C-208B start temp

[andy_mtl]

I fly a C208B for a skydive centre and we noticed this year a raise on start temperatures which makes us wonder if we should update to maybe the 300A starter generator.

The current Gen we have is a 200SGL119Q-2

On a 28 degrees Celsius day at 200asl we are getting
Battery start:760-780 degrees on start and the battery is 2 weeks old
GPU start:725 740 and it is a 28 volts startpack.
We used to get last year averaging temps of 660-680 on a hot day.

Any inputs? Would a new generator help? I have a friend that suggested the 300 A as it is a stronger motor but would it help for a colder start?

Any info is greatly appreciated.


Andy

[Boreas]

Is 760-780 really an issue?

You can climb-out at the lower end of that
range, so is it all that bad for an engine
start?

How many hours did it fly in the last year?
100deg increase does seem like a lot.

I would ask if its running hot in cruise as
well but I guess you don't do much of that.

[andy_mtl]

It flyes am average of 450-500 h per season.

In climb we limit at 740 not 765.

The temp isn't hot per say, but as you stayed is the increase from last year that worries us a bit.
The engine is about 1600 since new

Andy

[longjon]

why would a 300 A S/G be better than a 200 A.? The determination of start temp is directly related to the speed of your Ng when introducing Wf. If your battery is good and you get your 12, 14 or 16% or whatever the book calls for then it's not the starter or battery but cold section problem or a hot section problem, read the troubleshooting section of the P&WC Maint Manual as there is a very good chart on exactly this

[andy_mtl]

Again, that was suggested to me by a friend with 1200 h on a caravan .

What we notice is the spool up time between 25 to 40 on the ng is very long.
He told me with the stronger motor on the 300A it should be solved.

I just the pilot not the mechanic

Andy

[longjon]

Or replace the original S/G if its the problem. You are describing 2 problems. the long spool up time before introducing fuel and 2nd the hotter start after reaching desired start Ng. Is the S/G dragging and slowing the spool up? What if you introduce fuel and the S/G doesn't allow the Ng to spool up and you cook it?
Also it's running hotter than last year so another problem not related to starting. If your Wf and Ng are increased to maintain the same Tq then its a cold section problem, if your Ng has not increased and your Wf is the same but the T5 is up its a hot section problem.
I'd be calling the Engineer doing the maintenance and get it solved.

[andy_mtl]

Ok thank you for that.

We are Sked a maintenance this week and we ll see what he says too.
Appreciate it

[GA MX Trainer Dude]

Andy mtl


I don't have a lot of time on the 208 but I do have 40 years on PT6 engines. All of the installations that I have seen include a "Field Disconnect Relay" - or something similar but called a different name - that is installed in the "Generator" Field circuit.

The purpose of the disconnect relay is to prevent the starter generator "Generating" during an engine start.

When you activate the start sequence the field disconnect relay is usually powered "Open" - thus preventing electrical flow through the generator field and preventing the generation of electricity while starting.

If the field disconnect relay doesn't open then some of the power from the starter motor is being used to generate electricity in the generator side. This results in a normal spool-up at the start - but from about 25% and above causes a longer start time and higher temperatures during the start due to the reduced power available for accelerating the engine.

Have your maintenance guys check the system to see if this is your issue.

Regards,

Mx

[GyvAir]

I agree with longjon.. if the 200 amp s/g was adequate last year, it should be adequate this year too, so, you have a different problem. (Would it make any difference to spool up times having a 300 amp v.s. 200 amp rated starter-generator anyway? The rating is referring to the output. Is the starter amperage draw proportional?)
Could it be something as simple as a deteriorated cable or connection?

[TeePeeCreeper]

Andy,

I agree with you that the ITT your seeing on start up seems a bit high...
I am accustomed to seeing 685-700 on a cold start at sea level on +38 degree mornings when I worked in the sandbox.
Are you getting the 80-110 90-120 PPH (depending on what kind of nozzles) on your fuel flow gauge?

If I were in your shoes I wouldn't loose any sleep on it just yet...

All the best,
TPC

[Chuck Finley]

Seen the same issue on a different AC that was powered by a PT-6 after a battery swap. They cheaped out on the battery and after about a week, the starts were getting hotter and hotter ( don't remember numbers ). They changed the battery again with a "better one" and the issue was fixed.

[andy_mtl]

Teepee

On first start of the day I get 680 690

I normally fuel for 3 loads then shut down and like today at +30 I did 5 starts and all between 720-740 with the gpu I wouldn't dare doing it with the battery.
I paid close attention to the fuel flow:
As soon as I move the fuel lever it jumps to 100, then 140 and drops down to 110 as ng raises past 40, then settles at 130 pph.
With the gpu we introduce fuel at 18 ng a bit higher than as per POH but it was suggested by flight safety to my boss when he did his training , for starts that are done on a hot engine.


.,
The new battery we got isn't a cheap one.
We are all a bit overly concerned with hot starts and the last place one wants to cheap on is the battery in my opinion.

Cheers guys

[Boreas]

If the field disconnect relay doesn't open then some of the power from the starter motor is being used to generate electricity in the generator side. This results in a normal spool-up at the start - but from about 25% and above causes a longer start time and higher temperatures during the start due to the reduced power available for accelerating the engine.

Interesting, MX.

Would you get a Gen Amps readout if this
was the case? If so, you could easily
confirm the situation.

[GA MX Trainer Dude]

Boreas

Would you get a Gen Amps readout if this
was the case? If so, you could easily
confirm the situation.

Not that I have ever seen.

My understanding of the effect is that the generator windings act as a "Dynamic Brake" that works against the starter effort. In the same way for example as the gear motor dynamic brake action of the King Air electric electric motor when it is shut off. The electromotive braking action stops the motor almost immediately.

With twin engine aircraft we would just change it - or if away from base swap it with the other side to check. On most aircraft it isn't a big job to change.
I have seen battery, starter generators , and generator control units changed trying to "Shotgun" troubleshoot the problem.

If the field disconnect relay fails in the open position - rather than the closed position (Usual) the generator will not come on line. This is also why the generator won't come on line in the King Air when you forget to switch off the starter!! I always have to have a checklist item to remember to unlatch the starter switches on the King Air as so many other aircraft have the spring loaded start switches rather than the latching type. Like I stated in my original post I don't have much time on the 208. Have a look in the wiring diagrams for the generator system and it will show if you have the relay - so "easy peasy" to check.

Hope this helps.

Mx



Edit to add:

Beech King Air 200 Mx Training Manual excerpt.

Generator Control for BB-88 and after, BT-1 and after, BL-1 and after,
and BN-1 and after
The generator control switches are located under the Master Switch gang
bar on the pilots lower left sub-panel to provide the crew with control over
the starter-generators.
Whenever the generator control switch is in the OFF position, battery
voltage is routed from the generator control circuit breaker through the
generator control switch and the normally closed contacts of the field
disconnect relay to the field grounding relay which shorts the shunt field of
the respective starter-generator to the airframe structure. Regulator power is
interrupted, and, consequently, generator operation is disabled whenever
the generator control switch is selected OFF or when the respective engine
is being started.
During engine start, the field disconnect relay is energized, thus interrupting
the coil circuit of the field grounding relay.


Mx

[username here]

Nobody has mentioned the possibility of a bleed air leak causing high temps. Are your cruise trending temps higher than last year as well?
I would blank off the engine bleed air port first and see if that helps.

[andy_mtl]

Unfortunately per every 100 hours I fly I do maybe 1 h cross crown try for maintenance so not really much cruise experience.
Tho I fly with shorts and I have the hair always set to fwd cabin not defrost so if I had a leak I would feel it I think.

Andy

[username here]

No you would not feel a leak. It wouldn't take much to cause a rise in ITT due to a bleed air leak. Could be the bleed air gasket at the engine case or possibly a leak in the bleed air flex line. Best bet is to blank off the bleed air and see if it makes a difference. Easy enouh for your AME to do.

[Heliian]

You are a commercial operator. Snag it in the log and have an engineer look at it, could be a multitude of things. But you wouldn't want to be inconvenienced with silly things like actual maintenance. Maybe it'll make the next hundred? Maybe you'll torch the engine? Raise the bar for once instead of carrying on the tradition of clapped out p.o.s. meat bombers.

[andy_mtl]

Easy now.
As previously stated this aircraft is going I this week , and the beginning of the thread was a simple Question on weather or not a 300a S/G would develop better starts.
Now we all started talking about other possibilities and it's actually quite good to know all the different causes that could generate a hotter start than normal. Most of us are just pilots so it's good to have an engineer point of view.
As per he plane I fly, it's the newest c208b doing paradrop in Canada.
Fully functioning autopilot, tcas, weather radar, have a ETM that I download weekly and send in to be analyzed .
This isn't naves surely a snag, the aircraft didn't go from 650 degree start to 900 overnight.

Andy

[YYCAME]

Always good to make sure your ITT is properly calibrated before chasing stuff like this so you know its not just an indication problem, though it sounds like your normal run temps havn't changed so that probably isn't significant in this case. While as a pilot you won't be boroscoping it is always a good idea to use a flashlight down the inlet to check for significant blade damage on the impeller from FOD. I think if you had a bleed leak you would probably see it reflected a bit in an increased fuel burn and ITT overall and not just on start though probably would be hard to track unless you were very familiar with the normal numbers for that particular engine. While those other suggestion are probably more likely causes I would ask the very basic question of whether the GPU is actually providing proper power, because maybe your actually doing battery starts due to some sort of blown current limiter or bad external power relay.