RE: Spin exit
 

Thanks Evan for the confirmation of an aileron maneuver, but the rest of the considerations is a bit confusing for me. You know I have only the virtual Taurus and don't completely trust the simulator, but the basic influences on stall and spin are rendered. At least I could copy the differences reported about real models in the Taurus thread. There, stall was a matter of wing loading and elevator throw. If you have less of the one (Ed's and your copies) you just need more of the other (kick-up elevator with reeds, no aileron possible with only two simultaneous functions). Anyway, the virtual Taurus spins like crazy if enough of the ingedrients is provided. It's basically reluctant to spin (Kwik-Fli even more) and therefore (I believe) exits the stall gracefully.

That's why I can't believe there is a stall in "modern" spins at all. What Rusty and others here wrote seems to show that any stall is positively avoided. When 90% elevator is reached the model is still not stalled. Now releasing the elevator to start the "spin" lets the model drop its nose so it looks like a stall, and now a motion looking like a spin is commenced with aileron and rudder. Of course, it's possible that now a stall develops, but it hasn't to.

On the other hand, the full-size competition spin entry is possible also with models, but maybe does not conform to the judges guide. Even worse, models like Taurus and Kwik-Fli with soft-stalling (thick, blunt leading edge) airfoils and maybe even square wing planform, badly need that competition entry to get into a real spin. If you would stall these models (and full-size planes like the Cessnas and even the Z-526 with their huge washout) in the first place, you would get a straight-ahead mushy stall and buffeting and still no spin with even full rudder. That's why you need aileron, but then you could as well avoid any stall and autorotation and be in full control.

If Kwik-Fli or Taurus (or a Cessna) is slowed down slightly above stall speed and then yawed, only the inner wing stalls and only after beginning the yawing motion. (Is that zero points?) That's the only way to have also the wingtips stall at all and besides have the outer wing unstalled, what gives the rolling motion. In many if not most spins the outer wing isn't stalled.

With tapered-wing airplanes, maybe with sharp-stalling aifoils, we have the choice to really stall them completely what means a tip stall and rolling to one side or the other due to roll instability (negative roll damping). We may help and direct the spin with ailerons, which force one wing to stall first (another, nasty way to get a Cessna spinning). In the spin, both wings may stay stalled.

My bottom line (hopefully to the topic now): We can choose between several kinds of spin entry, with some models more than with others, which determine the kind of spin and even exit. Who does that consciously and deliberately? While I try that full-size, models are too small and fast for me. :D

Skylane, could it be that you really stall your models in spins and on Kwik-Fli only one wing is stalled while on Cutlass and Compensator both? And do they have a sharp leading edge (hysteresis)? Will full up elevator give a stall in straight flight? (By the way, big stabs on a short moment arm may be more effective in tight turns and spins than small stabs on long arms. The same, of course, for vertical tails.)

P.S.: Just to forestall one objection, Kwik-Fli's standard elevator throw (about 25 degrees) is likely not sufficient for stall, but if you slow down the model and finally hold full elevator, instead of slowing down further it will drop its nose, what may look like a stall. Now yawing lets the inner wing stall and initiate the spin. Letting the rudder go stops the inward slip and thus the stall and the whole spin, even with full up elevator. (It's not the initial yawing motion what lets the inner wingtip stall but the sustained inward sideslip.) No ailerons throughout!
(I'm not positive if "inward sideslip" is correct. I mean the airplane is yawed inward into the turn. But the outer wing is ahead, so it may be as well correctly called outward sideslip.)

RE: Spin exit
 

Hmm, not sure what you are getting at Stick, but my comments are only based on what my models do. For competition aerobatics, the model must be able to be stalled, that is, in straight flight. How easily the model will do that is determined by loading and wing section. Those two considerations determine the angle that the wing will stall and the speed it will stall. One simply arranges to have enough elevator, and suitable balance point, to do that. Indeed it is one of the trimming checks you have to do. Taurus stalls straight and autorotation occurs only after application of rudder, with full up elevator held. Aileron is required to maintain rotation, cause as you suggest, the outer wing panel will unstall as soon as rotation starts, and the added 'down' aileron keeps the outer panel AOA above the stall angle. The resulting spin is quick, quite nose high, and exits immediately on relaxation of any of the controls. My 'Atlas', on the other hand, is quite different in response. As it slows it tends to lose heading, stalls quite easily with, (my model, you understand) a bit of right wing drop as the nose drops. One simply bangs everything full 'right' while holding full elevator again, and the spin is a little slower, but the nose is well down and much more height is lost than with Taurus. Release of all controls stops the spin in about 1/2 a turn. You must allow the model to accelerate a little before correcting to S&L, or it will spin again, so it really is stalled. After a few '0's in comps one tends to make sure that your models really do stall. Flicks with this sort of set up are really easy, cause the elevator has plenty of movement and is much more effective with a bit of speed on. Timing the elevator 'on' and 'off' is not so easy, I still overcook it on most occasions. more practise.
Evan.

RE: Spin exit
 

I agree with Evan that my models are truly stalled as they enter the spin when everything works right. As the nose drops I add full rudder and aileron as Evan described above. What I did not appreciate when I started the thread is that it is normal for different models to require various amounts of rotation to exit the spin. That point is underscored by the 1/2 rotation reported for the Atlas above. Part of my problem may simply be to get the model to stall and spin the same way each time, so that a consistent recovery is possible. It does seem that sometimes I have a fast rotation and sometimes a slower one and that throws off the timing. I will work on getting predictable and repeatable spin characteristics as part of my practice program. Thanks for all of the insights in these posts.

Jeff

RE: Spin exit
 

Skylane, that's exactly what I assumed. I think your C... models are really and fully stalled before commencing the rotation, and there are different ways to commence the spin determining the kind of spin and exit. Kwik-Fli is different, though, I believe. Sorry for my long-winded posts, I just have to explain it to myself.

Evan, it's simply that I can't substantiate with "theory" what you explain practically. Your explanations work, mine don't. I had believed that your Taurus is partially stalled, the outer wing unstalled. I would explain the effect of ailerons by increased lift helping the wing rotation. I'd suspect the outer wing isn't even near stall, and even if it would be, ailerons, like flaps, increase lift at any AOA up to stall AOA, which is roughly unchanged by flaps, and even past critical AOA. Simply said: autorotation is weak because the outer wing has rather small AOA.

Now you said the spin is quick and nose-high, I'm confused again and try another explanation: The whole wing is deeply stalled so even the outer wing is just stalled and has quite high lift while the inner wing is stalled at very high AOA with less lift. This lift difference makes for autorotation, but it may be small due to the shallow slope of the post-stall lift (over AOA) curve so it needs help by ailerons, which are effective even post-stall. The fast motion may be due to the big drag difference, drag being huge at the inner wing in deep stall.

I had thought you set up moderate elevator throw so Taurus is hard to stall considering it's airfoil, but you might have set the C/G near the neutral point. Besides, Taurus has a not really big stab and a short tail moment arm, what might explain the nose-high spin. Might as well be that the fast rotation and slow vertical motion, both due to light weight and high lift, make for low AOAs like in my first scenario. And while I could copy the stall behavior in the simulator last year, now I can't. I wish I would really know (understand). There are so many possibilities and it's so late... [:o]

RE: Spin exit
 

Yeah Stick, just to really confuse you, the TF Taurus is more difficult to stall than the Meyer plan version. I know the longer moment of the TF should make the elevator and rudder more effective, but there it is, I can only report on what I see. The high rotation speed of the Taurus variants could be due to the relatively small side areas of the fuselage/fins compared to the later, more 'fishy' fuselage models, their lighter loadings also help, not so much inertia to overcome, both getting into the stall, and back out again. Different models, different reactions.
Evan.

RE: Spin exit
 

Thanks Evan, at least that one relieves me. Shorter tail moment arm gives more downwash helping the stab. :D

Don't think fishy fuselages are a major factor, but different wing layout including airfoil, and, of course, distribution of masses. Unfortunately, my simulator doesn't include gyroscopic forces so it's useless at this level of analysis.

RE: Spin exit
 

Downwash US? Wing is stalled, no lift, no downwash, just turbulent wash flowing over the top of the wing, and prolly over the top of the tailplane too, as it will have little (no) forward speed, but air coming at it from all sorts of strange places...I mean, just think about it, get your model and have a look, it's dropping vertically, and rotating about the CG as well. Can't have airflow straight over any of the surfaces, or any surface at an AOA less than stalled. No, the aerodynamics are completely different, and probably cannot be accurately modeled in any flight sim.
Evan.

RE: Spin exit
 

Argh, Evan, I'm working hard re-examining my German sources about spinning, and you are poking fun at me. But nothing to fear for an engineer. [8D]

You said the 1" longer TF version is more difficult to stall than the Myers version, and that should be simple, needs much stab effect to get it to stall what is helped by downwash. Post-stall lift is reduced but not lost so there's still downwash (though reduced), just with "embedded" turbulent wake, and maybe the stab isn't even hit by the wake. The stab must stall "later" than the wing, achieved by low aspect ratio. I agree that it's fully stalled in spin, mainly due to thin airfoil with sharp leading edge. The 2419 wing airfoil is thick and has a blunt leading edge so stalls softly, meaning loses lift slowly when AOA increases. There's still much lift even at huge AOAs.

Spin is a helical motion, the vertical axis near the inner wingtip, and even there the AOA is not 90 degrees but less than 45 because more than 45 degrees nose-up would be flat spin (by definition). Even in flat spin the axis is not in the C/G, though it's nearer. While the inner wing and likely the stab are stalled, the outer wing is not stalled in most spins. Because the stalled inner wing still has much lift, the unstalled outer wing has to give even more lift to maintain autorotation. If your Taurus spins flat with fast rotation, then there's still much forward motion of the whole wing, especially the outer one, and relatively small AOA. So probably the outer wing is not stalled and operating at a small AOA with little lift, so you have to help with aileron to maintain autorotation.

Spin is determined by equilibrium of aerodynamic moments and moments of inertia (centrifugal and gyro), that's the only reason why my simulator is useless because it has no inertia included (in contrast to me), at least no parameters. By the way, who was Gyro Gearloose? :D

RE: Spin exit
 

Cor Stick, you are an engineer! Been out flying Taurus and Atlas back to back all morning, so here's the 'real life' results. Taurus stalls straight, no wing drop, spins with fuselage around 45deg nose down, no detectable eccentricity, ie, appears to rotate about cg. Immediate unstall on release of any control. Atlas gets all waffly as it slows, gentle nose and right wing drop at the break. Spins about 70 deg nose down, slow spin, looks like the centre of the spin is about the side of the fuselage, ie only just detectable eccentricity. Takes the air about 1/3 turn to tidy up after release of all controls. The real difference between the models is about 10 years, Taurus is fun, Atlas is a pure competition 'arrow'. Chalk and cheese, but one begat the other...
Just a thought, but I doubt 'downwash' has any effect on our small models, not enough model to affect enough air to do that, beside, if it was something to consider, then why, despite where the wing and tailplane are situated, do we not take the effect into consideration when designing models? A 'T' tail, low wing model has exactly the same wing/tail chord relationship as a high wing, low tail model. Both seem to fly just the same despite one being in the mythical 'downwash' and the other not...but I am patently not an engineer, and a cynical modeler to boot.
Evan.

RE: Spin exit
 

No offense meant, Evan, on the contrary, I highly appreciate your reports from real life, it's just real life what I'm missing and I'm quite irritated that I don't get my theory working, not even my simulator. Hope you don't mind my weird and ironic kind of humour. (I had left the allusion Augsburg-Ducksburg to you.) Found a good R. A. Heinlein quote: “I never learned from a man who agreed with me.” I've learned a bit already.

But with each of your reports there are also more mysteries for me. Still no idea why just your Taurus flat-spins and Atlas spins more like expected. Still not found out why the spinning axis is more inboards on the models than on full-size airplanes. Maybe due to higher cubic/quad wing loading, but have not yet thought about it. It's just all food for thought for me.

Downwash is the only topic I feel quite sure about. At least we do consider it when designing models, or we rather neglect it and adjust for it later when trimming the model. It's just hard to calculate. Using a simplified method, I calculated for my parkflyer 6 degrees at 1.3 wing lift coefficient (pre-stall), 3.5 degrees at 0.7 (cruise) and still 2 degrees at 0.375 (fast). The textbook tells vertical position of stab is only a second-order influence on downwash, not to confuse with the turbulent wake.

Maybe I should follow another Heinlein quote: “Never worry about theory as long as the machinery does what it's supposed to do.” Thanks for any suggestions and representations!