Low Fuel Sensor

[Jerrytex]

If I understand correctly, you can add a low fuel sensor directly to the aluminum header from Kitfox? However, I see on this thread that the low fuel sensor goes in a small cylinder tank above the header tank? The aluminum tank I have from Kitfox, has a 1/4" pipe connection on the side. The low fuel sensor that I have, is 1/2". Did something change on the header tanks? Or is there an adapter to convert to 1/2"?

[JayHenry]

The Low Fuel sensor is a separate tank that installs just over the header tank and sold as a kit form Kitfox.

[Maverick]

In my first Kitfox 5TD, I never recognized the problem of fuel flowing forward in the tanks in a steeper descent. Dumb, I know! It was inadequate testing for sure on my part.

DesertFox4 and I flew to Apple Valley together once when I wish I'd had the low fuel sensor. I calculated that I had enough fuel to make it there from Phoenix and I actually did, although only by a very slight amount. That's when I was entering the traffic pattern having come down to altitude when at midfield the engine died. I looked up and saw fuel but it didn't register with me that it wasn't enough to feed the fuel port at the back of the tank. I declared my situation and did a dead-stick landing. As soon as I stopped, I tried the engine and it fired up and I taxied to the fuel station and filled up. I realize that my lack of diligence in getting to know my plane's quirks and cutting it too close on my reserve are pilot errors (as DesertFox4 doesn't let me forget, bless his heart) but, had I had the fuel sensor tell me I was running on fumes, I likely would have figured out the problem of the nose down attitude letting fuel move forward too much and could have raised the nose, slowed the descent and kept me from needing a clean pair of underwear. Certainly, after having this experience, my fuel management will be more conservative; partly because, like PapuaPilot, my bladder is not as young as it was 16 years ago but, certainly because experience is a good teacher, assuming you survive. . .

[109JB]

All I will say is this. For the past 21 years my job has been to investigate aircraft accidents. My project airplane is getting a new header tank fitted with a low fuel sensor.

[mooreaa]

Thank you for sharing these experiences. Wasn't something that was on my radar until reading your comments here. Interesting point about the steep descent attitude preventing fuel flow to the headers.

I assume the issue is mostly the same regardless of carbureted or fuel injected engines. I like the idea of having the low fuel sensor mounted directly to the header tanks. Does the fuel return path affect this at all? Curious what the installation options are and what to watch out for.

Thanks!

[Dave S]

Thank you for sharing these experiences. Wasn't something that was on my radar until reading your comments here. Interesting point about the steep descent attitude preventing fuel flow to the headers.

I assume the issue is mostly the same regardless of carbureted or fuel injected engines. I like the idea of having the low fuel sensor mounted directly to the header tanks. Does the fuel return path affect this at all? Curious what the installation options are and what to watch out for.

Thanks!

Regarding descent attitude and what a person can count on for fuel feed is something a person can and should figure out during build and fuel system proofing. Since the fuel feed from the wing tanks is located near the rear of the wing tanks, the design indicates that nose down attitudes will, at certain descent angles, unport the fuel feed from the rear of the tank. The attached photo shows the Kitfox in a nose down attitude of 10 degrees (courtesy of removing some bricks in the driveway and digging a hole), estimated to be twice the nose down that would be experienced during normal operations. What this test revealed is that a 10 degree nose down attitude will start to unport the fuel tank with 6 gallons in a tank (or 12 gallons between the two tanks) which is just a tad less than half tanks. It is better at 5 degrees nose down with approximately 3 gallons per tank or 6 considering both tanks.

Many aircraft have fuel system limitations that are accounted for and as long as a pilot knows what those are (hopefully published in the POH), operations can be performed in agreement with the limitations.

The header tank on a Kitfox is a really good deal for a number of reasons including this one.

The low fuel sensor is certainly a good idea and saves a person from having to do math in their head to keep from exceeding the capacity of the header tank on a long steep descent.

[mooreaa]

Why is everyone shying away from the factory optional low fuel sensor with its separate little reservoir? It works perfectly and is super easy to install with no modifications to the header tank. Just curious.

Hi ya Jim, not so much shying away from the factory as much as trying to see the creativity and wisdom of others on this forum. I have no doubt that the factory solution works, but I do also like the idea of the sensor being integrated into the header tank.


Dave, wow thats really very interesting. No fuel flow at half tank with just -10 degrees doesn't seem like much. If my maths right, thats 65mph at a -1000fpm is around -10 deg. Maybe thats an aggressive descent but still. Just out of curiosity, what about mounting the low fuel sensor in the wing tank or, maybe having two ports on the tank (I understand its not necessary, but would it mitigate this)? I suppose you can lose 1000fpm with wings level so... that aside, the point would be that this is equivalent with respect to coming down at that angle.

[Dave S]

The only time during phase 1 (and afterwords) the nose down ever got near 10 degrees was VNE testing.

I doubt that anyone will be getting beyond 5 degrees nose down for any normal operation - a power off best glide is considerably less than that - at least on our bird.

If a person considers the Kitfox fuel placard - the no takeoff band is right about 3 gallons if I recall correctly.

I feel that the design of the Kitfox fuel system on the S7 is solid.

[rv9ralph]

Just out of curiosity, what about mounting the low fuel sensor in the wing tank or, maybe having two ports on the tank.

If there are 2 ports in the wing tank, the port with the least resistance will be the one that flows... in other words, if there is a unported pickup, the the fuel draw sill suck air. That is why you can't burn off both tanks on a low wing aircraft. Low fuel sensor in the wing will be inaccurate due to the sloshing and shifting of the fuel when changing pitch or yaw.

An option for fuel sensor is from Belight. The have several fuel sensors that will indicate low fuel status that can be used in the header tank.

Ralph

[DesertFox4]

Jerry, just an FYI. The low fuel sensor you have pictured looks like the original sensor SkyStar sold way back when. As I recall that when auto fuel was predominantly used with that type, many of those sensors failed due to the plastic tips cold flowing (melting) into the bottom of the header tanks.
Also I believe it is an optical type sensor so I’m wondering if it will even work in a totally dark aluminum tank. There are several members here who are more familiar with that early set up that could shed light on the function of that type sensor. Hopefully you will hear from some of them or test it’s function before going to any more efforts to incorporate it into you fuel system. I hope my memory is faulty and it will work perfectly but just in case, I had to mention it. Good luck.