Jetranger startup question

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Theuns v V
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Jetranger startup question

Unread post by Theuns v V » Mon Sep 07, 2020 6:34 pm

I was looking at 206 startup on you tube and noticed that the pilot leaves the starter button depressed fr atleast 20 seconds after it starts up, why so long? wil the engine not be self sustainable if he lets go of the button after the "woof" when the fuel goes in??

T
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Re: Jetranger startup question

Unread post by cdfly » Mon Sep 07, 2020 7:09 pm

Starters on most Turbines remains on to about 49% to 55% ish, and then becomes a Generator.
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Re: Jetranger startup question

Unread post by hugo_visser » Mon Sep 07, 2020 10:23 pm

If I remember correctly, if you have a hot start to have no time delay to vent, not sure, maybe someone with more experience can tell. When starting my un completed conversion the instructor kept his finger on top of mine. That 1.25 hrs cost R 18 000.00 rand doll exchange rate.
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Re: Jetranger startup question

Unread post by Rotor kop » Tue Sep 08, 2020 6:24 am

hugo_visser wrote:
Mon Sep 07, 2020 10:23 pm
If I remember correctly, if you have a hot start to have no time delay to vent, not sure, maybe someone with more experience can tell. When starting my un completed conversion the instructor kept his finger on top of mine. That 1.25 hrs cost R 18 000.00 rand doll exchange rate.
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As Hugo said. I recall my instructor teaching me basically depress starter (throttle closed) until around 15% then open and close throttle (will stop at "indent" which is partially open), keep your finger on starter button and other hand on throttle in case of hot start later. Once around 40-50% ( my memory is failing me now) you can leave starter BUT keep eye on temps etc. If hot start then immediately push starter button and fully close throttle past indent until turbine cools 8-[
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Re: Jetranger startup question

Unread post by Kotze101 » Tue Sep 08, 2020 10:39 am

Is it not 58%?

That number rings a bell somewhere for me.
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Re: Jetranger startup question

Unread post by csparksfly » Tue Sep 08, 2020 2:19 pm

Theuns v V wrote:
Mon Sep 07, 2020 6:34 pm
I was looking at 206 startup on you tube and noticed that the pilot leaves the starter button depressed fr atleast 20 seconds after it starts up, why so long? wil the engine not be self sustainable if he lets go of the button after the "woof" when the fuel goes in??

T
when the "woof" happens the extremely hot gases need to escape though a series of turbine fins, which are not turning much yet. By keeping the starter engaged it keeps them turning and the hot gases can escape through the exhaust. If the gases, which have a temperature of about 800°C does not escape fast enough, it could start melting a couple things - i.e. it becomes a very expensive start. :oops:

To prevent "hot" starts (i.e. hot outside, or engine temp above 150 °C) the start sequence is done without the igniter (i.e. disabled) so as to get the hot air out without igniting any more gases. While "cranking", as soon as the temp falls below ±120°C, the igniter can be enabled (circuit breaker) again and fuel introduced to continue with the start.


Disclaimer - I have not had to do this in a very long while, and I am not an instructor either
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Re: Jetranger startup question

Unread post by Theuns v V » Tue Sep 08, 2020 3:12 pm

very interesting indeed
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Re: Jetranger startup question

Unread post by matt8 » Tue Sep 08, 2020 3:45 pm

Just to add to the above...pushing the starter button is not only about firing the igniters, it draws from the battery to turn the intake compressor (N1) - so yes there's a fire inside to keep it burning but it's only self sustaining (as mentioned above at 58% N1) once there's enough airflow being exhausted to spin the intake to keep drawing sufficient air into the system.
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Re: Jetranger startup question

Unread post by Balloothebear » Tue Sep 08, 2020 3:47 pm

Bat switch - on for start
Collective pitch- full down
Throttle - full closed
Rotors- clear
Starter - Engage ( observe engine starter limitations)
Engine oil pressure- indication of increase
Throttle- open to flight idle between 12 to 15% gas producer RPM with Turbine Outlet Temperature(TOT) at or below 150^c.
A start should not be attempted at N1 speeds below 12%
Verify that rotor is turning by 25% N1
Starter- release at 58% gas producer RPM (N1) Net soos Kotze101 gese het :-)
Engine and transmission oil -check pressure increasing
If the engine has been shut down for more than 15 min, stabilize at idle speed for one minute before increasing power - this allows the battery and starter to cool, and allow for correct thermal expansion.
Gas Producer RPM (N1) Check for 60 to 62% - at 60% is the minimum RPM for proper engine lubrication
Throttle - Open to 70% gas producer RPM -safe operation at N1
Gen switch -on
Collective -full down, friction removed
Rotor RPM (Nr) Set to 100%
As csparksfly has mentioned, the thermal expansion that takes place in the Alison 250 , requires 20-25% N1 for combustion ( the flame pattern is prevented from impinging on the wall of the combustion liner) and cooling, as the hot gasses as they leave the combustion chamber before passing through the turbine section.
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Re: Jetranger startup question

Unread post by cage » Tue Sep 08, 2020 10:26 pm

Starter motors can only power the compressor up to the upper end of the ignition range so somewhere around 12-15% N1.
The 206 is old school so won’t latch the starter like a fadec aircraft or even the R66 with it’s RR300 engine.
The motor is powered to help the engine become self-sustaining and to cool the turbine in case of an aborted start, something that is automatic on newer aircraft.
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Re: Jetranger startup question

Unread post by hugo_visser » Sun Sep 13, 2020 6:52 am

Thank You everybody.
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Re: Jetranger startup question

Unread post by Stephen Robertson » Sat Oct 10, 2020 12:03 am

The "self-sustaining" part is the key here. It differs from one engine to the next. Below are a few examples of aircraft I have flown:

BO105 (and most Allison 250 series that I am aware of) - starter is released at 58% N1, fuel is added between 12% and 15% N1
EC120 - starter is released at 50% N1, fuel is added around the 12% N1 mark but because we start at a given mark on the fuel control, it is almost unnoticed.
AS350 (excluding B3) - starter is released at around 45% N1, fuel is introduced at around 12% N1
BK117 (with Lycoming engines) - starter is released at 40% N1, fuel is introduced at 10% N1
Gazelle - well that's a whole other kettle of fish :lol: :lol:

So through the start procedure, regardless of whether your fuel has been introduced and is burning, keep the starter depressed until you come to self-sustaining speed prescribed in the manual. If you have a TOT spike, close the throttle without delay and continue to hold the starter button. This will ensure that all remaining fuel is burnt off, and that the chamber will continuously be vented until you have vented below 150 degrees celsius. That is your magic number for almost any turbine. One thing to remember too, is that not all helicopters have their starter buttons/switches on the fuel control. For instance, in the BO105 that I flew, it was a switch on the center console that would hold itself up in a "start/igniter" position while the fuel control was in the center of the ceiling panel. I liked this because I would just keep my hand off of it to prevent myself switching it off until I had closed the throttle and vented the engine as stated above. In the EC120 though, the starter switch is slid forward, and is connected to the fuel control. The design does have it's benefits, but I still start her with two hands. My left hand modulates the throttle while my right hand holds the switch up. It looks odd, but I have found that when I needed to roll off the throttle once, it worked to my advantage.

Hope it helps,

Steve
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