JustAnAvGeek
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Posts: 13
Joined: Tue Oct 23, 2018 5:36 am

Twin Otter Friction Knob

Tue Oct 23, 2018 6:19 am

A friend just came back from a trip in a twin otter and was asking me about this knob next to the feather knob on the overhead panel. He says it was labelled 'friction'. Could someone please explain what this does and why? If I'm wrong please correct me.
 
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Starlionblue
Posts: 18840
Joined: Fri Feb 27, 2004 9:54 pm

Re: Twin Otter Friction Knob

Tue Oct 23, 2018 6:53 am

At a guess, the two grey friction knobs control the "stickiness" of the throttles and the pitch ("prop") controls. The more friction, the harder the resistance to movement. Tighten to the max when you want them to stay in place, e.g. in the cruise. Loosen when you need to move them a lot, e.g. on the approach.

Image

The same sort of mechanism can be found on the throttle knob of many Cessnas. In the pic, you can see the knurled rotary control at the base (root?) of the throttle on a 172. Turn clockwise for more friction.

Image
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
JustAnAvGeek
Topic Author
Posts: 13
Joined: Tue Oct 23, 2018 5:36 am

Re: Twin Otter Friction Knob

Tue Oct 23, 2018 7:06 am

Great, this definitely answered that, thanks. Another question though:
Is the pitch levers for feathering control or is there a difference between the two?
 
BravoOne
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Re: Twin Otter Friction Knob

Tue Oct 23, 2018 11:40 am

As I recall....bringing the pitch levers full aft would bring the props to a full feathered position. There were several predeparture checks that required a full cycle of the props. In addition the props had a auto feather feature that sensed a power loss via torque loss and subsequently cause the prop to feather automatically.
 
Max Q
Posts: 6975
Joined: Wed May 09, 2001 12:40 pm

Re: Twin Otter Friction Knob

Wed Oct 24, 2018 12:58 am

Some of our B727 aircraft had a
small lever on the center pedestal
to adjust throttle friction
The best contribution to safety is a competent Pilot.
 
BravoOne
Posts: 2997
Joined: Fri Apr 12, 2013 2:27 pm

Re: Twin Otter Friction Knob

Thu Oct 25, 2018 1:43 pm

Max Q wrote:
Some of our B727 aircraft had a
small lever on the center pedestal
to adjust throttle friction


That was a carry over from the 707/720, Never saw it on the 727-200, only the -100 series. When autothrootles came to the scene, manual friction went away.
 
Max Q
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Joined: Wed May 09, 2001 12:40 pm

Re: Twin Otter Friction Knob

Sat Oct 27, 2018 11:25 pm

BravoOne wrote:
Max Q wrote:
Some of our B727 aircraft had a
small lever on the center pedestal
to adjust throttle friction


That was a carry over from the 707/720, Never saw it on the 727-200, only the -100 series. When autothrootles came to the scene, manual friction went away.



We had some ex PE -200’s that had the
friction adjustment levers, it never really
seemed necessary


The aircraft that didn’t have them had
no issues with throttles moving when
you didn’t want them to


The only problem I saw occasionally were
throttles that were very stiff and hard to
move, sometimes we would write them
up and Mx would adjust them



I think adjustable friction levers may have
been a holdover for Boeing from piston
engine days when everything vibrated
all over the place and needed to be
‘Locked down’ !
The best contribution to safety is a competent Pilot.
 
Yikes!
Posts: 309
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Re: Twin Otter Friction Knob

Mon Dec 03, 2018 4:25 am

The condition (prop) levers on the DH6 will also feather the propeller once moved fully aft (through the detents). The red levers in the initial post's photo are the fuel on/off levers.
 
BravoOne
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Re: Twin Otter Friction Knob

Mon Dec 03, 2018 10:06 am

Yikes! wrote:
The condition (prop) levers on the DH6 will also feather the propeller once moved fully aft (through the detents). The red levers in the initial post's photo are the fuel on/off levers.


I don't recall any friction locks on the B377:)
 
Max Q
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Joined: Wed May 09, 2001 12:40 pm

Re: Twin Otter Friction Knob

Mon Dec 03, 2018 11:59 am

BravoOne wrote:
Yikes! wrote:
The condition (prop) levers on the DH6 will also feather the propeller once moved fully aft (through the detents). The red levers in the initial post's photo are the fuel on/off levers.


I don't recall any friction locks on the B377:)



Did you fly the Stratocruiser ? !
The best contribution to safety is a competent Pilot.
 
BravoOne
Posts: 2997
Joined: Fri Apr 12, 2013 2:27 pm

Re: Twin Otter Friction Knob

Mon Dec 03, 2018 12:23 pm

Max Q wrote:
BravoOne wrote:
Yikes! wrote:
The condition (prop) levers on the DH6 will also feather the propeller once moved fully aft (through the detents). The red levers in the initial post's photo are the fuel on/off levers.


I don't recall any friction locks on the B377:)



Did you fly the Stratocruiser ? !


Never flew the B377 Stratocruiser, but did fly the Boeing C97 in the California ANG, VNY (146th). My Airman Cert says B377 on it. One of the Squadron Commanders was an FAA examiner so most of the pilots would snag a type rating after 500 hours or so. Went through the ANG/UPT after being hired by WAL.
 
Max Q
Posts: 6975
Joined: Wed May 09, 2001 12:40 pm

Re: Twin Otter Friction Knob

Tue Dec 04, 2018 6:35 am

BravoOne wrote:
Max Q wrote:
BravoOne wrote:

I don't recall any friction locks on the B377:)



Did you fly the Stratocruiser ? !


Never flew the B377 Stratocruiser, but did fly the Boeing C97 in the California ANG, VNY (146th). My Airman Cert says B377 on it. One of the Squadron Commanders was an FAA examiner so most of the pilots would snag a type rating after 500 hours or so. Went through the ANG/UPT after being hired by WAL.



That’s very interesting and it must have been quite an experience, I think the 377 was based on the C97 you flew ?


Which I think was derived from the B29
The best contribution to safety is a competent Pilot.
 
BravoOne
Posts: 2997
Joined: Fri Apr 12, 2013 2:27 pm

Re: Twin Otter Friction Knob

Tue Dec 04, 2018 10:09 am

Max Q wrote:
BravoOne wrote:
Max Q wrote:


Did you fly the Stratocruiser ? !


Never flew the B377 Stratocruiser, but did fly the Boeing C97 in the California ANG, VNY (146th). My Airman Cert says B377 on it. One of the Squadron Commanders was an FAA examiner so most of the pilots would snag a type rating after 500 hours or so. Went through the ANG/UPT after being hired by WAL.



That’s very interesting and it must have been quite an experience, I think the 377 was based on the C97 you flew ?


Which I think was derived from the B29


I believe that the C97 was more closely aligned with the B50, which of course was a derivative of the B29.
 
Max Q
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Joined: Wed May 09, 2001 12:40 pm

Re: Twin Otter Friction Knob

Wed Dec 05, 2018 3:34 am

BravoOne wrote:
Max Q wrote:
BravoOne wrote:

Never flew the B377 Stratocruiser, but did fly the Boeing C97 in the California ANG, VNY (146th). My Airman Cert says B377 on it. One of the Squadron Commanders was an FAA examiner so most of the pilots would snag a type rating after 500 hours or so. Went through the ANG/UPT after being hired by WAL.



That’s very interesting and it must have been quite an experience, I think the 377 was based on the C97 you flew ?


Which I think was derived from the B29


I believe that the C97 was more closely aligned with the B50, which of course was a derivative of the B29.




Thanks for that information B one, very interesting
The best contribution to safety is a competent Pilot.
 
747Whale
Posts: 294
Joined: Fri Dec 07, 2018 7:41 pm

Re: Twin Otter Friction Knob

Sat Dec 08, 2018 7:01 am

Max Q wrote:
BravoOne wrote:
Max Q wrote:
I think adjustable friction levers may have
been a holdover for Boeing from piston
engine days when everything vibrated
all over the place and needed to be
‘Locked down’ !


Friction didn't go away with autothrottles, and it's still found on a lot of aircraft, including virtually all turboprops (every one I've ever flown, single or multi), and a lot of turbojets, too. On newer transport category aircraft with autothrottles, friction is normally handled via servos, though friction in some aircraft, especially older aircraft, is pilot-adjustable.

The Twin Otter uses friction locks because the throttles are overhead, and one doesn't want to keep a hand up there all the time. It's tiring.

Feathering is conducted by placing the propeller lever to the full aft position, and requires moving past a detent (to preclude inadvertent feathering).
 
BravoOne
Posts: 2997
Joined: Fri Apr 12, 2013 2:27 pm

Re: Twin Otter Friction Knob

Sat Dec 08, 2018 3:08 pm

Please name a few aircraft with AT and friction locks installed? I can't recall any at the moment.

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