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3D Airframes

Old 08-25-2013, 06:26 PM
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fasteststang
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Default 3D Airframes

I'm wondering what the performance differences are between the airframes that are commonly used for 3D flying. Some have straight leading edges while others have straight trailing edges, while others have both tapered. How do these wing configurations (as well as other differences like the Cap 232's shorter elevator moment) affect certain 3D maneuvers.

Someone looking to get into 3D flying can be very overwhelmed by the number of different "3D" airframes. I know performances are dictated by wing loading, cg, thrust to weight ratio, etc, etc, etc.... My inquiry is more the theory of different configurations. Some of the airframes I would like to see compared are Yak 54 & 55, Extra 260 & 300, Edge 540, AJ Slick, Giles 202, MX-2, Cap 232, and any other pertinent airframes.

Thanks in advance for any and all contributions to this thread.
Old 08-26-2013, 08:59 AM
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daveopam
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WOW, thats going to be a lot of info :-) The shape of the wings and tails on the model is simply a matter of copying the full scale. On the full scale vesions there are of course different theories as to why one leading edge is straight and one is tapered. My knowlegde is limited on this but I will try and pass along what I have learned. On the Extra for example, the wing is tapered in the LE and TE. I believe this was done to increase the roll rate. The wing area needs to be of a certain size to get the right wing loading. So to make it roll faster you increase the septh of the wing at the root and decrease it at the tip. The Edge series of planes have a straight LE and a tappered TE. I think this was done to make the wing stall easier hence tunmle easier. A wing with a straight LE will stall all at once. A wing with a tapered LE will not stall all at once and will be a more gentle stall.
Comparing the Extra 260 to the 300. The 260 has a shorter tail moment. This makes the plane better at some of the tumbling type manuvers were most of the 300s are better at IMAC type. Same with the Yaks. The newer model Yaks are longer and smoother. They are great at 3D because the wing loading is light and the control surafaces are huge.

As I said at the start I am no expert on these subjects. I mostly posted to get the ball rolling give what little I thought I know and give other guys a chance to agree or tell me I am wrong about my conclusions.

david
Old 08-26-2013, 08:32 PM
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fasteststang
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David, thanks for your insight. This is exactly the theoretic discussion I am looking for. Truth be told only a select few people can fly these aircraft to there full potential anyway (Haha and I am definitely not one of them).

So from what I gather straight LE causes instant abrupt stalls and the more tapered they are the softer the stall. So does that mean a Giles 202 which has straight TE and very tapered LE will have an extremely soft stall? I also gather that wing configs that have both TE and LE sacrifice some softer stall as well as less wing area for a higher roll rate.

As far as tail moment goes, it just seems to me that longer or shorter will depend on pilots preference as to what type of 3d maneuvers he/she prefers.

So now we have laid down theory, how do certain airframes balance these configurations to produce better or worse 3D characteristics. The only example I can give is my Cap 232. It has a very slightly tapered leading edge with a very taped trailing edge. The elevator moment is short while the rudder moment is longer. It flies very nimble, has quick roll rate, and fairly low wing loading. One of the tendencies this airframe has though is it tends to snap roll very quickly/easily. Which can be good or bad depending on whether you were trying to snap roll.
Old 08-27-2013, 06:03 AM
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I think Caps have always been easy to snap. 25 years ago a friend had a 1/4 scale Cap (that was a big plane back then) that was very tricky to take off and land. It wanted to snap when airspeed was low and elev movement was high. This made it do some fantastic tumbles and flat spins. It was however a trade off. If you look at a Chipmunk like the one Goldberg used to kit. It has a very similar tail to the Cap. Hopefully we will get some insight from others on wing shapes. About the time I think I know something about it, I put a flight on my foamy which has no airfoil at all and it all goes out the window. The wing on it is tapered on LE and TE though :-)

David
Old 08-28-2013, 09:48 AM
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All that is great, but for 3D think percentage of control surface to the total surface, and the amount of physical throw you can get out of the surfaces.
Old 08-29-2013, 08:05 AM
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I can add 2 points?
1st is that ANY plane is a series of design compromises and 'best guesses'!

The other is that some of the airplanes contained in the OP list come in single and 2 place versions in full scale - with otherwise identical airframes (other than possible minor differences in tail moment and side area) getting different model numbers. Others variances may be due to engine size? Those factors removed for RC purposes, there really aren't THAT many different planes available.
Old 09-02-2013, 06:39 PM
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The taper on the wing actually has the opposite effect as mentioned above. A straight leading edge on a plane actually makes the plane more stable in a high angle of attack ( stalled harrier type maneuvers, hence requires less finesse and produces less wing rock). A swept leading edge allows for a more aggressive stall and allows faster and more precise snaps and spins, but requires more attention in high alpha flying, and landing. It depends on what you are trying to accomplish as each design has pros and cons, I prefer a Extra over a Edge because I like the snappiness of the wing design and have gotten to know the planes well after thousands of flights, but love flying a Edge around in a harrier. I don't like Yaks mainly because of the round fuselage and not so much of the way they fly, just a little draggy for my liking, the 3D Hobby Shop Slick is a great 3D bird and would probably go to it if I gave up on the Extra. They are all good flying birds and depends more on personal preference, todays designs are all good 3D machines so if you like the looks of a Yak over a Extra or a Sbach over a Edge, get the one you like, just recommend you get one from a established company like Aeroworks, PAU, Pilot, 3D Hobby Shop, etc. especially if its a giant scale, I have a couple of cheap 3D birds and like them but quality is crap but fun, the China 20cc profiles are good but built cheap and are fragile, but still love them. Good luck and remember that servos make the bird, I run cheap Solar servos on the profiles and they are great, but I stick with the big 3 on the giant scale stuff, MKS has some cool servos I haven't tried yet and Savox seems to be getting more popular.
Old 09-03-2013, 04:58 AM
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Wow, pretty informative for a first post. Welcome aboard!

Looking at your join date, you've been lurking for 3 years, or did your account/post count get screwed up?
Old 09-03-2013, 10:35 AM
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What about certain airframes tendency towards coupling? My Cap 232 couples fairly heavy towards the landing gear. My buddy says his Edge 540 is very neutral and has little to no coupling. He says that's because his Edge is a mid wing design as versus a low wing design (like my Cap). I have no reason not to believe his claim that his Edge has no coupling or his explanation of why. It sounds good, and I just don't know enough to agree or disagree with him. It does seem that is a perfect point of discussion for this thread.

Once again, this is for the pure theory of each design. I agree with someone who posted earlier that all the mentioned airframes make good 3D birds if they have aft cg, huge throws, and big power to weight ratio. But this thread is simply to explore the pros and cons of each design. Every airframe has to compromise certain traits in order to capitalize on others.

Last edited by fasteststang; 09-03-2013 at 10:38 AM. Reason: typo errors, stupid auto spell checker haha
Old 09-03-2013, 12:54 PM
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Re: coupling, tucking to gear or pulling to canopy, can often be traced to CG placement? When the plane rolls 90 degrees the elevator effectively becomes the rudder? This is why some will trim their plane for neutral elevator (so the elevator is not trying to turn the plane when in KE).

That said, some planes are notorious for coupling on KE. The one that really sticks out in my mind is a Citabria.

That's my experience on the topic anyway. -Al
Old 09-06-2013, 05:52 AM
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LOL, I have been on RCuniverse since 2007, but account issues three years ago caused a reset. I don't get on much anymore except to look at classifieds, but seldom post on forums anymore. Hope everybody has a great year of flying.
Old 09-06-2013, 06:30 AM
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You should come out to our Fly-in at Elk City this year. It is Sept 21st. Fall festival of the arts is also going on, can drop any females off there and then head to the field. We will have giant scale 3D and war birds, plus a turbine or two.

David
Old 09-06-2013, 12:20 PM
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Originally Posted by daveopam
You should come out to our Fly-in at Elk City this year. It is Sept 21st. Fall festival of the arts is also going on, can drop any females off there and then head to the field. We will have giant scale 3D and war birds, plus a turbine or two.

David
I would like to, but will be on call that weekend so I wont be able to make it. I just got back from the Mooreland Oklahoma funfly and had a great time as usual, thanks for the invite!
Old 09-07-2013, 05:57 AM
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I was at Moorland on Saturday. Small world. We were on the far South end next to Brian the heli guy. Darwin puts on a good show.


David

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