Be forewarned, there are NO pics in this long post! [Might want to grab a cup of coffee…]
Today turned into an all day planning, coordinating and all around down a dozen different rabbit holes day.
I’ve been having a back & forth email discussion with my buddy Dave Berenholtz on, well, just about everything involved in the build, but today specifically was on the sump tanks and the fuel system. I haven’t really communicated my fuel system since I have been researching, studying, and planning it for literally 4-5 years now.
Thus, today was the day to polish off the particulars on my fuel system and get it finalized so I can implement it. To understand my fuel system planning, I will be throwing out some big names in the canard world…. not to name drop, but to show the pedigree (not mine) and experience of those involved in this discussion.
It started a number of years ago as I was talking to Marco on the phone and sent him a link to Wayne Blackler’s Long-EZ to make a point as to what I was on about. After a few minutes he simply declared over the phone: “He has no external sumps.” He noted something I had failed to notice, and we pondered over that a bit. I bit later I discussed with Wayne his “no-management” fuel system, as I did with Ken Miller, Bill James, and Vance Atkinson, among others. So, although I started out ready to install the plans version fuel system, I made a distinct departure from that plan and decided on a GIB thigh-mounted central sump with no fuel selector valve system. I was going no-management all the way Baby!
Well, my planning was geared towards the no-management fuel system for years when last year before RR I made one final search online before installing my EFII fuel pump right below the CS spar…. and I mean it was going literally on the bottom surface of the CS spar, centerline. I have to say I had a nagging feeling about putting all that weight back there (it’s 2.5 lbs), and when I saw a pic of Joe Carragio and few others who had mounted there fuel pump under the pilot thigh support, it got the gears in my brain turning. Hmmm…
I did a quick mockup of the fuel pump up in the pilot thigh support area and realized it would fit perfectly. Hmmm…. Ok, well a big reason that I was going with the no fuel management system was the integral GIB thigh support sump, meaning: no external sumps. Why is that important to me? Simple. I have the Berkut-style armpit engine cooling intakes on my cowlings. These sit literally inches behind the plan’s external fuel sumps. This means not only accepting more drag in general, but bringing disrupted, disturbed, burbling air into my engine for cooling. Not optimal. The no management thing, well, that would be nice. Of course, that came with a decent, unique risk all its own. But added drag and disrupted engine cooling air! Well, I was not willing to accept that when I could simply move the fuel from an inch away from the GIB to an inch away from the GIB (IMO!)
Fast foreward. After pondering it for a number of months, looking at the pros & cons, I decided to do what “we” in Washington, D.C. are best at: COMPROMISE! I decided to go GIB thigh support sumps (yes, plural) by simply not making the mouse holes that would normally be made in the center rib of a single tank sump. I then would use the Andair fuel valve I bought many moons ago –since I was adding fuel weight going forward anyway. Moreover, since I needed a fuel line going to the pump, and a return coming back, what was the complexity or weight of one more?
The bottom line is I will be going with a hybrid fuel system. No external sumps with internal fuel sumps under the GIB thigh support (yes, I know the arguments of “bringing fuel into the cockpit” . . . and clearly I’ve weighed all my pros & cons, and risks & benefits). I will however keep the separate tank concept by running the fuel through the Andair L-R-OFF fuel selector valve.
Today I confirmed installation requirements with EFII for my fuel boost pump and Precision Airmotive for my Silver Hawk EX fuel injection system. After getting questions answered regarding size and location of filters, and fuel pressure sensor connection info, I finalized –after 7 years– my fuel system!
Now, to throw yet another wench in the works, I’m strongly considering knocking out my internal fuel sump in the back seat, which would then allow me to ACTUALLY run my fuel lines for the left & right sump feeds to the fuel valve. In addition, that would clearly give me the info on spacing requirements I need for fuel lines, wiring, etc. going down the right sidewall. This would also give me all the real world clearance specs I need for the pilot thigh support ribs and configuration, under armrest configuration for the right side, etc.
I will sleep on it, but I am strongly leaning in that direction as my next move.
Also today, besides updating my fuel system diagram (last updated June 2014) and my firewall components & wiring placement & configuration diagram (last updated Feb 2014), I also updated the fuel system wiring diagram and the engine information/management system wiring diagram. That may not seem like much, but the phone calls and digging into the manuals and websites to confirm, verify and update components, do analysis on part selection, prices, check inventory, etc. . . . well, that all consumed about 6 straight hours.
I then spent a good hour sitting in the back seat, marking up my thigh support requirements, and then trying to guesstimate how to translate that over for the passengers I’ll be carrying. As a comparison, the thigh support mod spelled out in CP 28 has the front wall at 37″ forward of the firewall, 4.5″ high, and then tapering back 6″. Before climbing into the back seat I looked at Dave B’s sump tank, which is a little too robust for me (in all fairness, he called that), and Bill James’, all online of course. I then looked at the Berkut GIB thigh support sump plans, reread emails from the whole gang I mentioned above, and then after a few machinations dialed mine in at 35.5″ forward of the firewall, with a height of 6.2″ and tapering back around 10″. I’ll continue to work out the particular specs over the next day or two, and then make my decision on whether to break ground on this part of the build or not.