Originally Posted by Tzeentech

Hmm thats weird because the FAI accepted some world records in the F3S class. What's your source Steve?

Edit: When do we get high performance outrunners from NEU like the inrunners??

You will find F3S in the F3A rules. The documents are here: http://www.fai.org/ciam-documents

Here is what the model definition is:
5.12 CLASS F3S – RADIO CONTROLLED AEROBATIC POWER JET MODEL AIRCRAFT
5.12.1 Definition of a Radio Controlled Aerobatic Power Jet Model Aircraft
Model aircraft, but not a helicopter, which is aerodynamically manoeuvred by control surface(s) in attitude, direction, and altitude by a pilot on the ground using radio control.
5.12.2 General Characteristics of a R/C Aerobatic Power Jet Model Aircraft
a) The R/C Aerobatic Power Jet Model Aircraft shall use as a propulsion device either
a) turbo jet/s or
b) ducted fan/s.
Ducted fans my use piston engines or electric motors as a power source.
b) The number of model aircraft eligible for entry is two (2).
c) Paragraph B.3.1.a) of Section 4B (Builder of Model Aircraft) is not applicable to class F3S.
d) For power device limitations, noise rule, and radio equipment: See 5.1.2
e) Noise limits apply to model aircraft with piston engines only.



Steve Neu

Originally Posted by AliasJack

It´s called F3Speed

I am only pointing out that F3S is not a speed class as far as the FAI is concerned.

There are ways to get a speed class into the rules--but someone needs to come up with a well defined set of rules as to what the event is and propose it to the FAI through their countries representative.

Steve

From an engineering standpoint a wave spar like that is not good for a plane. There is too much material near the chordline and thus not contributing to the bending strength of the wing. It is used in other applications(race car wings, etc) because they have very short wingspans and do not need the extreme bending strength that an airplane wing does. Using this construction method on a properly engineered airplane will result in a wing that is heavier and/or weaker than a traditional spar construction method for the same weight and dimension wing.

Originally Posted by biskit

From an engineering standpoint a wave spar like that is not good for a plane. There is too much material near the chordline and thus not contributing to the bending strength of the wing. It is used in other applications(race car wings, etc) because they have very short wingspans and do not need the extreme bending strength that an airplane wing does. Using this construction method on a properly engineered airplane will result in a wing that is heavier and/or weaker than a traditional spar construction method for the same weight and dimension wing.

So why should that matter? The wing is going in a self designed swept forward wing, the goal is in fact 250 mph. How would you suggest an innovative person to build a stronger foam core wing? I don't have CNC in my work shed. The stress is all in the skin and the wave holds it together dude.

The wave spar will have its advantage in torsion stiffnes,not bending strength.
on a swept forward wing especially torsion may be the biggest challange.

Yello

Originally Posted by sneu

I am only pointing out that F3S is not a speed class as far as the FAI is concerned.

There are ways to get a speed class into the rules--but someone needs to come up with a well defined set of rules as to what the event is and propose it to the FAI through their countries representative.

Steve

Hey,

so, F3S was the Speedcup-class of the German Aeroclub.
When F3S(Jet aerobatic) appeared it was renamed to F3Speed.
There is no FAI class concering speeding, just a type of record (No 175).

Jakob

That sounds like a reasonable application! It would surely help with rigidity I would think. As long as weight is not a top concern and the added complexity is OK then it seems like it would be well suited. It looks so cool it's a shame it will be hidden inside the wing!

How much wing sweep are you looking at? And why a swept forward wing? Note that no real military aircraft have a swept forward wing even when absolute speed or maneuverability is required and the resources(money and engineers) is unlimited. Not trying to be Debbie downer, just curious why you chose such a wing shape.

Originally Posted by ApexAero

So why should that matter? The wing is going in a self designed swept forward wing, the goal is in fact 250 mph. How would you suggest an innovative person to build a stronger foam core wing? I don't have CNC in my work shed. The stress is all in the skin and the wave holds it together dude.

Yello,
The top of the wing gets 6 oz S-glass/E-glass progressive laminate on exterior of the wing for compression, bottom has the same with carbon for tension. built up style. Its all experimental at this point! I hope to prove the design before attempting to mold it. The next few will be from my skill set using balsa and composite for prototyping to the final design.
Presently the fuselage will be planked, sanded and glassed with carbon accents and the wing will have a slightly thicker root eh1090 to the tips eh1070 that will with tortion along with carefully laminating the center section.

Biskit, Its just something I pulled out a dull spot about 11 years ago when I had a fist full of wings all bagged, I cut one up following a Cornelius design from 1936 and have been modifying it on and off since. Now I found the croco site and the German speed guys and found new breath in the hobby at the potential of the outrunner at speed and the efficiency of the swept forward wing verses all other wing designs because it is totally different thats all. There is another revision I will share when compleated..
Tom

The forward swept wing will have many disadvantages also, tanstaafl. That's engineer shorthand for there ain't no such thing as a free lunch.

Explain, pretty please. I don't understand your drift. In another thread a friend did a pressure analysis and found the swept forward to be way more effiecient than a straight or rear swept. Please explain your view point.
Tom

Just a rough layout, I was trying to leave room to cut in a servo pocket toward the rear. I would think this and a center layup should keep things stiff.

I think what biskit is trying to say is it's going to be more difficult to make a swept forward wing structually sound. Torsional rigidity is going to be your biggest issue I think.

I would try to make the wave spar go forward and back as much as possible. You really want to lock the top and bottom skins together as much as you can. Id probably cap each wave with carbon rovings also, just to give it something more solid to stick to.

Just my thoughts.

I think you can make the wing plenty strong enough with a normal spar / sub spar routine, but I have no problem with trying new things. You can make really strong bagged wings if you want to, but they usually come out a bit heavy.

As for the forward sweep, I built one for slope speed in 1989 and it was plenty strong with bagged carbon skins. Inspired by the Sitar Special, I used to spend 30 minuted getting it as high as I could for one big dive, though I was never satisfied that it had reached top speed and I was not flying in the Alps, so would probably never exceed 200 mph anyway.

I was recently looking at my old design and I think I'll be making a new version for powered flight. I had already started an electric fuselage plug because I thought this was the way to get it higher before diving, but now I can leave the motor running.

For a model the structural issues are no big deal. A swept forward wing is only marginally more efficient. Unless you are sparing no expense on the drivetrain and other parts it doesn't seem worthyhe hassle to me. It is not worthwhile on real planes either, that's why nobody makes them.

Say it is 2% more efficient, even if you have 5kw in the plane that's only good for an extra 100w! I doubt you're going to have 5kw in it running continuously?

Originally Posted by biskit

Say it is 2% more efficient, even if you have 5kw in the plane that's only good for an extra 100w! I doubt you're going to have 5kw in it running continuously?

Why not? Even a small Powercroco is capable of 4KW continous at 6S..