Hi folks - when I was asking about second planes a number of you said don't buy so and so plane because it has a tendance to 'snap'.

Could you explain what this means? When I asked members of the club I go to they talked about a manouver in an aerobatic display... I didn't quite understand either the manouver or how it was relevant to my second plane choice...

P

When they say snapping, they mean when the plane starts to stall, whether it has a tendency to very quickly start to do a snap roll, basically just a very fast roll. It's good to find a plane that doesn't tend to snap when stalling, mostly when you're trying to land.
I hope that kind of answers your question.

My English teacher always told me that when you define a word you should never use that word in the definition, so here goes:

A snap is what happens when one wing on a plane stalls before the other. Under normal flight, both wings are providing equal lift on the left and right side of the plane. If one wing stops providing that lift (because it stalls) but the other one is still lifting, the plane violently rolls to the side with no lift (as if it only has a wing on only one side of the plane). This manuever can be intentional and a real crowd pleaser. As a beginner though, it is hard to predict when it will occur on some planes during slow flight (such as takeoffs & landing approaches). Imagine what would happen if your plane is flying along straight and level and suddenly without warning it flips over. Whould you be able to recover?

Hope this helps.

"snap" generally refers to snap-rolls. It is a violent manuever where you induce a stall on on side of the wing. The resulting roll is fast and it's usually easier to do 2-3 than it is to do one. Normally, you can make a plane snap by simultaneously appling full up elevator and full rudder and maybe some aileron. It's a high stress manuever so don't do it unless your planes built for it.

The snap you're being warned about is a little different because it's unintentional. It usually occurs at slow speed during landing and again is caused by one side of the wing stalling before the other. The resulting roll is abrupt and often leads to a crash. Aerobatic models will often have the tendency to do this if you don't keep the speed up. The problem is that in order to have an aircraft capable of aerobatics some undesireable tendencies result including snaps.

I have a Super Decathalon that does this. On the third flight I learned a nasty lesson about airspeed and snaps that resulted in me rekitting the model. I rebuilt it and an cautious about keeping some speed on now during the landing approach. It's a great flying model. You just need to be cautious about an aircrafts shortfalls. Particularly when your close to the ground!

Some good definitions there.

There are several factors that affect how a plane stalls, if it has a strong tendancy to "snap" or not. Three of the biggest are the wingloading, the airfoil, and the wing planform.

A stall is when the Angle of Attack (AOA) of the wing in to the oncoming air get's beyond a certain angle, the "critical AOA" for that airfoil. Different airfoils have differnet critical AOA's, though most are actually pretty close to each other.

Wingloading matters because it measures how much lift the wing has to produce. You get more lift from a wing by increasing the AOA of the wing (assuming a constant airspeed). This means that a heavy plane flys at a higher AOA than a light one of the same design. As you slow down, you have to increase AOA to make more lift. But if you are already at a higher AOA, you don't have much room to increase the AOA before you hit the critical AOA and stall. This is why heavy planes have to land faster.

When a wing stalls it doesn't loose all lift, but the lift does fall off. Some airfoils loose more lift faster than others as AOA increases.

The airfoils on trainers tend to loose lift slowly as the AOA increases past the critical AOA. This makes the airplane mush forward, nose down, a "soft" stall. And if one wing stalls before the other, the result is only a very slight wing-down situation that is easily fixed. Espeically because the plane going nose-down quickly lowers the AOA, taking the wing out of the stall very quickly.

On the other hand, an airfoil on some kinds of acrobatic planes are designed so that the lift goes down in a hurry as you pass the critical AOA. This means that in the split second when one wing stalls before the other, the difference in lift between the two wings is very large, and you get a very fast roll.

And last, the planform, or shape of the wing, affects how the stall develops on the wing itself.

When a constant chord wing stalls, it usually starts to stall at the center, and the wing tips stall last. If one wing starts to stall before the other, and it's stalling from the root outwards, the difference in lift near the fuse creates a small amount of rolling force, maybe nothing at all noticeable. On many trainers, it's really hard to stall the wing tips, you stall the root, the lift goes down a bit, the nose drops, you pick up airspeed, and the AOA goes down. The wingtips never stall at all. Washout has the same effect, making sure the root stalls first.

On the other hand, tapered and swept wings can have either the whole wing stall at nearly the same time, or the tip can stall first, resulting in much higher rolling forces.

So, when you add these all together, you see that a trainer is the "best" of all worlds for preventing stalls.

A Cap is (nearly) the worst: high wingloading, acrobatic airfoil that drops lift in a hurry, and a tapered wing that stalls all at once rather than root-first.

If you notice, most recommended "2nd planes" have a straight wing, and a fairly thick blunt airfoil, and a wing that is between a trainer and something like a Cap (resulting in a mid-range wingloading).

Something like a Decathalon is deceptive. It looks "trainer like", with it's high wing. But the wingloading is much higher, and the airfoil is different. (there are other factors as well, like vertical tail size and placement that also make the Decathalon snap like it does)

How about a Taylorcraft? It is somewhat like the Decathalon. Is it snappy?

Several other meanings of the word "snap" which I think also give a fair indication why you should avoid aircraft that have a tendency to snap...
Break suddenly..
Emit or cause to emit a sudden sharp sound or crack..
Make a sudden bite...

"Snap" is what happens when you leave the field because the wind is blowing too hard to fly, and it slams the house door on the wing of your airplane as you're putting it away. "Snap" is what happens when the cat's favorite toy goes beneath your airplane and he attacks anyway. "Snap" is what happens when your daughter, who only wants to help, tries to pick your airplane up and looses her balance. "Snap" is also what happens when the same daughter, guiltily sneaking out of her bedroom after bedtime, dosen't notice that daddy spread airplane pieces over the living room floor and steps square in the center of the stab for your brand new Seagull Spacewalker arf.

BTW, I still love my daughter, and have forgiven her, yes I even forgave the cat, but that @#$%^$ wind!

Andy

Well: I no how you feel at least concerning the animals.
MY boston terrier got into my plane room as i was opening the
door and bolted through and jumped on a wing and put her foot
right through the left wing covering. Bad part is this was a hanger 9
(arf)cheroke piper that iam building for some one else. The covering
has those embed lines in it. Not sure how iam going to fix this problem.
Havent talked to the owner yet. [:@]