Aerosoft Twin Otter AP altitude set/hold problems

[roop298]

OK, I have to be doing it wrong.

I get up to where I want to add in the AP. I flick the switch. As I use a joystick with no spring return I wait a few seconds for the trim to settle the aircraft.

The plane then tends to drift upwards so I use the column nudge button to give some negative nose. It goes down for a few seconds then drifts up again.

If I press the AP 'Alt' button the planes rate of climb levels out but I'm now too high. I do the nudge nose down again. Same thing happens. It goes down 500 feet then climbs back up. I end up with a nose down of -10 selected but it still goes up.

 

The plane is set to hot and light from the start. All I'm doing at this stage is just trying to get familiar with the systems. I'm not.

 

I would imagine all Twotter vets know the instruction manual is useless in AP explanation and I can't find much on the subject so I'm guessing I'm acting like a dullard and missing something obvious.

 

Can anyone help?

[mrzippy]

Are you setting the A/P for a specific altitude or are you just trying to hold the altitude you are at?

[Mark Hurst]

I get up to where I want to add in the AP. I flick the switch. As I use a joystick with no spring return I wait a few seconds for the trim to settle the aircraft.

...I use the column nudge button to give some negative nose.

 

I wonder what your expectations are. When you engage the A/P it will hold the aircraft attitude and pushing the stick has no effect. Pressing ALT cancels the attitude hold and holds the altitude you are at when you press it.

[roop298]

Yes I understand it's not a autopilot in the usual sense, more an attitude holder.

 

'Pressing ALT cancels the attitude hold and holds the altitude you are at when you press it.'

 

So, are you saying if it has a tendency to go up it's because I am in a positive nose attitude before I flick the switch?

 

Oh, and what does the altitude selector to the left of the AP do? I can't find an explanation of the either. It bing-bongs when I'm not at the selected altitude and other than that doesn't appear to do anything.

[mallcott]

Probably failed to coincide the selected altitude with the ambient - Use the `B` key to reset the Kollsmann setting.

 

Again, the FSX Learning Center explains all this and much more. As a beginner you've paid for it, why not USE it?

[f16jockey_2]

As Mark explained, pressing AP ALT will keep you at the altitude you're at when you press it.

 

The way I fly the Twotter (dunno if it's correct, but it works OK for me).

- set wanted altitude on the alerter (just as a reminder, it's in no way linked to the AP)

- fly straight and level, engage AP

- press AP IAS (current airspeed hold)

- add throttle, the AP will try to keep the airspeed, so the plane will start a controlled climb

- adjust the climb rate by adding/lowering throttle

- when nearing the wanted altitude (you'll hear an alert) ease off on the throttle to flatten your climb

- at the desired altitude, press AP ALT and the plane will stay there

 

Descent is done the same way, but by lowering throttle with AP IAS set

 

Wim

[Mark Hurst]

- set wanted altitude on the alerter (just as a reminder, it's in no way linked to the AP)

 

Actually it is. You dial in the target altitude and press Alt Alert button, then initiate a climb. When you reach 1000ft before the target you get a chime and the little light beside the Altitude selector illuminates. The light goes out at 300ft to go and the AP switches to ALT mode to acquire the target altitude.

 

There are several ways to initiate a climb, but the most convenient is to dial in your target altitude and them press MDA. I'm not sure if this is a bug, but it initiates a climb and then acquires the target altitude as described above.

[Mark Hurst]

So, are you saying if it has a tendency to go up it's because I am in a positive nose attitude before I flick the switch?.

 

Yes, that's right. You can also tweak the attitude it's holding by nudging the thumb-wheel and dial on the top of the yoke pedestal. See my other response for the function of the altitude selector and alerter (didn't see your response until after I posted that). This is explained in the manual (Systems/p15).

[roop298]

Many thanks, all.

[roop298]

Erm, not wanting to hijack my own topic in another direction but I noticed the HSI on the left side didn't move when I put an ILS frequency in the radio but the right side did. IS this a bug?

[Mark Hurst]

Erm, not wanting to hijack my own topic in another direction but I noticed the HSI on the left side didn't move when I put an ILS frequency in the radio but the right side did. IS this a bug?

 

No, the co-pilot's HSI is slaved to NAV2. You will notice it shadows the secondary NAV instrument on the captain's side.