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-   -   Not drawing from the right hand tank (https://vansairforce.net/community/showthread.php?t=136164)

Saville 03-29-2016 11:29 AM

Quote:

Originally Posted by Toobuilder (Post 1066380)
I have not read every post, but have you considered doing a quick ground run on the right tank to verify it is feeding or not, and if so, take off on the left tank (which you KNOW is feeding), climb to a safe altitude over the airport and then switch to the right? You should have a definitive answer in about 5 seconds.

After that you can evaluate changing out the fuel selector, but if the right side feeds at least you can use the airplane again.

I thought of that but:

what if the selector itself is busted and doesn't really switch from the left tank to the right tank but stays on the left no matter how I have the knob set?

Oliver 03-29-2016 12:21 PM

Please excuse me, if my post sounds harsh, but this topic makes me really nervous. Firstly, because the builder thought that it might be a smart idea to install a fuel selector with a ‘both’ setting (what other brilliant ideas did he have?). Secondly, because this didn’t strike the OP as odd. :eek:
Frankly, I also wonder about the leap from believing that a ‘both’ setting is fine to some fancy testing of the fuel system.

This is what I would suggest:
  • Visually inspect / confirm the type of the fuel selector and the fuel system layout.
  • Remove one end of the fuel hose somewhere after the fuel pump and hang it into a gas can.
  • Turn on the auxiliary pump, test all positions of the fuel selector, confirm that they are in accordance with your observations and measure the flow rate (how long does it take e. g. to fill 3 gal. into the gas can and calculate the hourly flow rate based on that). This will also allow you to confirm your expectation regarding the fuel levels with a dip stick (one side should remain unchanged, the other should have dropped).

I strongly doubt that there is anything wrong with your fuel selector valve. Most likely, it is simply the wrong type which had been installed.

Mel 03-29-2016 12:45 PM

PLEASE!!!!!!!!!!
 
PLEASE change that valve to the proper one!

Do not fly this aircraft until done!

Saville 03-29-2016 12:48 PM

Quote:

Originally Posted by Oliver (Post 1066408)
Please excuse me, if my post sounds harsh, but this topic makes me really nervous.

If the post makes you nervous imagine my feeling when a system that worked just fine for months suddenly....behaved differently.

Firstly, because the builder thought that it might be a smart idea to install a fuel selector with a ?both? setting (what other brilliant ideas did he have). Secondly, because this didn?t strike the OP as odd.
:eek:

Sorry I'm not omniscient but I am here to learn. And I learned something.

Frankly, I also wonder about the leap from believing that a ?both? setting is fine to some fancy testing of the fuel system.

Not sure what "leap" you are talking about. The system worked fine until one day it didn't (tanks were never lower than half full at any time BTW). In other words - something changed. THAT is a red flag to me.

After making the original post, I've learned the dangers of a BOTH setting if one tank is low. I've digested that and have moved on to wanting to assess the fuel system.

The fact that it no longer worked as it did was pretty unnerving and now, to me, the OP, this calls into question the fuel system rigging.

The "leap" is because of what you yourself just suggested: what other brilliant ideas did the builder (not me) have? Just how DID he rig that fuel system? Well I'd like to test the fuel system, and, at the same time, determine how it is built. And do it before I fly again - as I've said..

If you are talking about some other leap I'm not sure what that is.





This is what I would suggest:

Your list has already been suggested and corroborated by other posters and is what I'm going to do.


I strongly doubt that there is anything wrong with your fuel selector valve.

Perhaps you'll find a way to pardon me for not just making that assumption - especially given your concern about "other brilliant ideas".

Most likely, it is simply the wrong type which had been installed.

Your post doesn't strike me as harsh.

It does strike me as yet another example of beating a very dead horse with regard to the BOTH setting and the fact that the selector has that setting.

Well I suppose everyone has to get their two cents in about that, and tell me what they would do with regard to signing off my airplane if they were inspecting it and so forth.

In fact I long ago, in this thread, made my decision about the selector.

What does not seem simple to me - what I need to figure out and hope to obtain aid from people in this forum - is figuring out the best way to test the fuel system and determine it's rigging. THAT is where my focus is in this thread.

gyoung 03-29-2016 01:54 PM

Quote:

Originally Posted by Saville (Post 1066423)
What does not seem simple to me - what I need to figure out and hope to obtain aid from people in this forum - is figuring out the best way to test the fuel system and determine it's rigging. THAT is where my focus is in this thread.

I think it was mentioned before but lost in the shuffle. Disconnect the fuel line to the carb/servo and redirect it to a suitable container. Then turn on the boost pump and cycle thru the valve positions. You can measure the fuel drop in the selected tank against the fuel output to the container to confirm where it's coming from. Worst case is you have to cap off the lines between the valve and tank to assure no flow from that tank. You could do that at the valve or at the wing root.

While you're at it you can also do the max attitude flow test. Put the tail in a hole/ditch and/or jack up the nose to an attitude well above stall and measure the flow rate from each tank with the boost pump. It needs to be greater than the max fuel consumption at SL WOT. There's more specifics in the construction manual (or at least there used to be).

RV7A Flyer 03-29-2016 02:51 PM

Quote:

Originally Posted by Saville (Post 1066423)
What does not seem simple to me - what I need to figure out and hope to obtain aid from people in this forum - is figuring out the best way to test the fuel system and determine it's rigging. THAT is where my focus is in this thread.

1. Open up/remove the covers over the valve
2. Remove any covers over the fuel lines in the cockpit
3. Look with Mark I Eyeballs at which tank is connected to which input on the valve.

RV6_flyer 03-29-2016 03:13 PM

Quote:

Originally Posted by Oliver (Post 1066408)
Please excuse me, if my post sounds harsh, but this topic makes me really nervous. Firstly, because the builder thought that it might be a smart idea to install a fuel selector with a ?both? setting (what other brilliant ideas did he have?). Secondly, because this didn?t strike the OP as odd. :eek:
Frankly, I also wonder about the leap from believing that a ?both? setting is fine to some fancy testing of the fuel system.

This is what I would suggest:
  • Visually inspect / confirm the type of the fuel selector and the fuel system layout.
  • Remove one end of the fuel hose somewhere after the fuel pump and hang it into a gas can.
  • Turn on the auxiliary pump, test all positions of the fuel selector, confirm that they are in accordance with your observations and measure the flow rate (how long does it take e. g. to fill 3 gal. into the gas can and calculate the hourly flow rate based on that). This will also allow you to confirm your expectation regarding the fuel levels with a dip stick (one side should remain unchanged, the other should have dropped).

I strongly doubt that there is anything wrong with your fuel selector valve. Most likely, it is simply the wrong type which had been installed.


I once was a DAR that would NOT issue the Special Airworthiness Certificate to an RV till after the Fuel Selector Valve was changed to one that did not have a BOTH position. It is my belief that it is UNSAFE to have a fuel valve with both position in the present low wing fuel tank RVs. I would not sign off the once a year Condition Inspection as being in a condition for Safe Operation with a BOTH position fuel valve on a low wing fuel tank Experimental aircraft.

Mel 03-29-2016 03:51 PM

Quote:

Originally Posted by RV6_flyer (Post 1066460)
I once was a DAR that would NOT issue the Special Airworthiness Certificate to an RV till after the Fuel Selector Valve was changed to one that did not have a BOTH position. It is my belief that it is UNSAFE to have a fuel valve with both position in the present low wing fuel tank RVs. I would not sign off the once a year Condition Inspection as being in a condition for Safe Operation with a BOTH position fuel valve on a low wing fuel tank Experimental aircraft.

I'm STILL a DAR. I have certificated over 800 aircraft. and like Gary, I would never sign off an RV with a "Both" position on the fuel selector.

David-aviator 03-29-2016 03:52 PM

An element of paranoia has crept into this thread.

There is nothing unsafe about the BOTH position of this valve. It MAY become unsafe if it is used but even then the airplane won't fall out of the sky.

There are a number of switches in every aircraft that create an unsafe situation if used in flight. Guess what happens if the ignition switch is moved to OFF or the mixture is pulled to OFF? Placards are even not required for these obvious unsafe situations.

It would appear this aircraft was built with some care. I would be most reluctant to condemn the builder, perhaps several EAA tech advisors who frequently inspect before certification, or the DAR (or perhaps FAA inspector) who certified it.

If the valve gives one night mares, change it. My 2 cents worth is I would have no qualms whatever about flying this aircraft with or without a placard to not use the BOTH position.

Toobuilder 03-29-2016 04:00 PM

Where is that "like" button?

Mel 03-29-2016 04:02 PM

Quote:

Originally Posted by David-aviator (Post 1066475)
There is nothing unsafe about the BOTH position of this valve. It MAY become unsafe if it is used but even then the airplane won't fall out of the sky.
There are a number of switches in every aircraft that create an unsafe situation if used in flight. Guess what happens if the ignition switch is moved to OFF or the mixture is pulled to OFF? Placards are even not required for these obvious unsafe situations.

Apples to oranges.

The pilot of this aircraft is lead to believe that the aircraft will function normally using a both position on a fuel valve. This is not normal.

The pilot of any aircraft is lead to believe that the aircraft will function normally if the ignition switches are left "on". This is normal!

If you bring an aircraft with a modified fuel system to me for inspection, you must prove to my satisfaction that your modifications are feasible.
If you think that a "both" position on an otherwise standard RV fuel system is feasible, then you shouldn't bring your aircraft to me for inspection.

David-aviator 03-29-2016 04:31 PM

Quote:

Originally Posted by Mel (Post 1066479)
Apples to oranges.

The pilot of this aircraft is lead to believe that the aircraft will function normally using a both position on a fuel valve. This is not normal.

The pilot of any aircraft is lead to believe that the aircraft will function normally if the ignition switches are left "on". This is normal!

If you bring an aircraft with a modified fuel system to me for inspection, you must prove to my satisfaction that your modifications are feasible.
If you think that a "both" position on an otherwise standard RV fuel system is feasible, then you shouldn't bring your aircraft to me for inspection.

With all do respect Mel, you do good work, but there is nothing normal about any experimental aircraft. That's why the FAA requires the warning to passengers that the aircraft has not been built to FAA standards.
This airplane was certified by someone who pulls their pants on just like everyone else here. I simply vote to give them a break.

Toobuilder 03-29-2016 05:02 PM

And to add, I'm convinced that adding a "both" position to an RV is going to increase pilot workload rather than reduce it - but properly managed (i.e., don't use the "Both" position), it is not "unsafe".

There are plenty of single engine certified aircraft with far more complex and difficult to manage fuel systems than an RV with a "Both" position. Some older Beech products and even the PA-22 with an aux tank comes to mind. Just about every Rocket has you pass through "OFF" every time you switch tanks - a very specific "Fail" in todays aircraft design philosophy.

Best to add the proper valve, but going so far as to ground an aircraft owned and flown by an aware pilot until that happens... a bit much.

Bevan 03-29-2016 05:19 PM

Quote:

Originally Posted by Mel (Post 1066474)
I'm STILL a DAR. I have certificated over 800 aircraft. and like Gary, I would never sign off an RV with a "Both" position on the fuel selector.

It is my understanding that the Andair two position valves have a "common" position that technically feeds fuel from both tanks. This is so that fuel is not interrupted from one tank before it begins to flow from the other tank (when switching tanks). If true, it is a safety feature. The difference with the OP's valve is that it may simply be labeled with a "both" position. So in this case, it may be prudent to simply order a new face plate or somehow cover/delete the word "both", and leave the valve itself as is. Best to check directly with Andair and post the findings back here for future reference.

Bevan

Bevan 03-29-2016 05:23 PM

Quote:

Originally Posted by rightrudder (Post 1065844)
Here's an alternate test rig. I recommend Stella Artois for test fluid, but this guy looks like a Bud man:


Stick this hat on the fan sitting in front and slightly below you (tell him it's a science project) with one cup empty. See what happens after you begin to suck...if you even get that far. :eek::D;)

Bevan

rv7charlie 03-29-2016 06:31 PM

Quote:

Originally Posted by Bevan (Post 1066495)
It is my understanding that the Andair two position valves have a "common" position that technically feeds fuel from both tanks. This is so that fuel is not interrupted from one tank before it begins to flow from the other tank (when switching tanks). If true, it is a safety feature. The difference with the OP's valve is that it may simply be labeled with a "both" position. So in this case, it may be prudent to simply order a new face plate or somehow cover/delete the word "both", and leave the valve itself as is. Best to check directly with Andair and post the findings back here for future reference.

Bevan

Ding!

Some variation on that theme likely applies to most selector valves. If the label says 'both', it *implies* it's ok to operate there, but if it just says 'left-right-off', the pilot should pick one. :-)

A friend sold an -8 with the current 'stock' valve; 45 degrees L & R for tanks. Buyer had fuel starvation in flight with fuel in the tanks; later said that he thinks he might have aligned the handle either fore/aft or in line with the spar because he'd previously owned an RV with one of the old style valves. Nothing wrong with the valve or the label; he just didn't select a labeled position.

To the OP:
If you don't find a blocked vent, is it possible that you finally found the right conditions for the plane to draw from only one side with the selector in 'both'? Even a high wing Cessna will feed unevenly when running on 'both', though it's difficult for it to suck air (unlike low wing planes).

As a FWIW, on my -4, with less than ~1/2 tanks I can disconnect the line from the tanks to the (stock) Van's selector valve without fuel flowing.

You can check for actual flow by selecting 'off', and disconnecting the fuel line at the engine or gascolator, as others have recommended. If you use a tank leak test setup (balloon on one leg of at T fitting, or a manometer tube on the T), you can select a tank and pressurize the tank through the vent. If there are no blockages, you can easily move fuel through the valve and out the line in the engine compartment. Then select the other tank, & repeat. The balloon or manometer tube will protect the tank from over-pressure, & still allow enough pressure to move the fuel through the open valve & line to the firewall area.

Charlie

edit: You won't get 'bubbles' in the fuel by blowing in the vent, unless you have the tank completely full & that wing is 'low'. The vent is (or should be) at the highest point inside the tank.

BobTurner 03-29-2016 06:53 PM

I'm with Mel here. As an A&P his finances are at risk here.
(Can you see the widow's lawyer in court? He'll hold up THIS thread, and say that if ordinary people thought this was bad, then an A&P should surely have known...)

Toobuilder 03-29-2016 07:21 PM

Are we still talking about the OP and this one specific instance of troubleshooting, or are we off in the twilight zone again?

Mel 03-29-2016 07:22 PM

You are correct. It is experimental and you can do what you wish. But when an airplane goes down because the pilot was flying "on both" and one tank became too low, it goes against all of us flying these homemade airplanes."

You may have the last word.

Please don't call me for an inspection.

David-aviator 03-29-2016 07:31 PM

Quote:

Originally Posted by Mel (Post 1066528)
You are correct. It is experimental and you can do what you wish. But when an airplane goes down because the pilot was flying "on both" and one tank became too low, it goes against all of us flying these homemade airplanes."

You may have the last word.

Please don't call me for an inspection.

If I do, it will be right. :)

Bottom line here is the RV's are a LEFT-RIGHT fuel system.

RV7A Flyer 03-29-2016 08:57 PM

Quote:

Originally Posted by Bevan (Post 1066495)
It is my understanding that the Andair two position valves have a "common" position that technically feeds fuel from both tanks. This is so that fuel is not interrupted from one tank before it begins to flow from the other tank (when switching tanks). If true, it is a safety feature. The difference with the OP's valve is that it may simply be labeled with a "both" position. So in this case, it may be prudent to simply order a new face plate or somehow cover/delete the word "both", and leave the valve itself as is. Best to check directly with Andair and post the findings back here for future reference.

Bevan

Well...sort of true. The L-R-Off valve has a sort of detent at each position, but it will flow (some) fuel when it is between positions, by design (IIRC). I believe the L-Both-R-Off valve has detents at all *four* positions. Flowing fuel while switching tanks is, as you say, a safety feature, but shouldn't be relied on, obviously.

Would be really unusual if a L-R-Off valve was shipped with a L-Both-R-Off faceplate, or would be *very* bad construction if the builder swapped out the correct faceplate for an incorrect one.

ETA: http://www.andair.co.uk/wp-content/u...ctors_FS20.pdf

The data sheet for the valves in question talk about the detents at each position.


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