Tailwheel pilots, need some help on a question about fuel qty. readings. Recently acquired a 1947 Luscombe. The warnings on the fuel gauges say no takeoff below 1/4 tank. Is the reading on the gauges calibrated for tail down, as parked.... or tail up in a level attitude?
The few flights I have made tell me the gauges are very conservative. When empty on the right.... I fueled up and turned out to have more than two gallons in tank. The dipstick had showed nothing at all.
I have read that the older Luscombes with a fuselage tank had feed problems because of the level relative to the carb. Mine has two wing tanks, so I don't think gravity feeding is any issue. So, should I heed the warnings at rest, or take a look at the gauges before landing to see what is left.
I imagine the answer to my question comes from design regulations and FAA, so it could apply to a variety of taildragger designs.

flightlogic wrote: The warnings on the fuel gauges say no takeoff below 1/4 tank. Is the reading on the gauges calibrated for tail down, as parked.... or tail up in a level attitude?

Let's see: If you are thinking about taking off, one would assume that the tailwheel is on the ground. Two gallons isn't much gas to be sloshing around out there. The certification regs require that the airplane be able to demonstrate adequate fuel flows at "all normal flight attitudes and power settings" at minimum fuel. No doubt, there is a reason for the 1/4 tanks admonition. I wouldn't want to fly with less than that in any case.

Our Top Cub has SIX gallons unuseable fuel, by the way, but it was certificated under a version of FAR 23, not CAR 3 as your Luscombe was.

MTV

There was some recent discussion about why Maules use an engine driven fuel pump, and the consensus was because of the possible angle of climb combined with a low fuel quantity situation overcoming the gravity feed. In that same thread was mentioned the "do not takeoff in the red" thing, for the same reason: fuel pickup/feed.

My guess would be that those gauges are meant to be read in the 3-point attitude AND in level flight, but not to be regarded with much accuracy. I calibrated my fuel dipper stick (on my 170B) in the 3-point attitude and that alone is what I trusted.

MTV/Zane, thanks for the replies. I should better explain one of my comments. I don't want to take off below or near the 1/4 mark. Doesn't make any sense to in day to day flying. There is gas all over for sale. We just don't like the prices!
No, I just wondered whether the gauges were meant to be read tail up or tail down. I suppose Zane has the right take on it.
The tail is down before you go..... so read them then.
I haven't done any calculations yet.... do you suppose the C-85 burns 4.5 an hour or closer to 5?
I notice the EGT and mixture have to be tweaked with any throttle position changes. I take off at 5040 ft. so always have some leaning to do where I fly.
Years ago, I took apart a Luscombe carb. The mixture was just a little brass plate with some holes of varying sizes drilled in it as I recall.
Not too sophisticated.
Anyway, thanks for the input guys.

Anyone else out there know the regs that were followed when the fuel float gauges were designed in the 40's?
No where in the POH is attitude of the plane mentioned for reading the fuel level.....
Must be some old timers reading that remember the guidance from the FAR's back then.

I think you're looking in the wrong place. The operational FARs simply require that, prior to launch you have ensured that you have adequate fuel to take you to your destination, and then for an additional time period at a "normal" cruise power setting. That time period varies depending on the type of operation you're engaged in.

THe point is the operational FARs do NOT address how to read fuel gauges.

WHat you need to do is look at the CERTIFICATION regulations. That airplane was certified under CAR 3. Here's a link---look it up: http://rgl.faa.gov/Regulatory_and_Guida ... enFrameSet

MTV

I once emptied the tanks on the C-170..I then added 5 gals at a time and marked the gauges accordingly, while it was sitting in a normal position (tail down). From then on I had a more accurate reading from the gauges...and the two gauges did not read the same on the old indications. Although this was a more accurate indication of the fuel I had left, I NEVER took off in the red.......and I still never fully trusted the gauges!! I kept track of my fuel burn, time left to fly and always had plenty of reserve left. Sticking the tank is still only the true way to find out how much fuel you have left. Gauges still only have about so much accuracy..DON"T trust them with your life!!

MTV, I will study the CAR 3 and how it was written back then. Thanks!
Appreciate the replies.... just one of those things that I get to wondering about... while flying low and slow. Plenty of time to look around the cockpit and notice stuff. Like the oil temp gauge. Noticed the other day it has no color coding at all. No red line... nada.
Maybe that wasn't required in CAR 3. Or maybe the paint fell off....

Not sure what model Luscombe you have, but the type certificate can be found here: http://rgl.faa.gov/Regulatory_and_Guida ... /a-694.pdf

MTV

flightlogic wrote:....I have read that the older Luscombes with a fuselage tank had feed problems because of the level relative to the carb. Mine has two wing tanks, so I don't think gravity feeding is any issue.....

It's my understanding that a Luscombe with only a fuselage tank is not approved for anything larger than a 65 horse. 75 or more requires at least one wing tank, due to the fuel flow (actually head pressure) issues you reference.

my old flight instructor once told me " never trust any fuel guage... the only time they are required to be accurate is when they read "E" ....

Purchased a Rans S-7LS in December and have been trying to figure out fuel. Was told that fuel was aprox 1/8th less than indicated when in a 3 point position. I can't seem to fill it enough to show full tanks.

I can tell you that in my M5 a steep turn to into feeding tank will dry out the pickup if you are not on "Both" and below 1/4 indicated on the gauge ( whatever that means in gallons).