CorvAircraft> fuel pump, valves, gascolators SUMMARY

[601corvair]

"
 Hello All:

I though I would post a summary of what a have learned about fuel selectors,
Gascolators, and fuel pumps.  Some of the information is gleaned from the posts everyone has read and some from folks communicating with me off list.     Unless the 
Idea was communicated on the list I will not identify the source and we will leave it as 
anonymous peer review and leave it at that.   I am including the information I consider 
actionable.  But first as a point of personal privilege ( and because I can), let me give you some back ground on our project.  

My partner, Steve, and I acquire a 601HDS 2000 kit second hand (before the sport pilot 
rule) from a very meticulous builder who moved into the dark side of ultra lights and  changed direction.  Our acquisition was not a spur of the moment.  We researched things for about a year.  We found the kit by chance when asking other zenith builders about their experiences and found this opportunity.  In researching home builts we had already decided on the Corvair conversion even before the aircraft itself.  Steve had acquired WW book, the old black and white version, and we were impressed with his philosophy  and what I consider the old spirit of the  EAA.....build it your self. So we acquired  all of Tony B's books and were considering plans building.  Steve had previous experience  building composite boats and wanted to try something different, or we could be Kr2 guys. 

So we started this project 4 years ago with a half built kit, 2 Corvair drive trains, lots of books, and a long time line.  We have had lots of fun along the way and have taken the 
advice of our  EAA Technical Counselor from the start.  Randy told us to remember we
 were building Aircraft  Parts and to enjoy building each part.  If you have fun and get a 
kick out of building the parts you will not get discouraged and eventually you will have
 an airplane.  Well the parts are getting bigger and bigger and the small parts are 
disappearing.  

We started off with the goal of building a simple, ramp storable, VFR aircraft that was
 not going to be a hanger Queen and was not the space shuttle.  We often say we will pay more to do it ours selves, but we do count cost.  However, our goal is NOT to see how much money we can dump into the project, we do not count our time.  Our panel will be old steam gauges traded in by others for glass etc.  The goal in to have fun in a plane we built, and can afford to fly, not to see how much cash I can spend (I have 3 teenage daughters for that task).  I  give all this background, in an attempt at full disclosure.

One of the challenges of building is that once you get comfortable with one component (like riveting and metal work), you are on to the next. ( like fuel system design and brake lines).  In my experience, each transition can be affected by " paralysis of analysis"�.  You can end up with to much to information to digest and the internet can exacerbate this to the nth degree.  Anyone been here?  So we got to the fuel system and in our Zenith plans there are a few ways to do it. So we researched and researched and found there are lots of approaches to moving fuel.  Here is a summary of what we found from list responders.  Keep in mind, I told the list have wing tanks and an MA3 carb, so this effected the responses, especially among the most knowledgeable.

General Summary:

Fuel valve and pumps.  My question here was: was a fuel selector valve necessary or could we use the Facet pumps in the wing root and do away with this.  Keep in mind our application is a gull winged 
airplane with gas in leading edge wing tanks, no header tank, and pumps in the wing root.
No one offered an objection, or a reason for keeping the fuel selector.  This was interesting 
and good news.  I our application, the location of the selector would be in a very busy 
area with cables and feet, plus it is forward of the spar and we expect our AC will be nose 
heavy so we need less weight forward and more aft.  The general consensus was that you needed to check each pump individually for performance and that some of the pumps may have design changes over time and yet still have the same part number.  One of the pump choice decision is whether to have pipe fittings or AN fittings.  This seemed to be a matter of opinion.  The pipe fittings allow you to use an available disposable low cost fuel filter.  AN fittings allowed you to use more AC type material.  There was some discussion of dual pumps with siphon braking valves, although it was not clear as to how to make this system redundant.  If a pump has this type valve and it fails, it would be difficult to pump through it.  You could use 2 pumps in parallel for each tank. That would make 4 pumps total.

With our gull wing HDS and its weight/balance challenges, pumps near the spar are helpful.  Again this brings specific application into the picture and not general issues.  If you search the archives here and WW site and others you can see the evolution of this topic in a very short time.  Starting with the old mechanical Corvair pump and header tanks, to mechanical pumps with additional electrical pumps, to complex series of electrical pumps, to relatively simple dual electrical pumps.  All have advantages.  The general trend is to a simple series of electrical pumps.  WW has written extensively on this, however we should remember his test platform is an XL tail dragger with wing tanks.  Other aircraft applications may require modifications

Gascolators:  This topic brought response that dealt both with engineering and regulations.  It seems they may be required in Canada by statute but I don't think they are in the US or down-under.  There were some anecdotal responses, but they warrant assessing.  If your AC is in the weather and some water gets into the tanks, it may fill lower fuel lines and over come the tank sumps.  Again this will depend on the application and how you move fuel.  It could be possible to use the pumps to hold fluid in the tanks above the sumps etc.  It will depend how your INDIVIDUAL pumps work.  The other issue with gascolators is where to place them.  The 601HDS has different suggested locations depending on the fuel system and number of tanks.  One version has a gascolator for each of 4 wing tanks ( in the extended range version).  Another version has one gascolator protruding through the belly directly in front of the spar between the pilot.  It sticks out much like a beacon light on
 the underside.  Some XL versions have it on the firewall.  The engineering issue seems to be on having it at the lowest point of the fuel system in a protected area.  We  assume this means the lowest point of the fuel system when sitting o the ground, because you want it to collect the water which accumulates when sitting.  Again, the specific AC version affects this.  This may not be the same for a trigear vs. TD configuration.  In the HDS trigear it could be anywhere along the bottom of the fuselage.  In the TD configuration, I suspect it is in front of the spar.  In nether case is it really the firewall, all thought that might be close enough.  There are some other issues to consider, such as how hot it gets, does its location conflict with noise gear etc.?  Each is application specific.  The issue each builder must consider is, does the additional complexity of the system caused be the addition of the gascolator warranted when you assess the additional margin of safety
 provided by the gascolator.

Clearly, the more complex we make a fuel system the more potential failure modes.  We each most decide if the additional complexity adds as much safety as it does weight and failure modes.  

It has been said that if you want to be one hundred percent safe stay on the ground.  I have to chuckle at that because instead of going to the airport last week, I stayed home and cut the grass and have gotten chigger bit from head to tail and sit here this beautiful Labor Day in the air conditioning  literally scratching my rump off.  I would have been much safer spending the day in the air!!

Phill.





       
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