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F27 V Speeds

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Anthony View Drop Down
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    Posted: 15 Sep 2018 at 7:33pm
Hi,

I've looked through the F27 Manual and cannot seem to find any V Speeds listed anywhere?  For example what are the speeds above which landing gear and various degrees of flaps should not be extended?

Regards,

Tony

Regards,

Tony
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ThomasAH View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ThomasAH Quote  Post ReplyReply Direct Link To This Post Posted: 16 Sep 2018 at 11:20am
I think the manual only lists V1 and V2 (in the take-off checklist on page 62).

You can find much more here:
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Anthony View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Anthony Quote  Post ReplyReply Direct Link To This Post Posted: 16 Sep 2018 at 12:53pm
Hi Thomas,

Thanks for that. I would have thought that the Just Flight would have been more comprehensive in this.  What I'm really interested in is knowing the safes speeds to lower gear and flaps on descent and landing.  From the link you provided it appears that gear should be lowered before flaps and only when aircraft is slower than 170 kts.  Flaps 16 degrees below 144 kts and 26 degrees below 110 Kts - does that seem correct?

In the tutorial flight I notice from page 52 that the HPC levers must not be put into Lock Out position until on final approach, but there is no further mention of this in the tutorial when you read the descent, approach and landing section.  At what point should the HPC levers be moved?

Regards,

Tony



Regards,

Tony
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The Vapor Trail View Drop Down
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Post Options Post Options   Thanks (1) Thanks(1)   Quote The Vapor Trail Quote  Post ReplyReply Direct Link To This Post Posted: 20 Sep 2018 at 2:42am
Hi Tony

I have just been leafing through a 1970's fokker manual and that seems roughly correct.

There is no chart of safe flap speeds - just guides for various procedures. But it seems it is safe to start lowering flaps after 144kts (after 130kts in some parts of the manual).

The landing gear has been designed to use as a speedbreak. Put the gear down early (after 170kts), then do your flaps, otherwise you will be flying too fast.

As for the HPC leavers? I have read all kinds of different advice. Some pilots apparently left them in all the way. I pull them out of lock out on climb and put them back in on approach.


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The Vapor Trail View Drop Down
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Post Options Post Options   Thanks (1) Thanks(1)   Quote The Vapor Trail Quote  Post ReplyReply Direct Link To This Post Posted: 20 Sep 2018 at 10:36pm
< ="text/"> p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px 'Helvetica Neue'; color: #000000; -webkit-text-stroke: #000000} p.p2 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px 'Helvetica Neue'; color: #000000; -webkit-text-stroke: #000000; min-height: 12.0px} span.s1 {font-kerning: none}

So after doing some research - the short answer is yes: the HPC levers should be moved as you climb out (blue lights off) and moved back in on approach (blue lights on).


Any time you are going to fly at low speeds or taxiing on the ground the propellors should be in Lock-Out (blue lights on).


The longer answer is this (and perhaps someone can verify this):


The propellers on the Dart engine can rotate between 0° (ground fine - flat against the airflow. Also the start position) to 87° (feathered - almost parallel to the fuselage, in line with the airflow).


When in cruise and flying at high speed it would be disastrous if there was a mechanical failure and the propeller blade rotated toward the 0° end of the range creating drag instead of thrust. For that reason a Pitch Lock is engaged when the HPC is forward of the “Open” position preventing the propeller blades from moving below 32°.


When on the ground or flying at low speed a propeller attempting to spin using 32° pitch or more would create drag on the rotation of the engine, slowing its RPM, if you then increase the throttle in that state  - the air to fuel ratio will be unbalanced and the engine will quickly overheat and burn out. The Lock-Out allows the propeller blades to travel below 32° and prevent drag on the rotation of the engine.


Probably the best explanation of this system, I have found, is in this crash report here:


https://assets.publishing.service.gov.uk/media/5422ef5f40f0b6134200023b/dft_avsafety_pdf_500083.pdf

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Post Options Post Options   Thanks (1) Thanks(1)   Quote The Vapor Trail Quote  Post ReplyReply Direct Link To This Post Posted: 21 Sep 2018 at 9:41pm
As a further note: If you read to the end of that crash report, it seems that during the 1990's it became standard practice with many operators to leave those blue lights on during the entire flight from startup to shutdown.

As the drag problems the cruise locks were designed for are hardly ever encountered at the usual cruise speed of 180IAS and there had been several accidents caused by pilots forgetting to put the HPC into Lock-Out under 140IAS and causing the engine to catch fire and burn out it was deemed safer to leave the engine in Lock-Out for the entire flight.

There is a handy calculator here: http://indoavis.co.id/main/tas.html to determine if you will bust the True Air Speed of 265 kts TAS. Combine that with measuring the temperature at 500hpa on https://earth.nullschool.net/



Notices To Aircrew 15 March 1993:

"HP Cocks MUST BE to lockout for take off and climb, there is no requirement to place the HP Cocks to open in the cruise.The temperature at 20,000 ft would have to be in excess of +20°C to exceed 265 knots TAS.

During descent, the HP Cocks must be moved from lockout to open if the TAS exceeds 265 knots.

Care must be taken when entering the hold or reducing speed after a high speed descent. If the HP Cocks are left at open (particularly in the hold) when the speed has reduced to 140 knots or less, and the throttles are opened, the engines can be destroyed in seconds."
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ThomasAH View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ThomasAH Quote  Post ReplyReply Direct Link To This Post Posted: 22 Sep 2018 at 6:03am
Thank you for all these details!
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