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Thread: Spins in Clipwing Cub

  1. #1

    Tongue Out Spins in Clipwing Cub

    I am in the process of exploring the spin characteristics of my recently completed Clipwing Cub. Spins left and right for one turn are completely normal with clean entry and recovery. When the spin is held for more than one turn it appears that the nose pitches down quite steep and the spin rate becomes quite fast. Recovery is within 1/4 turn with altitude loss of 1000 feet for two turns. Anybody out there have experience in a Clipwing Cub? Is this normal? What happens after 2 turns?

  2. #2
    KDoersom's Avatar
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    Jerry

    I invite you to Join J3-cub.com. We have nice lively discussions about these types of things all re time.

    Keith

  3. #3
    RetroAcro's Avatar
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    I fly a CWC a good bit, and just like a standard J-3, spins are very benign and normal. The one I fly is a bare bones stock J-3, Reed conversion, w/ 85 hp. I've never been able to get a true spin entry without a small burst of power as rudder is applied. Otherwise, and even with the stick fully aft and full rudder held, it spins in a spiral rather than a true spin, and the airspeed increases as it "spins". This is the only spin quirk associated with this particular airplane. I think it's CG related. With a quick burst of power, I can get it into a true spin where the airspeed stays locked on 40 indicated as it rotates.

    I'm not sure I've spun it more than about 2 1/2 turns, but in most airplanes, it takes around 2 turns for the spin to fully develop and stabilize. I haven't noticed much change in spin attitude after the Cub's spin fully develops...or maybe I haven't paid attention. Rate might increase slightly, but the main thing I noticed, is that it seems to take a slight bit of forward pressure to move stick off the aft stop when recovering. Before the spin fully develops, the stick wants to come forward on its own. In any case, 1 turn or 2 turns...the spin stops within 1/4 turn. If you're quick with the recovery and pullout, you can do a one turn spin in 300', 2 turns in about 600', and you might be surprised that 1 1/2 turns takes about 800ft. This is because the 1 1/2 turn spin stops in an attitude slightly negative of vertical, and takes more pitch change to re-establish level flight compared to a 1 or 2 turn spin, which stops less than vertical down, or in a positive attitude.

    I do a lot of competition spins in the Pitts, but it's always fun doing them in the Cub. Right from entry, the Cub is the smoothest and steadiest spinning airplane I've flown. If spinning left, due to the gyroscopics of the big metal prop, the Pitts will naturally oscillate a little, and vary it's rotation rate before it stabilizes around 2 turns or so. It's more steady spinning to the right, but still not as smooth as the Cub. Everybody should have a Cub. :-)

    Eric

  4. #4

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    As noted above, you can easily transition from the autorotation of a spin into a spiral dive. So today's question is what is your airspeed doing after that first turn? Is the stick still back against the aft stop? If your airspeed increases for turn 2, then you are in a spiral dive and no longer spinning. Transitioning into the spiral dive brings the risk of over speed and overstress during the recovery.

    Spin testing is often done in increments of 1/2 turn. Do several one turn spins and note whether or not the behaviour is consistent and record the length of recovery. Repeat for 1 1/2. Repeat for 2. etc. I think that I recall that the FAA requirement is that the recovery must not exceed one additional turn.

    I will also note that CG (center of gravity) is important. What is the CG when you fly your spins? Aft CG is generally the worst case for lengthening the spin recovery. Forward CG is the worst case for transitioning to a spiral dive. Calculating CG is boring, but important for spin testing.

    If you post more data, folks can offer more educated advice.

    Best of luck,

    Wes
    N78PS

  5. #5
    dillardrg's Avatar
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    Jerry,

    Sorry about coming late to the thread.

    If you look at the photos below, you will see that the Citabria does as you describe.

    The first pic is one full turn and is still in the incipient stage and the 2nd pic is 2 rull turns with recovery just started. The spin is fully developed. The attitude is more vertical and the spin rate has increased significantly.

    If you look closely at the first pic you can see that the rudder and elevator are fully deflected and the 2nd pic the rudder and elevator are neutral just before pull up.





    Ron
    advancedtailwheeltraining.com
    Last edited by dillardrg; 02-02-2012 at 08:13 PM.

  6. #6
    RetroAcro's Avatar
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    Ron, cool pictures :-) But I would make the point that it's hard to compare the spin "attitude" before and after the spin fully develops due to the fact that the attitude varies widely during the first couple rotations due to the parabolic trajectory of the airplane before it stabilizes into a perfectly vertical down trajectory.

    The first picture shows the plane's attitude after 1 turn, which is definitely more positive (nose up) than the second picture after 2 turns. But if you had taken a picture of the airplane after 1 1/2 turns, its attitude would be more nose down than the 2-turn picture...it should actually be slightly on its back just past vertical. Since the airplane doesn't stop in mid-air and immediately start falling in a vertical trajectory at the spin entry, the relative wind of the plane's forward trajectory during the first couple turns or so causes the wide ranging attitude before it stabilizes.

    You're typically inverted with the nose very high after 1/2 turn, you're upright with the nose lower after 1 turn, you're typically very slightly on your back past vertical after 1-1/2 turns, and a little more nose high and upright after 2 turns...but less so than after 1 turn, as your pictures show. Once the spin stabilizes, the attitude will remain constant, assuming it doesn't have an aerodynamic quirk that causes it to go flat on its own.

    Eric
    Last edited by RetroAcro; 02-02-2012 at 10:07 PM.

  7. #7
    dillardrg's Avatar
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    You are right, Eric, the 1 1/2 turn picture below is more nose down than the 1 turn picture above. It is not; however, more nose down than the 2 turn attitude.

    My Citabria is very stable in spins. Once the nose drops it does not ocillate up and down during the 1st turn or after.

    This first picture is 1 1/2 turns. Rudder and Elevator fully deflected.



    This picture is 2 full turns, recovery started.

    Last edited by dillardrg; 02-03-2012 at 07:57 AM.

  8. #8
    RetroAcro's Avatar
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    Ron, I think I mis-spoke a little. I was thinking about the airplane's attitude as the spin stops, and not during the spin itself. I've never spun a Citabria, but the Cub and Pitts are pretty much vertical down as the spin stops after 1-1/2 turns. The Citabria may spin a little differently. The Pitts actually takes a slight bump of back stick to get to vertical down upon stopping after 1-1/2 turns.

    But for consistency in what you're illustrating in the pics, I think both pics need to show the airplane with the controls either fully deflected in the spin, or shown at the same stage of recovery. Your picture after 2 turns should be more nose up if you snapped a shot with the controls fully deflected as you're showing in the pics for 1 and 1-1/2 turns. And your picture of the 1-1/2 spin would be a little more nose down if you snapped the picture of the plane in the same stage of recovery as shown in the 2-turn pic. The nose attitude of a fully-developed spin should be higher than the attitude shown in the 2-turn picture, since recovery had been initiated. I think the only way to get near that steep of an attitude during a developed spin is to push the stick full forward.

    Regarding the spin becoming more nose down after it stabilizes, I was just making the point that it depends on which degree of incipient rotation you're comparing the fully-developed spin to. Good discussion and pictures, though. I don't think these issues concern most pilots much beyond the pure discussion of mechanics. I just think about this stuff because competition spins typically come in 1-turn, 1-1/4, and 1-1/2 turn flavors. Each of these three types require different control inputs in order to establish a perfectly vertical down attitude after the spin stops due to the fact that the spin attitude is changing quite a bit within the first two turns. The 1-1/4 introduces a yaw problem as well as a pitch problem, and takes extra elevator pressure as well as rudder as the spin stops to get a perfect vertical down attitude.
    Last edited by RetroAcro; 02-03-2012 at 11:07 AM.

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