Van's Air Force
Don't miss anything! Register now for full access to the definitive RV support community.
Fuel Selector: Why Only Left or Right and no BOTH?
- Thread starter DanH
- Start date
- Status
FlyingArcher
Well Known Member
Hello,
I'm a low time pilot and as such have only flown half a dozen different airplane types with almost as many different fuel selector types
Van's offers a Left/Right/Closed selector and even if you opt for an Andair where a Left/Both/Right/Closed combo exists, it seems people stick to the L/R/C.
So, I'm asking experienced pilots if there is a good reason for this choice, or if it's just a question of preference. I would have thought that running on BOTH would help keep the plane balanced but I presume that it's not just that simple
Please enlight me.
Cheers
I'm a low time pilot and as such have only flown half a dozen different airplane types with almost as many different fuel selector types
Van's offers a Left/Right/Closed selector and even if you opt for an Andair where a Left/Both/Right/Closed combo exists, it seems people stick to the L/R/C.
So, I'm asking experienced pilots if there is a good reason for this choice, or if it's just a question of preference. I would have thought that running on BOTH would help keep the plane balanced but I presume that it's not just that simple
Please enlight me.
Cheers
On a low wing A/C with fuel tanks in the wings, when you run a tank dry with the valve on both, the fuel pump will suck air and no fuel will be pulled from the other tank. The motor will quit. A left and right valve will solve that problem.
Also, with a left and right valve, you can run out of gas twice!!!! On a Cessna with the valve on both, you run out of gas only once and have no where to switch to...........
Also, with a left and right valve, you can run out of gas twice!!!! On a Cessna with the valve on both, you run out of gas only once and have no where to switch to...........
Left/right balance and back-up
On my 6A I burn left gas first when solo as I tend to require a bit of aileron trim with me sitting slightly off to the left. No trim required with two people in plane (which happens about 50% of flights) so then I burn tanks 1/2 left, 1/2 right, back to left, and back to right.
I agree with previous post of always have a back-up tank. Even if you burn a tank way down (but not out) you can always go back to it if something happens with the other tank. I know there are threads with lots of people saying they run tanks dry. Not me. I like to know I have fuel, even if small amount, in another tank if needed.
On my Cessna 140 it is placard to not take-off on a tank that has less then 1/4 fuel level. If you have a both position (original 140s do not and I have the original valve still) you can not take-off if both tanks shows < 1/4 fuel. Since I do not burn both, I can take-off with that same amount of fuel if it is all on one side ie. > 1/4 tank on one side and empty on the other.
On my 6A I burn left gas first when solo as I tend to require a bit of aileron trim with me sitting slightly off to the left. No trim required with two people in plane (which happens about 50% of flights) so then I burn tanks 1/2 left, 1/2 right, back to left, and back to right.
I agree with previous post of always have a back-up tank. Even if you burn a tank way down (but not out) you can always go back to it if something happens with the other tank. I know there are threads with lots of people saying they run tanks dry. Not me. I like to know I have fuel, even if small amount, in another tank if needed.
On my Cessna 140 it is placard to not take-off on a tank that has less then 1/4 fuel level. If you have a both position (original 140s do not and I have the original valve still) you can not take-off if both tanks shows < 1/4 fuel. Since I do not burn both, I can take-off with that same amount of fuel if it is all on one side ie. > 1/4 tank on one side and empty on the other.
Last edited:
FlyingArcher
Well Known Member
That's a good reason!
Uh oh... I didn't think about this one, but that's a perfectly good reason to NOT have a BOTH position and you can consider me as educated now. I knew I missed the real point
Uh oh... I didn't think about this one, but that's a perfectly good reason to NOT have a BOTH position and you can consider me as educated now. I knew I missed the real point
pierre smith
Well Known Member
My Air Tractor only has "Both"....
...or "Off". That's because we're so preoccupied, we don't need to worry about which tank to run. The belly is six inches lower than the wings and there's a header tank made of a piece of six inch diameter tubing that both tanks dump into. It stays full regardless of the fuel in the tanks and the engine is fed from there.
Regards.
...or "Off". That's because we're so preoccupied, we don't need to worry about which tank to run. The belly is six inches lower than the wings and there's a header tank made of a piece of six inch diameter tubing that both tanks dump into. It stays full regardless of the fuel in the tanks and the engine is fed from there.
Regards.
A both setting on the valve is not an option on low wing airplanes. If one tank goes dry, the pump would gladly suck air rather than fuel up the hill to the engine.
David Clifford
Well Known Member
I have pondered this quite a bit and I was pushed to make a decision at the Andair booth to take advantage of their valve/filter/pump combo "special". Building the Cozy we wanted simplicity and went with only an ON/OFF valve. So far we are happy with that decision. On the RV-10 I wanted the option to set the valve to "Both" for T/O and Landings and having the Left/Right/Both option for normal flight. With this valve I can do everything the L/R/O valve can do plus have a Both position,,,and it was the same price. There are pros and cons for both types of valves but Cessna, Piper, Beech, Diamond, ect., have been using this type of valve for a long time and it seems to work OK for them,,, so right or wrong, thats what I ordered.
L.Adamson
Well Known Member
If you are low on fuel during the landing phase, and one tank "unports" during one of your banking turns, then the pump will be trying to push "air only". In a low wing, fuel can also move from one tank to the other as the wing rises and falls. You must have combinations of header tanks, check valves, etc. in order for this to work.
L.Adamson --- RV6A (flying)
Bubblehead
Well Known Member
Isolating a bad tank or pickup or fuel
One other reason, but that happens rarely, is if you get bad fuel in one tank, you can isolate it. Same thing if a tank flop tube (if so equipped) hangs up at the top of the tank or a pickup becomes clogged. All rare but if anything bad happens from the tank to the selector valve you have one option. If "Both" is the only option you have no options.
One other reason, but that happens rarely, is if you get bad fuel in one tank, you can isolate it. Same thing if a tank flop tube (if so equipped) hangs up at the top of the tank or a pickup becomes clogged. All rare but if anything bad happens from the tank to the selector valve you have one option. If "Both" is the only option you have no options.
IowaRV9Dreamer
Well Known Member
another low wing with on/off fuel
My Skipper is a low wing (certified) airplane and has only an on-off valve. Beech did it by using a small pipe to interconnect the tanks (maybe 1" diameter by the width of the fuselage) - this serves as a header tank. A wing tank conncts to either end of the pipe and the fuel selector connects to the center. There are check valves to prevent fuel from moving between tanks. BTW the vent system also includes "flame arrestors"!
The only limitations are no slips > 30 seconds (I think because you could empty out the header "pipe") and no takeoff with fuel below 1/4 (probably for the same reason).
The design is elegent, doesn't really add much weight, and could be adapted to an RV if somone wanted to do it, but with the higher power engines we are all using the pipe would probably have to be bigger!
Good to know the Skipper shares a design element with the Air Tractor! Now I just need spray bars...
My Skipper is a low wing (certified) airplane and has only an on-off valve. Beech did it by using a small pipe to interconnect the tanks (maybe 1" diameter by the width of the fuselage) - this serves as a header tank. A wing tank conncts to either end of the pipe and the fuel selector connects to the center. There are check valves to prevent fuel from moving between tanks. BTW the vent system also includes "flame arrestors"!
The only limitations are no slips > 30 seconds (I think because you could empty out the header "pipe") and no takeoff with fuel below 1/4 (probably for the same reason).
The design is elegent, doesn't really add much weight, and could be adapted to an RV if somone wanted to do it, but with the higher power engines we are all using the pipe would probably have to be bigger!
Good to know the Skipper shares a design element with the Air Tractor! Now I just need spray bars...
Fuel Selector Both
<<One thing I really like is the "both" setting on the fuel selector. The tanks are feeding exacty the same amount. I like not having to switch back and forth.>>
Stan, are you sure a "both" position is a good idea?
Dan,
For me, it's a great idea. I gave it a lot of thought before deciding to build in a Both selection and some of my reasoning follows.
I like not having to switch tanks. I'd heard the biggest problem with the both setting was uneven feeding from the fuel tanks. I solved that problem by making the length of fuel lines from both tanks the same length and with the same amount of degrees in the bends. Thus, the uneven feeding due to viscosity was solved - my tanks are feeding EXACTLY the same amount (as determined by flight tests).
Regarding the "A both setting on the valve is not an option on low wing airplanes. If one tank goes dry, the pump would gladly suck air rather than fuel up the hill to the engine," comment - it actually is an option on low wing airplanes - mine is an example. The tanks will feed evenly if properly designed. And since the tanks feed evenly, they will both be near zero at the same time. If both tanks are near zero, then I have more problems to worry about than sucking air from one tank. I need to worry more about sucking up the seat cushion. FYI, I have ops checked it on the ground and it will suck air from an empty tank rather than draw fuel from the other with fuel. The solution is the same as running a tank dry on an airplane without a "both" setting - switch to the tank with fuel in it.
For me, should I encounter a situation where the engine begins to lose power, my first step is to switch to the fullest tank (the same step an aircraft might have without a "both" setting). If selecting the fullest tank (as indicated by the fuel gauges) does not solve the problem, I will switch to the other tank (fuel gauges could be wrong). If that still did not solve the problem, then it is either not a fuel problem or I'm out of fuel. I will then proceed to solve the problem via other means ... or land.
The Left-Both-Right fuel selector is a valid option on RV (or other low wing aircraft) if the fuel feed system is properly designed (which, if I can do it, is not hard to do). If you were to use a fuel selector with a both setting and then discover during flight testing that your system design does not evenly feed from both tanks, then don't use the both setting. Simply revert to the Left-Right option - or redesign your system so it feeds evenly.
For me, the Both fuel selector setting is great. I never have a heavy wing due to fuel imbalance and I never have to worry about switching the tanks every 30 minutes.
If anyone is interested in how I bent my fuel lines to make them feed evenly, contact me off the forum at speedy11 at aol dot com. I'll explain and send photos.
Experimenting is fun.
Next, I'm tackling the cooling drag issue. Apparently Dave Anders has refined the science of reducing drag to an art. I am studying some of the things he has done and trying some of my own (easier?) ideas. I don't expect to reach his level of achievement, but I believe I can reduce cooling drag for the average RV without extensive modifications. We'll see.
Stan Sutterfield
Spruce Creek, FL
<<One thing I really like is the "both" setting on the fuel selector. The tanks are feeding exacty the same amount. I like not having to switch back and forth.>>
Stan, are you sure a "both" position is a good idea?
Dan,
For me, it's a great idea. I gave it a lot of thought before deciding to build in a Both selection and some of my reasoning follows.
I like not having to switch tanks. I'd heard the biggest problem with the both setting was uneven feeding from the fuel tanks. I solved that problem by making the length of fuel lines from both tanks the same length and with the same amount of degrees in the bends. Thus, the uneven feeding due to viscosity was solved - my tanks are feeding EXACTLY the same amount (as determined by flight tests).
Regarding the "A both setting on the valve is not an option on low wing airplanes. If one tank goes dry, the pump would gladly suck air rather than fuel up the hill to the engine," comment - it actually is an option on low wing airplanes - mine is an example. The tanks will feed evenly if properly designed. And since the tanks feed evenly, they will both be near zero at the same time. If both tanks are near zero, then I have more problems to worry about than sucking air from one tank. I need to worry more about sucking up the seat cushion. FYI, I have ops checked it on the ground and it will suck air from an empty tank rather than draw fuel from the other with fuel. The solution is the same as running a tank dry on an airplane without a "both" setting - switch to the tank with fuel in it.
For me, should I encounter a situation where the engine begins to lose power, my first step is to switch to the fullest tank (the same step an aircraft might have without a "both" setting). If selecting the fullest tank (as indicated by the fuel gauges) does not solve the problem, I will switch to the other tank (fuel gauges could be wrong). If that still did not solve the problem, then it is either not a fuel problem or I'm out of fuel. I will then proceed to solve the problem via other means ... or land.
The Left-Both-Right fuel selector is a valid option on RV (or other low wing aircraft) if the fuel feed system is properly designed (which, if I can do it, is not hard to do). If you were to use a fuel selector with a both setting and then discover during flight testing that your system design does not evenly feed from both tanks, then don't use the both setting. Simply revert to the Left-Right option - or redesign your system so it feeds evenly.
For me, the Both fuel selector setting is great. I never have a heavy wing due to fuel imbalance and I never have to worry about switching the tanks every 30 minutes.
If anyone is interested in how I bent my fuel lines to make them feed evenly, contact me off the forum at speedy11 at aol dot com. I'll explain and send photos.
Experimenting is fun.
Next, I'm tackling the cooling drag issue. Apparently Dave Anders has refined the science of reducing drag to an art. I am studying some of the things he has done and trying some of my own (easier?) ideas. I don't expect to reach his level of achievement, but I believe I can reduce cooling drag for the average RV without extensive modifications. We'll see.
Stan Sutterfield
Spruce Creek, FL
Caution!
I would be very very careful about using a fuel selector with a "both" setting in an RV- You have just made a MAJOR change to the fuel system design- a design that works fine as is! Imagine you are on short final and you slip for a crosswind or to accelerate your descent and your engine quits... Not good!
A lot of experimental planes have lost engine power due to builder changes to the fuel system design... Please be careful out there!
Hans
I would be very very careful about using a fuel selector with a "both" setting in an RV- You have just made a MAJOR change to the fuel system design- a design that works fine as is! Imagine you are on short final and you slip for a crosswind or to accelerate your descent and your engine quits... Not good!
A lot of experimental planes have lost engine power due to builder changes to the fuel system design... Please be careful out there!
Hans
But Cessna and Piper are very different fuel systems. Cessna is gravity feed (high wing) Piper is not (Low wing). Cessna uses a both position, Piper (as far as I am aware) never has used it on there low wing airplanes (that should tell us all something since they have built both high wing and low wing).
There is a very specific reason for this which has already been pointed out.
The only low wing certificated airplane that I am familiar with, that had both tanks plumbed together through an On/Off valve is the Varga Katchina. This airplane has had a very high # of accidents classified as engine stoppages for undetermined reason. Many of them have all appearances of being a fuel starvation type of failure.
One other point to seriously consider...
If you research the NTSB accident investigation archives, you will find that a large majority of engine stoppage accidents in RV's (and homebuilts in general) have been fuel system related.
I strongly caution anyone considering making what seems like even the smallest design change to their fuel system, to do so very carefully.
Many homebuilders have found out the hard way that even a small change that seems very minor can have a very unexpected effect in certain conditions.
My feeling is that keeping up with fuel management between two tanks that need to be monitored and manually selected is part of a pilot being properly trained and then using that training to properly execute a flight. The small amount of safety that someone feels they will gain in case they someday forget to switch tanks is far out weighed by the problems that can be induced by adding a both position to the fuel selector.
Toobuilder
Well Known Member
Good question... I've flown two RV's now and never could figure out the attraction of playing with the fuel valve every few minutes. Seems to me, the L/R/Both/Off is the way to go. When anything but nearly empty, the Both position should work fine as long as you have check valves. Switching tanks every XX minutes seems to be asking for trouble because there is a certain amount of risk every time that valve is actuated. And unlike another poster, when going cross country in my Hiperbipe (two fuselage tanks), I ALWAYS burn a tank dry... The reason being, once dry, I never have to worry about returning to that tank for any reason - it's as if it's not there in my mind. I can't imagine being low and slow and having to return to that little spit of fuel to carry me to the next landing. Way too much stress at the worst possible time and "false hope" in my mind. I'd rather concerntrate on a safe forced landing than hope the engine will run long enough to get me "just a little farther".
When I fly cross country I make the first tank switch at 30 minutes, then every tank switch is at 1 hours intervals after that (nothing close to every few minutes). This will provide a fuel imbalance that is never greater than 30 minutes (4-5 gallons) between one side or the other (very minor as far as trim goes). When nearing the time for switching tanks, I do time it (either do it slightly early or delay it slightly) to be within gliding distance of an airport or other suitable forced landing site on the remote chance that something would go wrong with the valve during the switch.
In 50 hours of flying my -8A, I discovered very quickly that I feel a ~2 gallon difference in the tanks in the aileron trim. I generally trim it out, but it acts as a good reminder to switch tanks. Now I just have to come up with a good routine for long cross countries with the autopilot on. I really don't understand what the big deal is switching between tanks. I think running in both is asking for trouble in a low wing aircraft. Takeoff and landing should be on the fullest tank - a both selection doesn't provide more safety, it provides less because either tank running dry or sucking air due to a slip will cause the fan up front to stop.
IowaRV9Dreamer
Well Known Member
Certified fuel system with low wing & on-off fuel
Anyway, I agree with Scott and fully support people building stock, proven fuel systems (that is what I'm putting in my RV). I'm posting here only in the spirit of experimental aviation.
Here is how Beech certified the low wing fuel system with an on/off fuel selector. Note that there is no left/right choice - just on or off.
The part marked as "Fuel Feed Tube" seems to perform the function of a header tank. Note that this is for an O-235 powered aircraft, so fuel flows are somewhat lower than for our RVs.
Again, my post is not an endorsement of this fuel system.... I'm just trying to spread knowledge.
No one is ever familiar with the Beech Skipper, the Rodney Dangerfield of General Aviation
The Skipper actually has a very low # of accidents, including fuel starvation, even lower rates than a Cessna 150/152. But of course statistics can mislead, since Beech only built 311 Skippers.
Anyway, I agree with Scott and fully support people building stock, proven fuel systems (that is what I'm putting in my RV). I'm posting here only in the spirit of experimental aviation.
Here is how Beech certified the low wing fuel system with an on/off fuel selector. Note that there is no left/right choice - just on or off.
The part marked as "Fuel Feed Tube" seems to perform the function of a header tank. Note that this is for an O-235 powered aircraft, so fuel flows are somewhat lower than for our RVs.
Again, my post is not an endorsement of this fuel system.... I'm just trying to spread knowledge.
Now a days our airplanes are full of timers (count up and count down). Even my Garmin 327 transponder has a timer. I just set it for the interval I want and let it remind me.
L.Adamson
Well Known Member
No it won't. There is still going to be cross-feed. Unlike a high wing gravity system to a header tank, both check valves cannot be closed to prevent draining one tank to the other while banking or slipping. Fuel has to be drawing up hill from an open check valve. A "both" position can't prevent crossflow. It will only promote it.
Now the problem comes from that empty tank..... due to cross flow. As previously stated, once one of the fuel lines is drawing air.............. the other will immediately cease from drawing fuel.
edit: From a previous reply, you can see that limitations are imposed on the Beech Skipper, which has a low wing header tank in addition to checkvalves.
"The only limitations are no slips > 30 seconds (I think because you could empty out the header "pipe") and no takeoff with fuel below 1/4 (probably for the same reason)."
Why would we want to build in header tanks and check valves, when switching tanks is so easy, less complex, and less weight? My Garmin 696 always reminds me too...
L.Adamson
Last edited:
Check valves prevent cross flow
There will be no cross-flow. The check valves prevent exactly that. Fuel can flow from the main tanks to the header tank (so long as the correct pressure differential is maintained), but can never flow from the header tank back to a main tank under any circumstances. That would require flowing "the wrong way" through the check valve.
Correct, except that it's not due to cross flow.
DISCLAIMER: To be clear, I'm not advocating that anyone mess around with their fuel system configuration. But if we're discussing it, we should at least get the facts straight.
There will be no cross-flow. The check valves prevent exactly that. Fuel can flow from the main tanks to the header tank (so long as the correct pressure differential is maintained), but can never flow from the header tank back to a main tank under any circumstances. That would require flowing "the wrong way" through the check valve.
Correct, except that it's not due to cross flow.
DISCLAIMER: To be clear, I'm not advocating that anyone mess around with their fuel system configuration. But if we're discussing it, we should at least get the facts straight.
Last edited:
N941WR
Legacy Member
That about covers it.
If you want to test the left/right/both theory, get two straws and a cup of water.
Put one end of both straws in your mouth and the other in a cup of water. Suck on the straws and you will draw water in both.
Next put the end of one straw outside the cup and the other in the water and suck again. You will just draw air, same as if you had a hole in your single straw and the same as if you had a both position in your RV and one tank ran dry.
Remember, your tank can run dry for a number of reasons, including and unexpected fuel leak. (Not that there is ever an expected fuel leak.)
Like Mel, as a Tech Councilor for my EAA chapter, I would never sign off an RV with a "both" in the fuel system.
Toobuilder
Well Known Member
I've heard heard of the "Do it my way, or you're stupid" aspect of this forum from other members... Now having seen it in person, I'm still not impressed.
L.Adamson
Well Known Member
L.Adamson
Well Known Member
I've heard heard of the "Do it my way, or you're stupid" aspect of this forum from other members... Now having seen it in person, I'm still not impressed.
Then "do it my way or die".... might be a stronger approach to the subject...
In this case, what's being said, has facts behind it.
L.Adamson --- RV6A (flying)
johnny stick
Well Known Member
Easy solution
There is an easy solution. The fuel pick ups in each tank can be designed to only suck fuel and not air; when the tank runs dry, the pick up will block air from being sucked into the line. These type of pickups are used in the aerospace industry. If someone like Andair wants to design one for the RVs, send me a PM and I will discuss the details. It is really quite simple. I will be doing this on my RV10, but you might have to wait a few years for my build to progress to that point.
Johnny Stick
RV10 wannabe
There is an easy solution. The fuel pick ups in each tank can be designed to only suck fuel and not air; when the tank runs dry, the pick up will block air from being sucked into the line. These type of pickups are used in the aerospace industry. If someone like Andair wants to design one for the RVs, send me a PM and I will discuss the details. It is really quite simple. I will be doing this on my RV10, but you might have to wait a few years for my build to progress to that point.
Johnny Stick
RV10 wannabe
I've heard heard of the "Do it my way, or you're stupid" aspect of this forum from other members... Now having seen it in person, I'm still not impressed.
People come to this forum to get advice. You can take it or leave it but if you critisize it, I ask the question "why are you on the forum if you do not want to take the advice provided by people who you have asked their opinion?". I come to the forum because others may know more than I.
N941WR
Legacy Member
I've heard heard of the "Do it my way, or you're stupid" aspect of this forum from other members... Now having seen it in person, I'm still not impressed.
Michael,
That is being a little harsh.
The truth is, no one on this forum wants to see someone get hurt or the reputation of home building damaged by a preventable accident, that is why the "fangs" come out when someone suggests doing something that goes against "standard practices".
If there was room to install a header tank in the bottom of an RV, then I don't think anyone would have an issue with this topic. But, there is not room and fuel starvation issues are the number one cause of accidents for homebuilts.
There are many thousands of RV's safely flying with the standard fuel system and a number of accidents attributed to fuel system "improvements", so the question is, why change what works?
That said, if someone came up with a truly unique and operational fuel system, all of us would be open to seeing it and a number of us would actually support it.
PS. This topic comes up from time to time, do a search on the subject and you will find a number of threads on the exact subject, along with a lot of suggestions.
PPS. With the timers built into modern EFIS's, remember to switch tanks is no longer an issue.
Last edited:
Andy Hill
Well Known Member
IMHO, a "both" selector on a low wing aircraft is only a valid design option if NRVs are installed between the tanks and the valve.
It's just like a X-Feed valve... you never connect the 2 tanks unless 1 pilot is constantly 100% monitoring the contents.
Stan - problem is your L tank develops a serious leak... unknown to you. With a L-R only valve, then your L Tank empties, and your engine either stops, or you notice at your next fuel check. If the engine stops, you switch to R and restart.
With "Both" selected, a single failure (tank leak) = you lose all fuel (the R tank fuel exits through the valve and out the Left).
Low Wing + Both is not unknown... the Bulldog has it, but uses the NRVs above. Are you sure you have these fitted?
Only IMHO of course
Andy
It's just like a X-Feed valve... you never connect the 2 tanks unless 1 pilot is constantly 100% monitoring the contents.
Stan - problem is your L tank develops a serious leak... unknown to you. With a L-R only valve, then your L Tank empties, and your engine either stops, or you notice at your next fuel check. If the engine stops, you switch to R and restart.
With "Both" selected, a single failure (tank leak) = you lose all fuel (the R tank fuel exits through the valve and out the Left).
Low Wing + Both is not unknown... the Bulldog has it, but uses the NRVs above. Are you sure you have these fitted?
Only IMHO of course
Andy
Frank Smidler
Well Known Member
Follow Van's instructions, it is proven
I have an RV-6 with the fuel line system/routing called for with RV-7's. It works, it's simple, it is easy to understand. Yes you can do it differently and yes it may also work just fine, but it may also involve new risks, known and unknown. Keep it simple, with a proven design and you will not regret it.
As a Design Engineer I know that it is easy to make something complicated with additional failure modes and much harder to make it simple with fewer failure modes. To their credit Van's took the challenging route and made it simple.
I have an RV-6 with the fuel line system/routing called for with RV-7's. It works, it's simple, it is easy to understand. Yes you can do it differently and yes it may also work just fine, but it may also involve new risks, known and unknown. Keep it simple, with a proven design and you will not regret it.
As a Design Engineer I know that it is easy to make something complicated with additional failure modes and much harder to make it simple with fewer failure modes. To their credit Van's took the challenging route and made it simple.
Last edited:
David Clifford
Well Known Member
OK,,,,I think I understand it now. If I go with the L/B/R/O valve,,,I stand a good chance of sucking air. If that happens, by the time I switch to a tank with fuel in it, I should just about get enough fuel to carry me to the scene of the crash! I'll call Andair Monday and have them change my order to the recommended valve. Thanks everyone.
Frank Smidler
Well Known Member
You will not crash if you "suck air" and then switch tanks. I have ran my left tank dry, and as soon as it sputtered I turned on the fuel pump and switched tanks. The windmilling prop allowed the engine to instantly re-start. Total time, was maybe 5 sec with no loss of altitude or airspeed. My heart may have skipped a beat but I was never in any danger (I expected it to happen, it was intentional).
N941WR
Legacy Member
Frank,
It all depends on what phase of flight you are in. I suspect that when this happened to you were in cruise flight and you are right, the engine does restart almost instantly.
However, if you are taking off from a short field, on a hot day, at high altitude, at gross when your engine go quiet and the passenger(s) start to make high pitch noises is not the same. In that situation, five seconds could be the difference between hitting the trees and clearing them or pancaking it on the end of the runway because thrust wasn't there when needed on short final.
As a DAR, I REFUSED to issue the Special Airworthiness Certificate to an RV-6A till the builder changed the fuel selector to one that did NOT have a both.
This was a couple of years ago. As a DAR, I am still NOT going to issue the Special Airworthiness Certificate to a LOW wing RV that has a both position.
Maybe you can get someone else to do it for you but all you will get from me is a DENIAL LETTER.
L.Adamson
Well Known Member
And here is one from yesterdays NTSB postings...
http://www.ntsb.gov/ntsb/brief.asp?ev_id=20090730X34821&key=1
Frank Smidler
Well Known Member
Poor management of fuel can happen with any system
The cases sited were pilots ran out of fuel during landing is due to poor fuel management. To use these examples as a reason for having a "both" option is not supportable since a pilots can mismanage a system with "Both" just as well. Since fuel issues account for 20% of all aviation accidents (see link below) I am sure there are many examples were aircraft with cross over systems were involved in fuel exhaustion accidents during landing as well. Cherry picking a couple data point does not change the facts that with proper fuel management, the standard Van's fuel system will be no more likely to run out of fuel on landing than a cross over system. My argument, as well as others, is that a proven, simple design is safe and eliminates the possibility of unforeseen failure modes of a modified system.
Please understand that I am not stating to do it my way or else. I am only providing an opinion that I am also providing some reasoning for. Your decision is yours and yours alone.
http://www.aopa.org/asf/publications/08nall.pdf
The cases sited were pilots ran out of fuel during landing is due to poor fuel management. To use these examples as a reason for having a "both" option is not supportable since a pilots can mismanage a system with "Both" just as well. Since fuel issues account for 20% of all aviation accidents (see link below) I am sure there are many examples were aircraft with cross over systems were involved in fuel exhaustion accidents during landing as well. Cherry picking a couple data point does not change the facts that with proper fuel management, the standard Van's fuel system will be no more likely to run out of fuel on landing than a cross over system. My argument, as well as others, is that a proven, simple design is safe and eliminates the possibility of unforeseen failure modes of a modified system.
Please understand that I am not stating to do it my way or else. I am only providing an opinion that I am also providing some reasoning for. Your decision is yours and yours alone.
http://www.aopa.org/asf/publications/08nall.pdf
Ron Lee
Well Known Member
That is fine as long as you never carry a passenger, never sell the plane and never fly over any populated area or anywhere where a loss of fuel to the engine might endanger others.
From the Technical Department: Check valves at the tank outlets increase the chance of vapor lock. It takes some pressure differential to open them. That's one of the reasons for the "no departures with less than 1/4 tank" in the certified example...low head pressure.
From the Flight Department: Ok, you're flying with a no-header "Both" setup. It un-ports a tank. Quick, to which one do you switch, "Left" or "Right"?
From the TC Department: Gary and Mel, thank you.
From the Department of Political Uncorrectness: No, you don't have to do it my way, our way, or any other way....but we get to laugh and post your Darwin Award on YouTube <g>
From the Flight Department: Ok, you're flying with a no-header "Both" setup. It un-ports a tank. Quick, to which one do you switch, "Left" or "Right"?
From the TC Department: Gary and Mel, thank you.
From the Department of Political Uncorrectness: No, you don't have to do it my way, our way, or any other way....but we get to laugh and post your Darwin Award on YouTube <g>
Yep, I'm familiar with the Andair web site and their spelling of simultaneously is the British way. Those silly Brits. : ) They act like they invented the language.
<With "Both" selected, a single failure (tank leak) = you lose all fuel (the R tank fuel exits through the valve and out the Left).>
A good theory, but not the way it actually happens according to my ground tests. The fuel from the right tank does not pass through the fuel selector valve and into the left tank. Rather, with one tank dry (unnoticed leak), the engine begins drawing air from the empty tank and falters or quits. Select the tank with fuel in it and restart - just like a L-R selector. Tell you what, I'll do an airborne test at 5k' over an airport and run one tank dry with the Both position selected. Then we'll know for sure how it functions.
<Low Wing + Both is not unknown... the Bulldog has it, but uses the NRVs above. Are you sure you have these fitted?>
I am sure I do not have the check valves fitted. They are not needed. The fuel in one tank is not transferring to the other tank. The tanks are feeding evenly (ops checked airborne). If one tank runs dry, the fuel will not transfer from the full tank to the empty tank - rather the fuel pump will draw air from the empty tank (ops checked on ground). I'll do an ops check airborne and report back.
Stan Sutterfield
<With "Both" selected, a single failure (tank leak) = you lose all fuel (the R tank fuel exits through the valve and out the Left).>
A good theory, but not the way it actually happens according to my ground tests. The fuel from the right tank does not pass through the fuel selector valve and into the left tank. Rather, with one tank dry (unnoticed leak), the engine begins drawing air from the empty tank and falters or quits. Select the tank with fuel in it and restart - just like a L-R selector. Tell you what, I'll do an airborne test at 5k' over an airport and run one tank dry with the Both position selected. Then we'll know for sure how it functions.
<Low Wing + Both is not unknown... the Bulldog has it, but uses the NRVs above. Are you sure you have these fitted?>
I am sure I do not have the check valves fitted. They are not needed. The fuel in one tank is not transferring to the other tank. The tanks are feeding evenly (ops checked airborne). If one tank runs dry, the fuel will not transfer from the full tank to the empty tank - rather the fuel pump will draw air from the empty tank (ops checked on ground). I'll do an ops check airborne and report back.
Stan Sutterfield
Andy Hill
Well Known Member
Stan...
You seem determined to defy established aviation practice and all attempts by others to suggest it might not be the way to go
Have a read of Link and see the DAR(s) refusing to sign off low wing RVs with "Both"... Maybe ask your DAR to re-assess your design in this area?
I am not familiar with the US system of 'Experimental' flying, but you are given more latitude to apply for the Darwin Award than we are in the UK
As an FI, I might be somewhat concerned that not only are you defying engineering practice, but your reason for doing so seems to be an inability to / unwillingness to / admission that you do not, carry out regular fuel management checks / actions?
Any ground test in an RV-8 I would suggest is a very poor indicator of what might happen airborne when the chips are down in terms of fuel flow / where it decides to go... 150kts of airflow into vents / around tanks / a leak will create a very different environment.
I'll bow out now - I and others have tried to politely put the point across...
Best regards and good luck - seems you'll need it
Andy
You seem determined to defy established aviation practice and all attempts by others to suggest it might not be the way to go
Have a read of Link and see the DAR(s) refusing to sign off low wing RVs with "Both"... Maybe ask your DAR to re-assess your design in this area?
I am not familiar with the US system of 'Experimental' flying, but you are given more latitude to apply for the Darwin Award than we are in the UK
As an FI, I might be somewhat concerned that not only are you defying engineering practice, but your reason for doing so seems to be an inability to / unwillingness to / admission that you do not, carry out regular fuel management checks / actions?
Any ground test in an RV-8 I would suggest is a very poor indicator of what might happen airborne when the chips are down in terms of fuel flow / where it decides to go... 150kts of airflow into vents / around tanks / a leak will create a very different environment.
I'll bow out now - I and others have tried to politely put the point across...
Best regards and good luck - seems you'll need it
Andy
FlyingArcher
Well Known Member
Wow!
As the OP of this thread, the first answer I received was enough to convince me of the right choice.
Now I'm happy I didn't ask if I needed to spray primer on the back of fuel selector plate
As the OP of this thread, the first answer I received was enough to convince me of the right choice.
Now I'm happy I didn't ask if I needed to spray primer on the back of fuel selector plate
Hold on......
I am learning a great deal here. What I have gotten so far here is that there is concern with sucking air (with or without an unknown leak). Which as far as I can tell is a situation we shouldn?t get to in the first place. But, if we are, it?s this or that rather than right or wrong. I do however; want to know for certain if there is a correct way to do this.
I don?t agree that this is 'going against engineering practice'. Engineering is a practice and practice implies investigating into new opportunities and doing research to expand our current knowledge. I am seeing some suggestions here that lead me to suspect that it can be done.
Is there a correct way to do this that addresses all of the aforementioned points.
I want a 'both' selection I my 7. But, I want to be safe more than I want a both selector. I also will never say that something can't be done. So, that said, how do we do this and do it right?
Respectfully,
Evans.
I am learning a great deal here. What I have gotten so far here is that there is concern with sucking air (with or without an unknown leak). Which as far as I can tell is a situation we shouldn?t get to in the first place. But, if we are, it?s this or that rather than right or wrong. I do however; want to know for certain if there is a correct way to do this.
I don?t agree that this is 'going against engineering practice'. Engineering is a practice and practice implies investigating into new opportunities and doing research to expand our current knowledge. I am seeing some suggestions here that lead me to suspect that it can be done.
Is there a correct way to do this that addresses all of the aforementioned points.
I want a 'both' selection I my 7. But, I want to be safe more than I want a both selector. I also will never say that something can't be done. So, that said, how do we do this and do it right?
Respectfully,
Evans.
pierre smith
Well Known Member
You can lead a horse to water..
......and all that!
Good luck,
Stan...
I am not familiar with the US system of 'Experimental' flying, but you are given more latitude to apply for the Darwin Award than we are in the UK
Andy
......and all that!
Good luck,
- Status
