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Forward swept wing?

Old 05-07-2002, 12:33 AM
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stick
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Default Forward swept wing?

I'm in the process of desinging an aircraft with a forward swept wing. Not only is it forward swept but it also has some anhedral in the wings. What is the characteristics of a forward swept wing and the characteristics of anhedral. This will be a twin boom desing with a large amount of verticle and horizontal stabalizers. What do you guys think about how it might handle?
Thanks
Old 05-07-2002, 01:00 AM
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Ollie
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Default Forward Sweep

Both forward sweep and anhedral result in adverse yaw to roll coupling. The large vertical tail will help to dampen any yaw oscillations. Rudder deflection may need to be kept to a minimum to minimize the adverse yaw to roll coupling. Lots of aileron differential will help minimize the need for rudder deflection. The center of the wing will probably stall first and protect against tip stall. The lack of tip stall will result in slower snap rolls.
Old 05-07-2002, 01:15 AM
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Hal deBolt
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Default Forward swept wing?

Dear Stick.
Are you trying to pull someone's leg? Forward sweep plus anhedral yet ! Believe you are serious?
I doubt if this combo has ever been tried. Forward sweep yes,
Anhedral yes but in combo ???
I have no way of knowing if you understand what you are going
to use or not. So will summarize briefly>
Wing sweep: it detracts a bit from lift. it reacts a bit like hedral,
tending to right a craft upright or inverted.
Sweep back is primarily used to delay compressability when approaching Mach 1.
Many years agoit was used on rubber powered models supposedly so less dihedral would be required
Sweep forward reacts similiar and it is said to be more efficent.
Dihedral and anhedral react in a similiar fashion. When the craft
turns laterally on the longitudinal axsis one wing panel effectively
becomes longer and closer to horizontal while the other panel
effectively becomes shorter with an increase in hedral.
The longer panel has a lift increase tending to right the craft.
When a dihedraled craft flys inverted it has anhedral. So when a
anhedraled craft flys inverted it has dihedral.
There could be different control reactions between the concepts
but that is beyond the scope of this message
Hope this helps, good luck!

Hal [email protected]
Old 05-07-2002, 01:52 AM
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stick
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Default Forward swept wing?

I will try to post a scan of my scketchs so you can see what I hope it will look like.
Thanks
Old 05-07-2002, 02:17 PM
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Jeremy Sebens
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Default Forward swept wing?

Originally posted by Hal deBolt
Dear Stick.
Are you trying to pull someone's leg? Forward sweep plus anhedral yet ! Believe you are serious?
I doubt if this combo has ever been tried. Forward sweep yes,
Anhedral yes but in combo ???
I have no way of knowing if you understand what you are going
to use or not. So will summarize briefly>
Wing sweep: it detracts a bit from lift. it reacts a bit like hedral,
tending to right a craft upright or inverted.
Sweep back is primarily used to delay compressability when approaching Mach 1.
Many years agoit was used on rubber powered models supposedly so less dihedral would be required
Sweep forward reacts similiar and it is said to be more efficent.
Dihedral and anhedral react in a similiar fashion. When the craft
turns laterally on the longitudinal axsis one wing panel effectively
becomes longer and closer to horizontal while the other panel
effectively becomes shorter with an increase in hedral.
The longer panel has a lift increase tending to right the craft.
When a dihedraled craft flys inverted it has anhedral. So when a
anhedraled craft flys inverted it has dihedral.
There could be different control reactions between the concepts
but that is beyond the scope of this message
Hope this helps, good luck!

Hal [email protected]
hmmm... the dihedral explanation given above is commonly quoted, but it's not entirely correct. if the aircraft is flying at zero sideslip, dihedral will have no effect. The reason that dihedral tends to right an aircraft is because when the airplane is banked over, it tends to "slip" downhill in the direction of the bank. This results in a sideslip angle which has a component in the y direction (y is the axis that runs out the right wing). This component creates a net upforce on the low wing, since the sideward component is hitting it from the bottom. The high wing, on the other hand, sees the crossflow hitting it from the top (since the dihedral angle is in the opposite direction on that side), and therfore is pushed down. This results in a moment (torque) that tends to right the airplane. It should be noted that the above argument neglects the fuselage's influence. In the case of a high wing airplane, due to the flow around the fuselage in a sideslip condition, a wing with zero geometric dihedral actually demonstrates positive effective dihedral. Likewise, a low wing aircraft with some positive dihedral can have no effective dihedral (witness the CAP 232).

If anyone is incredibly confused by this explanation and its lack of clarifying illustrations, let me know... I'll draw some pictures that should help. I know I had a hard time with it in Flight 2.

On the anhedral forward swept thingy... why? I don't see any reason to pursue such a design - other than that it would look cool, which is reason enough, I suppose. But in order to have something that behaves well, you'll probably want to sling the fuselage under the wing to counter some of the negative dihedral with the fuselage flow, and make sure to put a nice big vertical fin on it. (see below)

Starfire's design rule number 3: If you think the fin might be a little to big, make it bigger. Too much fin is a little extra weight and maybe spiral divergence, which won't hurt you in an R/C, but too little fin, and it'll do the "bonanza boogie". Poorly damped dutch roll is no fun.
Old 05-08-2002, 02:11 AM
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stick
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Default Forward swept wing?

Here is the sketch of the plane. If this design had a purpose it would be a mid to high altitude recon plane. but for now I think it looks different. what do you guys think about it and do you think it would fly? I'm in the process of building a small hand lanch glider of it to see about the CG. I will have acad plans for it in a while but have to finish some other projects first.
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Old 05-08-2002, 10:19 AM
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Ollie
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Default Forward swept wing?

With good engineering,"Form follows function." What we have here is a form in search of function.

The swept forward wings and tail booms mounted near the wing tips will put enormous torsional loads on the wing structure, especially during maneuvers involving elevator control deflection. The configuration will be difficult to control in roll because of the very large roll moment of inertia and the inboard ailerons. It will have negative roll stability which puts constant demands on roll control requiring gyros or some other automatic device to overcome the designed-in instability. The cranked wing planform will tend to stall at both the root and tip. The forward sweep results in the need for longer tail booms located near the tips thus, increasing the mass were it will do the most harm.

In aircraft design, novelty, in and of itself, is not a virtue. Novelty has its place when it results in improved functionality.
Old 05-08-2002, 03:24 PM
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Craig-RCU
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Default Forward swept wing?

Stick,
I like it a lot! Very innovative. I have a couple of suggestions though. If you give the outboard wing sections some dehidral, it would help correct some of the anhidral instability problems that the inboard sections will cause. It will also give a bit more wing tip clearance for landings, and it will look cool too to boot.

If you are going to have a controlable rudder, I would suggest rudder actuation like Rutan Verieze's use. Verieze's rudders only deflect outward. This means that when left rudder input is given, the left rudder deflects out while the right rudder stays straight. The effect is like a combination of regular rudder functioning and "drag rudder" functioning. The single outward deflecting rudder creates yaw with both drag forces and side-lift forces. This type of rudder actuation is most helpful for yaw control on any aircraft were its dual rudders are further from the centerline than they are aft of the C.G. If you have a computer radio, it should be possible to mix this type of rudder actuation by using a separate servo on each rudder. If not, I'm sure there is a way to get the same rudder functioning with a single servo and some clever mechanical linkages.

As Ollie pointed out, if you use the inboard main wing control surfaces as aileron, your roll authority will be somwhat lacking. To remedy this. I would suggest using the elevators as elevons. The elevons are further away from the aircraft's centerline than the main wing's ailerons and will be able to produce stronger rolling forces. I would then use the main wing control surfaces as flapperons or just plain ailerons. Oh, and use a little washout on the wingtips to avoid tip stall problems.
Old 05-08-2002, 04:16 PM
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stick
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Default Forward swept wing?

My intensions were to use the elevators as ailevators. the inboard control surfaces were gouing to be flaps. I can set them up as flapperons also though. It will also have retracts witch will ad to the eigth at the tips wicht will make the roll inertia even worse. It is really just an "i wonder if it will fly" type thing.
Thanks
Old 05-08-2002, 05:03 PM
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Craig-RCU
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Default Forward swept wing?

Now that I think about it, the tail booms may have a beneficial overall effect for your design. The deal with forward swept wings is that when flying, they will want to twist up and/or down and need to be very torsionally strong so as not to diverge. However, your tail booms mounted were they are will counteract the torsional forces on the swept forward wing. Therefore, you might not have to build your wings any more torsionally resistant (this will save weight) than a straight wing if the booms are not too long as to overcompensate. You may have to lengthen or shorten your booms (or use less hstab area) for optimum torsional stability though. How long is that? How much hsatb area? I'm not sure how to figure that out. All I can think of are trial and error methods, but I'm sure there must be a way to compute this.

The weight of the retracts will slow the roll accelleration but that will not make the design unflyable. It will only affect roll acceleration (and deceleration) and will not affect maximum roll rate itself. I think you have a good design here worthy of exploration.
Old 05-10-2002, 01:24 PM
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STUKA BARRY
 
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Default Forward swept wing?

THEY SNICKERED AT THE WRIGHT BROTHER,IN THEORY, THE BUMBLE BEE CANT FLY, HELICOPTERS WILL NEVER WORK (IGOR S.) WAS OUT OF HIS MIND, AND THE THOUGHT OF A FORWARD SWEPT WING FIGHTER WILL NEVER WORK (X-29). I SAY HOG WASH. GO WHIT YOUR DESIGN. I'M NO ENGINEER OR AERODYNAMICIST, BUT I THINK YOU HAVE A WINNER. IS IT POSSIBLE TO BRING THE BOOMS IN ENOUGH TO MATE THE HORIZONTALS, OR IS THAT TO MUCH P-38ISH IF YOU KNOW WHAT I MEAN?
Old 05-10-2002, 02:29 PM
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Ollie
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Default Engineering

The Wright brothers invented the windtunnel to collect the engineering data that would allow them to design their first airplane rationally on the basis of physical principal rather than as an exercise in "novelty." Novelty in and of itself isn't necessarily rational. The bumblebee's wings operate in a different flight mode (clap-twist-snap) than an airplane's wings and applying airplane wing theory to a bumble bee is just a misapplication of that theory. To imply that a misapplication of a theory invalidates that theory is not an example of rational thought. The X-29 only became practical with the development of fly-by-wire dynamic stability and control systems (another engineering triumph of rational thought).
Old 05-10-2002, 05:42 PM
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Jeremy Sebens
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Default true...

Well said, Ollie...

This isn't snickering that's going on here, just rational criticism of a design concept that may or may not be sound. In modeling, design for novelty's sake is an acceptable motive - just realize that the airplane emphasizing novelty may suffer in mission capability. However, the mission may be novelty! Remember, there's nothing quite like showing up at the field with something *really* wierd and fun.

FSW is probably no problem for this plane - the modest amount of sweep extant in your drawings is not going to cause structural or stability problems. A bit of anhedral won't be too bad, either, as long as the wing is above the fuselage, and you're willing to stay on the ailerons allthe time. The one concern I have is the boom structures and the possible aeroelasticity that they may cause. If you use the surfaces on the horizontal stabs as elevons, you run the risk of experiencing aileron reversal, and elevator response may be more than you expect. If we think about what's going on on the wing-boom ineteraction, this may be clearer. for the wing that you want to go down, you'd deflect the elevon up. However, this long moment arm about the attachement point (wing) may cause the wing to flex tosionally - to a higher angle of attack! (uh-oh) Now it wants to go up. Which influence wins out will depend on the torsional rigidity of your wings and the speed at which the aircraft is flying. As I inderstand it, the 777 actually experiences aileron reversal inside its normal flight envelope (at high speeds, of course), and the flight control system knows how to compensate. Unfortunately, the only flight control system we have on models is the guy behind the sticks, and we're notoriously bad at dealing with aileron reversals.

To prevent this, you're going to need to make sure that the wing is very torsionally stiff. This probably means fully sheeted, as wings get much more rigid in this axis when you "close the section" with sheeting. Also, the tailbooms need to be quite stiff to avoid elevator reversal from a similar phenomenon., but this time the stiffness needs to be be in bending.

Good luck with it, and keep dreamin'. Just remember that there is a good reason that most airplanes have a wing up front, a tail in back, and a tube in between.
Old 05-10-2002, 06:03 PM
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Hal deBolt
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Default Forward swept wing?

Hi Stick,
Your sketch helps a lot, now realize it is not true sweepforward
or anhedral. The portions that are normal could dilute the rest.
Like one thread says "it looks cool man!"
Bottom line, lesson to all the comments, you only have a first draft so changes for better are possible.
Your serious? Tactical approach would be a hand launch glider until that is fine, from there a simplistic small R/C, that works then
on to the real thing.
You are in virgin territory and the best would have a hard time
assuring success, even NASA uses development series.
Bottom line>> you have to want to do it and be willing to
concentrate.
OK? Good luck !

[email protected]
Old 05-11-2002, 04:07 PM
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Default Forward swept wing?

Going by what was said about control surfaces, i rember the British Vucan bomber had 4 surfaces, the outer two where mostly aileron, the inner two where mainly elevator, tho each had some or the other mixed in.
im a firm beliver on deltas and swept wings the elevator should be in the middle and at the rear, and ailerons at the tips and forwards, that way you avoid tip spins form uneven elevator movement and flap effects.
Thats why my own delta design had a swept forward TE. it either worked as i just explained, or it was the best set up delta i've ever flown.
in my mind, the surfaces on the wing in the center can only really be used as flaps, with maybe some aileron mixed in. the rear tail planes are elevator, again, maybe some aileron mixed in, and the outer wing pannels are aileron only.
reading back thats what you intend to do.
i like the rudder idea.
to help with strength and bending loads, you could have one full length tailplane maybe, but at the spans shown in your design that wouldnt be pleasing to the eye, which your whole idea so far is to me.
As for needing computers to fly jets, thats only coz the CofG is so far back the plane isnt stable + all the other bits they do. any model designed in our normal limits of weight and balance centers has potential to fly. i have a Spinsation and its very stable in flight.
Swept forward deltas are also self stablising in ground effect.
DAMN! now i've got that WIG craft in my head again
i want one of these

oh yer, i just remembered. you might have trouble taking off, the front wings will be in ground effect and sucked down, the rear wants to fly in ground effect, i can see a point as it just manages to get free from being sucked down the front section suddeny gets lift and it flips over. my susgestion is to have the gear longish ( wings out of ground effect), and a nose high sit. my Spinsation is too flat and it jumps into the air. i have to let the sticks go, wait for it to level on the rotation, climb a little on its own, then pull up.
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Old 05-13-2002, 01:48 AM
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Cdallas2
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Default Forward swept wing?

Hey, Stick

I think your design is at the very least worth the effort. I've got my own FSW design just about finished and I'll be test flying it next weekend.

When someone asks you why you want to try something totally differnet just explain that not everyone wants an Extra 300 with same trim scheme as half the other guys at the field.

Just imagine the satisfaction you'll feel when that bird takes off and flies like a dream.

Buy the way guys just so you know the Wright brothers were not the first to fly - They were the first to fly with power and Charles Lindberg was not the first to fly the Atlantic non-stop - he was the first to do it solo from West to East.
Old 05-13-2002, 03:12 AM
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Default Forward swept wing?

THE FRENCH FLEW LONG BEFORE THE WRIGHT BRO'S, BUT IT WAS NEVR DOCUMENTED. ALSO THERE IS MAN IN CONNECTICUT THAT SUPPOSEDLY FLEW BEFORE THE WRIGHTS, BUT IT WAS NEVER DOCUMENTED. LINDBERG FLEW TRANSCONTINENTAL WITH NO RADIO OR AVIONICS. JUST A COMPASS, AND HE WAS ONLY 12 MILES OFF COURSE. NOT TO SHABBY!
Old 05-13-2002, 08:52 AM
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Ollie
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Default Luck

Luck ocasionally beats skill. Luck and skill, as in Lindberg's case, is nearly unbeatable.

No one is claiming that the design in question can't fly. It can. It is a very, very novel configuration. If novelty is the objective then it is a winner. If stability, control, efficiency, structural integrity and maneuverability are objectives, then the configuration in question is handicapped.
Old 05-20-2002, 12:38 AM
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Hal deBolt
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Default Forward swept wing?

Hi Stick, again!
You sure have recieved a variety of advise and perhaps are
having a time deciding the worth of the project.
Two of Confucious's sayings might apply:
Nothing ventured, nothing gained and
Persistance pays dividends
Reason for this contact is that experience says there is some
substantial insurance of a successful test flight
Would believe you have noted the Co Pilot advertisements?
Believe they are all that is claimed and more. If your craft would
be near an optimum set up Co Pilot would be fine assistance on
the initial flights, give it a try?

Hal debolt
Old 05-20-2002, 01:44 PM
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Default Forward swept wing?

RE: the co-pilot... Good point, Pappy. The stuff my buddies and I work on is a lot less avant garde than this, but the PA-1 has been a great tool and I'm told that the newer versions are even better.

A question for Stuka, you say that the French flew long before the Wrights, but that it was never documented... can you point to any proof of that?
Old 05-20-2002, 02:23 PM
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Default Forward swept wing?

HEY AL, OF COURSE I CANT. IT WAS NEVER DOCUMENTED, MEANS JUST THAT. IF I COULD, I'D BE A MILLIONAIRE, OR ASSASSINATED, DEPENDING ON HOW YOU LOOK AT IT.
Old 05-21-2002, 01:42 PM
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Default Forward swept wing?

Hello Ronnie...
Just to add a couple of cents worth:
I flew an "Inversion" for the first time yesterday. This kit was available a couple of years ago. The wings are swept forward at about 45 degrees. Airfoil is symmetrical and the instructions suggest anywhere from zero to plus 4 degrees of dihedral. The less dihedral the more acrobatic, says the instructions. The plane flew pretty well with plus 3 degrees.

I noticed an interesting feature: While in level flight the tail would "waggle" without any apparent input from the controls...just as someone said about the V-tailed Bonanza. Perhaps that is why the vertical stab/rudder appears quite large on the Inversion. While in a bank the plane seems very sensitive to "up" elevator--it really jerks around quickly....probably because the forward wing sort of "catches the air when the angle of attack is increased.

It was not possible to stall the plane. With engine at idle and full up elevator (maybe it needs more) the plane descended in an almost level attitude, probably at about a 30 degree angle. Thus the lack of tip stall was clearly demonstrated.

As far as looking different...that is right! It takes a bit of getting used to as far as orientation in flight is concerned. Plus a lot of joking about "getting the wing on backward", "Does it fly backward?", etc.

Bill
Old 05-22-2002, 02:02 AM
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stick
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Default Forward swept wing?

I have been working on this for a while. I will get it built. I'm at the plans stage now and the hand launch glider to find out where the C of G will be. I will keep yall posted.
Thanks for the iinfo.
Old 05-31-2002, 07:05 PM
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Jeremy Sebens
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Default To digress even further...

EVEN IF the french flew before the Orville and Wilbur, ( a point I am not willing to stipulate in any case) the early french planes were really pretty poor in comparison to the Wright Flyers. The reason is of course roll control. The first time a Wright plane flew in France, the aviators over there were amzed at how well the airplane turned using the wing-warp roll control. French planes of the time only had rudders, and very little dihedarl, so they just kind of skidded awkwardly around the sky. It was the Wright's development of roll capability that distinguished them from the pack all the way up until WWI, when the Germans made the next major advance in aircraft design with the realization that thick arfoils are better than thin ones...
Old 06-01-2002, 04:06 AM
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stick
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Default wing warping

The wing warping idea worked great. But to me the prize in roll control had to go to Glen Curtiss and his crew for the ailerons. Yippee

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