I have seen the term "snap" used several times to define a bad trait in an airframe but do not fully understand what a plane does when it snaps. The term is used in the following context,......" if you slow down to much the plane will snap",... "if I apply full up elevator the plane snaps"...., what does a snap look like?

"Snap" is generally a shortened form of "Snap Roll". A snap roll occurs when one wing tip stalls before the other, causing the plane to roll over. Depending on the characteristics of the plane, it can occur very quickly, hence the "snap" term. Its generally executed by slowing the plane down and then applying full elevator (up for a positive snap, down for a negative snap). Adding a touch of rudder in the direction of the roll really makes it happen quickly.

Its a stall maneuver, as one wing tip must stall to start the rotation. If it occurs on take off because of over application of elevator without sufficient airspeed (beginner mistake with a highly aerobatic plane) or on approach while trying to slow the plane down to much for landing, it can be fatal.

If you're planning on it, it can be a very dramatic maneuver. If you're not planning on it, it can be easily mistaken for a radio hit.

Some planes are notorious for snap rolling every easily (eg the CAP 232). Others are very tame and controlled (eg. the EXTRA 300 series), and others have to be forced into it (eg Edge 540).

Very few trainers will do a snap roll without really forcing it.

Brad

Thanks Brad, that explains it very well. I have seen pilots do snap rolls but I was having a hard time seeing a plane do it on its own. That would be bad news with out enough alttitude! I have only flown 3 planes (Kadet LT-40, Ultra Stick 40, Pulse XT 60) and when stalled they just drop the nose and start flying again, so I have a hard time understanding how more advanced planes respond.

Following up on Bkdavy's excellent response...

Some planes are designed to snap roll quite easily.

All too often inexperienced pilots purchase one of these planes and treat it much like a trainer.

On a slow approach, they end up inducing a snap roll, rolling the plane nose first into the ground. They have little control at the point this happens, and the plane is destroyed. In turn the airframe is blamed for the "problem".

A plane that is easy to snap, can perform some interesting aerobatic maneouvers, but this type of plane is not for everyone.

The configuration of the wings greatly affects the snap roll tendancies.

All three designs you mention WILL do snap rolls if they are set up to do them.
It requires moving the balance point back and increasing the throws. The great thing about all three designs is with a constant chord wing, you can fly very aggressive without the airplanes trying to bite you. They take a very pro-snap control input to do the maneuver.

All to often the word "snap" is used in the pejorative sense; it's really not the 'bad habit' it is made out to be. I have most of my aerobatic models (Pitts Special, and two pattern aircraft) set up on the tail heavy side just to help them snap even more easily than the airframe design alone would allow. I like them that way because it makes many aerobatic maneuvers nearly effortless.

In my experience, most pilots accidentally snap their aircraft either when they are flaring too high, banking too steeply on approach, or when they are pulling out of a dive. Yes that's right, I said pulling out of a dive. Remember, it's an excessive angle of attack, not airspeed or attitude, that stalls a wing. The ingredients necessary for a snap to occur are always there.....waiting.

On the other hand, if a person tells you that YOU don't have "much snap" it means he doesn't think you are very bright.

Bruce, I know you have something more constructive to add to this conversation, I have read some of your post. Although you are correct, I know some people who are not very snappy!

The subject was being well covered so I thought I would just spice it up a bit.

I agree, the guys explained it very well. I still have a few terms I have heard I would like a better understanding of, does RC Universe have a glossary?

Blazer,

I'm sure if you have questions there are others here that have the same question...... So ask away!

Yes http://www.rcuniverse.com/community/glossary.cfm

You mean snap it up, don't-cha?

Sometimes people suddenly snap . And it ain't good !

I've seen a guy snap after his airplane snapped.

I give this thread 2 snaps up. *hand on hip* [sm=spinnyeyes.gif]

I just ate a big meal, and sat down to read this thread when my pants snapped...at least I think it was my pants.

My wife Snaps her finger quite often and man do i jump when she does that.
So my glossary definetion is SNAP- GET ER DONE NOW lol.

It might be a prelude to a Crackle, followed by a Pop.

It says above that a snap is induced by full elevator, possibly with some rudder guiding the direction of the stall. So if you give full aileron to induce a roll (maybe with a little rudder), is this not a snap roll?

Also, I'm thinking the Nexstar (without the wing droops) is prone to snapping with rudder. The reason I say this is because I think this is what inspired my first real crash on Wednesday. I was coming in for landing and needed some rudder to re-align. Being a beginner and it being the first landing in a week, I gave it rudder in the wrong direction. When I countered my mistake with opposite rudder, the plane rolled over and dove into the ground, wing tip first followed by nose.

Whenever I give rudder to the Nexstar, it rolls and dives, a lot. Does this mean it snaps? I'm learning/practicing how to react or pro-act to this action, although I've flown some other planes that don't do this or do this just a little.

Full aileron generally is not a snap, since that typically doesn't induce a stalled wing. Its just a roll.

The dihedral wing of the Nexstar causes it to roll when you add rudder. Again, the wing is not stalled, and this is not a snap roll.

The nexstar is normally set up a little nose heavy for stability purposes. When you add rudder or ailerons, this induces roll. When the plane rolls to the side, the nose will drop. If you don't counter this dropping tendency by reducing the bank angle, the plane will continue rolling and dropping the nose until it enters a dive.

The solution in your case is give less control motion. Add your input slowly and steadily.
Don't just slam the sticks to the extreme.

In any event, what you are experiencing is not a snap roll. The plane is doing exactly what you're telling it to do, you just don't realize it.

Are you working with an instructor? If not, did you know that the nexstar has a guarantee that if you crash it in the first 60 days while flying with an instructor (AMA member), they will replace the plane.

Brad

So it's not a snap roll. Thanks. I guess I probably haven't even seen or recognized a real 'snap roll'.

And by the way I don't 'slam the sticks to the extreme'. I fly pretty well, especially for a beginner, just made the mistake of ruddering one way, then the other, while a little under powered. It's what I call learning. Generally I can give rudder and counter it with ailerons and a little elevator, but rudder right then left produces some pretty serious nose-down rolls, and didn't have enough power for the elevator and ailerons to do much only 10 feet from the ground.

You'll know it when you do it. Your airplane will rapidly rotate without much or any aileron input.

To do a proper snaproll, get up three mistakes high and give full up, full left ail. and full left rudder. when it's done a complete 360 turn and let go of the controls and a good plane will stop dead, going in the same direction. Inverted or outside snap, fly level, give full down elev. full left ail. and full right rudder and hang on to your shorts.

As others have stated before: The primary controls for a snap roll are elevator and rudder. Depending on the geometry of the aircraft, some aileron may be needed. I have never had an aircraft that needed full aileron to perform a snap roll.
When you get used to snap rolling you may find that the elevator input should preceed the rudder input by some small amount.
Also, when the snap roll gets going it is often advantageous to reduce elevator input by a small amount. How much has to be determined by trial and error. Reducing elevator input minimizes the speed loss assiciated with snap rolling. This is especially so if one wants to perform a double snap.