"Cracking" the throttle

[gizmocat]

Could someone explain the process of "Cracking" the throttle to introduce fuel when starting a B206 ? and what part the idle-stop plays in the operation ?

Thanks.

[Woolf]

Any small to medium sized hammer will do (rubber mallets usually don't produce the desired effect). Just aim for the middle section of the Throttle and give it a good whack. If done correctly a small crack should appear, splitting the Throttle lenghwise by at least an inch. Take a small can of petrol and slowly infuse the Throttle with ordinary petrol (JET-A1 would be too difficult to set alight). The only other required ingredient is a box of matches and voila - sit back and enjoy .........

The above process will also stop the pilot from idling - hence idle stop ......


Sorry, I haven't a clue - You might have guessed, I have not flown a 206 before. If I do I'll let you know!

[Grainger]

Well, "cracking" is just a figure of speech for opening the throttle.

The crucial thing is that you need a flow of air before introducing and igniting fuel, otherwise you'll just burn the engine. So you crank the starter with the throttle closed until it reaches 12-15% N1. This establishes the necessary flow of air and you can then introduce fuel by opening ("cracking") the throttle.

The idle stop represents the minimum amount of fuel flow necessary for self-sustaining operation once the rpm gets up to 58%. You don't want to introduce any more than this until it gets up to speed, or again you'll cook the engine.

Until it reaches 58% you gotta keep cranking the starter to keep that flow of vital cooling air going, so stick your thumb on that button, and . . . whatever happens, don't let go !!!

[Vfrpilotpb]

AS in "Cracking Open a bottle" it is just a turn of crazy English language,

Like "Catch a Bus" you would need very big hands,

Grainger,

That start on the 206, was the only thing that ever put the fear of God into me when I was being taught, pressed that button till it left a mark in ma finger

Vfr

[gizmocat]

Thanks chaps, that's exactly what I was after. :ok: I thought that you quickly "cracked" it to well past the stop, then back to the stop after ignition. Good job I've never had to do it for real. :eek:

[B Sousa]

For the very basics. On the B206 there are two different fuel controls. One is Bendix, the other Seko? Procedures for starting are day and night. Bendix you run to 15% then "crack" it to the idle stop, all the time making sure that the Temp does not go through the roof. The other is a "Modulated" start in that when it gets to about 12-15% you "crack" barely and introduce fuel. You continue to slowly add throttle until at the Idle stop, all the time monitoring the temp. If you do to a Seko as is done with a Bendix you will see the Temp guage rap itself around a couple times and your tailboom will probably melt itself off.
Same thing in the B206L series. Modulated starts are the norm......
Now someone can come in and be so very technical and clean up my post...

[Blackhawk9]

The two types of FCU on the 206 Jetranger are the Bendix which is fitted to about 95% of 206's and the other is the CECO (Chandler Evans fuel COntrol) most civil 206's run the Bendix and some old 206's and Military OH 58's the CECO. If you want to watch an interesting scenario watch pilots start 206(Bendix), 206 (CECO), and 206L one after the other in a mixed fleet, someone always gets it wrong and i've seen a couple of Allisons cooked, something for young pilots to watch for.

[407 Driver]

Well done Grainger, had a good chuckle over your post !

Bert, If a CECO is set up correctly, there should be very little start differences over the Bendix. Unfortunately, you may find some "agressive" starting CECO's in your travels :eek:

Of course a fast - hot start is preferred....Remember that Allison article we talked of a year or two back, a proper C20 start may reach temps of 825C and have a time of 25 seconds from ignition to 58% N1. (Allison CSL 1176, or CSL 1192). That Old thread in starts is located Here (http://www.pprune.com/forums/showthread.php?s=&threadid=137877&highlight=CSL)

Personally, I always preferred the CECO system, as it allows the pilot a bit more control over the start.

When picking up a strange 206, (I worked in a fleet of 50 once)one should always look to see what FCU system is installed, (in addition to the obvious detailed D.I.) plus conduct the first CECO start as you would any L1-2-3-4...just in case it is set up a bit "agressive".

[The Rotordog]

As others have noted, there are two different FCU's that may be installed in 206A's and B's. There is a misperception that if you have a CECO in a B-model then you have to do a modulated start. However, if the CECO is tuned well, you *should* be able to go directly to the idle-stop during the start. But the CECO is much more sensitive to OAT and the quality of the start will vary. Also, the start quality varies as the FCU accumulates time. The CECO does provide *some* amount of modulation, but it is not the same as the amount in the 206L-series, which use a fully modulated start.

Grainger misspoke in one sense. Going to the idle-stop gives you the *maximum* amount of fuel, not the minimum. In fact, you can open the "throttle" all the way to full if you like, and the FCU will only deliver "start fuel" until the N1 gets up near idle, at which point you'll get more. I like to watch the look on the faces of so-called experienced 206 pilots when I (for fun) open the throttle completely to full during the start sequence on a Bendix or alternatively "pump" it as if it were an accellerator on an old car with a carburetor and accellerator pump.

But I digress. What many pilots use as "standard" procedure with both Bendix and CECO's is to just open the throttle enough to get a light-off (i.e. "cracking" it). In this way, both a Bendix and CECO-equipped B-model start the same way. Once you're assured that the TOT is under control, then you go to the idle-stop just to keep the engine from inadvertently shutting itself down.

"Cracking" the throttle is one of those vague aviation terms which everyone seems to use but nobody can really define.

[diethelm]

Any healthy series II engine (C20, C20B, C20J, C20R, C20R+, C20R1, C20R2 and the lonely C20W) should be able to start without modulating the throttle. Hot starts in series II engines are typically from faulty accessories, starter generators or battery conditions. Occasionally in certain circumstances R's and R+'s will require extra attention to avoid a hot start or hung start. In either case, hot starts are painfully expensive and focusing on start ups is financially appropriate.

Non FADEC series III engines such as C30's and the variants are prone to hot starts absent modulation even in the best of situations. In addition, on some models, a fuel check valve helps. Series III engines with FADEC do not have the same problem.

The main reason Bendix is more popular than CECO is simply money. CECO is a lot more expensive to overhaul.

[Giovanni Cento Nove]

Rotordog gets the cigar!!!!

Although technically a 206A would have an Allison C-18 in it and CECO (AFAIK) was never fitted to this engine.

CECO MC40 units are pretty rare these days and have a higher TBO over the Bendix. Problem is they rarely make it and cost a fortune to overhaul if you can find someone who can do it. In service the Bendix will pass small rocks through it figuritively speaking as compared to the CECO. Contamination was common in a CECO and it even had an extra HP filter fitted to it compared to the Bendix and it would seem that even wear in the fuel pump could contaminate it, we're talking 5 microns here, less than smoke particles.

The CECO is hydromechanical and the Bendix is mainly pneumatic. The CECO had the potential to be better as a governor but it was "de-tuned" and was all over the place when installed on the H500C. It came to the point in the early days in animal capture in NZ that guys would not fly CECO equipped aircraft. Self preservation and personal preference etc. The fix was to ring an Aussie operator and ask "Hey mate want to do a straight swap?" Suckered them every time - I know who got the better deal. For some reason the Aussies liked the CECO for it's modulated start and the Aussie Kiowa had it so there was some support for it.

CECO now appears to be part of Goodrich. They also make the HMU and ECU for the Allison C40 & 47 and I think ECU for the Arrius 2 where it is used. Brings back memories of the FADEC logic in the 407. Lets not go there.

BTW - never really understood how a "muscles valve" worked anyway.

diethelm. "Modulating" the start on a Bendix equipped C18, 20, 20B, 20J, 20F, 20W etc. probably just makes you feel better, see Rotordogs post.

[gizmocat]

Thanks again chaps, you've provided invaluable information... as always.

[Gomer Pylot]

In a B model, it really doesn't matter which fuel control is installed. If it goes hot when you go to the idle stop, it needs to be written up. Maintenance can adjust it, and it doesn't take that long. The only difference between the two is that with the CECO you can roll the throttle back just a little if it's looking iffy, while with the Bendix if you back it off it kills everything. There is no reason to live with hot starting engines.

[offshoreigor]

Geez..

I kinda liked the CEKO. You rolled it up on the horn, then hit the Starter and modulated a nice Hot (650C), quick start and bobs yer flippin uncle Mr. Scrooge!

Call me old fashioned but the were much more reliable than the BENDIX.

Cheers,

:ok: OffshoreIgor :ok:

[Pullin Pitch]

Assuming tht your start cart or battery could provide enough power, what would happen (if anything) if you cracked the throttle at say... 17%N1?

Cheers...

[Phoinix]

I did that, ok, my instructor wanted me to do that, came to N1 17% on a battery cart, well, it started... nothing else. All went pretty smooth, no TOT peaks. As i was instructed, a low N1 is the dangerous area during starting, not a high one.

We have bendix FCU.

So if i "crack" the throttle a little over idle stop (just to be sure it's over the idle stop), there will be no higher TOT? Our instructors want us to keep the idle stop button in during starting, so if anything goes wrong we won't forget to press it and kill the engine.
Once i let go the throttle and the idle stop was not fully out... and the instructor apperently checked... next thing was the engine out horn.

[diethelm]

Giovanni:

Read the post, I never suggested modulating the start on a Series II engine.

[Gomer Pylot]

As I recall from my days flying a 206, there is no danger in waiting for a higher N1 before introducing fuel - in fact, higher is better, but you'll seldom get that much.

To start a B model, I rolled directly to idle, then pressed the idle release with my thumb, trying not to move the throttle. Having the throttle a little above the stop shouldn't be a big problem. After the start, roll on more throttle to make sure you're above idle. It doesn't take many flameouts to learn this. If you don't have the idle stop depressed, it's really, really easy to have the throttle pressed hard against the stop, and pressing the release may have no effect, because of this. Just don't let go of everything until you're certain that you're above idle with the throttle.

[The Rotordog]

Many pilots experience anxiety or nervousness before starting a turbine engine. We've heard so many stories about how easy it is to torch one. So we barely squeak the "throttle" open, just enough to get a light-off, watching the TOT gauge intently, only to have the engine flame-out when our death-grip on the FC lever ("throttle") relaxes for a moment.

So unnecessary...in the RR A250 C-20 series that is.

Gomer Pylot wrote:To start a B model, I rolled directly to idle, then pressed the idle release with my thumb, trying not to move the throttle. Having the throttle a little above the stop shouldn't be a big problem. It isn't. In fact, no matter how far you open the throttle, the fuel control can *only* deliver start fuel. Whatever you get at "cracked" is what you're going to get at "Full." So go right to "full" if you want! It won't be any hotter. But just be sure to roll it back to "Idle" before the N1 gets up to 60% or that baby is really going to take off!

That "trick" won't work in a C-28 or C-30, or any other engine with a modulated start.

The scariest thing for me during a turbine transition is when the student hears the light-off and releases the starter button as he would with a piston engine. Oh nooooooooo! One guy did it to me after he'd made nearly a dozen starts. Complacency, man, I'll tell ya it's a killer.

[Gomer Pylot]

I'll bet you got really, really busy really, really quickly. For all the good it did you, huh?

[Aesir]

I know the feeling, happened to me once while instructing in 206. The guy had about 30 hrs in turbine and I would say that in every single flight lesson I told him to stay on the starter ´till 58%Ng.

Well this time he let go, but at about 30%. Seems she was already under self sustained start/run by then because the temp didn´t really seem to increase any for the fraction of the second it took me to hit the start button. I always keep my right hand on the collective, with my thumb resting on the collective switch panel (can you say that for B206, not that many switches there!) when instructing.

Sure was scary, but what impressed me was that there was no apparent temp rise.

Bendix, gotta love it : )

[Phoinix]

When you had that finger off the starter button, and the TOT didn't rise that much, what was the air temperature?

On a normal start, say air temp. 30°C, i've seen that needle coming close to 820, very close. I had already started the 10 sec countdown, but then it all came to normal. I have a bad feeling about that finger off on a hot day.

[skitzs]

hey all, rotor Dog is right, relax, crack it a little way past the stop pull it back then depress the stop, all before its passing through 500deg or so.
Regards to letting go the starter on a 40 degree day, cant say i notice any difference, always other variables, think its been over a year or so sinse the last and then 2 in 3 days! i know some instructors who say "keep finger over the idle stop incase" B***** hold it down, do a dry run and snap the throttle against the stop and see how hard it is to press it, ALL over by then!! i think this is the most important bit to me, :ok:

[Aesir]

"Phoinix" It was a cold day. -10° c so I figured that was why I didn´t see significant change in TOT

[The Rotordog]

Gomer Pylot:I'll bet you got really, really busy really, really quickly. For all the good it did you, huh?Who, me? Really, really busy? Nope. If you know how your ship starts, and if it's been starting consistently, then there is nothing to it. In a 206B, I merely open the throttle to...wherever. The engine lights off normally. As the start progresses, I just make sure that the throttle is back to the stop. No drama at all.

As far as releasing the starter button early...I know that the book says to hold the starter to 58%, but I also know from experimentation that a C-20B is self-sustaining from about 45% N1 up (depending). Releasing the button early (like between 20 and 30%) is not disastrous, and the TOT does not spike upward like a fuel control gone bad (although you do have to be quick to get the button back down). That compressor puts out quite a lot of cooling air. In fact, a C-30 compressor is so powerful that if you wait until too high an N1 to introduce fuel you might not even get it to light off.

Pilots do get anxious during a turbine start. But if you have your procedures down pat and you don't have your head up your arse, it's really no big deal. (On the other hand, if student starts a no-flywheel piston-engine ship like an Enstrom with the throttle open a little too much...watch out!)

[Axle]

Can anyone tell me how much modulation on a Bendix is available on start up.

On a 206 B2 start with a newly tuned Bendix, I cracked the throttle to idle detent and the temp quickly raced into the high 800's. This has never happened on this machine before. Throttle had to be wound back until flame-out to reduce TOT.

The question is: Is there any modulation available while closing the throttle, or is flaming out the engine the only way to reduce TOT?

Any help appreciated.

Ax

[rotormatic]

There is no modulation available for the Bendix system installed on 250-C20 series engines. The CECO systems used on 206BII ships had this feature.

With the Bendix system, if it is going hot, all you can do is cut the throttle, and then either charge the battery, hook up an APU, or adjust the fuel control.

The Bendix fuel control has two adjustments for the start cycle on a C20. A derichment adjustment (effects temps between 0 and 30 percent N1) and the tweeker (adjusts entire start cycle).

If you are going hot at the beginning of the start cycle, you need to adjust the derichment down.

If you are stagnating around 40 to 50 percent N1, you need to go up one click on the tweeker, and turn down the start derichment.

Bendix did upgrade their systems on the 250-C28 and 250-C-30 series engines to include modulation during start cycles.

If you can get a 206BII flight manual, there will be two start procedures available for the options (Bendix vs. CECO).

[Axle]

Thanks for your help. We figured as much (no modulation available), just wanted to get a second opinion.

[overpitched]

I would say it is much easier to pick a delayed start on a bendix. 15% n1 crack the throttle count 1000 2000 3000 then crap yourself and close the throttle if it hasn't lit off. Where as on a c30 modulated start you tend to keep opening the throttle a little bit more and a little bit more until whooomp then you crap yourself and close the throttle.

[Trevor KC]

In the same vein, what is the start procedure for a MD Explorer? I understand this has FADEC? could someone explain the advantages/disadvantages of this system.

Thanks

[Thud_and_Blunder]

Start sequence on an Explorer?

From memory:

- Walk (never run - it frightens the bobbies) to aircraft, open door, switch battery master on.

- Put "cooker switch" for required engine to "IDLE"

- Climb in/ strap-in while watching the FADEC do its thing.

- Put second engine's cooker switch to "IDLE" - watch the IIDS as FADEC does it all.

- Do all the other role equipment checks, wait for second bobby to join you on board, switches to "FLIGHT" and you're ready.

Best engine start system I've ever used - beats the Arrius 135 with its weird FADEC switches any day.

[Big_Johnno]

Are there any videos available for us novices to watch the correct start procedure for a turbine engine (B206). If so can someone please post a link to it. Sounds like to me thats why they invented FADEC to stop this from happening and make the starting a turbine fully automated. Might save on the cost of a cooked engine.
John

[The Nr Fairy]

Big Johnno:

I'm not aware of any video. Starting a 206 isn't rocket science.

If you're worried about cooking an engine, then I'd recommend two things:

1. Get a decent conversion course with a reputable instructor, express your concerns, get a very thorough brief he'll watch you on your first few starts anyhow.

2. Go through lots of dry runs / touch drills in the seat, practising different scenarios and what you'd do in each case.

And always run through what you're planning to do before every start - things happen quite predictably in most cases and it's a question of being prepared for the abnormal.

[paco]

As the man says, it isn't rocket science, but it can be intimidating when it's your first turbine. I can offer this:

"The best position to leave the blades in is actually around 30° from the longitudinal axis. You have a lot to look at when you start the engine, and one of the checks is to ensure that the blades are turning by 25% gas producer RPM. This actually happens at around the time of the first TOT peak, by which time, if the blades are set as described, they should be moving into your peripheral vision and you don’t need to take your eyes away from the TOT gauge. If they were at 90°, you wouldn’t see them until the gas producer was well over 25%, without taking your eyes away from the panel. If you put the blades fore-and-aft, there is a slight risk of exhaust gases scorching the underside of a blade, and you wouldn’t be really sure that you had untied the blades anyway."

Although the Bendix doesn't allow modulation, you can get a cooler start by watching the fuel pressure and stop opening the throttle when you see the needle flicker. Be prepared to wait a second or so for light off.

With regard to N1 RPM, don't wait until the engine rotation peaks, because you will be wasting battery power that will be needed later. The Allison book says you can open the throttle at around 13%, provided the engine is accelerating. However, you still need to be careful of a weak battery, which you can get an indication of by listening to how the igniter snaps. Better still, use external power.

One Most Important routine to get used to - if you think you are going to have a hot start, close the throttle first. Don't take your finger off the starter until you are sure the TOT will not go any higher

Phil

[The Nr Fairy]

I forgot one thing.

Remember BITT - Brake off, Igniters In, Tiedowns off / Throttle closed - or some other regular form of check which makes sure that BEFORE you finally commit to pressing the tit, everything is ready to go.

No I didn't, I forgot two things.

Make sure you don't hold the throttle closed hard against the idle stop - you won't be able to press the button and close the throttle if you do.