***Finding the True Wingloading of any plane!!!!!!!*****

***Finding the True Wingloading of any plane!!!!!!!*****

Post by LBrown81 » Mon, 04 Oct 1999 04:00:00



 Here is a copy of any artical that was published back in 1992. It has the
formula to calculate the wing loading of  "any" size plane. It is pretty long
so be patient.
Hope this helps everyone.
Ty

  True wing loading is calculated in weight per cubic foot of wing volume (
justlike the hull displacement in a boat ). Most people discuss it in ounces
per squarefoot. That doesn't work, which is why ppeople usually qualify it by
saying that a big airplane can have a heavier wing loading than a small one.
If you always use pounds per cubic foot, a particular wing loading will have
the same flying characteristics at the same speed, regarless of the airplane
size.  
        We want our models to fly and land a lot slower than the big ones, so we need
our wing loadings to be much less than those of big airplanes.  The big ones
fly smoother, of course.
        Here's how to calculate true wing loading in any size airplane, from a
***-band-powered "peanut" to a giant scale model:
        Take the wing area given on the plans (560 square inches, for example) and
multiply it by 2/3 the height of the average size rib (technically, the "mean
chord") in the wing (our rib was 1.25 inches high at the spar, so 22/3 is .834
inches).
        Use 2/3 of the height of the rib because the typical wing rib is 2/3 the area
of a rectangle drawn around it, and the wing volume is thereby reduced from
what you would expect just using  the real height of the rib times the wing
area.  If the wing is not tapered, you can use any rib, because they are all
the same size.
        The result (560 x .834 = 467) is the wolume of the wing in cubic inches, so
divide by 1728 (the number of cubic inches in a cubic foot) to get cubic feet
of wing.  This gives you 0.27 cubic feet (467/1728 = .27).  Multiply by 25
pounds (per cubic foot) for comfortable loading and you get 6.75 pounds (.27 x
25 = 6.75).  That should be the maximum weight of your airplane.
        Wasn't that easy?  This calculation will tell you a lot about the flying
characteristics of your model before it ever leaves the ground.
        This process, by the way, explains why biplanes are usually considered to have
only 75% of theirrr wing area available for use in the "square inch" wing
loading calculations.  The wing ribs in a biplane are much smaller than those
in a monoplane of the same wing area.  This simply reduces the wing volume/wing
area ratio in a biplane, and consequently makes it a less efficient lifter of
weight.  It isn't some arcane "interference"; it's just low wing volume.
        A reasonable wing loading is 25 pounds per cubic foot of wing for a scale
fighter of for a model of any powerful airplane.  Here are some other general
guidelines to wing loading"  15 pounds per cubic foot is a "floater" in any
size; 20 pounds per cubic foot is a sporty flier; and 30 pounds per cubic foot
is demanding!
        I tried 35, several times.  It can be done, but it takes a lot out of you, and
a lot out of your wallet.  It doesn't do your pride any good, either.
        It also takes a lot of really smooth runway, and runways are like money:
there's never enough, and what there is, you've used already.

 
 
 

***Finding the True Wingloading of any plane!!!!!!!*****

Post by Marker Beaco » Mon, 04 Oct 1999 04:00:00


"Mean Chord" or "Mean Aerodynamic Chord" means the average distance from the
leading edge to the trailing edge of the wing (in a constant chord wing this
is pretty easy to figure, tapered wings require you take into account the
average).  IT HAS SQUAT TO DO WITH THE HEIGHT OF THE RIB!!!!!  Which makes
me think the rest of the "artical" is just as bogus!  Would like to see some
references!

-Mark


Quote:
> Here is a copy of any artical that was published back in 1992. It has the
> formula to calculate the wing loading of  "any" size plane. It is pretty
long
> so be patient.
> Hope this helps everyone.
> Ty

>   True wing loading is calculated in weight per cubic foot of wing volume
(
> justlike the hull displacement in a boat ). Most people discuss it in
ounces
> per squarefoot. That doesn't work, which is why ppeople usually qualify it
by
> saying that a big airplane can have a heavier wing loading than a small
one.
> If you always use pounds per cubic foot, a particular wing loading will
have
> the same flying characteristics at the same speed, regarless of the
airplane
> size.
> We want our models to fly and land a lot slower than the big ones, so we
need
> our wing loadings to be much less than those of big airplanes.  The big
ones
> fly smoother, of course.
> Here's how to calculate true wing loading in any size airplane, from a
> ***-band-powered "peanut" to a giant scale model:
> Take the wing area given on the plans (560 square inches, for example) and
> multiply it by 2/3 the height of the average size rib (technically, the
"mean
> chord") in the wing (our rib was 1.25 inches high at the spar, so 22/3 is
.834
> inches).
> Use 2/3 of the height of the rib because the typical wing rib is 2/3 the
area
> of a rectangle drawn around it, and the wing volume is thereby reduced
from
> what you would expect just using  the real height of the rib times the
wing
> area.  If the wing is not tapered, you can use any rib, because they are
all
> the same size.
> The result (560 x .834 = 467) is the wolume of the wing in cubic inches,
so
> divide by 1728 (the number of cubic inches in a cubic foot) to get cubic
feet
> of wing.  This gives you 0.27 cubic feet (467/1728 = .27).  Multiply by 25
> pounds (per cubic foot) for comfortable loading and you get 6.75 pounds
(.27 x
> 25 = 6.75).  That should be the maximum weight of your airplane.
> Wasn't that easy?  This calculation will tell you a lot about the flying
> characteristics of your model before it ever leaves the ground.
> This process, by the way, explains why biplanes are usually considered to
have
> only 75% of theirrr wing area available for use in the "square inch" wing
> loading calculations.  The wing ribs in a biplane are much smaller than
those
> in a monoplane of the same wing area.  This simply reduces the wing
volume/wing
> area ratio in a biplane, and consequently makes it a less efficient lifter
of
> weight.  It isn't some arcane "interference"; it's just low wing volume.
> A reasonable wing loading is 25 pounds per cubic foot of wing for a scale
> fighter of for a model of any powerful airplane.  Here are some other
general
> guidelines to wing loading"  15 pounds per cubic foot is a "floater" in
any
> size; 20 pounds per cubic foot is a sporty flier; and 30 pounds per cubic
foot
> is demanding!
> I tried 35, several times.  It can be done, but it takes a lot out of you,
and
> a lot out of your wallet.  It doesn't do your pride any good, either.
> It also takes a lot of really smooth runway, and runways are like money:
> there's never enough, and what there is, you've used already.


 
 
 

***Finding the True Wingloading of any plane!!!!!!!*****

Post by Cliff Griffi » Mon, 04 Oct 1999 04:00:00


There was a similar article in one of the recent S&E Modeler magazines.
(Sailplane and electric...) Anyway, the author was trying to demonstrate
this same concept. When he brought his new glider to the club with
26oz/sq', he was laughed at for having such a huge wing loading.
However, it was on par for the size of it. He compared the wing loading
of his little 50" glider with this large one and a full sized glider.
Using the cubic method, the wing loading on all three gliders came
within a few percent percent of each other, and supposedly flew
appropriately.

Quote:

> "Mean Chord" or "Mean Aerodynamic Chord" means the average distance from the
> leading edge to the trailing edge of the wing (in a constant chord wing this
> is pretty easy to figure, tapered wings require you take into account the
> average).  IT HAS SQUAT TO DO WITH THE HEIGHT OF THE RIB!!!!!  Which makes
> me think the rest of the "artical" is just as bogus!  Would like to see some
> references!

> -Mark



> > Here is a copy of any artical that was published back in 1992. It has the
> > formula to calculate the wing loading of  "any" size plane. It is pretty
> long
> > so be patient.
> > Hope this helps everyone.
> > Ty

> >   True wing loading is calculated in weight per cubic foot of wing volume
> (
> > justlike the hull displacement in a boat ). Most people discuss it in
> ounces
> > per squarefoot. That doesn't work, which is why ppeople usually qualify it
> by
> > saying that a big airplane can have a heavier wing loading than a small
> one.
> > If you always use pounds per cubic foot, a particular wing loading will
> have
> > the same flying characteristics at the same speed, regarless of the
> airplane
> > size.
> > We want our models to fly and land a lot slower than the big ones, so we
> need
> > our wing loadings to be much less than those of big airplanes.  The big
> ones
> > fly smoother, of course.
> > Here's how to calculate true wing loading in any size airplane, from a
> > ***-band-powered "peanut" to a giant scale model:
> > Take the wing area given on the plans (560 square inches, for example) and
> > multiply it by 2/3 the height of the average size rib (technically, the
> "mean
> > chord") in the wing (our rib was 1.25 inches high at the spar, so 22/3 is
> .834
> > inches).
> > Use 2/3 of the height of the rib because the typical wing rib is 2/3 the
> area
> > of a rectangle drawn around it, and the wing volume is thereby reduced
> from
> > what you would expect just using  the real height of the rib times the
> wing
> > area.  If the wing is not tapered, you can use any rib, because they are
> all
> > the same size.
> > The result (560 x .834 = 467) is the wolume of the wing in cubic inches,
> so
> > divide by 1728 (the number of cubic inches in a cubic foot) to get cubic
> feet
> > of wing.  This gives you 0.27 cubic feet (467/1728 = .27).  Multiply by 25
> > pounds (per cubic foot) for comfortable loading and you get 6.75 pounds
> (.27 x
> > 25 = 6.75).  That should be the maximum weight of your airplane.
> > Wasn't that easy?  This calculation will tell you a lot about the flying
> > characteristics of your model before it ever leaves the ground.
> > This process, by the way, explains why biplanes are usually considered to
> have
> > only 75% of theirrr wing area available for use in the "square inch" wing
> > loading calculations.  The wing ribs in a biplane are much smaller than
> those
> > in a monoplane of the same wing area.  This simply reduces the wing
> volume/wing
> > area ratio in a biplane, and consequently makes it a less efficient lifter
> of
> > weight.  It isn't some arcane "interference"; it's just low wing volume.
> > A reasonable wing loading is 25 pounds per cubic foot of wing for a scale
> > fighter of for a model of any powerful airplane.  Here are some other
> general
> > guidelines to wing loading"  15 pounds per cubic foot is a "floater" in
> any
> > size; 20 pounds per cubic foot is a sporty flier; and 30 pounds per cubic
> foot
> > is demanding!
> > I tried 35, several times.  It can be done, but it takes a lot out of you,
> and
> > a lot out of your wallet.  It doesn't do your pride any good, either.
> > It also takes a lot of really smooth runway, and runways are like money:
> > there's never enough, and what there is, you've used already.

--
Cliff Griffin
Remove the obvious for no spam.
 
 
 

***Finding the True Wingloading of any plane!!!!!!!*****

Post by Marker Beaco » Mon, 04 Oct 1999 04:00:00


Still would like to see some text book references or something.  As far as I
know, the aviation industry, of which we are a "small" part, is still using
lbs/sq. ft.  Sorry, but it's a new concept to me.  However I am open to new
ideas.  May main reason for reply was the part about chord and rib height.

-Mark :)


Quote:
> There was a similar article in one of the recent S&E Modeler magazines.
> (Sailplane and electric...) Anyway, the author was trying to demonstrate
> this same concept. When he brought his new glider to the club with
> 26oz/sq', he was laughed at for having such a huge wing loading.
> However, it was on par for the size of it. He compared the wing loading
> of his little 50" glider with this large one and a full sized glider.
> Using the cubic method, the wing loading on all three gliders came
> within a few percent percent of each other, and supposedly flew
> appropriately.


> > "Mean Chord" or "Mean Aerodynamic Chord" means the average distance from
the
> > leading edge to the trailing edge of the wing (in a constant chord wing
this
> > is pretty easy to figure, tapered wings require you take into account
the
> > average).  IT HAS SQUAT TO DO WITH THE HEIGHT OF THE RIB!!!!!  Which
makes
> > me think the rest of the "artical" is just as bogus!  Would like to see
some
> > references!

> > -Mark



> > > Here is a copy of any artical that was published back in 1992. It has
the
> > > formula to calculate the wing loading of  "any" size plane. It is
pretty
> > long
> > > so be patient.
> > > Hope this helps everyone.
> > > Ty

> > >   True wing loading is calculated in weight per cubic foot of wing
volume
> > (
> > > justlike the hull displacement in a boat ). Most people discuss it in
> > ounces
> > > per squarefoot. That doesn't work, which is why ppeople usually
qualify it
> > by
> > > saying that a big airplane can have a heavier wing loading than a
small
> > one.
> > > If you always use pounds per cubic foot, a particular wing loading
will
> > have
> > > the same flying characteristics at the same speed, regarless of the
> > airplane
> > > size.
> > > We want our models to fly and land a lot slower than the big ones, so
we
> > need
> > > our wing loadings to be much less than those of big airplanes.  The
big
> > ones
> > > fly smoother, of course.
> > > Here's how to calculate true wing loading in any size airplane, from a
> > > ***-band-powered "peanut" to a giant scale model:
> > > Take the wing area given on the plans (560 square inches, for example)
and
> > > multiply it by 2/3 the height of the average size rib (technically,
the
> > "mean
> > > chord") in the wing (our rib was 1.25 inches high at the spar, so 22/3
is
> > .834
> > > inches).
> > > Use 2/3 of the height of the rib because the typical wing rib is 2/3
the
> > area
> > > of a rectangle drawn around it, and the wing volume is thereby reduced
> > from
> > > what you would expect just using  the real height of the rib times the
> > wing
> > > area.  If the wing is not tapered, you can use any rib, because they
are
> > all
> > > the same size.
> > > The result (560 x .834 = 467) is the wolume of the wing in cubic
inches,
> > so
> > > divide by 1728 (the number of cubic inches in a cubic foot) to get
cubic
> > feet
> > > of wing.  This gives you 0.27 cubic feet (467/1728 = .27).  Multiply
by 25
> > > pounds (per cubic foot) for comfortable loading and you get 6.75
pounds
> > (.27 x
> > > 25 = 6.75).  That should be the maximum weight of your airplane.
> > > Wasn't that easy?  This calculation will tell you a lot about the
flying
> > > characteristics of your model before it ever leaves the ground.
> > > This process, by the way, explains why biplanes are usually considered
to
> > have
> > > only 75% of theirrr wing area available for use in the "square inch"
wing
> > > loading calculations.  The wing ribs in a biplane are much smaller
than
> > those
> > > in a monoplane of the same wing area.  This simply reduces the wing
> > volume/wing
> > > area ratio in a biplane, and consequently makes it a less efficient
lifter
> > of
> > > weight.  It isn't some arcane "interference"; it's just low wing
volume.
> > > A reasonable wing loading is 25 pounds per cubic foot of wing for a
scale
> > > fighter of for a model of any powerful airplane.  Here are some other
> > general
> > > guidelines to wing loading"  15 pounds per cubic foot is a "floater"
in
> > any
> > > size; 20 pounds per cubic foot is a sporty flier; and 30 pounds per
cubic
> > foot
> > > is demanding!
> > > I tried 35, several times.  It can be done, but it takes a lot out of
you,
> > and
> > > a lot out of your wallet.  It doesn't do your pride any good, either.
> > > It also takes a lot of really smooth runway, and runways are like
money:
> > > there's never enough, and what there is, you've used already.

> --
> Cliff Griffin
> Remove the obvious for no spam.

 
 
 

***Finding the True Wingloading of any plane!!!!!!!*****

Post by Lars Steffenre » Mon, 04 Oct 1999 04:00:00


I think  that he tries to say that the technical term for "average size rib"
would be MAC.

Lars Steffenrem

 
 
 

***Finding the True Wingloading of any plane!!!!!!!*****

Post by Cliff Griffi » Mon, 04 Oct 1999 04:00:00


Maybe he messed up his terms, I don't know. The concept is the same.
Figure it out for all of your planes yourself, if you want a definate
answer, as "how it flies" is the only thing that really matters. We all
know that small planes need lighter wing loading measured in oz/sq', and
very large planes can handle a wing loading that would kill a small
plane. To me, it just makes sense, but I'm not going to fret over it
either way. The third value that turns it into cubic wing loading just
makes it so you can compare a 30" glider with a 30' glider.

Quote:

> Still would like to see some text book references or something.  As far as I
> know, the aviation industry, of which we are a "small" part, is still using
> lbs/sq. ft.  Sorry, but it's a new concept to me.  However I am open to new
> ideas.  May main reason for reply was the part about chord and rib height.

> -Mark :)



> > There was a similar article in one of the recent S&E Modeler magazines.
> > (Sailplane and electric...) Anyway, the author was trying to demonstrate
> > this same concept. When he brought his new glider to the club with
> > 26oz/sq', he was laughed at for having such a huge wing loading.
> > However, it was on par for the size of it. He compared the wing loading
> > of his little 50" glider with this large one and a full sized glider.
> > Using the cubic method, the wing loading on all three gliders came
> > within a few percent percent of each other, and supposedly flew
> > appropriately.


> > > "Mean Chord" or "Mean Aerodynamic Chord" means the average distance from
> the
> > > leading edge to the trailing edge of the wing (in a constant chord wing
> this
> > > is pretty easy to figure, tapered wings require you take into account
> the
> > > average).  IT HAS SQUAT TO DO WITH THE HEIGHT OF THE RIB!!!!!  Which
> makes
> > > me think the rest of the "artical" is just as bogus!  Would like to see
> some
> > > references!

> > > -Mark



> > > > Here is a copy of any artical that was published back in 1992. It has
> the
> > > > formula to calculate the wing loading of  "any" size plane. It is
> pretty
> > > long
> > > > so be patient.
> > > > Hope this helps everyone.
> > > > Ty

> > > >   True wing loading is calculated in weight per cubic foot of wing
> volume
> > > (
> > > > justlike the hull displacement in a boat ). Most people discuss it in
> > > ounces
> > > > per squarefoot. That doesn't work, which is why ppeople usually
> qualify it
> > > by
> > > > saying that a big airplane can have a heavier wing loading than a
> small
> > > one.
> > > > If you always use pounds per cubic foot, a particular wing loading
> will
> > > have
> > > > the same flying characteristics at the same speed, regarless of the
> > > airplane
> > > > size.
> > > > We want our models to fly and land a lot slower than the big ones, so
> we
> > > need
> > > > our wing loadings to be much less than those of big airplanes.  The
> big
> > > ones
> > > > fly smoother, of course.
> > > > Here's how to calculate true wing loading in any size airplane, from a
> > > > ***-band-powered "peanut" to a giant scale model:
> > > > Take the wing area given on the plans (560 square inches, for example)
> and
> > > > multiply it by 2/3 the height of the average size rib (technically,
> the
> > > "mean
> > > > chord") in the wing (our rib was 1.25 inches high at the spar, so 22/3
> is
> > > .834
> > > > inches).
> > > > Use 2/3 of the height of the rib because the typical wing rib is 2/3
> the
> > > area
> > > > of a rectangle drawn around it, and the wing volume is thereby reduced
> > > from
> > > > what you would expect just using  the real height of the rib times the
> > > wing
> > > > area.  If the wing is not tapered, you can use any rib, because they
> are
> > > all
> > > > the same size.
> > > > The result (560 x .834 = 467) is the wolume of the wing in cubic
> inches,
> > > so
> > > > divide by 1728 (the number of cubic inches in a cubic foot) to get
> cubic
> > > feet
> > > > of wing.  This gives you 0.27 cubic feet (467/1728 = .27).  Multiply
> by 25
> > > > pounds (per cubic foot) for comfortable loading and you get 6.75
> pounds
> > > (.27 x
> > > > 25 = 6.75).  That should be the maximum weight of your airplane.
> > > > Wasn't that easy?  This calculation will tell you a lot about the
> flying
> > > > characteristics of your model before it ever leaves the ground.
> > > > This process, by the way, explains why biplanes are usually considered
> to
> > > have
> > > > only 75% of theirrr wing area available for use in the "square inch"
> wing
> > > > loading calculations.  The wing ribs in a biplane are much smaller
> than
> > > those
> > > > in a monoplane of the same wing area.  This simply reduces the wing
> > > volume/wing
> > > > area ratio in a biplane, and consequently makes it a less efficient
> lifter
> > > of
> > > > weight.  It isn't some arcane "interference"; it's just low wing
> volume.
> > > > A reasonable wing loading is 25 pounds per cubic foot of wing for a
> scale
> > > > fighter of for a model of any powerful airplane.  Here are some other
> > > general
> > > > guidelines to wing loading"  15 pounds per cubic foot is a "floater"
> in
> > > any
> > > > size; 20 pounds per cubic foot is a sporty flier; and 30 pounds per
> cubic
> > > foot
> > > > is demanding!
> > > > I tried 35, several times.  It can be done, but it takes a lot out of
> you,
> > > and
> > > > a lot out of your wallet.  It doesn't do your pride any good, either.
> > > > It also takes a lot of really smooth runway, and runways are like
> money:
> > > > there's never enough, and what there is, you've used already.

> > --
> > Cliff Griffin
> > Remove the obvious for no spam.

--
Cliff Griffin
Remove the obvious for no spam.
 
 
 

***Finding the True Wingloading of any plane!!!!!!!*****

Post by Jeff Rei » Mon, 04 Oct 1999 04:00:00


Quote:
> True wing loading is calculated in weight per cubic foot of wing volume

The problem with all of these methods is trying to come up with a
"universal" method for determining the proper wing loading for a plane
or glider. There doesn't seem to be any simple solution. Size, weight,
targeted speed range, and air foil all seem to need to taken into
account for determining the proper wing loading.

Using wing volume is too sensitive to air foil thickness. Doubling
the thickness of a wing won't let you double the weight of a plane
and have it fly the same (even though it doubles the volume of a wing).

S&E modeler had a similar approach, they just raised the area to the
power 1.5 to determine "wing loading", so that it had a "cubic" factor,
instead of a "square" factor. This still didn't work in a lot of
cases, the author suggested maybe rasing the area to 1.6 or 1.7 might
give more accurate results.

Part of the problem is "scale factor", a  1/4 scale model displaces
1/64th of the volume of a full scale, but normally will weigh much
less than 1/64th of the weight of the full scale aircraft (with the
exception of some very light full scale aircraft). Typically the
model will fly at scale (1/4) speed or faster.

The only cases where the S&E article's "cubic" based wing loading
factor seems to get close is when the scale model has "scale weight".

 
 
 

***Finding the True Wingloading of any plane!!!!!!!*****

Post by Jeff Rei » Mon, 04 Oct 1999 04:00:00


Quote:
>True wing loading is calculated in weight per cubic foot of wing volume

When a wing produces lift, a pressure differential is created (and
air is accelerated downwards, mostly from above the wing, I'm not going
to get into which is the cause and which is the effect), and the
average pressure differential, times the area of the wing equals
the total lift from the wing. Note that pressure or pressure
differential is stated as a force per unit area, so it makes since
that wing loading would also be stated as a force per unit area.

Since in stable flight, lift equals weight, you can simply divide
a planes weight by the wing area to determine wing loading.

Given a certain wingspan / size and airfoil, wing loading can be
used to determine the speed range of a plane or glider, so
wing loading is useful for comparing similar models.

 
 
 

***Finding the True Wingloading of any plane!!!!!!!*****

Post by Craig Greenin » Mon, 04 Oct 1999 04:00:00


I think perhaps you misunderstood the context of Ty's reference to MAC. He
inferred that it be used as the chord length in a tapered wing, not as any
reference to the height of the rib.

Craig.


Quote:
> Still would like to see some text book references or something.  As far as
I
> know, the aviation industry, of which we are a "small" part, is still
using
> lbs/sq. ft.  Sorry, but it's a new concept to me.  However I am open to
new
> ideas.  May main reason for reply was the part about chord and rib height.

> -Mark :)



> > There was a similar article in one of the recent S&E Modeler magazines.
> > (Sailplane and electric...) Anyway, the author was trying to demonstrate
> > this same concept. When he brought his new glider to the club with
> > 26oz/sq', he was laughed at for having such a huge wing loading.
> > However, it was on par for the size of it. He compared the wing loading
> > of his little 50" glider with this large one and a full sized glider.
> > Using the cubic method, the wing loading on all three gliders came
> > within a few percent percent of each other, and supposedly flew
> > appropriately.


> > > "Mean Chord" or "Mean Aerodynamic Chord" means the average distance
from
> the
> > > leading edge to the trailing edge of the wing (in a constant chord
wing
> this
> > > is pretty easy to figure, tapered wings require you take into account
> the
> > > average).  IT HAS SQUAT TO DO WITH THE HEIGHT OF THE RIB!!!!!  Which
> makes
> > > me think the rest of the "artical" is just as bogus!  Would like to
see
> some
> > > references!

> > > -Mark



> > > > Here is a copy of any artical that was published back in 1992. It
has
> the
> > > > formula to calculate the wing loading of  "any" size plane. It is
> pretty
> > > long
> > > > so be patient.
> > > > Hope this helps everyone.
> > > > Ty

> > > >   True wing loading is calculated in weight per cubic foot of wing
> volume
> > > (
> > > > justlike the hull displacement in a boat ). Most people discuss it
in
> > > ounces
> > > > per squarefoot. That doesn't work, which is why ppeople usually
> qualify it
> > > by
> > > > saying that a big airplane can have a heavier wing loading than a
> small
> > > one.
> > > > If you always use pounds per cubic foot, a particular wing loading
> will
> > > have
> > > > the same flying characteristics at the same speed, regarless of the
> > > airplane
> > > > size.
> > > > We want our models to fly and land a lot slower than the big ones,
so
> we
> > > need
> > > > our wing loadings to be much less than those of big airplanes.  The
> big
> > > ones
> > > > fly smoother, of course.
> > > > Here's how to calculate true wing loading in any size airplane, from
a
> > > > ***-band-powered "peanut" to a giant scale model:
> > > > Take the wing area given on the plans (560 square inches, for
example)
> and
> > > > multiply it by 2/3 the height of the average size rib (technically,
> the
> > > "mean
> > > > chord") in the wing (our rib was 1.25 inches high at the spar, so
22/3
> is
> > > .834
> > > > inches).
> > > > Use 2/3 of the height of the rib because the typical wing rib is 2/3
> the
> > > area
> > > > of a rectangle drawn around it, and the wing volume is thereby
reduced
> > > from
> > > > what you would expect just using  the real height of the rib times
the
> > > wing
> > > > area.  If the wing is not tapered, you can use any rib, because they
> are
> > > all
> > > > the same size.
> > > > The result (560 x .834 = 467) is the wolume of the wing in cubic
> inches,
> > > so
> > > > divide by 1728 (the number of cubic inches in a cubic foot) to get
> cubic
> > > feet
> > > > of wing.  This gives you 0.27 cubic feet (467/1728 = .27).  Multiply
> by 25
> > > > pounds (per cubic foot) for comfortable loading and you get 6.75
> pounds
> > > (.27 x
> > > > 25 = 6.75).  That should be the maximum weight of your airplane.
> > > > Wasn't that easy?  This calculation will tell you a lot about the
> flying
> > > > characteristics of your model before it ever leaves the ground.
> > > > This process, by the way, explains why biplanes are usually
considered
> to
> > > have
> > > > only 75% of theirrr wing area available for use in the "square inch"
> wing
> > > > loading calculations.  The wing ribs in a biplane are much smaller
> than
> > > those
> > > > in a monoplane of the same wing area.  This simply reduces the wing
> > > volume/wing
> > > > area ratio in a biplane, and consequently makes it a less efficient
> lifter
> > > of
> > > > weight.  It isn't some arcane "interference"; it's just low wing
> volume.
> > > > A reasonable wing loading is 25 pounds per cubic foot of wing for a
> scale
> > > > fighter of for a model of any powerful airplane.  Here are some
other
> > > general
> > > > guidelines to wing loading"  15 pounds per cubic foot is a "floater"
> in
> > > any
> > > > size; 20 pounds per cubic foot is a sporty flier; and 30 pounds per
> cubic
> > > foot
> > > > is demanding!
> > > > I tried 35, several times.  It can be done, but it takes a lot out
of
> you,
> > > and
> > > > a lot out of your wallet.  It doesn't do your pride any good,
either.
> > > > It also takes a lot of really smooth runway, and runways are like
> money:
> > > > there's never enough, and what there is, you've used already.

> > --
> > Cliff Griffin
> > Remove the obvious for no spam.

 
 
 

***Finding the True Wingloading of any plane!!!!!!!*****

Post by Jeff Rei » Mon, 04 Oct 1999 04:00:00


Quote:
> I think perhaps you misunderstood the context of Ty's reference to MAC. He
> inferred that it be used as the chord length in a tapered wing, not as any
> reference to the height of the rib.

The original post mentioned wing volume, and talked about a "rib height" of
1.25 inches", but it also mentioned "mean chord" which would be something
different (I haven't seen very many models with a mean chord of 1.25 inches),
and not the volumne of a wing, so maybe the original post was a bit confusing:

Quote:
>>True wing loading is calculated in weight per cubic foot of wing volume
>>Here's how to calculate true wing loading in any size airplane
>>Take the wing area given on the plans (560 square inches, for example)
>>and multiply it by 2/3 the height of the average size rib (technically,
>>the "mean chord") in the wing (our rib was 1.25 inches high at the spar

Going back to the S&E article, as previously posted, even "cubic wing
loading" didn't factor down well unless the partial scale model had
partial scale weight.

Part of the problem is that air doesn't scale. The air molecules that a
model and full scale aircraft fly through remain the same size and mass.
If a model gets small enough, the air "gets sticky", surface friction
(as opposed to drag) becomes an issue for small models. At slower
speeds, and/or wing chords (smaller Reynolds numbers), airfoils become
less efficient (more drag for the same lift).

 
 
 

***Finding the True Wingloading of any plane!!!!!!!*****

Post by Ib Therkelse » Tue, 05 Oct 1999 04:00:00


Quote:

>  Here is a copy of any artical that was published back in 1992. It has the
> formula to calculate the wing loading of  "any" size plane. It is pretty long
> so be patient.
> Hope this helps everyone.

Some details and calculations concerning wing loading, scale effects,
Reynolds numbers, etc at:

http://blue.imbg.ku.dk/~ib/scalespeed.html

Regards
Ib Therkelsen

 
 
 

***Finding the True Wingloading of any plane!!!!!!!*****

Post by Marker Beaco » Tue, 05 Oct 1999 04:00:00


It's probably not going to make yours or mine airplane fly any better with
or without this "knowledge"

And, some people don't know chord from rope,

-Mark


Quote:
> I think perhaps you misunderstood the context of Ty's reference to MAC. He
> inferred that it be used as the chord length in a tapered wing, not as any
> reference to the height of the rib.

> Craig.



> > Still would like to see some text book references or something.  As far
as
> I
> > know, the aviation industry, of which we are a "small" part, is still
> using
> > lbs/sq. ft.  Sorry, but it's a new concept to me.  However I am open to
> new
> > ideas.  May main reason for reply was the part about chord and rib
height.

> > -Mark :)



> > > There was a similar article in one of the recent S&E Modeler
magazines.
> > > (Sailplane and electric...) Anyway, the author was trying to
demonstrate
> > > this same concept. When he brought his new glider to the club with
> > > 26oz/sq', he was laughed at for having such a huge wing loading.
> > > However, it was on par for the size of it. He compared the wing
loading
> > > of his little 50" glider with this large one and a full sized glider.
> > > Using the cubic method, the wing loading on all three gliders came
> > > within a few percent percent of each other, and supposedly flew
> > > appropriately.


> > > > "Mean Chord" or "Mean Aerodynamic Chord" means the average distance
> from
> > the
> > > > leading edge to the trailing edge of the wing (in a constant chord
> wing
> > this
> > > > is pretty easy to figure, tapered wings require you take into
account
> > the
> > > > average).  IT HAS SQUAT TO DO WITH THE HEIGHT OF THE RIB!!!!!  Which
> > makes
> > > > me think the rest of the "artical" is just as bogus!  Would like to
> see
> > some
> > > > references!

> > > > -Mark



> > > > > Here is a copy of any artical that was published back in 1992. It
> has
> > the
> > > > > formula to calculate the wing loading of  "any" size plane. It is
> > pretty
> > > > long
> > > > > so be patient.
> > > > > Hope this helps everyone.
> > > > > Ty

> > > > >   True wing loading is calculated in weight per cubic foot of wing
> > volume
> > > > (
> > > > > justlike the hull displacement in a boat ). Most people discuss it
> in
> > > > ounces
> > > > > per squarefoot. That doesn't work, which is why ppeople usually
> > qualify it
> > > > by
> > > > > saying that a big airplane can have a heavier wing loading than a
> > small
> > > > one.
> > > > > If you always use pounds per cubic foot, a particular wing loading
> > will
> > > > have
> > > > > the same flying characteristics at the same speed, regarless of
the
> > > > airplane
> > > > > size.
> > > > > We want our models to fly and land a lot slower than the big ones,
> so
> > we
> > > > need
> > > > > our wing loadings to be much less than those of big airplanes.
The
> > big
> > > > ones
> > > > > fly smoother, of course.
> > > > > Here's how to calculate true wing loading in any size airplane,
from
> a
> > > > > ***-band-powered "peanut" to a giant scale model:
> > > > > Take the wing area given on the plans (560 square inches, for
> example)
> > and
> > > > > multiply it by 2/3 the height of the average size rib
(technically,
> > the
> > > > "mean
> > > > > chord") in the wing (our rib was 1.25 inches high at the spar, so
> 22/3
> > is
> > > > .834
> > > > > inches).
> > > > > Use 2/3 of the height of the rib because the typical wing rib is
2/3
> > the
> > > > area
> > > > > of a rectangle drawn around it, and the wing volume is thereby
> reduced
> > > > from
> > > > > what you would expect just using  the real height of the rib times
> the
> > > > wing
> > > > > area.  If the wing is not tapered, you can use any rib, because
they
> > are
> > > > all
> > > > > the same size.
> > > > > The result (560 x .834 = 467) is the wolume of the wing in cubic
> > inches,
> > > > so
> > > > > divide by 1728 (the number of cubic inches in a cubic foot) to get
> > cubic
> > > > feet
> > > > > of wing.  This gives you 0.27 cubic feet (467/1728 = .27).
Multiply
> > by 25
> > > > > pounds (per cubic foot) for comfortable loading and you get 6.75
> > pounds
> > > > (.27 x
> > > > > 25 = 6.75).  That should be the maximum weight of your airplane.
> > > > > Wasn't that easy?  This calculation will tell you a lot about the
> > flying
> > > > > characteristics of your model before it ever leaves the ground.
> > > > > This process, by the way, explains why biplanes are usually
> considered
> > to
> > > > have
> > > > > only 75% of theirrr wing area available for use in the "square
inch"
> > wing
> > > > > loading calculations.  The wing ribs in a biplane are much smaller
> > than
> > > > those
> > > > > in a monoplane of the same wing area.  This simply reduces the
wing
> > > > volume/wing
> > > > > area ratio in a biplane, and consequently makes it a less
efficient
> > lifter
> > > > of
> > > > > weight.  It isn't some arcane "interference"; it's just low wing
> > volume.
> > > > > A reasonable wing loading is 25 pounds per cubic foot of wing for
a
> > scale
> > > > > fighter of for a model of any powerful airplane.  Here are some
> other
> > > > general
> > > > > guidelines to wing loading"  15 pounds per cubic foot is a
"floater"
> > in
> > > > any
> > > > > size; 20 pounds per cubic foot is a sporty flier; and 30 pounds
per
> > cubic
> > > > foot
> > > > > is demanding!
> > > > > I tried 35, several times.  It can be done, but it takes a lot out
> of
> > you,
> > > > and
> > > > > a lot out of your wallet.  It doesn't do your pride any good,
> either.
> > > > > It also takes a lot of really smooth runway, and runways are like
> > money:
> > > > > there's never enough, and what there is, you've used already.

> > > --
> > > Cliff Griffin
> > > Remove the obvious for no spam.

 
 
 

***Finding the True Wingloading of any plane!!!!!!!*****

Post by Mike » Tue, 05 Oct 1999 04:00:00


With all due respect, your 'article' is absolute RUBBISH.  Wing loading IS force per AREA
... NOT volume!

To compare winging loading of a model to a the full scale equivalent, it is SIMPLY the
scale factor times the loading.  With 'X' as the scale factor, force is a cubic in scale;
area is square in scale; force/area --- (X^3)/(X^2) = X    A 1/5 scale airplane will have
1/5 the wing loading. How's THAT for 'easy'?

Go get an real article on the subject if don't believe me. I'm pulling from one written
by  Thomas Purcell EAA 143338 entitled "Scale Aircraft Factors" September 1981.  Much of
his article relied upon work by Ernest G. Stout "Modeling of High Speed Watercraft"
Journel of The Aeronautical Sciences, 1950.  All straight up stuff.

What 'article' is yours anyway?  Who wrote it? Where did you find it?  Why didn't you
state any of this information? Did YOU write it?

Quote:

>  Here is a copy of any artical that was published back in 1992. It has the
> formula to calculate the wing loading of  "any" size plane. It is pretty long
> so be patient.
> Hope this helps everyone.
> Ty

>   True wing loading is calculated in weight per cubic foot of wing volume (
> justlike the hull displacement in a boat ). Most people discuss it in ounces
> per squarefoot. That doesn't work, which is why ppeople usually qualify it by
> saying that a big airplane can have a heavier wing loading than a small one.
> If you always use pounds per cubic foot, a particular wing loading will have
> the same flying characteristics at the same speed, regarless of the airplane
> size.
>         We want our models to fly and land a lot slower than the big ones, so we need
> our wing loadings to be much less than those of big airplanes.  The big ones
> fly smoother, of course.
>         Here's how to calculate true wing loading in any size airplane, from a
> ***-band-powered "peanut" to a giant scale model:
>         Take the wing area given on the plans (560 square inches, for example) and
> multiply it by 2/3 the height of the average size rib (technically, the "mean
> chord") in the wing (our rib was 1.25 inches high at the spar, so 22/3 is .834
> inches).
>         Use 2/3 of the height of the rib because the typical wing rib is 2/3 the area
> of a rectangle drawn around it, and the wing volume is thereby reduced from
> what you would expect just using  the real height of the rib times the wing
> area.  If the wing is not tapered, you can use any rib, because they are all
> the same size.
>         The result (560 x .834 = 467) is the wolume of the wing in cubic inches, so
> divide by 1728 (the number of cubic inches in a cubic foot) to get cubic feet
> of wing.  This gives you 0.27 cubic feet (467/1728 = .27).  Multiply by 25
> pounds (per cubic foot) for comfortable loading and you get 6.75 pounds (.27 x
> 25 = 6.75).  That should be the maximum weight of your airplane.
>         Wasn't that easy?  This calculation will tell you a lot about the flying
> characteristics of your model before it ever leaves the ground.
>         This process, by the way, explains why biplanes are usually considered to have
> only 75% of theirrr wing area available for use in the "square inch" wing
> loading calculations.  The wing ribs in a biplane are much smaller than those
> in a monoplane of the same wing area.  This simply reduces the wing volume/wing
> area ratio in a biplane, and consequently makes it a less efficient lifter of
> weight.  It isn't some arcane "interference"; it's just low wing volume.
>         A reasonable wing loading is 25 pounds per cubic foot of wing for a scale
> fighter of for a model of any powerful airplane.  Here are some other general
> guidelines to wing loading"  15 pounds per cubic foot is a "floater" in any
> size; 20 pounds per cubic foot is a sporty flier; and 30 pounds per cubic foot
> is demanding!
>         I tried 35, several times.  It can be done, but it takes a lot out of you, and
> a lot out of your wallet.  It doesn't do your pride any good, either.
>         It also takes a lot of really smooth runway, and runways are like money:
> there's never enough, and what there is, you've used already.

 
 
 

***Finding the True Wingloading of any plane!!!!!!!*****

Post by Jeff Rei » Tue, 05 Oct 1999 04:00:00


Quote:
> To compare winging loading of a model to a the full scale equivalent, it is SIMPLY the
> scale factor times the loading.  With 'X' as the scale factor, force is a cubic in scale;
> area is square in scale; force/area --- (X^3)/(X^2) = X    A 1/5 scale airplane will have
> 1/5 the wing loading. How's THAT for 'easy'?

The reason force is a cubic is that the force is the weight, which is proportional
to the volume, so it would be cubic. The problem is that many scale models are a
lot lighter than the X^3 factor.
 
 
 

***Finding the True Wingloading of any plane!!!!!!!*****

Post by Mike » Wed, 06 Oct 1999 04:00:00


The answer is balsa wood.

Consider that an an ant can carry many times its own weight and that hippos spend most of their
time in the water because they weigh so much. Basically, the 'materials' for animals don't
differ dramatically in strength.

If you made the model with the same material as the full scale and made all the parts to scale
- it would weigh  x^3 the FS weight.  The resulting model would be incredibly stronger - much
stronger than needed ... more like that ant.

Quote:

> > To compare winging loading of a model to a the full scale equivalent, it is SIMPLY the
> > scale factor times the loading.  With 'X' as the scale factor, force is a cubic in scale;
> > area is square in scale; force/area --- (X^3)/(X^2) = X    A 1/5 scale airplane will have
> > 1/5 the wing loading. How's THAT for 'easy'?

> The reason force is a cubic is that the force is the weight, which is proportional
> to the volume, so it would be cubic. The problem is that many scale models are a
> lot lighter than the X^3 factor.