Hot starts with Bill's mods

[expat 4]

Bill's mods make the B200 a different experience - terrific. What is not so good is I seem to now get a hot start most of the time and destroying lots of expensive PT-6's is burning a hole in my wallet!  It seems it is always starting the second engine regardless of whether you start the left or right engine first.  I some time ago learned (with the Aeroworx King Air) to be patient and wait for the starter RPM to reach a full 12.0% rpm before adding fuel.  But now though the first engine ITT doesn't overheat, the second start does and you get wonderful smoke, flames and a real barbecue. Gives "hot section" a whole new meaning. 

PT-6 experts out there - any tips? I seem to recall a procedure with Kinger's that when staring the second engine you first switch off the starter motor for the now running first engine, switch on the generator for the running engine briefly but then switch it off (for some reason re the electrical buss I don't clearly remember) to start the second engine. Otherwise, I am following the same procedure but always getting a good and a bad/hot start. 

Thanks in advance for your replies. 

[whamil77 183]

The hot starts come as a result of insufficient battery power available to accelerate the engine through the start cycle.  The battery is partially depleted from the first start and must be recharged prior to the second start.  Per the checklist, please ensure the generator load on the first engine started has decreased to below 50% before attempting to start the second engine.  You should be good to go.  

There were changes to P3Dv4.4 that affected engine starting in all of my turboprop mods.  Just in case you didn't get it, I have PM'd you the engine update for the B200 in P3Dv4.4. 

Regards,

Bill

[Victory103 2]

expat,

Sadly as you know MS didn't really do well modelling the PT6 or any turboprop engine for that matter. The 12% is actually the minimum to wait before introducing fuel, we would generally wait on those hot days well into the 20% range, of course this is on a GPU and not the battery. I doubt modeled as well, but downwind starts are also not going to help when trying to avoid hot starts. Your procedure is correct for an un-modded B200 and the high loads on the starter/gen, switching it to avoid the spike in load after the starter is engaged. I'll take a look at Bill's mod in P3Dv4.4, just have not had time lately to continue my beta tests on another developer's B350.

[expat 4]

Quote

 Just in case you didn't get it, I have PM'd you the engine update for the B200 in P3Dv4.4. 

Yes indeed, many thanks Bill. As these only work for P3Dv4.4 and above and I still need to summon the courage to upgrade (to 4.5) in the meantime I tried the B200 this morning with the above advice. Watching the distributor load gauge needle drop very slowly after starting engine #1, I went and made a cup of coffee, had a piece of pie, came back and it was just falling below the 50% mark at least 5 minutes later (maybe this is what the mod fixes?). Hit the starter and no hot start on the second engine. Really amazing BIll how you - a customer - run rings around the manufacturer/ developers - and can model this realism.  It's these little things that give you that immersion.

Now you and Victory can please help me understand better the generator sequencing. Hit the start switches with Gen already on or off? After engine 1 starts, the manual says "recycle" the Gen.  So switch off and then on again to recharge the battery until distrib. load is below 50%? It's really what to do with the started engine #1 Gen after it starts I'm not sure about. 

Thanks!

 

[whamil77 183]

It absolutely shouldn't take that long.  I don't know what may be going on but I just started mine and it took about 15 seconds to get the amperage down to 50% with the running engine at 70%.

Of course, ensure that all other loads are off (radios, lights other than the beacon, etc..).  But I can't imagine what would take so long.  Nothing in my coding does that to my knowledge. 

As for the sequencing...it goes like this.

1. Start the first engine with the battery.  The battery will then be too depleted to start the second engine.

2. Set the condition lever on the running engine to HIGH IDLE (about 70%).

3. Turn the generator on on the running engine so it can begin to recharge the depleted battery.  The battery is recharged enough (though not fully) to start the second engine with the operating generator's help when the generator has decreased to 50% output.  The amperage decreases as the battery is charged because the potential (voltage) in the battery begins to increase as it is charged therefore making the potential difference (difference in battery voltage and generator voltage) decrease.  If the battery were to reach 28 volts it would accept no charge at all.  It can't because it's a 24 volt battery, but you get the picture.  

4. This step has changed back and forth over the years and varies from manufacturer to manufacturer.  The peak amperage is drawn by an electric device, in this case a starter/generator, when it is first engaged then quickly decreases.  For that reason the current limiter for the operating generator (essentially a fuse) is most vulnerable when the second starter is initially selected.  Depending on the ruggedness of the current limiter some procedures have you just leave the operating generator running while the second start is initiated and some have you secure the operating generator prior to the second start so as not to blow the current limiter (fuse).  FSX/P3D does not model this current peak therefore it really doesn't matter in the sim. 

The procedure for the B200 tells you to turn off the operating generator until the engine being started reaches 12%. Then the operating generator can be reengaged.  A battery is a storage device but it is also electricity's version of a shock absorber.  In this case, the battery accepted the "shock" of the initial selection of the second starter.  By the time the second engine reaches 12% that shock has subsided and the generator can then be reengaged without danger of blowing the current limiter.  Again, FSX/P3D doesn't model the current peak so simply leaving the operating generator running will also work in the sim. 

Hope this answers some of your questions.

Regards,

Bill

[expat 4]

Crystal clearly expressed procedures. Also very interesting and fun part of flying/simming. This should be a sticky somewhere. Saving it as a reference in a text.file for my many PT-6 aircraft. Many thanks for taking the time Bill. 

[stans 702]

Bill, that is an excellent guide to starting a turbine engine.   Thank you for explaining not only the how-to, but the reason why generators are often turned off as a part of starting the second engine.

[norman_99 209]

Hi Bill, would you mind sending me the update for P3Dv4.4 too please. At the moment my starts hang at about 15-20% unless I disengage the starter, then they continue normally.

Many Thanks.