In the constant pursuit of "trimming perfection" I'm now working on the exit of the three turn spin. In the past this has never been a real problem - most of my planes would exit with about 1/8 turn. However, both my Cutlass and my Compensator have rather erratic exits (it couldn't be the pilot...) Typically, the problem manifests itself as an extra 1/8 to 1/4 turn on the exit, so I have to lead the exit more than normal. What has me scratching my head is that my Kwik Fli III exits beautifully! On the Compensator I have tried more/less rudder throw, more/less elevator throw, and more/less aileron throw. I haven't hit a set of throws that yields consistent exits. This is very perplexing, because I've never encountered this with my Deceptions, Tipo, or Escape. I have tried moving the CG back a bit on the Compensator and that seemed to help, but that was on the last flight of the day, so I don't have enough flights to prove that that is the solution. As it is, the Compensator will sit on its tail when the fuel tank is empty and it flies the other maneuvers well, so I don't believe that it is nose heavy. So my questions to the collective group are 1) have you ever had this problem and, if so, 2) did you find a solution?

Jeff

Not all models are created equal, Taurus exits just now, Orion takes 1/2 a turn. Atlas uses 1/4 turn, Sicroly about 3/4. You need to fly them a bit and just compensate for the model. Sometimes just releasing the controls is not enough, you may have to push a little 'down' to properly unstall the wing. A case for mode 1 pilots here, as you don't add any extraneous aileron when doing so.
Evan.

I suggest trying more elevator and less aileron. Should slow the spin rate down a little and make it easier to catch at the right point.

These are interesting points to consider. Thanks. Evan, what I'm really curious about is what factors affect the spin exit. As a physicist I look at this as an interesting problem in aerodynamics. I'd like to understand why this is happening, i.e., why the different models have such distinguishing characteristics. Of course, one possibility is that there is no single dominant cause and the effects are due to the combination of small design differences. But it is still an interesting topic to ponder. For example, the new Cessna Skycatcher had spin recovery problems in certain extreme configurations before modifications were made to the design.

Jeff

I second this question. As an engineer I share your interests even though I may see the problem from a slightly different point of view. From my experience, a heavy wing (moment of inertia) and an airfoil with much hysteresis, beside a tip-stall prone planform, make for nasty spin exit. I feel affirmed since [link=http://www.av8n.com/how/htm/spins.html#sec-spin-recovery]Denker[/link] refers to losing vertical and roll damping in spin. But [link=http://ntrs.nasa.gov/search.jsp?R=227470&id=1&as=false&or=true&qs=Ntt%3 Dd-6575%26Ntk%3Dall%26Ntx%3Dmode%2Bmatchall%26Ns%3DHa rvestDate%257c1%26N%3D0]this[/link] NASA report may give an authoritative overview.

May I in turn ask another, relating question? Do you all use ailerons in spins? A while ago I learned that it's customary using ailerons for snap rolls since maybe the 1970s. But I thought spins are still done the "pure", old-school way, except with the modern aerobats with special airfoils. And by the way, did you ever spin your Skylane?

Edit: Link was wrong, if it still doesn't work search for NASA-TN-D-6575.

<span style="font-size: 9pt; font-family: Arial; mso-fareast-font-family: 'Times New Roman'; mso-ansi-language: EN-US; mso-fareast-language: EN-US; mso-bidi-language: AR-SA">Interesting to me is that the comparisons are made between our model airplane and certificated (I presume) aircraft. Though not an engineer, nor an aerodynamicist, enough years of flying, teaching, some aviation science courses, and much studyingin both arenas, has led me to the conclusion that it often "all depends". As Pimmnz said, "not all models are created equal". The short of it is, that lacking any certifiable spin recovery technique (and you have to revert to spin recovery techniques since we are beyond the stall event),one age old recommendation is: ensure throttle is at idle, neutralize ailerons, then apply FULLrudder OPPOSITE to the rotation. In the case of an actual airplane,applying full rudder meansto the stops; however, with the model it may be somewhat less given the amount of rudder area typically found. I did experiment with this because back in the dayI also couldn't figure out why any of my pattern planes recovered from the 3-turn spin in like fashion. A number of years later I found the technique to be very useful in recovery the model from the spin. I fly single stick and typically twist the knob rapidly opposite the spin, and push, it generally takes a few moments of a second maybe two and the spin stops. Practice then makes for smoothness. Just amethod that you might want totry Jeff. The technique works well in actual aircraft too. I built and fly a RV-6. It has no spin recovery technique per say since it's an experimental. When it enters the spin it develops into a very rapid rotation which stops very abruptly with full opposite rudder and a bit of push. After five turns it requires a bit longer to stop and a bit more push toreduce the high angle of attack (I haven't gone beyondfive turns!) Oh, I do not use ailerons to enter the spin either (as best I can tell) the stick is neutral as far as the ailerons are concerned. There may be some wiggle, but it's not intentional on my part. Sorry to butt in, I did find it an interesting question and comparison.
Mark</span>
AMA 63845
SPA 384

Jeff

One extra fact to think about, "throttle is at idle".
But what is the power rate, and what is a reliable low idle ?
For that reason I think it is also interesting to try the opposite spin rotation.

Cees

Good idea. Try spinning it the other direction to see if a reliable exit is available for that direction of spin, and recovery.
Chris...

Starting the spin with left rudder seems to be the best.
With our normal engine rotating direction, theoretical, I expect some nose down reaction as result of stopping spin rotation of the plane that was started by that left rudder and that seems to be a profit.
The amount of “nose down� depends on gyroscopic forces of engine and propeller, so RPM (and a lot of other data). Maybe it isn’t much but it is interesting to observe if there is any difference.

Cees...

Great points being made in all the replies. Thanks! Regarding full scale spins, no I haven't spun the Skylane, but I've done spins in a CAP-10B and C-150 Aerobat. The Cap required 1/4 rotation and standard spin recovery techniques - opposite rudder, down elevator. You entered the spin using both rudder and ailerons, and up elevator, of course. As far as the idle setting is concerned, the engine is set to a slightly high idle to insure that the engine stays running through the various maneuvers. I have one of the channels set so that I have a ground/landing idle and a flight idle. But it isn't any higher than I've used on previous models. I understand that I can try exit techniques involving opposite rudder, etc, but I've never needed to do that before - just centering the controls has been enough and that is what I'd like to get back to. As far as direction, sometimes it seems that left works better and sometimes right. It isn't consistent. So, I think that the wind direction (crosswind, etc) has more to do with it than the idle speed.

There are a lot of variables - that's one of the reasons that it is fun to try to figure it out! Of course, it is also a bit frustrating at times.

Jeff

Spin...control deflection, timing...another approach?

(This has been edited for accuarcy and flow.)

If nothing else I like to ask top pilots "how" they fly various manuevers. Some chose to give little information, some share everything.

Try less elevator and less rudder during the spin...say 80% of elevator used to enter spin and 80% rudder and 10% more aileron.

Remember that you are still "flying" the model...timing is everything...try releasing rudder slightly before releasing elevator then the ailerons last. These are fractions of a second.

For Futaba 14MZ or 12MZ/FG users:

Positive spin/snap:

1. Create a new condition called "Postive Snap/Spin"
2. The condition is activated/"on" @ 90% of "up" elevator stick. The stick is the switch.
3. Using the "hysteresis" feature, the condition is "off"/normal @ 20% "up elevator.
4. Using AFR, reduce the elevator and rudder to 80%...or 20% less than it was...AND increase the aileron 10+% (fiddle until you like it.)

What did you just do? Typically, the model is driven into the spin entry with nose becoming progressively higher using "up" elevator. At 90% elevator, the new elevator rate becomes 80%...dropping the nose and beginning the spin. Simultaneously, the model rotates with the rudder (which intuitively one would assume more rudder is best...it is not). When the elevator stick is returned to 20% or less, the "normal" deflection response returns for the elevator/rudder/aileron.

Negative spin/snap:

Repeat the same steps as you did for positve spin/snap but all of the AFR values will be different!

Rules of thumb...the more rudder the deeper the stall, the more aileron the quicker the roll rate.

Rusty Dose
Team Futaba

Yes it's fun and most interesting! Asking for the Skylane had a certain motive, of course. I spinned Zlins and Cessnas, but no aileron was used. While the Zlins needed the usual recovery method, the Cessnas were different - more like models. Actually, they are made to be hard to spin, but if you know how to do it it's surprisingly easy. (The aerobat has the old unmodified airfoil and plain wingtips, while the newer Cessnas have the drooped nose and Hoerner wingtips and are even harder to get spinning.) Of course, you may manage it unintentionally (Denker mentions such a case) so fortunately it's easy to stop the spin: let the controls go - like with most of our models.

Therefore I would search for the reasons of the "abnormal" behavior in the aerodynamic layout and distribution of masses. The gyroscopic forces may play a role if the propeller is large and heavy and far ahead of the C/G (like in full-scale Zlins), so recovery from a left-hand spin might be hard. I think models show that only in flat spins (much power), but I have to admit I never calculated/guessed the inertia moments. However, an indication is that models don't do the real Lomcevaks like full-scale planes, which are gyroscopic-force maneuvers.

In the simulator, I can deliberately produce that delayed stop of spin by making the model heavy and the moments of inertia bigger (damping unchanged) - or vice versa. So maybe the case is rather simple in reality as well. Just a thought.

Neat! gotta play with that.

UStik, you mean the droop leading edges on the Cessnas? Not sure what you mean by the droop noses; but agreed, they do not spin easily. The Aerobat was different; the C172 would spin easier if you started with 10 degrees of flap but be sure to raise the flaps as she starts to rotate. Never flew the Zlin, but the Cap 10, Citabria (8A), T-34, and Christen Eagle all were good spinners. I once coaxed a PA-28-140 into a spin, it was uuuuuggllyyy. I would think the easiest, or at least the least fussiest, would be to simply experiment with the CG. Aft will get your attention while forward will bore you. When I learned aerobatics (the spin), I was taught PARE, well actually PEAR then PARE: power off (idle), elevator aft, aileron nuetral, rudder to rotate (apply in the direction you want to spin). To recover, power off (idle), aileron nuetral, opposite rudder, elevator forward. Of course, you'd hoped to learn from someone who had experience with applying these methods in that particularaircraft, if not, just try to have lots of extra altitude (lots). In the case of my RV-6, I was the test pilot and it was an interesting exploit! With the models it is likely different, I'm not sure that when they are designed that the designers factor in spin criteria as much as certain stability factors, such as a constant or non-shifting CG. By that I alsomean thatone can design a spin resistant aircraft or, an aircraft that will spin quite readily. I think our pattern ships would mostly spin quite readily, i.e. high wing loading etc. As a whole it's much more complex, but as you mention, a heavy propellor (gyroscopic forces not withstanding) actually makes for a forward CG and should make for an easier or less difficult recover. In any case, interesting thoughts here, but I still think it's a matter of rudder, rudder, rudder (at least until I get a computerized Tx!)
hook

If I may, and it's only an observation, the most useful 'tools' for changing the spin habits of your model are a bit of sandpaper and balance. Light wingtips, and a more forward balance will 'unstick' the spin with much less control input, providing that you also increase the amount of elevator and rudder movement to compensate. I always use aileron in the spin, several of my aerobats will not stay in for three turns without aileron assistance to keep the outboard wing stalled. This means, of course, that simply releasing the controls will usually stop the spin, but it is noticeable that different models still take different times to unstall. A couple won't actually stall unless the idle is pretty high, keeping good flow over the elevators so the wing actually gets to it's stall angle. How far forward is too far for the balance? When you can't reliably spin in a comp. And that is a lot further forward than most would consider 'normal', but it insures positive spin exit, and a consistent amount of anticipation so you end up on the correct exit heading every time, and that is what the judges are looking for.
Evan.

Yes Hook, I meant the drooped leading edge (I was thinking wing nose), and I was going to point out that an aircraft that is supposed to be spin-resistent will be the easiest to get out of a spin, just by letting the controls go. What I found surprising when I learned (was taught by a master) to fly aerobatics was that even the really spin-resistent Cessnas are easy to spin using the competion entry into spin - without ailerons and flaps, just slow down 2 knots above stall speed, then gently yaw with rudder and observe whats happening. Sooo smooth and gentle. We never tried a developed spin with a standard Cessna.

In addition to what I said above about charecteristics making for an easy spin recovery, I would say the two models mentioned by Skylane seem to have a small and somewhat shielded vertical tail. (I looked at the pictures in the Classic Pattern Image Base.)

UStik. I thought so. I agree on your other points also, especially about letting go of the controls. I used to demonstrate that to new CFIs in the C-150. You had to be sure to have altiitude because it wasn't unusual to lose over 800', also the airspeedrises quickly in the pull out. I doubt there are many planes that are spin proof. I learned many years ago mostly in a Citabria 7KCAB, inverted flight was tuff with that flat wing, the 8KCAB was much better. In my view, the method you describe is a very good one asinitiating it with rudder defines the direction of rotation. Plus you get a sharper, smoother yes, but sharper wing drop and entry into the rotation. Again, I like it simple so it's"rudder in and rudder out". Of course the other inputs apply and in general are combined at relatively the same time. I did get into a well developed spin once in a C-150, the prospective CFI froze on the controls. It took a hard elbow to the ribs before he let go, lost almost1800', and I won't say what the exit speed was...
I do agree on your rudder observations too, if it is blanketed it becomes less effective. I don't see how wind effects a spin (turbulence aside, other than how the plane moves in relation to the ground, which is our perception of movement). Also, both wings are stalled, it's just that one has a higher AoA than he other thus the yaw. I guess you can get into gyroscopic prop effects, tip mass,and inertia, etc., but then gravity could be considered too because it changes with altitude (minutely true) but... Now if you sand off material you reduce mass (weight) so that does effect theCG, either for or aft.Also, if the fuel tank is not on the CG but more forward, CG will shift as fuel burns, so one should try the spins with afulltank and say a third tank or less. I think you'll find the recovery a bit different than with a full tank. Good discussion topic Skylane, thanks UStik.
Hook

Hook,

You are correct that the wind shouldn't affect the spin since the plane would be moving with the air mass - unless you are trying to enter the spin from a line parallel to the flight line and centered on the judges. Then you have to make some heading adjustments to make the entry look correct from the ground. Also, the exit has to have the wings perpendicular to the flight line (1 downgrade for each 15 degrees of error). So, a contest spin becomes a ground reference, not wind reference, maneuver. That's part of the challenge. In such situations a left or right entry may have appearance advantages depending on the direction of the cross wind.

Jeff

UStik,

You make a good point about the possible blanking of the rudder. Here are some measurements in the form (CG to rudder hingeline, 1/2 wingspan):

Cutlass (33",31")

Compensator (34",31")

Deception (37", 31")

Kwik Fli III (31, 29.5")

So, the tail moment is shorter for the Cutlass and Compensator relative to the wingspan than for the Deception, meaning that the rudder and elevator of the Deception should be in cleaner air which could enhance the recovery. The Kwik Fli III has great exits, yet it seems be the exception to the above hypothesis since the half-span and tail moment are nearly the same. However, it does have large barn-door ailerons which would make them more effective at stopping (or entering) the spin since they concentrate the aileron area nearer the tips. A few measurement of aileron size and type:

Cutlass (1"x20") strip

Compensator (1.25"x23") strip

Deception (1.75"x20") strip, but centered further out than for the Cutlass or Compensator

Kwik Fli III (3.25"X13") barn door style

So, I would expect the KF III and Deception to have more effective ailerons, which agrees with my observations that these two have more predictable exits.

As was pointed out earlier in the thread, the behavior is most likely the result of the interactions of many small design choices.

Jeff

I thought you likely meant that Sky.Yet in reality all of the manuevers become ground reference manuevers too because of our orientation to the judges podium or central point ofviewing.The crosswind from in front beingthe most troublesome; I used to watch my downline out of the split S and just prior to level flight sneak in a bit of nose to the upwind side, probably worked because I was in Novice/Advanced and they didn't care too much. It also helped while slowing for the spin, since you're looking up a good angle it could be hard to perceive a bit of roll toward the upwind side too. In either case it was easier, JMHO, to spin toward the upwind side then, but as you say watch the exit so that the line continues as it started. All so easy isn't it...LOL. Have a good day Sky.
Mark

What I would add as to the Kwik-Fli is that it might have more roll damping than the other models mentioned. Even though the thick and blunt-leading-edge NACA 0019 airfoil has a not really steep lift-over-AOA curve, the square wing planform and lightweight construction make for a quick and clean stop of the roll movement in spin, even without ailerons. (In Denker's classification of spins, it's an example of a flat lift curve even post-stall, without hysteresis.) Besides the Mark III Kwik-Fli has a big vertical tail and high-leveled stab, and I think that all adds up to the clean spin exit. It's also a typical example of the airplanes that are actually reluctant to spin and, once brought to spinning, are easy to stop.

Skylane, the link to the NASA report in my post #5 above was corrupted but should be working now. Just a note as I'm not sure you've found the report.

Thanks, UStik. The link worked and I have the report now.

Jeff

Evan, seems you said it all, as always. BUT, I have to connect this practical knowledge to the "theory". Advice given by others is great as well to help me understand.

Two main factors defined in the NASA report, calculated for my favorites:
No surprise: That means our models are well below the density range of full-size airplanes. (The report starts with values of 6 and 10.) Still it's true that more density needs more rudder for spin recovery, or maybe low density needs even no rudder.

Well a surprise (for me) is the clearly negative inertia parameter of our models. (The "neutral" range is defined as -0.005 to +0.005.) That means the masses are distributed more along the fuselage and not the wing and in that case the primary control for spin recovery is aileron, according to the report. (For wing-heavy airplanes it would be elevator and for "neutral" ones rudder.) My (electric) glider has +0.012 (really measured) so the aerobatic models have a way too heavy tail (to be "neutral" ). A caveat is that the moments-of-inertia are (educated) guesses, but we're in the ballpark and clear is that a heavy engine up front and servos in the tail make things worse.

The third most significant factor for spin behavior is tail configuration, but the parameter is hard to calculate (means I'm too lazy). As to the significance of these factors for models: Same air, same rules!

The report not only states that for fuse-heavy planes the aileron is the primary recovery control, but also that it should be deflected with the spin! Evan, that confirms my suspicion that the spins (and snaps) done the usual modern way might be not developed spins but maneuvers looking alike but smoother and better controlled. And that seems to be the point, a true autorotation with much elevator doesn't look as good as a similar rotation driven and controlled by the ailerons and not really stalled. For me, that's the main conundrum.

Indeed UStik, what many call a spin or flick is actually an aileron maneuver. The Judges guide is specific, however, and calls it as the full size, ie the model must slow without losing or gaining height, the nose must drop straight at the point of stall, and autorotation must commence after the model stalls. Many modellers simply 'wingover' into a fast spiral dive without waiting for the stall, and wonder why they get a '0' from the judges. Same with a flick roll, if the controls are held the model should exit in a spin, if it simply spirals out of the maneuver then it wasn't stalled at the beginning, and you just did a fast roll. The aileron assistance is easily checked, try doing a spin with a Taurus without aileron, it simply falls out of the stall in a slow rudder turn. As you suspect, the main reason for the different response, model to full size, is mostly due to the really low wing loadings we fly, and the large size of the bits of air we fly in.
Evan.