Extra fuel for RV-9A

[Steve Brown]

I've been considering getting an extended fuel bladder for the baggage area:
http://turtlepac.com/sportdetails.htm

The only thing holding me back is deciding how to tie it into the fuel system.

I'm not great at wrenching so I'm thinking of minimally invasive approaches.

One variant is to use one of the tank vent lines to feed fuel into the tank. The idea is to gravity feed into the vent line, then let the airplanes fuel pump do the work, pulling aux fuel back through the line to fill the vacuum created by spent fuel.

So:
Aux bladder higher than the wing tank, but lower than the top of the vent line.

To do this I would install a T in the vent line with a valve. Opening the valve while running off of that tank starts the process. When axillary fuel is empty (bladder collapsed) the vent line would start puling air again.

Any pitfalls with this method?
Any simpler or better ideas?

[pierre smith]

......sells extended range tanks that fit in the large holes in the nose ribs, just in front of the spar with access from a door you install in the wingtip. They hold ten gallons and feed directly into the outboard end of the mains.
Visit www.safeair1.com.

Regards,

[Steve Brown]

Originally Posted by pierre smith

......sells extended range tanks that fit in the large holes in the nose ribs, just in front of the spar with access from a door you install in the wingtip. They hold ten gallons and feed directly into the outboard end of the mains.
Visit www.safeair1.com.

Regards,

I wish they did

[beechrv9a]

Safeair does not make one for the 9, but I am wondering if the diameter of the lightening holes in the 7 are the same as the 9. The er tank should work for the 9 then....You would just have the difference of wing length between the 7 and 9 and have to run a longer transfer line to the 9's existing tank. Dont' think the extra wing length on the 9 would make too much difference, but I don't really know. Once the wing is flying it does it really matter? I am considering this, so I have not put the bottoms on my wings yet to allow easier access.

[pierre smith]

....that if you called the manufacturer, that they would. However, the extra wingspan of the -9 might make them too heavy when they're full.

I'm with Jim in using the -7 tanks and having a little longer transfer fuel line to the mains.

One caveat, though....with the weight outboard, spin avoidance would have to be a must, IMO. The little Grummans are placarded against spins for this reason. The fuel is carried in their round tubing spars and the fear of not being able to recover from spins as all the weight would tend to aggravate recovery.

Regards,

[Mel]

The reason that HW don't yet have tanks for the -9 is not because of the tube diameter, but because of the tip shape. Because of the different airfoil on the -9, the tip is shaped quite differently. This is where the "fill" box and filler is installed.

[ergie63]

Not having built a 9, but having studied it for years, I'd suspect that the lower g (load) rating of the 9 wing combined with the longer arm of outboard wing tanks, eats more into the 9's wing safety margin compared to any other RV wing. Some people have done it and are happy with it. Its not for me. It would be interesting to compare V-speeds on a V-N chart with the two different wings.

I'm focusing on extending my range by some combination of: smaller engine, electronic ignition, prop optimized for cruise, and tight plenum.

[N941WR]

Originally Posted by Steve Brown

...One variant is to use one of the tank vent lines to feed fuel into the tank. The idea is to gravity feed into the vent line, then let the airplanes fuel pump do the work, pulling aux fuel back through the line to fill the vacuum created by spent fuel.

Any simpler or better ideas?

It is just as easy to tie into the fuel line as the vent line and probably safer. IMHO

Originally Posted by ergie63

Not having built a 9, but having studied it for years, I'd suspect that the lower g (load) rating of the 9 wing combined with the longer arm of outboard wing tanks, eats more into the 9's wing safety margin compared to any other RV wing...

I don’t believe this is true, someone correct me if I’m wrong. The weight is carried by the wings and not the fuselage, thus it does NOT compromise the G loading for the same reason fuel is not counted in the acro weights, if carried in the wings. However, the tanks and extra fuel will count towards your GW and will move the CG forward, when full.

[Mel]

Originally Posted by N941WR

It is just as easy to tie into the fuel line as the vent line and probably safer. IMHO

I don’t believe this is true, someone correct me if I’m wrong. The weight is carried by the wings and not the fuselage, thus it does compromise the G loading for the same reason fuel is not counted in the acro weights, if carried in the wings. However, the tanks and extra fuel will count towards your GW and will move the CG forward, when full.

By this same observation, extra fuel carried in the fuselage would be more of a factor.
Of course as long as you stay within GW & CG limits, you should be OK.

[ergie63]

Its true that the wings create all of the lift needed for flight and that g-loading is normally thought of as the amount of work the wings have to do in order to heft the fuselage around. The difference between what the flight surfaces want to do (turn) and what the fuselage wants to do (straight line) is revealed by how much the wings bend. This is a fine visual model for flight and wingtip tanks would not be much of a factor. But I don't think that this is the correct visual model for the occurence of disturbances at Vne, Vc or even Va.

There is always a tradeoff somewhere. Putting mass on the wingtip will affect the wing's natural frequency. It likely reduces the frequency and increases the amplitude caused by a given disturbance. The wing ends up bending less often, but more severely each time. If true, then V-speeds must be reduced in order to maintain a given margin of safety.