Hi,

Well I am sure that everything is OK due to all of the calculations I have done- but I am getting a little paranoid. Here is a picture of the fuselage in the early stages of drawing- can you guys please tell me if the dimensions look all right (such as the tail and nose arm lengths)? To me it looks ok, and the formulae seem happy with the dimensions to- but since I don't have a lot of experience in making aircraft, I cannot say if in practice the fuselage looks correctly sized. If you are wondering what the plane is meant to be able to perform and overall what kind of plane it will be, go to www.airwayaircraft.webs.com and subscribe for free if you like the website. Again, please comment on what you think of the fuselage. Thanks (all dimensions are in inches by the way).

Sincerely,

Lafayette.

PS. Send an email to [email protected] if you would like a 3d file for a closer look- if so please mention in what format you want it, I work in AutoCAD 2007

Nose moments are mostly for balancing. Commenting on the tail moment would be useless without knowing details about your wing and horizontal tail. The length really depends on the details of the horizontal tail and the area and chord of the wing.

A site that does all the computations for you is worth using. http://www.geistware.com/rcmodeling/cg_super_calc.htm

da Rock,

www.airwayaircraft.webs.com has a picture gallery with more information on the dimensions of the airplane than you will ever need. Here are some, I hope that is sufficient for a statement whether the fuselage is OK:

wing area= 2.719 ft^2
wing chord= 0.6145 ft
wing span= 4.425 ft

horizontal tail area= 0.2156 ft^2
horiontal tail chord= 0.2156 ft
horizontal tail length= 1 ft
horizontal tail volume coefficient= 0.3 (normal for light single engined aircraft according to one of my aerodynamics books)

veritcal tail area (not needed for a judgement but I'll just say it)= 0.5156 ft^2

static margin= 12% (distance between CG and neutral point divided by CG distance aft of the wing quarter-chord)

maneuver point= 13.2%

tail arm= 2.333 ft

Here are some dimensions

Sincerely,

Daniel.

Daniel,

What is the plane going to be used for? Fuselage length is not really critical except in special applications like aerobatics. A flying wing is a perfect example. No fuselage at all. If you get the C.G. correct on the wing, and the wing/tail incidences correct, the plane will fly. How it maneuvers will be another story. My dad used to say, "If it looks like it will fly, it will fly." I think your fuselage looks fine. Just watch the C.G.

pmw

I'm not seeing and further drawings in your gallery. Either that or I'm not getting access to them. Just the pictures of your calculations.

If this thread related to your glider project then I'd have to say that the fuselage looks far too short unless you're intending to install an electric motor up front. Also the fuselage tail length needs to be determined in a way that relates to the tail volume coefficient. Taken in isolation like this all I can say is that unless there's a big lump of weight up front on that first bulkhead then your model's nose is too short.

Keep in mind too that for reynolds number scale reasons it is always best to use a horizontal tail surface that has a smaller aspect ratio than the wing has. A good round number is that the tail should be about 2/3 and certainly no more than 3/4 the wing's aspect ratio. The apparent small tail chord would seem to indicate that you may not be going down that path. The reason for doing it that way is to help avoid the tail stalling out and losing it's influence on the wing.

Guys,

Everything is said on my sight. B matthews, yes there will be a 50 gram electric motor (battery also installed forward of CG, estimated total weight of plane 500 grams) installed up front on te glider- and yes the horizontal tail area was detemrined according to the tail volume coefficient- as I said it is 0.3.The horizontal tail aspect ratio is 4.6, while the wing aspect ratio is 7.201- whic makes the tail aspect ratio 3/5 of the wing spect ratio. The horizontal tail area is 0.2156 ft^2 and it is an all moving horizontal tail, and the wing area is 2.719 ft^2. What I am asking is that not too small of an elevator area (which is the horinzontal tail fin area because it is an all moving tail) for a plane with a wingspan of 4.425 ft and a length of about 2.9 feet (sinject to change) with a tail arm of 2.333 ft?

I am asking this not because I guessed the size for the horizontal fin, I did a lot of calculations for it, but because there is one formula that I ahve never used before which is suposed to tell me the required elevator deflection at any lcoation of the CG along the wingchord- which tells me that elevator deflections required are greater than 80 degrees except for one location where the CG if 15% back from the wing quarter chord; at this lcoation the required deflections range between 35 and -30 degrees. Now, there is no problem in locating the CG there, except for that a week ago a friend of mine told me that for a NACA 2312 I am using the max rearward CG possible is 10% back from the wing quarter chord. So, this is just theory and should I ignore it and just lcoate the CG at 15% back?] Will that be OK to fly?

Sincerely,

Daniel.

Your freind is wrong. With a high enough tail volume the CG could be on the wing's trailing edge or even further back. Mind you by that time the plane would look more like a tandem wing design....

I didn't bother to look at all the other numbers. I'm just not big on math until the general arrangement drawing is done and then I run some numbers to justify what I want the design to look like rather than do the numbers at the beginning. A 3 view sketch with the dimensions would make it much easier to see all the numbers at a glance and determine how they all fit together. One decision affects a lot of others and seeing a small scale drawing with the dimensions makes it easier to see if it looks about right before diving into the math for details. For example, off the top of my head your stabilizer area seems a little small at around .22 sq ft with 2.7 sq ft of wing. A longer tail can compensate for that but it implies such a long tail that the model will look rather ungainly and the tail boom may come out rather weak unless it's too heavy. A few years back gliders typically had spans that were 2.5 times the fuselage length. More recently more designers are going with spans that are 1.8 to 2.0 times the fuselage length. I like the newer numbers as they produce models that are more responsive to rudder-elevator setups and tend to be more stable in the thermal turns. At least that's what I've found with a couple I've flown with longer tail moments. But it's easy to end up with something really odd looking if you take this trend to extremes. Again a general 3 view sketch done to scale (CAD?) will help with this and help us to help you.

The case where your numbers call for an 80 degree deflection of your stabilator clearly shows that you've got some serious issues or you asked for an amount of control authourity that is far more in keeping with a 3D aerobatic design than for a soaring model. The only way the equation would call for that is if the stabilizer is MUCH too small or you put a decimal in the wrong place somewhere. No sailplane would ever need that amount of deflection for normal flying. 8 degrees would be more like it and very typical.