What are the design elements necessary for a good 3D plane?

Many other threads state elements from being light / strong / wing loading etc. So what is it that contributes to the best design for 3D?

At one time it was suggested (way before 3D was ever even thought of) that you could take all the elements of the current crop of upper level pattern designs and come up with an average for the best plane. Another perspective is you would end up with an !QUOT!average!QUOT! plane. The reasoning behind this is every design is a compromise to gain a given result. Do we design for the best tork roll / blender / wall or ????

I'm currently working on a design and have some of my own ideas. Just wondering how other opinions will surface that may change the direction of design. What airfoil / thrust line / moments etc. are some questions that come to mind. Should the wing be straight or tapered? Advantages/ disadvantages of each? Should the tail feathers be flat or air-foiled? There must be others that have addressed these same questions.

Input please.

EXCAP232

For Harriers, Elevators and hovering the straight leading edge of the Edge seems to be best. For tumbles and spins the swept wing of the Extra, SU and Cap seem to be better.The placement of the h stab on the Cap seems to give better performance for rudder in pos and neg maneuvers. A longer fuse seems to aid in stability and torques but it hampers the tumbles...

As you stated... There is always a trade off. I would be curious to see a raised stab placement on a straight edged wing, mixing the Cap and Edge a bit. Light loading the wings, slightly longer tail, more cord stretch than lengthening span. O'... Obscene power too.

Just thoughts...

Bean

What do you want the aircraft to be good at? There are small trade-offs changing just about every aspect of your airframe design. Thick, blunt L.E. airfoils are better for slow speed flight, harriers, elevators, parachutes... thin, sleek airfoils allow for a higher speeds and better tracking at speeds generally with the tradeoff being a slight degredation of slow speed characteristics... enhanced tip stalling at low speeds, buffetting on the "edge" of a stall for example. Thick = better downline braking as well.

As said previously by 3DRC I too have found that the more taper in a wing, the better it snaps but the more likely it is to tip stall at lower speeds. L.E. taper back increases the same characteristics as chord taper over the length of each wing.

Large control surfaces are a given as well... the more there is, the more control in every aspect. Especially large ailerons, bigger is better for slow speed, harriers, rolling harriers, counteracting the torque while toque rolling to stop the rolling and hover stationary... need the ailerons to come as far inboard as possible to get them in the prop blast.

Heavy airplanes "tumble" better. Heavy can mean a big model with light wing loading or a smaller one with higher wing loading. Without weight, you lose inertia hence the plane comes to a stop when you change the attitude quickly, or changes the direction of the flight path to "follow the nose". With a heavier aircraft you can change the angle of attack or the attitude quickly but the plane has so much inertia going in the direction of initial travel that a quick change in attitude will change the planes attitude instantly but the direction of travel will be maintained for a short time. A constantly changing attitude gives you a nice tumble because the airframe never "locks on" to one given direction because it's not pointed any given direction long enough for inertia to catch up. So there is a plus side to light AND heavy, depending on your flying style and what you want the plane to be best at, its hard to make a little plane that does both, not till you get to over 25% scale or so it seems, then you start having enough weight to tumble good and still have light enough wing loading to 3D too.

Airfoiled tails fly more true I think, you can get away with flat airfoils on smaller planes to keep the cost and complexity of the average kit/arf down. Not very familiar with what actual benefits there are when comparing the two.

This is getting long so... There is no one design that excels at everything, there is always a plane that does x better than that one, but that one does y better than this one. You cant have the best of everything in one, thats why our sickness requires "another" plane constantly, "Oh look at what that one does!... sweet, I need one. Mine wont do that." And as fast as you get one that does y, somebody invents x and you now need a plane that will do that. Now, only if I had a bigger basement...

I have designed a lot of planes, mainly for sport + hovering. Two things to note is that when a manufacturer designs a model (even Christophe designs) for 3D they invariably (i know there are some) are not true out + out 3D models. By which i mean they are a lot more stable than could be, this is for 2 reasons- the mass market (especially outside the U.S.) would potentially get into trouble with a specifacally designed out + out 3D model with instability designed/ built in. This is connected to the second reson, a manufacturers worst nightmare is lots of kits returning, claims, refunds and even lawsuits. A bad reputation arrives quickly, but doesn't go away as quick as it come. Even with all the disclaimers and prohiberters you can think of won't help. To make a model more for the expert in my opinion (but i could prove it) the models moment arm is critical, too long like many supposedly 3D models and you dont get the manourverability in pitch. You can go too short and the model starts to lose its pitch again. This is why so many rate scale planes for 3D, many dont realise it but the moment arm is as short as can be, much, much shorter than areobatic, sport, and many so called 3D ships. Next time you rip yourv tailplane off a so called 3Der, move it forward approx 90mm on a 50-60 incher for example and note the differnce. Yes move the battery back a tad to keep the same c+g.

it is possible to create a section that provides the instability required for chaos manouvres, stability for predictable 3D and for smooth aero, but it is not section alone that do the job. It is a fine balance of moment arm, surface areas, and weight.

In reference to "kunte" I don't plan to market this design for the very reasons you noted in your post.
In reference to "Archie" stating "It is a fine balance of moment arm, surface areas, and weight. and the proper section (assuming airfoil)." This is the reason for the question. My hope was the H-9 Funtana would be a good compromise. From posts here it seems that it isn't! I will find out first hand soon as mine is nearing completion. Some time on a friends before mine came in but not enough to really find out the capacity.

While experimtation is fine I don't want to re-invent the wheel. What airfoils / moment arms / wing loading // etc do you like and why. While the straight leading edge does seem to help with harriers and the like it also keeps the plane from stalling and entering flat spins etc. I'm sure the airfoil also has an effect. In larger planes (35% and up) the wings planform used on the Extra, CAP and Staudacher seem to be a good compromise. They have a slightly tapered leading edge with the trailing edge tapered more.

There are several planes already on the market with many of these characteristics.
CA models Widebody 40 and 60
CA models Extra
Capiche 50 (not available here in the states)

Building season will arrive soon. Several 3D planes are on the bench currently and will be tested. Winter projects include the CA Extra 27% which will most likely get a DA-50cc. The pattern forum has a number of threads on the Widebody planes. Many are reducing the size of control surfaces to get better "pattern" type performance.

Thanks to all for the information. Keep it coming.

EXCAP232