I don't know how much it has to move, but that's sure pretty wood.

Serge,
I have both an El Diablo and Ringmaster for OTS that have 20 deg at most elevator deflection, both can turn much tighter than needed, I think your 29 deg is going to work fine. If you need to tighten the turn you can always drop to a 9" diameter prop, will usually do the trick.

Best,        DennisT

I agree with Dennis.  Given a "normal range" of tail areas the CG location is a greater factor than are large amounts of elevator deflection...especially with an unflapped wing.

Yes, that's pretty dandy wood!

Ted

We used to be able to pick up better wood all the time. The sheet on the other side is much blander B stuff. They were 7-8 pound and 6.4 pound sheets respectively. What surprised me was that the two sheeting pieces totalled .60 oz, while the latticed stab, hinges, elevator, and horn attachment pads and dowels totalled only .70 oz. 'sure wish I had more of that C-grain stuff!

I had done pretty well laminating the first piece of 1/16" sheet with CF, except that I thought I 'd have used less epoxy, if it hadn't set up so fast. Nevertheless, I felt that I could still save .1 oz over the previous stab. So for the bottom, I tried a different order of application. I really got caught out this time, and instead of improving, I used noticeably more epoxy, and under weights, it squeezed out over the tape protecting the hinge gap and hinges. That adhered the tape and closed the beveled area. What a mess that was to fix - more or less. So now I've lost the weight advantage and have a bottom I don't like to look at. THEN, I dropped the thing and over-sanded in one place, necessitating an insert and patch. This age thing shows up in a lot of extra work. Incidentally, I'm not sure I'd do the CF veil in the seam again; the edge sands like steel and makes contouring much more laborious, if you want accuracy. It's stiff already, and when the outer layer is applied (FG, CF, or silkspan) it should be over-kill stiff.

Pictures show where I am now, with roughed contouring in progress. Lines are for bevelling equally on both sides to ensure some airfoil symmetry. The l.e is critical for me; so I've learned to get the CF edge accurately under my abrasive block by listening for the higher pitched sanding noise, when my sanding block or file angle is right.

    How much deflection you need (or can use...) is a function of the tail moment. The reason you only need (or can use...) +-3/8" in the Ringmaster is that the tail is really short. The "zero-lift angle" of the stab/elevator combined with the length of the tail define the maximum pitch rate for a given airspeed, or if you like, the ratio of the equilibrium pitch rate to the airspeed. The bigger the angle, or the shorter the tail, the higher the possible pitch rate. To first approximation, what you want is to be able to drive the pitch rate for given airspeed up as high as you can tolerate without stalling the wing. With the super-stubby tail on a typical Ringmaster, you can tolerate very little deflection. The heavier it is, the less you can have because the pitch rate that generates the stall is lower.

    Of course the are other considerations. The length the tail also figures heavily into the damping, the longer, the more damped. This has to be played off against the maximum rate issue. Clearly the Ringmaster is too short. I think the Skyray is marginally too long, leading me to use every possible degree of angle in the elevator deflection I can get, which makes it really sensitive around neutral since the ratios have to be so fast. This has led to me running the CG much further forward than I started. This has had nearly no effect on the ability to turn but does reduce the sensitivity around neutral.

    I think the Skyray would be better off overall with a slightly shorter tail with less elevator deflection. Somewhere between the stock setup, and a Flite Streak (which is pretty darn close to the same wing, minus a bit of aspect ratio). The 20FP Flite Streaks I have flown have been somewhat better behaved around neutral when the CG just right than the Skyray. The problem is the that even 2 ounces of fuel running out of the Flite Streak means you have to have it nose-heavy at the beginning and tail-heavy at the end, and it's razor-edge as far as the static CG goes. I have in the past suggested that someone try a Skyray with about 1 1/2" off the tail, with the tail enlarged to keep the same TVC, but I haven't tried it myself.

    Note that nowhere here have I mentioned the absolute torque capability of the tail. This is the driving factor on flapped airplanes, but these unflapped wings seem pretty darn easy to pitch around, so it doesn't seem to matter very much, compared the the torque/pitch rate ratio. You could pick the tail moment for the right ratio, then fiddle with the size of the tail to see where the limits are, but I would expect that it doesn't make much difference and that you could get away with a very small tail area before any serious issues were seen.

    Brett

To first approximation, what you want is to be able to drive the pitch rate for given airspeed up as high as you can tolerate without stalling the wing. With the super-stubby tail on a typical Ringmaster, you can tolerate very little deflection. The heavier it is, the less you can have because the pitch rate that generates the stall is lower.

Huh?

That's a funny way of looking at it.  I have visions of a wing chasing an elusive relative wind.  I hesitate to say it's wrong: one gets in trouble in aero thinking of one thing causing another.  I look at angle of attack and lift as having a pretty constant relationship.  You can draw a curve that gives you one as a function of another.  There are a few subtleties: 1) there's a second-order lag between angle of attack and lift (I looked for where I saw that recently and couldn't find it), there's the effect of Reynolds number, there's the effective camber as loop radius decreases that Igor wrote about (of which I'm not yet convinced, nor do I remember the sign), and there's probably some more alpha-dot stuff, but I don't think these subtleties amount to much.  Once you've put in elevator to get to the equilibrium alpha, it stays there, and the airplane turns a loop of radius mV²/L.  The longer the tail, the more it needs to deflect to get the angle of attack it needs to hold the wing at a given alpha, because air in a loop is round, as Igor showed in his recent Stunt News article.  I always thought of this as being OK.  It's a virtue in combat.  It lets you pick the loop radius you want more easily, and my people use δe/g as a measure of stability.  Mind you, if you have a traditional elevator and stabilizer, you'd need to operate it at some ugly angle of attack to get enough tail lift to rotate the wing to the angle of attack you want the wing to have.  This might make it hard to do a nice square corner, and I thought this is what you've been telling me is a disadvantage of a long tail.   

Good question but not so easy answer, there are minimally 3 effects to think about

1/ separation bubble on high pressure side of stab in corner ... it was that sharp vs blunt think so many times commented ... the effect of bubble is clear and its existence depends on tail length

2/ AoA of stab in corner also differs with tail length so the elevator needs different deflection depending on tail length ... yes, as Howard mentioned I wrote it in that my article

3/ there are transients depending on tail length and elevator to tail ratio - the response of tail moment regarding its AoA is not linear, good response needs strong force (and thus moment) when model still flies straight and elevator is already deflected, and less and less as the model goes to circular path ... short tail with large elevator (especially in case of small tail when it must overcome large flaps moment) can be easily stalled and its effect can grow as model enters circular path, so it can have for pilot some kind of difficulties to make corners repetitive