AOA vs fuel level in main tank

[PA1195]

I'm sure this subject has been discussed but here's another. I was made aware in conversation of a fellow T-Crafter that recently experienced an engine stoppage after takeoff. He mentioned the fuel level in his BC12D-85 was less than half in the main tank, possibly closer to 1/4...I'm not sure and didn't check. He runs approved 29" tires and I assume a normal tailwheel. Airframes has approval for tires to 31" assuming "heavy duty" brakes are installed (http://www.airframesalaska.com/Alask...els-s/1477.htm - http://www.airframesalaska.com/v/vsp...reak%20AML.pdf).

The plane's engine quit over the runway apparently from fuel starvation (the pilot's words). Carb heat was reportedly applied just prior to takeoff and a M/S carb is installed. He landed safely and because the engine had stopped rotating was unable to achieve a restart either in the air or on the ground. The landing was normal and no damage was mentioned. He pushed it off the runway where it was started normally with one of those battery drill assemblies.

I suggested he investigate further:

For any debris in the main tank, fuel filter, carb finger screen, or float bowl.
The internal diameter of the supply lines.
The relationship between the carb inlet and fuel level in the tank at that time on the large diameter tires, and after take-off in a normal climbing attitude.

As far as I know for the C-85 and 0-200 1A9 TCDS notes a limit of useable fuel (9 gallons; which implies 3 are unusable in certain condx), and that only applies to model 19's and F-19's, which are to be placarded accordingly. A-696 or others don't mention a fuel minimum. However the AOA versus fuel head pressure and flow availability may have been compromised prior to the actual takeoff (my suggestion only).

Any comments would be appreciated.

Gary

[astjp2]

Re: AOA vs fuel level in main tank

I am running 8.50's and on the ground can drain the tank completely. That being said, why would anyone fly an airplane with only 1/4 tank and to a steep climb? I wont even fly with less than 1/2 tank. I can out climb my fuel supply though with 1/2 tank and an O-200 but it takes a minute or two to drain the carb with having the finger screen uncovered. Tim

[PA1195]

Re: AOA vs fuel level in main tank

Good info Tim on the 8.50's, fuel drain, and the other limits you've experienced. But I wouldn't consider a drain to empty equivalent to required flow at full throttle.

My purpose for asking this is to discuss similar fuel starvation experiences, and question any additional limits potentially imposed by large tires. There was a time in my flying life that the FAA would never approve large tires that resulted in max AOA being approached or achieved. Axle heights were often specified as limits. That's no longer the case or someone has convinced someone else it's all good. I wonder if the tire manufacturers considered the Taylorcraft and others (like the J-3) with a non-wing main fuel supply fuel in their certification process?

As far as minimum fuel, why would a C-85 (or 0-200 or Stroker C-85) in a BC**** require any less fuel head than a C-85 in a Model 19 or 0-200 in a F-19? I assume FAA certification varied between models.

Edit: To answer your question "That being said, why would anyone fly an airplane with only 1/4 tank and to a steep climb?" I suggest it's simply because there's no written reason in the form of approved operating procedures or placards to not do so. That's why I asked for perspective from experienced Taylorcraft pilots.

Gary

[astjp2]

Re: AOA vs fuel level in main tank

It has to do with the differences in the BC series vs. the F series airplanes in how the fuel is setup. The header tank is sealed in the model 19 and newer airplanes, the BC has an open fuel cap. The early airplanes had 1/4" and 5/16" fuel lines also, where the higher HP ones were 3/8. It also has to do with engine mount length....CG limits, and a host of other 1940's engineering surprises. Tim

[M Towsley]

Re: AOA vs fuel level in main tank

And yes, this has been discussed before. To name a few....

http://vb.taylorcraft.org/showthread.php?5654-Minimum-Takeoff-Fuel&highlight=unporting+fuel+tank

http://vb.taylorcraft.org/showthread.php?8563-Engine-cut-out-on-takeoff-suggestions&highlight=unporting+fuel+tank

http://vb.taylorcraft.org/showthread.php?5939-quot-Engine-Problems-quot-Solved-!&highlight=unporting+fuel+tank

[PA1195]

Re: AOA vs fuel level in main tank

Thanks all for the replies. I've read the post above and found the discussion to be excellent. Now this topic is at least in one thread should the pilot I spoke with and his mechanic want to review the suggestions.

I've not yet compared the fuel flow requirements noted in CAR 3, 4, and 4a.

Assuming all plumbing, flow, and components are airworthy it still leaves the question of how to deal with large tires versus AOA and fuel onboard. I'm replacing my Goodyear 26" tires with dimensionally similar Airstreak 26" this Fall after I come off floats. I'll try to get some measurements of axle height, AOA (horizontal stabilizer angle plus ~3.8*), and fuel head versus quantity at that time. Those with even larger tires may choose to do the same.

Gary

[3Dreaming]

Re: AOA vs fuel level in main tank

I don't think AoA has anything to do with the problem described, otherwise there would be issues in other areas of flight. The bigger issue on takeoff is acceleration forces and deck angle. These will have a greater effect on un-porting the outlet on the tank.

[N96337]

Re: AOA vs fuel level in main tank

Are you confusing "deck angle" with AOA? Once you leave the ground, tires have nothing to do with AOA. I'm with Tim on this one...why would you try to do a performance takeoff with only a tiny bit of fuel in the main? I don't have the engineering background to run numbers on how much fuel the tank would need to keep from unporting during acceleration. Maybe someone else????
Personally, I'd say at least 4 gallons seems to be about the point that I'd not want to try to pull out and see how steep I could climb. I hear a lot of pilots complain about that fuel weighing 6#...but if it's 6# that keeps you from getting over an obstacle or not, do you really belong there?

Below are a couple pictures I posted on one of the other threads, with a Tcraft on 8.50's and a Maule Tailwheel... it shows the bottom of the fuel tank sitting there static. I'd say it wouldn't take that much extra fuel to keep the bottom covered.

[PA1195]

Re: AOA vs fuel level in main tank

When discussing AOA I had two venues...one (in Post #1) was to question fuel levels versus AOA, or deck angle if you prefer the latter measurement, and the second was to question how the large tires influence AOA when taking off or landing versus the stall AOA. They are separate unrelated questions when it comes to engine stoppage either while still on the ground or once airborne. I'm aware of the confusion I may have caused by my blending the topics and apologize for that.

I questioned this in Post #3: "My purpose for asking this is to discuss similar fuel starvation experiences, and question any additional limits potentially imposed by large tires. There was a time in my flying life that the FAA would never approve large tires that resulted in max AOA being approached or achieved. Axle heights were often specified as limits. That's no longer the case or someone has convinced someone else it's all good. I wonder if the tire manufacturers considered the Taylorcraft and others (like the J-3) with a non-wing main fuel supply fuel in their certification process?"

I believe this is a valid question as it applies to: AOA on tires when taking off or landing versus the stall AOA of the unmodified airfoil (no VG's), and any fuel flow issues as I suggest above.

Obviously having more fuel in the main tank is better. Taylorcraft placards 3 gal as a minimum on some models. Some here have reported stoppage with various levels of fuel. How much to initiate flight with is ultimately left up to the pilot but may change depending upon gear configuration and the condition of the fuel system.

Gary

[cvavon]

Re: AOA vs fuel level in main tank

Hank and i compared the angle of the horizontal stab angle of his stock 1941 and my not stock 1940 his has 600-6 tires and a solid tailwheel my plane has 26x12.50x6 AK Bush tires and a AK bush 3200 tailwheel and all that did was raise the plane up the angle of the stab was the same so no change of AOA.

[PA1195]

Re: AOA vs fuel level in main tank

Hank and i compared the angle of the horizontal stab angle of his stock 1941 and my not stock 1940 his has 600-6 tires and a solid tailwheel my plane has 26x12.50x6 AK Bush tires and a AK bush 3200 tailwheel and all that did was raise the plane up the angle of the stab was the same so no change of AOA.

This is good to know. Add wing incidence (~3.8*) to the stab angle for the static AOA on the ground. I didn't measure mine (formerly Goodyear 26") before installing floats. I personally wouldn't want any larger tires/axle height unless I was getting paid again to land in boulder patches. Can't see forward well, puts more weight on the tail.

I suppose I should use deck angle (typically fuselage, but sometimes wing chord C/L vs ground) vs AOA (wing chord vs relative wind) but admittedly I interchange them out of laziness. Airfoil descriptions use AOA so that's why I tend to also. Here's a Ph.D.'s take on all this terminology: http://members.localnet.com/~docstev...deck_angle.htm

Hopefully from all this the recommendation of a minimum of 3-4 gallons, non-abrupt ground maneuvers, and normal climb angle will be noted. I'd still make sure the fuel system wasn't clogged and flowed properly.

Gary

[cvavon]

Re: AOA vs fuel level in main tank

The fuel gauge wire on my plane is set at 2.5 gl when zero is indicated and that may be a way keep track of take off fuel needed. set zero at 3 gl .

[M Towsley]

Re: AOA vs fuel level in main tank

The wire is at a different level in-flight as opposed to on the ground. The reading would be different. Mine is set for in-flight reading.

[PA1195]

Re: AOA vs fuel level in main tank

On other aircraft I've owned I calibrated the fuel gauge(s) in three-point and fuselage level attitudes. I need to do that to my Taylorcraft but have put it off for other projects for some reason.

Drain the tank(s), add measured fuel, mark the quantity in the two attitudes.

I have the round gauge like the F-19 used and should find out how accurate the numbers are. I also have a wood dowel dipstick that's quick to use in the wings.

Gary

[Robert Lees]

Re: AOA vs fuel level in main tank

In the UK, the old BCAR* requirements for fuel flow, required 50% more than the normal flow at maximum angle of climb at stated minimal fuel capacity. These regs are not dissimilar (in principle) to the FAR regs.

In essence, these regs mean that the carb should see a head of pressure of 150% of the carb's normal intake.

A few years ago we did such a test on a Taylorcraft fitted with a C85, in the hangar. Keeping the tailwheel on the ground, we raised the main gear 12" to simulate an excessive angle of climb (first picture below).

Then we opened the fuel pipe at the carb and verified that we had the 150% of fuel flow (second picture below).

It is in this type of way that aircraft manufacturers determine the minimal fuel requirement in the header tank, and to approve fuel flow modifications. That is why there is a minimum fuel level in the likes of the F19. You may notice similar restrictions in all sorts of aircraft.

Rob

*BCAR = British Civil Aviation Requirements (now superseded, in the same way that US CARs have been superseded by FARs)