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Would you consider adding a BRS parachute to your plane ?

The BMAA document mentions the potentially increased gyroscopic effect of the propeller on microlights, and some may be quite wing loaded (wing versus fuselage) which may result in a flatter, higher rotation spin when stabilised, hence only testing to three seconds before initiating recovery.

Pronounced wing washout and limited elevator, and as LeSving mentioned, relatively forward CG range with a large margin to the neutral point, all contribute to spin resistance. Fuselage strakes, or the cross sectional shape of the fuselage and tail, and propensity to rudder blanking, also contribute to spin characteristics.

I am not sure I agree with LeSving’s comment that ease of entry equals ease of recovery, too many variables come into play once you go into the deep stall regime with autorotation.

Oxford (EGTK), United Kingdom

What I should have said, is, I don’t think LeSving’s thesis works in all cases, but for modern approved designs, it probably is fair.

Oxford (EGTK), United Kingdom

LeSving wrote:

There is something very wrong with the basic principles of causality and the basic principles of stability in that reasoning. How can you keep a sustained and developed spin if you don’t have enough elevator/rudder authority to even enter one.

I ran into the conjecture whilst reading up on a discussion regarding whether spin-resistant designs were less likely to have unrecoverable spin modes than aircraft that are designed to spin easily.

My reasoning had been that spin resistant aircraft are more likely to have complex aerodynamic tweaks – e.g. different angles of incidence across the wing – than non-spin resistant aircraft. The idea that spin-resistant aircraft tend to have smaller vertical stabilisers is the only explanation I’ve come across though.

Being spin-resistant might mean that you can’t enter a spin by stalling and ramming in full rudder, but what if you try a tailslide with full power in a PA28? Who knows what might happen – and it’s going to be hard to test, as it’ll be different every time.

I don’t know what Cirrus mean by spin resistant. Most light aircraft are already highly spin resistant in my opinion. For instance the C-172 will spin when doing a spin maneuver (stall, full rudder and full up elevator), but after max 2-3 rotations it will enter a spiral dive, which is easy to recover from, just straightening out. The RV-4 will spin for ever (until it meets the ground that is), but will stop spinning by simply centering the elevator, no need to apply opposite rudder, or even to center the rudder.

The elephant is the circulation
ENVA ENOP ENMO, Norway

Yes, but will they behave so nicely in every spin? I know an experienced instructor who got into a spin in a 152 where the standard recovery didn’t work. I would agree your observation argues against the tail being the problem though.

I don’t think any of the above makes a difference to whether I would fit a BRS parachute to an existing aircraft, as the aerodynamic design of the aircraft is what it is…

I would if I owned a single engine deiced turbo aircraft with weather avoidance, because I fly at night and in crappy weather, and I would do this because of the risk of engine failure than about low-level loss of control. VFR, I would do it more because of possible mid-airs.

Biggin Hill

kwlf wrote:

Yes, but will they behave so nicely in every spin?

Probably not, I have heard from an aerobatic instructor that there could be large differences between seemingly identical aircraft, which is a good reason to always use correct anti spin recovery technique, even though this isn’t always necessary from a physical point of view. I have spun in the 152 Aerobat many times myself, but only one, not several different ones. I guess the Cirrus is the same, some are “spin resistant” (whatever Cirrus mean by that), while others are not ?

The elephant is the circulation
ENVA ENOP ENMO, Norway

I did the first hours of my PPL in two C-152s of the same year. Apart from the color they were identical. We did spin training after the first couple of hours and while the one 152 would easily go into the spin and recover very easily … the other one would be very hard to get into the spin and harder to recover too.

I would say that Cirrus Aircraft are much more similar. All wings done in the same molds and little difference between the planes.

LeSving wrote:

I don’t know what Cirrus mean by spin resistant

The split wing is designed to delay full wing stall allowing full aileron use during stall. This gives more warning and gives the pilot a tool to level the wing using ailerons mitigating spin entry.

Last Edited by USFlyer at 15 Dec 16:18

I think pronounced washout may be a factor for a spin resistant aircraft being difficult to recover from a stable fully developed spin.

First, unless approved for spins, all certified normal and utility category aircraft (including the Cirrus in Europe) are only tested to an incipient spin with no more than one turn. Secondly, the incidence of unrecoverable spins of spin resistant aircraft is low – possibly close to nil, outside of flight testing – so this is somewhat theological as a threat assessment.

An aircraft with washout will enter incipient autorotation with the inner half of both wings stalled, with the inside wing being more stalled. The outer wing is less stalled and has a stronger lift vector, resulting in the roll which combined with the weather vaning from the fin and fuselage sets up the yawning and rolling. As only half of both wings is stalled, and the outer halves are protected by the lower angle of attack from the washout, the spin resistant aircraft still has anti spin roll control. However, at some point beyond the incipient stage the inside wing becomes the first wing to be stalled across the full wing span. This is likely to be due to the gyroscopic effects flattening the spin and increasing angle of attack deeper into the stalled region. Eventually resulting in the portion of the inside wing with washout also going past critical alpha. This combined with an efficient, well rounded fuselage resulting in less anti spin damping from the fuselage. The outer wing is now the only wing that is partially stalled, resulting in an increased lift vector differential effectively ‘locking in’ the spin beyond effective control inputs to achieve recovery.

This doesn’t mean the design is unsafe, it is just not approved for spinning.

Oxford (EGTK), United Kingdom
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