Spiral dive from a spin attempt.

[facthunter]

ALL the mechanical A/H's toppled (hit their gimbal stops) and had to be caged or they wrecked themselves so couldn't be used to help "unusual" attitude recognition/recovery. It all had to be done on "limited" panel as it was known. Nev

[facthunter]

With non Visual flying you have to absolutely RELY on your instruments and NOT on any "seat of the pants" feeling you get.. . OK I'm not in cloud.... Am I still OK ?Some spiral and spin events have a high rotation rate and DIRECTION is best determined by a TURN rate indicator. You might also be legally visual but NOT have a distinct horizon for a good reference especially if you are higher and there's smoke haze etc. IF you plane does funny things you won't know where you are. Nev

[Bruce Tuncks]

I actually have an old ww2 AH, in a carton somewhere. They were illegal to have in your glider for competitions in case you used them to get an advantage by cloud flying. So I had to take it out and pack it away. And they took Bert's Australian record height away because they deemed ( correctly ) that he climbed up the inside of the cloud instead of up the outside as he initially claimed. ( The climb was in a cu-nim near Alice Springs many years ago )

Getting back to electronic AH's, I don't even know the theory of how they work. Do they use mechanical halteres? Do they topple like Nev says the old AH's do?

[kgwilson]

My Dynon D6 has an A/H, Turn & Bank, Slip ball, Alt, VSI, Compass/heading plus inc/dec rates of turn, climb etc & even a voltmeter. It cost $1,800 in 2013 which is a lot but not bad for all the things it does. It also has configurable alarm settings & ASI colours. It uses electronic transducers, magnetometer, rate sensors & accelerometers. How it works is Magic.

[Yenn]

I had one of those magic Dynon setups demonstrated to me by a friend who also had it set up to fly the plane. He was demonstrating how it could turn by changing the heading setting and sure enough it went into a turn, all very nice, but he was watching the Dynon and the compass, while I was watching us turning into a nice big cumulous cloud. My warning was what stopped us going IFR. No doubt it would have continued and stabilised on a new heading, but it needs care in use.

[pmccarthy]

The phone AH app would be useful if all else failed.

[PaulMilo2]

The "Under the Hood" training covers it well and relies on a gyro turn needle as a prime instrument. Doing that sequence on limited panel, (learning it for the first time) is about as hard as anything you ever do in a plane. Spiral training is NOT permitted in RAAus aircraft. While that IS limiting of an opportunity, it's for a good reason. Recovery from a spiral must be quick and effective or you exceed the aircraft's limits easily. Nev

 

Spin training under the hood? Or just unusual attitudes? I think spinning under the hood would be exceptional! I have done unusual attitudes under the hood and on a very black night with no ground lighting. Fortunately the Instructor was as nervous as me at night, so the unusual attitudes were not that unusual at all :-)

[facthunter]

I would think what you did was not legal. In any case it's very dangerous as you realise. Unusual attitudes under the hood are very challenging especially for the first few times and particularly when on limited panel. IF you have done them welcome to a new world of appreciation. I don't think spinning under the hood is that difficult, depending somewhat on HOW you enter the spin.. Unusual attitudes, you just don't know what situation you will be in. To tell you a little secret when the plane was really all over the place and very slow, I would just put all controls in neutral and see what happened for about 10 seconds. By then it's usually settled into something more recognisable. I considered it cheating at the time but now I'd still recommend it. Till You KNOW just what the planes doing you cannot really start recovery action unless you are just trying your luck and guessing. Nev

[Dick Gower]

I have often wondered whether you could recover if you lost control in a cloud and emerged in a vertical dive at cruise speed in a non-aerobatic plane, say a PA28 or C172. Could you pull back to straight and level without destroying the airframe by excessive G or by overspeed?

The answer is no. Firstly it would be highly unlikely that you would emerge just at cruise speed, more likely Vne or more. Secondly, the rapid acceleration would continue until you got the nose attitude back above horizontal. By that time it would have broken up in flight ("the wreckage was found scattered over a large area") or completed the manoeuvere underground.

[facthunter]

A small point. It doesn't have to be above horizontal. You will reach an equilibrium point somewhere before that depending on the planes L/D. The risk is the rapid speed build up if the attitude is near vertical DOWN will see you at Vne very quickly and you are running out of sky very quickly.. Your rate of closure to the ground will be something like 18,000 feet per minute so you have B all time ( or room./height ) to pull it out of the dive even if you didn't pull the wings off trying. This is a seriously WORSE position to be in than a spin IS.. Nev

[Mike Borgelt]

Bruce, the old AH instruments had an actual spinning gyro which tended to maintain its orientation in space and a tricky series of mechanical devices to do long term stabilisation to keep the axis parallel to the Earyth's gravity vector. Basically a pendulum. The gyro will otherwise drift seriously in only a few minutes. It isn't a space or inertial nav grade gyro. Works well enough as if you don't generate a lift vector of 1 g directly opposite to the Earth's gravity vector on average over minutes you aren't in an aeroplane anymore.

The new gyros are what is called the "strap down" type. They use 3 orthogonal accelerometers and 3 orthogonal rate gyros. These are solid state MEMS devices (Micro Electro Mechanical Systems).

The 3 accelerometers generate the long term gravity vector (actually they measure the lift vector of the aircraft, that needs to be on average 1 g opposite the gravity vector). The gyros give you roll, pitch and yaw RATES but not attitude directly. You need to integrate the rates to get attitude or rather changes in attitude. The accelerometers give you "level flight"that when you turn on and start up on the ground The chip that does this can be as small as 3 x 3 x 1 mm as you'll find in the R/C aircraft stabilisation devices.

Now it isn't quite that simple because of limitations on the gyros and nasty things like "cross axis coupling" and gyro output noise. When you integrate noise you get a random walk as output. It IS NOT the same as averaging.

Dynon also use the rate of change of airspeed for pitch stabilisation for the short to medium term. Think of these units as a turn, slip and ASI for limited panel but a synthesised display to look like an AH. Great devices, I've had one in the BD-4 since 2008 and it has never missed a beat. I bought the external compass add on and get real time wind vector also.

[facthunter]

I wonder why the rate turn needle still works at all attitudes. It's a mechanical Gyro .Nev

[Mike Borgelt]

I wonder why the rate turn needle still works at all attitudes. It's a mechanical Gyro .Nev

The turn rate gyro is a single axis, strapdown mechanical gyro restrained by a spring. The MEMS gyros actually use a vibrating beam to detect turn rate. Works essentially the same as a spinning turn rate gyro. Somewhat surprisingly. As long as you rotate it around the axis it is designed to detect it will detect the rotation rate. Attitude has nothing to do with it.

 

When thinking about this stuff getting the reference frames right is essential, it is easy to mentally move from one to the other without realising what you just did.

There is the Earth reference frame and the aircraft reference frame. You are effectively trying to find the relationship between the two