Hi!

I'm new to the topics of flying wing, and I had my friend over here today, he was scratch building a plane of his own, so I though I make myself a project just to have something to do.
So I found an intact semisymmetric wing within the wreckage of an old hotliner, and I thought "Hey! Lets make a flying wing!"

But I know next to nothing about flying wings, so I have to ask:
Where shall CG be? This wing is a "plank", semisymmetric profile, so shall CG be where it would have been if it still had a fuselage attached to it?

And secondly, I know flying wings shall have reflexed airfoils. Obviously this wing doesn't, so I thought I would be a real cheapskate and just make this reflex by offsetting the neutral point of the elevons. But how much?

Edit:

Found it!
http://www.mh-aerotools.de/airfoils/flywing1.htm

It will in a flyable range at 10-15% MAC.

Add 2 "cool looking" wingtip fins and possibly a central fin if you like and program the elevons so that there is more "elevator" movement and not very much "aileron" movement. Have dual rates set up to give yourself an emergency option if you guess wrong on the set up....but there is no need for dual rates once you get the elevon movement and the CG figured out to your liking.

Flying wings do not need reflexed airfoils. I have built and flown several wings in the .049 to .50 size range and they only need the slightest amount of up trim to fly level. The faster they go and the lighter they are, the less up trim is needed.
Set the elevons dead neutral and let the airplane tell you how much "reflex" is needed while you trim it out.

Thank you!

How about motor alignment, is that very important?
Its tempting to just strip the motor onto the wing, but will the off-thrust set off the wing aswell?
I see most wings has the thruster dead centre in the rear, but not all wings.
But those where the motor is off center typically has sweep. Mine doesn't.

Hello Von Ohain
I have been flying my Flying Wing for about one year. The motor thrust is as close to being on center as possible. I would move it up at least 1/2 inch, for more prop-to-ground clearance, on my next one. Mine could have used a little more power. Occasionally it would stall at the top of a loop. Since it was not very acrobatic, and would occasionally nose over on landing I recently converted it to a twin boom pusher plane. Search for a Center of Gravity Calculator for a Flying Wing. I have seen MANY flying wings crash on the first flight because of the CG being wrong. I put landing gear on mine to minimize that.

If the engine is mounted on the centerline of the wing, make it 0-0 with the wing. Make sure that you do not have ANY left thrust. Some guys will put in a tiny amount of right thrust just to be sure that there is no left thrust.
Launch the plane with the plane tilted with the right wing low.
Launch it fairly level and allow the plane to build up some speed in the first critical second.
Before you try to fly it....Look the plane over from the rear holding the plane at a full arm's length from your eyes.
Scan the entire trailing edge for "trueness"...no warps or twists. Look for perfect symmetry.

Thrust angles can be a little bit off before you will notice a huge difference in how it flies...but left thrust is NO good.

If it has inboard flaps you can angle those up for some reflex. Or if the wing uses strip ailerons simply angle the strips up by around 5 degrees. If it uses outboard ailerons with no inboard flaps I'd suggest adding some reflex by glueing a strip of something thin and stiff enough to avoid bending from the air to the lower surface for the whole span such that it extends behind the present trailing edge by about 7 to 8% of the wing chord with an upward angle that is inline with the lower surface. This reflex "tab" will do much to reduce the amount of elevon up trim you need to achieve stable flight.

Until you find the trim point this model is going to be totally viscious in the pitch department. You WILL WANT to find a field with the proverbial 3 foot tall grass and do your first flight launches over that padding.

A small short fuselage below the wing would be by far the best way to go. It'll give you a hand hold for launching as well as a place to mount the motor and with a short stub behind the wing's trailing edge a place to mount a really big fin and possibly a rudder if you want to include one. A small fuselage like this will also let you install the flight battery and receiver in the "pod" instead of cutting into the wing more than it is now. A plank style wing really doesn't work well just with tip fins unless they are located towards the rear and swept back radically to move the vertical side area as far behind the CG point as possible. A short fuselage that puts a big centeral fin behind the wing by even a little is actually a common and better way to go.

Because of CG issues I have already gone the route of a fuselage. But its not extending backwards.
It will be a battery compartment, and was necessary to bring CG far enough ahead.
Its still a bit rear heavy, plus, the motor is already mounted on the rear of the wing, so Im not too happy about the thought of extending the fuse backwards.
But if necessity calls for it, then...

I hadn't relized or noticed that you are mounting the motor on the trailing edge.

There are usually too many drawbacks to a rear mounted engine and not enough bonuses.

Here is a control line combat planes' wing converted to RC Flying Wing. As a C/L combat plane it was powered by a Fox .36....but for the RC conversion it is powered with a Super Tigre .15.
[link]http://youtu.be/6Uu8nqqhYxo[/link]

It took very little extra weight to do the conversion, all of the RC components are inside the wing.

The thought behind a rear mounted motor was just to be a real cheapskate.
I have stripsed the motor in place, and since the angles of the wing is closer to the chordline on the rear, than it it on the front of the wing, I stripsed the motor in place there.
If I shall mount the motor in front, I have to start cutting into the wing itself to make a motor mount, and things gets a lot more complicated.
Another thought that hit me was that IF I have to start cutting into the wing anyway, I might just as well chop it in two, cut the surfaces at an angle, and make it a swept wing.
That solves both CG issues, pitch stability issues and placement of fins, which has to be far enough to the rear.
Am I understanding this right?
Maybe thats the route to go, it is a bit of extra work, but it seems to solve a lot of problems in one go.

If you chop the wing into 2 pieces, you could make a thick central section like control line profile planes have. Similar to profile 3D planes also. Splicing the wing panels back together isn't too hard if you have a razor saw to inlay some spar "splints".
Make the center section long enough to extend past the elevons and you can use that to support a vertical fin and give yourself a built in "handle" for hand launching the plane.
Sweeping the wings will create work that you do not need to do. If you make the center section long enough to mount an engine and fuel tank behind it, the plane will most likely have enough forward weight.
Without seeing your project in person, it's hard to give solid advice about your planes' best layout.

Swept wing flying wings DO fly very well, but so do non-swept wings.
You can get them to flat spin and do neat looking tumbles without a working rudder.
I don't think highly swept wing flying wings are as capable of these aerobatics.

Here is another control line combat plane's wing converted to RC flying wing.
This was the maiden voyage and the controls were cranked up too high for a comfortable flight, but the model was made tame enough to fly nicely after some adjustments.[link=http://youtu.be/Pel5OwLHZ6E]Fox .36 Powered Wing[/link]

Thanks for your input.
Unfortunately, Im a man of action so I have already chopped up the wing and made a 12.5 degree sweep angle to it.
I saw this as the simplest solution to solve CG aswell as getting stabilizing fins far enough rear.
Because the plank wing was rear heavy no matter how I arranged it (without the forward fuselage).
This means I scrapped the forward fuselage also for now.

How much does what you have there weigh...?

It looks like it has about a 4 or 5 foot span...?

I think sweeping that wing was a good idea on your part, since it has a narrow chord.

You could build a "fan tail" platform in back of what you have there and use a seperate elevator flap for pitch control.

This is what I visualize.........

Make some nice winglets that blend into the outline and curvature of the wing.

The "fantail" deck will help strengthen the plane as well as provide a place to put the elevator.

Nice drawing combatpigg, I like the looks of that
Good solution to stabilizing fins by adding very neat winglets.
The fantail also looks nice, allthough I think making it will be quite a bit of work.
The wing was 1.6 meters span before I chopped it, so around 1.5 to 1.55 meters I guess it is now.
Quick & dirty guesstimating makes that 4.5 feet in my head. Your eye is well calibrated, seeing that from a picture

[link=http://youtu.be/iJ6PFphoyR0]BATOUTTAHELL!!![/link]
Here is a flying wing that a drawing by Bruce Mathews inspired me to build.
The engine is laid flat and the cowl is assymetric, but it makes the frontal area the least possible for a front engine model plane.

It is powered with a 1 cc engine.
It took a little bit of work to build, but that is part of the challenge of "modelling".

The fantail and fins, looks like some real good modifications.
They give the plane a bit more wing area aft shifting the COG, a separate elevator and aileron function, and winglets for stability and low drag.
With a swept wing the elevator response with elevons can be a bit interesting.

I'm not sure, but I think GOD was the first one to try this planform...?

Sorry my example doesn't really match your project but thought I might encourage you to hang with it. Nearly 19 years ago I started tinkering with this 80" one. Had a blast exploring and overcoming different design problems (started out as a tail dragger !). Started out with a K&B 60 but have used a Fox .74 for most of its life. Last year I installed a 1.20 4c but haven't got around to trying that config.
Certainly have to agree with CP about the very different looking and feeling manuvers possible. Coolest flight to date was when one aileron pulled free and was dangling by the pushrod. Made it down with no problem and had decent right and left turning ability!

How much does it weight with the Fox .74...?

I've thought it would be fun to have one that size for a gas burner.

Right now with the 120 it weighs right at 12 lbs. I lengthened the motor mount area and was able to get rid of alot of lead so it might just be a little lighter now than with the Fox. I've been tempted a few times to see how much weight it could fly with.

[link=http://youtu.be/o136RpOSUOU]FOX .36 WINGER[/link]

Here's another look at the Fox .36 powered plane after the CG was moved forward and control movement set for finer control.
Model does flat spins and pinwheels with no rudder.

I've always had good performance with a verical stabilizer with Rudder and Horizontal Stabilizer (T tail) or 2 verticals connected by an elevator (No stabilizer)