Noah-Moore

I'm looking at the advantages/disadvantages of forward swept wings. Looking at the advantages it seems that they would be ideal on a slope soarer. i.e. tips maintain aileron authority, good slow speed characteristics, and good manueverablity. Why then, don't we see more in "service". Would something like a FSW zagi work? I've got an old one that i thought about converting. Instead of normal assembly, i would cut the wing roots opposite what they are to make the wings sweep forward instead of back. Is this feasible?

Please any response to this or other issues on forward swept wings are welcome. Let's make this the place to discuss these issues.

thanks,
Noah

Ollie

It takes a lot of vertical tail volume (area times moment arm) to overcome the adverse yaw to roll and yaw instability of a forward swept wing. Forward sweep also complicates the design of the planform taper, twist and sweep to get an efficient lift distribution over a wide speed range. See:
http://aero.stanford.edu/WingCalc.html

However, it can be done. The full scale Genesis is a case in point. It is currently one of the top performing 15 meter sailplanes.

Cactus.

My Feedback: (1)

i have a plan for one of these... ( below )
if you go to northeast/west??? sail planes site you'll see another glider with a straight LE and a swept forward TE, i guess this has the same kind of effect as the tip vortices can only travel out, not forwards

found the link...
http://www.nesail.com/sailplanes.html

flailing

My Feedback: (1)

Don't forget the Blanik I have many hours in one, great flying sailplane.

Amazo

Had one 1/2 A size in Model Airplane News years ago for thier design contest.
Give it a try! I use Andy Lennon's book R/C Model Airplane Design for all tail size and balance questions. He can be a little anal about the "right way" but the info is good.

Wing: Span 60" Area 600 sq. in. Airfoil S3016
1/8" cardboard over cardboard ribs. No spar or reinforcing tape.
4" of tip is blue styrofoam. 1 1/2" wide full span ailerons with
seperate servos (see upper right picture).

Fuselage: Length 38"
Blue foam. Reinforced with minimal strapping tape.

Tail: Plastic real estate sign.

Weight: 2lb 7oz

Performance: Very similar to Super Sidewinder. Stable fast or slow.Tight turns and loops.

iAlex

I'm not sure how a forward sweep would work on a small ship like a zagi. Like Flailing I have several hours in a Blanik. (About 30 right now, not a extremely high number but then I have been flying full scale for less than a year) The main advantage to the forward sweep in the Blanik is that the CG does not change much with respect to the Mean Aerodynamic Center when flying dual or solo.

Ollie

And, it improves visibility for the guy in the rear seat!

flailing

My Feedback: (1)

The Blanik is all alum. Dural actually and with no motor to drown out the noise you can hear all the creaks and pops when you start pulling on it hard. Kind of unnerving at times

Cdallas2

Now I've been researching the FSW theory for about a year now. The main thing you seem to have to watch out for is a twisting motion chordwise. Now this only seems to happen at higher speeds. The Germans tried to fix it on the Ju-287 in WWII by moving the engine postions around.

Just make sure you add about another 25%-30% af area on the Vertical tail.

Now this is all theory as my first prototype .40 powered FSW suffered from brain fade on the part of the designer (that would be me) as I miscalculated the nose moment and ended up about 3.5" too short. Fixed that by making an engine box only to discover the aileron geometry was out of whack due to error on the part of the builder (that would be me again). But prototype #2 is on the drawing board, so when my shop is ready this fall I'll start on that one.

Cadet

Try flying a Schweizer 2-33A! You can feel that fabric covered fuselage shake in a slip and the sound, it's deafening in the rear seat! For all that their bloody strong and handle like a *****cat. On the other hand I have had one is such a crazy spiral-dive that the wing was stalled and we were showing 80mph on the guage. Fun stuff!
Cheers,
Grant

4*60

My Feedback: (41)

2-33A. Fabric must be too loose or something. In my many years of instructing never ever had a deafening fabric sound and slipping was what I liked to do on approach. Although the "tin can" wings used to boing, etc whenever you put some G's on and the top aluminum dented in until you went back to normal flight.

FSW - Ka7, Blanik, Bergefalke - They flew great!
They do seem to have large vertical surfaces.

Cadet

Well I don't think that the fabric itself is really shaking so much as the whole aircraft is buffeting around and you can hear it so much better through the fabic than through aluminum. I do love flying them though, their a hoot.
Cheers,
Grant

Daniel Nelson

The main problem with a forward swept flying wing like a modified Zagi will be the aerodynamic center's position relative to the cg. Sweeping the wings forward will move the ac forward as well, and if the ac gets ahead of the cg, your ship now is statically unstable.

George Navarro

Try foamfly.com for a FSW. You build it yourself out of foam. Runs on a speed 400.
George

Birdofprey

This is my prototype combat glider. It flies very fast and handels quickly, but it will still slowdown for landing. If there are any questions or comments, I would like to hear them all.

billf

Ollie...

You are absolutely correct about a FSW requiring a larger vertical stabilizer volume. I recently completed an "Inversion", a kit offered several years ago for a .40 sized engine.

The vertical stab looks large and in level flight the plane tends to oscillate slightly in yaw.

Bill

BernieG

Schleicher ASK 13 also has forward swept wings. My understanding is this solution is used to avoid having an immensely huge tail to compensate for 2 persons weight in front. the ASK 13 is an incredible thermals sniffer, unlike the "trukish" feeling of the Blanik.

Bernard

Ollie

Three good reasons for swept forward wings on two place sailplanes are:

1. It allows the wing spar to pass through the fuselage uninterrupted by the body in the rear seat.

2. It provides better visibility for the person in the rear seat because the leading edge of the wing isn't so much in the way.

3. It allows the CG to be placed with a minimum of balast when operating with one person.

RC_MAN

My Feedback: (11)

When we used to fly combat I designed a swept forward flying wing and put the gas tank right on the CG. This way the trim didn't change. It would out loop any other plane around. When the engine quit I managed to get 5 to 7 minute flights as a glider.
Go for it!

franciscan

I was always under the impression that the sweep forward seen on 2 seat gliders was mainly to improve the cg position of the glider.
Franciscan

renxxx1981

Do you have plans for this beautiful bottle rocket?

Lownverted

My Feedback: (4)

You realize you've dug up a 20 year old thread right? Might be a new record!

renxxx1981

Internet is forever! :-)

H5606

I too found interest in this 20 year old discussion on the FSW design idea searching for any benefits to fuel tank proximity with a nose-mounted, IC engine for a prop-jet.

Since many jets have long noses and swept-back wings, preliminary thoughts are that you get the CG closer to the tank on suction for less pitch changes between full- and empty- fuel tank situations with FSW's.

Interested in any comments -