flybug

I am trying to see if I can design something that will actually fly in order to enter the contest, but I am lost and need some pointers.
What do you start off with the wings or the fuse? I started with the wings (straight LE and a V shape TE) and now I wonder how you make a fuse to match 'em (low wing set up)? The program I am using asked if I wanted dihedral I entered one degree (and I can see it in the preview of the 3D wing), but how do you draw a brace that will give you one degree of dihedral or do you even need a brace for it? What determines the length/width of the fuse in relation to the wing, and how do you know how to cut out a saddle that will fit with the wing? Is there a way you can tell if the wing/airfoil will fly or if it is worth investing more time and resources? I have some figures as well but I don't really know if I am interpreting them properly (see below), I know there is a story to tell with these figures, but I don't think I can tell it properly. How do you determine what wood to use 1/16, 3/32, etc ( so far what I have done I am doing it as 1/16) Any ways I have tons more questions but let me start with these and I will post along as these get answered. I will also try to attach some screen shots. I am aiming for a 0.061 engine and 4ch.


Wing span 40" Aspect Ratio 8.82
Major chord 5.8125" MAC 4.65
Minor chord 3.25" 25% MAC distance 1.16
Wing area 181.25 ACD 9.06
Camber 2.03%

subarubrat

My Feedback: (1)

Wing saddle, what I do is lay the rib down on a sheet of paper and trace it then cut out the area where the rib was and there was my saddle template.

Will it fly.... My wife is a Embry Riddle graduate with top honors, we are both scientists in the space program, so you would think I would get real involved with the mathematics of the design, testing etc. I also went through what I call the school of Gonzo engineering where you add another pound of gunpowder, double the voltage, use fire and hit the damn thing. So my approach to designing a wing is to go mostly by gut feel and then go fly the thing. For the dihedral question, I like to use a block under on wing and get the angle right (usually by looking at it till it seems right) and then I CA it. Then I take a sheet of paper and trace out the center section of the spars (left and right) and then trasfer that to ply or whatever. I did something a bit different on my Hawk for the contest.

Aussie Damo

i do the saddle the same way, for the dihedral i place one half of the wing level on the table and the other end propped up using a block just touching the tip. the block is the exact hieght need for the angle which can be found usind the maths rule SOHCAHTOA

the rule goes as follow: H*Sine(angle)=O
where O is hieght of block (which you want to find out, in centimetres though), (angle) is angle of dihedral and H is half of wing span in centimetres.
yours comes out to 52*SIme(1) =?
?=.9 cm (about 11/32 of an inch)

Half-A-Hec

Fly Guy,

This how I designed the dihedral brace in auto-cad for my Re-V-amped wing. I got the dimensional length between the top and bottom spar of my wing. Then I drew a vertical line with that dimension. From the bottom of this line now draw a line at 0 degrees the length of one wing. Draw another line from the top of the vertical line in the same manner. Now determine the distance between the center rib and first rib and offset the center line by this distance. Now rotate the top, bottom, and first rib line about the bottom of the vertical line 1/2 a degree. Now mirror everything about the vertical line which represents the center of the wing. You can get dimensions to verify that all is right with the world. I hope this doesn't confuse ya. BTW my wing has 4 degrees so if the pic looks a little exaggerated that is why.


Hec

ptulmer

My Feedback: (5)

In compufoil, set a rib at the width of your fuselage. Use this rib to make your fuse cutout. This is a must with a tapered wing!

indoorff

My Feedback: (2)

For airfoil testing, nothing beats windtunnel data. Most, if not all of us, dont have access to a windtunnel, and the software Profili is the next best thing. You can use it as a simulated windtunnel and the data seems to be quite accurate, when compared with actual windtunnel data. You can test existing airfoils, or design your own, and get all the important plots, such as what angle of attack the airfoil will stall at, and what the stall will be like (ie sharp or gentle). You can get the software from http://www.profili2.com/

BMatthews

The airfoil shape you posted is generic enough that it'll fly just fine. Having a big noisy fan on the front covers up a lot of shortcomings....

What I do have an issue with is your choice of a higher aspect ratio on a 40 inch span model and a fairly strong taper to boot. This will reduce your reynolds numbers to the point that it may produce some nasty side effects. In particular at the tips where the airfoil there will tend to tip stall more easilly. For 1/2 A models you're far better off to stick to an aspect ratio of around 5 to 6 and keep the wing taper to no more than 0.7 to 0.8.

The only other thing that I'm surprised no one has mentioned is the holes in the ribs. Forget them. You'll gain very little in the lightness department and loose a lot in the strength. Save the weight in other areas or even just learn to pick your wood so that it's all less than 7 lb/cuft stock except where you need something for a specific purpose.

And all my designs generally start as a silly little doodle on some important piece of paper.... important to whom I'm not sure but it often has something about "memo" or "directive" on the top....

combatpigg

My Feedback: (3)

I guess if flybug holds the tip chord to about 4.5" and chooses 3/16x 3x16 balsa for the spars, and 3/32 for the ribs, he'll have a nice wing. You don't have to fully shear web between the spars, but a 1/2 inch wide strip of scrap 3/32" balsa adjacent to each inboard rib, spanning from the top to bottom spar goes a long way to strengthen the frame work, will keep the inner ribs from buckling during those high G pull outs. Oh, round off the root chord dimension to 6 inches [instead of 5.8757245"] too, this is carpentry, not machine work !!

flybug

Thanks for all the input so far. I managed to get my Aspect ratio down to 7.6, by changing the root and tip chord (6 and 4.5) as suggested, also added a sweep of 0.75, my total wing area now is 210. Still trying to figure out how to design a matching fuse.

combatpigg

My Feedback: (3)

Look at TOADs' thread [about getting back into 1/2A pylon], he has laid out the basic distances and dimensions that will work well with your wing and lead to a model that will balance well, slick looking fuselage he's got there, too.

BMatthews

That's better but still a bit high unless you're looking to make it a sort of powered glider or more of a trainer style of model.

As for fuselages you first need to get the tail area and distance from the wing right and then put in the rest of the stuff while more or less second guessing the balance point. Finally, after that's done, you draw in a fusealge shape that makes you smile.

flybug

Well I'm trying to build a low wing plane, more like a sport plane flying style, rather than a trainer (already have bipe's LST and a size 40 trainer ). So how can I lower the AR, and can I achieve that (sport plane flying style) with this wing design? If not what changes do I need to implement?

flybug

Well I shortened the WS to 30" and I ended up with AR of 5.70, Will have a fuse length of 25", stab area 31.50, and distance from wing 18" and looking for about 3 to 3-1/8" of fuse height

BMatthews

Cutting it down to 30 inches is probably a bit much in the other direction unless you're looking for a pretty racy airplane. For general sportflying bring it up to 34 to 36 inch span and increase the chords to provide around 200 sq inches (basically 36 x 6). With 30 and AR=5.7 your wing area is only 158 sq inches. Fine if you can keep things really light but a slightly larger model is a far better transition from the trainers and slower types you've flown so far.

combatpigg

My Feedback: (3)

A rule of thumb layout for a light weight 1/2A engine on a 2 foot long fuselage places the firewall 6-7 inches in front of the wings L.E.. Your wings' root chord of 6 inches leaves a remainder of 11-12 inches to the rearend. 36" of span will seem pretty sporty if you keep the weight of the model below a pound.