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Fuel tank/burn questions

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andrew(at)nzactive.com
Guest

Posted: Thu Apr 02, 2009 11:56 pm Post subject: Fuel tank/burn questions

Guys, thanks for all the kind responses re fuel caps. It's all sorted.



I have some questions which may sound nuts, but which are better asked

here than figured out in the air:



1. Has anyone heard of (early) RV-4 tanks of less than 16 gallons

capacity? I ran a tank dry today, by mistake, switched over and

landed...and when I refuelled, it only took 12.5 gallons. I've got

aerobatic baffles, so it takes a while for the fuel to settle in, but I

took my time, and 12.5 it was. I then flew on that tank for exactly an

hour (2 x 30 mins) and it ran dry AGAIN, which leads me to ask...



2. Is a fuel burn of 16 gallons an hour, WOT, 5000 feet, and leaned ROP

reasonable? I was definitely leaned out, albeit conservatively. (Don't

have the instrumentation to support LOP running). Sounds crazy to me.

Anyone care to tell me what reasonable burns in an 0-360 at altitude,

FP, might be?



3. Anything y'all can think of that might reduce the effective volume of

a fuel tank? (A leak, I thought....but can't see one - and that doesn't

explain the fact that the tank took 12.5 gallons after having been

conclusively established as empty, and unseable fuel drained.)



4. OK, now it gets really weird. Anyone ever hear of fuel caps being

"sucked" out of the wing, in flight? This happened to me y/day, and

again (other wing) 2 days prior. I am aware it sounds bizarre. The RV is

just coming off long term sitting around, cos I mainly fly my beloved

Harmon Rocket, and I wonder if it's possible that caps could get old,

and not "spread" when the lever is snapped flush with the top of the

wing.



All comments from those more experienced in RVs than me would be

welcomed. Me and my RV are just getting to know each other again, after

a long time of being unfaithful to her, in the Rocket 



Cheers



Andrew

________________________________________________________________________

________________________________________________________________________

____________________________________________________________

 



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pitts_pilot(at)bellsouth.
Guest

Posted: Fri Apr 03, 2009 5:06 am Post subject: Fuel tank/burn questions

Andrew, I'm going to answer even though I'm not an experienced RVer just 

yet.  I am just now coming off a fuel related incident in my Pitts with 

an O-360 in it.   I don't believe you can eat up 16 gal of gas in an 

hour.  I get somewhere between 10 and 11 and hour when I'm WOT doing 

aerobatics.



However things you said may point to your possible problem: If you can 

suck the caps out, then you can suck fuel out too.  I'd replace the 

O-rings and/or adjust the cap so the caps are really tight ..... to the 

point where it's hard to open.   But what do I know???

Linn

ACTIVE NZ - Andrew wrote:

 	  Quote: 	
		   



 Guys, thanks for all the kind responses re fuel caps. It's all sorted.



 I have some questions which may sound nuts, but which are better asked

 here than figured out in the air:



 1. Has anyone heard of (early) RV-4 tanks of less than 16 gallons

 capacity? I ran a tank dry today, by mistake, switched over and

 landed...and when I refuelled, it only took 12.5 gallons. I've got

 aerobatic baffles, so it takes a while for the fuel to settle in, but I

 took my time, and 12.5 it was. I then flew on that tank for exactly an

 hour (2 x 30 mins) and it ran dry AGAIN, which leads me to ask...



 2. Is a fuel burn of 16 gallons an hour, WOT, 5000 feet, and leaned ROP

 reasonable? I was definitely leaned out, albeit conservatively. (Don't

 have the instrumentation to support LOP running). Sounds crazy to me.

 Anyone care to tell me what reasonable burns in an 0-360 at altitude,

 FP, might be?



 3. Anything y'all can think of that might reduce the effective volume of

 a fuel tank? (A leak, I thought....but can't see one - and that doesn't

 explain the fact that the tank took 12.5 gallons after having been

 conclusively established as empty, and unseable fuel drained.)



 4. OK, now it gets really weird. Anyone ever hear of fuel caps being

 "sucked" out of the wing, in flight? This happened to me y/day, and

 again (other wing) 2 days prior. I am aware it sounds bizarre. The RV is

 just coming off long term sitting around, cos I mainly fly my beloved

 Harmon Rocket, and I wonder if it's possible that caps could get old,

 and not "spread" when the lever is snapped flush with the top of the

 wing.



 All comments from those more experienced in RVs than me would be

 welcomed. Me and my RV are just getting to know each other again, after

 a long time of being unfaithful to her, in the Rocket 



 Cheers



 Andrew

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recapen(at)earthlink.net
Guest

Posted: Fri Apr 03, 2009 5:36 am Post subject: Fuel tank/burn questions

I've not heard of smaller fuel tanks - I thought the -4 and the -6 had similar configurations....so much for what I know...



I'm breaking in a new IO360B1F6 (180hp) in my 6A with 19 gal tanks and I see 16 gph fuel flows on my engine monitor - I'm running 25.5 squared for the break-in period.  I haven't done much leaning at all as I have been doing most of my flying at 3000' and below.  The total fill up matches what the engine monitor says.



Ralph

RV6A N822AR (at) N06 8.3 hrs



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khorton01(at)rogers.com
Guest

Posted: Fri Apr 03, 2009 5:47 am Post subject: Fuel tank/burn questions

On 3 Apr 2009, at 03:57, ACTIVE NZ - Andrew wrote:



 	  Quote: 	
		   

 >



 Guys, thanks for all the kind responses re fuel caps. It's all sorted.



 I have some questions which may sound nuts, but which are better asked

 here than figured out in the air:



 1. Has anyone heard of (early) RV-4 tanks of less than 16 gallons

 capacity? I ran a tank dry today, by mistake, switched over and

 landed...and when I refuelled, it only took 12.5 gallons. I've got

 aerobatic baffles, so it takes a while for the fuel to settle in,  

 but I

 took my time, and 12.5 it was. I then flew on that tank for exactly an

 hour (2 x 30 mins) and it ran dry AGAIN, which leads me to ask...



 2. Is a fuel burn of 16 gallons an hour, WOT, 5000 feet, and leaned  

 ROP

 reasonable? I was definitely leaned out, albeit conservatively. (Don't

 have the instrumentation to support LOP running). Sounds crazy to me.

 Anyone care to tell me what reasonable burns in an 0-360 at altitude,

 FP, might be?



 3. Anything y'all can think of that might reduce the effective  

 volume of

 a fuel tank? (A leak, I thought....but can't see one - and that  

 doesn't

 explain the fact that the tank took 12.5 gallons after having been

 conclusively established as empty, and unseable fuel drained.)



 4. OK, now it gets really weird. Anyone ever hear of fuel caps being

 "sucked" out of the wing, in flight? This happened to me y/day, and

 again (other wing) 2 days prior. I am aware it sounds bizarre. The  

 RV is

 just coming off long term sitting around, cos I mainly fly my beloved

 Harmon Rocket, and I wonder if it's possible that caps could get old,

 and not "spread" when the lever is snapped flush with the top of the

 wing.



 All comments from those more experienced in RVs than me would be

 welcomed. Me and my RV are just getting to know each other again,  

 after

 a long time of being unfaithful to her, in the Rocket 


	




Andrew,



Assuming the fuel tanks were built according to the plans, the tank  

capacity should be pretty close to 16 USG.  But, there are possible  

fuel pickup issues that could cause the fuel pickup to suck air wile  

there is still a lot of fuel left in the tank.  Possible fuel pickup  

issues are:



1. inverted fuel pickup hung up inside tank, such that it its end is  

no longer at the lowest point,

2. inverted fuel pickup unscrewed at the elbow inside the forward  

inboard end of the tank,

3. normal fuel pickup rotated so that its end is well above the bottom  

of the tank, or

4. normal fuel pickup tube broken off.



See http://www.vansaircraft.com/pdf/sb06-2-23.pdf



In all the above cases, you would be able to drain several gallons  

from the tank drain after a fuel starvation event.



One other possible cause is a fuel vent blockage that hinders the air  

from entering the tank to replace the fuel that is being sucked out.   

Ensure the fuel vents are completely clear.



If you can drain only a minimal amount of fuel from the drain after a  

fuel starvation event, and an unusually low quantity is required to  

fill the tank up, maybe there is a large quantity of solid matter in  

the tank.  It would be wise to remove the inspection cover on the  

inboard end of the tank to do an inspection.  Also inspect all fuel  

filters for contamination.



Good luck,



--

Kevin Horton (Grounded)

RV-8 (Flight Test Phase)

Ottawa, Canada

http://www.kilohotel.com/rv8

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john_s_bright(at)yahoo.co
Guest

Posted: Fri Apr 03, 2009 6:00 am Post subject: Fuel tank/burn questions

What does it mean to suck the caps out of the wing in flight?



do not archive



 Thanks,

John Bright

o:757-864-2305

h:757-874-0861

c:757-812-1909



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mrobert569(at)hotmail.com
Guest

Posted: Fri Apr 03, 2009 6:43 am Post subject: Fuel tank/burn questions

Some of the questions have already been answered but I still would like to throw my two cents in.

  

 The fuel caps are kept in place by the expansion of the large 'O' ring.  That 'O' ring will get hard over time and not expand properly.  With the low pressure over the top of the wing in flight C the fuel cap and fuel can definitely be sucked right out of the fuel tank (been there C done that once already).  O-360 f normal fuel flow for 5000 C properly leaned C should be somewhere in the vicinity of 8.5 - 9.2 gallons.  Obviously C leaning techniques will have quite a bit of influence on this.  Also C whether or not you have any electronic ignition installed will have a bearing.  With electronic ignition the fuel flow is somewhat lower.

  

 As to the capacity of the tank C I totally agree with Kevin Horton.  You really need to pull the in-board inspection plate and take a look.  

  

 Mike Robertson

 Das Fed

 

 

[quote] Subject: Fuel tank/burn questions

 Date: Fri C 3 Apr 2009 20:57:23 +1300

 From: andrew(at)nzactive.com

 To: rv-list(at)matronics.com

 

 --> RV-List message posted by: "ACTIVE NZ - Andrew" <andrew(at)nzactive.com>

 

 Guys C thanks for all the kind responses re fuel caps. It's all sorted.

 

 I have some questions which may sound nuts C but which are better asked

 here than figured out in the air:

 

 1. Has anyone heard of (early) RV-4 tanks of less than 16 gallons

 capacity? I ran a tank dry today C by mistake C switched over and

 landed...and when I refuelled C it only took 12.5 gallons. I've got

 aerobatic baffles C so it takes a while for the fuel to settle in C but I

 took my time C and 12.5 it was. I then flew on that tank for exactly an

 hour (2 x 30 mins) and it ran dry AGAIN C which leads me to ask...

 

 2. Is a fuel burn of 16 gallons an hour C WOT C 5000 feet C and leaned ROP

 reasonable? I was definitely leaned out C albeit conservatively. (Don't

 have the instrumentation to support LOP running). Sounds crazy to me.

 Anyone care to tell me what reasonable burns in an 0-360 at altitude C

 FP C might be?

 

 3. Anything y'all can think of that might reduce the effective volume of

 a fuel tank? (A leak C I thought....but can't see one - and that doesn't

 explain the fact that the tank took 12.5 gallons after having been

 conclusively established as empty C and unseable fuel drained.)

 

 4. OK C now it gets really weird. Anyone ever hear of fuel caps being

 "sucked" out of the wing C in flight? This happened to me y/day C and

 again (other wing) 2 days prior. I am aware it sounds bizarre. The RV is

 just coming off long term sitting around C cos I mainly fly my beloved

 Harmon Rocket C and I wonder if it's possible that caps could get old C

 and not "spread" when the lever is snapped flush with the top of the

 wing.

 

 All comments from those more experienced in RVs than me would be

 welcomed. Me and my RV are just getting to know each other again C after

 a long time of being unfaithful to her C in the Rocket 

 

 Cheers

 

 Andrew

 

 

 ________________________________________________________________________

 ________________________________________________________________________

 ____________________________________________________________

 

 

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Doug Gray

Joined: 10 Jan 2006
Posts: 112
Location: Sydney, Australia

Posted: Fri Apr 03, 2009 12:10 pm Post subject: Fuel tank/burn questions

On Fri, 2009-04-03 at 20:57 +1300, ACTIVE NZ - Andrew wrote:

  	  Quote: 	
		       it only took 12.5 gallons.

 	
 Kevin's response covers the options. Key question is if you can drain fuel from the 'dry' tank.

 

 If you have a fuel gauge, what does it read?

 Does the alternate tank have the same issue?

 

 Consider: (16 - 12.5) leaves 3.5 gallons in the tank. 3.5 gal is about 25% full scale on the Vans fuel gauge that is reasonably accurate at this level, so you are most likely sucking air when fuel is about 25% up the inboard tank rib. My money is on a loose/cracked/damaged fuel pickup.

 

 Doug     [quote][b]

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Doug Gray

Joined: 10 Jan 2006
Posts: 112
Location: Sydney, Australia

Posted: Fri Apr 03, 2009 12:26 pm Post subject: Fuel tank/burn questions

On Sat, 2009-04-04 at 06:08 +1000, Doug Gray wrote:

  	  Quote: 	
		       

      	  Quote: 	
		           it only took 12.5 gallons.

     	
 	
 

 Wait a minute - are you in New Zealand?   12.5 Imp Gallons * 1.2 => 15 USG

 

 You might also be losing fuel - check tank & gascolator drains under pressure, perhaps through the poorly sealed caps.

 

 Seems to me you are being punished for flirting with a Rocket!     [quote][b]

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denis.walsh(at)comcast.ne
Guest

Posted: Fri Apr 03, 2009 2:40 pm Post subject: Fuel tank/burn questions

first of all my money is with Doug's Imperial answer.



As to cap sucking.  My six has blown (had sucked) off a couple tank caps over the years.  I now carry a spare with me.  In my case they were left loose, either by the fueler or by me.

The good news is that in coordinated flight and reasonable attitudes and speeds, the fuel quits drooling after only a half  gallon or so.

I should add that I have also fliight checked another fascinating condition, which is having the fuel cap slightly cocked in the receptacle, but latched snug.  This can also result in fuel going overboard, due to the aforementioned low pressure area over the cap.  Again the fuel drool stops after a short time in coordinated flight, most likely because of the fortuitous dihedral of the Van's wing.

Denis

On Apr 3, 2009, at 2:24 , Doug Gray wrote:

 	  Quote: 	
		    On Sat, 2009-04-04 at 06:08 +1000, Doug Gray wrote:

  	  Quote: 	
		      

     	  Quote: 	
		          it only took 12.5 gallons.

    	
 	
 

 Wait a minute - are you in New Zealand?   12.5 Imp Gallons * 1.2 => 15 USG

 

 You might also be losing fuel - check tank & gascolator drains under pressure, perhaps through the poorly sealed caps.

 

 Seems to me you are being punished for flirting with a Rocket!  	  Quote: 	
		  

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