Saludos,

I have drawn my oun set of plans for this experimental model, the XP-54 Vultee but I can´t figure out yet how to determine the center of gravity.
I am posting the wing layout and the dimentions. Just hope some of you can give me a hand on this topic. I THINK one approach is to determine the CG on each "segment" of the wing but it´s just a guess...

Another mistery for me is that part of the wing that goes inside the fuselage... is this part considered on the "ecuation".

Un abrazo,

pó

The part in the fuselage is included in the wing area.

You can't find a CG location for JUST a wing. You need the tail area and distance between the wing and stabilizer. And for this application the wing and stabilizer both include the area of the ailerons and elevator.

Or are you trying to figure out the Mean Aerodynamic Chord? The MAC is sort of the same as the average chord but is more correct and represents the equivalent chord width and location as if it was a rectangular wing.

For both items there are online calculators available. Check the sticky threads at the top of this forum or the Designing and Scratch Building forum.

Xp-55 eh? A very interesting airplane and not one we see a lot. Best of luck with the project.

The dimension of the root is missing.

Could you add it?

Check this old thread:

http://www.rcuniverse.com/forum/m_87...tm.htm#8708615

Thanks for the information guys. I edited the wing layout already... it is 400mm at the root of the wing. Bmathews, you got me a bit confused about the extra data needed (tail area, wing/stabilizer distance, etc). I guess I´ll just have to do some more research on this.

I just finished the set of plans for the Vultee XP-54. It is 1:10 scale (cannot carry more than that in my car). Started this project one year ago when I fell in love with a book I got from amazon called "American Secret Pusher Fighters of World War II". After some search on the web I confirmed the plans were not available so I decided to go for it myself. It took four 32x48" and was my very first project of this nature.

The software I used: I began drawing with some crappy one I got called "modelmaker". Only the title of it got some substance so after a few dissapointments I turned my eyes to DevCad. It´s like working in autocad but much much easier and practical.

Promise I´ll get back to you when it´s done and ready to fly!!!

Here's a link that does the CG calculation for a multi panel wing like the one on your '55.

http://www.silentflight.net/index.ph...nt/view/24/45/

Don't mind that it's for a sailplane. The formulas are the same. For example distance S2 would be zero on the 55's wing.

Pollemix,

Great project!

How to determine the center of gravity for your model?

There are on-line calculators.

For a wing of this particular shape, you need to break it down in surfaces for which it is easier to calculate the area’s centroid.

I have attached five schematics that describe the graphic method.

You will obtain more than one area’s centroid (or aerodynamic center) and more than one mean aerodynamic chord (MAC) for one semi-wing.

Then, you will have to combine those into one equivalent AC and one equivalent MAC.
By definition, the equivalent AC will be located at 25% of the equivalent MAC.
That is the point where all the lift and drag created by your complex wing will act.

However, your model is more than two semi-wings; it has other surface that also creates lift and need to be considered.

You will need to determine the AC of the horizontal tail, in a similar manner.
For your model, it will be simpler, because the shape is a rectangle.

Next, you will calculate the neutral point (NP).
That is the point where the moments of both lifting forces get balanced.

Now you know where your limit for locating the CG is located.
That CG must be forward the NP for balanced flight.

The distance between the two points is selected by you, and it is called Stability Margin.
A margin of 20% of the equivalent MAC is a normal recommendation for the first flights.

All these calculations can be easily performed here:

http://adamone.rchomepage.com/cg2_calc.htm

http://www.geistware.com/rcmodeling/cg_calc.htm#cg

Regarding the second mystery for you, if the part of the wing that goes inside the fuselage is to be considered for the calculation:

I would say no, do not consider it, since I believe it does not create any lift.
However, several references and books say do consider it.

Note that I have performed my calculations considering this hidden area.
You could run your calculations excluding that area, and comparing the two CG locations.

Be aware that these calculations are only approximate, since many other surfaces of the model contribute to drag and lift, and that the final location of the CG will need to be determined for you during the first flights of your model.

Best luck building and flying it; just keep us updated!!

BMathews is right.
A WING on its own doesn't have a CG, you need to consider the Whole Aircraft.

The NP of a flying wing (Horten style) is around 25% of MAC

Add a H-stab and the NP of the combo moves back (see calculators mentioned)

but that big nose sticking way out in front in this case will move the NP of the Whole Aircraft forward a bit (maybe 5% of MAC???)

Don't forget to allow for the nose!

Is that a crimson skies airplane? You kow, from the video game?

It sort of looks like it doesn't it But no, it's an actual plane that was built as a prototype, tested and then passed over because the jets were on their way and promised so much more.

http://en.wikipedia.org/wiki/Vultee_XP-54

If you want to see some stuff that SHOULD be in Crimson Skies check out the links on that Wiki page for the XP-55 and XP-56. In these last two cases truth really was stranger than fiction.

A buddy of mine, "Flaps" Laffert, built one for us several years ago. It flew good, for a scale plane. As I recall, we eyeballed an average chord and used 25% back. Never changed anything.

I take that back, we did switch from a .91 4-stroke to a .91 2-stroke to get a little more power.

The WW II japanese had some of those babies with " USN carrier force " written on them when we were to invaded Japan. That style of plane caused the Germans to quickly develope a ejection seat .

Rich

Ed, looks like a bit of poetic license was taken on the color scheme. After all, a Vietnam style camo job on a plane that was only ever finished in bare metal for the testing phase then was abandoned?

I think the term "scale" has been used quite loosely here as well.

C/G GOES WITH THE WING. MOMENT IS A NEW TOPIC..