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Twin Otter proper landing configuration


degt
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I have been checking the PDF manuals and checklists to find the appropriate approach/landing configurations. What I normally do is to reduce the thrust to idle (but not into the Beta range that activates the two blue lamps) and if that is not enough (usual) then I also move the feather lever towards feather (as much as possible).

If I don't do that it is difficult to get to approach speed (80 knots) and descend on time, or at least that is what I experience. However upon landing I have to move feather to the unfeather so that the reverse thrust takes effect.

I have read in some places that for landing the DHC6 you put full RPM (thrust) and leave the propeller into unfeather (as in cruise). However, if I do that it either never reduces speed to approach speed or never manage to descent as it tried to float. What I do also is to pitch down about 5 degrees as I have seen on real Twin Otters during final approach and then level at the last minute.

So my question is whether there is a more detailed descent/approach configuration, in particular the use of the Propeller RPM and Torque (Thrust). The "fully detailed" checklist didn't clear my doubts on the subject and I want to use this plane properly.

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The Twin Otter is not really an aircraft that is flown 'by the digits' and there are many different ways to land depending on weight, runway lenght and condition, wind or temperature.

Personally I just put the prop in take-off setting because if you need to go around you don't often have the time to unfeather the prop. If you got to much speed just sideslip a little to loose it. It is important though to loose speed early on because as you have seen, it's hard to do so at the last moment.

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The flaps and drooping ailerons on the Twotter enable low speed flying. To do so in a free turbine safely requires a higher thrust setting (free turbines spool up more slowly with noticeable `lag` and you don't want that when low and slow and need to effect a go-around) so airframe designers usually provide more drag from the dangly bits to allow for a balanced approach thrust:drag ratio.

You can experience this in the Twotter by leaving the prop levers full forward, stay in level flight with no flaps and slowly retarding the power levers, until at a certain point it feels like someone has slammed on the brakes and the aircraft wants to fall from the sky. To stay out of that zone you need more power, but when you apply it the aircraft continues to slow until the power starts to recover. To avoid this scenario you use more power and you compensate by using flaps.

The difference in the Twotter is that if you are flying an airline style approach you use less flappage or even none at all, and if you need to pocket the bird into a clearing the size of tea leaf then you fly a military-style late, steep profile - for which you will need more flaps, but also a goodly amount of power.

Any and all combinations work - and that truly is the brilliance of the Twotter! :D

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Thanks for the various insights (more are welcome though), this is a plane I truly love to the point that I have not done a "Jet" flight in a long long long time (and jets were my favorites).

Usually I manage to do nice approaches by lowering the speed to around 80 knots and deploy flaps, then the approach is slow but very controlled until placing the bird down. I usually fly it into short landing strips or short island strips. On other ocassions however I fail to find that balance and my approach is conducted at around 100-120 knots which IMHO is pretty fast.

Anyway, I love to experiment with this Twotter

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If you are having problems being fast, most definitely move those prop levers forward, it's the normal approach setting anyway. The flat pitch will help slow you down quite a bit. As far as the throttles you can keep them just above beta as you mention but I also have no problem making an approach with beta blues shining away.

Personally I have the best success with a fairly shallow approach. With full flaps the nose is down so seeing the runway is not an issue.

It is an aircraft that is tempting to make the steep Khe Sanh approach with but with full flaps you don't gain that much since the increased speed seems to produce so much more lift that it floats. It is actually better to slow down early and make your approach stable and as shallow as the approach end obstacles allow.

The steeper the approach the more likely you are to be a few knots fast and that means distance wasted floating down the runway. Being slow and shallow means you have power on and that gives you options to lower power for fine tuning your approach. You are then able to pull power off to drop once clear of those approach obstacles. That ends up making for a shorter landing run than a steep approach. If you do need to lose a lot of altitude early on try making most of the approach with half flaps then full on short final. My approaches are usually made at just above Vmc, the red line on the ASI

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from this video it seems the prop levers are forward

I am new to the Twin Otter and wonder if anyone found a way to assign a key/knob for the reverse thrust. Or is the mouse the only way to activate reverse thrust?

cheers

Jaeger

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@Shaun, i had to find out about the F2 key! Thanks

As previously said, the Twin Otter is not flown by the numbers. You can come in step or shallow. Some styles i found out so far.

Step angle with 60 to 70 knots and full flap

80 to 90 knots in a more shallow approach and flaps at 30

100 to 120 knots, shallow and now flaps

have as much fun as i do with that great bird

Jaeger

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