Temperature and Engine start!

[Old Fella]

Ground Idle - Ground Start Throttle positions

Hi Andrew

I am a bit confused. (Some might ask what's new). Are you saying that the L382G you operate has both a Ground Idle and a Ground Start position on the throttle quadrant? Ground Idle is the normal throttle position for start on the models I operated on. It gave/gives minimum blade angle to minimize starter load and to assist in smooth acceleration to ground idle RPM after starter cut-out. Have never seen a Ground Start position labelled on a C130. If you have it, is it slightly behind the Ground Idle detent?

[JammedStab]

"Ground Idle" - (Approximately 10 degrees coordinator travel) is a detent position. This is the ground operating position at which blade angle is set for minimum thrust.
"Ground Start" - (Approximately 18 degrees coordinator travel) is a detent position. This position sets blade angle for engine starting.

Maybe it is G model stuff only. Less blade angle drag. Probably would work with the older models as well(at leat with 54H60 props) but no detent for positioning the throttle, only guesswork.

[A Squared]

Yep, both are marked on the quadrant. Like Jammed Stab pointed out, the Ground Start position is just ahead of the Ground Idle position.

For what it's worth, on the L382 the "G" designation only has to do with the fuselage length not the production series. An L382G is one with 2 fuselage plugs (180 inch total stretch) either when built or as a retrofit. Also called the L100-30 A short fuselage plane would be a L382B (L100) and one with a single 100 inch stretch would be an L382E or F (L100-20)

All our planes are L382G's but some have GTCs and some have APUs which if I'm not mistaken, makes then equivalent to the C-130E and C-130H respectively.

[deefer dog]

In Europe most airports give you the OAT with the start clearance. In the last 39 years I have NEVER heard the dew point mentioned, except on ATIS.

All engines have min and max OAT's for start. Perhaps it is related to that?

[M Invernoz]

The short answer is no. By the time you start you should have copied the ATIS long ago for whatever you needed those info. Rwy, wind, temp etc.

Yes, You are right. But here at Mar del Plata Airport we don´t have ATIS Information. The MET office give us the METAR and we tell to every aircraft incoming or outgoing the information.

So the critical point of the OAT is below 10°C and/or with a narrow temp/dew pt spread?? No matter if the aircraft has FADEC or not, or autostart or not??

[M Invernoz]

i'm flying around in europe and ATC has never given me the temperature or an update on the temperature before startup. Of course you need to stay inside your environmental envelope and temperature is needed for various performance calculations, use of engine anti ice as pointed out be zerozero, etc. for engine start up itself i am more concerned about the wind direction since a strong tailwind might lead to a start malfunction.

Some kind of flameout? or a hot start, right?

[M Invernoz]

Well, on some non-FADEC engines (PW123 for example) a high OAT in combination with a hot engine might lead to considering switching the fuel levers to on at a slightly higher compressor speed to keep the exhaust gas temperatures a bit lower - but this is no exact science and no exact figures are needed for this decision.

So. I understand at a high N1 Percent??

[JammedStab]

Originally Posted by A Squared

All our planes are L382G's but some have GTCs and some have APUs which if I'm not mistaken, makes then equivalent to the C-130E and C-130H respectively.

APU is better, much better.

[A Squared]

Originally Posted by JammedStab

APU is better, much better.

Especially in the Desert.

[Tu.114]

Originally Posted by M Invernoz

So. I understand at a high N1 Percent??

The shafts are not all named the same on individual engines. Typically, the high pressure compressor shaft is the one the starter acts upon (if there is more than one shaft installed, of course). So the relevant number is usually N2, Nh (on the PW120 series) or whatever else the high pressure spool RPM figure may be called in the individual engine. There may be limitations involving other spools: for example on the RR Tay engine, N1 rotation must be indicated before the fuel levers may be opened.

Originally Posted by M Invernoz

Some kind of flameout? or a hot start, right?

When starting the engine, not only the compressors have to come up to speed, but also the normal gas flow pattern in the engine has to be established. A strong tailwind will increase the pressure the hot gas flow has to overcome when leaving the engine, and also (try to) spin the fan backwards, thereby applying some adverse/opposite torque to the respective turbine, resulting in more drag that also needs to be overpowered by the gas flow. Generally, higher drag and slower turbine speeds will lead to higher exhaust gas temperatures (nicely visible on a turboprop: an identical power setting will show higher EGTs with lower prop RPM and vv.). So the flameout is not really a problem, but a hot start definitely is.

[Tu.114]

Originally Posted by M Invernoz

So the critical point of the OAT is below 10°C and/or with a narrow temp/dew pt spread?? No matter if the aircraft has FADEC or not, or autostart or not??

It seems that You are after the definition of icing conditions here - those are relevant for takeoff, but only rarely for engine startup. The exact definition varies a bit by aircraft type: on the Fokker 70/100, it is "OAT below +5°C AND spread below 3°C", on the DH8 on the ground, it is OAT at or below 10°C AND visible moisture (i. e. precipitation of any kind, drifting or blowing snow or the like, or mist with visibility below 1600m). So it is not really possible to give You an answer suiting all types, engines and also operators.

[Old Fella]

Ground Start/Ground Idle Detents

JS & AA. Had a busy day and only just able to respond. You point out that you have a Ground Idle position at about 10 degrees throttle position and a Ground Start (with Detent) at 18 degrees.

As I said, none of the Military C130's (A-E-H) that I operated on had a Ground Start throttle position. Ground Idle is a detent position at 18 degrees, which lines up with where you reckon you have a Ground Start detent. I can't fathom why you would then have a ground idle position a further 8 degrees back toward Reverse. As a matter of interest do you start in Low Speed Ground Idle or Normal?

And yes, I also reckon the APU was a much better setup than having the GTC/ATM combo.

[de facto]

I think CFM 56 are certified to start up to 60 kts TW,not like i ever tried

[A Squared]

Originally Posted by Old Fella

I can't fathom why you would then have a ground idle position a further 8 degrees back toward Reverse.

I can't say really. Honestly I didn't know that the military Hercs were different. I will say that the 18 degree detent (ground start on the L382) is not a neutral thrust position. A light plane on level ground will roll along quite nicely with the throttles in that position. The Neutral thrust position for the throttles would be a bit aft of that detent, about where "ground Idle" is marked on the quadrant.

Originally Posted by Old Fella

As a matter of interest do you start in Low Speed Ground Idle or Normal?

LSGI. Unless the engineer forgets to punch the buttons before start. Then we start the other three in LSGI after he pushes the buttons down. Then he buys the beer after the flight.

[Old Fella]

GI/GS

AA Don't doubt your word for a second mate. I know the aircraft will taxy easily without any movement from GI and, especially on the A model with no LSGI a tad of throttle position aft of GI was needed to control taxy speed on flat taxiways.

Only problem which needed to be mindful of was that the oil temps can come up quickly in hot wx. Doesn't take too much to get to 100 C.

Hope you guys can continue in the Lockheed Legend for many years to come!!