Spin vs. Flat Spin vs. Spiral Dive

[bmcd308 0]

This question on terminology was inspired by another thread. My real question is whether all three of these terms have relevance to skydiving.

I am not a pilot, so my understanding of the three terms as they relate to aircraft may be incorrect. In fact, I am positive that they are at least incomplete. But here go my initial thoughts on defining the terms, followed by my take on their relevance to skydiving.

Spin - a state in which at least one wing of the aircraft is stalled where the aircraft is rotating about its center of gravity on its yaw axis.

Flat spin - a spin in which the aircraft's artificial horizon remains level. i.e. it is my understanding that there is really nothing special about a "flat spin" except that the aircraft has neither positive nor negative pitch and neither left nor right roll.

Spiral dive - a maneuver in which the aircraft is performing a balanced turn (i.e. not slipping) at its maximum turning rate while losing altitude at a rate sufficient to maintain an airspeed sufficient for maneuvering.

A maximum performance toggle turn would result in a spiral dive, in my estimation. I have not really encountered situations that I can think of right now where the other two terms are relevant to canopy flight.

Feel free to correct the above terms and to expand on this idea. I think that establishing a common vocabulary will assist in discussion of how parachutes behave.

Brent

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www.jumpelvis.com

[diablopilot 2]

Well are you limiting this to canopy flight?

Spiral dive - Agreed that it would be a toggle, or riser turn.

Spin - Bringing one side of the canopy to it's stall point to affect a turn.

Flat Spin - Stall turns in which the whole canopy has been brought to the edge or begining of a stall and a turn is affected through a greater input on one side of the canopy.

One of the problems in comparison is on an airplane the wing is usually ridgely affixed to the fusalage. Not so in skydiving.

Of course these are just my opinions of a definition.

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You're not as good as you think you are. Seriously.

[bmcd308 0]

And a discussion of opinions on what the definitions should be is exactly the point - agreeing on a vocabulary promotes productive discussion of the concept.

Brent

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www.jumpelvis.com

[Stumpy 284]

If it is possible under a skydiving canopy i would envisage a "spin" as the thing i have seendone by top paragliders where the whole caboodle rotates around an axis running through the centre of the canopy and down through the pilot. Thiunk they call it a helicopter or something.

Never try to eat more than you can lift

[drakeshelby 0]

Brent, your descriptions on the manuvers are as good as it gets but I will put in my 2 cents in terms that we can relate to.


Flat spin: Both wings are stalled on the air craft, it does not roll, horizon stays level. Imagine an aircraft spinning like the rotor blades on a helicopter but without the lift. There is a center point on the spin and no roll at all.

Spin: One wing of the aircraft is stalled. The aircraft yaws slightly to the stalled side while the wing on the outside still has lift.

Spiral Dive: Resembles close to a spin. This dive has a steep angle of attack(nose of the plane points down). The plane rotates around a center point not on the aircraft but slightly in front of the nose of the plane. Both wings have lift. For skydivers it is a hard toggle turn!!

drakeshelby

[kallend 2,106]

Quote

Brent, your descriptions on the manuvers are as good as it gets but I will put in my 2 cents in terms that we can relate to.


Flat spin: Both wings are stalled on the air craft, it does not roll, horizon stays level. Imagine an aircraft spinning like the rotor blades on a helicopter but without the lift. There is a center point on the spin and no roll at all.

Spin: One wing of the aircraft is stalled. The aircraft yaws slightly to the stalled side while the wing on the outside still has lift.

Spiral Dive: Resembles close to a spin. This dive has a steep angle of attack(nose of the plane points down). The plane rotates around a center point not on the aircraft but slightly in front of the nose of the plane. Both wings have lift. For skydivers it is a hard toggle turn!!

I believe those to be correct definitions.

In a normal spin the nose is down, and most certificated aircraft recover when the control inputs that got the plane there in the first place are removed. You cannot enter a spin without stalling at least one wing. The descent rate is limited because of the high drag of the stalled wing.

My experience with flat spins is limited to flying R/C models. One wing is actually going backwards, the tail is stalled too, and recovery may be impossible regardless of what you do with the controls. It is a very stable aerodynamic state, somewhat reminiscent of a maple seed's flight. Descent rate can be very slow because the autorotation of the wing generates lift rather like the autorotation of an autogyro rotor.

In both normal and flat spins the rotation axis passes through the aircraft's center of mass. In a spiral, the aircraft describes a helical path about the rotation axis.

The rate of descent increases in the order: flat spin < normal spin < spiral dive.

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The only sure way to survive a canopy collision is not to have one.

[diablopilot 2]

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For skydivers it is a hard toggle turn!!

Or risers.

I'd agree with your interpretation of the above terms, and think mine as they apply to a canopy are apt. I have duplicated each of those on several different planforms at various loadings, some much more interesting than others.

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You're not as good as you think you are. Seriously.

[Patkat 0]

One relevant difference is that a stalled canopy loses its shape, unlike a rigid aircraft wing. If a canopy enters a spin state as defined by fixed wing flyers, it will tend to depressurize and start acting like a pile of nylon attached to some strings.
Of course, because it has a weight suspended below it, and because of the way it is trimmed, and because of it's leading edge and crossports, it will reopen and become a functional airfoil again, given sufficient altitude and no tangles.
So, speaking from relatively minimal experience with both aeronautics and canopy flight, I'd say that any stall induced spin will quickly be transitioned to a repressurized, normal canopy flight, or a ball of s*** that will recover if you're lucky. An attitudinal, straight-ahead stall is possible, and even fun to do with your canopy, given a safe altitude for recovery. Just haul down your toggles til it folds in half and you start falling fast! Then let 'em up slowly and evenly, lest you spin it and have to chop it.
As for the flat spin, worry about that in freefall

Patkat
gotta exercise my demons!

[diablopilot 2]

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One relevant difference is that a stalled canopy loses its shape, unlike a rigid aircraft wing. If a canopy enters a spin state as defined by fixed wing flyers, it will tend to depressurize and start acting like a pile of nylon attached to some strings

Not always.

There are degrees of stall and it is possible to fly a canopy on the edge thus maintaining the shape. Infact puting a spin into it helps maintain the shap through centrifigal force (or is it centrpidial)

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You're not as good as you think you are. Seriously.

[pilotdave 0]

In a spin, both wings are stalled...one is "more stalled" than the other, causing an autorotation. A flat spin will occur when the center of gravity is too far aft. The autorotation of the spin will tend to pull the center of gravity outward, lowering the tail and raising the nose. The problem is that in most aircraft the pilot will not have the control authority to lower the angle of attack to get out of the spin.

A spiral does look like a spin, but the angle of attack is lower, not higher, so the wings are not stalled. The danger there is that the plane will pick up speed very quickly, unlike in a spin where the speed stays pretty low because of the high angle of attack.

Dave