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Martinlest
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Twin Otter - prop lever usage?

Thu Feb 20, 2020 9:43 pm

Would anyone be able to explain to me, please, the 'normal' usage of the prop levers during a 'normal' flight... that is, how they are usually positioned by pilots, (course/fine), at engine start, taxi, takeoff, climb, cruise, descent and so forth...?

I have watched a few videos explaining the technicalities of fixed props, some of which I knew already of course, some of which I did not, but from a practical point of view I am still not sure how a DHC-6 pilot would co-ordinate the prop with the throttle at each stage of a flight.. taxiing out is a case in point. At the moment I think that my flights in the (X-Plane) DHC6 are far too much 'on the fly': I just move the throttles and props as I need to maintain speed and climb, but I have no real method.

Have ordered a copy of this:

http://www.worldairroutes.com/Maldivian.html

but would appreciate some input here, as to the practice rather than theory, if anyone is able.

Many thanks,

Martin
 
GalaxyFlyer
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Joined: Fri Jan 01, 2016 4:44 am

Re: Twin Otter - prop lever usage?

Thu Feb 20, 2020 9:57 pm

Search is your friend...

viewtopic.php?t=729941
 
Martinlest
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Re: Twin Otter - prop lever usage?

Thu Feb 20, 2020 10:16 pm

Search is your friend...


Rarely my friend - I spent half the evening looking around (the internet generally) with not quite the results I was looking for. That thread did not come up within that time...

Thank you, I'll read it carefully, though at first glance most of it seems to describe the theory of the various levers, which I have already found and read about by this stage, rather than where the pilot in practice places them (throttles in relation to prop levers) at each moment of the flight . :smile:
 
GalaxyFlyer
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Re: Twin Otter - prop lever usage?

Thu Feb 20, 2020 10:51 pm

Throttles and props in turbines is not like in pistons. Props set high rpm for flight, low for ground, line up go to high rpm, clear the runway, go low rpm. All power adjustments for flight are done with the throttles.
 
BravoOne
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Re: Twin Otter - prop lever usage?

Thu Feb 20, 2020 11:03 pm

During taxi props are forward as they are in takeoff. Climb and cruise they are pulled back and for landing they are once again full forward. Lots of variables. My experience is in a Twotter amphibious float plane. Galaxy Flyer has it down pretty well.
 
Martinlest
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Re: Twin Otter - prop lever usage?

Fri Feb 21, 2020 12:18 am

Right, thank you. Only thing is, there's a mixture of terms being used: 'high'/forward'/'back'/'coarse'/'low'/'fine', but I think I see your meaning!

Throttles and props in turbines is not like in pistons. Props set high rpm for flight, low for ground, line up go to high rpm, clear the runway, go low rpm. All power adjustments for flight are done with the throttles.


I think that that is pretty much what I have been doing really, except that I am pretty sure I have not always remembered to move the props to low rpm again after takeoff.

So there's not really any 'fine tuning' of the prop levers necessary? Either course or fine... But (sorry to ask a stupid question, I realise how much I don't know when it comes to prop a/c after all the Airbus/Boeing flying!!) where does the coarse/low zone end and where does the feather begin? I presumably don't want to fly with the props feathered!

Can't wait to watch the 3 hour DVD now so that, hopefully, I can see this put into practice...
 
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Starlionblue
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Re: Twin Otter - prop lever usage?

Fri Feb 21, 2020 1:27 am

Martinlest wrote:
Right, thank you. Only thing is, there's a mixture of terms being used: 'high'/forward'/'back'/'coarse'/'low'/'fine', but I think I see your meaning!

Throttles and props in turbines is not like in pistons. Props set high rpm for flight, low for ground, line up go to high rpm, clear the runway, go low rpm. All power adjustments for flight are done with the throttles.


I think that that is pretty much what I have been doing really, except that I am pretty sure I have not always remembered to move the props to low rpm again after takeoff.

So there's not really any 'fine tuning' of the prop levers necessary? Either course or fine... But (sorry to ask a stupid question, I realise how much I don't know when it comes to prop a/c after all the Airbus/Boeing flying!!) where does the coarse/low zone end and where does the feather begin? I presumably don't want to fly with the props feathered!

Can't wait to watch the 3 hour DVD now so that, hopefully, I can see this put into practice...


Caveat: I've only driven piston props but the basic principles are the same.

- Fine pitch is lower blade angle, giving higher RPM. This is "forward" on the prop lever. Used in take-off, (depending on aircraft) climb, and landing (in case of a go around).
- Coarse pitch is higher blade angle, giving lower RPM. This is "back" on the prop lever. Used in cruise and descent.
- Feather is "full coarse", if you will, since the blades are at 90 degrees to the airflow.

You don't really fine-tune pitch in the cruise because the prop governor does it for you by automatically controlling pitch to give a fixed RPM. E.g. if you add power the prop governor will coarsen pitch to maintain RPM, and the prop will provide more thrust since more air is being displaced.

In single engine props, if you lose prop control the prop goes to full fine, so that if you still have the engine you can still continue, albeit with much lower efficiency. In multi-engine props, on the other hand, if you lose prop control the prop goes to feather, because you still have the other engine(s) and want minimum drag on the failed prop.
 
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Francoflier
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Re: Twin Otter - prop lever usage?

Fri Feb 21, 2020 2:24 am

Starlionblue wrote:

You don't really fine-tune pitch in the cruise because the prop governor does it for you


Years of fine tuning prop levers so the engines would stop going 'waowaowaowaow' all the freaking time has taught me otherwise... :wink2:
 
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Starlionblue
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Re: Twin Otter - prop lever usage?

Fri Feb 21, 2020 2:53 am

Francoflier wrote:
Starlionblue wrote:

You don't really fine-tune pitch in the cruise because the prop governor does it for you


Years of fine tuning prop levers so the engines would stop going 'waowaowaowaow' all the freaking time has taught me otherwise... :wink2:


Fair point. :D
 
spacecadet
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Re: Twin Otter - prop lever usage?

Fri Feb 21, 2020 3:15 am

Martinlest wrote:
So there's not really any 'fine tuning' of the prop levers necessary? Either course or fine... But (sorry to ask a stupid question, I realise how much I don't know when it comes to prop a/c after all the Airbus/Boeing flying!!) where does the coarse/low zone end and where does the feather begin? I presumably don't want to fly with the props feathered!


You're going to need to find either a POH for the specific model you're flying (because they do differ in their prop settings) or someone who flies it for real who can tell you. I think you're more likely to find a POH.

In most constant speed prop planes you only want to be a couple to a few hundred RPM slower in cruise than at takeoff and landing, so you can probably do that for now and be safe. Go too coarse with power applied and you can overstress the prop. It's better to be too fine (high rpm) than too coarse (low rpm) if you're not sure. You won't get as much power, but the prop will have less stress and the engine will be more responsive. And yes, in most planes it's one setting for takeoff and landing and another for cruise and that's it. Though yeah, that asymmetrical prop noise is something a lot of pilots do try to fine tune out.

But look for a POH. It's probably going to be more helpful than a video, if you're really interested in realistic procedures.
 
Martinlest
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Re: Twin Otter - prop lever usage?

Fri Feb 21, 2020 10:41 am

Thank you for the helpful comments.

I found this, though much is a bit technical for my purposes:

https://drive.google.com/open?id=14JXRT ... qPmVp2KGY8
 
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Starlionblue
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Re: Twin Otter - prop lever usage?

Fri Feb 21, 2020 10:47 am

If you're willing to part with a little bit of money, Transition to Twins by David Robson is an excellent introduction to the world of multi-props.

Image
 
Martinlest
Topic Author
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Re: Twin Otter - prop lever usage?

Fri Feb 21, 2020 10:12 pm

Thanks, but it's probably a bit more detailed than I need right now :-)
 
Max Q
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Joined: Wed May 09, 2001 12:40 pm

Re: Twin Otter - prop lever usage?

Fri Feb 21, 2020 11:26 pm

While we’re on the subject of float planes and amphibians why are the throttles / prop controls mounted on the overhead?
 
BravoOne
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Re: Twin Otter - prop lever usage?

Sat Feb 22, 2020 12:18 am

I don't have a definitive answer for that. Gruman and a few others have done it that way since the beginning, and I must say it feels more natural, especially when maneuvering on the water. The Twotter on amphibious wheels is like steering a shopping cart.
 
GalaxyFlyer
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Re: Twin Otter - prop lever usage?

Sat Feb 22, 2020 12:18 am

Simple—easy cable runs to the engines. At least, that’s fact for DeHaviland planes
 
Max Q
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Re: Twin Otter - prop lever usage?

Sun Feb 23, 2020 12:00 am

GalaxyFlyer wrote:
Simple—easy cable runs to the engines. At least, that’s fact for DeHaviland planes



Not sure why that’s simple, there’s no reason why control cables couldn’t be run under the floor


Perhaps what you meant was underfloor cables would be vulnerable to corrosion from water entering the hull
 
GalaxyFlyer
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Re: Twin Otter - prop lever usage?

Sun Feb 23, 2020 12:13 am

With the high-mounted engines, the control runs are much simpler than underfloor, up the sidewalls then out to the engines. Lots of pulleys and tension ers needed underfloor. Or, at least, that’s what the DeHaviland guys told me when I asked the question. No doubt, overhead kept them out of the corrosion “hot spots” on amphibs, but that doesn’t explain the Twotter
 
BravoOne
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Joined: Fri Apr 12, 2013 2:27 pm

Re: Twin Otter - prop lever usage?

Sun Feb 23, 2020 2:58 pm

The fuel tanks are under the floor of this aircraft. Small aux tanks in the wings.
 
BravoOne
Posts: 4094
Joined: Fri Apr 12, 2013 2:27 pm

Re: Twin Otter - prop lever usage?

Sun Feb 23, 2020 5:03 pm

BravoOne wrote:
The fuel tanks are under the floor of this aircraft. Small aux tanks in the wings.


In addition, there is a requirement to replace all control cables every one or two years if operated in salt water, as I recall.

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