Warbird Information Exchange

I’m researching a BT-15 accident that occurred in 1943. The official accident report differs from the pilot’s statements and I’m hoping to determine who is more correct.
According to the official report:
“The student pilot apparently changed from the right tank to the reserve in the same tank and upon noticing fuel signal light, used wobble pump and caused an air lock in the gas line. Recommendation after the accident: The students were cautioned to change gas tanks often enough to keep both tanks within ten gallons of each other and not to use the wobble pump until they are sure the selector valve is on the tank that contains fuel.”
According to the student pilot statement from the official report:
“Approximately 10 minutes before the accident occurred, I changed from my right tank which was low to my left tank, which was full and cruised along normally for about 8 minutes. I was flying along straight and level when I noticed the fuel pressure warning light flicker several times. I then proceeded to use wobble pump slowly. The engine seemed to be functioning perfectly, the pressure came back up and red light went off. I continued cruising along for 1 or 2 minutes and decided it might be advisable to gain some altitude when the red light came on and the engine quit. This occurred at approximately 1500 ft.“ The pilot made a successful dead stick landing in a plowed field and was uninjured with minor damage to the plane.

The pilot later wrote a story about the incident that stated that they tried to blame the student pilot for the accident, but when they looked in the left tank they found a rag stuffed in it. The incident was intentionally covered up as to not blame the people who serviced the plane earlier. The student pilot graduated and went on to be a successful pilot.

The question is which story is more likely true. Did the pilot screw up and incorrectly use the wobble pump in flight and incorrectly transfer fuel. OR Is it more likely that a rag stuffed in the left tank the cause of this accident and it was not the pilot’s fault?

I need an expert on wobble pumps, fuel tranfers and what could cause an engine to quit like that.

The BT-13/-15 doesn't transfer fuel: there are two fuel cells (the inner wings contain a 60 US gallon wet fuel cell each) and the selector has four positions, Left, Right, Reserve, and Off. The only difference between "Right" and "Reserve" is the fuel pickups - with the selector in "Right" the engine will starve for fuel when there's still 17 gallons in that cell, but to get at that last 17 gallons you have to select "Reserve". You can burn all the fuel in the aircraft using only the "Left" and "Reserve" selections. There's two fuel gauges down below you, one sticking out of each inner wing, and the right hand gauge has an extra marking denoting the reserve fuel. If you ran the right tank completely dry (you'd need to select "Reserve" to do it) and then had a blocked intake on the left tank, it would quit, or if the engine driven fuel pump failed and you didn't use the wobble pump to maintain fuel pressure it would also quit. Taking off on the "Right" selection will ensure you don't pick up any water off the bottom of the tank like you could in "Reserve" or "Left", unless of course, you had about 17 gallons of it.

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Defending Stearmans on WIX since Jeff started badmouthing them back in 2005.

Wobble pump is also used in the T-6.
I'm not that familiar with the Bt-13 but think it is the same setup.
The wobble pump is a manual fuel pump. You pump a handle for and aft that is connected to a fuel pump. That will move the fuel to the engine driven fuel pump and then to the carb.
There is also a fuel selector to allow you to select which tank to use to feed the fuel to the engine.
The items in order are fuel tanks, selector, wobble pump with fuel filter/screen and pressure regulator, the engine driven fuel pump and then the carb. Carb is a float type.
The engine will quit due to lack of fuel. A low pressure warning light is an indication of insignificant fuel pressure. These only run 4-5 psi for fuel pressure. That is why a wobble pump is sufficient to build pressure when needed.
The BT features a wet wing for both fuel tanks with some kind of sump as a pickup point. The six has a bottom sump bolted to the bottom of both alum tanks inside the wing. There is also a chamber above the sump that is made of alum walls with flapper valves to allow fuel and retain it near the sump and fuel pickup points. In the six the sumps have a finger screen about 1/2" in dia a few inches long that sticks up into the tank. On models other than the G model there is a reserve pickup that is elevated off of the bottom of the tank. On the T-6 the rag probably wouldn't make it to the pick up and if it did I'm unsure whether it would be able to close it off to totally stop fuel flow.
Maybe Mark Denest can fill us in with details of BT fuel system operation.

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Rich Palmer

Remember an Injured Youth
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Darn

You people have done it now - I am having horrible flash backs of PRC and ice box rivits and more PRC!! and....
ok - I am fine now. The only way I think a rag could get in there is if they did a re-seal job in the bay that has the fuel sumps. There are 4 fuel bays on each side that makes up the 60 gallons per side. I am hard pressed to believe that a rag could accidently get dropped through the filler neck and make its way to the sump. The rib immediately outboard of the sump area is a solid rib with a one way rubber flapper sort of like in your toilet bowl, that when uncoordinated turns are made, the fuel does not get out of the bay with the fuel sumps. There 3 flapper valves on that rib for both tanks, one in the middle, one in front and back and the hole for the fuel to get through to the sumps is only 2" in diameter iirc. I will see the plane next week for an annual and can't wait to see if my PRC job is still holding up.

The sump - the short screen in the Reserve (17 Gal) and the other is the Main (43 Gal)


This is the sump bay on the right side - the rib to the right is nothing more than sheet and extrusions. The holes toward the bottom of the rib is where the "flapper" valves go. They are mounted on the sump side of the rib and they let fuel in but not out.


Top view


Here is all 4 bays sealed - fun and sealing the top skin with the corrugated sheet metal is a treat - I highly recomend it

Hi Mark,

When you took yours apart, what did the sealant look like? Mine looked like tar soaked sawdust. As soon as I started pulling it out I remember thinking "Well, now I know why it leaked!" A few years ago, flipping through an old copy of Air Classics or Warbirds International, there was a photo of three or four girls kneeling on the ground with some buckets of "tar", reaching up through the holes in the center section, "sealing" up the wings. Pretty primitive looking operation.

Your airplane turned out just stunning, btw - congrats again.

Dan

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Defending Stearmans on WIX since Jeff started badmouthing them back in 2005.

What's up with the three 'bonus' #30 holes drilled in the radius of that rib stiffner (and a bit close on center to center too)? Donot submit those for consideration to the weight saving program

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Don't make me go get my flying monkeys-

Thank you Dan

I have seen others that have the same dried sawdust look but our center section was already cleaned by the previous group. I do remember that photo of those girls trying to spread that crap in there - I may have that article. Those 3 holes The Inspector noticed were on the left and right side ribs - not my doing - I wondered about them myself. It was a strange feeling sitting in the back seat for the photo thinking how anti climatic it was that it was finished and here it was flying - now what. I would love to do one for myself the way we rebuilt this one but it would probably take me 15 years. I'll let you know if the under side is dry when I see it next week. Dan I can make you a CD of the rebuild if you want.

PM sent - thanks!

_________________
Defending Stearmans on WIX since Jeff started badmouthing them back in 2005.

Thanks for all the information and pictures.

I want to add a twist to this thread.

The "student pilot" was a WASP . Pilot name was Lamphere, Marlyene E., graduated in the 1st class of WASP pilots. This one was a BT-15, serial number 42-41341, crashed Jan 27 1943, 2 1/2 miles N of Beasley TX. I interviewed her and she said many of the "new" planes from the factories had bad engines that quit in flight. She also said that in this case she claimed sabotage! She also said that men looked for any excuse to get rid the the women and that they were considered expendable. She said that she was lucky to have survived her time as a WASP.
I praised her for her service during difficult times. She recently recieved a gold metal for her service.