I am starting up my next project for the start of the winter. I am looking for info on forward swept wings. The plane I am hoping to draw up will sport a 30 inch wing give or take as needed and be powered by a .049 sized engine.

Thanks alot,
Tim

Personally, I have no experience with forward swept wings, but here are the results of a "Google" search, which may help.

http://www.google.com/search?q=forwa...UTF-8&oe=UTF-8

I've only had one such, The Goose I think the name was, made from plans in RCM. A 40 size. I don't know if it was because of the design or if it is typical for forward sweep; but, it was very difficult to recover from a spin unless you had scads of altitude when you started the exit. That is what finally did it in, got to slow on the final turn on landing and it dropped off into a spin that I never recovered from. Roll rate was fantastic and general flight characteristics pretty good.

If you want to email me, I can copy you a couple of old articles on sweptforward free flight flying wings. I've built a couple of DMECO Sportwings for control line and they fly very nicely. I don't see why one couldn't modify the design a little and make a 1/2A RC airplane out of it.

Jim

Hi Tim, I have no personal experience yet of FSW but have the wing cores cut.......and have seen some good model articles on the subject. Try to find RCM February and March 1988 issues where Don Sobbe treats the topic and shows interesting designs. Furthermore Model Builder from May 1988 has a theoretical article on FSW............Good Luck.....Cheers/Harald

My first question is what is to be gained by forward sweep? Other than to have a different looking airplane, there is no real advantage and several disadvantages to swept forward wings. The first drawback is the effect on stability. A swept back wing has positive lateral stability in that it will tend to roll away from a sideslip whenever it is generating lift. (When operating at zero lift it generates zero rolling moment so in conditions such as knife edge flight there is no roll coupling.) One benefit of this is the ability for a swept back wing to be laterally stable both right side up and inverted without any dihedral. On the other hand, a swept forward wing with no dihedral is laterally unstable.

Another problem is structural. A swept back wing tends to deflect in a direction that reduces flight loads while a swept forward wing tends to deflect in a direction that increases flight loads. This requires that a swept forward wing be more rigid to avoid such things as flutter.

A simple straight “plank� wing has neither the advantages nor problems associated with sweep, and is a good choice for general sport flying. A swept back wing is a good choice for an aerobatic airplane because it offers good handling in positive and negative g flight while it minimizes roll coupling in knife edge flight. A wing with forward sweep has no particular advantage to offer.

Can a swept forward wing be made to fly? Of course it can. If the sweep is moderate is shouldn’t present any serious problems, but it will likely be a little touchy to fly.

My Ripmax Alienator flies fine.

Maybe I should have stated the wing will be swept forward and that I am not looking to build a forward swept flying wing? The plane will have a fuse like a normal ship of course. I have a set of plans out of a RCM mag of a plane with forward swept wings. It's a .40 size job that was said to fly very well. I believe it is swept 30degrees or so.

Later,
Tim

I read about some wind tunnel tests that were conducted back in the 1930s by NACA, as I recall, of both swept back and swept forward wings. Swept forward wings were found to have a slightly reduced induced drag, but not enough to offset the structural problems, or we would see far more airplanes with swept forward wings. The tests were done at low Mach numbers, and the investigator concluded that both sweepback and sweepforward had no future, but this was long before the supersonic era.

Doug, how is that alienator doing these days?

Tim, I recall a early 50's rubber job called, maybe, the Nightmare, It had swept forward wings and large sweptback stab. Could be redesigned into a 1/2A radio aiplane eaisly. I have the article out in the shop. I think it was in Air Trails.

Jim

Hi Vic, it's still underpowered with the AP .15. I'm really disappointed in that engine...However, MikeSell and I are going to order a bunch of nice, light Norvel .25s from the LHS (we get better than catalog pricing and no shipping when we get a few of us together and buy in bulk. We made an order for 10 .074s and got them for 48.00 each.). That ought to perk it right up.

Back in the 1980s I designed and built 3 swept forward wing planes for a .60 sized engne. They all flew very well. On the design, I would say to not go small on the vertical tail.

I designed 3 different configurations: low wing single fin,; low wing twin fins, shoulder wing single fin. I liked the shoulder wing version best as the forward sweep gave anhedral effect so no anhedral was needed in the wing to eliminate roll coupling.

[link=http://members.cox.net/moorman1/pgvector1.htm]Vector 1[/link]
[link=http://members.cox.net/moorman1/pgvector2.htm]Vector 2[/link]
[link=http://members.cox.net/moorman1/pgvector3.htm]Vector 3[/link]

The Klingon "Bird of Prey" seems to work ok... (At least, with Sulu at the controls) And bonus, it can carry whale aquariums.

Interesting designs Ed. The guys should remember that if you take a airplane that is flying really nicely and replace the straight wing with a swept forward wing with the mean aerodynamic chord of the swept forward wing at the same location as the non swept wing that the airplane is still going to fly really nicely. There are things that a swept forward wing does differently at the extremes of the lift curve slope and also in yawing maneuvers but in general for normal flying around you won't notice much if any difference. I do think they look pretty ugly (sorry Ed) so don't consider them when designing my own airplanes.

Tim, you trying out something funny for the design contest?!
I played with a forward swept design. I can't remember specifics, but the pic should tell alot. It flew, but my wing joining technique needed some help. I was still fairly new to the hobby at this point and wanted to play with different configurations.
There was a little buzz and people running for the hills when they thought I was going to fly it. After handing the transmitter to an experienced guy they came back. I'll be getting back to it and finishing the second one. (started it three years ago...) Actually, this might make a good 1/2a plane. The light wing loading would help with the wing flex that might have been a problem. hmmm.... Well, not for the design contest. I'm going to do the RV-9.

hmmm... can't get the pic to upload. Keeps saying "error saving file to disk". I'll try from my home pc after work

Here is a link that briefly covers the advantages of forward sweep (in an SU-47 Berkut) and the structural problems that had to be overcome.

[link]http://www.flymig.com/aircraft/Su-47/[/link]

Hello,

In the late 80s there was a design called "Sweepee", by Sanjay Dahl, in AMA magazine. The construction article can be found online in the AMA website. It is a forward swept wing canard. Looks very unusual. Great flying characteristics, except no stall so no spin. I have built probably 6 of these from scratch. Make certain the CG is correct and you will have a lot of fun. A lot of people will just plain stop what they re doing to see it fly.
It uses a .40 to .60. Any questions feel free to email me.

There are advantages to the fsw, in that the spanwise flow that normally contributes to bad tendencies of swept wings to tip stall. The reverse is true here. The planform is very resistant to tip stall. It generally can fly much slower without high lift devices as a result.

The problem for planes at high speeds and g's is the structural problem of the wings trying to peel back on themselves. This is a consideration, but not really a problem for models. Thick wings as found on most sprot planes can easily be built stiff enough to take the stresses of sub-100 mph flight. There have been a few kits & plans out there.

There have even been scale jet models of the X-29, but I haven't seen one fly.

Assuming a standard configuration, wing in front - tail back, and suitable control power and structural stiffness - what happens as you go through the full 90 degree angle of attack range. A normal airplane like the TOC airplanes (as if those monsters are normal) can go fairly smoothly without roll through the wing separation into high angle of attack without asymmetric rolling moment being produced.

I am guessing that the forward sweep does the same thing only smoother, you just never get the asymmetric-separation/tip-stall/inboard-stall that is indicative of a tapered no sweep wing. It would be nice if the 3mm foam I use on the little ones had the required thickness to handle the torsonial loads.

You know, that's a great point. The Edge 540 technically has forward sweep. I wonder how one would do as you exagerate the sweep angle. I wonder if they get to where they won't snap roll?


One other thing I meant to mention earlier. While there may be some advantages to this, obviously it's not very practical for a fighter. The X-29 was flown for quite a while, then retired. Since then, the US has designed the two main next generation fighters, at least - and fsw is nowhere in sight.

It could be practical for fuselage space reasons. There was a business jet built in Germany called the Hansa jet that had the wings forward swept and the engines mounted on top of the wings. That was so the spar would run behind the passenger compartment. This was an all metal airplane with moderate sweep. And I've seen at least one high perf glider design where the spar runs behind the seat but the wing is kicked forward.

The FSW has not been used in the newer US fighters but it is in use for the next generation of Russian fighters. The Russian Sukhoi S-37 is the first such example. Here's a decent link: [link]http://www.popularmechanics.com/science/defense/1281276.html[/link]

The S-37 is just the Russian counterpart of the X-29. It's a research airplane. There's no indication it or it's features will be designed into a production fighter. Impressive in size & presence though. The similarities between that and the X-29 program are interesting. Obviously, the S-37 has some heritage with the Su-27. The verticals look like a straight carryover, and the fuselage looks pretty common too. The X-29 borrowed parts from existing designs as well. The forward fuselage section is literally an F-5 fighter. The landing gear is F-16.

Many years ago I designed and built several 40 size forward-swept tailless planes. They were all double tapered planform and flew very well, you just need to be sure you have the CG right. I used foam cores sheeted w/ 1/16" balsa and a 6" wide piece of 2 oz glass cloth to reinforce the wing joint. I never had a wing failure and I crash tested a few of them! Most of the airfoils were Evans Simitar series. I also learned that while it was next to impossible to tip-stall the wing, if you're going fast enough and pull a tight enough turn, you can can stall the root of the wing. When that happens, it looks like someone reached up and slapped the plane out of the sky. It just tumbles until you release the elevator and let the wing begin to fly again. Leading edge root extensions (LERX) pretty much stop this from happening.

My only advise would be to design the wing so that about 2/3 of the wing area is behind the CG. If you're designing a plane with a tail, the desired CG is calculated the same as any other wing.

Here you have a fully functioning Su-47 for a .45. You can also watch some videos of the plane in flight.




http://www.rcuniverse.com/forum/fb.a...86&key=Su%2D47