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I got a message from a forum member on my phone on Saturday, August 17, about the valving on my dual-use fuel/smoke tank. I can't find it on the phone, so I hope whoever sent it sees this. The main fuel tank is plumbed to MAIN on the Andair valve and has a flop tube. Only the main tank can be used for aerobatics. When in the AUX position fuel is drawn from the aux tank at the bottom rear of the tank. There is no flop tube for fuel in the aux tank. When the aux tank has smoke oil in it the Andair valve must be in the MAIN position. When the aux tank has fuel in it the smoke valve must be locked in the OFF position.
For cross-country flight I fill both tanks with fuel, with the smoke valve locked OFF. I burn off the aux fuel first so that tank is empty on arrival for the show. The smoke tank can then be filled with smoke oil. When the smoke oil valve is ON oil is drawn from the tank thru a flop tube, completely separate plumbing from the fuel system. However, if fuel is in the aux tank and the smoke valve is opened and the pump turned on, fuel will be injected into the exhaust system and a fire would surely start. If smoke oil is in the aux tank and the Andair valve is turned to AUX smoke oil will be drawn into the engine and engine failure is assured.
It is all a matter of procedure. I had the same type system on my Pitts S-1S with an external belly tank, and a split main tank for fuel and smoke, and never had any trouble or cross contamination problems at all. Just be careful! Next week I can post a schematic of the system, but I am leaving town in the morning for a show in Sheridan, WY, so can't post until I get back.
For cross-country flight I fill both tanks with fuel, with the smoke valve locked OFF. I burn off the aux fuel first so that tank is empty on arrival for the show. The smoke tank can then be filled with smoke oil. When the smoke oil valve is ON oil is drawn from the tank thru a flop tube, completely separate plumbing from the fuel system. However, if fuel is in the aux tank and the smoke valve is opened and the pump turned on, fuel will be injected into the exhaust system and a fire would surely start. If smoke oil is in the aux tank and the Andair valve is turned to AUX smoke oil will be drawn into the engine and engine failure is assured.
It is all a matter of procedure. I had the same type system on my Pitts S-1S with an external belly tank, and a split main tank for fuel and smoke, and never had any trouble or cross contamination problems at all. Just be careful! Next week I can post a schematic of the system, but I am leaving town in the morning for a show in Sheridan, WY, so can't post until I get back.
