JollyPopper

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Hello Again Folks:

You guys explained "tip Stall" to me so that even I could understand it. Now I am wondering what a "snap" is. I read so much about models "snapping", especially on final approach. What is it? Thank you all

Max

paladin

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So, you want to know what a snap is! To a pattern flier a snap role is an axial role where the empinoge rotates with some yaw induced. To a war bird pilot it is the result of a tip stall. Depending on the severity of the stall the tip can rotate up to 180 degrees in no time at all.

While teaching a friend how to land war birds we had added flaps to his H9 P-51D and the landing gear were not up to the task. So he was finishing out the day without flaps, because the LG were so fragile he would pull hard elevator just as he was ready to touch down. I warned him this was a bad habit to get into but realize now I should have said a nose in is much preferable to the other option. But I did not and when yanking the elevator back on his last landing of the day. He was a little hot and the plane zoom climbed and snapped. It had climbed just high enough to clear the wing and in that split second he found his plane inverted and landed on the runway with no damage. I saw it and still do not believe it could have happened so perfectly as to cause no damage, but it did. An it happened in less time than it took you to read this.

Now, you can make your plane snap (most planes). At two+ mistakes high with a perfectly trimmed airplane reduce the throttle to idle and keep adding elevator to keep it flying level. Eventually it will stall and most war birds will snap into a spin. This snap will be rather slow because you are changing the elevator slowly. If it does not snap try again only this time just before it stalls go to full up, fast! If it still will not snap try it with some rudder and aileron, then elevator fast. If it still will not snap this plane is to stable try with another. I've never found a plane I could not snap.

Now that it has snapped and is spinning towards the ground you need to know how to recover. It's really simple advance the throttle to half (a setting you know will fly the plane, full is OK but it makes the pullout longer). The lower throttle setting also acts as adding down elevator because the model is trimmed to full throttle. Then take both thumbs (and fingers) off the sticks tap the sides of the gimbals and when they get back to the sticks the spin will have stopped. Then just pull elevator to level off. There is a possibility this will not stop the spin that means it needs to be flown out of the spin. That is well above the head of someone who has never seen one so it is very important that if you plan to try this you have the plane checked out by the club expert first.

The purpose of removing your hands from the controls is because the plane is trimmed to fly level and 99.44% of the time it will recover on its own. The other reason is that you are holding up elevator to stall it, if you forget to let it go nothing will save the plane. It will stay stalled right to the ground!

Good Luck

Joe Felice

FHHuber

Simplified... a snap-roll is a purposeful tip-stall at speed. Snapping out of a loop is tip-stalling from too much elevator and/or loss of speed in the loop. A snap is a tip-stall that flips the aircraft.

iflynething

Even simpler (no offense FH): the plane stalls, you move the sticks (both left and right in certain directions at the right time) and the plane rolls faster then it would with just using ailerons

P.S. But the plane has to be stalled first.......

I have tried to snap, but have not succeded with my Somethin' Extra because I'm afraid about the stalling (I've only had 4 flights on it )

FHHuber

To practice your snaps... just take the model high. The SE will go into a shallow dive when you release the sticks after a snap-roll.

If you have it you balanced it too far aft... then it may need help getting out of a spin... Full power down elevator and opposite rudder. if upright. If inverted its full up. Leave the ailerons ALONE durring spin recovery, they can drive you into a FLAT SPIN, and that is harder to get out of if the CG is too far back. (opposite aileron applied slowly flattens a spin every time.)

You don't have to be flying slow to snap-roll.. Just hit the elevator and rudder hard. (by the definition of a snap-roll... no aileron needed.) Amazing to watch the way a Dynaflite Butterfly's wing will twist when you do a high speed snap-roll... (that plane has no ailerons)

LouW

A snap roll is an abrupt rolling maneuver. It is similar to a spin except that it occurs when the wing is stalled at a little higher than the normal stall speed (called an accelerated stall).

To enter a spin, the throttle is closed and the airplane slowed by increasing the angle of attack with the elevator until just as the stall occurs, full rudder is applied. This yawing motion causes one side of the wing to stall first, that wing drops, and the airplane begins to rotate nose down in the direction of the applied rudder. If the controls are held, the airplane descends with the wing rotating in a stalled condition. To recover, opposite rudder is applied until the spinning stops, then forward stick is applied to relieve the stalled condition and recovery is made from the resulting dive.

To enter a snap roll, the airplane is flown at some speed above the normal stall speed, and the airplane is pitched up abruptly to the stalling angle of attack while simultaneously applying full rudder. The wing on the side toward which the rudder is applied stalls, while the opposite wing is still flying. This results in an abrupt roll toward the stalled wing. Recovery is accomplished by neutralizing the rudder to stop the rotation, and pitching forward with the elevator. Usually snap rolls are limited to a couple of rotations. If the controls are held longer, the airplane slows down, the nose drops, and the maneuver becomes a normal spin.

The snap maneuver does not require a “tip stall”. Any aircraft with enough elevator control to stall the wing at higher than normal speeds will snap. It is only necessary that one side of the wing stall before the other. Of course if an airplane has sharply tapered wings and is otherwise prone to tip stall the maneuver is more easily accomplished.

Some of the sudden wing drops described above are not true “snaps” but either inadvertent spin entries, or actual tip stalls.

J_R

In answer to your question about snapping on landing... If a plane is correctly built and trimmed, it will stall and the nose will drop. If for any reason, it is not setup correctly, one wing may drop... your tip stall. When this takes place low to the ground, as on landing, the plane will not have enough speed for the control surfaces to be effective. The result is a snap into the ground generated by the tip stall.

Generally, on the maiden flight of a new aircraft, I try to trim it for straight and level flight. Then take it up, 3, 4, maybe 5 mistakes high. Keep reducing the throttle, as explained before. If it reaches a point where the throttle is zero, start to add elevator slowly. If it falls off on one wing you have a problem. It should simply stall, and the nose drop straight ahead. This may be a very smooth stall, or quite pronounced, depending on the plane and it's setup.

If it stalls off to the side... a tip stall... check it again, and again, all on the same first flight, at high altitude. If it is consistent to one side you will need to keep the speed up more than normal on landing to avoid snapping it in.

Usually, you can induce some washout into the offending tip, assuming that everything else is correct (split elevators have the correct incidence, ailerons are at the same incidence, etc) and eliminate the snap.

Flying a snap roll is another animal and other have addressed it well.

FHHuber

The confusing part is what we call a "tip-stall."

A stall is a stall. We tend to call it a tip-stall when it drops one wing... but its really just a stall where one wing retained a lifting airflow pattern just a LITTLE longer than the other.

Most wings stall near the wing root earlier than near the wingtip. Part of this is design, part is becuse of an effect of the fuselage creatng some turbulence at the root... acclerating the breakdown of the airflow from the smooth lifting pattern into the turbulent patern that produces little to no lift.

The design of the Cap232's and Extras is such that the whole wing really stalls almost at the same time. It doesn't really stall at the wingtip first. With an entire wing panel stalling at once... just a small portion of the other wing retaining lift (usually near the opposte wingtip....) gives a large imbalanced force applied to the aircraft, so the airplane rotates quickly. (the "snap")

If an airplane was designed to always stall at the wingtip first... it would be extremely unstable at low speeds and landings would need to be done nearly at MUCH higher speed. (which would be unacceptable to any pilot) You wouldn't dare attempt a "3-point landing" with an Extra if the tips stalled first.

LouW

You are correct. I wrote an analysis called "understanding tip stall" but unfortunately I posted it under the beginners forum and got no response. It's currently on page 2 of that forum if anyone is interested.