I think the correct US spelling is weighnotanium.  Isn't that an alloy of aluminum, titanium and unobtainium?

At some point it'll start looking goofy with that long tail.  If the weighnotanium corrodes it'll look worse, of course.

At some point it won't corner well because of the circular airflow effect around the square corners -- the effective angle of attack of the wing goes down, and the elevator up, when you are in curved flight.  This is exactly opposite of what you want to turn.

On the other hand, it'll probably help smoothness in level flight, for exactly the same reason.

I'm not sure at what point these effects will kick in.

If you used a long CF tube to hold a regular balsa tail you could probably stretch a Skyray out to a considerable degree, and experiment with this in real life.

Here's an excerpt of a piece I posted here awhile back:

It's sort of a race among the aerodynamic, elasticity, and mass effects of the tail length.  I actually wrote stuff on this here on this very forum, but nobody read it.  This isn't surprising, because hardly anybody read aerodynamic stuff I got paid a lot of money to write.  Here is a combination of a couple of posts:

1. The effect of downwash: the more lift, the more downwash.  Downwash is destabilizing: you put in a little up elevator, and the downwash acts as even more up elevator. Longer tails make this better.

2. Pitching moment due to pitch rate.  This is caused by the change of angle of attack on the tail because of the air being round in a loop, rather than flat in level flight and maybe from the change in direction of the wind on the tail from airplane rotation.  The longer the tail, the more negative pitching moment due to pitch rate is, hence the more stable the airplane is.  Longer tails make this better.

3. Pitching moment due to rate of change of angle of attack.  The tail contribution to this is maybe (according to Etkin) due to the time between when the wing starts making downwash and the downwash gets to the tail.  I would reckon that this effect would make the airplane worse as tail length increases, but I don't know. 

4. Contribution of pressure distribution on the tail to pressure distribution on the wing.  An elevator hinged at the trailing edge of the wing acts as a flap going the wrong way, limiting the lift capability of the wing.  Longer tails make this better, but may not have to be very long to make this evil go away.  Maybe that's why the later, balanced-elevator Fierce Arrows fly better than the original.

5. Tail lift fighting wing lift.  The longer the tail, the less it has to push down to rotate the airplane to the requisite angle of attack, hence the higher net airplane lift capability.  Also, given the stabilizing effects of a longer tail, a longer tail lets you get away with a farther aft CG, hence even less force required of the tail.  Longer tails make this better.

6. Structure and pushrod weight.  Weight goes up fast as tails get longer, particularly if the airplane is designed to withstand indignities such as hitting the ground.  Pushrods get fatter to maintain stiffness.  Longer tails make this worse.

7. Pitch moment of inertial (barbell effect).  Longer tails make this worse, although the leverage of longer tails helps them get the airplane rotating.

8. Ground handling (fitting into cars and shipping boxes). Longer tails make this worse.

9. Reduction in dynamic pressure at the tail due to wing "wake".  Serge read something that Martin Simons wrote saying this is a big deal.  It's not.  Here is something quantitative: http://naca.central.cranfield.ac.uk/reports/1939/naca-report-648.pdf 

10. Sensitivity to CG position.  The stabilizing effect of a longer (and larger) tail let you get away with a wider CG range.  Longer tails make this better. 

Sorry.  I wasn't paying attention.  For constant fuselage length, assuming you keep the structure stiff, I'd reckon the bigger the better: we don't care much about drag.  There's the hinge moment issue that Phil mentions, though.  Hinge moment for a given elevator deflection would increase as the cube of enlargement in one axis, but tail power would only go up as the square.  

I was right with you, Kim. That "no-way-tanium" is real zoot chit, not all that rigid, and way too expensive to waste on a lowly Skyray 35. Assuming that you'd not want to change the pushrod, your hingline would stay in the same place. As the horizontal tail gets larger, the TMA would get shorter (but there's plenty to spare). And it might tend to flutter...   Is the hingeline sealed? 

Current stunt designs have used up to 30% horizontal tail (I'm not up on Wild Bill's low A/R design, but Doc Holliday has one, so maybe he can give some specs?).  Experience has shown that the bigger tail allows a more rearward CG. You'd think that if you increased the tail size without moving the CG aft, the "groove" would get better, not worse, as Phil predicts. As the elevator gets bigger and especially wider, the control loads would increase, subtracting from the line tension when deflecting it. This should make it groove better too, I'd think. Sort of like a "friction shock absorber", if you're up on antique car technology. If it doesn't flutter, of course! Wider is more likely to flutter, I'm pretty sure.

Logically,  a particular wing only needs so much tailplane for stability, and can only use so much tailplane lift to make it maneuver to its maximum ability. Basically, enough is enough, and more isn't going to help anything. But those control loads would not be a good thing, being as they detract from line tension when deflecting the bigger elevator. I think there's your limits.  Steve

Your CG, and Leadout position will have to be moved forward with each change. Before you reach the "Canard" condition, you will reach the "Tandem wing" configuration, where the forward, and the aft wing, has the same lifting area. in such  cases, the CG will be ~ mid way between the wings. 

I am thinking more along the lines of the tail starting to replicate what the wing does as it increases in size, it starts to become a true lifting surface.

The ultimate demonstration of this would be transforming a conventional model into a canard.

   A more interesting question is which way you should want to move the elevator, and what effect it might have.

     Brett

Kim may be giving us a quiz to find the impostors. 

Kim may be giving us a quiz to find the impostors. 

Still easy.

You find the total lift on the aircraft, and we know we always must have d(Cm)/d(elevator deflection) be <0 for stability, and that the intercept must be positive to find a neutral trim point. The airplane will progress from a conventional configuration, to a tandem wing, and eventually a canard, but the stability conditions remain unchanged.

Since the sum of the moments of all the surfaces is what matters, at some point you'll have to look at the tail volume ratio, and decide which surface becomes the horizontal tail and which the main lifting wing.

But, you end up with a canard...the most vile, inefficient, unpractical configuration a subsonic aircraft can have.  Even in nature, on a real canard, the horizontal tail is located aft.

Canards are BAD airplane designs. For many reasons, and hence you never see one.

...Logically, a particular wing only needs so much tailplane for stability, and can only use so much tailplane lift to make it maneuver to its maximum ability. Basically, enough is enough, and more isn't going to help anything...

Yes, which raises the question are we there yet?  By analogy from the world of flappers, if you had asked the big boys back in the day of 20% tail percentages if they had enough TVC in their then-current designs (bringing TMA back in here after I artificially removed it in the thought experiment), they would have shrugged and said of course. If not, then they would already have been flying planes that look more like what is flown today. Applying the analogy to flapless, have we found the optimum TVC yet?  Has anyone gone looking for it experimentally?  

And, BTW, is 30% looking like the upper limit for tail % in flappers before the Law of Diminishing Returns kicks in (or maybe it has already kicked in), or will flapper flippers continue to grow?  

Yes, which raises the question are we there yet?

Perhaps the answer is to be found with a nice profile Skyray with a good set of bolt-on horizontal stab/elevators.

I suspect that you would want to play around not only with tail area, but with the relative location of the hingeline.

Kim, I just finished up my SkyRat( Rat rodded skyray) after being beat about the head and shoulders by Fernandez for over a year. He said try it you will like it. Anyway, my mods include enlarging the stab/elev (mostly in chord) to 86.36 in/sq. The stab is 49.56in/sq and the elev is 36.8in/sq.  The wing area was increased with fixed flaps ,2" cord at root and .5" at tip for an additional 52.5 of wing area. Not sure what the original area specs. are on the wing and tail areas. The elev. hinge line ended up 14.625" from original trailing edge or 12.625" from new trailing edge of fixed flaps. I estimate the hingline is moved back about 1.5" from plans location. The hinges are cloth all the way accross(no gaps) I figure this will have similar effect as using tape on the hinge line. Flew it two flights the other weekend but results inconclusive due to less than stellar engine runs with FP20. I tried to duplicate the dirty dan/ Brett Buck set up with inboard hayes thank , but must have blown chillies somewhere. Will put different tank on it and mount it outboard on muffler pressure and give it a go this weekend. will report back

Your new beastie would be perfect for some cool grafix like Ed "Big Daddy" Roth's Rat Fink stuff.  Like a manta ray with a rat face or such.  

The guys at Alameda had good results with FP20s and inboard Hayes tanks on short-nose Flite Streaks, but I don't know what their secret was.  I could ask if you're interested.  Questions:  How much does it weigh?  Where is the CG (in inches behind the LE).  How wide is the elevator?  How is the control sensitivity and tracking in level flight, once you get the engine run sorted out?  

I've always been interested in whether or not fixed flaps do much beside making a rectangular wing look better.  If they do add lift in turns, then they are an easy, lightweight way to do that.

IIRC, Derek Moran finished 2nd (I think) in Advanced with a 'Ray/FP20 against a very large field with lots of sophisticated equipment at GSSC some years ago.

I am very interested in how the SkyRat performs for you.  Please do report back.  Got any pix?  

As "Stunt Fairy" Fernandez always says to me, "Just trust me."  You can't go wrong (unless the subject is dating tips).  

Best of luck to you!

Kim I will get all that info and pictures togeather and put it in another thread . It is a good excuse for me to learn how to post photos.

Incidentally, there is one of the Tarzan books, where he makes a journey to Pelucidar, in the center of the earth.  The trip is made in an airship constructed of a material something like that discussed here, but it also has a gravity repelling characteristic.