Wing help??

Homebuilt Aircraft & Kit Plane Forum

Help Support Homebuilt Aircraft & Kit Plane Forum:

StRaNgEdAyS

Well-Known Member
Joined
Oct 20, 2003
Messages
816
Location
Northern NSW Australia
Hey there all,
I know I am new to all of this, and I also know that this is the first time I have attempted to design and build a "big" plane of my own, as the only ultralight builds I have been involved with before have been out of a box.
So naturally I am taking every step very slowly and carefully.
I am trying out DesignFOIL, and it is very comprehensive, and I like it a lot, but I'm a little confused about my figures here.
I have put in the figures for my wing design, and heres what it came up with. (see attached Pic)
Airfoil NACA 0006-63
Span 24.93 ft
Root Chord 7.89 ft
Tip Chord 3.40 ft
LE sweep 30 deg
Oswald E. 0.9 (What exactly IS this? I'm guessing it is the efficiency factor, but like I said, I'm new to this side of things)
Speed 225 MPH
Altitude 1000 ft
Net weight of 640 Lbs (319 empty+321 load)
Angle of attack 2 deg (Is this the same as angle of incidence?)
The reynolds # was taken from the flight velocity
Ran the whole lot thru the wind tunnel, and got an interesting set of result, the most astonishing was the lift force of 4014.6 Lbs!!!
I'm not sure how this works yet, so I hope someone here can clear it up for me, but that seems like a awfully large amount of lift for a craft that is only designed to weigh 640Lbs fully loaded!
Incidentally, the stall speed generated of 42.3 MPH came VERY close to the initially calculated stall speed from AirplanePDQ of 41.5MPH
Like I said I am still in the experimental stage of the design, and I am learning the capabilities and limitations of the tools at my disposal.
This is all a learnig curve for me, as it is a FAR cry form knocking up a quick R/C model over a weekend, and it is sooo much more challenging than putting together a prefab plane. (not that I didn't enjoy that experience immensly:D)
Any input is greatly appreciated
Thanx
Pete.
 

Attachments

HeliDev

Well-Known Member
Joined
Jul 7, 2003
Messages
108
Hey man, by no means the most qualified here to help but I have this program.
Try to work out the reynolds No your self. I have noticed that sometimes it doesnt work well on the program.
I dont have the lift Coeff for that wing section so I cant work it out for you now.
Heres the formula,

L = Cl * 1/2(p.V^2) * S

L= total lift (in Newtons)
Cl = Lift Coeff (no units)
p = Rho, the density of the air, 1.225 @ sea level
S = total wing area
Use that formula and see if the sums work. My guess would be youre reynolds number is in error.
One other thing that I noticed is youre wing sweep of 30deg. May be a little high, especially for the speeds youre talking about, would consider dropping the sweep to 19 or so. At 30 deg you may pay a high is peanalty in induced drag.
Have fun.
 

orion

R.I.P.
Joined
Mar 2, 2003
Messages
5,800
Location
Western Washington
Several points to consider.

1) What your'e trying to do does require a certain level of understanding of aerodynamic priciples and design guidelines. If you don't have this background, you stand a very good chance of hurting yourself or at least spending a lot of time and money on something that in the end will not work at all. The very selections you made so far indicate that it would be a great idea for you to do a lot of reading before you really dive into this endeavor.

2) The airfoil you selected is awful from many standpoints. It is very thin (6%) thus you'll pay a substantial structural penalty. It has very poor lift-to-drag characteristics, a sharp stall and a very steep drag curve at high angles of attack, which results in extremely critical (fast drag rise with increased angle of attack) climb performance.

3) Contrary to the last post, sweep has nothing to do with induced drag. However, sweep will affect your structural weight and may give you a few surprises around stall.

4) Your last sentence is correct, this is a very steep learning curve, especially if you don't have the educational background and work experience to start from. The tools you are using have been designed for playing around with several variables however, they are not design tools, especially for the amateur. Failing to take into account even the basics, such as making sure you use three dimensional data for your airfoil selection instead of two dmensional, will cause you endless grief.

If you're willing to take a lesson from many who have tried to do this before, you'll find that the more you get into this cycle, the more you'll realize how much you don't know.

The purpose of this board is certainly to help each other with specific design and/or fabrication issues or ideas however, it is beyond the scope of its capabilities to design a whole airplane for you. I can comfortably say this since this is what I do for a living (www.oriontechnologies.net) and despite having done this for over twenty years now, I still run into issues from time to time that need input from others.

So, on one hand I'd encourage you to not get discouraged but on the other hand, I would strongly urge you to get help. Despite the initial overview of what's involved in designing an airplane (which tends to look relatively simple and straight forward), it is a relatively involved process that even for professionals takes a certain amount of time and effort.
 

StRaNgEdAyS

Well-Known Member
Joined
Oct 20, 2003
Messages
816
Location
Northern NSW Australia
Thank you for your input there Orion.
One thing I have learned over the years is, the more you learn, the more you realise you don't know :gig:
I am by no means discouraged, rather the opposite.
I very much relish the chance to expand my knowlege. I did drop by your site and had a read, and I found the piece on airfoil selection espescially interesting.
I did have concerns about the size of the foil I had selected for these initial tests, and I thought I would have to revise it somewhat. :D
I am off to do some more in depth reading, and also examine some existing designs to compare and correlate to what I learn from the books.
I have checked out the posts regarding appropriate and quality texts and I shall be placing an order for a few.
By the way I just got a copy of rhinoCAD, and I have to say, I am impressed!
I can see I will have many hours reading, drawing and reading some more. :cross: :ponder:
Thanks for the quality advice!
Much appreciated
Pete.
 
Top