The check valves are a simple flapper valve that  prevents any X flow and I cannot see how they can be a problem.

 I am not familiar with the check valves on a  CJ6

  

 Thanks and cheers,

 Chris.

  

  

  

 Chris Wise

GT Propellers  Australia

__________________________________________________________

Tel.       +61 415 195 095            Fax.   +61 8 8326 7268

 

Email     chris(at)gtpropellersaustralia.com.au (chris(at)gtpropellersaustralia.com.au)  

Website   www.gtpropellersaustralia.com.au

 

The  information transmitted in and with this email is intended only for the person  or entity to which it is addressed and may contain confidential and/or  privileged material. Any review, retransmission, dissemination or other use of,  or taking of any action in reliance upon this information, by persons or  entities other than the intended recipients is prohibited. If you received this  transmission in error, please contact the sender and delete this e-mail and  associated material from all computers and/or systems. The intended recipient of  this e-mail may only use, reproduce, disclose or distribute the information  contained in this e-mail and any attached files, with the permission of the  sender.



 [quote]   ---

dsavarese0812(at)bellsout
Guest

Posted: Mon May 17, 2010 4:43 am Post subject: feul feed

One of the key problems with the vent system, particularly on  the Yak 52 with the single overboard vent tube (pre-1989), is the vent line from  the header tank to the fuel vent junction on the left side of the front cockpit  just below the seat.  It looks like a cross.  I'll  explain.

  

 First,  when looking at the fuel junction,  the tube  on the top of the junction is the vent line from the left tank.  No problem  here as the left fuel tank seems to feed properly on most 52's.  The line  on the right that goes forward from the vent (let's call it the "east" side) is  the overboard vent line which loops up and around the back side of the  instrument panel.  The line on the left or "west" side of the junction is  the right tank vent.  That leaves the only other vent line, the header tank  vent line which attaches at the bottom of the junction and is sometimes BELOW  the end that attaches to the header tank.  And this is where the problem  starts because of fuel in the vent lines.

  

 Many times the vent line from the header tank does not have a  high enough loop in it.  This causes the fuel from the header tank to  overflow into the into the fuel junction.  The loop in the header tank vent  line must be up above the height of the header tank or the header tank vent line  will feed fuel into the vent junction.  The Yak 52 rests on the ground at  about a 1.5-2 degree angle of attack.  The fuel from the header tank  line that overflows into the fuel junction flows into the right  tank vent line, which is the one at the rear or "west" side of the fuel  junction.  Now the vent line is blocked off.  Until the vent line can  clear, no air can displace the fuel in the right fuel tank and thus the right  fuel tank does not feed.

  

 Lastly, to solve the problem, bring the loop from the header  tank up above the top of the vent junction.  If you are unable to do this  with the existing tubing, remove the vent line from the header tank to the vent  junction and fabricate a new line with a loop in it that goes above the top  of the vent junction.  This will prevent the fuel that is in the header  tank vent line from flowing into the right fuel tank vent line.

  

 Dennis

 [quote]   ---

cjpilot710(at)aol.com
Guest

Posted: Mon May 17, 2010 8:22 am Post subject: feul feed

Guys,

    

   The problem has always been aircraft yaw.  The T-34 which has the same fuel setup (on one model anyway) has had the same problem.  If you do not apply enough rudder on climb out, engine seem to pull out of the left tank more.  I have separate tank vent lines that go to the wing tips.  I was told that this would cure the uneven flow, when I put in the long range tanks.  It didn't.  Yaw is the most likely cause of fuel imbalance.

    

   Jim "Pappy" Goolsby

 

 

   --

stephenmorrey(at)gmail.co
Guest

Posted: Mon May 17, 2010 6:48 pm Post subject: feul feed

So just to be sure, am I correct in saying an in flight remidy is to

step on the side showing the lowest fuel level.  If this is the case

is it best to simply step on the low side or is it needed to step and

"hold" for an extended period of time on the low side ?  Do I have

this backwards?  steve "old school"



On Mon, May 17, 2010 at 12:19 PM,  <cjpilot710(at)aol.com> wrote:

[quote] Guys,



 The problem has always been aircraft yaw.  The T-34 which has the same fuel

 setup (on one model anyway) has had the same problem.  If you do not apply

 enough rudder on climb out, engine seem to pull out of the left tank more.

 I have separate tank vent lines that go to the wing tips.  I was told that

 this would cure the uneven flow, when I put in the long range tanks.  It

 didn't.  Yaw is the most likely cause of fuel imbalance.



 Jim "Pappy" Goolsby



 --

dsavarese0812(at)bellsout
Guest

Posted: Tue May 18, 2010 3:25 am Post subject: feul feed

Steve,

 In the Yak 52, the purpose of stepping on the low side tank is  two fold: in case one of the flapper valves in the fuel junction under the front  seat is stuck closed, forcing the weight of the fuel against the flapper  valve may free the flapper valve thus permitting fuel to flow; secondly and more  likely, there is fuel in the vent line of the tank that is not feeding and by  stepping on the low side you are trying to force the fuel out of the vent  line.

  

 Assuming the airplane is trimmed properly as Pappy says, which  definitely causes fuel imbalance, a vent line with fuel in it will definitely  affect the fuel feed.  I didn't realize I was probably forcing the  fuel into the vent lines on the Yak 52 by filling the tanks all the way up to  the lip.  Because of the sitting angle of attack, the vent line at the top,  rear, inside corner of the tank can get fuel in it by filling the tank to the  lip.  This is particularly true on the right tank because the vent line  sits lower in the fuselage than the left tank.  Remember, the left vent  line enters the fuselage and turns down and connects at the top of the vent  junction.  The right tank vent line is attached to the left side of the  vent junction which ends up being lower than the left tank vent line.  So  when fuel enters the right vent line by filling to the lip of the filler neck,  it may force the fuel into the vent line and into the vent junction, blocking  air back to the tank through the vent line.

  

 Also when the fuel heats up in the tank it expands and guess  where it expands to?  Right into the vent line.  Have you ever seen a  Yak 52 "puking" fuel overboard on the ramp during hot weather?  The reason  is the fuel has expanded in the tank and is forced out of the vent line through  the vent junction and out through the overboard vent line exiting out the  belly of the airplane.  Once the siphon has been set up by the expansion,  the siphoning effect can siphon out 5+ gallons.  No kidding.....it happened  to me.  I filled the airplane and left it on the ramp in the sun for 2  days.  When I came back the fuel instrument no longer read 60/60.  I  refilled the tanks and it took over 5 gallons of fuel to bring the tanks back to  60/60.  The telltale sign was the dark, black spot in the blacktop under  the fuselage directly under the vent line.

  

 Dennis

 [quote]   ---

pa3arw(at)euronet.nl
Guest

Posted: Tue May 18, 2010 3:49 am Post subject: feul feed

Dennis,  

   

It can be very scary though….When I ferried my Yak from Estonia via Lithuania back to Holland I found it to be very scary.   

I flew from Palanga (Lithuania) to Gdansk(Poland) over the middle of the Baltic  Sea outside the airspace of Bullarus when the left tank showed only 12 liters and the right hand tank was still at 60 liters. I made a 90 degree bank turn to the left and a full 360 back to the original course…after a while I saw the right hand tank indicator flip to 50 ......man I was glad to see that happening…..problem solved….scary though….  

   

Hans  

RA3326K  

        

  

Van: owner-yak-list-server(at)matronics.com [mailto:owner-yak-list-server(at)matronics.com] Namens A. Dennis Savarese

 Verzonden: dinsdag 18 mei 2010 13:24

 Aan: yak-list(at)matronics.com

 Onderwerp: Re: feul feed  

  

     

Steve,  

    

In the Yak 52, the purpose of stepping on the low side tank is two fold: in case one of the flapper valves in the fuel junction under the front seat is stuck closed, forcing the weight of the fuel against the flapper valve may free the flapper valve thus permitting fuel to flow; secondly and more likely, there is fuel in the vent line of the tank that is not feeding and by stepping on the low side you are trying to force the fuel out of the vent line.  

    

   

    

Assuming the airplane is trimmed properly as Pappy says, which definitely causes fuel imbalance, a vent line with fuel in it will definitely affect the fuel feed.  I didn't realize I was probably forcing the fuel into the vent lines on the Yak 52 by filling the tanks all the way up to the lip.  Because of the sitting angle of attack, the vent line at the top, rear, inside corner of the tank can get fuel in it by filling the tank to the lip.  This is particularly true on the right tank because the vent line sits lower in the fuselage than the left tank.  Remember, the left vent line enters the fuselage and turns down and connects at the top of the vent junction.  The right tank vent line is attached to the left side of the vent junction which ends up being lower than the left tank vent line.  So when fuel enters the right vent line by filling to the lip of the filler neck, it may force the fuel into the vent line and into the vent junction, blocking air back to the tank through the vent line.  

    

   

    

Also when the fuel heats up in the tank it expands and guess where it expands to?  Right into the vent line.  Have you ever seen a Yak 52 "puking" fuel overboard on the ramp during hot weather?  The reason is the fuel has expanded in the tank and is forced out of the vent line through the vent junction and out through the overboard vent line exiting out the belly of the airplane.  Once the siphon has been set up by the expansion, the siphoning effect can siphon out 5+ gallons.  No kidding.....it happened to me.  I filled the airplane and left it on the ramp in the sun for 2 days.  When I came back the fuel instrument no longer read 60/60.  I refilled the tanks and it took over 5 gallons of fuel to bring the tanks back to 60/60.  The telltale sign was the dark, black spot in the blacktop under the fuselage directly under the vent line.  

    

   

    

Dennis  

  [quote]    

---

stephenmorrey(at)gmail.co
Guest

Posted: Tue May 18, 2010 6:40 am Post subject: feul feed

Dennis, Three points of clarification.

1. Say the left side is low and I want to try and get more fuel

flowing from the right side I would step on the left side this would

in effect yaw the fuel junction under the front seat to the right of

center thus having a tendency to open the right side flapper valve

which I believe opens toward the center line of the plane.  Am I

picturing this correct.



2. If the most likely issue is fuel in the vent line and over filling

is a likely culprit then what is the effect if the fuel is filled

"below" the lip and then while climbing to altitude the plane is

pitched up.  Would this not create the same problem of filling the

vent line, in this case during climb out, especially if the climb is

steep.  Or is there some other force in effect after fuel is flowing

such as pulling a vacuum that prevents this from being a problem.

Same question re filling the vent line in flight during acrobatics.



3. As you recall I have the bladders installed with the recommended

added check valve under the front seat..

I am not sure I remember correctly but is this check valve designed to

prevent back flow and the filling of vent lines or does it serve a

different purpose.  If I have this check valve am I assured I will not

have a back flow problem?

On Tue, May 18, 2010 at 7:23 AM, A. Dennis Savarese

<dsavarese0812(at)bellsouth.net> wrote:

[quote] Steve,

 In the Yak 52, the purpose of stepping on the low side tank is two fold: in

 case one of the flapper valves in the fuel junction under the front seat is

 stuck closed, forcing the weight of the fuel against the flapper valve may

 free the flapper valve thus permitting fuel to flow; secondly and more

 likely, there is fuel in the vent line of the tank that is not feeding and

 by stepping on the low side you are trying to force the fuel out of the vent

 line.



 Assuming the airplane is trimmed properly as Pappy says, which definitely

 causes fuel imbalance, a vent line with fuel in it will definitely affect

 the fuel feed.  I didn't realize I was probably forcing the fuel into the

 vent lines on the Yak 52 by filling the tanks all the way up to the lip.

 Because of the sitting angle of attack, the vent line at the top, rear,

 inside corner of the tank can get fuel in it by filling the tank to the

 lip.  This is particularly true on the right tank because the vent line sits

 lower in the fuselage than the left tank.  Remember, the left vent line

 enters the fuselage and turns down and connects at the top of the vent

 junction.  The right tank vent line is attached to the left side of the vent

 junction which ends up being lower than the left tank vent line.  So when

 fuel enters the right vent line by filling to the lip of the filler neck, it

 may force the fuel into the vent line and into the vent junction, blocking

 air back to the tank through the vent line.



 Also when the fuel heats up in the tank it expands and guess where it

 expands to?  Right into the vent line.  Have you ever seen a Yak 52 "puking"

 fuel overboard on the ramp during hot weather?  The reason is the fuel has

 expanded in the tank and is forced out of the vent line through the vent

 junction and out through the overboard vent line exiting out the belly of

 the airplane.  Once the siphon has been set up by the expansion, the

 siphoning effect can siphon out 5+ gallons.  No kidding.....it happened to

 me.  I filled the airplane and left it on the ramp in the sun for 2 days.

 When I came back the fuel instrument no longer read 60/60.  I refilled the

 tanks and it took over 5 gallons of fuel to bring the tanks back to 60/60.

 The telltale sign was the dark, black spot in the blacktop under the

 fuselage directly under the vent line.



 Dennis



 ---

stephenmorrey(at)gmail.co
Guest

Posted: Tue May 18, 2010 6:41 am Post subject: feul feed

Again I am a little confused on this, it seems if the 360 turn was

coordinated then the turn should have had no effect.  Do I understand

this correctly?



On Tue, May 18, 2010 at 7:49 AM, Hans Oortman <pa3arw(at)euronet.nl> wrote:

[quote] Dennis,



 It can be very scary though….When I ferried my Yak from Estonia via

 Lithuania back to Holland I found it to be very scary.



 I flew from Palanga (Lithuania) to Gdansk(Poland) over the middle of the

 Baltic Sea outside the airspace of Bullarus when the left tank showed only

 12 liters and the right hand tank was still at 60 liters. I made a 90 degree

 bank turn to the left and a full 360 back to the original course…after a

 while I saw the right hand tank indicator flip to 50 ......man I was glad to

 see that happening…..problem solved….scary though….



 Hans



 RA3326K



 ________________________________



 Van: owner-yak-list-server(at)matronics.com

 [mailto:owner-yak-list-server(at)matronics.com] Namens A. Dennis Savarese

 Verzonden: dinsdag 18 mei 2010 13:24

 Aan: yak-list(at)matronics.com

 Onderwerp: Re: feul feed



 Steve,



 In the Yak 52, the purpose of stepping on the low side tank is two fold: in

 case one of the flapper valves in the fuel junction under the front seat is

 stuck closed, forcing the weight of the fuel against the flapper valve may

 free the flapper valve thus permitting fuel to flow; secondly and more

 likely, there is fuel in the vent line of the tank that is not feeding and

 by stepping on the low side you are trying to force the fuel out of the vent

 line.



 Assuming the airplane is trimmed properly as Pappy says, which definitely

 causes fuel imbalance, a vent line with fuel in it will definitely affect

 the fuel feed.  I didn't realize I was probably forcing the fuel into the

 vent lines on the Yak 52 by filling the tanks all the way up to the lip.

 Because of the sitting angle of attack, the vent line at the top, rear,

 inside corner of the tank can get fuel in it by filling the tank to the

 lip.  This is particularly true on the right tank because the vent line sits

 lower in the fuselage than the left tank.  Remember, the left vent line

 enters the fuselage and turns down and connects at the top of the vent

 junction.  The right tank vent line is attached to the left side of the vent

 junction which ends up being lower than the left tank vent line.  So when

 fuel enters the right vent line by filling to the lip of the filler neck, it

 may force the fuel into the vent line and into the vent junction, blocking

 air back to the tank through the vent line.



 Also when the fuel heats up in the tank it expands and guess where it

 expands to?  Right into the vent line.  Have you ever seen a Yak 52 "puking"

 fuel overboard on the ramp during hot weather?  The reason is the fuel has

 expanded in the tank and is forced out of the vent line through the vent

 junction and out through the overboard vent line exiting out the belly of

 the airplane.  Once the siphon has been set up by the expansion, the

 siphoning effect can siphon out 5+ gallons.  No kidding.....it happened to

 me.  I filled the airplane and left it on the ramp in the sun for 2 days.

 When I came back the fuel instrument no longer read 60/60.  I refilled the

 tanks and it took over 5 gallons of fuel to bring the tanks back to 60/60.

 The telltale sign was the dark, black spot in the blacktop under the

 fuselage directly under the vent line.



 Dennis



 ---

pa3arw(at)euronet.nl
Guest

Posted: Tue May 18, 2010 7:07 am Post subject: feul feed

Stephen,



Negative...it did have an effect...de valve opened.  

Left tank empty...right full...bank 60/90 degrees left..it did the trick..



Hans

-----Oorspronkelijk bericht-----

Van: owner-yak-list-server(at)matronics.com

[mailto:owner-yak-list-server(at)matronics.com] Namens Stephen Morrey

Verzonden: dinsdag 18 mei 2010 16:42

Aan: yak-list(at)matronics.com

Onderwerp: Re: feul feed






Again I am a little confused on this, it seems if the 360 turn was

coordinated then the turn should have had no effect.  Do I understand this

correctly?



On Tue, May 18, 2010 at 7:49 AM, Hans Oortman <pa3arw(at)euronet.nl> wrote:

 	  Quote: 	
		   Dennis,



 It can be very scary though….When I ferried my Yak from Estonia via 

 Lithuania back to Holland I found it to be very scary.



 I flew from Palanga (Lithuania) to Gdansk(Poland) over the middle of 

 the Baltic Sea outside the airspace of Bullarus when the left tank 

 showed only

 12 liters and the right hand tank was still at 60 liters. I made a 90 

 degree bank turn to the left and a full 360 back to the original 

 course…after a while I saw the right hand tank indicator flip to 50 

 ......man I was glad to see that happening…..problem solved….scary

though….
	


 	  Quote: 	
		  

 Hans



 RA3326K



 ________________________________



 Van: owner-yak-list-server(at)matronics.com

 [mailto:owner-yak-list-server(at)matronics.com] Namens A. Dennis Savarese

 Verzonden: dinsdag 18 mei 2010 13:24

 Aan: yak-list(at)matronics.com

 Onderwerp: Re: feul feed



 Steve,



 In the Yak 52, the purpose of stepping on the low side tank is two 

 fold: in case one of the flapper valves in the fuel junction under the 

 front seat is stuck closed, forcing the weight of the fuel against the 

 flapper valve may free the flapper valve thus permitting fuel to flow; 

 secondly and more likely, there is fuel in the vent line of the tank 

 that is not feeding and by stepping on the low side you are trying to 

 force the fuel out of the vent line.



 Assuming the airplane is trimmed properly as Pappy says, which 

 definitely causes fuel imbalance, a vent line with fuel in it will 

 definitely affect the fuel feed.  I didn't realize I was probably 

 forcing the fuel into the vent lines on the Yak 52 by filling the tanks

all the way up to the lip.
	


 	  Quote: 	
		   Because of the sitting angle of attack, the vent line at the top, 

 rear, inside corner of the tank can get fuel in it by filling the tank 

 to the lip.  This is particularly true on the right tank because the 

 vent line sits lower in the fuselage than the left tank.  Remember, 

 the left vent line enters the fuselage and turns down and connects at 

 the top of the vent junction.  The right tank vent line is attached to 

 the left side of the vent junction which ends up being lower than the 

 left tank vent line.  So when fuel enters the right vent line by 

 filling to the lip of the filler neck, it may force the fuel into the 

 vent line and into the vent junction, blocking air back to the tank

through the vent line.
	


 	  Quote: 	
		  

 Also when the fuel heats up in the tank it expands and guess where it 

 expands to?  Right into the vent line.  Have you ever seen a Yak 52

"puking"
	


 	  Quote: 	
		   fuel overboard on the ramp during hot weather?  The reason is the fuel 

 has expanded in the tank and is forced out of the vent line through 

 the vent junction and out through the overboard vent line exiting out 

 the belly of the airplane.  Once the siphon has been set up by the 

 expansion, the siphoning effect can siphon out 5+ gallons.  No 

 kidding.....it happened to me.  I filled the airplane and left it on the

ramp in the sun for 2 days.
	


 	  Quote: 	
		   When I came back the fuel instrument no longer read 60/60.  I refilled 

 the tanks and it took over 5 gallons of fuel to bring the tanks back to

60/60.
	


[quote] The telltale sign was the dark, black spot in the blacktop under the 

 fuselage directly under the vent line.



 Dennis



 ---

wlannon(at)persona.ca
Guest

Posted: Tue May 18, 2010 7:59 am Post subject: feul feed

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

---

dsavarese0812(at)bellsout
Guest

Posted: Tue May 18, 2010 8:50 am Post subject: feul feed

Walt,

 Although it seems questionable regarding the vent system as  the cause of fuel not feeding from one tank or the other, particularly in the  52, the Yakovlev design bureau redesigned the vent system in the 89 and up model  years.  Two things happen on a pre 1989 Yak 52's which most Yak 52 owners  have experienced.  When the fuel tanks are close to full and the  temperature builds causing the fuel to expand in the tank, if one were to remove  the fuel caps, you will hear a rather large "whoosh" and the fuel will spill out  of the filler neck all over the wing.  This is caused by pressure building  in the tank.  The only way the expanded fuel can exit is via the vent line  with the tank cap in place.  The second reason the vent system was  redesigned was  because of the expansion and contraction of the very thin  aluminum metal of the fuel tanks.  This expansion and contraction of the  metal (ie: flexing) created cracks in many of the fuel tanks as evident of  the weld marks on the bottom of the tanks seen in most pre 1989 Yak  52's.

  

 The post 1989 vent system was far superior to the pre 1989  system.  The fuel tanks had two vent lines; one at the top, rear on the  inside (the same as pre 1989) and one on the top of the tank near the outboard  edge.  This second vent line eliminated the expansion of the fuel and the  puking of the fuel overboard because the tank could "breath".   There  are 2 separate vent systems on the post 1989 airplanes.  One system for  each tank.  And here's the most important fact,......no more fuel feeding  imbalance.   The tanks are the same size.  The flapper valves are  identical.  The only thing that changed was the vent system.

  

 Dennis

 [quote]   ---

talew(at)bellsouth.net
Guest

Posted: Tue May 18, 2010 10:06 am Post subject: feul feed

Think " G load" on the fuel to force the valve to open .

Terry



---

wlannon(at)persona.ca
Guest

Posted: Tue May 18, 2010 2:03 pm Post subject: feul feed

A perfectly coordinated turn should produce the same "G" load on all the 

fuel therefore no relative change to the force on each side of the valve.

Walt

---

wise(at)txc.net.au
Guest

Posted: Tue May 18, 2010 3:44 pm Post subject: feul feed

G'Day Dennis,

  

 It allways seems to come back to the  vents.

 Doing some aero's in the 18T one day, we got too  slow around a hesitation roll and sort of hung upside down.

 Not a good thing in a 18T as no inverted oil  sysyem. What a mess.

  

 The point is that I was not at my home  airfield.

 So put a splash in each side before departing, then  flew on to another strip and then about 35 min flight home. About 55  min.

 The right tank hardly fed at all and the left tank  was way down. Blew the line out with compressed air and it seems to be behaving  again.

 This sort of indicates that when inverted the feul  may have got into the vent line and stopped the tank from feeding.

  

 It is a huge puzzle to me, as I explained, I  relocated the left tank vent to about 3/4 inch away from the right vent thinking  that they are hence "breathing" from the same  locality.

  

 The problem is not consistant. A 3 hour 40 min trip  last month with 2 feul stops the tanks were within 10 litres of each other when  refeuling.

 And yet the feul man at one stop had a spill by  overfilling the left tank and no problems. One would have thought that the feul  would have got into the vent line and caused theleft tank to not  feed.

 It would seem that when there is a bit of  turbulance around the tanks feed in a more even manner.

  

 There is no doubt that flying the  aircraft without the rudder input does affect it.

  

 Hell, it's got me beat.

  

 By the way, thanks to all for the  input.

  

 Cheers,

 Chris.

 Chris Wise

GT Propellers  Australia

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 [quote]   ---

wlannon(at)persona.ca
Guest

Posted: Tue May 18, 2010 8:33 pm Post subject: feul feed

Hi Dennis;

  

 It would be interesting to see the 52 flapper  valve. It could very well be an improved version of the early CJ6 valve which  were likely direct copies from the Yak 18 era.

 The Chinese did at some point in time make a minor  change that would improve the flow.  I have seen that improved valve  in 1980's aircraft but also the original 1960 type in the same  aircraft.

  

 I personally do not like the single point vent  system since one leaf cutter bee (common in this area) can spoil your whole day.  If your aircraft is parked outside here you are well advised to use a pitot  cover AND a vent cover. Lack of airspeed indication is a minor annoyance.   Lack of engine power is a major one.

  

 The CJ has an advantage over the 52 for fuel tank  venting in that the outer wing has a 7 deg dihedral,  The filler is at the  inboard end and the vent outlet at the outboard forward corner.  This  allows a fairly generous expansion space that cannot be filled.  Of course  if the temperature is high enough it can still vent fuel.

 If I convert to an individual tank vent system  (which I am considering) I may install Parker MS series fuel vent valves  with pin hole bleeds.

  

 Best;

 Walt

  

  

 [quote]   ---

dsavarese0812(at)bellsout
Guest

Posted: Wed May 19, 2010 7:37 am Post subject: feul feed

Walt,

 I will see if I can scrounge up some photos of the fuel  junction and flapper valves and send them to you off-list.  

 Dennis

 [quote]   ---

wlannon(at)persona.ca
Guest

Posted: Wed May 19, 2010 1:56 pm Post subject: feul feed

Thanks Dennis

  

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