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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? |
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:
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. |
PLEASE!!!!!!!!!!
PLEASE change that valve to the proper one!
Do not fly this aircraft until done! |
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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. |
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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). |
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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. |
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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. |
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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. |
Where is that "like" button?
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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. |
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This airplane was certified by someone who pulls their pants on just like everyone else here. I simply vote to give them a break. |
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. |
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Bevan |
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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. |
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...) |
Are we still talking about the OP and this one specific instance of troubleshooting, or are we off in the twilight zone again?
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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. |
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Bottom line here is the RV's are a LEFT-RIGHT fuel system. |
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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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