acjbbj
Topic Author
Posts: 19
Joined: Sat Mar 17, 2018 7:06 pm

DHC-8 reverse thrust?

Sat Mar 24, 2018 3:48 am

I've been on Olympic Air's DHC-8 Q400 once, and when we landed during our flight from Athens to Naples, I noticed that the engines were powered up briefly. I am curious to know how the props reverse thrust during landing. Do they change the pitch to push forward? Or what happens with the props? Or does the Q400 not reverse thrust?
Favourite plane: "Lockheed-Martin L-1011-855-1 TriStar NextGen" :mrgreen: (3-Engine cargo jet approximately the size of a 777-9, but with more range and payload than the standard 772F. Powered by three 450-kN upscaled GP7000)
 
stratclub
Posts: 83
Joined: Fri Jan 05, 2018 10:38 pm

Re: DHC-8 reverse thrust?

Sat Mar 24, 2018 8:47 am

Like most turbo-prop aircraft, they have variable pitch props which goes to reverse pitch during landing. https://en.wikipedia.org/wiki/Constant-speed_propeller
 
CanadianNorth
Posts: 3199
Joined: Sat Aug 24, 2002 11:41 am

Re: DHC-8 reverse thrust?

Tue Mar 27, 2018 12:22 am

acjbbj wrote:
Do they change the pitch to push forward?


Yes, the prop blades simply change pitch past the flat position and into a range where they're actually pushing air forward instead of aft. Not sure the exact details for the Dash but I believe it's pretty similar to the ATRs, and on those the little bit of reverse pitch you get is actually pretty effective and slowing down the airplane, seems to be one of those simple but works well things.
HS-748, just like a 747 but better!
 
opticalilyushin
Posts: 490
Joined: Tue Oct 22, 2013 6:35 pm

Re: DHC-8 reverse thrust?

Tue Mar 27, 2018 7:57 am

I work with a Q400 operator in Europe, and the use of reverse is forbidden by the company. The pilots find that the aircraft has good enough braking performance without the use of it. I did once see (or hear) a training captain use it, it was bloody loud!!!
 
T1a
Posts: 53
Joined: Tue Apr 24, 2012 5:41 pm

Re: DHC-8 reverse thrust?

Tue Mar 27, 2018 10:33 am

I also work for a European Q400 operator. We use reverse when it's useful. Short runway (like less then 2000m) or to get an early exit/avoid back-track to shorten taxi time. We also use reverse for power-backs on ocasion.
But generally speaking, even the disc position is to much braking 9 out of 10 times, if used right after touch-down. The Q400 has no autobreak system, so the wheel-brakes may be used at pilots discretion. Often we don't use them at all. Discing the propellers a couple 100 meters before a high speed turn-off is usually sufficent.

Greets,
T1a
All views expressed under this username are mine as a private person and don't necessarily reflect the views of my employer.
 
CCGPV
Posts: 702
Joined: Tue Jan 16, 2018 5:18 pm

Re: DHC-8 reverse thrust?

Tue Mar 27, 2018 4:50 pm

opticalilyushin wrote:
I work with a Q400 operator in Europe, and the use of reverse is forbidden by the company. The pilots find that the aircraft has good enough braking performance without the use of it. I did once see (or hear) a training captain use it, it was bloody loud!!!


What is their reasoning for the ban? Noise? Maintenance?
I have all day.
 
opticalilyushin
Posts: 490
Joined: Tue Oct 22, 2013 6:35 pm

Re: DHC-8 reverse thrust?

Wed Mar 28, 2018 7:46 am

A good question, i have no idea! Perhaps all of the above, or that it is deemed to not be required. They don't fly to many short runways anyway.
 
estorilm
Posts: 234
Joined: Fri Jan 16, 2009 3:07 am

Re: DHC-8 reverse thrust?

Wed Mar 28, 2018 4:00 pm

I think this has been adequately been answered already as far as the technicalities of how it's performed (ie. reversing pitch) but as for why operators choose not to do it - probably the same as for turbofan operators honestly. Many have come to the conclusion that unless wx / performance mandates it, only idle should be used. Much like turbofans, throwing a prop into beta creates a giant wall of drag and can slow the aircraft down very quickly.

Though it sounds like many operators don't even want that performed... can't be a fuel concern but maybe just wear and tear on prop asm. and bearings, etc? Kinda splitting hairs though - beta operation isn't going to change the TBO on anything anyways.
 
bruh
Posts: 43
Joined: Mon Nov 20, 2017 9:18 pm

Re: DHC-8 reverse thrust?

Wed Mar 28, 2018 9:19 pm

Hi,
I recently talked with a Q400 pilot who works for a major operator of Q400s in europe and he told me that his company strictly advises them to avoid the use of reverse thrust unless it's an emergency situation. One factor that also comes into play is that the reverses lead to a very uncomfortable experience, simply because of the intense deceleration but also due to the fact that the reversers are quite loud.
 
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InnsbruckFlyer
Posts: 59
Joined: Sat Nov 25, 2017 1:35 pm

Re: DHC-8 reverse thrust?

Wed Apr 11, 2018 9:05 am

T1a wrote:
I also work for a European Q400 operator. We use reverse when it's useful. Short runway (like less then 2000m) or to get an early exit/avoid back-track to shorten taxi time. We also use reverse for power-backs on ocasion.
But generally speaking, even the disc position is to much braking 9 out of 10 times, if used right after touch-down. The Q400 has no autobreak system, so the wheel-brakes may be used at pilots discretion. Often we don't use them at all. Discing the propellers a couple 100 meters before a high speed turn-off is usually sufficent.

Greets,
T1a


What do you do at LOWI, where the runway is exactly 2000m?

:)
2018: B738 (LG, UA), B77W (LX), DH8D (LG), E195 (OS)
 
strfyr51
Posts: 2705
Joined: Tue Apr 10, 2012 5:04 pm

Re: DHC-8 reverse thrust?

Wed Apr 11, 2018 2:02 pm

acjbbj wrote:
I've been on Olympic Air's DHC-8 Q400 once, and when we landed during our flight from Athens to Naples, I noticed that the engines were powered up briefly. I am curious to know how the props reverse thrust during landing. Do they change the pitch to push forward? Or what happens with the props? Or does the Q400 not reverse thrust?

The Propellers go into reverse pitch. to help slow the airplane. Staying in reverse pitch could actually back the airplane up.
 
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Acey559
Posts: 1164
Joined: Wed Jan 24, 2007 3:30 pm

Re: DHC-8 reverse thrust?

Fri Apr 20, 2018 4:41 pm

I flew the Q for a US operator and while not prohibited, use of reverse was abnormal, only to be used in extreme cases. Beta range was more than enough to get us stopped and reverse is very tough on the airframe. In 700 hours of flying the Q, I never needed to use reverse.

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