View previous topic :: View next topic |
Author |
Message |
jbalonso777 Member
Joined: 05 Jul 2012 Posts: 1501 Location: Never, never land
|
Posted: Sat Jan 04, 2014 1:33 pm Post subject: Question on propellers? |
|
|
Hello everyone!
I just flew on a JetKonnect ATR 72.
A few months ago, I flew on a Helitours Xian MA60.
Both completely different aircraft types, but with similar propellers.
However, I found quite a significant difference in the start up procedures of the two.
Onboard the Xian, the props start spinning slowly, before finally gaining enough speed and then the whole 'engine' comes on.
http://youtu.be/ZdsSCkDlzCI
However, on the more common ATR, the sound of the engine suggests that they are being switched on, while the propellers start spinning much later, and seems to have gained full speed to start spinning.
http://youtu.be/dVe_56LHcLk
Are there any significant reasons for this?
Thanks in advance! _________________ http://www.youtube.com/c/JishnuBasu777 |
|
Back to top |
|
 |
The_Goat Member

Joined: 03 Mar 2007 Posts: 3260 Location: South of France
|
Posted: Mon Jan 06, 2014 1:52 am Post subject: |
|
|
There are two things, the propeller itself and the turbine engine that drives it.
In the ATR, I believe that the two can be decoupled. So the turbine engine can be kept running while keeping the propeller stationary. This is useful when there is no ground power available or if the APU of the airplane is not functional. The running turbine can provide electrical power to the aircraft and the non-spinning propeller won't cause any inconvenience to ground ops.
What you heard in the ATR was the turbine engine revving up first, followed by the propeller getting coupled to it later. So there is a lack of sync between the engine revving up and the prop spinning.
I don't know if this feature is universal. Maybe it doesn't exist in the Xian, so the prop speed and the engine speed would be perfectly in sync.
Maybe some of the resident techsperts can shed more light? _________________ I don't know which is the more pampered bunch : AI's widebodies (the aunties) or Jet's widebodies (the planes).
-Jasepl |
|
Back to top |
|
 |
ALT STAR Member

Joined: 24 Dec 2009 Posts: 70
|
Posted: Wed Jan 15, 2014 12:26 pm Post subject: |
|
|
Nice trip report. I thoroughly enjoyed it,especially the ATR flight.Takes me back to the good times flying that airplane.
Regarding the prop not spinning while the gas generator is running is a feature on the ATR ,available only on the no 2 engine.
I believe the previous reply has pretty much summed it up but i will add a few more details to it.
They call this feature "Hotel Mode".
Instead of having an additional APU installed, the no 2 engine prop can be disconnected from the gas generator via hydraulic pressure and supply electrical power and bleed air on ground when the aircraft is parked.
There is guarded switch on the overhead panel which can be used to disconnect/reconnect the prop to the shaft as required, provided you have blue hydraulic pressure and prop feathered(iirc..long time since i flew the airplane).
So what you saw was the no 2 engine running with prop brake "on" and later with the prop brake "off" the prop is reconnected to the gas generator unit.
Quote: | Also, there is a part of the flap which comes down...I hope you notice that in the video!
HD: JetKonnect ATR 72-500 take off from Bengaluru |
What you see is not part of the flap but part of the aileron.It is called a balance horn or tab.On the ATR it is on the elevators and rudder as well.Since the ATR has no hydraulically assisted control surfaces(only one hydraulic roll spoiler on each wing i think) these tabs reduce to the amount of force required to move the control surfaces in flight(although on some occasions during gusty winds and engine failures it does require quite a bit of force ).Forces acting on the control surface and horn are opposing so it cancels out some of the effort required to move the main control surface.
Hope that answers your questions. _________________ Flickr photostream
http://www.flickr.com/photos/45883928@N04/ |
|
Back to top |
|
 |
Optimus.Prime Member

Joined: 21 Dec 2009 Posts: 302 Location: VAJJ (No, not Va-Jay-Jay)
|
Posted: Sat Jan 25, 2014 4:38 am Post subject: Re: Question on propellers? |
|
|
jbalonso777 wrote: | Hello everyone!
I just flew on a JetKonnect ATR 72.
A few months ago, I flew on a Helitours Xian MA60.
Both completely different aircraft types, but with similar propellers.
However, I found quite a significant difference in the start up procedures of the two.
Onboard the Xian, the props start spinning slowly, before finally gaining enough speed and then the whole 'engine' comes on.
http://youtu.be/ZdsSCkDlzCI
However, on the more common ATR, the sound of the engine suggests that they are being switched on, while the propellers start spinning much later, and seems to have gained full speed to start spinning.
http://youtu.be/dVe_56LHcLk
Are there any significant reasons for this?
Thanks in advance! |
The Infamous "Hotel" mode rears it's head again! _________________ Why can't Donuts be square? |
|
Back to top |
|
 |
jbalonso777 Member
Joined: 05 Jul 2012 Posts: 1501 Location: Never, never land
|
Posted: Mon Mar 10, 2014 7:06 pm Post subject: |
|
|
Thank you all for your inputs!
All of this makes a lot of sense now  |
|
Back to top |
|
 |
|
|
You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum
|
|