Wing engineering?

Bending loads on the spar will be less if tanks are wing mounted, because
the lift from the wings acts directly on the mass of the fuel.

It has to do with the concept of load path -- when a laod is applied to the
airplane at any point other than the CG, the load must get to the CG through
the structure of the airplane.

That's why the Questair Venture has its nosegear attached to the engine
instead of the airplane, because it is always advantageous to feed loads
directly into a major mass.

Regards,

Gordon.

PS: What design are we talking about?


"Ernest Christley" wrote in message
. com...
Lou wrote:
Ok, a question or 2 about the wings. I'm building a wooden aircraft
that could go either fixed tri-gear or retract. I choose fixed seeing
how this is my first plane to build and I wanted to keep it simple. The
fuel was supposed to go behind the firewall but I choose to build tanks
in each wing where the wheels where to go.
What will this do to the loading of the aircraft? Does this effect
the useful load and how? Does it raise my useful load or lower it or
niether? Since the wings create lift, and the fuel was in the fuselage
and now in the wing should it screw up the center of gravity? Anybody,
Anybody, Anybody????


You have to worry about 3 axis. With now knowledge of the airplane, it is
possible that the fuels position may not have not changed fore or aft. If
that it true then your CG is safe. If not, then you will have to be very
careful in your weight and balance calculations. The nice thing about
wing tanks is that the fuel tends to sit on the center of lift. When this
is the case, the draining fuel doesn't cause your trim to creep.

Next is the vertical axis. If you move a lot of weight from up high to
down load, but leave the center of thrust untouched, then you've created a
situation where adding thrust will cause the plane to tend to nose over.
You're trying to move a filing cabinet by pushing the top. So, you're on
short final, just before the flair, all trimmed out and smooth. A deer
jumps on the runway. You firewall the throttle. Do you have enough
elevator to keep from eating a mouthful of dirt.

The other issue is lateral loading. Move all that weight to the wings and
you've modified your roll response. Just like an ice skater that changes
her spin by extending her arms or retracting her arms (moving weight in
and out.) When you try to start a roll, you have to have enough
differential lift in the ailerons to get everything moving...and THEN get
everything stopped. Moving the tanks could make the plane difficult to
control.


The upshot is that the wing ROOT doesn't have to carry the bending moment
of the fuel load. If the wing root was the limiting factor in your load
allowance, then this move very well could increase your plane's usefull
load. Airplanes have to be light, though. It's doubtful that the
designer cut the wing root to the bare minimum and then beefed up
everthing else, like landing gear, tail surface area, elevator surface
area, etc. I wouldn't bet MY life on an increased load allowance from
moving the fuel tank.


--
This is by far the hardest lesson about freedom. It goes against
instinct, and morality, to just sit back and watch people make
mistakes. We want to help them, which means control them and their
decisions, but in doing so we actually hurt them (and ourselves)."

Lou wrote:
Ok, a question or 2 about the wings. I'm building a wooden aircraft
that could go either fixed tri-gear or retract. I choose fixed seeing
how this is my first plane to build and I wanted to keep it simple. The
fuel was supposed to go behind the firewall but I choose to build tanks
in each wing where the wheels where to go.
What will this do to the loading of the aircraft? Does this effect
the useful load and how? Does it raise my useful load or lower it or
niether? Since the wings create lift, and the fuel was in the fuselage
and now in the wing should it screw up the center of gravity? Anybody,
Anybody, Anybody????



Run a weight and balance

Lou wrote:
What will this do to the loading of the aircraft?

Fuel weighs more than air and wood. At full fuel your wing loading will
increase, with all that that entails.

Does this effect the useful load and how? Does it raise my useful load or
lower it or niether?

Neither. Your aircraft has a gross weight, does it not? Useful load remains
the same, difference between empty weight and gross weight.

Since the wings create lift, and the fuel was in the fuselage and now in
the wing should it screw up the center of gravity?

Come on, you're not telling me you're building an aircraft and don't know
how to do a CG calculation? What L.D. said, do a weight and balance
calculation!

Juan Jimenez wrote:
Lou wrote:

What will this do to the loading of the aircraft?


Fuel weighs more than air and wood. At full fuel your wing loading will
increase, with all that that entails.

True, fuel is heavier than air or wood however there's a lot more to
this than weight of fuel. Assume you've got a fuel load of 120 pounds.
If that fuel was in the fuselage that weight is supported by the
wing attachment bolts. If that fuel was IN the wings, then the wing
attachment bolts are not supporting that extra 120 pounds in the
fuselage. This is the reason most larger aircraft are designed to carry
most of their fuel in the wing structure. Less stress on the wing
attachment bolts. The WING LOADING is the same assuming the weight of
the fuel remains the same. Wing Loading is simply the weight of the
aircraft divided by the area of the wing.



Does this effect the useful load and how? Does it raise my useful load or
lower it or niether?


Neither. Your aircraft has a gross weight, does it not? Useful load remains
the same, difference between empty weight and gross weight.



Since the wings create lift, and the fuel was in the fuselage and now in
the wing should it screw up the center of gravity?


Come on, you're not telling me you're building an aircraft and don't know
how to do a CG calculation? What L.D. said, do a weight and balance
calculation!

"John Ammeter" wrote in message
...


Juan Jimenez wrote:
Lou wrote:

What will this do to the loading of the aircraft?


Fuel weighs more than air and wood. At full fuel your wing loading will
increase, with all that that entails.

True, fuel is heavier than air or wood however there's a lot more to this
than weight of fuel. Assume you've got a fuel load of 120 pounds. If that
fuel was in the fuselage that weight is supported by the wing attachment
bolts. If that fuel was IN the wings, then the wing attachment bolts are
not supporting that extra 120 pounds in the fuselage. This is the reason
most larger aircraft are designed to carry most of their fuel in the wing
structure. Less stress on the wing attachment bolts. The WING LOADING is
the same assuming the weight of the fuel remains the same. Wing Loading
is simply the weight of the aircraft divided by the area of the wing.

All true, except I thought he said he wanted to add fuel in the wings, not
remove the fuselage tank and put tanks in the wings...

Yes, I want to add fuel to the wings and remove the fuselage tank..