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top drawl tanks

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tc1917(at)bellsouth.net
Guest

Posted: Tue Mar 10, 2009 3:43 am Post subject: top drawl tanks

I have two five gal. tanks on my slingshot as per directions.  I have had 

one tank not siphon correctly on a short trip and I found it was the vent 

was slightly clogged.  no problem.  I believe it a leak on one of the top 

lines would prevent equalization but I also believe the bottom feeders are 

more problematic.  I have had those and the push in type plugs that hold the 

fittings would normally leak or deteriorate and have to be replaced (not 

sure if they would stand up to alki or not) requiring a great deal of 

trouble getting to them.  Also, if the same leak that stopped the top 

feeders happened to the bottom feeders -- well, you have to call the fire 

department (while flying)!!  So, I guess it is what it is.  I would have 

definately put a ten gal tank or better in stead of my two fives had I have 

known better.

p.s. I have a go cart type tank, two gals I believe that slips right in back 

on a firestar on top of the other tank that is great as a gravity feeder for 

extended flights.  I do not need it now.  It has a weird shape and fits in 

perfectly.  will send pics to someone who is interested.  Ted Cowan, 

Alabama, Slingshot 912 ul  zoom zoom

aslsa.rng(at)gmail.com
Guest

Posted: Tue Mar 10, 2009 4:07 am Post subject: top drawl tanks

Ted, Ditto on the problem of the grommets when putting the fuel feeds on the bottom of the tanks. I got very lucky when I made the decision to replace both tanks in my Mk III. The grommet flanges had split all the way up to the body, but had not started to leak, yet. I bought new top draw tank taps from TNK and the bottoms of the new tanks are pristine. It may not be the best way to do it, but I don't loose any sleep worrying about tank grommets that are nearly impossible to inspect. 



Rick



On Tue, Mar 10, 2009 at 6:40 AM, Ted Cowan <tc1917(at)bellsouth.net (tc1917(at)bellsouth.net)> wrote:

 	  Quote: 	
		   --> Kolb-List message posted by: "Ted Cowan" <tc1917(at)bellsouth.net (tc1917(at)bellsouth.net)> 	
 

[quote] 

 

 I have two five gal. tanks on my slingshot as per directions.  I have had one tank not siphon correctly on a short trip and I found it was the vent was slightly clogged.  no problem.  I believe it a leak on one of the top lines would prevent equalization but I also believe the bottom feeders are more problematic.  I have had those and the push in type plugs that hold the fittings would normally leak or deteriorate and have to be replaced (not sure if they would stand up to alki or not) requiring a great deal of trouble getting to them.  Also, if the same leak that stopped the top feeders happened to the bottom feeders -- well, you have to call the fire department (while flying)!!  So, I guess it is what it is.  I would have definately put a ten gal tank or better in stead of my two fives had I have known better.

  p.s. I have a go cart type tank, two gals I believe that slips right in back on a firestar on top of the other tank that is great as a gravity feeder for extended flights.  I do not need it now.  It has a weird shape and fits in perfectly.  will send pics to someone who is interested.  Ted Cowan, Alabama, Slingshot 912 ul  zoom zoom 

  

 

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 [b]

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Tue Mar 10, 2009 5:41 am Post subject: top drawl tanks

I don't use grommets to pull fuel out the bottom of  my tank, which is aluminum.

  

 Seems the plastic tanks today are not nearly as  rigid and thick as they were back in the 80's.

  

 john h

 mkIII

 [quote]    

Ted, Ditto on the problem of the    grommets when putting the fuel feeds on the bottom of the tanks.     



   Rick

 

[b]

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

JetPilot

Joined: 10 Jan 2006
Posts: 1246

Posted: Tue Mar 10, 2009 8:13 am Post subject: Re: top drawl tanks

 	  tc1917(at)bellsouth.net wrote: 	
		  

Also, if the same leak that stopped the top 

feeders happened to the bottom feeders -- well, you have to call the fire 

department (while flying)!!  

	




It would be difficult to keep a thin bottom feed plastic tank sealed, which is exactly why I still use the top feed on my Kolb fuel tanks.  The top feed tank is not preferred in aviation, but it works fine if much care is used not to get any type of leak anywhere above the fuel level.  In the thin plastic tanks as we have in our Kolbs, I will keep using top feed.  Given this top feed, there are several things you need to be careful of and consider though !



As far as a leak goes, air leaks at a MUCH faster rate than fuel does, and air is generally not detectable.  A pinhole that would just cause a bit of gas moisture on a fitting on the bottom of the tank, would flood the system with air and result in an engine failure at the top of the tank.  If a valve, or filter develops a small leak under positive pressure would quickly be caught in a preflight as an area being moist with gas, the same pinhole in above the tanks ( in an area of suction ) would not be detectable in most cases until the engine quit.   I have no sparks or flames around my fuel fittings in my Kolb, and while a very slow drip or even moisture would not be acceptable and would be immediately corrected before any flight, such a slow leak as a drip every couple of minutes would NOT result in an in-flight fire.  The same slow leak with air leaking in as opposed to gas leaking out would result in an emergency though ! I would rather see some gasoline moisture in a preflight, or a very small slow drip than having my engine suddenly quit.  This is why I place all  my fuel valves, filters, and gascolators below the tank level in my Kolb, this is good fuel system design.



A forced landing in bad terrain is much more likely to result in a fire than a very slow drip that can be caught in a preflight    



Mike

_________________
"NO FEAR" - If you have no fear you did not go as fast as you could have !!!

Kolb MK-III Xtra, 912-S

NeilsenRM(at)comcast.net
Guest

Posted: Tue Mar 10, 2009 9:35 am Post subject: top drawl tanks

Mike/All



You make a lot of good points. Top draw fuel tanks just seem to add 

unnecessary opportunities for problems. Also top draw tanks would seem to be 

less forgiving of a low fuel level. A turn or turbulence could uncover a 

fuel feed causing at least higher hart rate much quicker than with bottom 

feed. I have never landed with less than three total gallons and normally 

get nervous when I get to 5 gallons but if I were to need it.



As for leaks on bottom draw tanks I have never had one. At six years I 

purchased new tanks and new rubber plug things. I think it is three years on 

the new tanks. Another 3-4 years I will replace the current tanks with the 

new 6 gallon tanks. I have always used a step drill and cleaned up the holes 

before inserting the plugs, then the fittings. I have never had a leak and 

have used that 10% ethanol crap for at least 6 years since that is the only 

fuel they sell in Michigan. On trips I use 110LL but that isn't the norm.



Rick Neilsen

Redrive VW powered MKIIIC



---

tlongo

Joined: 17 Jul 2007
Posts: 14

Posted: Tue Mar 10, 2009 10:20 am Post subject: Re: top drawl tanks

If you are worried about fuel problems put a pressure gauge in carburetor feed line and you will know even before problem gives you an engine out. I have the new 6 gal tanks with top feed and have never had any problems, had the older 5 gal with bottom feed and also never had any problems.

JetPilot

Joined: 10 Jan 2006
Posts: 1246

Posted: Tue Mar 10, 2009 11:15 am Post subject: Re: top drawl tanks

Rick, 



Where did you get the bottom draw fittings ?   If they work on the thin Kolb plastic tanks that well without leaking, it would be worth it for me to change to bottom draw in my present tanks.  The only reason I have not done this already is that I was not aware of any good fittings that would not leak for the Kolb tanks.

 	  tlongo wrote: 	
		  If you are worried about fuel problems put a pressure gauge in carburetor feed line and you will know even before problem gives you an engine out. 	




I don't know how much change in pressure you would see as more and more bubbles enter the system, it may show up in time or it may not ???   This is not always the case though as Rick Points out.   If air floods the system, it could be very sudden, you would see the fuel pressure drop at the same time your engine quits.  Bottom draw is definitely the way to do if you can find a way to do it without leaks.



Mike

_________________
"NO FEAR" - If you have no fear you did not go as fast as you could have !!!

Kolb MK-III Xtra, 912-S

tlongo

Joined: 17 Jul 2007
Posts: 14

Posted: Tue Mar 10, 2009 12:09 pm Post subject: Re: top drawl tanks

I did have an air leak back when I had the 5 gal tanks with bottom feed. I use the clear blue type fuel line so I can see the fuel, that is how I spotted the air problem that ended up being a leaking squeeze bulb, but it did not leak fuel. I have since replaced squeeze bulb with electric fuel pump for prime and back up. The see trough line lets you know right away, just change it every year with maintenance. Tom

by0ung(at)brigham.net
Guest

Posted: Tue Mar 10, 2009 1:16 pm Post subject: top drawl tanks

You make a lot of good points. Top draw fuel tanks just seem to add 

unnecessary opportunities for problems. Also top draw tanks would seem to be



less forgiving of a low fuel level.

 	  Quote: 	
		  >>>>>>>>>>>>>>>>


	


I guess I am having problems deciding on the difference between top and

bottom feed tanks....



With a bottom feed tank your fuel pump is sucking gas from the bottom of the

tank and forcing it to the engine via external lines to the tank.



With a top feed tank  your fuel pump is sucking gas from the bottom of the

tank and forcing it to the engine via internal lines in the tank..   



In either case if there are leaks there are problems   if the leaks are

above the tank it is going to suck air,,,,  and if below the tank it is

going to leak gas in the belly of the plane...   neither sounds like a lot

of fun.  



The only difference I could imagine is if one method left more unusable fuel

in the tank when the tank was empty.



Boyd Young

KOLB MKIIIC

16 gal aluminum tank bottom fed at 2 points.

zeprep251(at)aol.com
Guest

Posted: Tue Mar 10, 2009 2:25 pm Post subject: top drawl tanks

Rick et all,

    3 weeks after I bought the MK-3 I opened the hanger to see fuel dripping out of the drain holes in the bottom of the fuselage.I really can't say how old the grommets were,but I converted to top feed tanks and use  clear line from the tanks thru the filter mounted on top of the tanks where I can see it.From the gascolater, to elec pump, to the engine  driven pump are all plumbed with black fuel injection quality hose.Need to see if any air is getting in at the top and the clear  line lets me check that easily.And Rick,,where can you get that110LL? : )

 

                               G Aman

 

   

 

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