Oh, I'm gonna get it now!
Ok, let's throw some more avgas on the fire
On this thread so far we've seen the full spectrum of admonitions from (paraphrase) "never ever deviate from the original design" to "it's experimental, so do whatever you want". I disagree with both. I think it is possible to improve on the original design (and that's true generally, not just about the fuel system), but it would be foolhardy to make substantial changes without a thorough understanding and rigorous engineering analysis and testing. Having said that, many of us builders are quite capable of meeting those requirements.
Now, here's an example of a potential improvement to the standard RV fuel system. But first the usual disclaimer: I am NOT advocating that anyone do this on their aircraft, and in fact I'm not doing this either on my aircraft (at least not initially).
Ok, down to business. While I don't see L/R/OFF fuel management as a major burden, it does have a few issues:
- Adds to the pilot's task loading.
- Prone to pilot error (whether by general carelessness or even the occasional error by a thorough pilot).
- Creates an appreciable left-right imbalance even if switching tanks relatively frequently, like every 30 minutes.
- Creates long-term left-right imbalance and/or left-right fuel remaining uncertainty due to different fuel burns in different phases of flight.
One possible solution is to keep the existing fuel system architecture, but automate the left-right switching under computer control, i.e. an "auto-switch" selection. Since this no longer burdens the pilot, the switching could happen much more frequently, say every 3 minutes instead of 30 minutes. That effectively eliminates the left-right imbalance issues, practically as if we were drawing fuel from "both". There would also be manual settings for "left only", "right only", and "off" for emergency situations and optionally for critical phases of flight. Now, since fuel switching is now under computer control, the computer could even detect and handle certain fault conditions. Like say if switching to a particular tank results in a fuel pressure drop to below a critical threshold, then the computer will switch back immediately to the other tank and stay there (and alert the pilot via an annunciator or EFIS message). There are all kinds of automated safety features that can be built in once you have electronics in the loop. Yes, I know, that makes the fuel system electrically dependent. But many new aircraft power plants are electrically dependent anyway, and it is not a problem if designed with sufficient safeguards, whether through electrical redundancy or mechanical/manual backups and overrides
Now, before the traditionalists unleash their fury on me for even suggesting such a thing, I'd like to point out that designs like this have been used successfully on high performance aircraft already. In fact, I believe Lancair is doing something along these lines on the Evolution. Ok, now you may begin to flog me if you wish.
