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Pulsar Fuel Tanks
By Sonja Englert, December 2004
Pulsar fuel tanks are integral tanks, which means they are part of the wing structure, which has been sealed. On the outboard end is a vent line. When sealing the tank this vent line must not be plugged if sealant. If the vent line is plugged, this will be most noticeable when opening the fuel cap after a flight and air is sucked in. The engine will run at least for a while even with a plugged vent.
On the inboard end is an aluminum plate, which seals the tank against a partial rib. The tank end plate usually contains the fuel sender and the fuel outlet fitting. In the lowest spot of the tank, usually right in front of the spar should be a drain fitting. There are several suitable fuel tank sealants and a lot of unsuitable ones. The ones that work are:
All those sealants are two-components, and are available from AC Spruce. Maintenance shops often have the flexible ones available, because they are also used to seal riveted metal tanks. Of the flexible sealant there are two viscosities. One is rather liquid and is suitable for brushing on tank surfaces, the other one is thicker and does not flow from a vertical surface. Don’t use anything else, it is unlikely to work.
To remove the tank end plates, drain all fuel and remove the wings. I have been unsuccessful in sealing any even small leaks from the outside, be prepared to remove the tank end plates to fix any leaks. This job can be done in a day, excluding the draining and wing removal and curing of sealant, which can take up to a week.
The tank end plate is attached to the wing rib with countersunk screws and nutplates. There usually is not enough room for screws other than countersunk. The end plate can be removed by slicing between plate and rib with a knife. Be careful not to damage the rib.
Capacitance Fuel Probe (left), Float Type Fuel probe (right)
The fuel sender / probe may be attached to the end rib with threads in the aluminum plate (worst case, threads are easily stripped), or with nutplates, which have been sealed (best case). There needs to be a gasket between sender and rib, or at least plenty of sealant, but that makes removal more difficult.
After the end plate has been removed, clean all the old sealant off from all parts. Check the composite structure for damage. If there is any damage, clean off sealant, coat it with new resin, and cure before covering it again with sealant. Composite materials are porous enough to let fuel leak through them if they are not properly sealed.
Do not reinstall the fuel probe until the sealant on the inside of the tank has cured, otherwise it might stick to it (float).
Inside Fuselage with Wing Attached, Drain Valve
Tank End Plate From Outside
Open Tanks
Closed Tank
To reinstall the end plate, do a dry fit check first if you have modified anything. If it fits, make sure it is completely clean. Coat all mating surfaces thickly with sealant. When the screws are tightened, sealant must squeeze out everywhere. Protect all parts of the airplane where you don’t want sealant on with masking tape, that stuff is messy and hard to clean off. Wear gloves. Small stains can usually be removed after a day with acetone, before it is fully cured. The pot life depends on temperature, ½ hour and 2 hour pot lives are available. If you have some experience, the ½ hour pot life will work fine, but if it is hot and you are not sure about it, use the 2 hour pot life.
After the tank is resealed, it is best to wait a few days to a week before putting fuel in the tank due to the slow cure.
If anyone has questions or comments on this article, please send an e-mail to webmaster@pulsaraviators.com.